C.X. Qiu

Study of CuInSe2 thin films prepared by electrodeposition

Abstract Thin films of p-type CuInSe2 prepared by a one-step electrodeposition method have been studied by constructing CdS/CuInSe2 junctions. After the electrodeposition, the CuInSe2 films were treated either in vacuum or in Ar. Cells of the form CdS (high σ)/CdS (low σ)/CuInSe2 were then fabricated for studying the electrodeposited films. Measurements were specifically carried out to determine the diffusion length of minority carriers in the p-type CuInSe2. It was found that the minority carrier diffusion length in CuInSe2 films treated in Ar was generally greater than that for films treated in vacuum under similar conditions. A small area cell (active area 0.11 cm2) with a conversion efficiency of about 7% (under 125 mW/cm2 illumination) has been fabricated.

Effects of heat treatment on a MgOSi structure: a possible buffer layer structure for high-Tc superconductors

Abstract Thin films of MgO with a thickness of 0.1 μm were deposited by reactive rf sputtering on monocrystalline p-type Si substrates as a diffusion barrier for high- T c superconductor/semiconductor hybrid devices. After a heat treatment at temperatures from 700 to 1000°C in oxygen, the MgO Si samples were investigated by Auger electron spectroscopy (AES) for elemental distribution and differential capacitance measurements for surface electrical properties. The AES results showed the formation of a mixed MgO SiO x layer with a thickness of about 500 A after a treatment at 900°C for 1 h. The differential capacitance results showed a decrease of the minority carrier lifetime in Si after the treatment at temperatures above 800°C. The interface state density estimated from the preliminary capacitance results was about 10 11 cm −2 eV −1 .

ZnO/CdS/CuInSe2 photovoltaic cells fabricated using chemical bath deposited CdS buffer layer

Abstract CdS thin films have been prepared by using chemical bath deposition. The effects of bath temperature and concentration of NH4OH were studied. Optimum deposition conditions were established. The resulted CdS thin films exhibit optical transmissions in excess of 90% over the majority of the solar spectrum. ZnO/CdS/CuInSe2 solar cells were fabricated on electrodeposited CuInSe2 thin films. A conversion efficiency of 6.3% was obtained with an active area of 7.8 mm2 (no AR coating).

Some properties of bulk Y-Ba-Cu-O compounds containing SiO2

Bulk Y‐Ba‐Cu‐O samples containing Si with nominal compositions of Y:Ba:Cu:Si=1:2:3:x (x=0.2, 0.4, and 0.6) have been prepared by adding SiO2 to the source materials. After a relatively short heat treatment, the resistance transition characteristics of the samples were found to improve as the SiO2 content was increased. Results from ac susceptibility measurements also showed improved values as the SiO2 content was increased. However, as the solid‐state reaction was carried out at a lower temperature but for a longer time, the sample resistance increased and the superconductivity was found to degrade.

Preparation of CuInSe2 films by an electrophoretic deposition technique

Abstract Films of CuInSe 2 with a thickness of about 10 μm have been prepared by an electrophoretic method from a suspension containing CuInSe 2 powder, acetone, alcohol and tetramethylammonium hydroxide. The as-deposited films were soft; however, the quality was improved after a heat treatment at temperatures above 700 °C.

Epitaxial growth of tellurium by electrodeposition

Abstract Thin films of tellurium with a thickness up to 4 μm have been grown on monocrystalline tellurium substrates by an electro-deposition method. X-ray diffraction showed that the films deposited at 90°C with a current density of 0.5 mA/cm2 or less were monocrystalline. Films with a blade-like structure were produced as the deposition current density was increased to 1 mA/cm2.

Preparation of CdTe films by electrodeposition

Abstract Single-phase CdTe thin films have been prepared by depositing sequentially a layer of tellurium and a layer of cadmium on a molybdenum substrate followed by a short thermal treatment. Deposition of tellurium films was done in an aqueous solution containing TeO 2 at a current density of ≈ 1 mA/cm 2 . An aqueous solution containing cadmium sulfate was used for cadmium deposition with a current density of ≈1 mA/cm 2 . Solution temperature was ≈ 95°C for tellurium film deposition and was 50°C for cadmium deposition. It was found that after a heat treatment at ≈ 370°C for 10 min the deposited Te/Cd layers were converted to CdTe thin films with a cubic structure. Compositional uniformity of the films was also investigated by electron probe microanalysis.

Evidence of deep levels in crystalline CuInSe2

Abstract Differential capacitance measurements have been made on one-sided CuInSe 2 homojunctions to investigate effects of deep levels in this material. The measurements were made at different frequencies and biasing voltages. It was found that the room temperature differential capacitance value decreased continuously as the frequency was increased from 10 2 to 10 5 Hz. From a transient capacitance technique under different initial biasing conditions, evidence of hole traps was observed. A thermally stimulated differential capacitance method was also used. These experiments showed a rapid increase in capacitance at about 200 K, suggesting the rapid release of trapped holes in the junction at this temperature.

Refractive index of electrodeposited CuInSe2 films

Abstract Optical reflection measurements have been carried out in the wavelength range from 2 to 10 μm on polycrystalline CuInSe 2 thin films. The CuInSe 2 films, having a thickness from 1.5 to 2 μm, were electrodeposited on smooth Mo-coated glass substrates. From reflection interference, the optical refractive index was calculated to be 4.7.

Diffusion length measurements on electrodeposited CuInSe2 cells

Abstract Polycrystalline thin films of p-type CuInSe2 (thickness about 1 μm) have been prepared by an electrodeposition method. Heterojunction devices of the forms of CdS(low resistivity)/CdS(high resistivity)/CuInSe2 and ZnO(low resistivity)/CdS(high resistivity)/CuInSe2 were fabricated for both electrical and optical measurements. Experiments were specifically carried out to determine the diffusion length of minority carriers in the p-type CuInSe2. It was observed that the diffusion length in CuInSe2 films treated in Ar (with the CdS prepared by a chemical bath deposition method) was generally greater than the length for films treated in vacuum under similar conditions.