The results of a new experiment, which records transient, pulsed-laser-induced surface photovoltages by following photoemission shifts measured with synchrotron radiation, are reported. Comparison of the surface photovoltage decays with numerical simulations reveals large surface-recombination rates for a variety of Si(l 11) surface preparations. The space-charge layer near the surface is found to govern the surface and bulk carrier concentrations to a remarkable extent, particularly when band bending is large.PACS numbers: 73.25.+i, 72.20.Jv, 72.40,+w Electron-hole pairs introduced with a light pulse near the space-charge layer (SCL) at the surface of a semiconductor move to reduce the band bending, thereby producing a transient surface photovoltage (SPV). Since band bending represents a potential barrier to one sign of carrier and a potential well to the other, its instantaneous magnitude strongly influences the carrier densities near the surface. In spite of the importance of the surface carrier density to photochemical processes, such as etching, deposition, and desorption, there is little experimental knowledge of SPV transients and their role in controlling surface recombination and carrier density, particularly in larger excitation regimes. Here we report the first measurements and analyses of SPV on well characterized surfaces using a new photoemission technique which combines pulsed-laser excitation with synchrotron radiation and provides nanosecond resolution. 1 The method uses a pulsed copper-vapor laser to inject carriers within 1 //m of SiCl 11) surfaces, and the SPV is measured in real time via the shift of the Si 2p core-level photoemission spectrum.The principal conclusions of the work thus far are as follows. To high accuracy, the core-level spectrum shifts rigidly with excitation up to carrier concentrations of 5xl0 18 cm" 3 at the surface. A numerical transport model has been shown to simulate the SPV decay over a wide range of excitation levels, strongly suggesting that for this set of n-and p-type Si(l 11) samples with clean, hydrogenated, air-oxidized, or disordered surfaces, the primary determinant of the SPV decays on nanosecond and longer time scales is carrier transport within the SCL as opposed to dynamics of trapped surface charge. For all surfaces investigated, the recombination velocity at the surface, so, is large, of the order of 10 6 cm/s. In addition, we have discovered that, for large initial band bending, the SCL can play a dominant role in governing carrier diffusion into the bulk, because it acts as a reservoir for photoexcited carriers. Recombination is suppressed in the reservoir because electrons and holes are separated, and this can enhance carrier density long after
