Unusually long free carrier lifetime and metal-insulator band offset in vanadium dioxide

Single crystalline vanadium dioxide (VO2) nanobeams offer an ideal material basis for exploring the widely observed insulator-metal transition in strongly correlated materials. Here, we investigate nonequilibrium carrier dynamics and electronic structure in single crystalline VO2 nanobeam devices using scanning photocurrent microscopy in the vicinity of their phase transition. We extracted a Schottky barrier height of similar to 0.3 eV between the metal and the insulator phases of VO2, providing direct evidence of the nearly symmetric band gap opening upon phase transition. We also observed unusually long photocurrent decay lengths in the insulator phase, indicating unexpectedly long minority carrier lifetimes on the order of microseconds, consistent with the nature of carrier recombination between two d-subbands of VO2.