Effects of thermal strain on the optical properties of heteroepitaxial ZnTe

Abstract

Optical measurements have been used to study the biaxial tensile strain in heteroepitaxial ZnTe grown by molecular-beam epitaxy on both GaAs and GaSb substrates, and its effect on the low-temperature photoluminescence (PL) spectrum of the material. The observed strain (0.92 X 10 ' for ZnTe/GaAs and 0.45X10 ' for ZnTe/GaSb) agrees with that expected for differential thermal contraction from the growth temperature to low temperature, based on the difference in thermal expansion coefficients. The amount of strain increases with growth temperature, as expected, but decreases slightly in thin layers on GaAs. The latter effect is due to incomplete relaxation of the large (7.6%%uo) lattice mismatch strain between ZnTe and GaAs, the unrelieved part of which constitutes a biaxial compressive strain. Reflectance and variable temperature PL measurements show that the free exciton splits into heavy-hole (I») and light-hole (X&h) components, which both shift to lower energy. The J =1 (allowed) and J =2 (forbidden) components of the oxygen isoelectronic center bound exciton are mixed and shifted to lower energy by the strain. Temperature-dependent PL measurements show that the oscillator strengths of the two components are strongly redistributed by the strain. We calculate the strain-induced splittings in the 0-bound exciton and in the excitons bound to neutral acceptors and neutral double acceptors, and find good agreement with the experimentally observed peak positions. Further confirmation of our assignrnents of the strain-split and shifted bound exciton peaks is obtained using magnetospectroscopy in fields up to 12 T. The diamagnetism, g factors, and splitting patterns of the free and bound excitons in the magnetic field are discussed.

Raman spectroscopy and photoluminescence of ZnTe thin films grown on GaAs

“…1, where luminescence spectra from sample A obtained with excitation wavelengths 496.5 nm ͑lower line͒ and 486.9 nm ͑upper line͒ are shown. The assignments of the emission energies are consistent with previous works 2,5 corresponding to thicker epilayers. The descriptions and the corresponding energies of the PL peaks are listed in Table I.…”

“…Although the electronic and vibrational properties of bulk ZnTe are already well known, some discrepancies concerning the interpretation of the photoluminescence ͑PL͒ results have appeared in literature 2,4 most of them arising from the different methods of growth and thermal expansion effects. Zhang et al 2 reported a comparison of the different assignments of the PL features in literature for ZnTe bulk and the epilayers ZnTe/GaAs and ZnTe/GaSb. A more recent work on ZnTe epilayers 5 gives a detailed study of the PL emissions including the dependence on temperature of the band gap as well as the intensity and full width at half maximum of the free exciton peak and acceptor bound excitonic emissions.…”

“…In recent years, much work, including Raman scattering, [1][2][3] has been devoted to the study of the optical properties of ZnTe. Although the electronic and vibrational properties of bulk ZnTe are already well known, some discrepancies concerning the interpretation of the photoluminescence ͑PL͒ results have appeared in literature 2,4 most of them arising from the different methods of growth and thermal expansion effects.…”

Photoluminescence properties of ZnTeO and ZnSeO alloys with dilute O concentrations

“…Two sharp peaks are seen in the spectrum of undoped ZnTe. The higher energy peak is assigned as the exciton bound at As acceptor (I 1 As ) [9] and the lower energy peak as the exciton bound at zinc vacancy (V Zn ) [10]. The emissions of light and heavy hole free excitons were observed at the higher energy side of I 1…”

Evaluation of crystal structure and photoluminescence for ZnTe epilayers grown on a 2o off‐oriented GaAs (100) substrate

“…In recent years, ZnTe has been mainly studied in terms of its optical properties including Raman scattering. Although the electro-optical and lattice vibration properties of bulk ZnTe are already well documented, some inconsistent photoluminescence (PL) results arising from the growth methods and a difference in the thermal strain effects have been reported [1][2][3]. The ZnTe characteristics of pressure dependent Raman scattering [4] and resonance Raman scattering [5] were studied.…”