Influence of oxygen partial pressure on properties of monoclinic Ga2O3 deposited on sapphire substrates

Abstract

Thin monoclinic Ga2O3 films were deposited on c-plane sapphire substrates by low pressure chemical vapor deposition. The thin films were synthesized using high purity metallic gallium (Ga) and oxygen gas (O2) as precursors. The effect of oxygen volume percentage on the growth rate of thin films was observed at two growth temperatures. Within the investigated growth window, a maximum growth rate of ∼2.9 μm/h was obtained for an oxygen volume percentage of 4.8% with a growth temperature at 800 °C. The film growth rate decreased as growth temperature increased when other growth parameters were kept the same. X-ray diffraction indicates that all films have the β-Ga2O3 structure with (−201) orientation, and those deposited with higher oxygen partial pressure are thicker and have improved crystalline quality. Polarized micro-Raman scattering is consistent with small grains of (−201) β-Ga2O3 having random in-plane orientations. The large variation of the relative intensities of overlapping emission bands contributing to the broad luminescence emission extending between 1.5 and 4.5 eV (∼825 and 275 nm) suggest that deposition conditions strongly affect different defect concentrations. Films deposited at 800 °C with a higher oxygen partial pressure yielded higher resistance, which may result from the incorporation of gallium vacancies, identified as a compensating point defect affecting the electrical conductivity of bulk monoclinic Ga2O3.