A Photoconductor Intrinsically Has No Gain

Dan, Yaping; Zhao, Xingyan; Chen, Kaixiang; Mesli, A.

doi:10.1021/acsphotonics.8b00805

Cited by 81 publications

(93 citation statements)

References 20 publications

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“…Otherwise, the photocurrent will not be linear with applied electric field. 14 The gain equation fits well with the experimental data shown in Figure 4d. As the light intensity Ilight gets weaker, the gain approaches to its maximum value Gmax according to eq.(9).…”

Section: Resultssupporting

confidence: 69%

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Explicit Gain Equations for Single Crystalline Photoconductors

Chen

Huang

et al. 2020

ACS Nano

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Photoconductors based on semiconducting thin films, nanowires and 2-dimensional (2D) atomic layers have been extensively investigated in the past decades. But there is no explicit photogain equation that allows for fitting and designing photoresponses of these devices. In this work, we managed to derive explicit photogain equations for silicon nanowire photoconductors based on experimental observations. These equations may be

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Section: Resultssupporting

confidence: 69%

“…'), we can write the photo gain as eq (14). which can fit well to the experimental data as shown inFigure 5d.…”

mentioning

confidence: 54%

Explicit Gain Equations for Single Crystalline Photoconductors

Chen

Huang

et al. 2020

ACS Nano

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“…However, this classical gain theory is an implicit function and may even be questionable. [ 7 ] It is implicit in that it is a function of carrier lifetime and transit time and cannot quantitatively fit the light‐intensity‐dependent photogains. More importantly, the classical gain theory was derived on two misplaced assumptions.…”

Section: Figurementioning

confidence: 99%

“…More importantly, the classical gain theory was derived on two misplaced assumptions. [ 7,8 ] First, the classical theory assumes no metal–semiconductor boundary confinement, which leads to the questionable conclusion that high gain can be obtained as long as the minority recombination lifetime is much longer than the transit time. After the metal–semiconductor boundary confinement is considered, it turns out that a photoconductor intrinsically has no gain or at least no high gain no matter how long the minority recombination time and how short the transit time is.…”

Section: Figurementioning

confidence: 99%

Explicit Gain Equations for Hybrid Graphene‐Quantum‐Dot Photodetectors

Chen

Zhang

Zang

et al. 2020

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Graphene is an attractive material for broadband photodetection but suffers from weak light absorption. Coating graphene with quantum dots can significantly enhance light absorption and create extraordinarily high photo gain. This high gain is often explained by the classical gain theory which is unfortunately an implicit function and may even be questionable. In this work, we managed to derive explicit gain equations for hybrid graphene-quantum-dot photodetectors. Due to the work function mismatch, lead sulfide (PbS) quantum dots coated on graphene will form a surface depletion region near the interface of quantum dots and graphene. Light illumination narrows down the surface depletion region, creating a photovoltage that gates the graphene. As a result, high photo gain in graphene is observed. The explicit gain equations are derived from the theoretical gate transfer characteristics of graphene and the correlation of the photovoltage with the light illumination intensity. The derived explicit gain equations fit well with the experimental data, from which physical parameters are extracted.Graphene is a zero-bandgap semimetal with extraordinarily high carrier mobility, 1, 2, 3, 4, 5 as a result of which graphene is an attractive material for broadband photodetection. Photodetectors based on graphene operating in the mid-infrared spectrum have been demonstrated in recent years. 6,7,8,9 However, due to its nature of being atomically thin, graphene suffers from weak light absorption, resulting in poor photoresponsivity. 10,11,12,13 Coating graphene with semiconducting quantum dots (QDs) can strongly enhance the light absorption and introduce an interesting high photo gain at an order of 10 8 , 14, 15, 16 several orders of magnitude larger than photodetectors based on pure semiconducting QDs (often have a photo gain of 10 2 -10 3 ). 17,18,19 The classical carrier-recycling gain mechanism is often used to explain the origin of high gain, 14,15,16 that is, the high gain originates from the photoexcited carriers circulating the circuits many times before recombination due to the long response time and short transit time. 20 However, this classical gain theory is an implicit function and may even be questionable. 21 It is implicit in that it is a function of carrier lifetime and transit time and cannot quantitively fit the light-intensitydependent photo gains. More importantly, the classical gain theory was derived on two questionable assumptions. 21,22 Firstly, the classical theory assumes no metal-semiconductor boundary confinement, which leads to the questionable conclusion that high gain can be obtained as long as the minority recombination lifetime is much longer than the transit time. After the metal-semiconductor boundary confinement is

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“…Some studies have shown that Equation is a simplified model, and I p could be affected by a lot of effects . Dan et al pointed out that ∆ n is always spatially nonuniform and decreases with the increase of E , which would result in I p becoming saturated; while G should come from the different concentrations of the excess electrons and holes, which is caused by one type of carriers is trapped …”

Section: Device Working Principlementioning

confidence: 99%

Strategies toward High‐Performance Solution‐Processed Lateral Photodetectors

Lin

Wang

2019

Advanced Materials

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Since the device performance mainly depends on the active materials and device architectures, they are the subject of extensive work, and there have been many achievements. Dispersible inorganic materials vastly simplify the preparation of films while maintaining good electrical conductivity; [1][2][3][4][5] organic small-molecule materials and polymer materials have wide wavelength response, especially in visible region, and can be adjusted easily by changing the functional groups; [6][7][8][9][10] organic-inorganic hybrid material systems are also a promising development direction, combining good electrical and optical properties; [11][12][13][14][15] in addition, the perovskite series of organic-inorganic hybrid materials has become a new research direction due to their excellent optoelectronic properties. [16][17][18][19][20] In addition, varieties of microstructures including nanoparticles, nanowires, nanosheets etc., have been widely investigated, and they have a wide range of applications in devices benefiting from their peculiar characteristics, like quantum size effect and anisotropy. [21][22][23][24][25] Besides working on active materials, constructing diverse device architectures is also a convenient and effective approach. [26][27][28][29][30] The fabrication of blend, bilayer, and multilayer architectures would be conducive to increasing responsivity, extending detection range, and accelerating response speed.Here, from active materials to device architectures, we systematically introduce and discuss the strategies for improving the device performance of solution-processed lateral PDs. To begin with, we briefly expound the working mechanism of the lateral PDs and clarify the key device figures-of-merit. Then, based on the active materials, we divide the devices into four categories: inorganic, organic, hybrid, and perovskite, and their corresponding improvement methods are summarized respectively. To close, we conduct a physical generalization and propose detailed suggestions for the further development of the field. Device Working PrincipleThe structures of lateral PDs are quite simple: an active layer between two parallel electrodes or using three electrodes (source, drain, and gate) for better control; and the detection of light mainly originates from the change of conductivity, which is caused by the increase of the carrier concentration under illumination.Due to their low cost and ease of integration, solution-processed lateral photodetectors (PDs) are becoming an important device type among the PD family. In recent years, enormous effort has been devoted to improving their performances, and great achievements have been made. A summary of the core progress, especially from the perspective of design principles and device physics, is necessary to further the development of the field, but is currently lacking. Here, to address this need, first, the working mechanism of PDs and the device figures-of-merit are introduced. Second, by classifying the active materials into four categories, including in...

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A Photoconductor Intrinsically Has No Gain

Cited by 81 publications

References 20 publications

Explicit Gain Equations for Single Crystalline Photoconductors

Explicit Gain Equations for Single Crystalline Photoconductors

Explicit Gain Equations for Hybrid Graphene‐Quantum‐Dot Photodetectors

Strategies toward High‐Performance Solution‐Processed Lateral Photodetectors

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