K. Prabakar

Dielectric and electric modulus properties of vacuum evaporated Cd0.8Zn0.2Te thin films

Abstract Cd 0.8 Zn 0.2 Te thin films were prepared by vacuum evaporation technique. The variation of dielectric constant and dielectric loss tangent were found to depend on temperature and frequency. Impedance and electric modulus formalisms were employed in order to gain an insight into the microstructural details of films. A comprehensive study on the relaxation mechanism revealed that the presence of grain and grain boundaries across the film thickness were the basic relaxation phenomenon. The activation energies calculated from the loss tangent and spectroscopic modulus mechanism were found to vary between 1.24 and 0.91 eV for the film of thicknesses 230–800 nm. The frequency analysis of modulus properties showed a distribution of relaxation times. Conductivity plots against frequency at higher frequency suggested the response obeying the universal power law. The role of bulk and grain boundary in the overall conduction process has been discussed with realistic justification. The defect density varies between 2 and 5×10 15 eV −1 m −2 for the films of thicknesses studied.

Impedance and Electric Modulus Analysis of Cd0.6Zn0.4Te Thin Films

Cd 0.6 Zn 0.4 Te thin films were deposited by single source vacuum evaporation technique. The impedance of polycrystalline Cd 0.6 Zn 0.4 Te thin films has been measured as a function of frequency. The experimental data were measured in the temperature range of 300 - 445K and have been analyzed in the complex plane formalism and suitable equivalent circuits have been proposed in different regions. The values of resistance and capacitance of bulk and grain boundary contributions have also independently calculated from the peak of spectroscopic plots. The role of bulk and grain boundary in the overall conduction process has been discussed with realistic justification. The frequency analysis of ac conduction properties showed distribution of relaxation times due to the presence of multiple grain boundaries in the films. The activation energy calculated from the complex impedance analyses was found to be 0.29eV. The values of activation energies decrease with increase in frequency and are in agreement with that calculated from the impedance plot.

Effect of annealing on the optical constants of Cd0.2Zn0.8Te thin films

The optical response of vacuum evaporated Cd0.2Zn0.8Te thin films in the 1.5–5.6-eV photon energy range at room temperature has been studied by spectroscopic ellipsometry. The films of Cd0.2Zn0.8Te were deposited at room temperature onto well-cleaned glass substrates of 1-μm film thickness. The measured dielectric-function spectra reveal distinct structures at energies of the E1, E1+Δ1 and E2 critical points corresponding to the interband transitions. The films annealed at higher temperatures show slightly lower value for the band gap. Dielectric related optical constants, such as complex refractive index, the absorption coefficients and the normal incidence reflectivity, are presented. Pinhole free thin films facilitated the analysis of high energy regions of the absorption coefficient spectra. Results are in satisfactory agreement with calculations over the entire range of photon energies.

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.