Semiconducting Sn-doped β-Ga₂O₃ homoepitaxial layers grown by metal organic vapour-phase epitaxy

Sn-doped β-Ga₂O₃ epitaxial layers have been grown on (100) β-Ga₂O₃ substrates by metal organic vapour-phase epitaxy. Triethylgallium (TEGa), molecular oxygen (O₂) and tetraethyltin (TESn) were used as Ga, O and Sn precursors, respectively. Layers grown at optimized temperature and chamber pressure, i.e. 850 °C and 5 mbar, had flat surfaces with a rms roughness of about 600 pm. Structural analysis by transmission electron microscopy revealed that the main defects in the layers were stacking faults and twin lamella. The incoherent boundaries of these defects are supposed to act as compensation and scattering centres, limiting the carrier mobility. Sn was homogeneously incorporated with a flat profile throughout the whole layer at concentration levels ranging from 2 × 10¹⁷ to 3 × 10¹⁹ cm⁻³ proportionally to the used TESn flux. All layers were electrically conductive. However, an unambiguous Hall effect was measurable only for Sn concentrations higher than 1 × 10¹⁸ cm⁻³, resulting in electron concentrations from 5 × 10¹⁷ to 2 × 10¹⁸ cm⁻³ at room temperature. For increasing free carrier concentrations, the electron mobility showed the tendency to increase from 10 to 30 cm²/Vs. The maximum mobility of 41 cm²/Vs, measured in a sample with free carrier concentration of 1 × 10¹⁸ cm⁻³, represents the highest value reported for β-Ga₂O₃ layers grown by MOVPE so far.