The movement of the Fermi level in heavily C doped GaN

It is empirically well acknowledged that C doping makes GaN high-resistive. However, the detailed doping type and high-resistivity mechanisms of C doped GaN, which are extremely essential for GaN power electronics, still remain unclear. In this work, we clarify the mutative (from downward to upward) shift of the Fermi level and the n-type conductivity in heavily C doped GaN grown by MOCVD for the C concentration increases over a critical value, by combining photo-assisted KPFM and Seebeck coefficient measurements. We also discuss the reverse transition of Fermi level and ultimately n-type conductivity should be attributed to the self-compensation and other donor-type compensation centers introduced along with C doping. (C) 2022 The Japan Society of Applied Physics