GaAsAlAs and SiSiGe quantum well structures for applications in nonlinear optics

Abstract In this paper we present a full scale evaluation of optical spectra of GaAsAlAs and SiSiGe quantum well structures in which the linear and nonlinear responses arise due to virtual optical transitions between valence minibands. We aim at structures which could operate in the 10–15 μm range. We present both the magnitude and the frequency dependence of the second order susceptibility. We begin with a brief outline of our results concerning the first order response (absorption) in SiSiGe quantum well structures. We show that the valence band structure offers several advantages compared to the conduction band and that it is an excellent material for infrared detector manufacture. We find that—contrary to commonly held views—the strongest contributions to the second order response originate from regions lying farther from the zone centre. Also, the frequency of the peak response does not correspond to that expected from simple models.