Nonalloyed Cr/Au-based ohmic contacts to n-GaN

Nonalloyed Cr/Au-based metal contacts to n-GaN have been demonstrated. The deposited Au/Cr/n-GaN contacts exhibited a specific contact resistance (rho(c)) of approximately 5.6 x 10(-5) Omega cm(2). Although the nonalloyed Ti/Al-based contacts to n-GaN can also exhibit a comparable rho(c) 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 degrees C. However, the annealed Cr/Au-based contacts exhibited an Ohmic characteristic and had a smooth surface when annealing temperatures did not exceed 700 degrees 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. (C) 2007 American Institute of Physics.