We show that energy position and line shape of donor-acceptor-pair luminescence bands in ZnSe:N/ GaAs epilayers depend very sensitively on excitation density and compensation. A continuous development from structureless red-shifted broad to well structured donor-acceptor-pair ͑DAP͒ bands is observed for increasing excitation density. The red shift is explained by the fluctuating potential affecting the bands and impurity levels and is caused by random distribution of charged impurities in highly compensated samples. The shift is reduced when these charge fluctuations are diminished due to an increasing number of impurities being neutralized via light-induced carrier excitation. These effects have not been taken into account in previous work concerning doped II-VI materials; however, they have to be considered when evaluating the frequently used hypothesis of a deep donor in ZnSe:N as an explanation of low-energy broadband DAP emission. The influence of band fluctuations on the behavior of the DAP luminescence and excitation spectra is qualitatively discussed.

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The line shape of donor-acceptor pair luminescence bands in doped but partially compensated semiconductors exhibits a distinct broadening effect with increasing compensation ratio. We present a very sensitive Monte Carlo simulation of pair band emission highly suitable for typical compensated materials such as ZnSe:N, serving not only as a model material but being also of high-technological relevance. For low compensation, the line shape of the pair bands is calculated by taking into account the shift of the recombination energies due to charged impurities resulting in a very good agreement with the experiment. The model is perfectly applicable also to codoped ZnSe:N:Cl with Cl allowing for a precise control of the compensation ratio. By modelling the line shapes and comparing with the experiment, the density of compensating impurities could be determined even to values as low as several 10 16 cm Ϫ3 . However, for high-compensation ratios, the model fails because relaxation between the excited donor-acceptor pairs is neglected.

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