Germanium under glass ...

[jalbers@bsu.edu]

Is it safe to assume that all diodes with a glass enclosure are
germanium? I have a 1N3600 for example with a glass enclosure. Is it
silicon or germanium? I guess I could check the forward voltage
drop ...

Why are glass enclosures used?

When a glass enclosure is used, is the junction shielded from outside
light since light has an effect on the diodes reverse saturation
current?

I am trying to experiment using a common glass diode as a photo
diode. I want to reverse bias a glass diode and try to measure the
reverse saturation current with a DVOM set on micro amps. I know that
there are photodiodes designed for this but just for giggles, I wanted
to see what would happen with a glass diode.

Any help would be greatly appreciated. Thanks

 

[John Larkin]

On Wed, 24 Sep 2008 12:44:45 -0700 (PDT), "jalbers@bsu.edu"
<jalbers@bsu.edu> wrote:

Is it safe to assume that all diodes with a glass enclosure are
germanium? I have a 1N3600 for example with a glass enclosure. Is it
silicon or germanium? I guess I could check the forward voltage
drop ...

Silicon... you can google the datasheets.

Why are glass enclosures used?

Nice hermetic seal.

When a glass enclosure is used, is the junction shielded from outside
light since light has an effect on the diodes reverse saturation
current?

Most glass diodes are photosensitive, more so the older ones with the
edges of the chip exposed. LEDs are photosensitive, too.

Either can be photovoltaic, or you can reverse bias them and measure
leakage, which is maybe more common.

I am trying to experiment using a common glass diode as a photo
diode. I want to reverse bias a glass diode and try to measure the
reverse saturation current with a DVOM set on micro amps. I know that
there are photodiodes designed for this but just for giggles, I wanted
to see what would happen with a glass diode.

If you don't see much signal on the uA range, apply 9 volts or so
reverse bias and use the meter on its *voltage* range. Most DVMs have
a 10 meg input resistance so act as very sensitive ammeters at low
currents. 1 volt indicated corresponds to 100 nA, 1 millivolt to 100
pA.

Early plastic transistors were sometimes potted in translucent brown
plastic, so could be very photosensitive.

John

 

[John Fields]

On Wed, 24 Sep 2008 12:44:45 -0700 (PDT), "jalbers@bsu.edu"
<jalbers@bsu.edu> wrote:

Is it safe to assume that all diodes with a glass enclosure are
germanium?

---
No.
---

I have a 1N3600 for example with a glass enclosure. Is it
silicon or germanium?

---
Silicon.
---

I guess I could check the forward voltage drop ...

---
Better yet, check the data sheet:

http://www.microsemi.com/datasheets/1n3600.pdf
---

Why are glass enclosures used?

---
Wets the plugs and matches their thermal coefficient of expansion, which
makes a perfect hermetic seal.
---

When a glass enclosure is used, is the junction shielded from outside
light since light has an effect on the diodes reverse saturation
current?

---
No.
---

I am trying to experiment using a common glass diode as a photo
diode. I want to reverse bias a glass diode and try to measure the
reverse saturation current with a DVOM set on micro amps. I know that
there are photodiodes designed for this but just for giggles, I wanted
to see what would happen with a glass diode.

---
I don't think you'll have much luck.

I just tried it with a 1N4148 reverse biased at 25V and got 10nA through
it with shop lights on, and then with a flashlight beam on it it went up
to 20nA.

Try this:

http://www.national.com/an/AN/AN-31.pdf#page=1

Page 29.

JF

 

[John Fields]

On Wed, 24 Sep 2008 14:22:43 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

If you don't see much signal on the uA range, apply 9 volts or so
reverse bias and use the meter on its *voltage* range. Most DVMs have
a 10 meg input resistance so act as very sensitive ammeters at low
currents. 1 volt indicated corresponds to 100 nA, 1 millivolt to 100
pA.

---
Good trick.

With a 1N4148 reverse-biased with 10 volts I get about 40mV under shop
lights and about 250mV under a flashlight.


JF

 

[Eeyore]

"jalbers@bsu.edu" wrote:

Is it safe to assume that all diodes with a glass enclosure are
germanium?

Not even remotely.

