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Damage caused by laser irradiation on the surface of ZnTe epilayers was studied by micro-Raman and atomic force microscopy (AFM). ZnTe LO-phonon overtones up to four order and TO + (n − 1)LO zone-center phonons were observed in the resonant micro-Raman spectra at room temperature. Discrepancies in the literature regarding the origin of two features observed at low frequencies around 120 and 140 cm −1 in the Raman spectrum of ZnTe are discussed and resolved. These Raman peaks were not detected by using a low excitation laser power density on a Zn-terminated ZnTe surface; however, with the increase of the laser power density they were found to arise irreversibly. The correspondence of these peaks in a wave number with the strongest Raman peaks of the crystalline tellurium phase and the intensity enhancement behavior with the laser power in a similar way as for CdTe strongly suggests the formation of crystalline tellurium aggregates on the layer surface due to laser irradiation damage. AFM data reveal the occurrence of laser ablation on the ZnTe surface even though the surface temperature of the sample is below the melting point.

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The mechanisms controlling the growth rate and composition of epitaxial CdTe and Cd 1−x Zn x Te films were studied. The films were grown by isothermal closed space configuration technique. A GaAs(100) substrate was exposed sequentially to the elemental sources (Zn, Te, and Cd) in isothermal conditions. While growth of ZnTe followed an atomic layer epitaxy (ALE) regime [self-regulated at one monolayer (ML) per cycle]; the CdTe films revealed different growth rates in dependence of the growth parameters (exposure and purge times). Combination of short purge times and larger Cd exposure times led to not self-regulated growth regime for CdTe. This is ascribed to large Cd coverages that were dependent on Cd exposure times (following a Brunauer-Emmett and Teller-type adsorption). However, for longer purge times and/or short Cd exposure times, an ALE self-regulated regime was achieved with 2 ML/ cycle. In this sense, the self-regulation of the growth is limited by desorption, instead of absorption, as in the traditional growth technique. Cd atoms substitution by Zn atoms and subsequent evaporation of surface Cd atoms during Zn exposure has been proved. The influence of these facts on the growth and composition of the alloy is discussed.

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A theoretical procedure based on the model dielectric function is used to fit the room temperature reflectivity spectra of Zn x Cd 1−x Te alloys in the range 1.5-4.5 eV. This procedure allows calculation of the thickness of very thin films as well as determination of the composition dependence of the critical points. A parabolic dependence on Zn molar fraction is reported. Calculated optical data, such as refractive index and extinction coefficient, are also presented.

Laser irradiation damage in ZnTe epilayers was analyzed in situ by power-density-dependent and time-resolved micro-Raman spectroscopy. Damage by ablation or compound decomposition on the sample surface was revealed by the decrease of the ZnTe-nLO mode intensity with the increase of laser power density. The appearance of the peaks associated with the stronger crystalline-tellurium modes, tellurium aggregates and second-order Raman scattering at room temperature μ-Raman spectra was observed for higher power densities than 4.4 × 10 5 W cm −2 . The Raman signal time transients of ZnTe-nLO and crystalline-tellurium modes reveal an exponential evolution of the laser irradiation damage and a fast formation of crystalline tellurium aggregates on the layer surface.