reverse breakdown voltage

B

Bernhard Kuemel

Guest
Hi seb!

I tried to measure the Vrbd of LEDs and found the resistance dropping:

Vr R(MOhm)

3.18 244.6153846154
3.97 59.2537313433
4.23 48.6206896552
4.82 36.7938931298
5.65 27.5609756098
6.08 22.7715355805
7.61 16.295503212

I guess I have not reached the breakdown voltage and I need a power
supply with more voltage.

However, I wonder, what the definition of breakdown voltage is. Usually
you see the sharp increase in current at Vbd in the diode characteristic
curve. But isn't this a matter of zoom? When I use nA instead of mA on
the current axis the curve will look similar with the breakdown
(forward) voltage shifted towards 0. IMHO the curve will look exactly
the same if it's a purely exponential curve and you zoom in or out.

Or is there a voltage below which no impact ionization occurs and this
can be seen as lowest possible definition of Vbd? But I rather think
there is always a chance for a free electron to gain enough energy to
knock free another electron. It'll just never make an avalance through
the whole barrier below a certain voltage. OTOH if a single electron
travels through the barrier due to a low voltage and at the other side
it happens to get bounced around by the lattice atoms to enough energy
to kick free a second electron that's an avalanche that made it through
the whole barrier. So at any voltage there'll be avalanches and
avalanche current will increase (exponentially, I guess) over the whole
voltage range.

Then there's zener breakdown which I think is some kind of tunneling.

Bernhard
 
On 04/25/2012 09:38 PM, George Herold wrote:
On Apr 25, 1:49 pm, Bernhard Kuemel <bernh...@bksys.at> wrote:
Hi seb!

I tried to measure the Vrbd of LEDs and found the resistance dropping:

Vr R(MOhm)

3.18 244.6153846154
3.97 59.2537313433
4.23 48.6206896552
4.82 36.7938931298
5.65 27.5609756098
6.08 22.7715355805
7.61 16.295503212

Oh no didn't you lose credit in school for too many digits!
:^)
Click to expand...
I don't remember. I never gave too many digits when I was in school :).
I thought about trimming it, but nah, not worth the trouble :).

I stuck a red LED backwards with a 100k ohm resistor is series... at
about 24V I got all these 'beautiful' RC spikes. ~ 1 volt peak, rc
time ~20us. Cranking up the voltage more and it was noise everywhere,
on a DC background. (I was monitoring the voltage across the
resistor.)
Click to expand...
RC? What C? RC spikes? 1V at the resistor and 23V at the diode doesn't
look like a huge breakdown. Maybe I'll really connect a rectifier to
230V and do:

325V - -LED+ - 10MOhm (input resistance of multimeter) - 0V

Any reason you need to know this?
Click to expand...
Mostly curiosity. I have various LEDs here, including 3 Cree XP-G R5
cool white, which are specified as 5V reverse voltage.

Bernhard
 
On Apr 25, 1:49 pm, Bernhard Kuemel <bernh...@bksys.at> wrote:
Hi seb!

I tried to measure the Vrbd of LEDs and found the resistance dropping:

Vr      R(MOhm)

3.18    244.6153846154
3.97    59.2537313433
4.23    48.6206896552
4.82    36.7938931298
5.65    27.5609756098
6.08    22.7715355805
7.61    16.295503212
Click to expand...
Oh no didn't you lose credit in school for too many digits!
:^)

I stuck a red LED backwards with a 100k ohm resistor is series... at
about 24V I got all these 'beautiful' RC spikes. ~ 1 volt peak, rc
time ~20us. Cranking up the voltage more and it was noise everywhere,
on a DC background. (I was monitoring the voltage across the
resistor.)


Any reason you need to know this?

George H.


I guess I have not reached the breakdown voltage and I need a power
supply with more voltage.

However, I wonder, what the definition of breakdown voltage is. Usually
you see the sharp increase in current at Vbd in the diode characteristic
curve. But isn't this a matter of zoom? When I use nA instead of mA on
the current axis the curve will look similar with the breakdown
(forward) voltage shifted towards 0. IMHO the curve will look exactly
the same if it's a purely exponential curve and you zoom in or out.

Or is there a voltage below which no impact ionization occurs and this
can be seen as lowest possible definition of Vbd? But I rather think
there is always a chance for a free electron to gain enough energy to
knock free another electron. It'll just never make an avalance through
the whole barrier below a certain voltage. OTOH if a single electron
travels through the barrier due to a low voltage and at the other side
it happens to get bounced around by the lattice atoms to enough energy
to kick free a second electron that's an avalanche that made it through
the whole barrier. So at any voltage there'll be avalanches and
avalanche current will increase (exponentially, I guess) over the whole
voltage range.

Then there's zener breakdown which I think is some kind of tunneling.

Bernhard
Click to expand...
 
Bernhard Kuemel wrote:
Hi seb!

I tried to measure the Vrbd of LEDs and found the resistance dropping:

Vr R(MOhm)

3.18 244.6153846154
3.97 59.2537313433
4.23 48.6206896552
4.82 36.7938931298
5.65 27.5609756098
6.08 22.7715355805
7.61 16.295503212

I guess I have not reached the breakdown voltage and I need a power
supply with more voltage.

However, I wonder, what the definition of breakdown voltage is. Usually
you see the sharp increase in current at Vbd in the diode characteristic
curve. But isn't this a matter of zoom? When I use nA instead of mA on
the current axis the curve will look similar with the breakdown
(forward) voltage shifted towards 0. IMHO the curve will look exactly
the same if it's a purely exponential curve and you zoom in or out.

Or is there a voltage below which no impact ionization occurs and this
can be seen as lowest possible definition of Vbd? But I rather think
there is always a chance for a free electron to gain enough energy to
knock free another electron. It'll just never make an avalance through
the whole barrier below a certain voltage. OTOH if a single electron
travels through the barrier due to a low voltage and at the other side
it happens to get bounced around by the lattice atoms to enough energy
to kick free a second electron that's an avalanche that made it through
the whole barrier. So at any voltage there'll be avalanches and
avalanche current will increase (exponentially, I guess) over the whole
voltage range.

Then there's zener breakdown which I think is some kind of tunneling.

Bernhard
Did you also subject the LED to various light sources concentrated on
Click to expand...
the package while doing this? Might be interesting on the results
differences.

Jamie
 
On Wed, 25 Apr 2012 19:49:31 +0200, Bernhard Kuemel
<bernhard@bksys.at> wrote:

Hi seb!

I tried to measure the Vrbd of LEDs and found the resistance dropping:

Vr R(MOhm)

3.18 244.6153846154
3.97 59.2537313433
4.23 48.6206896552
4.82 36.7938931298
5.65 27.5609756098
6.08 22.7715355805
7.61 16.295503212

I guess I have not reached the breakdown voltage and I need a power
supply with more voltage.

However, I wonder, what the definition of breakdown voltage is.
Click to expand...
---
Generally, it's defined as the minimum voltage required to force a
certain reverse current through the LED.


--
JF
 
On Wed, 25 Apr 2012 17:39:42 -0400, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charte

Bernhard
Did you also subject the LED to various light sources concentrated on
the package while doing this? Might be interesting on the results
differences.
Click to expand...
---
Hardly germane.

