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-te mperature optical spectroscopy. The samples were grown by molecular-be am epitaxy on nominal (001) ZnTe surfaces. This structure allows the s imultaneous observation of the quantization of the center-of-mass moti on of both light-hole and heavy-hole excitons. The Light- or heavy-hol e characters are assigned by piezomodulated reflectivity experiments. The observed quantized energies are in reasonable agreement with the r esults of a simple model of an infinite quantum well, including ''tran sition layers'' near the well-barrier interfaces, This model cannot, h owever, 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 dis persion, in addition to more complex additional boundary conditions, f or exciton polaritons with small wave vectors (approximately equal to twice the wavevector of light in the material). [S0163-1829(97)51140-4 ].