Electronic Structure of Tungsten-Doped <i>β</i>-Ga₂O₃ Compounds

Abstract

Tungsten (W) doped gallium oxide (Ga2O3) (Ga2-2xWxO3, 0.00≤x≤0.30, GWO) polycrystalline ceramic compounds were synthesized via conventional, high-temperature solid-state reaction method. The effect of W-doping on the crystal structure and electronic structure of the resulting GWO materials is studied in detail. The GWO compounds were single-phase, crystallized in β-Ga2O3 for x≤0.15, at which point the Ga2O3-WO3 composite formation occurs. The average crystallite size increases with increasing W-content; however, the effect is predominant only in the single phase GWO compounds. Corroborating with structural analyses, the X-ray photoelectron spectroscopy (XPS) measurements reveal the chemical state of W ions vary in GWO compounds as a function of W concentration. The mixed chemical valence states of W (W4+ and W6+) were evident in single-phase GWO compounds where the W-concentration is lower. However, W ions exhibit the highest chemical valence state (W6+) for higher x values, which resulted in the Ga2O3-WO3 composite formation. The Ga ions exists in their highest chemical valence state (Ga3+) in all of the GWO compounds. The scientific understanding of the electronic structure of the GWO materials derived as function of W concentration could be useful while considering the W-doped Ga2O3 materials and/or W-Ga2O3 contacts for electronic and optoelectronic device applications.