Graham

 

[Eeyore]

Michael Black wrote:

Maybe today there won't be silicon in glass

1N914, 1N4148, 1N4448 and many zener types for starters.

Graham

 

[Eeyore]

Eeyore wrote:

"jalbers@bsu.edu" wrote:

Is it safe to assume that all diodes with a glass enclosure are
germanium?

Not even remotely.

Although if you can see a 'cat's whisker' it may be quite likely.

Graham

 

[Jasen Betts]

On 2008-09-24, jalbers@bsu.edu <jalbers@bsu.edu> wrote:

Is it safe to assume that all diodes with a glass enclosure are
germanium?

what? like 1N914 ? (NO)

I have a 1N3600 for example with a glass enclosure. Is it
silicon or germanium? I guess I could check the forward voltage
drop ...

easiest way to tell... otherwise google for 1N3600 datasheet

Why are glass enclosures used?

keeps the die clean, anchors the leads, heat resistant,

When a glass enclosure is used, is the junction shielded from outside
light since light has an effect on the diodes reverse saturation
current?

only if the glass is opaque or painted black.

I am trying to experiment using a common glass diode as a photo
diode. I want to reverse bias a glass diode and try to measure the
reverse saturation current with a DVOM set on micro amps. I know that
there are photodiodes designed for this but just for giggles, I wanted
to see what would happen with a glass diode.

I've detected the photovoltaic effect with a moving coil VOM and a 1N914
in sunlight.

Bye.
Jasen

 

[Jasen Betts]

On 2008-09-24, John Fields <jfields@austininstruments.com> wrote:

Try this:

http://www.national.com/an/AN/AN-31.pdf#page=1

Page 29.

you can express that more concisely as

http://www.national.com/an/AN/AN-31.pdf#page=29

In a URL everything after the # symbol is an instruction to the browser on
where to locate the cursor. That part is called the local part and is never
sent to the server, so it will not effect the data delivered to the user.
It only effects where they start.

Bye.
Jasen

 

[John Fields]

On 25 Sep 2008 09:25:26 GMT, Jasen Betts <jasen@xnet.co.nz> wrote:

On 2008-09-24, John Fields <jfields@austininstruments.com> wrote:
Try this:

http://www.national.com/an/AN/AN-31.pdf#page=1

Page 29.

you can express that more concisely as

http://www.national.com/an/AN/AN-31.pdf#page=29

In a URL everything after the # symbol is an instruction to the browser on
where to locate the cursor. That part is called the local part and is never
sent to the server, so it will not effect the data delivered to the user.
It only effects where they start.

---
Thanks. I didn't know that.

JF

 

[Rich Grise]

On Wed, 24 Sep 2008 12:44:45 -0700, jalbers@bsu.edu wrote:

Is it safe to assume that all diodes with a glass enclosure are
germanium? I have a 1N3600 for example with a glass enclosure. Is it
silicon or germanium? I guess I could check the forward voltage
drop ...

Why are glass enclosures used?

When a glass enclosure is used, is the junction shielded from outside
light since light has an effect on the diodes reverse saturation
current?

I am trying to experiment using a common glass diode as a photo
diode. I want to reverse bias a glass diode and try to measure the
reverse saturation current with a DVOM set on micro amps. I know that
there are photodiodes designed for this but just for giggles, I wanted
to see what would happen with a glass diode.

Any help would be greatly appreciated. Thanks

So, build your lash-up, mesure the forward voltage, that will tell you
if it's silicon or germanium (the 1N3600 is silicon) and the reverse
current, both light and dark.

Then report back with your results, preferably as a follow-up. (i.e.,
don't start a new thread - find this one.)

Have Fun!
Rich

 

[John Popelish]

ian field wrote:

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:48DACE48.3027914D@hotmail.com...

Eeyore wrote:

"jalbers@bsu.edu" wrote:

Is it safe to assume that all diodes with a glass enclosure are
germanium?
Not even remotely.
Although if you can see a 'cat's whisker' it may be quite likely.

Graham


Just out of curiosity, what's the spectral response of a germanium
photo-diode?

The spectral response goes well into the near infrared.
Here is an example:
http://www.thorlabs.com/thorcat/13800/13846-S01.pdf


--
Regards,

John Popelish

 

[John Fields]

On Fri, 26 Sep 2008 16:34:00 +0100, "ian field"
<gangprobing.alien@ntlworld.com> wrote:

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:48DACE48.3027914D@hotmail.com...


