Intensity-dependent energy and lineshape variation of donor-acceptor-pair bands in highly compensated ZnSe:N

The photoluminescence (PL) of donor-acceptor-pairs (DAP) in ZnSe:N/GaAs epilayers at different levels of nitrogen doping and various compensation ratios is studied. The PL spectra of moderately doped and weakly compensated samples show a DAP zero-phonon line and clearly distinguished phonon replica shifting to the red by 10 meV for strongly decreasing excitation density. At medium nitrogen doping and compensation level, well-structured, but red-shifted and broadened DAP emission shows a more pronounced dependence on excitation density. For highly doped and strongly compensated samples, the DAP band continuously develops from a structureless red-shifted broad emission to a well-structured one for increasing excitation density. More heavily doped and strongly compensated samples show strongly red-shifted and structureless broad band emissions for all excitation densities, and a very pronounced dependence of the maximum position on excitation density. We present a general explanation by charged impurities randomly distributed in highly compensated samples and causing a fluctuating potential affecting the bands and impurity levels.