P.S. Reddy

Structural and optical properties of Cd1−xZnxTe thin films

Abstract Polycrystalline thin films of Cd 1− x Zn x Te ( x = 0.0 to 0.5) deposited by co-evaporation of CdTe and ZnTe in a vacuum better than 5 × 10 −6 Torr on Corning 7059 glass substrates maintained at 300 °C and subsequently annealed in vacuum at 400 °C for 1 h were found to be single-phase and nearly stoichiometric. The structural, electrical and optical properties of these films were studied. The lattice parameter and the optical energy gap in relation to the composition were estimated and the results are discussed in detail.

Characterization of two-source evaporated cadmium zinc telluride thin films

Abstract Thin films of Cd 1− x Zn x Te (0 ≤ x ≤ 1) have been deposited by two-source vacuum evaporation technique onto Corning 7059 glass substrates maintained at 573 K. The structural and optical properties of these films were studied. The composition dependence of the optical band gap for the films was found to be curvi-linear. The wavelength dependence of the refractive index and extinction coefficientof the films was studied. Reflectance spectra of the films exhibited the prominent E 1 . E 1 + Δ 1 and E 2 peak energies of the interband transitions. These peak energies were found to vary linearly with composition of the films.

Physical investigations of DC magnetron sputtered indium tin oxide films

Indium tin oxide films were prepared using the DC magnetron reactive sputtering technique onto Corning glass substrates by controlling the deposition parameters. The films were characterised by studying their composition and structure, and electrical and optical properties. The low resistive and high transparent films were generated at 2.4 mTorr of oxygen by maintaining the substrate temperature at 473 K.

Optical absorption studies on p-CuGa0.5In0.5Se2 thin films

The optical absorption spectra of CuGa0.5In0.5Se2 thin films reveal absorption humps which were attributed to valence subband transitions. (αhν)2 vs. photon energy curves indicated a direct fundamental gap of 1.29 eV. Band splitting by crystal-field and spin-orbit effects were observed respectively at 1.39 and 1.58 eV. The crystal-field and spin-orbit parameters were estimated.

Structural, electrical and optical properties of CuGa0.75In0.25Se2 thin films

CuGa0.75In0.25Se2 thin films (0.1-2.0 mu m) grown on Corning 7059 glass substrates at Ts=598-648 K were nearly stoichiometric, single phase, polycrystalline and exhibited electrical resistivity in the range 30-300 Omega cm. Thermoelectric power and Hall effect measurements indicated p-type conduction in the films. The temperature dependence of the electrical conductivity suggested that above 480 K the conduction mechanism was intrinsic, whereas extrinsic/impurity conduction dominated in the range 303-450 K. The optical absorption spectra of CuGa0.75In0.25Se2 thin films revealed absorption humps which were attributed to valence subband transitions. The ( alpha h nu )2 versus photon energy curves indicated a direct fundamental gap of 1.50 eV. Band splitting by crystal-field and spin-orbit effects were observed respectively at 1.57 and 1.75 eV.

Characterization of CuGa0.25In0.75Se2 thin films

Abstract CuGa 0.25 In 0.75 Se 2 thin films prepared by the flash evaporation technique onto Corning 7059 glass substrates at T s = 598–648 K were single phase, nearly stoichiometric and polycrystalline with a strong (112) preferred orientation. The electrical resistivity of the films was in the range 30–350 Ω cm. Thermoelectric power and Hall effect measurements indicated p-type conduction in the films. Optical absorption studies indicated a direct fundamental bandgap of 1.16 eV.

Photovoltaic performance of n-CdS/p-CuGa0.25In0.75Se2 thin film heterojunctions

Abstract Polycrystalline thin film n-CdS/p-CuGa 0.25 In 0.75 Se 2 heterojunctions were fabricated and current density-voltage, capacitance-voltaǵe and spectral response of the junctions were studied. The heterojunction was illuminated in the back-wall configuration and an open-circuit voltage of 500 mV, a short-circuit current density of 23.5 mA cm -2 and an electrical conversion efficiency of 7.6% have been obtained for a cell 1 cm 2 in area under a solar input of 85 mW cm -2 .

Characterization of thin film CuGa0.5In0.5Se2 heterojunctions

Abstract CuGaxIn1−xSe2 is a potential absorber material for the fabrication of heterojunction solar cells. CuGa0.5In0.5Se2 films (0.5–3 μm) growns at Ts = 598–648 K on Corning 7059 glass substrates using the flash evaporation technique were nearly stoichiometric and polycrystalline with a chalcopyrite structure ( a = 5.689 A , c = 11.343 A ). Thermoelectric power and Hall effect measurements indicated p-type conduction in the films. The resistivity and Hall mobility of the films were in the range 50–350ωcm and 2–20 cm2V−1s−1 respectively. Optical absorption studies revealed a direct fundamental band gap of 1.29 eV. Band splitting by crystal field and spin-orbit effects was observed at 1.39 and 1.58 eV respectively. n-CdS/p-CuGa0.5In0.5Se2 thin film heterojunctions were fabricated and current density-voltage, capacitance-voltage and spectral response of the junctions were studied. The heterojunction was illuminated in the back-wall configuration and an open-circuit voltage of 575 mV, a short-circuit current density of 20mA cm−2 and an electrical conversion efficiency of 6.7% have been obtained for a cell 1 cm2 in area under a solar input of 85 mW cm−2.

Characterization of thin film n-CdS/p-CuGa0.5In0.5Se2 heterojunctions

CuGaxIn1−xSe2 is a potential absorber material for the fabrication of heterojunction solar cells. CuGa0.5In0.5Se2 films (0.5–3 μm) grown at Ts = 598–648 K on Corning 7059 glass substrates using the flash evaporation technique were nearly stoichiometric and polycrystalline with a chalcopyrite structure (a = 5.689 A and c = 11.343 A). Thermoelectric power and Hall effect measurements indicated p-type conduction in the films. The resistivity and Hall mobility of the films were in the range 50–350 ohm-cm and 2–20 cm2 V−1 s−1, respectively. The optical absorption studies revealed a direct fundamental band gap of 1.29 eV. Band splitting by crystal-field and spin-orbit effects were observed, respectively, at 1.39 and 1.58 eV. n-CdSp-CuGa0.5In0.5Se2 thin film heterojunctions were fabricated and current density-voltage, capacitance-voltage and spectral response of the junctions were studied. The heterojunction was illuminated in the back-wall configuration and an open-circuit voltage of 575 mV, a short-circuit current density of 20 mA cm−2 and an electrical conversion efficiency of 6.7% have been obtained for a 1 cm2 area cell under a solar input of 85 mW cm−2.

Characterization of n-CdS/p-CuGaxIn1−xSe2 thin film heterojunctions

Abstract CuGa x In 1− xSe 2 is a potential absorber material for the fabrication of heterojunction solar cells. CuGa x In 1− x Se 2 films (0.5−3.0 μm), grown at T s =598−648 K on Corning 7059 glass substrates using the flash evaporation technique, were p-type, nearly stoichiometric and polycrystalline with a chalcopyrite structure. Polycrystalline thin film n-CdS/p-CuGa x In 1− x Se 2 heterojunctions were fabricated with a back-wall configuration and the junction characteristics were evaluated in terms of current density-voltage, capacitance-voltage and spectral response measurements. The electrical conversion efficiency obtained for cells with an active area of 1 cm 2 under a solar input of 85 mW cm −2 was 7.6%, 6.7% and 6.5% respectively for CuGa x In 1− x Se 2 cells with x =0.25, 0.50 and 0.75.