Promros, Nathaporn

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Promros, Nathaporn
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Promros, N.
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nathaporn.pr@kmitl.ac.th

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    Silver thin films deposited by compact magnetron sputtering system
    (2010-02-08)
    Promros, N.
    ;
    Paosawatyanyong, B.
    A compact dc magnetron sputtering system capable of silver thin films depositions was designed and constructed. The novel small footprint sputtering head with target diameter of 52 mm was constructed utilizing powerful neodymium alloy magnet. Silver metal was sputter-deposited under various powers. Plasma parameters were analyzed by using the sweeping-bias single langmuir probe. The electron temperatures of the plasma glow were constant at approximately 2 eV even with the increasing of input power whereas plasma density increases with the increasing of the input power. The X-ray diffraction analysis (XRD) and scanning electron microscope (SEM) were used to study the crystalline structure and the surface morphology of the obtained silver thin films. Crystalline orientations of (111) and (200) in the silver films deposited on slide glass substrates were revealed from XRD pattern. The highest degrees of (111) and (200) orientations was obtained at the sputtering power between 0.228 and 0.265 Wxcm<sup>-2</sup>. Sub-micron crystalline silver grain structure were observed using SEM micrographs. Facetted grain size and deposition rate of silver thin films increases as the sputtering power increases. © (2010) Trans Tech Publications.
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    Electrical characteristics of n-type nanocrystalline FeSi2/intrinsic Si/ p-type Si heterojunctions prepared by facing-targets direct-current sputtering
    (2014-01-01)
    Promros, Nathaporn
    ;
    Funasaki, Suguru
    ;
    Iwasaki, Ryuhei
    ;
    Yoshitake, Tsuyoshi
    n-Type nanocrystalline FeSi<inf>2</inf>/intrinsic Si/p-type Si heterojunctions were prepared by FTDCS. In order to estimate their diode parameters such as ideality factor, barrier height and series resistance, their current-voltage characteristics were measured in the temperature range from 300 to 77 K and analyzed on the basis of thermionic emission theory and Cheung's method. Based on thermionic emission theory, the ideality factor was calculated from the slope of the linear part from the forward lnJ-V characteristics. The barrier height was calculated once the saturation current density was derived from the straight line intercept of lnJ-V plot at a zero voltage. The obtained results exhibit an increase of ideality factor and a decrease of barrier height at low temperatures, which might be owing to inhomogeneity of material and non-uniformity of charge at the interface. Based on Cheung's method, the ideality factor and barrier height were estimated from y-axis intercept of dV/d(lnJ)-J plot and y-axis intercept of H(J)-J plot, respectively. The series resistance was analyzed from the slopes of dV/d(lnJ)-J and H(J)-J plots. The values of ideality factor and barrier height obtained from this method are in agreement with those obtained from the thermionic emission theory. The obtained series resistances from dV/d(lnJ)-J and H(J)-J plots, which were approximately equal to each others, were increased as the temperature decreased. This result should be owing to the increased ideality factor and remarkably reduced carrier concentrations at low temperatures. © (2014) Trans Tech Publications, Switzerland.
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    Near-infrared light detection of n-type β-FeSi2/Intrinsic Si/p-Type Si Heterojunction Photodiodes at Low Temperatures
    (2013-01-01)
    Iwasaki, R.
    ;
    Yamashita, K.
    ;
    Promros, N.
    ;
    Izumi, S.
    ;
    Funasaki, S.
    n-Type β-FeSi2/intrinsic Si/p-type Si heterojunction photodiodes were prepared by facing-targets direct-current sputtering, and their near-infrared light detection performances were evaluated in the temperature range of 50 - 300 K. The rectification current ratio at bias voltages of ±1 V and the ratio of the photocurrent to the dark leakage current were remarkably enhanced with a decrease in the temperature. The detectivity at zero bias was estimated to be 3.8- 109 cmHz1/2/W at 300 K, and it was enhanced to be 8.9-1011 cmHz1/2/W at 50 K. It was demonstrated that β-FeSi2 is a potential material applicable to near-infrared photodetectors that are compatible with Si. © The Electrochemical Society.
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    Temperature dependent current-voltage characteristics of n-type nanocrystalline-FeSi2/p-type Si heterojunctions fabricated by pulsed laser deposition
    (2014-01-08)
    Promros, Nathaporn
    ;
    Iwasaki, Ryuhei
    ;
    Funasaki, Suguru
    ;
    Yamashita, Kyohei
    ;
    Li, Chen
    n-Type NC-FeSi<inf>2</inf>/p-type Si heterojunctions were successfully fabricated by PLD, and their forward current-voltage characteristics were analyzed on the basis of thermionic emission theory (TE) in the temperature range from 300 down to 77 K. With a decrease in the temperature, the ideality factor was increased while the zero-bias barrier height was decreased. The calculated values of ideality factor and barrier height were 3.07 and 0.63 eV at 300 K and 10.75 and 0.23 eV at 77 K. The large value of ideality factor indicated that a tunneling process contributes to the carrier transport mechanisms in the NC-FeSi<inf>2</inf> films. The series resistance, which was estimated by Cheung's method, was strongly dependent on temperature. At 300 K, the value of series resistance was 12.44 Ω and it was dramatically enhanced to be 1.71× 10<sup>5</sup> Ω at 77 K. © (2014) Trans Tech Publications, Switzerland.
