I'm trying to understand this I-V curve (see Ascii art below.)* the sample is a piece of n-type Si (I don't know doping density.. lightly doped.) There are Ti/Au contacts (made into a Hall bar, A stripe of current input on each end and four voltage probe points along the length (3mm x 6mm maybe)) This is just the I-V across the large current contacts. |(I) ~150 uA -| -------- | / | / | / Slope ~20k ohm | / |/ ----------+-------------- (V) /| ^ / | 3 V / | / | symmetrical at reverse bias.
So the contacts look ohmic to about 150 uA @ 3V where they roll off and become constant current (tested only to 10 V bias) I'm not sure the process steps in making the contacts, but I'm assuming a layer of silicon oxide, or some other surface crud. (I'll be sending off an email on Monday to gather more information.) I'm trying to understand what's going on. It's like a depletion fet with S-G shorted.
I cooled the device down and the curve collapses rapidly (data book's at work) at something like 200 K the resistance had increased the 'corner' voltage decreased to (~300 mV) and the 'saturation' current decreased proportionally. The 'resistance' increase may be partially due to the round-i-ness of the corners. (not shown in ascii art.)
Any thoughts?
Oh I should add that I've seen similar things (not as high a voltage) with 'crappy' rectifying Schottky diode contacts. So a string of crappy diodes at each end is a possible model... in which case I'm just trying to understand the 'crappy' part.
George H.
*I wanted to start this with a rant about co-worker, but instead put it here.