High temperature stable WSi/sub x/ ohmic contacts on GaN

Abstract

We have sputter-deposited 500- 120081 thick wSi0.4~ metallization onto n' GaN (e10'9cm-3) doped either during MOCVD growth or by direct Si ion implantation (5~10'~cm-~, 100 keV) activated by RTA at 1100°C for 30 secs. In the epi samples ~c values of -10-14szcm2 were obtained, and were stable to -1OOOC. The annealing treatments up to 600°C had little effect on the WSiXlGaN interface, but the p-W2N phase formed between 700-800C, concomitant with a strong reduction (approximately a factor of 2) in near-surface crystalline defects in the GaN. Spiking of the metallization down the threading and misfit dislocations was observed at 800C, extending >5000A in some cases. his can create junction shorting in bipolar or thyristor devices, Rc values of <106Qcm2 were obtained on the implanted samples for 950oC annealing, with values of after 1050°C anneals. The lower & values compared to epi samples appear to be a result of the higher peak doping achieved, -5~10~' ~m-~. We observed wide spreads in & values over a wafer surface, with the values on 950°C annealed material ranging from 10- There appear to be highly non- uniform doping regions in the GaN, perhaps associated with the high defect density ( 1010cm-2) in heteroepitaxial material, and this may contribute to the variations observed. We also believe that near- surface stoichiometry is variable in much of the GaN currently produced due to the relative ease of preferential NP loss and the common use of Hz- containing growth (and cool-down) ambients. Finally the ohmic contact behavior of WSix on