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    Tetramethyl ammonium hydroxide etchant improvement for aluminum passivation and smooth of silicon surface
    (2019-03-01)
    Suttijalern, Kamonwan
    ;
    Prabket, Jirawat
    ;
    Muanghlua, Rangson
    ;
    Niemcharoen, Surasak
    This paper purpose to the structural design and improvement of etchant solution for U-shaped Metal-Semiconductor-Metal (UMSM) photodetector fabrication on Al/n-Si/Al with anisotropic wet etching technique, the etchant solutions include tetramethylammonium hydroxide (TMAH), ammonium persulfate (AP) and silicic acid with different concentrations. Experimental design of photodetector structure to optimize the photodetector and improvement conditions of the etching solution by adding AP and silicic acid into the TMAH solution to increase the silicon surface roughness and reduce the rate of etching aluminum as electrodes. For structural design experiments, increasing the exposure area on the U-shaped groove up to 1.73 times. The results from the addition of AP to TMAH solution showed that the silicon surface is smoothness. It has a highest silicon etching rate and the addition of silicic acid to TMAH solution can reduce aluminum and silicon dioxide etching rate. Therefore, this research has the effective condition is 5 wt% TMAH with 7 g/1 AP and 34 g/1 silicic acid added. The results show the silicon surface has smooth about 5 nm and high silicon etch rate including etching aluminum equal to 0.26 μm/hr that suitable for design photodetector in further research.
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    Fabrication, characterization and analysis of ITO/n-Si Schottky photodetector
    (2010-07-30)
    Ueamanapong, Surada
    ;
    Srithanachai, Itsara
    ;
    Atiwongsangthong, Narin
    ;
    Pengpad, Putapon
    ;
    Niemcharoen, Surasak
    In this article, we have studied contact between indium tin oxide (ITO) and n-type silicon. First, the characteristics of ITO thin films have been identified. The films have high transparent and low resistivity (∼88 % of transmittance and 2.8×10<sup>-3</sup> Ω-cm). Fabrication of the ITO/n-Si photodetector was presented which was ITO thin layer deposited on 10 Ω-cm resistivity silicon wafer by R.F. sputter method. Finally, a study of characteristics of the photodetector such as I-V characteristics, C-V characteristics, and frequency response has been done. The photodetectors have built in voltage (V<inf>bi</inf>) about 0.26 V, the dark current of 5 μA and light current of 1.5 mA at 25,000 lux, 5V. Capacitance and frequency response are about 110 pF and 120 kHz, respectively.
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    On laterally spreading of space-charge-region in planar metal-semiconductor-metal structures
    (2003-10-01)
    Khunkhao, S.
    ;
    Yasumura, Y.
    ;
    Kitagawa, K.
    ;
    Masui, T.
    ;
    Sato, K.
    Lateral spreading along the surface of space-charge-region (SCR) of planar metal-semiconductor-metal (MSM) structures has been investigated. Planar MSM structures have been attracted much attention as viable optical sensor structures. For this purpose, the SCR of such a structure plays a key role in generating photocurrent and thus, in dc (static) and/or low frequency scheme, the wider SCR along the active surface is the better from the efficiency point of view. To study the spreading properties of the SCR along the surface of MSM structures, we prepared planar MSM structures leaving the undepleted region between the electrodes. We examined their SCR spreading through the photocurrent-bias voltage characteristics. The experimental results were compared with the numerical simulation using a quasi-1D (one-dimensional) model of such a planar structure. It was found that the change in the photocurrents is proportional to the square root of the bias applied, implying that the current varies with the lateral spreading of the SCR. Further, the value of the surface spreading of the SCR might be roughly equal to the results predicted from the numerical simulation. These results also suggest that the effective photocurrent generation is occurring principally at the very surface of the SCR. © 2003 Elsevier Ltd. All rights reserved.
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    White noise due to photocurrents in planar MSM structures on low-resistivity Si
    (2003-10-01)
    Khunkhao, S.
    ;
    Niemcharoen, S.
    ;
    Supadech, S.
    ;
    Sato, K.
    The noise due to photocurrent at low frequencies (3-100 kHz) has been observed of planar aluminum/n-type silicon/aluminum (Al/n-Si/Al) structures based on low-resistivity silicon. It was found that these structures exposed to illumination showed much lower noise than the full shot noise above 5 kHz under a certain operating condition. If the current noise power spectrum is expressed as S(ω) = 2eI<inf>p</inf>Γ<sup>2</sup>, where e is the electronic charge and I<inf>p</inf> is the photocurrent, the noise ratio Γ<sup>2</sup> lies between 0.2 and 1.0, depending on the bias voltage. These results are attributed to the planar structures of the samples having wide electrode separation. Spatially uniform carrier generation due to illumination at the active surface and the decrease in the cross-correlation between the current components in the structure might be playing the key role to reduce the noise to lower levels than that of full shot noise under a certain operating condition. © 2003 Elsevier Ltd. All rights reserved.
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    UV photodetector from Schottky diode diamond film
    (2002-03-01)
    Thaiyotin, L.
    ;
    Ratanaudompisut, E.
    ;
    Phetchakul, T.
    ;
    Cheirsirikul, S.
    ;
    Supadech, S.
    Diamond film was synthesized on a silicon substrate by hot-filament CVD and used to fabricate a Schottky photodiode for the detection of UV light. This paper presents an improved structure of photodiode, which reduces the effect of grain boundaries in the polycrystalline diamond film. The Schottky photodiode was fabricated on free-standing diamond film and operation in a vertical direction can be expected to reduce the effect of grain boundaries. The device shows good response to UV light and a very low response to visible light. The dark current is less than 10 pA. The device response time is less than 20 μs. Furthermore, the device reveals little change in spectral response with increasing temperature at all wavelengths. © 2002 Elsevier Science B.V. All rights reserved.