Ultrafast Optical Measurement of Defect Dynamics in β-Ga₂O₃using Supercontinuum Pump-Probe Spectroscopy.

Ga₂O₃ polymorphs have shown great promise for high power devices. β-Ga2O3 has a large number of intrinsic and extrinsic defects with poorly understood properties. Non-equilibrium optical spectroscopy has proven to be a valuable tool in studying midgap defects in materials. In this work, we use optical pump-probe spectroscopy that employs a supercontinuum pulse to probe the defects and their ultrafast dynamics in a wide energy interval within the material bandgap. Our results show transient absorption of the probe pulse by midgap defects that is highly polarization selective. Our results show that hole capture times of defects scale with their separation in energy from the valence band with defects furthest away from the valence band exhibiting the slowest hole capture rates. Temperature dependence of hole capture rates indicate a thermally activated capture process involving lattice relaxation (multi-phonon process) that can be fitted with a Mott-Seitz expression. We present models to explain the nature of these defects and the ultrafast dynamics associated with the capture of photoexcited carriers by these defects.