Effect of non-centrosymmetry on nonlinear refraction in semiconductors

Most of the crystalline materials used in optoelectronic devices do not possess inversion symmetry and due consideration is required to be given to the contribution of a non-centrosymmetry (NCS). In the present paper, a density matrix approach has been followed to obtain different orders of nonlinear optical susceptibilities. The effect of NCS has been incorporated by assuming that it gives rise to the loss of parity. The numerically estimated ratio of the third-order susceptibility in the absence and presence of the NCS property, in the GaAs crystal, is found to be in good agreement with that reported in literature. We have also obtained the expression for the first-order nonlinear refractive index in an NCS system. It has been found that the NCS contribution to the nonlinear refractive index increases significantly as one approaches the band gap resonance condition in direct gap semiconductors.