Halide vapor phase epitaxy 2: Heteroepitaxial growth of α- and ε-Ga2O3

Abstract

Halide vapor phase epitaxy of metastable α- and ε-Ga2O3 is reviewed. The both polymorphs were grown using GaCl and O2 as precursors. Phase-pure corundum α-Ga2O3 was heteroepitaxially grown on (0001) sapphire at temperatures of approximately 550 °C or lower. The n-type electrical conductivity was controlled by Ge doping using GeCl4 as the dopant source, and very low resistivity of 8.6 mΩ cm was achieved. Epitaxial lateral overgrowth was shown to be effective in improving the crystal quality, and the dislocation density was reduced from 1010 cm−2 to less than 5 × 106 cm−2 in the laterally grown wing region. Morphology of α-Ga2O3 islands was controlled such that inclined facets well develop, and dislocation density above mask openings remarkably decreased due to dislocation bending caused by the inclined facets. Orthorhombic ε-Ga2O3 was grown on (0001) GaN and (0001) AlN using virtually the same growth recipe as that used for α-Ga2O3. Fundamental material properties of ε-Ga2O3, such as the optical bandgap energy, thermal stability, and thermal expansion coefficient, were investigated using the epitaxial film.