R.D. Pilkington

Structural and optical investigations on CdS thin films grown by chemical bath technique

Cadmium sulphide (CdS) thin films have been prepared by using a chemical bath deposition (CBD) method. Structural analysis (XRD and TEM) revealed that the films showed hexagonal structure with lattice constants a=0.4015 nm and c=0.6545 nm. On annealing, the films exhibited secondary phase of beta -CdS (cubic) along with hexagonal phase, but density of dislocations decreased. The stacking faults have been observed in the crystalline arrangement by high resolution transmission electron microscopy (HRTEM). The direct band gaps of as-grown and annealed films were found to be 2.42 and 2.62 eV with sub band gap of 2.35 eV, respectively, which were confirmed by optical analysis. On annealing, the resistivity of the films decreased from 3 x 10(6) to 1 x 10(3) Omega cm. Multiple Cd and S defects were observed by employing photoluminescence (PL) method. The intensities of emission peaks for annealed films differed with that of as-grown films. As was discussed with giving reasons.

Optical, structural and electrical properties of tin doped indium oxide thin films prepared by spray-pyrolysis technique

Tin doped indium oxide (In2O3:Sn) or indium tin oxide (ITO) thin films have been successfully deposited by the low cost spray-pyrolysis method. Low sheet resistance and high mobility films were obtained when the films were deposited at the substrate temperature of 793 K. The direct optical bandgaps for the films deposited at 793 (a) and 753 K (b) were found to be 3.46 and 3.40 eV, respectively. Similarly, the indirect bandgaps for a- and b-type films were found to be 3.0 and 2.75 eV, respectively. The Burstein-Moss shift was observed in the films. The refractive index (n) and extinction coefficient (k) were found to be in the range of 2.1 to 1.1 and 0.6 to 0.01, respectively. The various scattering mechanisms such as lattice, ionized impurity, neutral impurity, grain boundary and alloy scattering due to variation of theoretical mobilities with temperature are discussed, in order to compare experimental results. In the lattice scattering mechanism, the quantum size effect phenomena were employed to estimate the energy dilation (EI). The a-type films exhibited SnO2 as secondary phase whereas b-type films showed single phase In2O3:Sn with high sheet resistance. The lattice constants were found to be 10.16 and 10.09 A for a- and b-type films, respectively.

The effect of ambient pressure on laser-induced silicon plasma temperature, density and morphology

Laser-induced breakdown spectroscopy of silicon was performed using a nanosecond pulsed frequency doubled Nd?:?YAG (532?nm) laser. The temporal evolution of the laser ablation plumes was characterized under a range of low pressures. Electron densities were determined from the Stark broadening of the Si (I) 288.16?nm emission line and were found to be in the range 2.79 ? 1016?cm?3 to 5.59 ? 1019?cm?3. Excitation temperatures of 9000?21?000?K were calculated using the Si (I) 288.16?nm emission line to continuum ratio. The morphology of the laser plume, observed with respect to time, was seen to be strongly dependent on the ambient pressure. The density and temperature of the plasma were also found to vary critically with plasma morphology. Three ambient pressure regimes were identified where the plasma evolution was observed to differ markedly. Requirements for the existence of local thermal equilibrium conditions in the laser-induced plasmas are discussed with respect to these results.

Advanced coatings through pulsed magnetron sputtering

Abstract Pulsed magnetron sputtering (PMS) has become established as the process of choice for the deposition of dielectric materials for many applications. The process is attractive because it offers stable arc free operating conditions during the deposition of, for example, functional films on architectural and automotive glass, or antireflective/antistatic coatings on displays. Recent studies have shown that pulsing the magnetron discharge also leads to hotter and more energetic plasmas in comparison with continuous dc discharges, with increased ion energy fluxes delivered to the substrate. As such, the PMS process offers benefits in the deposition of a wide range of materials. The present paper describes three examples where PMS has led to either significant enhancement in film properties or enhanced process flexibility: in low friction titanium nitride coatings, in Al doped zinc oxide transparent conductive oxide coatings sputtered directly from powder targets and in thin film photovoltaic devices based on copper (indium/gallium) diselenide. These examples demonstrate the versatility of PMS and open up new opportunities for the production of advanced coatings using this technique. SE/499

