Low-Pressure Chemical Vapor Deposition of In2O3 Films on Off-Axis c‑Sapphire Substrates

Heteroepitaxial In2O3 films were grown on transparent c-sapphire substrates with 0, 3.5, 6, and 8° off-axis angles via low-pressure chemical vapor deposition (LPCVD). Metallic solid indium and oxygen gas were used as the precursors. X-ray diffraction (XRD) spectroscopy and cross-sectional scanning transmission electron microscopy (STEM) were used to study the effects of substrate off-axis on the crystalline quality of the as-grown films. The XRD 2θ–ω spectra confirmed the growth of body-centered-cubic bixbyite In2O3 films with (111) out-of-plane orientation. STEM images revealed the suppressed dislocation density in the films grown on substrates with off-axis angles. The crystal structure was further confirmed by Raman spectroscopy. Fifteen peaks corresponding to bcc-In2O3 Raman modes were observed at room temperature. XRD ω-rocking curves, XRD Φ-scan profiles, and STEM images indicate improved crystalline quality in films grown on substrates with, particularly, 3.5 and 6° off-cut angles. Growth rates in a wide range of ∼0.5–30 μm/h were achieved. A room-temperature photoluminescence peak at ∼2.15 eV is attributed to the deep level defect transitions. A room-temperature photoluminescence excitation peak at ∼3.38 eV corresponds to the optical band gap of bcc-In2O3. Room-temperature electron Hall mobilities of ∼88–116 cm2/(V s) were measured with background carrier concentrations of ∼(6–9) × 1017 cm–3.