【International Papers】Understanding Phase Stabilization and Transformations in  Ga₂O₃ Wide-Bandgap Semiconductors Through In Situ Transmission Electron Microscopy

      Researchers from the Sandia National Laboratories have published a dissertation titled "Understanding Phase Stabilization and Transformations in Ga₂O₃ Wide-Bandgap Semiconductors Through In Situ Transmission Electron Microscopy" in Microscopy and Microanalysis.

Abstract

      The wide bandgap (∼4.8 eV) semiconductor gallium oxide (Ga₂O₃) is of significant interest for applications in high-power electronics and UV photodetection. Of its four commonly accepted polymorphs – trigonal α, monoclinic β, cubic γ, and orthorhombic κ(ε) – β is calculated to the most thermodynamically stable polymorph while γ is the least. In high-power electronics, β-Ga₂O₃ is the most widely used, but despite its thermodynamic stability, γ-Ga₂O₃ inverse-spinel inclusions often form during the growth of β-Ga₂O₃ films, particularly when doped, as with Ge, Sn, or Sl; alloyed with Al or Mg; or even at some contact metallization interfaces. The potential detrimental effect of these γ inclusions on the performance of devices based on β-Ga₂O₃ has not been well-studied, and the mechanism(s) of their formation have remained speculative. The κ-Ga₂O₃ phase exhibits excellent UV photodetection properties, but is very difficult to stabilize. It has been recently reported that slight doping during low-temperature deposition may be capable of facilitating the growth of κ-phase, but details of the resulting structure and its thermal stability are important outstanding questions.

      Herein, we present the application of aberration-corrected and in situ environmental Scanning/Transmission Electron Microscopy (S/TEM), correlated with other ex situ and in situ techniques, for understanding the nature and formation of these phase transformations. The role of processing conditions and subsequent thermal treatments on the growth of and transformations between β- and γ-phase Ga₂O₃ were investigated in Ga₂O₃ films heteroepitaxially grown on (100) MgAl₂O₄ substrates. In addition to determining key growth and stability regimes for the various phases (and mixtures), the mechanisms behind these dynamics and the driving role of the substrate were elucidated. The structure and stability of κ-phase Ga₂O₃ were studied in Sn-doped films grown on sapphire, providing a more complete understanding of this system. Both systems highlight the value in situ S/TEM brings to the study of these systems, with its unique combination of spatial resolution, temporal resolution, and chemical sensitivity.

DOI：doi.org/10.1093/mam/ozae044.794