Evidence of defect band in carbon-doped GaN controlling leakage current and trapping dynamics

Analysis of carbon doped GaN (GaN:C) layers in a wide temperature range reveals the same non-Arrhenius thermal behavior of capacitance transients related to trapping/detrapping dynamics on carbon defects and of the leakage current. Our results indicate that GaN:C does not behave like a classical semiconductor but is rather determined by a defect band (DB). Leakage via DB is the slowest process in charging/discharging dynamics, thus controlling it. We propose a microscopic model of carrier exchange between the carbon atom and the DB which can also explain the wide range of activation energies attributed previously to carbon. Understanding of leakage mechanisms and its interplay with charging is an important step towards optimization of GaN HEMT buffers.