Photoluminescence characterization of ZnSe doped with Ga by bulk and planar doping techniques in molecular-beam epitaxy

Abstract

Room-temperature and low-temperature (1.7-K) photoluminescence (PL) characteristics of heteroepitaxial ZnSe layers on GaAs which are doped with Ga by either conventional (bulk) or planar doping techniques are described. Low-temperature PL peaks at 2.27 and 2.0 eV involving deep acceptor levels are introduced by Ga doping, as well as newly reported shallow acceptor levels with binding energies of approximately 68 and 85 meV. The behavior of these peaks and the excitonic transitions is studied as a function of Ga-doping level and, for the case of the planar-doped layers, surface stoichiometry during doping. The exciton peaks exhibit substantially greater broadening for doping on Zn-rich surfaces than for Se-rich surfaces, corresponding to the higher carrier concentrations observed by electrical measurements in the former case. The deep acceptor levels are found to be incorporated to a lesser degree for doping on Zn-rich surfaces, while the incorporation of the 85-meV acceptor is enhanced in this case. The net electrical compensation is evidently dominated by the behavior of the deep levels. The results are explained by assuming that both deep levels involve donor-Zn vacancy complexes, whose formation is suppressed by the excess Zn flux supplied during the planar-doping process. A comparison of the exciton spectra of nominally undoped and bulk Ga-doped samples is used to demonstrate that the residual donor in the undoped material is Ga.