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Effect of oxygen flow rate on physical properties of Al-doped ZnO transparent conducting films prepared by reactive dc magnetron sputtering using metallic Zn:Al target
(2020-04-06)
Gaewdang, T.
;
Wongchaoen, Ng
In this work, Al-doped ZnO transparent conducting thin films were prepared by a reactive dc magnetron sputtering method on slide glass substrate using single metallic Zn:Al (2 wt.% Al) target with the oxygen flow rate 1, 3, 5, 7 and 9 sccm, respectively. From XRD patterns, the films prepared at R(O2) of 1 sccm showed amorphous characteristics. In contrast, the films prepared at R(O2) of 3, 5, 7 and 9 sccm showed the preferred orientation (002) plane of hexagonal structure. Surface morphology and diameter of nanocolumns of the films were observed by AFM and FESEM. From transmittance spectra, energy gap value was found to vary between 3.24 and 3.32 eV. Electrical resistivity and Hall effect measurements were performed on the films with van der Pauw configuration. The temperature-dependent conductivity was performed in the range 20-300 K. Three types of conduction mechanisms were expected. Thermally activated band conduction at the high temperature range (250-300 K), Mott variable-range hopping (Mott-VRH) at the low temperature range (100-210 K) and Efros-Shklovskii variable-range hopping (ES-VRH) at the very low temperature range (<100 K) can be found in the films prepared with different oxygen flow rate conditions. Except for the oxygen flow rate at 5 sccm, the behavior of weakly localized electrons was observed. Then, the sets of parameters explaining the properties of localized electrons in each conduction regime were determined. The results indicated that the reactive dc magnetron sputtering using a single metallic Zn:Al (2 wt.% Al) target is suitable for TCO films since it can be easily obtained at low temperatures with good physical properties.
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Structural, optical and electrical properties of (CdS)1-x (ZnTe)x solid solution thin films prepared by vacuum thermal evaporation method
(2019-09-16)
Thueman, D.
;
Gaewdang, T.
The II-VI compounds and their solid solutions are promising source for various types of thin film devices such as thin film transistors, optoelectronic devices and solar cells. The formation of (CdS)<inf>1-x</inf>(ZnTe)<inf>x</inf> layer by interdiffusion of CdS and ZnTe during the fabrication of CdS/ZnTe heterojunction thin film was previous reported. This layer is thought to be important because it relieves strain at the CdS/ZnTe interface that would otherwise exist due to the excess 10 % lattice mismatch between the two materials. Therefore, it is essential to have a full understanding of the physical properties of (CdS)<inf>1-x</inf>(ZnTe)<inf>x</inf> alloy thin films. In this work, (CdS)<inf>1-x</inf>(ZnTe)<inf>x</inf> thin films in the entire composition range (0≤x≤1.0) were prepared by vacuum thermal evaporation on glass substrate using mixed powders of high purity of CdS and ZnTe compounds as the precursor. XRD revealed that the films exhibited a hexagonal structure with the preferred orientation of (002) plane when x ≤ 0.2. However, when x ≥ 0.8, they belonged to a cubic structure with the preferred orientation of (111) plane. For the composition 0.4 ≤ x ≤0.6, the hexagonal and cubic phases coexisted in the system and the films became less preferentially oriented. SEM and EDS were used to study the surface morphology and elemental composition of the samples. The crystallite size of the as-deposited films in the range 88-361 nm was observed by AFM image. The FTIR transmission spectra in the range 400-1,000 cm-1 revealed the characteristics of Cd-S and Zn-Te vibrational modes. Optical properties of the films were performed with UV-Vis spectrophotometer in the wavelength range 400-1,000 nm. The variation of direct energy gap with composition (x) was in good agreement with the quadratic form, giving an upward bowing parameter (b) of 1.23 eV. Electrical properties of the films were evaluated by resistivity and Hall effect measurements in the van der Pauw configuration. From transient photoconductivity measurement, the decay current data were better fitted with multiple exponential functions resulting in the several slow decay times. Density of trap states corresponding to its decay time was also evaluated from the decay current data.
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Electron transport mechanisms in CdSxTe1-x solid solution thin films prepared by thermal evaporation method
(2019-09-10)
Gaewdang, T.
;
Wongcharoen, Ng
In this paper, CdS<inf>x</inf>Te<inf>1-x</inf> (0≤x≤1.0) thin films were prepared by thermal evaporation method in vacuum. X-ray diffraction (XRD) revealed that the films exhibited a zincblende structure with the preferred orientation of (111) plane when x ≤ 0.2. However, when x ≥ 0.8, they had a wurtzite structure with the preferred orientation of (002) plane. For the composition 0.2 ≤ x ≤ 0.6, the zincblende and wurtzite phases coexisted in the system and the films became less preferentially oriented. Atomic force microscopy (AFM) was used to study the morphological features of the samples. Energy gap values in the range of 1.45-2.39 eV were deduced from optical transmission spectra. The temperature dependence of electrical conductivity from room temperature down to liquid-helium temperature of CdS<inf>x</inf>Te<inf>1-x</inf> thin films was performed in order to identify the dominant conduction mechanism. It was shown that three types of conduction mechanisms can be expected. In the high temperature range about 220-300 K, Seto's model of thermionic emission dominated, whereas, in the low temperature range (about 145-185 K), the dominant hopping conduction was Mott variable range hopping. However, the lower temperature region (about 70-105 K) Efros-Shklovskii variable range hopping was observed. The set of parameters describing the properties of localized electrons in each conduction behavior were examined.
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Temperature-dependent electrical transport characteristics of p-SnS/n-WO3:Sb heterojunction diode
(2018-07-04)
Gaewdang, T.