--
JF
 
On Apr 25, 5:39 pm, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
Bernhard Kuemel wrote:
Hi seb!

I tried to measure the Vrbd of LEDs and found the resistance dropping:

Vr      R(MOhm)

3.18       244.6153846154
3.97       59.2537313433
4.23       48.6206896552
4.82       36.7938931298
5.65       27.5609756098
6.08       22.7715355805
7.61       16.295503212

I guess I have not reached the breakdown voltage and I need a power
supply with more voltage.

However, I wonder, what the definition of breakdown voltage is. Usually
you see the sharp increase in current at Vbd in the diode characteristic
curve. But isn't this a matter of zoom? When I use nA instead of mA on
the current axis the curve will look similar with the breakdown
(forward) voltage shifted towards 0. IMHO the curve will look exactly
the same if it's a purely exponential curve and you zoom in or out.

Or is there a voltage below which no impact ionization occurs and this
can be seen as lowest possible definition of Vbd? But I rather think
there is always a chance for a free electron to gain enough energy to
knock free another electron. It'll just never make an avalance through
the whole barrier below a certain voltage. OTOH if a single electron
travels through the barrier due to a low voltage and at the other side
it happens to get bounced around by the lattice atoms to enough energy
to kick free a second electron that's an avalanche that made it through
the whole barrier. So at any voltage there'll be avalanches and
avalanche current will increase (exponentially, I guess) over the whole
voltage range.

Then there's zener breakdown which I think is some kind of tunneling.

Bernhard

   Did you also subject the LED to various light sources concentrated on
the package while doing this?  Might be interesting on the results
differences.
Click to expand...
Yeah I did, When you biased it right to the breakdown region you
could definitely see the effect of sticking an light up to it. Try
it. Everyone's got a red 5mm LED, 100k ohm and ~30V power supply.

George H.
  Jamie- Hide quoted text -

- Show quoted text -
Click to expand...
 
On Apr 25, 5:14 pm, Bernhard Kuemel <bernh...@bksys.at> wrote:
On 04/25/2012 09:38 PM, George Herold wrote:





On Apr 25, 1:49 pm, Bernhard Kuemel <bernh...@bksys.at> wrote:
Hi seb!

I tried to measure the Vrbd of LEDs and found the resistance dropping:

Vr      R(MOhm)

3.18    244.6153846154
3.97    59.2537313433
4.23    48.6206896552
4.82    36.7938931298
5.65    27.5609756098
6.08    22.7715355805
7.61    16.295503212

Oh no didn't you lose credit in school for too many digits!
  :^)

I don't remember. I never gave too many digits when I was in school :).
I thought about trimming it, but nah, not worth the trouble :).

I stuck a red LED backwards with a 100k ohm resistor is series... at
about 24V I got all these 'beautiful' RC spikes.   ~ 1 volt peak, rc
time ~20us.  Cranking up the voltage more and it was noise everywhere,
on a DC background.  (I was monitoring the voltage across the
resistor.)

RC? What C? RC spikes? 1V at the resistor and 23V at the diode doesn't
look like a huge breakdown. Maybe I'll really connect a rectifier to
230V and do:

325V - -LED+ - 10MOhm (input resistance of multimeter) - 0V

Any reason you need to know this?

Mostly curiosity. I have various LEDs here, including 3 Cree XP-G R5
cool white, which are specified as 5V reverse voltage.

Bernhard- Hide quoted text -

- Show quoted text -
Click to expand...
The voltage across the 100k R looked like


<----peak here about 1 volt
|\
| -\
| - \ <--- that's an exponential decay...sorta
| --

-------+ \ ---------

^----2/3 (1/e) time constant about 20 us.

Those came at random times... more of them with the light on...
avalanche break down.

Kinda fun, thanks.

George H.
 
George Herold wrote:

On Apr 25, 5:39 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

Bernhard Kuemel wrote:

Hi seb!

I tried to measure the Vrbd of LEDs and found the resistance dropping:

Vr R(MOhm)

3.18 244.6153846154
3.97 59.2537313433
4.23 48.6206896552
4.82 36.7938931298
5.65 27.5609756098
6.08 22.7715355805
7.61 16.295503212

I guess I have not reached the breakdown voltage and I need a power
supply with more voltage.

However, I wonder, what the definition of breakdown voltage is. Usually
you see the sharp increase in current at Vbd in the diode characteristic
curve. But isn't this a matter of zoom? When I use nA instead of mA on
the current axis the curve will look similar with the breakdown
(forward) voltage shifted towards 0. IMHO the curve will look exactly
the same if it's a purely exponential curve and you zoom in or out.

Or is there a voltage below which no impact ionization occurs and this
can be seen as lowest possible definition of Vbd? But I rather think
there is always a chance for a free electron to gain enough energy to
knock free another electron. It'll just never make an avalance through
the whole barrier below a certain voltage. OTOH if a single electron
travels through the barrier due to a low voltage and at the other side
it happens to get bounced around by the lattice atoms to enough energy
to kick free a second electron that's an avalanche that made it through
the whole barrier. So at any voltage there'll be avalanches and
avalanche current will increase (exponentially, I guess) over the whole
voltage range.

Then there's zener breakdown which I think is some kind of tunneling.

Bernhard

Did you also subject the LED to various light sources concentrated on
the package while doing this? Might be interesting on the results
differences.


Yeah I did, When you biased it right to the breakdown region you
could definitely see the effect of sticking an light up to it. Try
it. Everyone's got a red 5mm LED, 100k ohm and ~30V power supply.

George H.

Jamie- Hide quoted text -

- Show quoted text -


Oh, I've already done this not to long ago when I was pondering on an idea.
Click to expand...

How ever, I am trying to see where you are getting the noise from?
When I did it, all I saw on the scope was a PV effect at 1 uA, it
could've been more, been a while.

I used my over head light which is nothing more than a incandescent
52 watt. I did see the 120 hz in the signal, too, when getting the
exposure to where I was getting 50% forward biasing voltage for that LED.

But I was able to get over 1 V as a PV with out any biasing, just the
LED on the leads. It would make for a nice photo detector in a pinch
though if you have the hi-z circuit for it.

I guess if one was to have a few LED's in series with HV applied and
wait for a few photons to stop by for visit it would then act as a photo
multiplier and push things a long, thus giving you a very sensitive
detector. Or at least I think it would :)


I'll have to set that experiment up again at work, this time using the
Lecroy maybe and see if I can see anything I may have missed before.


Jamie
 
On 04/25/2012 11:14 PM, Bernhard Kuemel wrote:
325V - -LED+ - 10MOhm (input resistance of multimeter) - 0V
Click to expand...
Hmm, the DMM showed the full input voltage. No voltage drop due to the
LED. IIRC before that I tried the LED in forward direction and got some
voltage drop. However, after trying the reverse direction the behaviour
was the same in either direction. No light, except for a short flash
when I closed the circuit. The DMM showed ca. 330 mV diode drop and 445
Ohm resistance, both in each direction. I was convinced the LED was
dead, but when hooked up normally it was still shining without appearant
loss in brightness.

Ohh, I also had a 10uF film capacitor across the input voltage.

