Study of a common deep level in GaN

A deep level with the activation energy around 0.45 to approximately 0.6 eV has persistently appeared in GaN samples grown by hydride vapor-phase epitaxy, organometallic vapor-phase epitaxy and molecular beam epitaxy. However, the origin of this deep level still remains unclear. In this study, we investigated this deep level trap E2 of GaN films by using deep level transient spectroscopy. The GaN films were grown by a conventional low pressure organometallic vapor-phase epitaxy technique with different V/III ratios. Frequency-dependent capacitance measurement was performed to determine the most proper frequency for capacitance measurements. Capacitance-voltage measurements were then applied to obtain the carrier concentrations. The carrier concentration became higher as the flow rate of NH3 got lower. The deep level E2 is found in GaN samples grown with higher V/III ratios. The trap concentration of level E2 increased with increasing NH₃ flow rate. Compared with the theoretical prediction of the nitrogen antisite level in GaN, the level E2 was believed to be related to nitrogen antisites.