Characterization Of CdTe Thin Films Research Articles

Characterization of CdTe Thin Films Using Orthogonal Double-Pulse Laser-Induced Breakdown Spectroscopy

Orthogonal reheating double-pulse laser-induced breakdown spectroscopy (LIBS) was applied to the elemental analysis of CdTe thin film samples. Films were grown through nanosecond pulsed laser ablation over silicon and glass substrates. The analysis was performed by applying a 266 nm pulsed laser devised to minimize sample damage. Re-excitation was conducted using a nanosecond laser emitting at 1064 nm that induced air breakdown 1 mm above the target. Emission enhancement was investigated as a function of both time acquisition delay and inter-pulse delay. The plasma temperature and electron density calculations made showed that the double-pulse scheme produced higher temperature values and a longer plasma duration than single-pulse LIBS. The self-absorption coefficient of the lines was determined from the measured ablated matter, plasma volume and collected spectra. The results of the double-pulse LIBS configuration showed a significant increase in emission intensity, reducing the self-absorption effect. In addition, the relative concentration of the thin films was determined for both experimental schemes. The calculated elemental values for the double-pulse configuration coincide with those expected and are more accurate than those obtained using a single laser.

Electrodeposition and Characterization of CdTe thin films for photovoltaic applications

Cadmium Telluride (CdTe) is direct band gap semiconductor, ∼ 1.45 eV at room temperature. It is one of the promising absorber materials for heterojunction thin film solar cell application due to high absorption coefficient and less carrier diffusion length. We have electrodeposited CdTe thin film using conventional three-electrode geometry onto FTO coated glass substrate from non-aqueous electrolyte at potential −0.625 V. As-prepared samples of CdTe were characterized thoroughly to study structural, optical, morphological, compositional and transport properties. The films were polycrystalline in nature with mixed cubic and hexagonal crystal structure without metallic phases. Highly crystalline, large grain, compact CdTe thin films have been obtained without post-deposition heat treatment. The calculated electrical parameter can be further improved upon post-deposition thermal heat treatment and/or chemical surface treatment to produce high efficiency thin film solar cell devices. The reported growth procedure could be suitable for development of flexible thin film solar cells devices on to plastic substrates.

Characterization of CdTe thin films with different compositions obtained by CMBD for thin film solar cells

CdTe thin films with different compositions, i.e. Cd/Te ratio of ∼0.79, 0.88, 0.94, 1.01, 1.05, 1.08, were fabricated by a novel and low cost chemical molecular beam deposition method (CMBD) under hydrogen flow in atmospheric pressure. For this purpose, Cd and Te granules were used as precursors. Thin films were deposited on glass and metal substrates at 600°C. The growth rate was varied in the range of (10–30)Å/s. The composition ratio in the samples was controlled by varying the molecular beam intensity (MBI) ratio. The morphological, structural, electrical and optical properties of the CdTe thin films were investigated by SEM, XRD, Hall-effect and photoluminescence (PL) measurements, respectively.

Preparation And Physical Characterization Of CdTe Thin Films Deposited By Vacuum Evaporation For Photovoltaic Applications

The present communication reports the preparation and physical characterization of CdTe thin films for photovoltaic application. The thin films of thickness 660 nm and 825 nm were deposited on glass and ITO coated glass substrates employing thermal vacuum evaporation deposition method. These as-deposited films were characterized using XRD, UV-Vis spectrophotometer, source meter, SEM and AFM for physical properties. The XRD patterns reveal that the films are crystallized zinc-blende structure of cubic phase with preferred orientation (111) as well as polycrystalline in nature. The optical and crystallographic parameters are calculated and widely discussed. The optical band gap is found in the range 1.52 - 1.94 eV and observed to decrease with thickness. The current-voltage characteristics show that the current is found to be decreased with thickness and the resistivity is increased. The SEM studies show that the films are homogeneous, uniform and free from crystal defects. The grains in the thin films are similar in size and densely packed. The AFM studies reveal that the surface roughness is observed to increase for higher thickness. The experimental results reveal that the films of thickness 825 nm may be used as absorber layer in CdTe/CdS thin film solar cells due to its optical band gap 1.52 eV which is almost identical with the optimum band gap of CdTe and good crystallinity.

