Greetings.
I have struggled with Al ohmic contacts between a Ge Hall bar and Au electrodes. I thought the problem was the Ge/Al interface (increased resistance due to native oxide formation on the Ge side of the contact), but to be sure the problem was not on the metal side of the contact, I made two Au electrodes connected by an Al contact. All done by metal evaporation.
I proceeded then to apply from -10^-6 to 10^-6 A and I measured resistance of the system of nearly 10k Ω , much higher than what I was expecting for a system composed only of metals but of the same order as I was measuring with a 2-terminals measurement of my Hall bar. Besides, a few of these contacts showed a non-ohmic behaviour similar to what I have experienced before with the Hall bar, leading me to believe the Au/Al contact is the problem. What could be causing this?
Upon checking my samples before and after annealing, I noticed that the Au electrodes are shinning golden before the annealing, but become somewhat transparent afterward. Is this due t diffusion into the SiGe layer the hall bar sits on top of? Could SiGe be mixing with the Au because of the annealing process, leading to an increased resistivity?
The annealing time is 1h in forming gas and the sample has a Si substrate, followed by layers of SiGe, Ge, SiGe, Si (cap layer).
Thank you very much.
Dear Gabriel G. Maia,
As I know, diffusion of anode material at the interface into the active layer can be possible, resulting in changing the work function of neighbor materials. In fact, sometimes annealing can prevent the electron migration by creating a buffer condition due to diffusion of material into each other. But often, annealing results in better crystallinity and lower resistivity. I guess your problem is related to the temperature and time of annealing.
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