Metal-Semiconductor contacts.

Hi All, I'm headed back to the CNF

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shortly. It's a user clean room facility for semiconductor processing. My goal is to make some very simple samples. 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.

Samples 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 post.

George H.

Reply to
George Herold
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Have you been to the Uris Library at Cornell? It's about the most beautiful rooms that I've ever seen. Get a book and sit for a while in one of the leather chairs that look out on the river.

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John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
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John Larkin

Cool, Last time there I stayed at the Robert H. Treman state park.

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Any free time was spent hiking the gorges.

George H.

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George Herold

The Brat went to Cornell (she majored in softball and beer pong) so we visited a few times. It's really beautiful up there. The main road on-campus passes over a waterfall. We hiked one gorge where you drove in by basically fording a stream in the rental car. We wound up at Buttermilk Falls or something.

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
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John Larkin

I live on the same Allegheny plateau. There is a creek and falls behind my house, smaller but similar. I take a walk and come back and tell my kids what a beautiful place they live in, they mostly ignore me.

Hey this a good about contacts,

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but it stops in the 1940's...

It says that you can't make ohmic contact to n-type Ge. Here's my I-V curve. (I is y-axis with gain listed.)

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the piece of intrinsic Ge with Al was a weird sort of diode...

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these are two of the same contacts back to back, so a diode "should" look like this,

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At least I think...

George H.

Reply to
George Herold

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