Bernhard
 
On Apr 25, 10:10 pm, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
George Herold wrote:
On Apr 25, 5:39 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

Bernhard Kuemel wrote:

Hi seb!

I tried to measure the Vrbd of LEDs and found the resistance dropping:

Vr      R(MOhm)

3.18       244.6153846154
3.97       59.2537313433
4.23       48.6206896552
4.82       36.7938931298
5.65       27.5609756098
6.08       22.7715355805
7.61       16.295503212

I guess I have not reached the breakdown voltage and I need a power
supply with more voltage.

However, I wonder, what the definition of breakdown voltage is. Usually
you see the sharp increase in current at Vbd in the diode characteristic
curve. But isn't this a matter of zoom? When I use nA instead of mA on
the current axis the curve will look similar with the breakdown
(forward) voltage shifted towards 0. IMHO the curve will look exactly
the same if it's a purely exponential curve and you zoom in or out.

Or is there a voltage below which no impact ionization occurs and this
can be seen as lowest possible definition of Vbd? But I rather think
there is always a chance for a free electron to gain enough energy to
knock free another electron. It'll just never make an avalance through
the whole barrier below a certain voltage. OTOH if a single electron
travels through the barrier due to a low voltage and at the other side
it happens to get bounced around by the lattice atoms to enough energy
to kick free a second electron that's an avalanche that made it through
the whole barrier. So at any voltage there'll be avalanches and
avalanche current will increase (exponentially, I guess) over the whole
voltage range.

Then there's zener breakdown which I think is some kind of tunneling.

Bernhard

  Did you also subject the LED to various light sources concentrated on
the package while doing this?  Might be interesting on the results
differences.

Yeah I did,  When you biased it right to the breakdown region you
could definitely see the effect of sticking an light up to it.  Try
it.  Everyone's got a red 5mm LED, 100k ohm and ~30V power supply.

George H.

 Jamie- Hide quoted text -

- Show quoted text -

Oh, I've already done this not to long ago when I was pondering on an idea.

  How ever, I am trying to see where you are getting the noise from?
When I did it, all I saw on the scope was a PV effect at 1 uA, it
could've been more, been a while.

   I used my over head light which is nothing more than a incandescent
52 watt. I did see the 120 hz in the signal, too, when getting the
exposure to where I was getting 50% forward biasing voltage for that LED.

   But I was able to get over 1 V as a PV with out any biasing, just the
LED on the leads. It would make for a nice photo detector in a pinch
though if you have the hi-z circuit for it.

   I guess if one was to have a few LED's in series with HV applied and
wait for a few photons to stop by for visit it would then act as a photo
multiplier and push things a long, thus giving you a very sensitive
detector. Or at least I think it would :)

  I'll have to set that experiment up again at work, this time using the
Lecroy maybe and see if I can see anything I may have missed before.

Jamie- Hide quoted text -

- Show quoted text -
Click to expand...
Hi Jamie, Here’s some quick ‘scope shots. (Still set up on my
bench.)

The first is just when the PD starts to reverse conduct, with no
light.
http://bayimg.com/CAOCcaade

And then at same voltage with the light shinning.
http://bayimg.com/CaoCDAadE

The shot of a single pulse.

http://bayimg.com/CAOCEAaDe

And then with a higher reverse voltage... conducting all the time.
http://bayimg.com/CAoCGaade

(Voltage scale changed for the last.)

George H.
 
On Wed, 25 Apr 2012 19:13:11 -0500, John Fields
<jfields@austininstruments.com> wrote:

On Wed, 25 Apr 2012 17:39:42 -0400, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charte

Bernhard
Did you also subject the LED to various light sources concentrated on
the package while doing this? Might be interesting on the results
differences.

---
Hardly germane.
Click to expand...
The currents he is seeing are in the range of possible photodiode
operation.


--

John Larkin Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation
 
On Thu, 26 Apr 2012 06:20:20 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Apr 25, 10:10 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
George Herold wrote:
On Apr 25, 5:39 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

Bernhard Kuemel wrote:

Hi seb!

I tried to measure the Vrbd of LEDs and found the resistance dropping:

Vr      R(MOhm)

3.18       244.6153846154
3.97       59.2537313433
4.23       48.6206896552
4.82       36.7938931298
5.65       27.5609756098
6.08       22.7715355805
7.61       16.295503212

I guess I have not reached the breakdown voltage and I need a power
supply with more voltage.

However, I wonder, what the definition of breakdown voltage is. Usually
you see the sharp increase in current at Vbd in the diode characteristic
curve. But isn't this a matter of zoom? When I use nA instead of mA on
the current axis the curve will look similar with the breakdown
(forward) voltage shifted towards 0. IMHO the curve will look exactly
the same if it's a purely exponential curve and you zoom in or out.

Or is there a voltage below which no impact ionization occurs and this
can be seen as lowest possible definition of Vbd? But I rather think
there is always a chance for a free electron to gain enough energy to
knock free another electron. It'll just never make an avalance through
the whole barrier below a certain voltage. OTOH if a single electron
travels through the barrier due to a low voltage and at the other side
it happens to get bounced around by the lattice atoms to enough energy
to kick free a second electron that's an avalanche that made it through
the whole barrier. So at any voltage there'll be avalanches and
avalanche current will increase (exponentially, I guess) over the whole
voltage range.

Then there's zener breakdown which I think is some kind of tunneling.

Bernhard

  Did you also subject the LED to various light sources concentrated on
the package while doing this?  Might be interesting on the results
differences.

Yeah I did,  When you biased it right to the breakdown region you
could definitely see the effect of sticking an light up to it.  Try
it.  Everyone's got a red 5mm LED, 100k ohm and ~30V power supply.

George H.

 Jamie- Hide quoted text -

- Show quoted text -

Oh, I've already done this not to long ago when I was pondering on an idea.

  How ever, I am trying to see where you are getting the noise from?
When I did it, all I saw on the scope was a PV effect at 1 uA, it
could've been more, been a while.

   I used my over head light which is nothing more than a incandescent
52 watt. I did see the 120 hz in the signal, too, when getting the
exposure to where I was getting 50% forward biasing voltage for that LED.

   But I was able to get over 1 V as a PV with out any biasing, just the
LED on the leads. It would make for a nice photo detector in a pinch
though if you have the hi-z circuit for it.

   I guess if one was to have a few LED's in series with HV applied and
wait for a few photons to stop by for visit it would then act as a photo
multiplier and push things a long, thus giving you a very sensitive
detector. Or at least I think it would :)

  I'll have to set that experiment up again at work, this time using the
Lecroy maybe and see if I can see anything I may have missed before.

Jamie- Hide quoted text -

- Show quoted text -

Hi Jamie, Here’s some quick ‘scope shots. (Still set up on my
bench.)

The first is just when the PD starts to reverse conduct, with no
light.
http://bayimg.com/CAOCcaade

And then at same voltage with the light shinning.
http://bayimg.com/CaoCDAadE

The shot of a single pulse.

http://bayimg.com/CAOCEAaDe

And then with a higher reverse voltage... conducting all the time.
http://bayimg.com/CAoCGaade

(Voltage scale changed for the last.)

George H.
Click to expand...
Cool. I wonder if you're approaching some sort of single-photon
avalanche/Geiger mode. The dark behavior looks like a typical small
zener diode at low current, a really noisy sawtooth oscillation.




