Ohmic junction in Cat's-whisker detector

[wasia]

Hello,

I have read (wiki and physicsforums besides other sources) about how preparing an ohmic junction is hard on wafers in the clean room and that usually one gets a Schottky barrier instead, if one is not careful enough. This makes me wonder, how come that people used to get an ohmic contact on the ancient"[URL detector[/URL] by just "clamping (the crystal) with setscrews" ?

Or if I am wrong with my assumptions and it is not an ohmic contact, just a random collection of p-n junctions, why does the device work at all?

Thanks in advance.

 

[caffenta]

Technically, only one contact should be rectifying (the springy one). The other should be ohmic. Clamping down is a sort of brute-force way to make ohmics. You have a very large area and the surface gets ground up which removes the surface layer (oxide or whatever). Eventually, electrons might find an ohmic or quasi-ohmic path. And if it doesn't work, you wiggle it some more. But in some cases, you will never get a properly ohmic contact. It depends on the material, doping, etc.

And I'm pretty sure the specs were much lower then. They could live with higher-resistance contacts, as long as they were more or less linear. Now we need the contacts to have a low resistance and work reliably every time (especially in production).

 

[shawl]

I suggest a method usually used in our experiment.

Depositing Au film on the sample first, and then you have 2 choices:
1. sticking the detecting wire by sliver adhesive.
2. preparation with the indium electrode.