Growth and characterization of rutile-type GexSn1−xO2 alloy thin films via RF magnetron sputtering

Ultrawide bandgap (UWBG) semiconductors are increasingly of interest for developing energy-efficient technologies. Among UWBG materials, rutile-type oxides, such as GeO2 and SnO2, exhibit promising characteristics for power electronics and optoelectronics. Here we investigate the structural and morphological properties of rutile GexSn1−xO2 alloy thin films synthesized via RF magnetron co-sputtering with compositions ranging from x = 0.13 to x = 0.84. The films, grown on r-plane sapphire substrates, underwent post-deposition annealing (PDA) at 750, 850, and 950 °C. Epitaxial crystallization occurs at 750 °C for compositions with x = 0.69 and 0.64, exhibiting a (101)-oriented alloy peak. Enhanced epitaxial alignment and increased crystallinity is achieved at higher PDA temperatures of 850 and 950 °C. However, PDA at 950 °C promotes binary SnO2 crystallite formation in certain alloy compositions. As a result, 850 °C PDA is identified as the optimal PDA temperature to achieve (101)-oriented thin films across a range of compositions. The optical bandgap energy of the alloys was found to be tunable from 3.77 to 4.38 eV as Ge(x) composition is increased, opening the door to future heterojunction devices for high-performance power and optoelectronic applications.