Mechanism for Long Photocurrent Time Constants in α-Ga2O3 UV Photodetectors

Deep centers and their influence on photocurrent spectra and transients were studied for interdigitated photoresistors on alpha-Ga2O3 undoped semi-insulating films grown by Halide Vapor Phase Epitaxy (HVPE) on sapphire. Characterization involving current-voltage measurements in the dark and with monochromatic illumination with photons with energies from 1.35 eV to 4.9 eV, Thermally Stimulated Current (TSC), Photoinduced Current Transients Spectroscopy (PICTS) showed the Fermi level in the dark was pinned at E-c-0.8 eV, with other prominent centers being deep acceptors with optical thresholds near 2.3 eV and 4.9 eV and deep traps with levels at E-c-0.5 eV, E-c-0.6 eV. Measurements of photocurrent transients produced by illumination with photon energies 2.3 eV and 4.9 eV and Electron Beam Induced Current (EBIC) imaging point to the high sensitivity and external quantum efficiency values being due to hole trapping enhancing the lifetime of electrons and inherently linked with the long photocurrent transients. The photocurrent transients are stretched exponents, indicating the strong contribution of the presence of centers with barriers for electron capture and/or of potential fluctuations.

Automated summary

The influence of deep centers on photocurrent spectra and transients of interdigitated photoresistors on alpha-Ga2O3 undoped semi-insulating films was investigated. Characterization techniques including current-voltage measurements, Thermally Stimulated Current (TSC), and Photoinduced Current Transients Spectroscopy (PICTS) revealed the presence of deep acceptors and deep traps, along with a pinned Fermi level at E-c-0.8 eV. Photocurrent transients and Electron Beam Induced Current (EBIC) imaging indicated that the high sensitivity and external quantum efficiency values were attributed to hole trapping, which enhanced the electron lifetime and were associated with long photocurrent transients. The stretched exponents observed in the photocurrent transients suggest the contribution of centers with electron capture barriers and/or potential fluctuations.