R. Pal

Photoconductivity in CuInSe2 films

Abstract CulnSe2 films with different Cu/In ratios (0.4–1.2) were deposited on glass substrates by three source evaporation techniques. The films were polycrystalline in nature with partially depleted grains. Photoconductivity in the films was measured in the temperature range 170–370 K. The data at low temperatures (T

CdSxTe1-x films: preparation and properties

CdSxTe1-x films (0<x<1) were deposited by simultaneous evaporation of CdS and CdTe powders from a vertical two-zone hot wall evaporation jig onto glass substrates. Electrical conductivity, thermoelectric and optical properties along with microstructural properties were studied in order to derive information on the electron transport processes in the films. Raman scattering was also studied for the films.

Nanostructured ZnTe films prepared by D.C. magnetron sputtering

Abstract ZnTe films in nanostructured form have been deposited by high pressure d.c. magnetron sputtering of a ZnTe target onto different substrates kept at various temperatures ranging from 223–373 K. Shift of the band gap to higher energies depended on the relative magnitudes of substrate temperature and gas pressure during deposition.

Au/CdS Schottky Diode Fabricated with Nanocrystalline CdS Layer

Schottky diodes of structure Au/nano-CdS/CBD-CdS/SnO 2 were fabricated with the nanocrystalline CdS layer deposited by the high pressure magnetron sputtering technique. The devices were characterized by current-voltage (I-V) anti capacitance-voltage (C-V) measurements. It was observed that the presence of a large amount of surface states might explain the high values of n in the nano-devices. The quantization effects of the active nano-CdS layer in the devices was confirmed from the observed peaks in the plot of conductance versus reverse bias voltage.

ZnSe films: preparation and properties

Abstract ZnSe films were prepared by the hot wall evaporation technique onto glass, NaCl and KCl substrates at different substrate temperatures during deposition. The effect of deposition parameters on the grain growth, grain distribution and surface roughness were studied. Information on their optical properties was also obtained. Strength of grain boundary scattering in these films was critically studied and it was observed that the films are partially depleted of carriers. The density of trap states at the grain boundaries decreased for films deposited at higher substrate temperatures while an increase in carrier concentration was observed for films deposited at higher substrate temperatures. The films deposited at higher deposition temperature contained less stress than those deposited at lower temperatures.

Variation of trap state density and barrier height with Cu/In ratio in CuInSe2 films

Abstract Optical properties of CuInSe 2 films, deposited by the three-source evaporation technique at a substrate temperature of 670 K, were studied critically to determine the grain boundary scattering effects from the tailing of the absorption edge. The experimental data were analysed in the light of the grain boundary trapping model in polycrystalline films. The crystallites were found to be partially depleted of carriers. The barrier height along with the carrier concentration in the films were determined from optical reflectance measurements. The effect of the variation of the Cu/In ratio (0.4–1.18) on the grain boundary scattering parameters has been critically discussed. The density of trap states in the intercrystalline region of the films was found to increase with increasing Cu/In ratio. The built-in electric field in the crystallites was evaluated for different sizes of the crystallites. The effect of illumination on the grain boundary barrier height was studied and this indicated that the grain boundary charges are depleted by subbandgap photons resulting in the reduction of the barrier height with increase of illumination level.

NANOCRYSTALLINE ZnSe FILMS PREPARED BY HIGH PRESSURE MAGNETRON SPUTTERING

Abstract Nanocrystalline ZnSe films were deposited onto glass, quartz and NaCl substrates by sputtering of a ZnSe target in argon plasma. Optical, microstructural, and photoluminescence studies were carried out in order to understand the quantization effect, along with optical absorption and emission processes, in the material in nanocrystalline form.

Polycrystalline thin film ZnSexTe1-x: preparation and properties

ZnSexTe1-x films were prepared by co-evaporating ZnSe and ZnTe powders from a two-zone hot wall evaporation jig onto glass substrates. The optical band gaps for different x were determined and this showed a bowing behaviour. The refractive indices and extinction coefficients have been determined as a function of wavelength. Variations of surface roughness with composition and microstructural details were also reported. Grain boundary scattering effects were found to be a dominant factor controlling electron transport processes in these films.

Studies on the grain boundary effect in polycrystalline CdTe films using optical reflectance measurements

Abstract The grain boundary effect in polycrystalline CdTe films deposited at various substrate temperatures has been studied critically. The grain boundary potential, the density of trap states at the boundary region and the carrier concentration in the films were obtained by an alternative technique that utilizes the reflectance measurements of the highly resistive films deposited on a nonabsorbing substrate. The barrier height in the CdTe films decreased from 0.34 to 0.2 eV as the grain size increased from 60 to 133 nm, owing to the increase in the deposition temperature from 373 to 523 K. Correspondingly, the density of trap states in the grain boundary region decreased from 1.63 × 10 13 to 6.15 × 10 12 cm −2 .

Estimation of stress in polycrystalline CuInSe2 films deposited on Mo-coated glass substrates

Stress and strain in polycrystalline thin films of CuInSe 2 deposited on soda-lime glass and Mo-coated glass substrates were determined from the optical reflectance spectra by utilizing the broadening of the optical absorption band tail. The contributions of both intrinsic (due to grain boundary and lattice vibrations) and extrinsic stresses (due to thermal mismatch of film and substrate) were considered. It was observed that the films deposited on Mo-coated glass substrates had lower grain size and higher stress (3 x 10 7 Pa) compared to those of the bare glass substrates (1.1 x 10 7 Pa). This process of estimation of mechanical properties of thin films from optical measurements on both absorbing (Mo/glass) and non-absorbing (glass) substrates appears to be very attractive due to its non-destructive nature. The defect state density (Q t ) at the grain boundary region along with the internal built-in average electric field (F av ) were determined with the variation of the Cu/In ratio in the films, deposited on glass and Mo-coated glass substrates. It was observed that both Q t and F av were higher for Cu/In < 1.0 and decreased as the stoichiometric composition was approached.