Structural And Surface Studies Of Vacuum Evaporated Cadmium Telluride Thin Films

Cadmium Telluride (CdTe) is one of the most well established II–VI compounds largely due to its use as a photonic material. Existing applications, as well as those under consideration, are increasingly demanding stringent control of the material properties. The deposition of high quality thin films is of the utmost importance to such applications. This tendency has also manifested itself in the structural and surface morphology with higher structural perfection yielding smoother surfaces. The present investigations are about the structural and surface characterization of CdTe thin films. Thin films of CdTe with thickness around 4000A have been deposited by the thermal evaporation method at room temperature. The structural characterization of this film was carried out using XRD (X-ray diffraction technique) and TEM (Transmission electron microscopy). The structure of CdTe film was found to be hexagonal. Also, the lattice parameters, grain size (D), dislocation density (ρ) and micro strain (e), were taken from the XRD data. From TEM of CdTe thin films, the polycrystalline nature was confirmed. A surface morphology study was done by SEM (Scanning electron microscopy) technique. Atomic Force Microscopy (AFM) provides numerical data of surface height at digitized locations, which are usable for various surface characterizations. In this paper, the results have been analyzed to draw some conclusions which are also presented here.

Characterization of CdTe thin films fabricated by close spaced sublimation technique and a study of Cu doping by ion exchange process

CdTe thin films were prepared onto water-white glass substrates by the close spaced sublimation technique. The films annealed right after the deposition were then immersed in copper nitrate solution for different periods of time. These films were again annealed at 500 o C for 1 h to ensure the diffusion of copper in the films. The samples were characterized by X-ray diffraction and scanning electron microscopy. The electron microprobe analyzer showed an increase of copper-content in composition. The dc electrical conductivity showed a credible increase with increasing copper-content in the films. With the increase of copper-content, the hole mobility increased systematically. The optical parameters were deduced by fitting the optical transmittance in the wavelength range 300–2500 nm.

Characterization of CdTe thin films grown on glass by hot wall epitaxy

In this work we have investigated the properties of CdTe thin films grown on glass substrates by Hot Wall Epitaxy. Its most important feature is the growth at very low temperatures, which would allow the growth even on polymer substrates. Our samples were grown at temperatures between 150 and 250 oC at a growth rate between 0.2 and 2 µm/h. The CdTe films were characterized by x-ray diffraction, scanning electron microscopy and optical transmission. The x-ray teta-2teta scans revealed films with cubic structure and a very high degree of preferential orientation. In fact, for films thicker than 1 µm, no other reflections have been observed on the spectra besides the (111), (333) and (444). The scanning electron micrographs showed a grain size about 0.3 µm and the optical transmission indicated a very good optical quality of the interfaces, showing pronounced interference fringes.

Structural characterization of CdTe thin films developed on metallic substrates by close spaced sublimation

Cadmium telluride (CdTe) is one of the most investigated semiconductors for photovoltaic applications in the last four decades and is one of the most promising photovoltaic materials due to low-cost, high-efficiency, nearly optimum band gap (1.5 eV) for efficient photo conversion, high optical absorption coefficient (>104 cm−1) at band edge and the variety of deposition techniques available for its deposition as thin films. The close spaced sublimation (CSS) is one of the most promising methods to develop good quality CdTe films on large area substrates. There are various reports of the CdTe/CdS solar cells with efficiencies exceeding 16%, all prepared by CSS [1, 2]. In conventional solar cells, the CdTe is developed on the CdS window layer deposited on conducting glass substrates. But devices on glass substrates have the disadvantage of weight, inability to withstand high processing temperatures and are prone to damages. On the other hand devices on flexible metallic substrates can overcome all the above mentioned disadvantages of the glass based devices. Hence the development and characterization of CdTe on thin flexible metallic substrates are interesting. There are a number of reports regarding the characterization of CdTe thin films developed on CdS substrates by CSS, but practically no reports regarding the characterization of CdTe films developed on metallic substrates by CSS technique. We have deposited CdTe films on stainless steel by CSS at various source and substrate temperatures and the films were characterized using SEM and XRD. In this paper we are reporting the influence of the temperatures of substrate and source on the various structural parameters such as lattice parameter, grain size and stress. The investigations regarding the development of an interlayer between CdTe and the substrate are in progress and will be published in subsequent papers. The CSS system consists of a graphite reactor enclosed in a quartz tube. The tube was evacuated and