--

John Larkin Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation
 
On Apr 26, 7:14 pm, John Larkin <jlar...@highlandtechnology.com>
wrote:
On Thu, 26 Apr 2012 06:20:20 -0700 (PDT), George Herold





gher...@teachspin.com> wrote:
On Apr 25, 10:10 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
George Herold wrote:
On Apr 25, 5:39 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

Bernhard Kuemel wrote:

Hi seb!

I tried to measure the Vrbd of LEDs and found the resistance dropping:

Vr      R(MOhm)

3.18       244.6153846154
3.97       59.2537313433
4.23       48.6206896552
4.82       36.7938931298
5.65       27.5609756098
6.08       22.7715355805
7.61       16.295503212

I guess I have not reached the breakdown voltage and I need a power
supply with more voltage.

However, I wonder, what the definition of breakdown voltage is. Usually
you see the sharp increase in current at Vbd in the diode characteristic
curve. But isn't this a matter of zoom? When I use nA instead of mA on
the current axis the curve will look similar with the breakdown
(forward) voltage shifted towards 0. IMHO the curve will look exactly
the same if it's a purely exponential curve and you zoom in or out.

Or is there a voltage below which no impact ionization occurs and this
can be seen as lowest possible definition of Vbd? But I rather think
there is always a chance for a free electron to gain enough energy to
knock free another electron. It'll just never make an avalance through
the whole barrier below a certain voltage. OTOH if a single electron
travels through the barrier due to a low voltage and at the other side
it happens to get bounced around by the lattice atoms to enough energy
to kick free a second electron that's an avalanche that made it through
the whole barrier. So at any voltage there'll be avalanches and
avalanche current will increase (exponentially, I guess) over the whole
voltage range.

Then there's zener breakdown which I think is some kind of tunneling.

Bernhard

  Did you also subject the LED to various light sources concentrated on
the package while doing this?  Might be interesting on the results
differences.

Yeah I did,  When you biased it right to the breakdown region you
could definitely see the effect of sticking an light up to it.  Try
it.  Everyone's got a red 5mm LED, 100k ohm and ~30V power supply.

George H.

 Jamie- Hide quoted text -

- Show quoted text -

Oh, I've already done this not to long ago when I was pondering on an idea.

  How ever, I am trying to see where you are getting the noise from?
When I did it, all I saw on the scope was a PV effect at 1 uA, it
could've been more, been a while.

   I used my over head light which is nothing more than a incandescent
52 watt. I did see the 120 hz in the signal, too, when getting the
exposure to where I was getting 50% forward biasing voltage for that LED.

   But I was able to get over 1 V as a PV with out any biasing, just the
LED on the leads. It would make for a nice photo detector in a pinch
though if you have the hi-z circuit for it.

   I guess if one was to have a few LED's in series with HV applied and
wait for a few photons to stop by for visit it would then act as a photo
multiplier and push things a long, thus giving you a very sensitive
detector. Or at least I think it would :)

  I'll have to set that experiment up again at work, this time using the
Lecroy maybe and see if I can see anything I may have missed before.

Jamie- Hide quoted text -

- Show quoted text -

Hi Jamie,  Here’s some quick ‘scope shots.  (Still set up on my
bench.)

The first is just when the PD starts to reverse conduct, with no
light.
http://bayimg.com/CAOCcaade

And then at same voltage with the light shinning.
http://bayimg.com/CaoCDAadE

The shot of a single pulse.

http://bayimg.com/CAOCEAaDe

And then with a higher reverse voltage... conducting all the time.
http://bayimg.com/CAoCGaade

(Voltage scale changed for the last.)

George H.

Cool. I wonder if you're approaching some sort of single-photon
avalanche/Geiger mode. The dark behavior looks like a typical small
zener diode at low current, a really noisy sawtooth oscillation.

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot comhttp://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation- Hide quoted text -

- Show quoted text -
Click to expand...
Yeah the low current looks pretty much like a ~20V zener biased to the
corner.
Where I assume it's the whole diode capacitance discharging..

Here I've got 100k ohm and ~10-20 us TC so 100- 200pF. That seems
like a lot for a little LED. .. ohh.. I just had some coax with
'grabber clips'... ~170pF...

A x10 probe tomorrow.

Hey for those digital type guys, you could stick a comparator on the
output and count pulses.
As you keep increasing the voltage you hit a quiet region, where it
looks resistive.

Well I've only looked at one red LED. (I hope it's not a golden
part.)

George H.
 
On Thu, 26 Apr 2012 16:08:04 -0700, John Larkin
<jlarkin@highlandtechnology.com> wrote:

On Wed, 25 Apr 2012 19:13:11 -0500, John Fields
jfields@austininstruments.com> wrote:

On Wed, 25 Apr 2012 17:39:42 -0400, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charte

Bernhard
Did you also subject the LED to various light sources concentrated on
the package while doing this? Might be interesting on the results
differences.

---
Hardly germane.

The currents he is seeing are in the range of possible photodiode
operation.
Click to expand...
---
The currents he reported, I suspect, were measured under a single - or
not widely variable level of illumination - so it's likely that the
changes in current were due to the changes in reverse voltage across
the diode and not due to changes in illumination.

--
JF
 
On Fri, 27 Apr 2012 07:49:12 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Apr 26, 9:05 pm, George Herold <gher...@teachspin.com> wrote:
On Apr 26, 7:14 pm, John Larkin <jlar...@highlandtechnology.com
wrote:





On Thu, 26 Apr 2012 06:20:20 -0700 (PDT), George Herold

gher...@teachspin.com> wrote:
On Apr 25, 10:10 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
George Herold wrote:
On Apr 25, 5:39 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

Bernhard Kuemel wrote:

Hi seb!

I tried to measure the Vrbd of LEDs and found the resistance dropping:

Vr      R(MOhm)

3.18       244.6153846154
3.97       59.2537313433
4.23       48.6206896552
4.82       36.7938931298
5.65       27.5609756098
6.08       22.7715355805
7.61       16.295503212

I guess I have not reached the breakdown voltage and I need a power
supply with more voltage.

However, I wonder, what the definition of breakdown voltage is. Usually
you see the sharp increase in current at Vbd in the diode characteristic
curve. But isn't this a matter of zoom? When I use nA instead of mA on
the current axis the curve will look similar with the breakdown
(forward) voltage shifted towards 0. IMHO the curve will look exactly
the same if it's a purely exponential curve and you zoom in or out.

Or is there a voltage below which no impact ionization occurs and this
can be seen as lowest possible definition of Vbd? But I rather think
there is always a chance for a free electron to gain enough energy to
knock free another electron. It'll just never make an avalance through
the whole barrier below a certain voltage. OTOH if a single electron
travels through the barrier due to a low voltage and at the other side
it happens to get bounced around by the lattice atoms to enough energy
to kick free a second electron that's an avalanche that made it through
the whole barrier. So at any voltage there'll be avalanches and
avalanche current will increase (exponentially, I guess) over the whole
voltage range.

Then there's zener breakdown which I think is some kind of tunneling.

Bernhard

  Did you also subject the LED to various light sources concentrated on
the package while doing this?  Might be interesting on the results
differences.

