STRAINED PIEZOELECTRIC [111]-MULTIPLE QUANTUM-WELLS - CLAMPED OR FREE

We illustrate a procedure whereby the nonlinear optical response can b e used to determine the strain distribution in properly engineered InG aAs/GaAs multiple quantum well (MQW) structures with piezoelectric fie lds along the growth direction. We do this by fabricating two p-i(MQW) -n samples which are designed such that, if the materials are mechanic ally clamped, the quantum well exciton of one will shift to the blue u pon optical excitation, whereas the quantum well exciton of the other will shift to the red. However, if the materials are mechanically free , the quantum well excitons of both samples will shift to the red. We illustrate the technique by determining that InGaAs/GaAs MQWs grown on [111]-oriented GaAs substrates are (as expected) mechanically clamped . That is, that we observe an excitonic blue shift in one sample, and a red shift in the other.