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Processing and characterization of amorphous copper oxide thin films prepared by reactive magnetron sputtering
(2018-01-01)
Gaewdang, Thitinai
;
Wongcharoen, Ngamnit
In this paper, copper oxide (CuO<inf>x</inf>) thin films with amorphous phase were prepared on glass substrates by reactive dc magnetron sputtering. The influence of the flow rate of O<inf>2</inf> on the structural, optical and electrical properties of the as-deposited films was systematically studied. XRD revealed that the as-deposited films remained amorphous in the whole range of adjusted oxygen flow rate. Surface morphology and nanoparticle size of the films were observed by AFM. Electrical resistivity and Hall effect measurements were performed on the films with van der Pauw configuration. The positive sign of the Hall coefficient confirmed the p-type conductivity in all studied films. From temperature-dependent electrical conductivity of the films prepared at R(O<inf>2</inf>) of 1.5 sccm, it was show that three types of behavior can be expected, nearest-neighbor hopping at high temperature range (200-300 K), the Mott variable range hopping at low temperature (110-190 K) and Efros-Shklovskii variable range hopping at very low temperature (65-100 K). Some important parameters corresponding to Mott-VRH and ES-VRH like density of localized states near the Fermi level (N(E<inf>F</inf>)), localization length (ξ), degree of disorder(T<inf>0</inf>), hopping distance (R) and hopping energy (W) were determined. These parameters would be helpful for optimizing the performance of photovoltaic applications.
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Structural, optical and photoconductive properties of thermally evaporated CdSxTe1-x thin films
(2017-10-01)
Gaewdang, Thitinai
;
Wongcharoen, Ngamnit
The formation of a CdS<inf>x</inf>Te<inf>1-x</inf> layer by the interdiffusion of S into the CdTe and of Te into CdS films occurs during the fabrication of CdS/CdTe thin film solar cells. The CdS<inf>x</inf>Te<inf>1-x</inf> layer is thought to be important because the real electrical junction is located in this interdiffused CdS<inf>x</inf>Te<inf>1-x</inf> region. Thus, it is important to have a full understanding of the physical properties of CdS<inf>x</inf>Te<inf>1-x</inf> alloy thin films. In this study, CdS<inf>x</inf>Te<inf>1-x</inf> thin films with composition 0 ≤ x ≤ 1 were prepared by thermal evaporation method on glass substrate using powder of pure CdS and CdTe compounds pressed in pellet form as the source in a vacuum of 5.5 10-5 mbar. X-ray diffraction (XRD) revealed that the films exhibited a cubic zincblende structure with the preferred orientation of (111) plane when x < 0.2. However, when x ≥ 0.8, they had a hexagonal wurtzite structure with the preferred orientation of (002) plane. For the composition 0.2 ≤ x ≤ 0.6, the cubic and hexagonal phases coexisted in the system and the films became less preferentially oriented. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to study the morphological features of the samples. The transmission spectra of the films were studied using a double beam spectrophotometer in the wavelength range of 300-900 nm. Optical band gap value of the films was determined from the transmittance spectra. The variation of band gap (E<inf>g</inf>) with composition (x) of the films was in good agreement with the quadratic form, giving a bowing parameter of (b) =1.85 eV. From the transient photoconductivity measurements, persistent photoconductivity (PPC) behavior was observed. The decay current data fit better with multiple exponential functions, resulting in five slow decay times. The longest carrier lifetime of approximately 6,000 s was observed in the films with x = 0.8. Density of trap states corresponding to decay time was also evaluated from the decay current data.
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Influence of annealing temperature on the properties of SnS thin films prepared by vacuum thermal evaporation
(2017-01-01)
Wongcharoen, Ngamnit
;
Gaewdang, Thitinai
SnS thin films were deposited by thermal evaporation in vacuum on glass slide substrate. The as-deposited films were thermally annealed in a controlled N<inf>2</inf> atmosphere with annealing temperature in the range 100-500°C for 30 min. XRD, AFM, UV-VIS transmittance, FTIR and Hall effect measurements were used for characterization the as-deposited and annealed films. Based on the XRD patterns, the as-deposited and annealed films were indentified as the orthrombic structure. The band gap was found to increase from 1.15 to 1.42 eV when the annealing temperature increased from 100 to 500°C. The lowest resistivity and highest carrier concentration values were observed to be 12.95 Ω. cm and 1.98×1016cm-3on the films annealed at 100 and 200°C, respectively.
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Physical properties of CdSxTe1-x thin films prepared by close spaced sublimation method
(2017-01-01)
Gaewdang, Thitinai
;
Wongcharoen, Ngamnit
CdS<inf>x</inf>Te<inf>1-x</inf>(0 ≤ x ≤ 1) thin films were prepared on clear quartz glass substrate by close spaced sublimation method using stoichiometric mixed powders of pure CdS and CdTe compounds. Crystal structure of CdS<inf>x</inf>Te<inf>1-x</inf>thin films was cubic structure with a preferential orientation of (111) plane when the S mole ratio less than 0.2. However, For the composition 0.2 ≤ x ≤ 0.8, the cubic and the hexagonal phases were found to coexist in the system and the films became less preferentially oriented whereas CdS thin films formed in the hexagonal phase with a preferential orientation of (002) plane. SEM micrographs showed the grain size decreased when the S content increased. As the S content increased, the energy gap value of CdS<inf>x</inf>Te<inf>1-x</inf>thin films varied from 1.48 eV (for CdTe) to 2.25 eV (for CdS). Dark electrical sheet resistance of CdS<inf>x</inf>Te<inf>1-x</inf>thin films decreased as a function of S content to minimum value about 2.24×107Ω/sq for x=0.8 and then slightly increased to 4.13×107Ω/sq for x=1.0. From the transient photoconductivity measurements, the highest photosensitivity value about 60.0 was obtained for the films with x = 0.8.

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