Vapor phase epitaxy of pure VO2 and V1−xCrxO2

The vapor phase epitaxy of thin epilayers of VO₂ and V_1−xCrxO₂ on TiO₂ transparent substrates is described. Chemical vapor deposition occurs by reacting a (VOCL₃/CrO₂Cl₂/H₂O/H₂) mixture at about 800°C using argon as a carrier gas. The preparation of pure VO₂ requires special care to make it homogeneously stoichiometric and to obtain steep concentration profiles at the TiO₂/VO₂ interface. Layers were obtained which had electrical and optical properties comparable to the best bulk crystals grown by other techniques. Homogeneous solid solutions of V_1−xCr_xO₂ epilayers were also grown for the first time in the range o < x < 0.17. Chromium concentration and homogeneity were determined by electron microprobe analysis. The separation coefficient k was also found to vary with x. It is close to unity below x = 0.001 and above this value Cr is incorporated more easily. High quality heteroepitaxial layers (1 cm² area, 1 to 30 μm thickness) of V_1−xCr_xO₂ have for the first time allowed the measurement of the optical absorption coefficient.