【Epitaxy Papers】Heteroepitaxial Growth of High-Mobility Ge-Doped β-Ga₂O₃ Films on Sapphire Substrate by Low-Pressure CVD

      Researchers from University of Massachusetts Lowell have published a dissertation titled " Heteroepitaxial Growth of High-Mobility Ge-Doped β-Ga₂O₃ Films on Sapphire Substrate by Low-Pressure CVD " in ACS Applied Electronic Materials.

Abstract

      In this work, high-quality Ge-doped（-201）β-Ga₂O₃ thin films were heteroepitaxially grown on c-plane sapphire substrates with offcut angles of 0°, 2°, 6°, and 8° using low-pressure chemical vapor deposition (LPCVD). Increasing the sapphire offcut promoted step-flow growth, resulting in improved terrace alignment, reduced surface roughness, and enhanced crystalline quality. Phase-pure monoclinic β-Ga₂O₃ with strong （-201）preferential orientation was confirmed by X-ray diffraction and Raman spectroscopy, while X-ray photoelectron spectroscopy revealed a near-stoichiometric composition with an O/Ga ratio of 1.48. Electrical transport properties exhibited a strong dependence on the substrate offcut angle, with room-temperature Hall mobility increasing from 15 to 117 cm²/V·s as the offcut angle increased from 0° to 6°, across carrier concentrations spanning 1.43×10¹⁷ to 2.75×10¹⁸ cm⁻³. The 6° offcut sample achieved a room-temperature mobility of 117 cm²/V·s at a carrier concentration of 1.43×10¹⁷ cm⁻³ and a peak low-temperature mobility of 337 cm²/V·s at 128 K with a carrier concentration of 8.96×10¹⁶ cm⁻³, representing the highest reported room-temperature and low-temperature mobilities for Ge-doped β-Ga₂O₃ films grown on sapphire substrates. Carrier concentration and mobility data were analyzed using charge-neutrality and Boltzmann transport models incorporating donor activation together with polar optical phonon, ionized impurity, neutral impurity, acoustic deformation potential, and dislocation scattering mechanisms. The fitting revealed shallow donor activation energies of 12.5–19 meV, a deeper donor level at 80 meV, low acceptor compensation (<5×10¹⁵ cm⁻³), and threading dislocation densities on the order of 10⁹ cm⁻². These results establish sapphire offcut engineering as an effective pathway for achieving high-mobility, LPCVD-grown Ge-doped β-Ga₂O₃ heteroepitaxy on scalable foreign substrates, which is critical for the development of high-performance β-Ga₂O₃ power devices.

DOI：

https://doi.org/10.1021/acsaelm.6c01043