Photoeffect at Semiconductor-Solution Interface

There appeared several treatments of photoeffect at the semiconductor-solution interface which, except few, concentrated mainly on the happenings inside the semiconductor and neglected the properties of the interface and the acceptor or donor ions in solution. These treatments are all classical and hence no discussions are given here. 

A quantal treatment of photoeffect at the semiconductor-solution interface can be obtained using the general expression of the photocurrent of the following form  

S is the distance between the semiconductor surface and the reaction plane at OHP, and Np(x = 0) is the number of photoexcited minority carriers per unit volume in the surface region of the semiconductor which arrive from the interior of the semiconductor to this region. f E, hv) is the Fermi distribution of photoexcited minority carrier. This quantity, Np x = 0), depends on the intensity, energy, and absorption coefficient of incident light, diffusion length of electron in the semiconductor, and its band gap, etc. Furthermore, it depends on the charge transfer phenomena and the surface recombination rate at the interface. The surface recombination rate constant depends on the induced density of surface states due to adsorbed anions at the electrodesolution interface. The recombination rate constant can be expressed as 

Surface recombination rate constant, Kr, at the interface is one of the most important factors that influence the overall rate, and this quantity depends mainly on the density of surface states, Dss E) and can be determined quantum mechanically, using the Anderson Hamiltonian formalism/ In this expression (76), cTc is the recombination cross section. The value of cTc can be obtained using the scattering theory. Sp E) is the velocity of photoexcited electron, and f E) represents the distribution of surface states which one may consider to be of Gaussian type of distribution, centered at the midgap energy. 

hv) is the transition rate which determines the fraction of the photocarriers that can transfer across the interface and join an electronic state in an ion in solution per unit time. 

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