Yeah I did,  When you biased it right to the breakdown region you
could definitely see the effect of sticking an light up to it.  Try
it.  Everyone's got a red 5mm LED, 100k ohm and ~30V power supply.

George H.

 Jamie- Hide quoted text -

- Show quoted text -

Oh, I've already done this not to long ago when I was pondering on an idea.

  How ever, I am trying to see where you are getting the noise from?
When I did it, all I saw on the scope was a PV effect at 1 uA, it
could've been more, been a while.

   I used my over head light which is nothing more than a incandescent
52 watt. I did see the 120 hz in the signal, too, when getting the
exposure to where I was getting 50% forward biasing voltage for that LED.

   But I was able to get over 1 V as a PV with out any biasing, just the
LED on the leads. It would make for a nice photo detector in a pinch
though if you have the hi-z circuit for it.

   I guess if one was to have a few LED's in series with HV applied and
wait for a few photons to stop by for visit it would then act as a photo
multiplier and push things a long, thus giving you a very sensitive
detector. Or at least I think it would :)

  I'll have to set that experiment up again at work, this time using the
Lecroy maybe and see if I can see anything I may have missed before.

Jamie- Hide quoted text -

- Show quoted text -

Hi Jamie,  Here’s some quick ‘scope shots.  (Still set up on my
bench.)

The first is just when the PD starts to reverse conduct, with no
light.
http://bayimg.com/CAOCcaade

And then at same voltage with the light shinning.
http://bayimg.com/CaoCDAadE

The shot of a single pulse.

http://bayimg.com/CAOCEAaDe

And then with a higher reverse voltage... conducting all the time.
http://bayimg.com/CAoCGaade

(Voltage scale changed for the last.)

George H.

Cool. I wonder if you're approaching some sort of single-photon
avalanche/Geiger mode. The dark behavior looks like a typical small
zener diode at low current, a really noisy sawtooth oscillation.

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot comhttp://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation- Hide quoted text -

- Show quoted text -

Yeah the low current looks pretty much like a ~20V zener biased to the
corner.
Where I assume it's the whole diode capacitance discharging..

Here I've got 100k ohm and ~10-20 us TC so 100- 200pF.  That seems
like a lot for a little  LED.  .. ohh.. I just had some coax with
'grabber clips'... ~170pF...

A x10 probe tomorrow.

Hey for those digital type guys, you could stick a comparator on the
output and count pulses.
As you keep increasing the voltage you hit a quiet region, where it
looks resistive.

Well I've only looked at one red LED.  (I hope it's not a golden
part.)

George H.- Hide quoted text -

- Show quoted text -

HEY! I think I may be counting single photons! (At extremely low
efficiency) This is amazing. (So just try it yourself.)

A variable power supply reverse biased red LED in 5mm package (Vr~24
volts). 100 kohm current limiting (and sense) resistor, look at
current through the 100k ohm with a x10 scope probe. Adjust voltage
till you see some RC spikes. Now cover the LED with something black.
The pulses stop! I turned out the lights in my lab and can still
'see' the light that's coming in from the room next door. I need a
bit of buffering so I can send the pulses into a counter.

The count rate is highly dependent on the bias level.
24 V no counts (at 200mV threshold)
24.5 V 500 counts/sec in room light
25 V 4.5k counts/ s in same light.
25.5 V 19kk/sec.

Total Friday Fun! (I've gotta put some final changes into a pcb
too.)

I should hit up google 'cause it seems like someone must have done
this before.

George H.
Click to expand...
You may be in possession of a Geiger mode photon detector at about
1/1000 the regular price. But expect a high rate of dark counts.

I wonder how you could demonstrate single photon counting. Probably
put the detector in a box with an LED and a lot of optical
attenuation, and drive the LED on/off, and measure something.


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
 
On Apr 26, 9:05 pm, George Herold <gher...@teachspin.com> wrote:
On Apr 26, 7:14 pm, John Larkin <jlar...@highlandtechnology.com
wrote:





On Thu, 26 Apr 2012 06:20:20 -0700 (PDT), George Herold

gher...@teachspin.com> wrote:
On Apr 25, 10:10 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
George Herold wrote:
On Apr 25, 5:39 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

Bernhard Kuemel wrote:

Hi seb!

I tried to measure the Vrbd of LEDs and found the resistance dropping:

Vr      R(MOhm)

3.18       244.6153846154
3.97       59.2537313433
4.23       48.6206896552
4.82       36.7938931298
5.65       27.5609756098
6.08       22.7715355805
7.61       16.295503212

I guess I have not reached the breakdown voltage and I need a power
supply with more voltage.

However, I wonder, what the definition of breakdown voltage is. Usually
you see the sharp increase in current at Vbd in the diode characteristic
curve. But isn't this a matter of zoom? When I use nA instead of mA on
the current axis the curve will look similar with the breakdown
(forward) voltage shifted towards 0. IMHO the curve will look exactly
the same if it's a purely exponential curve and you zoom in or out.

Or is there a voltage below which no impact ionization occurs and this
can be seen as lowest possible definition of Vbd? But I rather think
there is always a chance for a free electron to gain enough energy to
knock free another electron. It'll just never make an avalance through
the whole barrier below a certain voltage. OTOH if a single electron
travels through the barrier due to a low voltage and at the other side
it happens to get bounced around by the lattice atoms to enough energy
to kick free a second electron that's an avalanche that made it through
the whole barrier. So at any voltage there'll be avalanches and
avalanche current will increase (exponentially, I guess) over the whole
voltage range.

Then there's zener breakdown which I think is some kind of tunneling.

Bernhard

  Did you also subject the LED to various light sources concentrated on
the package while doing this?  Might be interesting on the results
differences.

Yeah I did,  When you biased it right to the breakdown region you
could definitely see the effect of sticking an light up to it.  Try
it.  Everyone's got a red 5mm LED, 100k ohm and ~30V power supply.

George H.

 Jamie- Hide quoted text -

- Show quoted text -

Oh, I've already done this not to long ago when I was pondering on an idea.

  How ever, I am trying to see where you are getting the noise from?
When I did it, all I saw on the scope was a PV effect at 1 uA, it
could've been more, been a while.

   I used my over head light which is nothing more than a incandescent
52 watt. I did see the 120 hz in the signal, too, when getting the
exposure to where I was getting 50% forward biasing voltage for that LED.

   But I was able to get over 1 V as a PV with out any biasing, just the
LED on the leads. It would make for a nice photo detector in a pinch
though if you have the hi-z circuit for it.

   I guess if one was to have a few LED's in series with HV applied and
wait for a few photons to stop by for visit it would then act as a photo
multiplier and push things a long, thus giving you a very sensitive
detector. Or at least I think it would :)

  I'll have to set that experiment up again at work, this time using the
Lecroy maybe and see if I can see anything I may have missed before.

Jamie- Hide quoted text -

- Show quoted text -

Hi Jamie,  Here’s some quick ‘scope shots.  (Still set up on my
bench.)

