CENTER-OF-MASS QUANTIZATION OF LIGHT-HOLE AND HEAVY-HOLE EXCITONS IN WIDE ZNTE-(ZN,MG)TE QUANTUM-WELLS

ZnTe-(Zn,Mg)Te quantum wells having widths 6 times larger than the exc iton Bohr radius have been grown by molecular beam epitaxy on the (0 0 1) surface of ZnTe substrates. This configuration allows the direct o bservation of the so-called ''center-of-mass'' quantization of exciton s involving both light (Ih) and heavy (hh) holes, in the form of numer ous reflectivity resonances and photoluminescence lines. The unambiguo us assignment of these features to Ih and hh is provided by the select ive coplanar piezomodulation of reflectance spectra. Due to the value of the well width compared with one quarter of the effective wavelengt h of light (similar to 175 nm), resonances with odd quantization numbe rs are stronger than those with even numbers. The experimental resonan ce energies are in good agreement with an infinite quantum-well model, including ''transition layers'' at the well boundaries. Moreover, the lowest exciton-polariton levels are seen below the energy of the exci tonic gap of bulk ZnTe which indicates that these resonances lie in th e regime of strong exciton-photon coupling (the polariton effect). (C) 1998 Elsevier Science B.V. All rights reserved.