Distinct center-of-mass quantization of light-hole and heavy-hole excitons in wide ZnTe-(Zn,Mg)Te quantum wells

Samples consisting of a 36–38-nm-wide ZnTe quantum well with barriers made up of short-period ZnTe-MgTe superlattices were studied by low-temperature optical spectroscopy. The samples were grown by molecular-beam epitaxy on nominal (001) ZnTe surfaces. This structure allows the simultaneous observation of the quantization of the center-of-mass motion of both light-hole and heavy-hole excitons. The light- or heavy-hole characters are assigned by piezomodulated reflectivity experiments. The observed quantized energies are in reasonable agreement with the results of a simple model of an infinite quantum well, including “transition layers” near the well-barrier interfaces. This model cannot, however, account quantitatively for the observation of the fundamental resonances slightly below the transverse-exciton energy of bulk ZnTe. This effect is tentatively attributed to the strongly nonparabolic dispersion, in addition to more complex additional boundary conditions, for exciton polaritons with small wave vectors (approximately equal to twice the wave vector of light in the material).