Improvement of Ni nonalloyed ohmic contacts on p-GaN films by changing thickness of p-InGaN capping layers

The influence of the thickness of p-type InGaN (p-InGaN) capping layers grown on p-type GaN (p-GaN) on the electrical properties of Ni contacts on p-GaN was investigated in this study. Experiments and simulations indicated that a thicker p-InGaN capping layer grown on p-GaN led to the formation of a higher concentration of a two-dimensional hole gas (2DHG) at the interfaces. In addition, owing to a low barrier at the interfaces, holes can be easily injected into the p-GaN layer through recessed channels and a 2DHG channel, resulting in the formation of nonalloyed ohmic contacts with a low specific contact resistance of 1.7 x 10(-5) Omega cm(2).