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    Investigation of electrical transport properties in heterojunctions comprised of silicon substrate and nanocrystalline iron disilicide films
    (2016-01-01)
    Promros, Nathaporn
    ;
    Sittimart, Phongsaphak
    ;
    Kaenrai, Weerasaruth
    In this study, n-type nanocrystalline FeSi<inf>2</inf>/p-type Si heterojunctions were fabricated using facing-target direct-current sputtering (FTDCS). The possible transportation mechanisms of carriers were investigated by analysing the dark J-V characteristics at temperatures ranging between 60 and 300 K. The ideality factor (n) was estimated from the slope of the linear region for the forward lnJ-V characteristics. The value of n was 1.87 at 300 K and nearly constant at temperatures ranging from 140 to 300 K, suggesting that a recombination process at the junction interface was dominant in the transportation mechanism of carriers. At temperatures below 140 K, the value of n increased by more than two and the value of A was virtually constant. Owing to the consistency of A, combined with the temperature dependent value of n, the implication is that a trap-assisted multi-step tunnelling mechanism governed the carrier transport. From the analysis of J-V characteristics, the value of barrier height was 0.58 eV at 300 K and decreased to 0.19 eV at 60 K.
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    Diode parameters of heterojunctions comprising p-type si substrate and n-type β-FeSi2 thin films
    (2014-01-01)
    Promros, Nathaporn
    ;
    Funasaki, Suguru
    ;
    Takahara, Motoki
    ;
    Shaban, Mahmoud
    ;
    Yoshitake, Tsuyoshi
    N-Type β-FeSi<inf>2</inf>/p-type Si heterojunctions have been successfully fabricated by facingtargets direct-current sputtering at a substrate temperature of 600 °C without post-annealing and their current-voltage characteristics were measured at low temperatures ragne from 300 K down to 50 K. The ideality factor, saturation current and series resistance were estimated by the thermionic emission theory and Cheung’s method. By the thermionic emission theory, we calculated the ideality factor from the slope of the linear part from the forward lnJ-V and estimated the saturation current density from the straight line intercept of lnJ-V at a zero voltage. As decreasing temperatures from 300 down to 50 K, the value of ideality factor increased from 1.2 to 15.6, while the value of saturation current density decreased from 1.6 × 10<sup>-6</sup> A/cm<sup>2</sup> to 3.8 × 10<sup>-10</sup> A/cm<sup>2</sup>. From the plots of dV/d(lnJ)-J and H(J)-J by Cheung’s method, the obtained values of series resistances are consistent with each other. The series resistances analyzed from both plots increased as decreasing temperatures.
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    Characterizations of mesa structural near-infrared n-type nanocrystalline-FeSi2/p-type si heterojunction photodiodes at low temperatures
    (2013-10-04)
    Promros, Nathaporn
    ;
    Iwasaki, Ryuhei
    ;
    Funasaki, Suguru
    ;
    Yamashita, Kyohei
    ;
    Yoshitake, Tsuyoshi
    In order to reduce the parasitic capacitance, mesa structural n-type NC-FeSi<inf>2</inf>/p-type Si heterojunctions were fabricated by photolithography. Their current-voltage characteristics were measured in the dark and under illumination using a 1.31 μm laser in the temperature range of 60 - 300 K. Their junction capacitance density was evidently reduced as compared with that of the normal structural diodes. The dark current was markedly reduced with a decrease in the temperature. At 60 K, a rectifying current ratio in the dark became more than five orders of magnitude at ±1V. The ratio of the photocurrent to the dark current was dramatically enhanced to be approximately two orders of magnitude, and the detectivity was calculated to be 1.5 × 10<sup>11</sup> cmHz<sup>1/2</sup>/W at -1V. The obtained results showed a remarkable improvement in the device performance as compared with those at 300 K. © (2013) Trans Tech Publications, Switzerland.
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    Necessity of epitaxial growth of β-FeSi2 Thin Films in Formation of n-Type β-FeSi2/p-Type Si Heterojunction Photodiodes
    (2013-01-01)
    Iwasaki, R.
    ;
    Promros, N.
    ;
    Yamashita, K.
    ;
    Izumi, S.
    ;
    Funasaki, S.
    n-Type β-FeSi2 thin films were epitaxially and non-epitaxially grown on p-type Si(111) substrates by facing-targets direct-current sputtering (FTDCS) at a substrate temperature of 600°C. Whereas the n-type epitaxial β-FeSi2/p-type Si heterojunctions exhibited a typical rectifying behavior with a rectification ratio of more than two orders of magnitude at bias voltages between ±1 V, the heterojunctions comprising non-epitaxial β-FeSi2 films rarely exhibited rectifying action. The epitaxial growth of β-FeSi2 is an significant factor for forming the heterojunction diodes. © The Electrochemical Society.
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    Surface morphology and wettability for thin films of beta-iron disilicide produced through direct-current sputtering utilizing a pair of facing targets
    (2018-08-14)
    Charoenyuenyao, Peerasil
    ;
    Promros, Nathaporn
    ;
    Chaleawpong, Rawiwan
    ;
    Yoshitake, Tsuyoshi
    In the current work, beta-FeSi2 films were epitaxially produced onto Si(111) wafer substrates via usage of facing-targets direct-current sputtering (FTDCS). The temperature for substrate heating was maintained at 600 °C and the sputtering pressure was set at 1.33 × 10<sup>-1</sup> Pa. The surface morphology and contact angles of the beta-FeSi<inf>2</inf> films were explored consistently in this research. Images of three-dimensional AFM and FESEM for the beta-FeSi2 film surface revealed a smooth surface with a root mean square roughness of 1.31 nm and a porous area. The average contact angle between the dropped water and beta-FeSi<inf>2</inf> film surface was found to be 98.7°, establishing that the surface of the beta-FeSi<inf>2</inf> films was hydrophobic. The acquired experimental results revealed the commencement of the hydrophobic surface feature of the beta-FeSi<inf>2</inf> films produced via FTDCS approach.
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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<sup>-5</sup> 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.