Thin-film growth of (110) rutile TiO₂ on (100) Ge substrate by pulsed laser deposition

The deposition conditions of (100) rutile TiO₂ grown on p-type (100) Ge substrates by pulsed laser deposition (PLD) were optimized to improve the electrical properties of the TiO₂/Ge structure. Increasing the substrate temperature (Tsub) enhanced the grain growth, the surface roughness of the film, and Ge diffusion into the TiO₂ layer. The growth rate, which was controlled by the laser density in PLD (Ld), affected the Ge diffusion. Ld of 0.35 J/cm2 (0.37 nm/min) enhanced the Ge diffusion and improved the crystallinity and surface roughness at a temperature of 450 °C, at which GeOx undergoes decomposition and desorption. However, the Ge diffusion into TiO₂ degraded the electrical properties. By using the optimized conditions (Ld = 0.7 J/cm2 and Tsub = 420 °C) with postannealing, the TiO₂/Ge structure showed an improvement in the leakage current of 3 orders of magnitude and the capacitance-voltage property characteristics indicated the formation of a p-n junction.