Characterization of the surfaces of CdTe(111) single crystals after laser processing

Abstract

Optical properties and morphology of the opposite polar faces of CdTe(111) single crystals subjected to irradiation with nanosecond pulses of the second harmonic of a YAG:Nd laser in a wide range of energy densities have been studied by multiple-angle-of-incidence single-wavelength ellipsometry and atomic force microscopy. The ellipsometric data have been interpreted by the semi-infinite medium model and it is assumed that there are no films on the crystal surface. Also the one-layer model is applied and the crystal relief is considered as a top layer. The refraction n and absorption k indexes of the surface layer are calculated using the fundamental ellipsometric equation and method of thickness curves. Laser irradiation results in an increase in the refractive index of the CdTe surface layer due to laser-induced transformation of the surface structure and it is associated with enriching of the CdTe surface with tellurium. The surface morphology of the crystals is modified at higher laser pulse energy densities because of the beginning of melting of prominent irregularities and thin surface layer. The effects of irradiation with nanosecond laser pulses on the polar surfaces of CdTe(111) crystals are analyzed.

Characterization of Functional Layers of CdTe Crystals Subjected to Different Surface Treatments

“…The difference between the curves in Fig. 3(b) is an evidence just of a decrease in the roughness of the external layer surface after the processing [8] and [9].…”

“…The angular dependences of the ellipsometric parameters of the chemically etched and laser irradiated samples differ from those of the CdTe crystals after long-term storage in air. This is associated with formation of an oxide film on the Te side of the crystals [6]- [9].…”

“…The samples were polished by mechanical and chemical procedures. The crystallographic feature of CdTe(111) samples is the presence of two polar surfaces namely Cd-terminated and Te-terminated ones and results of surface processing of the different stoichiometric surfaces can differ [7]- [9] and [14]. The measurements were performed on the Te-terminated face ( mm ) of CdTe crystals.…”

“…The measurements were performed on the Te-terminated face ( mm ) of CdTe crystals. Br-methanol solution is a standard etchant commonly used for primary surface treatment as etching and polishing of Cd(Zn)Te semiconductors at room temperature [5]- [9]. After washing in acetone and methanol, the crystals were subjected to chemical polishing etching in 3% Br-methanol solution and then the samples were thoroughly rinsed in methanol.…”

“…are used [5]- [13]. The chemical etching is generally used as treatment of the CdTe crystals to remove the damaged surface regions after cutting, lapping, and mechanical polishing [6]- [9]. Recently, laser irradiation with nanosecond pulses is efficiently employed for local surface annealing, and modification of the surface states of CdTe crystals [8]- [13].…”