【Member Papers】Impact of Deep Levels in Iron-Doped Gallium Oxides on Electron Transport

      Researchers from the Xiamen University and Shanghai Institute of Optics and Fine Mechanics have published a dissertation titled "Impact of Deep Levels in Iron-Doped Gallium Oxides on Electron Transport" in Journal of Physical Chemistry C.

Project Support

      The authors acknowledge funding support from the National Natural Science Foundation of China (grant nos. 22473093, 22403078, and 22175154), the Fundamental Research Funds for the Central Universities (grant no. 20720240150), the China Postdoctoral Science Foundation (grant no. 2024M751767), and the Shenzhen Science and Technology Program (grant no. JCYJ20220530143016036).

Background

      The monoclinic gallium oxide (β-Ga₂O₃) is garnering intense research interest due to its promising application in power electronics, solar-blind ultraviolet photodetection, and deep ultraviolet optoelectronics. Owing to the ultrawide bandgap (E_g∼ 4.8 eV) and high theoretical breakdown field, the Baliga figure of merit of β-Ga₂O₃ surpasses those of its rival materials (such as Si, SiC, and GaN) rendering it ideal for high-voltage power electronics. Like other semiconductors, the electronic properties of β-Ga₂O₃ can be tailored for device fabrication by controlled doping. Iron (Fe) doping in β-Ga₂O₃ is particularly notable. As a transition metal with multiple oxidation states (Fe²⁺/Fe³⁺), Fe introduces deep acceptor levels that compensate intrinsic n-type conductivity and thus Fe-doped Ga₂O₃ typically serves as a semi-insulating substrate for epitaxial thin film growth and device fabrication (i.e., lateral MOSFETs and solar-blind ultraviolet photodetectors)

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.

Conclusion

      In summary, the influences of intrinsic shallow defects and extrinsic dopant on the electron transport are both assessed by measuring the temperature-dependent photoconductivity using time-resolved THz spectroscopy. The shallow defects can greatly suppress the electron mobility, whereas the deep levels fostered by the Fe³⁺ dopant lead to severe electron localization. The free electron lifetime in the Fe-doped Ga₂O₃ crystals depends on the probability that electrons encounter the Fe³⁺ dopants. In other words, a high Fe doping level could lead to a short electron diffusion length because of its short lifetime. Our results provide quantitative information about the interplay between Fe³⁺ dopants and free electron dynamics, which is of importance particularly for the development of the Ga₂O₃ optoelectronic devices.