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 (T-sub) 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/cm(2) (0.37 nm/min) enhanced the Ge diffusion and improved the crystallinity and surface roughness at a temperature of 450 degrees 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/cm(2) and Tsub = 420 degrees 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. (C) 2016 The Japan Society of Applied Physics