Indium incorporation in homoepitaxial β-Ga₂O₃ thin films grown by metal organic vapor phase epitaxy

Homoepitaxial β-(In,Ga)₂O₃ thin films were grown on (100) β-Ga₂O₃ substrates by metal organic vapor phase epitaxy using triethylgallium (TEGa) and triethylindium (TEIn). Deposition temperatures from 650 to 825 °C and pressures from 5 to 20 mbar have been explored. The growth rate decreased linearly with increasing deposition temperature and decreased exponentially with increasing pressure. The resulting films were characterized by atomic force microscopy (AFM), high resolution x-ray diffraction (HR-XRD), and transmission electron microscopy (TEM). As the flow rate of TEIn varied from 0 to 0.13 μmol/min during the growth, AFM showed the surface roughness of about 1 nm, while HR-XRD measurements revealed an increase of the vertical lattice spacing. The maximum atomic concentration of indium incorporated in monoclinic β-(In,Ga)₂O₃ is about 3.5% and shifts the optical absorption edge to lower energy by ∼0.18 eV. Further increase of the indium flow rate leads to an increase of the surface roughness and a decrease in the vertical lattice spacing due to the formation of a separate cubic In₂O₃ phase that was confirmed by HR-TEM images. X-ray reciprocal space maps showed that the β-(In,Ga)₂O₃ thin films were grown coherently on β-Ga₂O₃.