Photoluminescence of Nitrogen-Doped ZnSe Layers

Abstract

ZnSe layers have been epitaxially grown by MOVPE on GaAs substrates and were doped with nitrogen plasma. Photoluminescence measurements at different light intensities and in the temperature range of 4.2 K to 80 K have been performed on the layers. It is shown that the presence of nitrogen leads to photoluminescence spectra revealing acceptor- and donor-bound exciton lines, together with a donor–acceptor pair (DAP) band at 2.69 eV and a free-to-bound (FB) transition accompanied by their longitudinal-optical (LO) phonon side bands. A detailed and coherent analysis of the position, shape and relative intensities of the spectral lines is carried out by means of an analytical model correlating the position of the zero-phonon lines to the relative intensities of the phonon side bands. The model includes central-cell correction and describes the effect of the charge carrier LO-phonon interaction in the framework of the adiabatic approximation within the envelope function approach. The same model is successfully used to analyse the excitation intensity and temperature dependence of the zero-phonon lines associated to the DAP and FB transitions. Comparison between experiment and theory leads to the following physical parameters: S = 0.5 ± 0.1 for the Huang-Rhys factor; EA = 112 ± 2 meV, rA = 5.8 ± 0.5 Å for the acceptor ionization energy and radius, respectively, and ED = 25 ± 2 meV; rD = 24 ± 0.5 Å for the donor ionization energy and radius, respectively.