Amorphous silicon phototransistors

Kaneko, Yoshiyuki; Koike, N.; Tsutsui, K.; Tsukada, T.

doi:10.1063/1.102726

Cited by 51 publications

(33 citation statements)

References 3 publications

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“…This excellent I Ph / I Dark is similar to that of a BPTT device 23 of 2.0ϫ 10 5 and 100 times greater than previously reported values for OPTs, [18][19][20][21][22] even for amorphous silicon. 30 Moreover, those performances were reproduced with the same devices even after storage under ambient conditions for more than 1 month. The transfer curves for the pentacene OPTs showed a V Th shift with increasing incident optical power.…”

Section: Resultsmentioning

confidence: 89%

Highly sensitive thin-film organic phototransistors: Effect of wavelength of light source on device performance

Noh¹,

Kim²,

Yase³

2005

Journal of Applied Physics

194

138

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Organic phototransistors (OPTs) were fabricated from pentacene and copper phthalocyanine (CuPC) based on the geometry of organic field-effect transistors (OFETs); and the effect of the wavelength of the incident light source on their performance was examined. High performance OFETs with pentacene and CuPC were fabricated and the characteristics of the OPTs were examined under UV and visible-light irradiations with top illumination. The CuPC and pentacene OPTs show a high responsivities of 0.5–2 and 10–50A∕W and maximum IPh∕IDark of 3000 and 1.3×105, respectively, under 365nm UV light. However, under visible light, at a wavelength of 650nm, the pentacene OPTs had 100 times less responsivity, 0.15–0.45A∕W, and a IPh∕IDark of 1000, even though an absorption coefficient three times larger was observed at this wavelength than at 365nm. A strong correlation was found between the performance of the OPTs and the incident photon to current conversion efficiency spectra of an organic semiconductor. The strong dependence on the wavelength of incident light of the performance of the prepared OPTs can be explained by an internal filter effect in which light with a large absorption coefficient is filtered at the top surface and through the bulk of the film when light is directed onto the opposite side of the OFET gate electrode. Thus, light cannot efficiently contribute to the generation of charge carriers in the channel regions that were formed in the first two molecular layers adjacent to the dielectric interface. Consequently, the most efficient OPTs were produced when the following conditions of incident light were satisfied: The photon energies (or frequencies) should be (i) larger than the band gap and (ii) have a relatively small absorption coefficient, since the light can penetrate down to the channel layer more efficiently when it is near the dielectric interface without any loss in absorption through the film.

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Section: Resultsmentioning

confidence: 89%

Highly sensitive thin-film organic phototransistors: Effect of wavelength of light source on device performance

Noh¹,

Kim²,

Yase³

2005

Journal of Applied Physics

194

138

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“…and most other organic phototransistors; [ 7c ] furthermore, these values are comparable to those obtained from amorphous silicon-based devices ( R = 300 A W −1 and P = 1000). [ 17 ] Considering the low photoresponsivity of pentacene itself (≈10 A W −1 ), we conclude that the high photoresponsivity of our functional devices predominantly originates from the photoisomerization of SP units in SP-co -MMA (>95% contribution), in stark contrast to other small-molecule-based phototransistors where the P values mainly originated from the photoresponses of the semiconductor itself. [ 7 ] These results demonstrate the effi ciency of our strategy for constructing organic phototransistors with high responsivity by developing new types of photoactive polymer gate dielectrics based on photochromic molecules, regardless of the R and P values of organic semiconductors themselves.…”

Section: Doi: 101002/aelm201500159mentioning

confidence: 98%

Synergistic Photomodulation of Capacitive Coupling and Charge Separation Toward Functional Organic Field‐Effect Transistors with High Responsivity