Eeyore wrote:

"jalbers@bsu.edu" wrote:

Is it safe to assume that all diodes with a glass enclosure are
germanium?

Not even remotely.

Although if you can see a 'cat's whisker' it may be quite likely.

Graham


Just out of curiosity, what's the spectral response of a germanium
photo-diode?

---
http://www.google.com/search?hl=en&q=Germanium+photodiode+spectral+response&aq=f&oq=

JF

 

[Eeyore]

John Popelish wrote:

ian field wrote:
"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
Eeyore wrote:
"jalbers@bsu.edu" wrote:

Is it safe to assume that all diodes with a glass enclosure are
germanium?
Not even remotely.
Although if you can see a 'cat's whisker' it may be quite likely.

Just out of curiosity, what's the spectral response of a germanium
photo-diode?

The spectral response goes well into the near infrared.
Here is an example:
http://www.thorlabs.com/thorcat/13800/13846-S01.pdf

Germanium's transparent to IR isn't it ? Don't they make IR lenses out
of it ?

Graham

 

On Sep 26, 12:05 pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:

John Popelish wrote:

The spectral response goes well into the near infrared.
Here is an example:
http://www.thorlabs.com/thorcat/13800/13846-S01.pdf

Germanium's transparent to IR isn't it ? Don't they make IR lenses out
of it ?

Beyond the long wave side of the spectral response peak (where there
is not enough energy per photon to create hole-electron pairs), it
gets rapidly more tranparent for about a decade. But it is not very
transparent, even in the middle of this IR window. Usable for lenses
and filters, but not great.

See:
http://www.harricksci.com/infoserver/Optical%20Materials/Germanium.cfm

--
Regards,

John Popelish

 

On Sep 26, 2:50 pm, "ian field" <gangprobing.al...@ntlworld.com>
wrote:

In some documentary or other it was stated that the FLIR camera lens on
police helicopters had a micron thick coating of germanium - probably vacuum
deposited.

The basic technology was adapted from military applications.

A coating of that thickness is notfunctional as an absorption filter,
but is acting as a quarter wave trap to act as an anti-reflective
coating. It is so thin that its actual absorption losses can be
neglected.

 

[Michael Black]

On Wed, 24 Sep 2008, jalbers@bsu.edu wrote:

Is it safe to assume that all diodes with a glass enclosure are
germanium? I have a 1N3600 for example with a glass enclosure. Is it
silicon or germanium? I guess I could check the forward voltage
drop ...

I don't think glass is a reliable indicator. Maybe today there won't

be silicon in glass, I don't know, but there was definitely a time
when it was common.

What I have noticed in recent years is that germanium diodes
were significantly larger than silicon, so when I see a glass packaged
diode that's larger on a circuit board, I've made the assumption it
is a germanium, and using a meter has verified it each time.

The meter is the best way, compare the reading to a diode you
know to be silicon, and you will see a significantly lower reading
on the germanium. Schottky will appear somewhere else on the scale,
so it does work out as a useful sorting method. Useful too, since
a lot of those diodes never seemed to have markings on them, and
besides, once you find germanium diodes likely they will be fine
for anything you need a small signal germanium diode for.

Why are glass enclosures used?

I can't remember.

When a glass enclosure is used, is the junction shielded from outside
light since light has an effect on the diodes reverse saturation
current?

No it's not. Decades ago, there was an article in one of the magazines

where someone needed some voltage variable capacitors, so he went
through whatever he had, and found some glass enclosed diodes that
worked particularly well. Later, he couldn't figure out where the
60Hz modulation was coming from, and he ended up doing unneeded
work on the filter in the phase locked loop. Finally, he discovers
the clear package was letting light get to the diode, and a nearby
incandescent lamp was modulating the diode with 60Hz from the AC
line.

Michael

I am trying to experiment using a common glass diode as a photo
diode. I want to reverse bias a glass diode and try to measure the
reverse saturation current with a DVOM set on micro amps. I know that
there are photodiodes designed for this but just for giggles, I wanted
to see what would happen with a glass diode.

Any help would be greatly appreciated. Thanks