Analysis of deep levels in n-type GaN by transient capacitance methods

Abstract

Transient capacitance methods were used to analyze traps occurring in unintentionally doped n-type GaN grown by hydride vapor-phase epitaxy. Studies by deep-level transient spectroscopy (DLTS) and isothermal capacitance transient spectroscopy indicated the presence of three majority-carrier traps occurring at discrete energies below the conduction band with activation energies (eV) ΔE1=0.264±0.01, ΔE2=0.580±0.017, and ΔE3=0.665±0.017. The single-crystal films of GaN were grown on GaN formed by metal-organic chemical-vapor deposition and on sputter-deposited ZnO; a similar deep-level structure was found in both types of samples. Pulse-width modulation tests using DLTS to determine the capture rates of the traps showed that the capture process is nonexponential, perhaps due to the high trap concentration. The origins of the deep levels are discussed in light of secondary-ion-mass-spectroscopy analysis and group theory results in the literature.