Electronic structure, structural and optical properties of thermally evaporated CdTe thin films

Abstract

Thin films of CdTe were deposited on glass substrates by thermal evaporation. From the XRD measurements it is found that the films are of zinc-blende-type structure. The lattice parameter was determined as a = 6.529 Å, which is larger than 6.48 Å of the powder sample, because the recrystallized lattice of the grown films is subjected to a compressive stress aroused as a result of the lattice mismatch and/or differences in thermal expansion co-efficient between the CdTe and the underlying substrate. Transmittance, absorption, extinction, and refractive coefficients are measured. Electronic structure, band parameters and optical spectra of CdTe were calculated from ab initio studies within the LDA and LDA+U approximations. It is shown that LDA underestimates the band gap, energy levels of the Cd-4d states, s-d coupling and band dispersion. However, it calculates the spin-orbit coupling correctly. LDA+U did not increase much the band gap value, but it corrected the s-d coupling by shifting the Cd-4d levels towards the experimentally determined location and by splitting the LDA-derived single s peak into two peaks, which originates from admixture of s and d states. It is shown that the s-d coupling plays an important role in absorption and reflectivity constants. The calculated optical spectra fairly agree with experimental data. Independent of wave-vector scissors operator is found to be a good first approximation to shift rigidly the band gap of CdTe underestimated by LDA.

Electronic structure and optical properties ofZnX(X=O,S, Se, Te): A density functional study

“…This is demonstrated, for example, for all diamond-like group IV and ztype group III-V, II-VI, and I-VII semiconductors, 28 wtype AlN, GaN, and InN, 29 ZnX-w and -z (X=S, Se, and Te), 21,22 and CdTe. 31 76,77 Systematic study of the SO coupling parameters was performed for zinc-blende II-VI semiconductors (Ref. To study the role of the SO coupling in band dispersion the present ab initio calculations have been performed by VASP and MindLab packages and spin orbit splitting energy is found.…”

Phase stability, electronic structure, and optical properties of indium oxide polytypes

“…Not only the band gap, but also the band dispersion comes out incorrectly and this effect is well pronounced in transition metal oxides (see, e.g., Ref. 55,56,58,[61][62][63][64][65][66] Analysis shows that calculated effective masses for In 2 O 3 -I and -II are almost the same, while those for In 2 O 3 -III are much smaller. Hence, carrier mobility in In 2 O 3 -III is expected to be larger than that in In 2 O 3 -I and -II.…”

“…rigid shift of all the CB states, so that the optical spectra shall also be shifted accordingly. 56,65,66,80 The search of literature shows that among In 2 O 3 -I and -II experimental data is available for the latter in Ref. 48, where reflectivity and transmittance spectra were measured by spectrophotometry at room temperature.…”

STRUCTURAL AND OPTICAL PROPERTIES OF CdTe THIN FILMS OBTAINED BY ELECTRODEPOSITION

“…CdTe in the shape of thin film can be polycrystalline or nanocrystalline, which can contribute towards the change of its characteristics [4]- [6]. Different methods are used for the preparation of thin films of CdTe, including electrodeposition [4], [7], [8], magnetron sputtering [9], [10], thermal evaporation [5], [11], close space sublimation [12] - [14] and others [15], [16].…”