The first is just when the PD starts to reverse conduct, with no
light.
http://bayimg.com/CAOCcaade

And then at same voltage with the light shinning.
http://bayimg.com/CaoCDAadE

The shot of a single pulse.

http://bayimg.com/CAOCEAaDe

And then with a higher reverse voltage... conducting all the time.
http://bayimg.com/CAoCGaade

(Voltage scale changed for the last.)

George H.

Cool. I wonder if you're approaching some sort of single-photon
avalanche/Geiger mode. The dark behavior looks like a typical small
zener diode at low current, a really noisy sawtooth oscillation.

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot comhttp://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation- Hide quoted text -

- Show quoted text -

Yeah the low current looks pretty much like a ~20V zener biased to the
corner.
Where I assume it's the whole diode capacitance discharging..

Here I've got 100k ohm and ~10-20 us TC so 100- 200pF.  That seems
like a lot for a little  LED.  .. ohh.. I just had some coax with
'grabber clips'... ~170pF...

A x10 probe tomorrow.

Hey for those digital type guys, you could stick a comparator on the
output and count pulses.
As you keep increasing the voltage you hit a quiet region, where it
looks resistive.

Well I've only looked at one red LED.  (I hope it's not a golden
part.)

George H.- Hide quoted text -

- Show quoted text -
Click to expand...
HEY! I think I may be counting single photons! (At extremely low
efficiency) This is amazing. (So just try it yourself.)

A variable power supply reverse biased red LED in 5mm package (Vr~24
volts). 100 kohm current limiting (and sense) resistor, look at
current through the 100k ohm with a x10 scope probe. Adjust voltage
till you see some RC spikes. Now cover the LED with something black.
The pulses stop! I turned out the lights in my lab and can still
'see' the light that's coming in from the room next door. I need a
bit of buffering so I can send the pulses into a counter.

The count rate is highly dependent on the bias level.
24 V no counts (at 200mV threshold)
24.5 V 500 counts/sec in room light
25 V 4.5k counts/ s in same light.
25.5 V 19kk/sec.

Total Friday Fun! (I've gotta put some final changes into a pcb
too.)

I should hit up google 'cause it seems like someone must have done
this before.

George H.
 
George Herold wrote:
On Apr 26, 9:05 pm, George Herold <gher...@teachspin.com> wrote:
On Apr 26, 7:14 pm, John Larkin <jlar...@highlandtechnology.com
wrote:





On Thu, 26 Apr 2012 06:20:20 -0700 (PDT), George Herold

gher...@teachspin.com> wrote:
On Apr 25, 10:10 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
George Herold wrote:
On Apr 25, 5:39 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

Bernhard Kuemel wrote:

Hi seb!

I tried to measure the Vrbd of LEDs and found the resistance dropping:

Vr R(MOhm)

3.18 244.6153846154
3.97 59.2537313433
4.23 48.6206896552
4.82 36.7938931298
5.65 27.5609756098
6.08 22.7715355805
7.61 16.295503212

I guess I have not reached the breakdown voltage and I need a power
supply with more voltage.

However, I wonder, what the definition of breakdown voltage is. Usually
you see the sharp increase in current at Vbd in the diode characteristic
curve. But isn't this a matter of zoom? When I use nA instead of mA on
the current axis the curve will look similar with the breakdown
(forward) voltage shifted towards 0. IMHO the curve will look exactly
the same if it's a purely exponential curve and you zoom in or out.

Or is there a voltage below which no impact ionization occurs and this
can be seen as lowest possible definition of Vbd? But I rather think
there is always a chance for a free electron to gain enough energy to
knock free another electron. It'll just never make an avalance through
the whole barrier below a certain voltage. OTOH if a single electron
travels through the barrier due to a low voltage and at the other side
it happens to get bounced around by the lattice atoms to enough energy
to kick free a second electron that's an avalanche that made it through
the whole barrier. So at any voltage there'll be avalanches and
avalanche current will increase (exponentially, I guess) over the whole
voltage range.

Then there's zener breakdown which I think is some kind of tunneling.

Bernhard

Did you also subject the LED to various light sources concentrated on
the package while doing this? Might be interesting on the results
differences.

Yeah I did, When you biased it right to the breakdown region you
could definitely see the effect of sticking an light up to it. Try
it. Everyone's got a red 5mm LED, 100k ohm and ~30V power supply.

George H.

Jamie- Hide quoted text -

- Show quoted text -

Oh, I've already done this not to long ago when I was pondering on an idea.

How ever, I am trying to see where you are getting the noise from?
When I did it, all I saw on the scope was a PV effect at 1 uA, it
could've been more, been a while.

I used my over head light which is nothing more than a incandescent
52 watt. I did see the 120 hz in the signal, too, when getting the
exposure to where I was getting 50% forward biasing voltage for that LED.

But I was able to get over 1 V as a PV with out any biasing, just the
LED on the leads. It would make for a nice photo detector in a pinch
though if you have the hi-z circuit for it.

I guess if one was to have a few LED's in series with HV applied and
wait for a few photons to stop by for visit it would then act as a photo
multiplier and push things a long, thus giving you a very sensitive
detector. Or at least I think it would :)

I'll have to set that experiment up again at work, this time using the
Lecroy maybe and see if I can see anything I may have missed before.

Jamie- Hide quoted text -

- Show quoted text -

Hi Jamie, Here’s some quick ‘scope shots. (Still set up on my
bench.)

The first is just when the PD starts to reverse conduct, with no
light.
http://bayimg.com/CAOCcaade

And then at same voltage with the light shinning.
http://bayimg.com/CaoCDAadE

The shot of a single pulse.

http://bayimg.com/CAOCEAaDe

And then with a higher reverse voltage... conducting all the time.
http://bayimg.com/CAoCGaade

(Voltage scale changed for the last.)

George H.

Cool. I wonder if you're approaching some sort of single-photon
avalanche/Geiger mode. The dark behavior looks like a typical small
zener diode at low current, a really noisy sawtooth oscillation.

--

John Larkin Highland Technology, Inc

jlarkin at highlandtechnology dot comhttp://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation- Hide quoted text -

- Show quoted text -

Yeah the low current looks pretty much like a ~20V zener biased to the
corner.
Where I assume it's the whole diode capacitance discharging..

Here I've got 100k ohm and ~10-20 us TC so 100- 200pF. That seems
like a lot for a little LED. .. ohh.. I just had some coax with
'grabber clips'... ~170pF...

A x10 probe tomorrow.

Hey for those digital type guys, you could stick a comparator on the
output and count pulses.
As you keep increasing the voltage you hit a quiet region, where it
looks resistive.

Well I've only looked at one red LED. (I hope it's not a golden
part.)

George H.- Hide quoted text -

- Show quoted text -

HEY! I think I may be counting single photons! (At extremely low
efficiency) This is amazing. (So just try it yourself.)

A variable power supply reverse biased red LED in 5mm package (Vr~24
volts). 100 kohm current limiting (and sense) resistor, look at
current through the 100k ohm with a x10 scope probe. Adjust voltage
till you see some RC spikes. Now cover the LED with something black.
The pulses stop! I turned out the lights in my lab and can still
'see' the light that's coming in from the room next door. I need a
bit of buffering so I can send the pulses into a counter.

The count rate is highly dependent on the bias level.
24 V no counts (at 200mV threshold)
24.5 V 500 counts/sec in room light
25 V 4.5k counts/ s in same light.
25.5 V 19kk/sec.

