LOCALIZATION OF EXCITONS BY POTENTIAL FLUCTUATIONS AND ITS EFFECT ON THE STOKES SHIFT IN INGAP INP QUANTUM-CONFINED HETEROSTRUCTURES/

We present investigations of the temperature evolution of the photolum inescence (PL) and optical absorption spectra of a series of tensile-s trained InGaP/InP multiple quantum wells (MQW) samples. As in previous work on compressive-strained InAsP/InP MQW, the results support the a ssignment of the low temperature PL transitions to recombination from excitonic band-tail states. The energy of such transition is redshifte d with respect to the free exciton recombination energy. This results in a large apparent energy difference between PL and optical absorptio n peaks which is, at 6 K, about 5 meV in the coherently strained sampl es and less than 1 meV in the partially relaxed ones. The analysis of the low temperature PL line shape which we present enables the determi nation of the excitonic band-gap energy for all the samples. The diffe rence between the energy of the optical absorption transition and the excitonic band-gap energy thus determined gives a measure of the Stoke s shift arising from thermalization effects alone. The values of the S tokes shift thus obtained are in better agreement with the sharpness o f the optical absorption transitions which indicate samples of high cr ystalline quality. (C) 1998 American Institute of Physics. [S0021-8979 (98)00722-1].