Near-band-edge luminescence in heavily doped gallium arsenide
The near-band-edge photoluminescence at 80K of heavily tellurium-doped degenerate liquid-phase-epitaxial gallium arsenide layers (n=2*1018 cm-3) is investigated. The layers are compensated with shallow germanium acceptors (the values of the degree of compensation are K=0.05-0.7) during the epitaxial growth process. It is established that even at very low concentration of shallow acceptors (K=0.05), the so-called mobile band appears in the near-band-edge luminescence spectra. The peak energy of this band shifts to lower energies, the non-equilibrium carrier generation rate decreases and saturates at values E0T, which are considerably lower than those calculated for the filling of the valence band density-of-states tails. It is assumed that this discrepancy between theory and experiment is due to the uncertain knowledge of the pre-exponential term in the expression for the density-of-states tails and to the formation of some deeper fluctuation states when there is a considerable difference between the concentrations of shallow donors and acceptors. It is assumed that in this case some of these states act as associates.
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