Electronic degeneracy conduction in highly Si-doped Al0.6Ga0.4N layers based on the carrier compensation effect

Abstract

Electronic degeneracy to express metallic conduction in Al-rich AlGaN for the electron injection layer enhances the efficiencies of deep ultraviolet light emitters. This study systematically demonstrates the Si doping range and conditions to realize degenerate n-type Al0.6Ga0.4N layers based on the electron compensation effect. The temperature-independent electron concentrations resulting from the degenerate band appear in high Si doping conditions to overcome the electron compensation due to carbon on nitrogen sites (CN). However, excessive Si doping of over 4.0 × 1019 cm−3 leads to the collapse of the electronic degeneracy and a switch to the temperature-dependent electron transport via the impurity bands, where the luminescence bands originating from III vacancy-Si complexes (VIII-nSi) are dominant. The key parameter is the effective donor concentration, Nd − Na, based on the reduction in electron concentrations via acceptor-like deep levels such as CN and VIII-nSi. The Hall-effect analyses for n-type Al0.6Ga0.4N layers with various Si concentrations yielded an Nd − Na value of (9.5 ± 2.9) × 1018 cm−3 to vanish the ionization energy of Si donors, which is approximately six times higher than that in GaN. The results suggest not only the optimal doping range to obtain an Al-rich AlGaN layer with metallic conduction but also the necessity of the growth condition to minimize electron compensation.