Effects of the thickness of capping layers on electrical properties of Ni ohmic contacts on p-AlGaN and p-GaN using an ohmic recessed technique

In this study, the effects of the thickness of p-GaN (p-InGaN) capping layers grown on top of p-AlGaN (p-GaN) on electrical properties of Ni ohmic contacts on p-AlGaN (p-GaN) were investigated. The experiments and simulations indicated that the thicker p-GaN (p-InGaN) capping layer grown on p-AlGaN (p-GaN) led to the formation of the higher concentration of a two-dimensional hole gas (2DHG) at the interfaces. Consequently, we deduce that holes can be easily injected into the p-AlGaN (p-GaN) layer through recessed channels and a 2DHG channel, which results in the formation of the low contact resistivity. This provides a rational guideline for the development of new processing methodologies to enhance nitride semiconductor-based optoelectronic devices.