Influence of the dielectric environment on the radiative lifetime of quantum-well excitons

Due to the large mismatch in the refractive index of semiconductor material and air, time-integrated and spectrally resolved four-wave mixing experime nts reveal strong influence of the cladding layer thickness, its refractive index, and the reflectivity of the sample-air interface on the radiative d ephasing time of excitons in single quantum wells and multiple quantum well structures. A cladding layer thickness of lambda/2 and lambda/4 enhances a nd decreases, respectively, the radiative contribution to the exciton linew idth and causes radiative shifts to higher and lower energies, respectively . All our experiments are well described by solutions of the semiconductor Maxwell-Bloch equations.