Defect Assisted Carrier Multiplication in Amorphous Silicon

Miah, Mohammad Abu Raihan; Niaz, Iftikhar Ahmad; Lo, Yu‐Hwa

doi:10.1109/jqe.2020.2988263

Cited by 5 publications

(5 citation statements)

References 34 publications

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“…Defect engineering has been one of the key strategies of material design and defect‐assisted CM had been previously reported in amorphous silicon. [ 33 ] Various defects and impurities are unavoidable during the growth processes of TMDCs. Among different defects, chalcogen vacancies are known to create sub‐gap states in TMDCs, [ 34 ] which provide possibilities to manipulate the threshold energy of CM.…”

Section: Resultsmentioning

confidence: 99%

Carrier Multiplication in Transition Metal Dichalcogenides Beyond Threshold Limit

2022

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Carrier multiplication (CM), multiexciton generation by absorbing a single photon, enables disruptive improvements in photovoltaic conversion efficiency. However, energy conservation constrains the threshold energy to at least twice bandgap (2E g ). Here, a below threshold limit CM in monolayer transition metal dichalcogenides (TMDCs) is reported. Surprisingly, CM is observed with excitation energy of only 1.75 E g due to lattice vibrations. Electron-phonon coupling (EPC) results in significant changes in electronic structures, which favors CM. Indeed, the strongest EPC in monolayer MoS 2 leads to the most efficient CM among the studied TMDCs. For practical applications, chalcogen vacancies can further lower the threshold by introducing defect states within bandgap. In particular, for monolayer WS 2 , CM occurs with excitation energy as low as 1.51 E g . The results identify TMDCs as attractive candidate materials for efficient optoelectronic devices with the advantages of high photoconductivity and efficient CM.

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Section: Resultsmentioning

confidence: 99%

Carrier Multiplication in Transition Metal Dichalcogenides Beyond Threshold Limit

2022

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“…In addition, the specific defects in AlN formed during the ALD deposition 38 , 44 , were believed to be responsible for the multiplication of the transported carriers due to the significantly increased tunneling current via the mechanism of trap-assisted tunneling 33 , 45 . Generally, the substitutional oxygen for nitrogen (O N ) and aluminum vacancy (V Al ) are the dominated defects in the ALD prepared AlN films 38 , and would form the shallow level defects with the corresponding energy level about 0.8 and 1.0 eV, respectively.…”

Section: Resultsmentioning

confidence: 99%

Engineered tunneling layer with enhanced impact ionization for detection improvement in graphene/silicon heterojunction photodetectors

et al. 2021

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Here, an engineered tunneling layer enhanced photocurrent multiplication through the impact ionization effect was proposed and experimentally demonstrated on the graphene/silicon heterojunction photodetectors. With considering the suitable band structure of the insulation material and their special defect states, an atomic layer deposition (ALD) prepared wide-bandgap insulating (WBI) layer of AlN was introduced into the interface of graphene/silicon heterojunction. The promoted tunneling process from this designed structure demonstrated that can effectively help the impact ionization with photogain not only for the regular minority carriers from silicon, but also for the novel hot carries from graphene. As a result, significantly enhanced photocurrent as well as simultaneously decreased dark current about one order were accomplished in this graphene/insulation/silicon (GIS) heterojunction devices with the optimized AlN thickness of ~15 nm compared to the conventional graphene/silicon (GS) devices. Specifically, at the reverse bias of −10 V, a 3.96-A W−1 responsivity with the photogain of ~5.8 for the peak response under 850-nm light illumination, and a 1.03-A W−1 responsivity with ∼3.5 photogain under the 365 nm ultraviolet (UV) illumination were realized, which are even remarkably higher than those in GIS devices with either Al2O3 or the commonly employed SiO2 insulation layers. This work demonstrates a universal strategy to fabricate broadband, low-cost and high-performance photo-detecting devices towards the graphene-silicon optoelectronic integration.

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“…The current of a photodetector is composed of particle current and displacement current. Particle current is due to the flow of electrons and holes generated by photon absorption, dark current, and carrier multiplication such as impact ionization or CEP effect [1], [21]. Displacement current is due to charging/discharging of the device capacitance (Cj).…”

Section: Model Derivation and Pspice Implementationmentioning

confidence: 99%

“…For conventional SPADs, the carrier multiplication layer has a p-n or p-i-n structure, and for CEP detectors, the gain medium is a thin disordered medium such as undoped amorphous-silicon (a-Si). During operation, a voltage is applied to reverse bias the p/n junction or the disordered layer, allowing photo generated electrons (holes) to gain sufficient energy from the applied bias, and subsequently generate secondary electron-hole pairs via the effect of impact ionization or cycling excitation process (CEP), the latter of which also involves localized states and phonons [4], [21], [22]. The device dynamics such as gain build-up time and device response time depends on the multiplication process.…”

Section: Introductionmentioning

confidence: 99%

A Physics Based Unified Circuit Model for Single Photon and Analog Detector

Miah

Jiang

2021

IEEE Access

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Photodetectors having an internal carrier multiplication mechanism such as avalanche detectors and recently discovered detectors with cycling excitation process (CEP) have attracted tremendous interests for their high sensitivity and flexibility of being operable in analog, sub-Geiger and Geiger mode. Detection of single or few photons in Geiger mode or sub-Geiger mode is particularly interesting as LiDAR systems are finding a wide range of applications in autonomous driving, augmented and virtual reality, robotics, imaging, sensing, and communications. In this paper, we present a universal detector equivalent circuit model, applicable to all modes of operation, for photodetectors with carrier multiplication gain. The biasdependent gain, bandwidth, as well as gain buildup dynamics are rooted in device physics and translated into an equivalent circuit model that can be readily incorporated into integrated circuit design. The model simulates the characteristics of devices biased below and above breakdown voltage, making seamless transitions between analog, sub-Geiger, and Geiger mode with the same set of parameters directly obtained from the material properties. As a result, circuit designers can choose detectors using different gain medium (e.g. Si, InP, InAlAs) to simulate device effects on system performance. The circuit model is implemented in Orcad PSpice circuit simulator. Its wide applicability is demonstrated by simulating the device in linear, sub-Geiger and Geiger mode with external amplifiers and quenching circuits, as well as the gain-bandwidth product of detectors with a Si and InAlAs gain medium.

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Defect Assisted Carrier Multiplication in Amorphous Silicon

Cited by 5 publications

References 34 publications

Carrier Multiplication in Transition Metal Dichalcogenides Beyond Threshold Limit

Carrier Multiplication in Transition Metal Dichalcogenides Beyond Threshold Limit

Engineered tunneling layer with enhanced impact ionization for detection improvement in graphene/silicon heterojunction photodetectors

A Physics Based Unified Circuit Model for Single Photon and Analog Detector

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