A K Chaudhuri

Optical constants of vacuum-evaporated polycrystalline cadmium selenide thin films

The optical constants (n,K) of vacuum‐evaporated polycrystalline CdSe thin films are determined over 900–3100 nm photon wavelengths. Variation of band gap and optical constants with film thickness and substrate temperature is studied. Anomalous variation of refractive index near the band gap is explained by the volume and surface imperfections. Average spin‐orbit splitting of valence band (0.32) is estimated for the films deposited on mica substrates. A theoretical plot of refractive index near the band edge is done. The dispersion of refractive index in films is studied by considering a single‐oscillator model.

Some optical properties of evaporated zinc telluride films

The absorption and transmission of ZnTe thin films are measured at wavelengths of 0.32-2.3 mu m. The optical constants (n, K) are measured in this range, although the short wavelength refractive index n measurement is limited by the band gap. A theoretical calculation of n near the band gap is made from experimental parameters. An explanation is given for the abnormal decrease of refractive index near the band gap. The effects of film thickness and doping with impurities like In, PbCl2, BaF2 have also been investigated. Effective crystallite size and strain have been determined by the method of variance analysis of the X-ray diffraction line profile on the same films. Lattice constants have also been calculated using the Nelson-Riley plots. It has been observed that there is an increase in optical band gap with decrease in crystallite size, increase in strain and decrease in lattice constant value.

Structural characterization of cadmium selenide thin films by X-ray diffraction and electron microscopy

X-ray diffraction, transmission electron microscopy and transmission electron diffraction studies on cadmium selenide thin films deposited on glass substrates have been carried out. X-ray line profile analysis of the diffraction panems has been performed to study the microstructural parameters. The variation of different microstructural parameters. such as crystallite size, RMS strain. dislocation density and stacking fault probability with film thickness as well as substrate temperature is studied. The optimum growth condition is fixed to a film thickness of the order of 1 .Opm. The change of preferred orientation is observed for films deposited at and above 473 K. 0

Electrical characterization of stable air-oxidized CdSe films prepared by thermal evaporation

Stabilization of the electrical resistivity of CdSe thin films has been studied by air oxidation at room temperature (300 K). Depending on the film thickness, the dark- and photoconductance of the films stabilize over 12 to 25 days of air exposure. The variation of photosensitivity of the films has been explained on the basis of inherent slow recombination states (k centres) and oxygen-assisted conversion of selenium vacancy, cadmium vacancy, cadmium interstitial to cadmium vacancy - cadmium interstitial complexes. The variation of oxygen adsorption with film thickness is studied. The temperature variation of dark- and photoconductance measurements in these films reveals a thermal quenching of photoconductivity at about 265 K. The k centres are located at about 0.23 eV above the top of the valance band. A selenium vacancy-related level is revealed at about 0.12 eV below . This level disappears as a result of long time exposure of the films to atmospheric oxygen. An oxygen-assisted excitonic transition is revealed along with the band edge transition in the spectral distribution of photocurrent of oxygen-adsorbed stabilized films.

Study of the microstructure and optical properties of polycrystalline Cd1 − xZnxTe thin films

Abstract Different microstructural parameters like particle size, rms strain and dislocation density of thermally evaporated Cd 1 − x Zn x Te (0 x

X-ray line profile analysis studies on SnSe thin films deposited at different substrate temperatures

Abstract Crystallite size and microstrain values for SnSe thin films of thickness 210–240 nm deposited on glass substrates kept at different high temperatures have been estimated using the method of variance and Fourier analysis of the X-ray diffraction line profiles. Variability of the interlayer spacings has also been studied. Growth of the high temperature phase of SnSe, usually found above 807 K, has been observed along with room temperature phase in films deposited at 472 K and above. It is observed that initially there is a growth of the crystallites. The r.m.s. strain and the mean fractional change in the interlayer spacing also initially increase with the temperature of the substrate. With the nucleation of the high temperature phase a fall in the crystallite size value accompanied by release of strain is observed.

Electrical and photoelectronic properties of SnSe thin films

Conductivity, photoconductivity and Hall measurements have been carried out on vacuum evaporated, air exposed SnSe films of different thicknesses in the temperature range 300K-85K to probe into the mechanism of photoconduction in these films. Photoconductivity has been explained by the trapping of majority carriers at the crystallite boundaries.

The anomalous photovoltaic effect in polycrystalline zinc telluride films

The anomalous photovoltaic effect has been studied in polycrystalline ZnTe films. Increase of photovoltage on Te doping and a decrease on Zn doping is observed. The effect of phase transition, grain‐boundary potential barrier, and surface space charge on the photovoltaic effect are reviewed and studied. Analysis of different experimental results reveals that the generation of emf in angularly deposited films on an insulating surface is mainly due to formation of p‐n or p‐p+ junctions at the grain boundaries and the surface band bending.

Study of long-period relaxation in photoconduction in SnSe films

Hall coefficient, photoconductivity and photoconductive relaxation measurements have been carried out on vacuum-evaporated air-exposed SnSe films in the temperature range 300-130K to probe into the mechanism of photoconduction in these films. The results have been explained by the trapping of majority carriers in the grain boundary region. The barrier height estimated from the temperature variation of the photorelaxation time is of the order of 0.16 eV, which agrees well with the values obtained from the temperature variation mobility as well as from the temperature variation of steady-state excess photoconductivity. The value of the trap density obtained from this analysis is of the order of 2*1025 m-3.

Structural characterization of thin films of cadmium telluride

Abstract X-ray diffraction patterns of vacuum-deposited thin films of cadmium telluride have been recorded and X-ray line profile analysis studies have been carried out after correcting for instrumental broadening. Size of the crystallites, r.m.s. strain, dislocation density and stacking fault probabilities have been estimated using the method of variance analysis and peak shift of the line profiles. It is observed that with increase in the thickness of the films there is an increase in the stacking fault probability and this inhibits the growth of the crystallites and results in the increase in r.m.s. strain and dislocation density. The photosensitivity of the films is measured and it is observed, that at about 400 nm thickness, the photosensitivity is at a maximum. An attempt is made to correlate the results.