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Shot noise behavior of planar Mo/n-Si/Mo photodetector structure in avalanche mode
(2010-07-30)
Khunkhao, S.
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Umjaruan, C.
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Thaworn, A.
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Nuanloy, S.
;
Niemcharoen, S.
Low-frequency (3 to 50 kHz) shot noise behavior of planar metal/semiconductor/metal photodetector (MSM-PD) structure operating under pre avalanching and avalanching conditions has been observed. The structure examined is Mo/n-Si/Mo structure with electrode separation of 20μm. In higher voltages applied, both device current and its photocurrent component showed a rapid increase at a critical bias voltage due to onset of avalanche multiplication. It was found that the associated shot noise factor Γ2 varies in wide range from the order 0f 0.1 at pre-breakdown conditions to three orders of magnitude larger than unity corresponding to simple shot noise by avalanche multiplication. This result implies that the biasing condition for appropriate operation must be satisfied from the view point of signal-to noise ratio (S/N), when one operates this structure with high optical sensitivity. The value of noise factor obtained seems basically expressible by using existing theory with a little smaller exponent of multiplication factor.
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Multiplication of photocurrent in silicon planar metal-semiconductor-metal structures
(2009-10-22)
Khunkhao, S.
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Titiroongruang, W.
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Niemcharoen, S.
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Ruangphanit, A.
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Phongphanchanthra, N.
DC photocurrent gain properties of planar metal-semiconductor-metal (MSM) optical sensor structures on have been investigated experimentally. The test structure has two co-planar Mo/n-Si Schottky-barrier junctions on silicon of resistivity 9-12 Ω-cm and the electrode separation is 20 μm. The current-voltage (I-V) characteristics measurements under illumination in visible range showed a rapid increase in photocurrent at higher biases examined. From the temperature, the dependence of I-V characteristics and noise measurements, such photocurrent increase was ascribes to avalanche multiplication of carriers photogenerated in the Schottky junction reversed-biased. From low-frequency (10-50kHz) signal measurements, it was found that multiplication factor larger than 100 at 10kHz and 30 at 50kHz was achieved. ©2009 IEEE.
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Substrate bias effects on Drain Induced Barrier Lowering (DIBL) in short channel NMOS FETs
(2009-07-01)
Ruangphanit, A.
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Phongphanchantra, N.
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Poyai, A.
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Hruanan, C.
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Muanghlua, R.
The substrate biasing characteristics of the Drain-Induced Barrier Lowering (DIBL) effects in short-channel NMOS devices with n+ polysilicon gate that fabricated at TMEC by 0.8 CMOS technology were presented. It was found that by increasing the substrate bias form -1 to -5V, DIBL in NMOS devices with mask channel length (L) from 0.6 to 3.0 micron shows the interesting feature. As the channel length decreased, the threshold voltage shift caused by DIBL first increased with increasing substrate bias and then decreased as the channel length decreased further for the range of L# 0.6 micron. But the DIBL increased with increasing substrate bias for the length of L between 0.8 and 1.2 micron. And almost neglected the substrate bias effect for the range of L > 1.2 micron. The substrate bias effect on subthreshold DIBL coefficient (ETAb) is approximately 3.5, 7.0, 8.0 and 0.7 mV/V for L of 0.8, 1.0, 1.2 and 3.0 micron respectively. Whereas the subthreshold DIBL coefficient (ETA0)is around 44, 10, 5 and 1.25 mV/V respectively. This change in DIBL with substrate bias for a short channel device can be explained as the transition of the surface DIBL effect to the subsurface DIBL effect and the onset of the punchthrough effect. Design considerations of the channel doping profile in short channel NMOS device for substrate bias based on improving the punchthrough and DIBL are also briefly discussed. © 2009, INSInet Publication.
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White noise in silicon-based planar metal-semiconductor-metal photodiodes
(2008-10-06)
Khunkhao, S.
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Nanthivatana, P.
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Niemcharoen, S.
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Titiroongruang, W.
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Sato, K.
Low-frequency 3-100 kHz shot noise (white noise) emerging from photoinduced current in Mo/n-Si/Mo structures leaving undepleted region has been observed under different bias and optical intensity conditions. The measurements revealed that the current noise observed depends not only on the illumination intensity levels but also on bias voltage. The current noise observed is expressed as S(ω)=2IΓ2 and analyzed, where I and Γ2 is the average current and noise factor, respectively. The measurements reveal that Γ2 has strong bias dependence, lying Γ2- 0.01 to about unity corresponding to simple shot noise. Such experimental results are explained, stating that the reduction of cross correlation between drift and diffusion currents and autocorrelation of drift current component determining the level of noise occurs with decrease in SCR width bias-dependent. To explain the behavior of observed noise more properly, we propose, in addition to the mechanisms above, that the reduction in autocorrelation effect of each current component plays an important role to decrease the relevant noise to such extremely low levels. © 2008 IEEE.
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Optical-beam profiling by field-controlled metal-semiconductor-metal structures
(2005-10-01)
Kitagawa, K.
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Aoki, T.
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Khunkhao, S.
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Wongprasert, Y.
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Titiroongruang, W.
Optical-beam profiling properties of Schottky-barrier metal-semiconductor- metal (MSM) structures have been investigated experimentally. Making use of a planar molybdenum/n-type silicon/molybdenum (Mo/n-Si/Mo) MSM structure with a wide electrode separation, one-dimensional (1-D) profiling of optical-beam intensity distribution from a helium-neon (He-Ne) laser was carried out. It was confirmed that, in addition to the existing photosensing function, the sensitivity (output photocurrent) of such a structure could be controlled by applying a bias via lateral spreading of the surface space-charge-region (SCR) at the side of the reverse-biased Schottky-junction.
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On laterally spreading of space-charge-region in planar metal-semiconductor-metal structures
(2003-10-01)
Khunkhao, S.
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Yasumura, Y.
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Kitagawa, K.
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Masui, T.
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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.
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Niemcharoen, S.
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Supadech, S.
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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>Γ2, where e is the electronic charge and I<inf>p</inf> is the photocurrent, the noise ratio Γ2 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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Photosensing properties of interdigitated metal-semiconductor-metal structures with undepleted region
(2003-08-01)
Masui, T.
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Khunkhao, S.
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Kobayashi, K.
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Niemcharoen, S.
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Supadech, S.
We previously reported that it is possible to achieve bias-controllable photocurrent characteristics using planar metal-semiconductor-metal (MSM) structures with depleted and undepleted regions at the active area under optical illumination. To make the structures of this type more sensitive to dc and/or ac optical quantities, interdigitated Schottky-barrier MSM (SB-MSM) structures for visible range having voltage-controllable iris function have been fabricated and examined. By introducing an undepleted region between Schottky barriers on both sides, the depleted region width at the front surface under illumination varies with bias applied, where this region would be more sensitive to optical quantity than the undepleted region to generate the photocurrent. Making use of planar molybdenum n-type silicon molybdenum (Mo/n-Si/Mo) structures, it has been experimentally demonstrated that such a structure exhibits voltage controllability of photocurrents whilst maintaining the inherent function converting optical signal into electronic signal. An appreciable improvement in obtaining output photocurrent was confirmed from both dc and low frequency (1-20) kHz signal measurements. It was found that the experimental results are substantially explained by the simplified model of this structure. © 2003 Elsevier Science Ltd. All rights reserved.

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