Generation of the second harmonic and nonlinear electroreflection from the surface of a centrosymmetric semiconductor

A theory of second-harmonic generation by reflection from the surface of a centrosymmetric semiconductor is proposed. This theory takes account of the absorption of the pump and of the second harmonic in the semiconductor, and also of modulation of the nonlinear optical properties of the surface layer of the semiconductor by an electrostatic field (nonlinear electroreflection). An exponential approximation of the distribution of the modulating electrostatic field in the semiconductor is used to deal with electroreflection. Expressions are obtained for the dependences of the second-harmonic intensity and of the nonlinear electroreflection coefficient on the surface potential of the semiconductor. It is shown that the nature of these dependences is governed by the relationship between the characteristic depths of penetration of the pump, second harmonic, and modulating field in the nonlinear medium. A method for determination of the flat-band potential is suggested.