Microstructure, chemical inhomogeneity, and electronic properties of tin-incorporated Ga2O3 compounds

We report on the microstructure, dopant-induced changes in the chemical bonding, and electronic structure, chemical valence states of cations in Sn-incorporated gallium oxide (Ga2O3). Spectroscopic characterization of Sn-mixed Ga2O3 compounds (Ga2−2xSnxO3, 0.00 ≤ x ≤ 0.3, Ga–Sn–O), which were produced by the high-temperature solid-state chemical reaction method, indicates that the Sn-mixing-induced changes in the microstructure and electronic structure are significant. X-ray photoelectron spectroscopic (XPS) analyses, which considered the Ga 2p doublet (Ga 2p3/2 and Ga 2p1/2 peaks), indicate that the Ga exists in its highest chemical valence state (Ga3+) in all of the samples, irrespective of Sn-content. The evolution of Sn peaks in XPS data indicates progressive increase in the Sn-content in Ga–Sn–O samples as x increases from 0.0 to 0.3. However, while no significant changes are seen in the Ga chemistry, formation of SnO2 secondary phase was evident, especially with increasing Sn-concentration. The XPS data confirm the Sn4+ chemical valence state of Sn-ions in all of the Ga–Sn–O samples. The energy-dispersive X-ray spectroscopic (EDS) mapping analyses reveal the localization of SnO2 secondary phase in the parent matrix of Ga2O3. Combined EDS and XPS analyses indicate the secondary phase (SnO2) formation becomes dominant for higher Sn-content. Corroborated with chemical analyses made by EDS and XPS, the Fourier infrared (FTIR) spectroscopic analyses also reveal the evolution of Sn–O bonds, which is reflected in the shift for the high-frequency stretching and bending of the GaO4 tetrahedra, which structurally form the β-Ga2O3 phase. The detailed analysis of the FTIR data and peak evolution suggests a stronger interaction of Sn with Ga2O3 for x ≥ 0.15. A correlation between composition, crystal chemistry, and electronic properties is established in Ga–Sn–O compounds.