Photoluminescence of nitrogen-doped ZnSe layers

ZnSe layers have been epitaxially grown by MOVPE on GaAs substrates and wer e doped with nitrogen plasma. Photoluminescence measurements at different l ight intensities and in the temperature range of 4.2 K to 80 K have been pe rformed on the layers. It is shown that the presence of nitrogen leads to p hotoluminescence spectra revealing acceptor- and donor-bound exciton lines, together with a donor-acceptor pair (DAP) band at 2.69 eV and a free-to-bo und (FB) transition accompanied by their longitudinal-optical (LO) phonon s ide bands. A detailed and coherent analysis of the position, shape and rela tive intensities of the spectral lines is carried out by means of an analyt ical model correlating the position of the zero-phonon lines to the relativ e intensities of the phonon side bands. The model includes central-cell cor rection and describes the effect of the charge carrier LO-phonon interactio n in the framework of the adiabatic approximation within the envelope funct ion approach. The same model is successfully used to analyse the excitation intensity and temperature dependence of the zero-phonon lines associated t o the DAP and FB transitions. Comparison between experiment and theory lead s to the following physical parameters: S = 0.5 +/- 0.1 for the Huang-Rhys factor; E-A = 112 +/- 2 meV, r(A) = 5.8 +/- 0.5 Angstrom for the acceptor i onization energy and radius, respectively, and E-D = 25 +/- 2 meV; r(D) = 2 4 +/- 0.5 Angstrom for the donor ionization energy and radius, respectively .