Total Friday Fun! (I've gotta put some final changes into a pcb
too.)

I should hit up google 'cause it seems like someone must have done
this before.

George H.
Click to expand...
That _is_ fun. Do you have enough ND filters lying around that you can
make a 1 photon per millisecond per die area light source for it? You
can figure out the threshold number of photons by looking at how the
count rate goes up with light level-- a few ND1 filters in a row would
allow a simple measurement of that.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net
 
On Apr 27, 10:49 am, George Herold <gher...@teachspin.com> wrote:
On Apr 26, 9:05 pm, George Herold <gher...@teachspin.com> wrote:





On Apr 26, 7:14 pm, John Larkin <jlar...@highlandtechnology.com
wrote:

On Thu, 26 Apr 2012 06:20:20 -0700 (PDT), George Herold

gher...@teachspin.com> wrote:
On Apr 25, 10:10 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
George Herold wrote:
On Apr 25, 5:39 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

Bernhard Kuemel wrote:

Hi seb!

I tried to measure the Vrbd of LEDs and found the resistance dropping:

Vr      R(MOhm)

3.18       244.6153846154
3.97       59.2537313433
4.23       48.6206896552
4.82       36.7938931298
5.65       27.5609756098
6.08       22.7715355805
7.61       16.295503212

I guess I have not reached the breakdown voltage and I need a power
supply with more voltage.

However, I wonder, what the definition of breakdown voltage is. Usually
you see the sharp increase in current at Vbd in the diode characteristic
curve. But isn't this a matter of zoom? When I use nA instead of mA on
the current axis the curve will look similar with the breakdown
(forward) voltage shifted towards 0. IMHO the curve will look exactly
the same if it's a purely exponential curve and you zoom in or out.

Or is there a voltage below which no impact ionization occurs and this
can be seen as lowest possible definition of Vbd? But I rather think
there is always a chance for a free electron to gain enough energy to
knock free another electron. It'll just never make an avalance through
the whole barrier below a certain voltage. OTOH if a single electron
travels through the barrier due to a low voltage and at the other side
it happens to get bounced around by the lattice atoms to enough energy
to kick free a second electron that's an avalanche that made it through
the whole barrier. So at any voltage there'll be avalanches and
avalanche current will increase (exponentially, I guess) over the whole
voltage range.

Then there's zener breakdown which I think is some kind of tunneling.

Bernhard

  Did you also subject the LED to various light sources concentrated on
the package while doing this?  Might be interesting on the results
differences.

Yeah I did,  When you biased it right to the breakdown region you
could definitely see the effect of sticking an light up to it.  Try
it.  Everyone's got a red 5mm LED, 100k ohm and ~30V power supply.

George H.

 Jamie- Hide quoted text -

- Show quoted text -

Oh, I've already done this not to long ago when I was pondering on an idea.

  How ever, I am trying to see where you are getting the noise from?
When I did it, all I saw on the scope was a PV effect at 1 uA, it
could've been more, been a while.

   I used my over head light which is nothing more than a incandescent
52 watt. I did see the 120 hz in the signal, too, when getting the
exposure to where I was getting 50% forward biasing voltage for that LED.

   But I was able to get over 1 V as a PV with out any biasing, just the
LED on the leads. It would make for a nice photo detector in a pinch
though if you have the hi-z circuit for it.

   I guess if one was to have a few LED's in series with HV applied and
wait for a few photons to stop by for visit it would then act as a photo
multiplier and push things a long, thus giving you a very sensitive
detector. Or at least I think it would :)

  I'll have to set that experiment up again at work, this time using the
Lecroy maybe and see if I can see anything I may have missed before.

Jamie- Hide quoted text -

- Show quoted text -

Hi Jamie,  Here’s some quick ‘scope shots.  (Still set up on my
bench.)

The first is just when the PD starts to reverse conduct, with no
light.
http://bayimg.com/CAOCcaade

And then at same voltage with the light shinning.
http://bayimg.com/CaoCDAadE

The shot of a single pulse.

http://bayimg.com/CAOCEAaDe

And then with a higher reverse voltage... conducting all the time.
http://bayimg.com/CAoCGaade

(Voltage scale changed for the last.)

George H.

Cool. I wonder if you're approaching some sort of single-photon
avalanche/Geiger mode. The dark behavior looks like a typical small
zener diode at low current, a really noisy sawtooth oscillation.

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot comhttp://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation- Hide quoted text -

- Show quoted text -

Yeah the low current looks pretty much like a ~20V zener biased to the
corner.
Where I assume it's the whole diode capacitance discharging..

Here I've got 100k ohm and ~10-20 us TC so 100- 200pF.  That seems
like a lot for a little  LED.  .. ohh.. I just had some coax with
'grabber clips'... ~170pF...

A x10 probe tomorrow.

Hey for those digital type guys, you could stick a comparator on the
output and count pulses.
As you keep increasing the voltage you hit a quiet region, where it
looks resistive.

Well I've only looked at one red LED.  (I hope it's not a golden
part.)

George H.- Hide quoted text -

- Show quoted text -

HEY!  I think I may be counting single photons! (At extremely low
efficiency)  This is amazing.  (So just try it yourself.)

A variable power supply reverse biased red LED in 5mm package (Vr~24
volts).  100 kohm current limiting (and sense) resistor,  look at
current through the 100k ohm with a x10 scope probe.  Adjust voltage
till you see some RC spikes.  Now cover the LED with something black.
The pulses stop!  I turned out the lights in my lab and can still
'see' the light that's coming in from the room next door.  I need a
bit of buffering so I can send the pulses into a counter.

The count rate is highly dependent on the bias level.
24   V no counts (at 200mV threshold)
24.5 V 500 counts/sec  in room light
25   V 4.5k counts/ s in same light.
25.5 V 19kk/sec.
Click to expand...
Just a quick addition, At the higher voltages it's not as light
sensitive.

The diode is just avalanching away on it's own... with or without any
light.
Geo
  Total Friday Fun!  (I've gotta put some final changes into a pcb
too.)

I should hit up google 'cause it seems like someone must have done
this before.

George H.- Hide quoted text -

- Show quoted text -
Click to expand...
 
George Herold wrote:
On Apr 27, 1:18 pm, Phil Hobbs
pcdhSpamMeSensel...@electrooptical.net> wrote:
George Herold wrote:

On Apr 26, 9:05 pm, George Herold <gher...@teachspin.com> wrote:
On Apr 26, 7:14 pm, John Larkin <jlar...@highlandtechnology.com
wrote:

On Thu, 26 Apr 2012 06:20:20 -0700 (PDT), George Herold

gher...@teachspin.com> wrote:
On Apr 25, 10:10 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
George Herold wrote:
On Apr 25, 5:39 pm, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

Bernhard Kuemel wrote:

Hi seb!

I tried to measure the Vrbd of LEDs and found the resistance dropping:

Vr R(MOhm)

3.18 244.6153846154
3.97 59.2537313433
4.23 48.6206896552
4.82 36.7938931298
5.65 27.5609756098
6.08 22.7715355805
7.61 16.295503212

I guess I have not reached the breakdown voltage and I need a power
supply with more voltage.

