Properties of κ-Ga₂O₃ Prepared by Epitaxial Lateral Overgrowth

The structural and electrical properties of undoped and Sn doped κ-Ga₂O₃ layers grown by epitaxial lateral overgrowth on TiO₂/sapphire substrates using stripe and point masks show that the crystalline structure of the films can be greatly improved relative to conventional planar growth. The undoped films are semi-insulating, with the Fermi level pinned near E_C-0.7 eV, and deep electron traps at E_C-0.5 eV and E_C-0.3 eV are detectable in thermally stimulated current and photoinduced current transient spectra measurements. Low concentration Sn doping results in net donor concentrations of ≈ 10¹³ cm⁻³, and deep trap spectra determined by electron traps at E_C-0.5 eV, and deep acceptors with an optical ionization threshold near 2 and 3.1 eV. Treatment of the samples in hydrogen plasma at 330 °C increases the donor density near the surface to ≈ 10¹⁹ cm⁻³. Such samples show strong persistent photocapacitance and photoconductivity, indicating the possible DX-like character of the centers involved. For thin (5 µm) κ-Ga₂O₃ films grown on GaN/sapphire templates, p-type-like behavior is unexpectedly observed in electrical properties and we discuss the possible formation of a 2D hole gas at the κ-Ga₂O₃/GaN interface.