Self-Trapped Hole in Ultra Wide Bandgap β-Ga2O3 Films; Its Temperature Dependent Luminescences

Self trapped Hole (STH) is an intriguing property of Ultra-wide Bandgap β-Ga₂O₃ that inhibits deep-UV luminescence (PL), as well as p-type conductivity. STH formation in Ga₂O₃ is due to a strong electron-phonon coupling so that holes in the valence band induce crystal distortion with electrostatic potential that spatially localizes the holes. In order to obtain the activation energy of the trapped holes, we studied the thermal quenching of the STH PL, at ~3.56 eV, in the temperature range 77 K - 622K. We found the activation energy of the holes to be ~71 meV, which is significantly lower than the theoretical holes’ self-trapping energy ~0.53 eV.^[1] Thus, implying that the STH PL channels could be via other processes. These other channels will be discussed in terms of a configurational model in which the trapped holes are free into a non-luminescence state. Additionally, we found that the STH PL redshifts by ~14 meV in the range 77 K - 622 K. This shift is small in comparison to the thermal response of ~200 meV for β-Ga2O3 film optical band gap that we previously found.[2] The slight shift also suggests that STH is a deep level energy state. Our work has found this level to be ~1.30 eV relative to the valence band of β-Ga₂O₃.^[2]