Structural and optical characterizations of chemically deposited cadmium selenide thin films

Synthesis of cadmium selenide thin films by CBD method has been presented. The deposited film samples were subjected to XRD, SEM, UV-vis-NIR and TEP characterization. X-ray diffraction analysis showed that CdSe film sample crystallized in zinc blende or cubic phase structure. SEM studies reveal that the grains are spherical in shape and uniformly distributed all over the surface of the substrates. The optical band gap energy of as deposited film sample was found to be in the order of 1.8 eV. The electrical conductivity of the film sample was found to be 10⁻⁶ (Ω cm)⁻¹ with n-type of conduction mechanism.     

Effect of thermal annealing on properties of zinc selenide thin films deposited by chemical bath deposition

Zinc selenide films have been deposited on glass substrate by chemical bath deposition method. The resultant films were annealed up to 473 K temperature. The structural properties of zinc selenide thin films have been investigated by X-ray diffraction techniques. The X-ray diffraction spectra showed that zinc selenide thin films are polycrystalline and have a cubic structure. The most preferential orientation is along the (111) direction for all films. The lattice parameter, grain size, and microstrain were calculated and correlated with annealing temperature. The optical properties showed direct band gap values were found to be in the region of 2.69–2.81 eV. The electrical studies shows conductivity increases with increase in annealing temperature. The optoelectric and structural data are discussed from the point of applications based on achieving high performance devices.     

Studies on chemical bath deposited cadmium sulphide films by buffer solution technique

Cadmium sulphide films were grown by a chemical bath technique using cadmium acetate and cadmium chloride as the Cd ion source and thiourea as the sulphur source. The solution growth process was carried out with and without buffer solutions containing ammonium acetate and ammonium chloride onto glass substrates. Various properties of the films such as surface morphology, crystallinity, composition, optical properties and dark resistivities were compared for both the above techniques.     

Photoelectrochemical studies on spray deposited copper selenide thin films

Thin films of copper selenide have been deposited by spraying a mixture of aqueous solutions (0.50 M) of copper chloride hydrate (CuCl₂·2H₂O) and selenourea [H₂NC(Se)NH₂] on preheated fluorine doped tin oxide coated glass substrates at various substrate temperatures. The cell configurations copper selenide/0.5 M K₂SO₄/C are used for studying the capacitance–voltage (C–V) characteristics in the dark, current–voltage (I–V) characteristics in dark and under illumination, photovoltaic power output and spectral response characteristics of the as deposited films. Photoelectrochemical study records that as deposited copper selenide thin films are of p-type. The spectral response characteristics of the films at room temperature show a prominent, sharp peak at 550 nm. The measured values of efficiency (η) and fill factor (FF) are found to be 0.99 % and 0.51 respectively for film deposited at 350 °C.     

Cobalt selenide thin film: photovoltaic and impedance spectral studies by simple chemical grown technique

A thin film of cobalt selenide is deposited on the fluorescence tin oxide-coated glass surface material using a simple chemical growth technique. In this article, we report on the study of photoelectrochemical characteristics (PEC), including current–voltage, capacitance–voltage characteristics, photovoltaic power output, and spectral response in dark and light conditions. For the above parameter study, we prepared using cobalt selenide and carbon electrode (using polysulfide as electrolyte), the battery configuration is expressed as n-CoSe/NaOH (1 M)?+?Na₂S (1 M)?+?S (1 M)/C (graphite). The performance of the cobalt selenide thin film material the resulted values of respective series (R_S) and shunt (R_Sh) resistance 2.280 kΩ and 1.224 Ω, respectively. The efficiency and fill factor of these PEC cells were found to be 0.899 and 28.72%. The junction ideality value are found to be (n_D) is 0.69 in the dark and 2.72 in the light (n_L). The M–S plots are constructed using C^?2 against applied bias voltage (with respect to SCE) for CoSe PEC cell. The positive slope of the M–S plot confirms n-type conductivity of the CoSe films. The carrier density values of the samples obtained from the M–S plots varied from 3.48?×?10¹⁴ cm^?3.

     

Preparation of indium selenide thin film by electrochemical technique

Indium Selenide (In_xSe_y) layers were potentiostatically deposited on glass/fluorine-doped tin oxide (FTO) substrates, using electro-chemical technique from aqueous solution containing 0.10 M InCl₃ and 0.02 M SeO₂. The electrodeposits were characterised using a wide range of analytical techniques; X-ray diffraction (XRD), scanning electron microscopy (SEM), Atomic force microscopy (AFM), optical absorption and photoelectrochemical (PEC) cell, for their structural, morphological, optical and electrical properties. The XRD show that the prepared films consist of mixed phases of InSe and In₂Se₃. The films grown at all voltages in this work were p type in electrical conduction, with bandgaps in the range of (1.70–1.80) eV in both as-deposited and heat-treated forms. The wetting property of In_xSe_y on glass/FTO surfaces indicates that In_xSe_y layers can be helpful as buffer layers or window layers in thin film solar cell development due to their ability to uniformly cover the substrate. The cross-section morphology show smoothening effect of these layers. The experimental results to date are presented in this paper.     

