A comprehensive study of metal-organic chemical vapor deposition of ultrawide bandgap MgSiN2 thin films on sapphire

Abstract

While remaining compatible with III-nitride material systems and other materials utilized in complementary metal-oxide semiconductor applications, II–IV-nitride materials offer opportunities to broaden the semiconductor platform with new properties and/or new functionalities. MgSiN2 stands out among other II–IV-nitrides because of its ultrawide bandgap, enabling its potential applications in the ultraviolet-C region, while also being a promising candidate to exhibit ferroelectricity. In this work, a comprehensive study of MgSiN2 film growth on sapphire substrates via metal-organic chemical vapor deposition was performed to correlate the growth conditions with the properties of these films. The effects of the growth temperature from 745 to 960 °C, the NH3 molar flow rate, the Mg:Si flow rate ratio, and the growth pressure, from 450 to 550 Torr, on the crystallinity and surface morphology of MgSiN2 films were investigated. The cation-ordered orthorhombic single-crystal structure was observed via high-resolution scanning transmission electron microscopy in a sample grown at 945 °C. The refractive index of an MgSiN2 film was measured using ellipsometry. Optical transmittance measurements revealed a direct bandgap in the range of 6.13–6.39 eV, depending on the growth conditions. Optical absorption at wavelengths below the direct bandgap was higher than that predicted by two orders of magnitude, obscuring efforts to measure the indirect gap.