I’m headed back to the CNF (http://www.cnf.cornell.edu/) shortly.
It’s a user clean room facility for semiconductor processing.
My goal is to make some very simple samples, for use in student teaching labs.
I’ll take Ge and Si wafers and sputter or evaporate metal on them. The first task is to make ohmic contacts for transport measurements. (Hall effect and conductivity.)
I then had the brilliant (or silly) idea of also making non-ohmic (Schottky) contacts to the sample. One can then do CV measurements and get a third measure of the doping density. As well as having a built in diode.. it could be used as a temperature sensor.
My first trip there was wildly successful.
I sputtered two dots of titanium followed by aluminum on the samples and then evaporated two dots of Al alone.
Table of results: Sample Ti/Al Al only Si-p diode w/anneal ohmic contact Si-n ohmic diode w/anneal Si-int. ohmic (unsure.. I broke it.) Ge-n ohmic ohmic Ge-int ohmic some diode behavior. Poor adhesion.
Sample I-V was done back in Buf. And then samples were annealed up to
300C on a hot plate. Except for the intrinsic Ge the metal adhesion was good.
(They all pasted the scotch tape test.)
I must say that titanium looks to be a nice metal for contacts.
OK after that intro some questions.
I feel I’m reinventing the wheel, I’ve done a lot of on-line and library reading
but there is not very much practical advice for making contacts to semiconductors.
(There is a lot of theory.) I keep wondering if there is some old Bell labs technical document that could help me. If anyone knows of anything like that I hope you’ll share.
I still would like to make a diode with Ge. Any ideas of a metal to try?
Probing the Ge samples with Gold pogo pins it did look like the gold made a rectifying contact. But I’m guessing gold won’t stick very well. I thought I’d try Indium.
The Ti/Al metal on Si developed a black layer around the edges.
I assume this is oxidation of the Al.
And I’m going to try Gold for the top layer.
Finally, are there any other things/ experiments
I could make/try by putting down metal on semiconductors?
I should add that the diodes displayed a nice photo-response.
Thanks for reading this rather long question.
Edit: adding Link to I-V curves (I is vertical (y) axis, chan. 2, with gain shown.) https://www.dropbox.com/sh/v7roajd0dumt1o4/AABU1luSZvJFH2IND6SkRnnWa?dl=0 Excuse the messy lab pictures, I've now got pogo sticks on my "probe station."