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

Abstract

ZnTe-(Zn,Mg)Te quantum wells having widths 6 times larger than the exciton Bohr radius have been grown by molecular beam epitaxy on the (0 0 1) surface of ZnTe substrates. This configuration allows the direct observation of the so-called “center-of-mass” quantization of excitons involving both light (lh) and heavy (hh) holes, in the form of numerous reflectivity resonances and photoluminescence lines. The unambiguous assignment of these features to lh and hh is provided by the selective coplanar piezomodulation of reflectance spectra. Due to the value of the well width compared with one quarter of the effective wavelength of light (∼ 175 nm), resonances with odd quantization numbers are stronger than those with even numbers. The experimental resonance 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 excitonic gap of bulk ZnTe which indicates that these resonances lie in the regime of strong exciton-photon coupling (the polariton effect).