Investigation of Defect Characteristics and Carrier Transport Mechanisms in GaN Layers With Different Carbon Doping Concentration

In this article, a metal/carbon-doped GaN (GaN:C)/Si-doped GaN (GaN:Si) structure was used to investigate the defect characteristics and carrier transport mechanisms in GaN:C layers with different carbon doping concentration. Capacitance-voltage, current–voltage, and deep-level transient spectroscopy measurements were performed at different temperatures. At forward bias, a pinning effect was found at the interface of the GaN:C/GaN:Si layer, due to the defects capturing electrons. The forward currents of the samples with high carbon doping concentration ( ${N}_{C}> {1} \times 10^{{19}}$ cm−3) increase gradually with increasing forward bias voltage. Ohm’s law, space-charge-limited current, and variable-range-hopping mechanisms may dominate the forward current. For the samples with low carbon doping concentration ( ${N}_{C} cm−3), a device turning on behavior was observed, which is attributed to the carriers overcoming a potential barrier. In addition, the DLTS spectra reveal that only electron trapping happens at forward bias for the samples with high carbon doping concentration, while, in addition, hole trapping was observed for the samples with low carbon doping concentration. The process of the carrier capture by defects was demonstrated.