Nitrogen-displacement-related electron traps in n-type GaN grown on a GaN freestanding substrate

Energy levels due to intrinsic point defects are identified by deep-level transient spectroscopy (DLTS). Electron-beam (EB) irradiation created nitrogen vacancies (V-N) and nitrogen interstitials (N-I) in n-type GaN layers grown via metalorganic vapor phase epitaxy on freestanding GaN substrates, where the irradiation energies were selected to be within 100-401keV to displace only nitrogen atoms in GaN. Two electron traps, EE1 (0.13eV) and EE2 (0.98eV), were observed in the DLTS spectra. The production rates of EE1 and EE2 were 0.093 and 0.109cm(-1) under 401keV irradiation, which were nearly equal values. In the DLTS spectra recorded for EB-irradiated samples at the energy ranging from 100 to 401keV, EE1 and EE2 were found to appear simultaneously at an irradiation energy of 137keV and were observed at energies greater than 137keV. On the basis of a comparison with the results of recent first-principles calculations, we attributed the EE1 and EE2 peaks to nitrogen vacancies V-N (+/0) and nitrogen interstitials N-I (0/-), respectively. Furthermore, annealing led to reductions of the densities of these traps at the same rate. The reduction of the densities of EE1 and EE2 can be explained by the migration of N-I and the subsequent recombination with V-N. The displacement energy of 21.8eV for nitrogen in GaN was obtained from the irradiation-energy dependence of EE1.

Automated summary

In this study, energy levels due to intrinsic point defects in n-type GaN layers were investigated using DLTS. Two electron traps, EE1 and EE2, were observed, corresponding to nitrogen vacancies and nitrogen interstitials. Annealing led to a reduction in the trap densities at the same rate, indicating the migration of nitrogen interstitials and subsequent recombination with nitrogen vacancies.