Surface Photovoltage Spectroscopy over Wide Time Domains for Semiconductors with Ultrawide Bandgap: Example of Gallium Oxide

Abstract

A nonconventional approach is proposed for the measurement of surface photovoltage (SPV) signals over very wide ranges in photon energy and time. Regimes for AC, DC, and combined AC–DC measurements are defined and applied for the characterization of a β-Ga2O3 crystal by transient and modulated SPV spectroscopy, spectroscopy in the mode of a Kelvin probe and single-pulse SPV transients from 10 ns to 1000 s with the same electrode. Numerous electronic transitions are distinguished in β-Ga2O3 depending on the measurement regime, the time response and the history of measurement. An accumulation of negative charge at the surface of β-Ga2O3 is observed at long times independent whether the SPV signals are positive or negative before. The nonconventional approach of measuring SPV signals opens new opportunities for investigating electronic properties of semiconductors with ultrawide bandgaps and any other photoactive materials.