Abstract

The dependence of electroabsorption in GaAs/Al_xGa_1-xAs multiple quantum well (MQW) structures on well width (L_z) is of considerable importance in optimizing optical modulation devices.^1,2 However, a complete characterization including the narrow well width limit has still been lacking. Previously, we have reported that for GaAs/Al_0.32Ga_0.68As MQWs with 100 Å barriers the maximum obtainable change in the absorption coefficient (Δα_max) increases monotonically with decreasing Lz (from 260 to 50 Å) at the cost of an increasing applied electric field (ε_max).² It was predicted that a peak value would be reached near L_z = 25 Å, being limited at lower L_z by either dielectric breakdown or reduced carrier confinement in the well. In order to determine the complete well width dependence of band edge electroabsorption in GaAs/Al_xGa_1-xAs MQW structures, our experiments were extended to cover the range from 47 to 17 Å. We demonstrate that this range does indeed contain an optimum value of L_z that provides a peak value in Δα_max. But contrary to our prediction, we shall show that enhanced broadening of the heavy hole excitonic resonance, resulting from phonon scattering at small L_z, is responsible for this result.

© 1989 Optical Society of America