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Author: search.filters.author.Khunkhao, S.Subject: search.filters.subject.Photodetector

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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.