Kinetics of charge carrier recombination in beta-Ga2O3 crystals

TL;DR

This study investigates the luminescence and carrier recombination dynamics in beta-Ga2O3 crystals using cathodoluminescence, revealing insights into defect-related emissions, carrier trapping, and temperature effects.

Contribution

It provides new understanding of defect-related luminescence and carrier recombination mechanisms in beta-Ga2O3, especially regarding impurity centers and defect interactions.

Findings

UV emission dominated by self-trapped excitons with 48 meV activation energy

Blue luminescence linked to oxygen vacancies increased after hydrogen plasma treatment

Carrier recombination kinetics explained by trapping at Fe impurity centers

Abstract

Cathodoluminescence spectra were measured to determine the characteristics of luminescence bands and carrier dynamics in beta-Ga2O3 bulk single crystals. The CL emission was found to be dominated by a broad UV emission peaked at 3.40 eV, which exhibits strong quenching with increasing temperature; however, its spectral shape and energy position remain virtually unchanged. We observed a super-linear increase of CL intensity with excitation density; this kinetics of carrier recombination can be explained in terms of carrier trapping and charge transfer at Fe impurity centres. The temperature-dependent properties of this UV band are consistent with weakly bound electrons in self-trapped excitons with an activation energy of 48 +/- 10 meV. In addition to the self-trapped exciton emission, a blue luminescence (BL) band is shown to be related to a donor-like defect, which increases significantly in concentration after hydrogen plasma annealing. The point defect responsible for the BL, likely an oxygen vacancy, is strongly coupled to the lattice exhibiting a Huang-Rhys factor of ~ 7.3.