Effects of Carrier Injection on the Recombination Velocity in Semiconductor Surfaces

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Abstract
The effects of carrier injection on the surface recombination velocity are discussed on the basis of the Shockley-Read model. The relevant parameters are the surface potential φs, bulk resistivity, the injection density δn, and the properties of the surface states. At low injection the behavior of the surface recombination velocity s can be described by excursions over the usual s vs φs curves and, depending on the values of the various parameters, s can either increase or decrease with injection. At high injection s approaches a constant value that depends only on the cross sections and densities of the recombination states, and can be larger (as is predicted for the case of Ge) or smaller than the plateau value of the near-equilibrium curve. The predictions of the theory are illustrated with curves of s vs the fractional excess carrier density δn/n0 where, in the case of Ge, use is made of experimentally determined surface parameters. The curves can be used in applied work as a guide in controlling and possibly utilizing the effects of injection on s. The effects of appreciable injection on s could be used for studying the surface recombination centers.