It is noticed repeatedly that, the Al/n-SiC contacts are exhibiting both p- and n-type Schottky barriers even though the contacts are prepared under the same conditions. Why is it happening? How to go about it?
(Here the SiC substrate is n-type and highly doped >10^17)
What Schottky barrier height do you measure for the different types and what kind of behaviour do they show if the temperature is increased?
Dear Arnulf,
Thanks for replying.
I could see metal/n-type and metal/p-type I-V characteristics for identical Al contacts fabricated on the same n-type SiC substrate (under same biasing conditions).
Unfortunately, I could not able to perform temperature dependent I-V studies. But, instead I tried with the annealing of contacts, but it has not altered greatly in this behaviour.
The problem could be related to any of these three effects:
i) local surface contamination of the SiC substrate prior to deposition of the Al;
ii) partial oxidation of the Al layer in air or during preparation;
iii) chemical reactions at the SiC/Al interfaces due to annealing (lilely only at very high temperatures)
One way to study this would be to analyse cross-sections through the contacts by analytical TEM.
However, the results for not similar for all the contacts either before or after annealing. Further, the annealing temperature was kept not greater than 100 C.
Any explanation on "doping induced effects" or "effective work functions"?
(as Al acts as a p-type donor in SiC).
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