Temperature-Dependent Optical Absorption and DLTS Study of As-Grown and Electron-Irradiated GaSe Crystals

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Optical absorption spectra of 9 MeV electron-irradiated GaSe crystals measured at temperatures in the range from 9.5 to 300 K were analyzed. The absorption spectra with features caused by Ga vacancies in two charge states and direct interband transitions were fitted by a model equation. Temperature dependencies of the defect concentrations and optical transition energies, as well as of the GaSe band gap, were determined. Current- and capacitance-voltage characteristics and DLTS spectra were measured for as-grown and electron-irradiated GaSe slabs with Sc (barrier) and Pt (ohmic) contacts. An experimental Sc/GaSe Schottky barrier height of 1.12 eV was determined in close agreement with a theoretical estimate. The activation energy and the hole capture cross-section deduced from the DLTS data are 0.23 (0.66) eV and 1.5 × 10−19 (2.3 × 10−15) cm−2 for the supposed VGa−1 (VGa−2) defect. For the electron-irradiated GaSe crystals, the found activation energies are close to the values inferred from the optical measurements.