Anisotropic luminescence and third-order electric susceptibility of Mg-doped gallium oxide under the half-bandgap edge

Strong anisotropy of photoluminescence of a (100)-cut beta-Ga2O3 and a Mg-doped beta-Ga2O3 single crystals was found in UV and visible spectral range, the bands of which were attributed to different types of transitions in the samples. Green photoluminescence in the Mg-doped sample was enhanced approximately twice. A remarkable enhancement of two-photon absorption and self-focusing in beta-Ga2O3 after doping was revealed by 340-fs laser Z-scanning at 515 nm. The absolute value of complex third order susceptibility chi((3)) determined from the study increases by 19 times in [001] lattice direction. Saturable absorption and associated self-defocusing were found in the undoped crystal in the [010] direction, which was explained by the anisotropic excitation of F-centers on intrinsic oxygen defects. This effect falls out of resonance in the Mg-doped crystal. The chi((3)) values which are provided by a decrease of bandgap in Mg-doped beta-Ga2O3 are chi((3)) [001] = 1.85 .10(-12) esu and chi((3)) [010]=chi((3)) (yyyy) = 0.92 . 10(-12) esu. Our result is only one order of magnitude lower than the best characteristic in green demonstrated by a Mg-doped GaN, which encourages subsequent development of Mg-doped beta-Ga2O3 as an effective nonlinear optical material in this region. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Automated summary

The study revealed strong anisotropy of photoluminescence in (100)-cut beta-Ga2O3 and Mg-doped beta-Ga2O3 single crystals in the UV and visible spectral range, with different types of transitions attributed to the observed bands. The Mg-doped sample exhibited enhanced green photoluminescence and increased two-photon absorption and self-focusing effects at 515 nm. The nonlinear optical properties of Mg-doped beta-Ga2O3 were found promising, encouraging further development in this area.