Nonalloyed Cr∕Au-based Ohmic contacts to n-GaN

Abstract

Nonalloyed Cr∕Au-based metal contacts to n-GaN have been demonstrated. The deposited Au∕Cr∕n-GaN contacts exhibited a specific contact resistance (ρc) of approximately 5.6×10−5Ωcm2. Although the nonalloyed Ti∕Al-based contacts to n-GaN can also exhibit a comparable ρc value, their thermal stability is inferior to the Cr∕Au-based contacts. This could be attributed to the fact that Al tends to ball up during thermal annealing. Thus, the surface morphology of most of the annealed Ti∕Al-based contacts was quite rough, and the contacts became rectified when they were annealed at a temperature below 700°C. However, the annealed Cr∕Au-based contacts exhibited an Ohmic characteristic and had a smooth surface when annealing temperatures did not exceed 700°C. In addition, the thermal stability could be further improved by inserting a Pt layer between the Cr and Au layers. This scheme could prevent the diffusion of Au into the Cr layer, thus preventing Au from reaching the Cr∕GaN interface where it could form a possible Ga–Au phase, which would degrade the Ohmic contacts.