RESONANT LUMINESCENCE OF EXCITONS, CL-DONORS AND N-ACCEPTORS IN EPITAXIALLY GROWN ZNSE/GAAS-LAYERS

In this work, we report on resonant photoluminescence (RPL) investigations of epitaxially ZnSe/GaAs layers grown by MBE and MOVPE. Lattice mismatch between ZnSe and GaAs causes a strain in the layer material which is relaxed by nucleation of misfit dislocations during growth. The relaxation process depends on layer thickness and growth conditions. Different thermal expansion coefficients of ZnSe and GaAs lead to a further strain component when the samples are cooled to RT or 2 K. The resulting compressive or tensile strain causes a splitting of exciton states and a shift of exciton recombination energies to higher and lower energies respectively. The strength of this shift depends on the \m(j)\ value of holes. We determine the recombination energy of free and bound excitons for different strain conditions (from fully relaxed ZnSe/GaAs layers to samples without any strain relaxation) with interband excitation. The resulting deformation potentials are compared to results from measurements with high pressure diamond cells. Additionally, these investigations enable us to identify donor and acceptor bound excitons in biaxially strained ZnSe/GaAs layers as heavy or light hole exciton states for compressive or tensile strain respectively. The characteristic binding energies of Cl-donors are investigated with RPL. A comparison of transition energies from the ground state to excited states in doped and undoped materials allows an identification of impurities in as-grown ZnSe. The ground state energy of N-acceptors is determined by temperature dependent measurements. Binding energies of Cl-donors and N-acceptors in biaxially strained ZnSe/GaAs layers are compared to their corresponding energy levels in strain-free ZnSe. The strain in the layer lowers the symmetry of acceptor states and changes their binding energy. Excited acceptor states are again investigated by RPL measurements.