TEM, AFM, and cathodoluminescence characterization of CdTe thin films

The morphology, microstructure, and luminescent properties of polycrystalline CdTe films were investigated. The films were deposited by close-spaced sublimation at relatively low temperatures. The evolution of the film morphology and microstructure was studied as a function of deposition temperature and post-deposition heat treatment. Films deposited at low temperature exhibited fine, equiaxed grains. Dramatic grain growth was observed as a consequence of heat treatment. The film microstructure is heavily faulted and strongly dependent on the deposition and post-deposition treatment temperatures. The extended defects are mostly lamellar twins and stacking faults with similar densities. These defects often form a closely spaced arrangement, which leads to the formation of a local hexagonal phase. The presence of this hexagonal phase is expected to have significant effects on the electrical properties of the cubic CdTe films.

Electrodeposition and characterization of CdTe thin films on Mo foils using a two voltage technique

Polycrystalline thin film CdTe-based solar cells are one of the most promising candidates for low-cost terrestrial conversion of solar energy because of the optimum energy band gap ( E g =1.44 eV ) and high absorption coefficient of CdTe. In this work, a two-step electrodeposition technique has been used to prepare CdTe thin films from acidic solutions. In the first step, a thin Te rich CdTe layer was deposited at –300 mV (SCE) on a Mo foil substrate. On top of this film, a Cd rich CdTe layer was deposited at more negative voltages. The resulting films showed good adherence to the substrate and very low contact resistance between the substrate and the p+ Te rich CdTe layer. The composite film was of nearly stoichiometric composition. From X-ray diffraction results, the as-deposited films show very small grain sizes but after annealing the grain size increases considerably showing very well-defined peaks. The morphological, structural and composition results of CdTe thin films obtained by Scanning Electron microscopy, X-ray diffraction, and X-ray fluorescence will be presented. Electrical properties such as conductivity type and contact resistance values for the Mo/CdTe structures will also be presented.

95/06225 Preparation and characterization of CdTe thin films deposited by CSS

95/06225 Preparation and characterization of CdTe thin films deposited by CSS

Preparation and characterization of CdTe thin films deposited by CSS

In this work a new procedure based on the close-spaced sublimation (CSS) technique has been developed to prepare CdTe thin films. The role of various preparation parameters has been investigated and the optimum conditions have been outlined. Studies of the structural properties of the CdTe films, carried out by XRD and SEM, showed a strong influence of the substrate and evaporation temperatures on the crystallographic orientation of the films, which grow with a structure composed by a mixture of cubic and hexagonal phases. Special emphasis has been made on the effect of introducing O 2 during the deposition of the CdTe films on the resistivity of the samples. It was possible to shift the resistivity of the films by an adequate choice of the oxygen partial pressure and the source-substrate separation, from values around 10 4 Ω cm to values of about 0.4 Ω cm.

Photoreflectance characterization of CdTe thin films grown by Molecular Beam Epitaxy on GaAs(100)

CdTe films have been grown on top of GaAs(100) by means of Molecular Beam Epitaxy (MBE) at 300 °C substrate temperature. Different procedures for the CdTe growth and for the preparation of the GaAs substrates resulted in diverse crystalline qualities of the CdTe films. We present the results obtained from PhotoReflectance (PR) measurements of these films employing HeNe and Ar-ion lasers as modulating excitation. For Ar excitation, the ratio of CdTe to GaAs signal strength for the E0 transition is enhanced, allowing a differentiation of the contributions from film and substrate. Both the PR line shape and intensity are correlated to the structural quality of the CdTe films. One of the samples presented a below-band-gap transition of the GaAs substrate around 30±5 meV from E0 which is attributed to donor states produced by Te atoms diffused in the interface; this result demonstrates the high sensitivity of the photoreflectance technique to the structural properties of interfaces.