Zener Diode: germanium vs. silicon

[Number2Pencil]

I have to utilize a Curve Tracing machine on a 5V Zener Diode for a lab. The curve tracer shows voltage vs. current. The lab asks me to examine the curve and determine whether it is a Silicon or Germanium diode, but I'm wondering...what would be different about the graphs of the two types? Wont they both have a shoulder near -5V?

Oh yeah, I only get to do it reversed biased, as it doesn't show 4 quadrants worth of graphs. So I can't look at the shoulder for forward biased. Is there a trick or is the question a trick?

 

[electricsheep]

This is a strange one, and I'm afraid I cannot help much. However, are you sure you're supposed to determine whether a *zener* diode is made of silicon or germanium? (If it's just a diode, we can inspect the forward threshold voltage, but I'm not sure about zener diodes. Could it be a question asking you to distinguish between a zener diode and an avalanche diode?)

What I'd do is look up data sheets on the two types of zener diodes beforehand and ascertain the differences in the region of interest on the characteristic curve, then do the lab work.

 

[berkeman]

Maybe the Isat value is different between them? That's the reverse leakage current in the reverse bias region before you reach the Zener breakdown region. I don't know whether the Isat values will be different, but it's worth looking into.

 

[Number2Pencil]

I looked for a good while and couldn't find any data sheet online that specified a germanium zener diode. I did look at several Silicon zeners and found zener voltages ranging from 3V to 100V.

I guess I can't throw Silicon out just yet. And yes, I've double checked and it does ask to determine if the *zener* is silicon or Germanium

 

[NoTime]

Don't know if this will help but there is a reference
http://prola.aps.org/abstract/PR/v83/i3/p650_1

 

[marcusl]

Doesn't Ge has high reverse leakage compared to Si? (Or is my memory too hazy?) I think the difference is a very large factor (10's of uA/cm^2 vs 0.1 nA/cm^2), but maybe soemone can check in a book like, e.g., Sze.

 

[Averagesupernova]

Marcus, I think you hit it. I had forgotten about this and was reluctant to post since I couldn't think of anything other than to test it forward biased.

 

[pooface]

EDIT:yea you are right Supernova. my bad. Sorry I don't have an answer for the thread starter.

 

[Averagesupernova]

Read the first post again poo. He's only allowed to do it in reverse.

 

[marcusl]

Number2Pencil, can you share your results with us?

 

[AlephZero]

The cheapskate way is forget about the curve tracer and read the part number. BZ... is a silicon zener, AZ... would be germanium, if such a thing exists.

 

[leright]

hmmm...wouldn't the fact that the Ge bandgap is smaller than Si's (higher valence shell) indicate that, as marcusl stated, the reverse leakage would be higher?