Investigation of free and bound excitons in strained ZnTe films grown by MBE on GaAs(100) substrates

Abstract

A study is reported of the reflectance and low-temperature photoluminescence (PL) spectra of ZnTe films grown by molecular-beam epitaxy (MBE) on GaAs substrates [(100) orientation, 3° deflection toward 〈110〉]. It is shown that the strain-induced splitting of the free-exciton energy level (ΔEex) does not depend on ZnTe film thickness within the 1–5.7 µm range and is due to biaxial in-plane film tension. The stresses are primarily determined by the difference between the thermal expansion coefficients of the film and the substrate. It is also shown that the residual stresses originating from incomplete relaxation of the film lattice parameter to its equilibrium value at the growth temperature likewise provide a certain contribution. The position of the spectral line of an exciton bound to a neutral acceptor (As) is well approximated in terms of the present models, taking into account the stresses calculated using the value of ΔEex.