;
Wongcharoen, Ng
The p-SnS/n-WO<inf>3</inf>:Sb heterojunction diode was successfully obtained by thermal evaporating SnS thin films on WO<inf>3</inf> doped with 2.0 mol% Sb<inf>2</inf>O<inf>3</inf> of 1 mm thick ceramic pellet substrate. The electrical properties of p-SnS/n-WO<inf>3</inf>:Sb heterojunction were investigated by forward current-voltage-temperature (I-V-T) characteristics in the temperature range of 20-300 K. It was found that at low forward bias voltage (<0.25V), the conduction mechanism of the diode exhibits Ohmic conduction. At intermediate voltage (0.25<V<1.0V), the conduction mechanism is dominated by thermionic emission (TE). At bias voltage above 1.0 V, the current transport is due to space charge limited current (SCLC) controlled by an exponential trap distribution in the band gap of WO<inf>3</inf>:Sb. The temperature dependence of the saturation current and ideality factor are well described by tunneling enhanced recombination model occurring at junction interface with E<inf>a</inf> and E<inf>00</inf> values about 1.565 eV and 99.5 meV, respectively.
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Effect of source temperature on the electrical transport, microstructural and optical properties of tin monosulfide thin films prepared by close spaced sublimation method
(2018-07-04)
Wongcharoen, Ng
;
Gaewdang, T.
Tin monosulfide (SnS) thin films were prepared by close spaced sublimation method at three different source temperatures of 550, 575 and 600°C. Structural, textural and compositional features were investigated by XRD, SEM, EDS and Raman spectroscopy. From absorption spectra, direct band gap increased from 1.18 to 1.23 eV with increasing source temperature. Electrical resistivity, Hall constant, carrier concentration and mobility values of the films prepared at source temperature of 600°C were 0.54 ω.cm, 40.76 cm3/C, 1.537#x00D7;1017 and 75.48 cm2/(V.s), respectively. The temperature-dependent conductivity was performed in the temperature range of 50-300 K. It was shown that three types of conduction mechanisms can be expected: thermionic emission passing through grain boundary at high temperature range (240-300 K), the Mott variable-range hopping (Mott-VRH) at low temperature range (135-235 K) and the Efros-Shklovskii variable-range hopping (ES-VRH) at very low temperature range (80-130 K).
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Influence of substrate temperature on some properties of close-spacing thermally evaporated CdTe thin films
(2008-01-01)
Gaewdang, T.
;
Wongcharoen, Ng
;
Siribuddhaiwon, P.
;
Promros, N.
CdTe thin films with different substrate temperatures have been deposited by thermal evaporation method on glass substrate in vacuum chamber having low pressure about 3.0×10-5 mbar. According to XRD analysis, CdTe thin films are polycrystalline belonging to cubic structure with preferential orientation of (111) plane. The strongest peak intensity of XRD is observed in the film prepared with substrate temperature of 150°C. Band gap and band tail values of the as-deposited films were evaluated from the optical transmission spectra. The lowest dark sheet resistance value was obtained from the film prepared with substrate temperature of 150°C as well. Regarding to our experimental results, it may be indicated that the 150°C substrate temperature is the most suitable condition in preparing CdTe thin films for solar cell applications. © 2008 Trans Tech Publications, Switzerland.
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Investigations on chemically deposited Cd1-xZnxS thin films with low Zn content
(2005-12-01)
Gaewdang, Ng
;
Gaewdang, T.
Thin films of Cd<inf>1-x</inf>Zn<inf>x</inf>S (0 ≤ x ≤ 0.8) were deposited on glass substrates by the chemical bath deposition technique. The as-deposited films were exposed to a stream of slowly flowing nitrogen at annealing temperature ranging 100-500 °C. XRD patterns of as-deposited Cd<inf>1-x</inf>Zn<inf>x</inf>S over all mixture ratio values showed the cubic zincblende structure of which reflection peaks associated to (111), (220) and (311) planes were clearly identified. However, XRD characteristics of hexagonal wurtzite structure appeared at annealing temperature beyond 400 °C. From scanning electron microscope, the as-deposited films were formed by different sizes of clusters of grains of which average grain size smaller than 50 nm was observed. The increase in mixture ratio value in the starting solution was found to produce a decrease in the grain size. Energy gap value of annealed films, which is obtained from optical transmission measurements, seems to shift to lower energy as the annealing temperature increases. Electrical sheet resistance of the films, performed in the darkness and under illumination conditions by using a halogen lamp, as a function of annealing temperature was also investigated. The variation of energy gap of thin films with annealing temperature was discussed by employing quantum size effect phenomena. © 2005 Elsevier B.V. All rights reserved.
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Luminescence of Ce3+ in the InxSC1 - xB03 (0 ≤ x ≤ 1) solid solution
(1994-01-01)
Gaewdang, T.
;
Chaminade, J. P.
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Garcia, A.
;
Pouchard, M.
;
Hagenmuller, P.
The formation of a complete solid solution in the In<inf>itx</inf>Sc<inf>1 - x</inf>BO<inf>3</inf> (0 ≤ x ≤ 1) system with a linear variation in unit cell parameters is reported. Crystal growth of the In<inf>0.359</inf>Sc<inf>0.639</inf>Ce<inf>0.002</inf>BO<inf>3</inf> composition was performed by slow cooling of a high temperature solution using LiBO<inf>2</inf> as a solvent in an Ar atmosphere. The luminescence of Ce3+ in the In<inf>x</inf>SC<inf>1 - x</inf>BO<inf>3</inf> solid solutions and in the as-grown single crystals was investigated. The influence of In content on the luminescent intensity of Ce3+ is discussed in relation to heat treatment conditions. © 1994.
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