Origin of Surface Barrier Temperature Dependence for the Polar GaN Surface

Combining the mature technology of gallium nitride (GaN) with emerging materials such as van der Waals crystals is presently an important path in applied science research. Up to now, a broad spectrum of optoelectronic devices including light emitters, photodetectors, and solar cells based on mentioned materials has been presented. Understanding and controlling the surface-related phenomena is a crucial aspect for proper electrical device operation. In particular, an insight into the impact of external conditions such as elevated temperature on technologically important parameters such as surface barrier is of great importance. In this study we propose the first spectroscopic investigation of the vulnerability of the surface barrier on temperature for the Ga-polar GaN surface. Studies performed in the 300-440 K temperature range using contactless electroreflectance (CER) enabled nondestructive probing of GaN surface states. The range of investigated materials was extended to graphene/GaN and h-BN/GaN hybrids together with GaAs as a reference in order to provide a comprehensive case study. We show that GaN surface densities of states revealed robust temperature dependence compared to the energy gap. The mechanism of temperature-induced carrier redistribution at the surface is proposed as an explanation.