Per-carrier nonlinear optical response of [111]-oriented piezoelectric InGaAs/GaAs multiple quantum wells

Abstract

We measure the per-carrier nonlinear responses caused by photoexcited carriers in two strained [111]-oriented InGaAs/GaAs multiple-quantum-well structures, and we compare them to that measured in a [100]-oriented structure. Without an external bias, we find that the absorption coefficient changes per photogenerated carrier for the [111]-oriented piezoelectric materials are smaller than for the [100]-oriented materials, not larger, as originally suggested. Subsequently, measurements of the per-carrier nonlinear responses as a function of reverse bias voltage demonstrate that the smaller per-carrier nonlinearities measured for the [111] structures are partially the result of a broadening of the excitons by the huge in-well fields, but can be primarily attributed to the quality of the [111]-grown materials. When corrected for differing in-well fields and for differing excitonic linewidths, the per-carrier responses are similar in magnitude, suggesting that the [111] response may eventually approach that of [100] material, but probably will not significantly exceed it.