Gap Energies, Exciton Binding Energies and Band Offsets in Ternary ZnMgSe Compounds and ZnSe/ZnMgSe Heterostructures

Measurements of optical and photoelectron spectra are presented to determine the band offsets of ZnSe/Zn_1—xMg_xSe heterostructures. The samples are grown on GaAs(001) by MBE and investigated by absorption, photoreflection, photoluminescence, photoluminescence-excitation and photoelectron spectroscopy using a synchrotron light source. In the visible spectra discrete excitonic states are observed at the E_o and E₀ + Δ₀ gap up to a composition of x ≤ 0.36. The optical transitions of ZnSe/Zn_1—xMg_xSe single quantum wells are fitted to a model. It contains the conduction band offset as the only free parameter, which is then determined by a least-squares fit of the data. Photoelectron spectra (UPS) are measured on ZnSe which was in situ deposited on MgSe in several monolayer thickness. The valence band edges of ZnSe and MgSe are simultaneously observable and thus a direct determination of the valence band offset was possible. The values of the band offsets from the two different methods agree reasonably well within the errors of the measurements. Different from other systems ZnSe/Zn_1—xMg_xSe does not fulfil the common anion rule, which may be due to the filled d-shell of Zn which is lacking in Mg.