We achieved the successful fabrication of Sn-doped α-Ga 2 O 3 thin films with higher electron mobility and wider conductivity controls by improving the crystal quality. α-Ga 2 O 3 films showed n-type conductivity with a maximum electron mobility of 24 cm 2 V %1 s %1 . The carrier concentration was successfully controlled in the range of 10 17 -10 19 cm %3 . Crystal defects such as dislocations severely compensate the free carriers in α-Ga 2 O 3 films and restrict the mobility at low carrier concentrations. Therefore, to achieve further conductivity control and higher mobility, improving the crystallinity of α-Ga 2 O 3 films is necessary.

We report the fabrication of electrical conductive tin-doped α-Ga2O3 thin films on c-plane sapphire substrates. The mist chemical vapor deposition method brought tin-doped α-Ga2O3 thin films with high crystallinity without noticeable other phases, as highlighted by the full-width of X-ray diffraction ω-scan rocking curves as small as 40 arcsec, for the tin atomic density in the film upto ∼1020 cm-3. The resistivity decreased by more doping of tin, and the α-Ga2O3 thin film with minimum resistivity exhibited n-type conductivity with the Hall mobility of 2.8 cm2 V-1 s-1 and the carrier density of 2.7 ×1019 cm-3.

We investigated the effect of Sn doping on the optical, electrical, and magneto transport properties of epitaxial α-Ga2O3 thin films grown by mist-Chemical Vapour Deposition. Sn introduces a shallow donor level at ∼0.1 eV and has a high solubility allowing doping up to 1020 cm−3. The lowest obtained resistivity of the films is 2.0 × 10−1 Ω cm. The Sn doped films with a direct band gap of 5.1 eV remain transparent in the visible and UV range. The electrical conduction mechanism and magneto-transport have been investigated for carrier concentrations below and above the insulator-metal transition. The magnetic properties of the neutral Sn donor and the conduction electrons have been studied by electron spin resonance spectroscopy. A spin S = 1/2 state and C3V point symmetry of the neutral Sn donor is found to be in good agreement with the model of a simple SnGa center.

High quality single crystalline alpha gallium oxide (α‐Ga2O3) films, as highlighted by the X‐ray diffraction ω‐scan full‐width at half maximum of as small as 30 arcsec, were prepared by the mist chemical vapor deposition (CVD). The quality of the film was markedly dependent of the carrier gas flow rate, so we need careful attention for the optimum growth conditions. The thermal stability of α‐Ga2O3 films was investigated by studying their thermal stability under thermal annealing in terms of the structural and optical properties. It was found that α‐Ga2O3films grown at 470 °C are stable until 550 °C, but are gradually transformed to β‐Ga2O3over 600 °C. Finally, β‐Ga2O3films only existed at 700 °C. So the device processes for α‐Ga2O3 should be done below 550 °C to avoid phase transformation. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)