Abstract

Recently semiconductors have been of growing interest as nonlinear optical materials.¹ Among the more important for low-power (e.g., milliwatt) medium-speed (e.g., nanosecond) applications in, for example, phase conjugation and optical bistability are direct gap semiconductors. These materials (e.g., InSb, GaAs) have absorptive and refractive effects associated with absorption saturation resonant with the band gap. However, one major disadvantage has been that the resonant effects showed too much thermal broadening for room temperature operation. Multiple quantum well (MQW) materials, consisting of alternate ~100-Å GaAs layers or quantum wells separated by GaAlAs carrier confining layers, have recently shown exceptional excitonic resonances near the band gap, which persist to room temperature.^2,3 reason for this persistence is that the confinement of the exciton (which would have the electron and hole in a hydrogenic orbit of ~300-Å diam in bulk GaAs) within the ~100-Å layers significantly increases its binding energy (i.e., its separation below the band gap) without increasing its thermal broadening.³ Furthermore, the strong absorption (~10⁴ cm⁻¹) at these peaks shows strong saturation effects.^2–4

© 1983 Optical Society of America