Evidence for formation of self‐trapped excitons in a β‐Ga2O3 single crystal

Abstract We have investigated photoluminescence (PL) and absorption properties of a β‐Ga 2 O 3 single crystal from the viewpoint of the stability of self‐trapped excitons (STEs). A broad PL band with a large Stokes shift, which is conventionally assigned to the STE, was observed. To reveal the stability of the STE, we precisely measured the temperature dependence of the Urbach tails in absorption spectra. It was confirmed that the Urbach tails at all temperatures converge into a specific point, which verifies the validity of the treatment of the Urbach tail. We analysed the temperature dependence of the exponential slope, the so‐called steepness constant, of the Urbach tail and evaluated the exciton‐phonon coupling constant g , which defines the stability of the STE, to be g = 5.4. Based on a previously reported theory for exciton‐phonon interactions, g > 1 generally results in that the STE is a stable state relative to a free exciton. Consequently, the above large g factor demonstrates that the STE formation is stable in β‐Ga 2 O 3 . (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)