Structural,electrical and optical properties of copper selenide thin films deposited by chemical bath deposition technique

A low cost chemical bath deposition (CBD) technique has been used for the preparation of Cu_2–xSe thin films on glass substrates. Structural, electrical and optical properties of these films were investigated. X-ray diffraction (XRD) study of the Cu_2–xSe films annealed at 523 K suggests a cubic structure with a lattice constant of 5.697 Å. Chemical composition was investigated by X-ray photoelectron spectroscopy (XPS). It reveals that absorbed oxygen in the film decreases remarkably on annealing above 423 K. The Cu/Se ratio was observed to be the same in as-deposited and annealed films. Both as-deposited and annealed films show very low resistivity in the range of (0.04–0.15) × 10^–5 -m. Transmittance and Reflectance were found in the range of 5–50% and 2–20% respectively. Optical absorption of the films results from free carrier absorption in the near infrared region with absorption coefficient of 10⁸ m^–1. The band gap for direct transition, E_g.dir varies in the range of 2.0–2.3 eV and that for indirect transition E_g.indir is in the range of 1.25–1.5 eV.     

Nanocrystalline copper selenide thin films by chemical spray pyrolysis

Thin films of copper selenide were deposited onto amorphous glass substrates at various substrate temperatures by computerized spray pyrolysis technique. The as deposited copper selenide thin films were used to study a wide range of characteristics including structural, surface morphological, optical and electrical, Hall Effect and thermo-electrical properties. X-ray diffraction study reveals that the films are polycrystalline in nature with hexagonal (mineral klockmannite) crystal structure irrespective of the substrate temperature. The crystalline size is found to be in the range of 23–28 nm. The SEM study reveals that the grains are uniform with uneven spherically shaped and spread over the entire surface of the substrates. EDAX analysis confirmed the nearly stoichiometric deposition of the film at 350 °C. The direct band gap values are found to be in the range 2.29–2.36 eV depending on the substrate temperature. The Hall Effect study reveals that the films exhibit p-type conductivity. The values of carrier concentration and mobility for the film are found to be 5.02 × 10¹⁷ cm^?3 and 5.19 × 10^?3 cm² V^?1 s^?1; respectively for film deposited at 350 °C.     

Studies on thin films of cadmium sulphide prepared by a chemical deposition method

A new method of chemical deposition consisting of the formation of thin films of a substance at the interface of a solution and a gas was used to form thin films of semiconducting and photoconducting CdS. The structural, electrical and optical properties of these films were studied. A special feature is the cubic zinc-blende structure of the films. A possible explanation for the optical and electrical properties of these films is given.     

Observation of phase transitions in chemical bath deposited copper selenide thin films through conductivity studies

Electrical conductivity of non-stoichiometric copper selenide thin films of different phases prepared using chemical bath deposition was examined in the temperature range 10 to 500 K. Samples showed phase transitions at 45 and 450 K attributed to copper deficiency or excess of selenium in copper selenide samples arising during the preparation. A prominent defect level was also detected at 250 K; such effect vanishes upon annealing and is attributed to copper vacancy. Conductivity measurements also confirmed phase transformation of Cu₃Se₂ phase to Cu_2−xSe at 413 K.     

Studies on Seebeck effect in spray deposited CuO thin film on glass substrate

Undoped thin films of cupric oxide have been prepared by a simple chemical spray technique. Obtained samples were mostly polycrystalline and p-type semiconductor. Thermopower of a set of as-deposited samples with thickness between 340 and 620 nm have been measured in the temperature range 300-450 K. The thermovoltages were found to change sign with thickness. The dominating carrier scattering process that can limit the electrical conductivity or the Hall mobility values at room temperature may be the lattice phonon scattering. The observed variations of the position of Fermi level with the film thickness have been qualitatively explained invoking the principle of modulation of the acceptor density profile by the density of donors during the time of growth of film.     

不同厚度对分子束外延生长GaSb薄膜的影响

采用分子束外延(MBE)在GaAs衬底上生长GaSb薄膜,为了减小因晶格失配度较大所引起的位错密度,采用低温GaSb作为缓冲层.通过X射线双晶衍射仪和原子力显微镜分析得出,当低温GaSb缓冲层的厚度为20nm时,GaSb外延层中的位错密度最小,晶体质量最好.此外,缓冲层和外延层的厚度共同对GaSb薄膜晶体质量和表面形貌产生影响.     