However, I wonder, what the definition of breakdown voltage is. Usually
you see the sharp increase in current at Vbd in the diode characteristic
curve. But isn't this a matter of zoom? When I use nA instead of mA on
the current axis the curve will look similar with the breakdown
(forward) voltage shifted towards 0. IMHO the curve will look exactly
the same if it's a purely exponential curve and you zoom in or out.

Or is there a voltage below which no impact ionization occurs and this
can be seen as lowest possible definition of Vbd? But I rather think
there is always a chance for a free electron to gain enough energy to
knock free another electron. It'll just never make an avalance through
the whole barrier below a certain voltage. OTOH if a single electron
travels through the barrier due to a low voltage and at the other side
it happens to get bounced around by the lattice atoms to enough energy
to kick free a second electron that's an avalanche that made it through
the whole barrier. So at any voltage there'll be avalanches and
avalanche current will increase (exponentially, I guess) over the whole
voltage range.

Then there's zener breakdown which I think is some kind of tunneling.

Bernhard

Did you also subject the LED to various light sources concentrated on
the package while doing this? Might be interesting on the results
differences.

Yeah I did, When you biased it right to the breakdown region you
could definitely see the effect of sticking an light up to it. Try
it. Everyone's got a red 5mm LED, 100k ohm and ~30V power supply.

George H.

Jamie- Hide quoted text -

- Show quoted text -

Oh, I've already done this not to long ago when I was pondering on an idea.

How ever, I am trying to see where you are getting the noise from?
When I did it, all I saw on the scope was a PV effect at 1 uA, it
could've been more, been a while.

I used my over head light which is nothing more than a incandescent
52 watt. I did see the 120 hz in the signal, too, when getting the
exposure to where I was getting 50% forward biasing voltage for that LED.

But I was able to get over 1 V as a PV with out any biasing, just the
LED on the leads. It would make for a nice photo detector in a pinch
though if you have the hi-z circuit for it.

I guess if one was to have a few LED's in series with HV applied and
wait for a few photons to stop by for visit it would then act as a photo
multiplier and push things a long, thus giving you a very sensitive
detector. Or at least I think it would :)

I'll have to set that experiment up again at work, this time using the
Lecroy maybe and see if I can see anything I may have missed before.

Jamie- Hide quoted text -

- Show quoted text -

Hi Jamie, Here’s some quick ‘scope shots. (Still set up on my
bench.)

The first is just when the PD starts to reverse conduct, with no
light.
http://bayimg.com/CAOCcaade

And then at same voltage with the light shinning.
http://bayimg.com/CaoCDAadE

The shot of a single pulse.

http://bayimg.com/CAOCEAaDe

And then with a higher reverse voltage... conducting all the time.
http://bayimg.com/CAoCGaade

(Voltage scale changed for the last.)

George H.

Cool. I wonder if you're approaching some sort of single-photon
avalanche/Geiger mode. The dark behavior looks like a typical small
zener diode at low current, a really noisy sawtooth oscillation.

--

John Larkin Highland Technology, Inc

jlarkin at highlandtechnology dot comhttp://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation- Hide quoted text -

- Show quoted text -

Yeah the low current looks pretty much like a ~20V zener biased to the
corner.
Where I assume it's the whole diode capacitance discharging..

Here I've got 100k ohm and ~10-20 us TC so 100- 200pF. That seems
like a lot for a little LED. .. ohh.. I just had some coax with
'grabber clips'... ~170pF...

A x10 probe tomorrow.

Hey for those digital type guys, you could stick a comparator on the
output and count pulses.
As you keep increasing the voltage you hit a quiet region, where it
looks resistive.

Well I've only looked at one red LED. (I hope it's not a golden
part.)

George H.- Hide quoted text -

- Show quoted text -

HEY! I think I may be counting single photons! (At extremely low
efficiency) This is amazing. (So just try it yourself.)

A variable power supply reverse biased red LED in 5mm package (Vr~24
volts). 100 kohm current limiting (and sense) resistor, look at
current through the 100k ohm with a x10 scope probe. Adjust voltage
till you see some RC spikes. Now cover the LED with something black.
The pulses stop! I turned out the lights in my lab and can still
'see' the light that's coming in from the room next door. I need a
bit of buffering so I can send the pulses into a counter.

The count rate is highly dependent on the bias level.
24 V no counts (at 200mV threshold)
24.5 V 500 counts/sec in room light
25 V 4.5k counts/ s in same light.
25.5 V 19kk/sec.

Total Friday Fun! (I've gotta put some final changes into a pcb
too.)

I should hit up google 'cause it seems like someone must have done
this before.

George H.

That _is_ fun. Do you have enough ND filters lying around that you can
make a 1 photon per millisecond per die area light source for it? You
can figure out the threshold number of photons by looking at how the
count rate goes up with light level-- a few ND1 filters in a row would
allow a simple measurement of that.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot nethttp://electrooptical.net- Hide quoted text -

- Show quoted text -

So I tried comparing light levels with a photodiode. In the room
lights this was hopeless. (vastly different wavelength
sensitivity.)

But then I turned off the room lights and stuck a red LED onto a PD
and then onto the reversed biased (RB)LED. Trying for maximum signal
each time.

The numbers for the RBLED are a bit scattered. The maiximum light
input was 'tweaky' wrt angle and position. Here's some data

Vf red led photodiode RBLED
1 kohm in voltage counts/sec.
series 100k ohm gain

0 0.004 0-3 some light in the room.
2.05 0.25 25
3.03 1.22 72
4.06 2.14 120
5.33 2.8 160
10.0 4.4 280

Then the same but with a yellow (high brightness) LED as the light
source.

Vf PD RBLED
2.03 0.303 260
2.6 1.35 1.4k
3.04 2.57 2.4k
4.14 4.4 4.3k
5.02 7.7 5.6k
6.38 11.5 7.2k

So the RBLED is a lot more sensitive to the yellow light. (as you
would expect.) The count rate is at least roughly linear with the
light intensity. (I think that means it can't be some weird two
photon process that gives the pulses.) At the highest count rates
for the yellow LED I was getting some overlapped pulses on the
scope... those might not have been counted. So the apparent fall off
in sensitivity for the high light intensity yellow LED is expected.
I've got a piece of coax with clip leads connecting it to a little amp
and the pulse width is still about 10-20 us. I need a little one or
two transistor buffer to hang on it.

The photon generated count rate is a strong function of the bias
voltage. All the above data was taken with Vb= 24.3V. This gives
counts in the room light of ~450 per sec. At 24.9 V the room light
count rate is 4800. (And this is still all photon generated, I can
trun off the lights and cover it with black plastic and get zero
counts per second.

I'm not sure if I answered your threshold question or not Phil.

Well I tried another brand of red LED. (Avago HLMP-EG30-NR000)
635nm. And this showed none of the pulsing avalanche breakdown
behaviour.

The LEDs we purchased were from Newark part number 92N5331. No longer
carried. :^(

So I don't know if these are 'special' in some way. I tried three of
them from the drawer and all avalanched at ~24 volts.

I've got a few other different color LEDS that I'll try.

George H.
Click to expand...
Now _that_ is cool. It really does look like a single-photon process,
albeit inefficient.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net
 
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