Interfacial Phase Modulation-Induced Structural Distortion, Band Gap Reduction, And Nonlinear Optical Activity In Tin-Incorporated Ga2o3

We report the structural chemistry and optical properties of tin (Sn)-mixed gallium oxide (Ga2O3) compounds, where the interfacial phase modulationinduced structural distortion in turn induces variations in the band gap and nonlinear optical activity. The Sn incorporation into Ga2O3 causes significant reduction in the band gap and induces nonlinear optical activity upon chemical composition tuning. Detailed investigation performed on the structural chemistry, phase stabilization, surface morphology, and optical and electrochemical properties of Sn-mixed Ga2O3 compounds (Ga2-2xSnxO3, 0.00 <= x <= 0.3, Ga-Sn-O) indicates that the Sn-incorporation-induced effects are significant. To produce Ga-Sn-O materials of high structural and chemical quality, we adopted a simple solid-state chemical reaction route involving first calcining and then sintering the material at higher temperatures. Structural chemistry analyses of sintered Ga-Sn-O compounds by X-ray diffraction (XRD) showed solid solution formation at lower Sn concentrations (x <= 0.10). The XRD analyses indicate the SnO2 secondary phase formation at higher (x > 0.10) Sn concentrations. Surface morphology analysis using scanning electron microscopy (SEM) also showed a positive relationship between phase separation and Sn concentration. Optical absorption spectra showed a substantial redshift in the band gap (E-g), which would allow Ga-Sn-O compounds to have wide spectral selectivity. At higher Sn concentrations (x = 0.25-0.30), corroborating with structural/chemical analyses, an additional lower-energy sub-band transition that explicitly corresponds to SnO2 appears in the optical absorption data. Importantly, the evidence of nonlinear optical activity in Ga-Sn-O, which is otherwise not traditionally known for such an activity, as well as dipolar- and quadrupolar-shaped dependence of activity with the polarization angle of the excitation source was detected. At higher concentrations (x >= 0.15), Sn was found to be insoluble, which can be attributed to Ga2O3 and SnO2 possessing different formation enthalpies and cation (Ga3+ and Sn4+) chemistries. The fundamental scientific understanding of the interdependence of synthetic conditions, structure, chemistry, and optical and electrochemical properties could be useful to optimize Ga-Sn-O inorganic compounds for optical, optoelectronic, and photocatalytic device applications.