PER-CARRIER NONLINEAR-OPTICAL RESPONSE OF [111]-ORIENTED PIEZOELECTRIC INGAAS GAAS MULTIPLE-QUANTUM WELLS/

We measure the per-carrier nonlinear responses caused by photoexcited carriers in two strained [111]-oriented InGaAs/GaAs multiple-quantum-w ell structures, and we compare them to that measured in a [100]-orient ed structure. Without an external bias, we find that the absorption co efficient changes per photogenerated carrier for the [111]-oriented pi ezoelectric materials are smaller than for the [100]-oriented material s, not larger, as originally suggested. Subsequently, measurements of the per-carrier nonlinear responses as a function of reverse bias volt age demonstrate that the smaller per-carrier nonlinearities measured f or the [111] structures are partially the result of a broadening of th e excitons by the huge in-well fields, but Can be primarily attributed to the quality of the [111]-grown materials. When corrected for diffe ring in-well fields and for differing excitonic linewidths, the per-ca rrier responses are similar in magnitude, suggesting that the [111] re sponse may eventually approach that of [100] material, but probably wi ll not significantly exceed it. (C) 1996 American Institute of Physics .