Rutile germanium dioxide: An emerging ultrawide bandgap semiconductor for power device applications - A review

In recent years, the demand for wide and ultrawide bandgap (UWBG) semiconductors for advanced power electronics and optoelectronic devices has surged. Materials in this class, including GaN, AlN, AlGaN, diamond, c-BN, Ga2O3, and emerging candidates like rutile GeO2, are of particular interest due to their potential for high-efficiency, high-power applications. Rutile GeO2, with a bandgap around 4.7 eV, possesses excellent electrical, optical, mechanical, and thermal properties, making it a strong contender among UWBG semiconductors. This review examines rutile GeO2's structural, electronic, and optical characteristics, focusing on films deposited using methods such as MOCVD, MBE, CVD, and sputtering. The rutile phase of GeO2 demonstrates notable versatility, as it can be doped for both n- and p-type conduction with elements like Al, In, and As. Recent advancements have enabled the growth of high-quality, epitaxial rutile GeO2 films, broadening its potential applications. Additionally, largescale rutile GeO2 can be produced through melt and flux methods, an advantage for commercial scalability. These qualities highlight rutile GeO2's promise as a next-generation material for power devices and optoelectronics, meriting increased research and investment to fully leverage its capabilities.