M. Sridharan

Characterization of vacuum evaporated polycrystalline Cd0.96Zn0.04Te thin films by XRD, Raman scattering and spectroscopic ellipsometry

Cd 0.96 Zn 0.04 Te thin films are deposited onto well cleaned glass substrates (Corning 7059) kept at room temperature by vacuum evaporation and the films are annealed at 423 K. Rutherford Backscattering Spectrometry and X-ray diffraction techniques are used to determine the thickness, composition and crystalline structure and grain size of the films respectively. The films exhibited zinc blende structure with predominant (111) orientation. The surface morphology of the films is studied by Atomic Force Microscopy. The rms roughness of the as-deposited films is 3.7 nm and on annealing the films at 423K, the rms roughness value decreases to 3.4 nm. The Raman spectra of the Cd 0.96 Zn 0.04 Te films are recorded at room temperature to study lattice vibrations and their interactions with other excitations. The intensity of the peak increases and the FWHM decreases on annealing the films. The pseudodielectric-function spectra, e(E) = e 1 (E) + i e 2 (E), of polycrystalline Cd 0.96 Zn 0.04 Te thin films in the 1.3 - 5.5eV photon energy range at room temperature are measured by spectroscopic ellipsometry. The measured dielectric function spectra reveal distinct structures at energies of the E 1 , E 1 +Δ 1 and E 2 critical points are due to interband transitions.

Optical constants of vacuum-evaporated Cd0.96Zn0.04Te thin films measured by spectroscopic ellipsometry

The pseudodielectric-function spectra, ε(E)=ε1(E)+iε2(E), of polycrystalline Cd0.96Zn0.04Te thin films in the 1.3–5.5 eV photon energy range at room temperature were obtained using spectroscopic ellipsometry. The measured dielectric-function spectra reveal that distinct structures at energies of the E1, E1+Δ1, and E2 critical points are due to interband transitions. The Cd0.96Zn0.04Te thin films investigated were deposited by vacuum evaporation under a pressure better than 1.3×10−3 Pa onto well-cleaned glass substrates kept at 300 K. The films exhibited zinc blende structure with predominant (1 1 1) orientation. The root mean square (r.m.s.) roughness of the vacuum-evaporated Cd0.96Zn0.04Te thin films evaluated by ex situ atomic force microscopy is 3.7 nm. Dielectric-related optical constants, such as the refractive index (n), extinction coefficient (k), absorption coefficient (α) and normal incidence of reflectivity (R) determined from the spectroscopic ellipsometry data are presented and analyzed. The optical constants of the films were also determined using optical transmittance measurements and the results are discussed.

Effect of boron ion implantation on the structural and optical properties of polycrystalline Cd0.96Zn0.04Te thin films

Abstract Structural and optical studies have been carried out on Cd0.96Zn0.04Te thin films implanted with mass analyzed boron ions (10B+). We have analyzed the properties of the as-deposited and 10B+ implanted Cd0.96Zn0.04Te thin films using X-ray diffraction, roughness measurement, Raman scattering and optical transmittance measurements. The optical band gap of the as-deposited film is 1.539 eV and the value is found to reduce with the increase in implantation dose. This was accompanied by a progressive reduction in the sharpness of the absorption band edge. Raman spectrum of the as-deposited film shows longitudinal optic and transverse optic modes, which arise from CdTe and ZnTe like vibrations. On implantation the FWHM as well as the relative peak intensity are found to be increased. These results are explained on the basis of the implantation induced surface roughness and lattice disorder.

Determination of optical constants of Cd1−xZnxTe thin films by spectroscopic ellipsometry

Abstract The optical response of vacuum-evaporated Cd 1− x Zn x Te thin films in the 1.5–5.6 eV photon energy range at room temperature has been studied by spectroscopic ellipsometry. The films of Cd 1− x Zn x Te ( x =0.04) were deposited at room temperature onto well-cleaned glass substrates of film thickness 450 nm. The measured dielectric-function spectra reveal distinct structures at energies of the E 1 , E 1 +Δ 1 and E 2 critical points corresponding to the interband transitions. Dielectric related optical constants such as complex refractive index, the absorption coefficients and the normal incidence reflectivity, are presented. Results are in satisfactory agreement with the calculations over the entire range of the photon energies.

Raman scattering, photoluminescence and spectroscopic ellipsometry studies on polycrystalline Cd0.96Zn0.04Te thin films

Abstract Cd 0.96 Zn 0.04 Te thin films are deposited onto well-cleaned glass substrates (Corning 7059) kept at room temperature by vacuum evaporation. Rutherford backscattering spectrometry and X-ray diffraction techniques are used to determine the thickness, composition and crystalline structure and grain size of the films, respectively. The films exhibited zinc blende structure with predominant (111) orientation. The surface morphology of the films is studied by scanning electron microscopy and atomic force microscopy. The rms roughness of the as-deposited films is 3.7 nm. The Raman spectra of the films show longitudinal- and transverse-optical (LO, TO) modes, which arise from CdTe- and ZnTe-like vibrations. The photoluminescence spectrum of the films shows intense emission due to free and bound exciton recombination and no emission associated with crystal imperfection and deeper impurity levels. The pseudodielectric-function spectra, e ( E )= e 1 ( E )+ ie 2 ( E ), of the films are measured by spectroscopic ellipsometry at room temperature. The measured dielectric function spectra reveal distinct structures at energies of the E 1 , E 1 +Δ 1 and E 2 critical points.

X-ray diffraction and Raman scattering studies in 10B+-implanted Cd0.96Zn0.04Te thin films prepared by vacuum evaporation

Polycrystalline Cd0.96Zn0.04Te thin films prepared by vacuum evaporation onto thoroughly cleaned glass substrates kept at room temperature were implanted with mass-analyzed beams of 100 keV boron ions (10B+) at various doses ranging from 1012 to 1014 ions cm−2. The X-ray diffraction pattern of the as-deposited film shows zinc blende structure with a predominant orientation along the 〈1 1 1〉 plane. The implanted films show a decrease in the 〈1 1 1〉 peak intensity and increase in the full-width at half-maximum (FWHM) with implantation dose. The surface roughness (rms) of the as-deposited film evaluated by atomic force microscopy is 3.7 nm and the value of roughness is found to increase with implantation dose. Raman spectra of the as-deposited films show longitudinal optic (LO) and transverse optic (TO) modes, which arise from CdTe-and ZnTe-like vibrations. There is no significant change in the Raman peak position due to implantation but the FWHM is found to be increased. This is probably due to the implantation-induced lattice disorder. The relative intensity of the Raman peaks and the area under the peaks were found to increase with implantation dose. These results are explained on the basis of the implantation-induced surface roughness and lattice disorder.