Trap dynamics in the carbon-doped GaN buffer of AlGaN/GaN HEMTs through back-gate bias and sub-bandgap illumination

The dynamic interactions among multiple trap states in the carbon-doped (C-doped) GaN buffer of AlGaN/GaN high-electron-mobility transistors have been studied and quantitatively characterized through a time-resolved optoelectronic spectroscopy approach. This technique combines transient channel current analysis, back-gate bias stress, and tunable sub-bandgap illumination to elucidate the underlying ionization and recombination mechanisms, which govern trap behaviors under combined electrical and optical excitation. According to the back-gating measurements, the ionization of C-related acceptor traps in the buffer layer can be confirmed as the dominant mechanism. Compared with dark conditions, red illumination accelerated current delay, indicating enhanced ionization of acceptor traps under the combined influence of electric and optical fields. Conversely, the current increase observed under blue and green illumination confirmed the presence of donor traps. Notably, the activation of donor traps under blue illumination, which are classified as CN (0/+) traps, was further confirmed by cathodoluminescence spectroscopy. The proposed method is able to effectively reveal both acceptor and donor traps in the GaN layer, which cannot be achieved by conventional approaches.