Optical properties of high-quality CuInSe2 single crystals

CuInSe2 single crystals have been studied employing photoluminescence (PL), optical reflection (OR), optical absorption (OA) and wavelength derivative reflection (WDR) techniques at temperatures from 4.2 to 300 K. Exciton-related peaks were observed in the near-band-edge region of the PL spectra: several narrow lines, with full width at half maximum (FWHM) of about 0.3 meV, and two wider peaks (FWHM about 0.7 meV) at 1.0414 (A) and 1.0449 eV (B). The A and B peaks were also observed in the OR and OA spectra and identified as A and B free excitonic states. The narrow lines were attributed to bound exciton recombination on intrinsic defects. A third exciton resonance (C) was observed in the WDR spectra at 1.2779 eV. The crystal-field and spin-orbit splittings were derived to be 5.3 and 234.7 meV, respectively.

The effect of sulfur concentration on the properties of chemical bath deposited CdS thin films

We study the structural, surface morphology and optical properties of chemical bath deposited (CBD) cadmium sulfide (CdS) thin films under the effect of variation of S/Cd ratio. CdS thin films have been successfully deposited by CBD technique with solutions containing S/Cd ionic concentration ratio of 5.0, 2.5, 1.0, 0.5 and 0.25. Single phase CdS, with a hexagonal structure, is observed for the concentration of S/Cd = 5.0, 2.5, 1.0 and 0.5 films while for the ratio of 0.25, the films exhibited a partially amorphous nature. These have been confirmed by X-ray diffraction (XRD), transmission and scanning electron microscopy (TEM and SEM) analyses. The band gaps of the films obtained by transmission and photoacoustic spectra are found to be in the range of 2.40 to 3.26 eV. The large variation of band gaps of the films with composition is discussed by employing quantum size effect phenomena. The transition levels of CdS are also studied using photoacoustic spectroscopy.

Changes in the opto-electronic properties of CuInSe 2 following ion implantation

The development of efficient thin-film solar cells based on CuInSe2 absorber layers has encouraged fundamental research on both thin films and single crystals of this chalcopyrite semiconducting compound. The resistance to radiation and ion bombardment is of technical importance particularly for a material which could find future applications in space photovoltaic power systems. In this paper results are described for an ion implantation study using CuInSe2 single crystal substrates. Oxygen, helium and neon implantations have produced significant changes in surface resistivity and photoconductivity. Also the near-surface regions ofn-type crystals have been type-converted top-type following ion implantation. It is apparent that the ion implantation process creates defects which affect surface state densities and recombination probabilities. In the case of oxygen there is an additional doping effect caused either by the introduction of acceptor states or by the reduction of the existing donor state population. Following implantation there appears to be an overall decrease in carrier recombination at the surface which leads to an enhanced photoconductive response.

The plasma enhanced chemical vapour deposition of CuInSe2

Abstract We report the first successful chemical vapour deposition (CVD) of chalcopyrite CuInSe 2 . Thin films with compositions around the Cu : In : Se stoichiometric ratio 1:12 have been grown using a glow discharge enhanced CVD process. Film structure is analysed using X-ray camera techniques and Rutherford backscattering spectroscopy.

On the Shape of the Close-to-Band-Edge Photoluminescent Emission Spectrum in Compensated CuGaSe2

Photoluminescence (PL) properties of compensated as-grown and air-annealed CuGaSe2 single crystals, grown by the vertical Bridgman technique, in the edge emission spectral region were studied. The intensity maximum of the broad asymmetrical PL band at T= 8 K was found to be at hν max = 1.586 eV. After air annealing at 673 K for 15 min the PL band shifts towards higher energies, and its intensity slightly decreases but the shape remains the same. It is shown that this typical asymmetric PL band is not associated with a certain acceptor level but originates from the bandtail recombination. The valence band tail is formed by the potential fluctuations of charged defects. The average depth of these fluctuations is determined by the Debye-Huckel correlation in the distribution of donors and acceptors. The low-temperature air-annealing reduces the concentration of charged defects, but the sample remains highly compensated.

Photoacoustic spectroscopy of CuInSe2 thin films

Abstract Polycrystalline CuInSe 2 thin films grown by the three-source co-evaporation technique are assessed near their fundamental absorption edge with a high resolution photoacoustic spectrometer of the gas-microphone type. The results are presented for films differing in uniformity, composition and thickness. The effect of heat treatment in various ambients on the properties of these films have also been investigated using in addition to photoacoustic spectroscopy, X-ray diffraction, Rutherford backscattering spectroscopy and scanning electron microscopy.