Relaxations of the surface photovoltage effect on the atomically controlled semiconductor surfaces studied by time-resolved photoemission spectroscopy

We have systematically investigated relaxation of the surface photovoltage effect on the atomically controlled In/Si(111) surfaces with distinctive surface states and different amounts of the surface band bending. The temporal variations were traced in real time by time-resolved photoemission spectroscopy using soft x-ray synchrotron radiation. The relaxation is found to be temporally limited by two steps of the carrier transfer from the bulk to the surface: the tunneling process at a delay time <= 100 ns and the thermionic process on the following time scale (>= 100 ns). Crossover of the two mechanisms can be understood by breakdown of the quantum tunneling regime by the increase in width of the space-charge layer during the relaxation.