Impact of Deep Levels in Iron-Doped Gallium Oxides on Electron Transport

Abstract

Iron-doped gallium oxide (Ga₂O₃) is extensively exploited as semi-insulating substrates for epitaxial thin film growth to fabricate next-generation high-power electronics and ultraviolet optoelectronics. However, the influence of iron (Fe) dopants on electron transport dynamics remains poorly understood, particularly in the context of defect-mediated scattering and trapping mechanisms. Here, we employ time-resolved terahertz (THz) spectroscopy to investigate the temperature-dependent photoconductivity and free electron dynamics in Fe-doped Ga₂O₃ crystals. The frequency-dependent THz conductivities demonstrate dispersive charge transport dominated by heterogeneous scattering, modeled effectively by the Drude–Smith formulizm. The temperature dependence of both electron mobility and electron scattering time indicates a transition from phonon-dominated scattering to a defect-mediated scattering mechanism. Moreover, the kinetics of transient photoconductivity further uncover that the free electrons collapse into a highly localized state fostered by Fe³⁺ dopants on a sub-100 ps timescale. Nevertheless, this trapping process is suppressed at low temperature because the itinerant electrons are trapped at the shallow defects before encountering deep centers associated with the Fe³⁺ dopant. Our results offer a fundamental understanding of the microscopic electron transport mechanism in Fe-doped Ga₂O₃ crystals.