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Rutile germanium dioxide (r-GeO2) has been identified as an ultrawide bandgap semiconductor recently, featuring a bandgap of 4.68 eV—comparable to Ga2O3—but offering bipolar dopability, higher electron mobility, higher thermal conductivity, and higher Baliga figure of merit (BFOM). These superior properties position GeO2 as a promising material for various semiconductor applications. However, the epitaxial growth of r-GeO2, particularly in its most advantageous rutile polymorph, is still at an early stage. This work explores the growth of r-GeO2 using metal-organic chemical vapor deposition (MOCVD) on an r-TiO2 (001) substrate, utilizing tetraethyl germane as the precursor. Our investigations reveal that higher growth temperatures significantly enhance crystalline quality, achieving a full width at half maximum of 0.181° at 925 °C, compared to 0.54° at 840 °C and amorphous structures at 725 °C. Additionally, we found that longer growth durations increase surface roughness due to the formation of faceted crystals. Meanwhile, adjusting the susceptor rotation speed from 300 to 170 RPM plays a crucial role in optimizing crystalline quality, effectively reducing surface roughness by approximately 15 times. This study offers a foundational guide for optimizing MOCVD growth conditions of r-GeO2 films, emphasizing the crucial need for precise control over deposition temperature and rotation speed to enhance adatom mobility and effectively minimize the boundary layer thickness.
Rahaman et al. (Mon,) studied this question.