GAAS-ALAS AND SI-SIGE QUANTUM-WELL STRUCTURES FOR APPLICATIONS IN NONLINEAR OPTICS

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 mum range. We present both the magnitude and the frequency dependen ce of the second order susceptibility. We begin with a brief outline o f our results concerning the first order response (absorption) in Si-S iGe quantum well structures. We show that the valence band structure o ffers several advantages compared to the conduction band and that it i s an excellent material for infrared detector manufacture. We find tha t-contrary to commonly held views-the strongest contributions to the s econd order response originate from regions lying farther from the zon e centre. Also, the frequency of the peak response does not correspond to that expected from simple models.