Direct Probing of Transient Photocurrent Dynamics in p-WSe2 by Time-Resolved Scanning Tunneling Microscopy

We have carried out time-resolved scanning tunneling microscopy on a layered semiconductor with an indirect bandgap, p-WSe2, and the dynamics of nonequilibrium photocurrent generated by ultrashort-pulse-laser excitation was analyzed. The photocurrent dynamics reflecting the flow of excited photocarriers at the surface, which is determined by the balance between the diffusion and tunneling rates, was successfully probed. Furthermore, the excess minority carriers transiently trapped at the surface for a few nanoseconds, which produce a transient surface photovoltage and cannot be detected by conventional methods, were directly observed and evaluated. (C) 2013 The Japan Society of Applied Physics