Giant photoinduced inverse spin Hall effect of the surface states in three dimensional topological insulators BiTe with different thickness.

The photoinduced inverse spin Hall effect (PISHE) has been studied in three dimensional (3D) topological insulator (TI) BiTe thin films with different thicknesses (3, 5, 12 and 20 quintuple layer (QL)). The sign of the PISHE current flips only once in the 3- and 20-QL BiTe films, but it flips three times in the 5-, 7- and 12-QL samples. The three-times sign flip is due to the superposition of the PISHE current of the top and bottom surface states in BiTe films. By analyzing the x-ray photoelectron spectroscopy (XPS) of the BiTe films, we find that the top surface of the 3- and 20-QL BiTe films are severely oxidized, leading to only one sign flip in the PISHE. The PISHE contributed by the top and bottom surface states in BiTe films have been successfully separated by fitting a theoretical model to the PISHE current. The impact of the bulk states on PISHE current has been determined. The PISHE current is also measured at different light powers, and all the measurement results are in good agreement with the theoretical model. In addition, it is found that the PISHE current in BiTe films grown on Si substrate is more than two orders larger than that grown on SrTiO substrates, which can be attributed to the larger absorption coefficient for BiTe/Si samples. It is revealed that the PISHE current in 3D TI BiTe is as large as 140 nA/W in the 3-QL BiTe film grown on Si substrate, which is more than one order larger than that reported in GaAs/AlGaAs heterojunction (about 2 nA/W) and GaN/AlGaN heterojunction (about 1.7 nA/W). The giant PISHE current demonstrates that the TIs with strong SOC may have good application prospects in spintronic devices with high spin-to-charge conversion efficiency.