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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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