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Keywords:

  • High-density luminescence;
  • Non-linear transmission;
  • ZnTe;
  • Metal-organic vapour phase epitaxy;
  • Inelastic exciton scattering;
  • Electron–hole plasma;
  • Pump-and-probe method;
  • Exciton screening;
  • Band gap renormalization

Abstract

We investigated the high-density luminescence and non-linear transmission of ZnTe layers grown by metal-organic vapour phase epitaxy (MOVPE). For the high-density luminescence we compared ZnTe layers on (001) GaAs substrate with free-standing ZnTe layers of equal thickness. At high excitation intensities a strong luminescence P band appears a few meV below the free exciton energy which is assigned to resonant exciton-scattering processes. A second strong luminescence N band occurs only in free-standing layers. It shows a remarkable red shift with increasing intensity and becomes the dominant emission for an excitation intensity Iexc > 1.5 MW cm−2. This lower-energy band was interpreted as electron–hole plasma recombination.

The optical non-linearity of thin ZnTe layers in the excitonic region was investigated by pump-and-probe experiments at 2 K and room temperature (RT). For these experiments we used two different pump energies, one above (at 2 K and RT) and one below (at 2 K) the band gap energy. In all cases a red shift and a large non-linear decrease in the excitonic absorption with increasing pump intensity was observed. The experimental results can be explained by many-body effects of exciton screening.