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

摘要

A nonconventional approach is proposed for the measurement of surfacephotovoltage (SPV) signals over very wide ranges in photon energy and time.Regimes for AC, DC, and combined AC–DC measurements are defined andapplied for the characterization of a β-Ga_2O_3 crystal by transient and modulatedSPV spectroscopy, spectroscopy in the mode of a Kelvin probe and single-pulseSPV transients from 10 ns to 1000 s with the same electrode. Numerous electronictransitions are distinguished in β-Ga_2O_3 depending on the measurementregime, the time response and the history of measurement. An accumulation ofnegative charge at the surface of β-Ga_2O_3 is observed at long times independentwhether the SPV signals are positive or negative before. The nonconventionalapproach of measuring SPV signals opens new opportunities for investigatingelectronic properties of semiconductors with ultrawide bandgaps and any otherphotoactive materials.