Abstract

The nonlinear optical effects utilized in various optoelectronics devices are the variations of the refractive index (n) or of the absorption coefficient (α) induced by an optical or by a static electromagnetic field. In semiconductors these nonlinearities exhibit large enhancements close to the excitonic resonances that are observed at low temperature near the band gap in bulk materials. Recently, modern techniques of crystal growth have permitted the fabrication of ultra-thin semiconductor layers (L_z ~ 100Å) with atomically smooth interfaces and perfectly controlled composition. One important effect of the confinement of carriers in ultra-thin layers is to stabilized excitonic resonances which become consequently observable at room temperature. In quantum wells it is therefore possible to observed and utilize enhanced nonlinear optical effects in very convenient conditions for applications. In addition excitons at room temperature exhibit interesting new specific properties not observed at low temperature. In our laboratory multiple quantum well structures (MQWS) of high enough quality to exhibit excitonic resonances at room temperature have been grown in the GaAs/AlGaAs and in the GaInAs/AlInAs systems (1,2). The excitonic resonances occur at 0.85 μm and 1.6 μm for the two systems respectively.

© 1985 Optical Society of America