Surface/structural characteristics and band alignments of thin Ga2O3 films grown on sapphire by pulse laser deposition

Comprehensive structural, electrical and optical studies are performed on a series of gallium oxide (Ga2O3) ultrathin films grown on sapphire with different growth temperatures (400–1000 °C) by pulsed laser deposition, via X-ray absorption spectroscopy (XAS), Raman scattering (RS) and X-ray photoelectron spectroscopy (XPS). For samples grown at different temperatures, the XAS results showed the coordination numbers of the materials varying, while their bond lengths remained nearly similar value. The RS revealed a low frequency vibration translation tetrahedral-octahedral mode (202 cm−1) of GaO4 and a mid-frequency deformation octahedral mode (346 cm−1) of GaO6 for films grown at higher temperatures. XPS analyses suggested the surface of samples composed of GaO bonds with binding energy decreasing as the growth temperature increased. The β-Ga2O3/sapphire heterojunction is identified with the staggered-gap (type II) structure, and the valence-band offset (VBO) is found between (−0.52)–(−0.74) eV while conduction-band offset (CBO) from (−2.32)–(−3.32) eV. The band gap of the β-Ga2O3 was deduced from the energy loss signals for O 1s photoelectrons. With the increase of the growth temperature, the band gap increases and both the VBO and CBO decrease. The identification of band alignment for heterojunction may facilitate interests in designing advanced opto-electronic devices.