Transport properties and c/a ratio of V_2O_3 thin films grown on C- and R-plane sapphire substrates by pulsed laser deposition

摘要

We prepared V_2O_3 thin films on C- or R-plane sapphire (Al_2O_3) substrates by a pulsed laser deposition method. X-ray diffraction analyses confirmed that single-phase V_2O_3 films were epitaxially grown on both C- and R-planes under an Ar gas ambient of 2 × 10~(-2)mbar at a substrate temperature of 873 K. Depending on the deposition conditions, cla ratios at room temperature of (0001)-oriented V_2O_3 films widely ranged from 2.79 to 2.88. Among them, the films of 2.81 ≤ c/a ≤ 2.84 showed complex metal (M)-insulator (Ⅰ)-M transition during cooling from 300 to 10 K, while those of larger cla ratios were accompanied by metallic properties throughout this temperature range. All the films on R-plane substrates underwent simple M-I transition at ～150K, which was more abrupt than the films on C-plane, whereas their c/a ratios were narrowly distributed. The distinct difference of M-I transition properties between C- and R-plane films is explained by the intrinsic a- and c-axes evolution through'the transition from M to I phases.