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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    Epitaxial growth of β-FeSi2 thin films on Si(111) substrates by radio frequency magnetron sputtering and their application to near-infrared photodetection
    (2016-01-01)
    Promros, Nathaporn
    ;
    Baba, Ryuji
    ;
    Takahara, Motoki
    ;
    Mostafa, Tarek M.
    ;
    Sittimart, Phongsaphak
    β-FeSi2 thin films were epitaxially grown on p-type Si(111) substrates at a substrate temperature of 560 C and Ar pressure of 2.66 10<sup>-1</sup> Pa by radio-frequency magnetron sputtering (RFMS) using a sintered FeSi2 target, without postannealing. The resultant n-type β-FeSi2/p-type Si heterojunctions were evaluated as near-infrared photodiodes. Three epitaxial variants of β-FeSi2 were confirmed by X-ray diffraction analysis. The heterojunctions exhibited typical rectifying action at room temperature. At 300 K, the heterojunctions showed a substantial leakage current and minimal response for irradiation of near-infrared light. At 50 K, the leakage current was markedly reduced and the ratio of the photocurrent to dark current was considerably enhanced. The detectivity at 50 K was estimated to be 3.0 10<sup>11</sup> cm Hz<sup>1/2</sup>/W at a zero bias voltage. Their photodetection was inferior to those of similar heterojunctions prepared using facing-target direct-current sputtering (FTDCS) in our previous study. This inferiority is likely because β-FeSi2 films prepared using RFMS are located in plasma and are damaged by it.
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    Fabrication of mesa structural n-type nanocrystalline-FeSi2/p-type Si heterojunction photodiodes by liftoff technique combined with photolithography
    (2013-12-01)
    Funasaki, Suguru
    ;
    Promros, Nathaporn
    ;
    Iwasaki, Ryuhei
    ;
    Takahara, Motoki
    ;
    Shaban, Mahmoud
    Mesa structural n-type nanocrystalline (NC) FeSi<inf>2</inf>/p-type Si heterojunctions were fabricated by a liftoff technique combined with photolithography in order to improve the diode performance, particularly to reduce the parasitic capacitance. Their current-voltage characteristics were experimentally studied in the dark and under illumination using a 1.31 μm laser at room temperature. Their junction capacitance density and leakage current density were evidently reduced as compared with those of the normal structural diodes. The mesa diode exhibits a good rectifying action with a rectification ratio of approximately three orders of magnitude at bias voltages of ±1 V. The photodetection was clearly observed owing to the suppression in the dark current. The estimated detectivity is 2.0 × 10<sup>9</sup> cm√Hz/W at zero bias, which is an order of magnitude larger than that of the normal structural diodes. This should be because the formation of interface states is reduced accompanied by the interface area reduction. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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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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    Near-infrared photodetection of β-FeSi2/Si heterojunction photodiodes at low temperatures
    (2013-01-21)
    Izumi, Shota
    ;
    Shaban, Mahmoud
    ;
    Promros, Nathaporn
    ;
    Nomoto, Keita
    ;
    Yoshitake, Tsuyoshi
    n-type β-FeSi<inf>2</inf>/p-type Si heterojunction photodiodes were fabricated by facing-targets direct-current sputtering, and their near-infrared photodetection properties were studied in the temperature range of 50-300 K. At 300 K, devices biased at -5 V exhibited a current responsivity of 16.6 mA/W. The measured specific detectivity was remarkably improved from 3.5 × 10 <sup>9</sup> to 1.4 × 10<sup>11</sup> cmHz<sup>1/2</sup>/W as the devices were cooled from 300 K down to 50 K. This improvement is mainly attributable to distinguished suppression in heterojunction leakage current at low temperatures. The obtained results indicate that β-FeSi<inf>2</inf>/Si heterojunctions offer high potential to be employed as near-infrared photodetectors that are compatible with the current Si technology. © 2013 American Institute of Physics.
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    Photodetection characteristics of heterojunctions comprising p-type ultrananocrystalline diamond films and n-type Si substrates at low temperatures
    (2017-01-01)
    Hanada, Takanori
    ;
    Ohmagari, Shinya
    ;
    Zkria, Abdelrahman
    ;
    Promros, Nathaporn
    ;
    Yoshitake, Tsuyoshi
    0.06 at.% boron-doped p-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films were deposited on n-type Si substrates by pulsed laser deposition, and the resultant heterojunctions were evaluated as photodiodes in the deep-ultraviolet range. The rectifying action of the heterojunctions were improved accompanied by a reduction in the leakage current with decreasing temperature. The leakage current was decreased by more than three orders of magnitude at 60 K as compared with that at 300 K. Although the detectivity for 254 nm monochromatic light was gradually enhanced with decreasing temperature, the illumination current at reverse voltages was decreased along with the decrease in the leakage current. This might be because a spike due to a heterojunction band offset gets higher in the conduction band at low temperatures and it act as a barrier for photogenerated electrons flowing from the UNCD/a-C:H film to the Si substrate.
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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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    Computation of Heterojunction Parameters at Low Temperatures in Heterojunctions Comprised of n-Type β -FeSi2 Thin Films and p-Type Si(111) Substrates Grown by Radio Frequency Magnetron Sputtering
    (2017-01-01)
    Sittimart, Phongsaphak
    ;
    Nopparuchikun, Adison
    ;
    Promros, Nathaporn
    In this study, n-type β-FeSi<inf>2</inf>/p-type Si heterojunctions, inside which n-type β-FeSi<inf>2</inf> films were epitaxially grown on p-type Si(111) substrates, were created using radio frequency magnetron sputtering at a substrate temperature of 560°C and Ar pressure of 2.66×10-1 Pa. The heterojunctions were measured for forward and reverse dark current density-voltage curves as a function of temperature ranging from 300 down to 20 K for computation of heterojunction parameters using the thermionic emission (TE) theory and Cheung's and Norde's methods. Computation using the TE theory showed that the values of ideality factor (n) were 1.71 at 300 K and 16.83 at 20 K, while the barrier height (φb) values were 0.59 eV at 300 K and 0.06 eV at 20 K. Both of the n and φb values computed using the TE theory were in agreement with those computed using Cheung's and Norde's methods. The values of series resistance (Rs) computed at 300 K and 20 K by Norde's method were 10.93 Ω and 0.15 MΩ, respectively, which agreed with the Rs values found through computation by Cheung's method. The dramatic increment of Rs value at low temperatures was likely attributable to the increment of n value at low temperatures.