用PECVD制备高抗腐蚀性能SiNx薄膜的工艺研究

研究了一种可抗高温强碱溶液腐蚀的氮化硅薄膜的等离子增强化学气相淀积(PECVD)生长工艺。通过X射线光电子能谱(XPS)、椭圆偏振仪、湿法腐蚀等手段分析了所生长薄膜的元素含量、折射率、抗腐蚀特性等性质随淀积工艺条件的改变所产生的变化。制备出的氮化硅薄膜可在高温强碱溶液(70℃、33.3%KOH溶液)中支撑12h而无明显变化,并实现自支撑全镂空薄膜。     

Improving low pressure chemical vapor deposited zinc oxide contacts for thin film silicon solar cells by using rough glass substrates

Compared to zinc oxide grown (ZnO) on flat glass, rough etched glass substrates decrease the sheet resistance (R_sq) of zinc oxide layers grown on it. We explain this R_sq reduction from a higher thickness and an improved electron mobility for ZnO layers deposited on rough etched glass substrates. When using this etched glass substrate, we also obtain a large variety of surface texture by changing the thickness of the ZnO layer grown on it. This new combination of etched glass and ZnO layer shows improved light trapping potential compared to ZnO films grown on flat glass. With this new approach, Micromorph thin film silicon tandem solar cells with high total current densities (sum of the top and bottom cell current density) of up to 26.8 mA cm^− 2 were fabricated.     

Annealing effect on cadmium in situ doping of chemical bath deposited PbS thin films

This paper describes the effect of annealing on PbS and Cd-doped PbS thin films prepared by chemical bath deposition at different bath temperatures (T_b). The X-ray diffraction (XRD), optical absorption, scanning electron microscopy, and energy dispersive X-ray (EDX) analyses have been performed to explore the properties of PbS and PbCdS films. From the XRD measurements, the particle size (D) of as-deposited PbS and PbCdS films is estimated to be 22 (27) and 12 (9) nm, respectively, for a T_b of 75 (85) °C. A reduction in D was noticed upon annealing the films at 200 °C, irrespective of the T_b and the doping. The optical band gap energy (E_g) of as-deposited PbS films grown at different T_b is found to be in the range of 1.22-1.42 eV. Doping of PbS with Cd and annealing have led to increase in E_g up to 2.61 (2.66) eV. Optical studies revealed prominent blue shifts in the E_g of as-deposited and annealed films due to quantum confinement effect. The addition of Cd into PbS was confirmed by EDX analysis.     

Characterization of Cd1−x Zn x Se thin films deposited at low temperature by chemical route

Optoelectronic technologically important pseudo-binary Cd_1−x Zn _x Se thin films with a variable composition (0 < x < 1) has been developed by chemical bath deposition method. The objective to study growth kinetics, physical, microscopic, compositional, optical, electrical and structural changes. Cd_1−x Zn _x Se have been deposited on non-conducting glass substrate in tartarate bath containing Cd⁺² and Zn⁺² ions with sodium selenosulphate with an aqueous alkaline medium at 278 K. The quality and the thickness of the films are depends upon deposition temperature, deposition time and pH, etc. X-ray diffraction (XRD), atomic absorption spectroscopy, optical absorption, scanning electron microscopy and thermoelectric technique characterized the films. The XRD study indicates the polycrystalline nature in single cubic phase over whole range of composition. Analysis of absorption spectra gave direct type band gap, the magnitude of which increases non-linearly as zinc content in the film is increased and dc electrical conductivity at room temperature was found to decreases from 10⁻⁷ to 10⁻⁸ (Ω cm)⁻¹. All the films show n-type conductivity. The promising features observed are the formation of continuous solid solutions in a single cubic phase.     

Conversion of a plasma enhanced chemical vapor deposited silicon-carbon-nitride thin film at ultra-low temperature by oxygen plasma

In this work we present an ultra-low temperature method for the oxidation of an amorphous silicon-carbide-nitride (SiCN) material. The SiCN is deposited on silicon substrates by plasma enhanced chemical vapor deposition using CH₄, SiH₄, and N₂ chemistry. The physical and chemical properties are characterized for the as-deposited SiCN and post-oxidized films are discussed. The SiCN film is exposed to oxygen plasma, where it undergoes a chemical transformation into a binary SiO₂ material system. A 1.7 nm/min oxidation rate is typical for this process and compares favorably to oxidation methods utilizing much higher temperatures. The substrate temperature remains extremely low throughout the oxidation process, T_s < 200 °C. Changes in film stress, optical constants, film thickness, surface roughness, and film density are measured. Chemical analysis by X-ray photoelectron spectroscopy is reported for both the as-deposited and oxidized film and confirms the resultant film to be the chemical equivalent of thermally grown SiO₂. We discuss applications specifically targeted to the conversion of SiCN to SiO₂.