Layer-dependent ultrafast dynamics of α-In2Se3 nanoflakes

Photodetectors based on a-phase In2Se3 ultrathin films demonstrate unusually high photoresponsivity comparing to those based on other two-dimensional (2D) materials, such as MoS2. To understand the underlying mechanism, we investigate the ultrafast dynamics of In2Se3 ultrathin films ranging from 11 nm to 40 nm on mica and Au substrates, respectively, analogous to the practical layout of a photodetector. Our results show that the carrier lifetime of a-phase In2Se3 on mica is nearly independent of thickness and comparable to that of MoS2, and the efficient charge carrier separation occurs on Au substrate. Because all of the key parameters of In2Se3 nanoflakes that determine its photoresponsive behavior are of similar values to those of MoS2, we suggest that the interface effect, i.e. photogating effect and contact resistance, should be responsible for the dramatic photoresponsivity reported for field-effect transistor-type optoelectronic devices.