Electrical signatures of nitrogen Frenkel pairs in GaN

Abstract

Deep level transient spectroscopy (DLTS) has been applied to electron-irradiated GaN grown homoepitaxially on highly conductive ammono-GaN substrates. Electron beam energies of 350 and 370 keV were employed, with doses of 12 000 kGy and 1500 or 5000 kGy, respectively. Three electron traps were detected, with concentrations in the range of 1012–1014 cm−3. In addition to the E1 and E3 traps present in as-grown samples, an electron-irradiation-induced peak with a maximum at ∼100 K was observed in the DLTS spectra, consistent with the so-called EE1 trap. EE1 has frequently been associated with a donor level of the nitrogen vacancy {VN (0/+)}. However, the unusual dependence of the EE1 peak magnitude, position, and shape on the filling pulse duration (tp) indicates that the signal does not originate from electron emission from a single level of a simple point defect but instead comprises multiple-level components. We argue that the EE1 DLTS signal in electron-irradiated GaN consists of electron emission contributions from isolated nitrogen vacancies and N-related Frenkel pairs. Furthermore, DLTS analysis reveals a strong electric-field enhancement of the electron emission rate for all components of the signal, consistent with the donor nature of the EE1-related defect levels. The observed DLTS features are attributed to the influence of negatively charged Ni atoms on the electronic properties of VN, with the electron emission and capture rates of electrons by the VN component of the pairs depending on the separation between the pair constituents.