Zhang

Hui

Chen

et al. 2015

Adv Elect Materials

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effectively built by interface engineering because the nature of the interfaces that are ubiquitous in OFETs plays an important role in the performance and stability of devices. [ 8 ] Among different interfaces, the dielectric/semiconductor interface is particularly vital as, under an applied electric fi eld, charge carriers are directly generated and transported at this interface. Hence, the polarity, charge distribution, and surface roughness of the dielectric/semiconductor interface can dramatically affect the device performance. Besides these factors, intrinsic characteristics of dielectric materials, such as permittivity, can also infl uence the carrier transport in the semiconductor. Therefore, it is essential to modify the dielectric/semiconductor interface and functionalize dielectric layers for providing straightforward methods to tailor the carrier density and/or install new functions. [ 9 ] In this study, we demonstrate such a general approach to fabricate a new type of organic phototransistor, which is capable of reversibly photomodulating the carrier density at the dielectric/semiconductor interface; this phototransistor was constructed using photochromic spiropyran (SP)-methyl methacrylate (MMA) copolymers (hereafter referred to as SP-co -MMA) as the photoresponsive gate dielectrics ( Figure 1 ). SP is a type of organic chemical compounds known for its photochromic properties; [ 10 ] it was chosen as the photosensitizer because SPs can revert back-and-forth between a neutral, closed form (SP-closed) and a zwitterionic, open form (SP-open) when exposed to light of different wavelengths. Such a unique conformational transition caused by the photoisomerization of SP molecules leads to a signifi cant modulation of the electric dipole moment ( P mol ) (≈6.4 D of SP-closed and ≈13.9 D of SP-open), [ 11 ] thus forming the basis of the development of novel photoswitchable sensors and functional optoelectronic devices. [ 12 ] In this case, reversible P mol changes of SPs in polymer dielectrics result in two distinct capacitance values that induce different capacitive coupling. In addition, under UV irradiation, SPs at the dielectric/semiconductor interface could change from a neutral form (SP-closed) to a charge-separated form (SP-open), thus producing scattering sites that can trap the photoexcited electrons and correspondingly leave hole carriers in the conductive channel. A synergistic combination of both effects realizes the photomodulation of the threshold voltage ( V T ) values, and thus channel conductance. This study is established from previous cases where SP was simply mixed with poly(methyl methacrylate) (PMMA) as the gate dielectric; unfortunately, the SP concentration was signifi cantly limited by its low solubility in PMMA. [ 9d,f ] The important distinction in this study is that the use of SP-co -MMA copolymers allows for the substantial tuning of the SP ratios in polymer dielectrics, thus signifi cantly Organic fi eld-effect transistors (OFETs) are the basic building blocks in numerous f...

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“…Recombining with holes, the accumulated electrons effectively lower the potential barrier for hole injection from source, leading to photoinduced V th reduction and, consequently, a poor SS and high off-state leakage current. That is the so-called photovoltaic effect, which commonly happens in hydrogenated amorphous Si 10,11 and organic TFTs. 12,13 Obviously, the feature of improved SS in Ge-QD TFTs under light modulation could not be explained well by the photovoltaic effect.…”

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confidence: 99%

Photoresponses in polycrystalline silicon phototransistors incorporating germanium quantum dots in the gate dielectrics

Tseng

Chen

2008

Applied Physics Letters

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Polycrystalline silicon (poly-Si) thin-film transistors (TFTs) incorporating germanium (Ge) quantum dots (QDs) in the gate oxide were fabricated as efficient blue to near ultraviolet phototransistors for light detection and amplification. Under 405–450 nm light illumination, Ge QDs poly-Si TFTs exhibit not only strong photoresponses in the drive current but also much improved subthreshold characteristics than that measured in darkness. This originates from the fact that only photoexcited holes within Ge QDs are injected into the active channel via vertical electric field and contribute excess mobile carriers for photocurrent but without the associated photogenerated electron induced junction barrier lowering.

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Amorphous silicon phototransistors

Cited by 51 publications

References 3 publications

Highly sensitive thin-film organic phototransistors: Effect of wavelength of light source on device performance

Highly sensitive thin-film organic phototransistors: Effect of wavelength of light source on device performance

Synergistic Photomodulation of Capacitive Coupling and Charge Separation Toward Functional Organic Field‐Effect Transistors with High Responsivity

Photoresponses in polycrystalline silicon phototransistors incorporating germanium quantum dots in the gate dielectrics

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