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 Popelish]

jpopelish@rica.net wrote:

Most diodes ever encased in glass are silicon, but the larger glass
cases are sometimes germanium.
(snip)

Meant to add that if you can see a fine wire connecting one
side of the die to the device lead, it is more likely to be
germanium and more likely to be silicon if both leads look
like they are welded directly to the die on both sides.

I think this is because the germanium doe cannot stand the
high temperature needed to form the glass package that
contains no air space. The germanium die is placed in a
glass tube that is pre-attached to a one lead, then a second
lead with the whisker is touched to the die and the tube is
melted around that lead, while the first lead heat sinks the
die. I think.

--
Regards,

John Popelish

 

On Sep 24, 4:08 pm, "jalb...@bsu.edu" <jalb...@bsu.edu> wrote:
(snip)

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

Most diodes ever encased in glass are silicon, but the larger glass
cases are sometimes germanium. Both are light sensitive, though the
diode area exposed to light is a lot lower than large area diodes made
with transparent conductive coatings (or edge connections, only) made
for photo diode use. It might be helpful to use a transistor as a
current amplifier that will increase the diode current by a factor of
a hundred or so.

But large area photo diodes are available for modest cost if you want
to get some of the real McCoy to play with. For instance these
http://www.semicon.panasonic.co.jp/ds2/SHE00042CED.pdf
Are less than $2 from Digikey, as are these that include a blue filter
to make their response more similar to the eye:
http://document.sharpsma.com/files/BS120E0F_SS_4-28-05.pdf
They sell hundreds of types, also.