Large optical nonlinearities in SiGe superlattices

Abstract

A nonlinear optical response in a SiGe superlattice can be achieved by means of a multi-photon virtual excitation process. The nonlinearity can be greatly enhanced by engineering the energy levels and transition probabilities across the band gap and between higher lying conduction subbands. In this paper we discuss how such an enhancement can be realized in a SiGe superlattice and predict structural parameters for systems in which these conditions are fulfilled, resulting in a ‘direct’ gap superlattice structure with a potentially large value of χ (3). This virtual excitation mechanism is particularly attractive in that the excitation energies are below the absorption edge. Consequently, the strong dissipative effects associated with band filling processes do not occur.