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Current transport mechanisms in n-type ultrananocrystalline diamond/p-type Si heterojunctions
(2016-12-01)
Zkria, Abdelrahman
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Shaban, Mahmoud
;
Hanada, Takanori
;
Promros, Nathaporn
;
Yoshitake, Tsuyoshi
Nitrogen-doped ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films were deposited on p-type Si substrates by coaxial arc plasma deposition. The deposited films possessed n-type conduction, and evidently formed pn heterojunctions with p-type Si substrates. The heterojunction devices showed typical rectification properties similar to those observed for conventional abrupt pn heterojunctions. The conduction mechanisms that govern current transport in these devices were analyzed using dark current-voltage measurements in the temperature range from 300 K to 80 K. The results revealed that a trap-assisted multi-step tunneling process is a dominant mechanism at lower temperatures and low forward bias. At least two defect levels with activation energies of 42 and 24 meV appear to activate this process. At moderate forward bias, the current followed a power-law dependence, attributable to a space-charge-limited current. This junction behavior might be owing to a large number of grain boundaries in the UNCD/a-C:H film that provide active centers for carrier recombination-tunneling processes at the junction interface.
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Characterization of n-Type nanocrystalline iron disilicide/intrinsic ultrananocrystalline diamond/amorphous carbon composite/p-Type silicon heterojunctions at low temperatures
(2016-01-01)
Promros, Nathaporn
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Baba, Ryuji
;
Kishimoto, Hirokazu
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Sittimart, Phongsaphak
;
Hanada, Takanori
N-Type nanocrystalline iron disilicide/intrinsic ultrananocrystalline diamond/amorphous carbon composite/p-type Si heterojunction photodiodes were successfully fabricated using pulsed laser deposition and coaxial arc plasma deposition. Their current-voltage (I-V) curves were measured at low temperatures ranging from 300 K to 60 K. The possible carrier conduction mechanisms were determined by analyzing the dark I-V curves. The NIR photodetections were evaluated using a 1.31 μm laser. The dominant conduction mechanisms through the heterojunctions from 300 K to 200 K and 180 K to 60 K were recombination and trapassisted multi-step tunneling processes, respectively. At 60 K, the difference in ratio between photocurrent and dark current was three orders of magnitude, with detectivity of 1.10×1011 cm Hz1/2/W at zero bias voltage, which was comparable to the existing values of commercial NIR photodiodes at the same temperature.
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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 10-1 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 1011 cm Hz1/2/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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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 × 10-6 A/cm2 to 3.8 × 10-10 A/cm2. 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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Fabrication of mesa structural n-type nanocrystalline-FeSi2/p-type Si heterojunction photodiodes by liftoff technique combined with photolithography
(2013-12-01)
Funasaki, Suguru
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Promros, Nathaporn
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Iwasaki, Ryuhei
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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 × 109 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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Near-infrared photodetection of β-FeSi2/Si heterojunction photodiodes at low temperatures
(2013-01-21)
Izumi, Shota
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Shaban, Mahmoud
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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 9 to 1.4 × 1011 cmHz1/2/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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