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Nanomaterials A Way to Chemical Sensor and Biosensor—Fundamentals
Published in Jayeeta Chattopadhyay, Nimmy Srivastava, Application of Nanomaterials in Chemical Sensors and Biosensors, 2021
Jayeeta Chattopadhyay, Nimmy Srivastava
There are a variety of optical semiconductor sensors, the most common of which is the photodiode, a type of photodetector that converts light into either current or voltage. Photodiodes normally have a window or optical fiber connection to allow light to reach a p-n or a PIN junction (an intrinsic semiconductor region between p-type and n-type semiconductor regions). Photodiodes often use a PIN junction rather than a p-n junction to increase the speed of response. When a photon of sufficient energy strikes the depletion region of the diode, it may hit an atom with sufficient energy to release an electron, thereby creating a free electron (and a positively charged electron-hole). Free electrons and holes in the depletion region, or one diffusion length away, are pulled away in an applied electrical field. The holes move toward the anode and the electrons move toward the cathode, resulting in a photocurrent. This photocurrent is the sum of both the dark current (without light) and the light current, so the dark current must be minimized to enhance the sensitivity of the device. Photodiodes are used in a variety of applications, including pulse oximeters, blood particle analysers, nuclear radiation detectors and smoke detectors.
Normal Incidence Detection of Infrared Radiation in P-type GaAs/AlGaAs Quantum Well Structures
Published in Manijeh Razeghi, Long Wavelength Infrared Detectors, 2020
Gail J. Brown, Frank Szmulowicz
Dark current is defined as the current in the device that arises from sources other than photoexcitation. In quantum well infrared detectors, the dark current components are usually classified as either thermal or tunneling in origin. Three known components of the dark current are: thermionic emission, thermally-assisted tunneling, and temperature independent tunneling. Thermionic emission refers to the process in which carriers are thermally excited to current-carrying continuum states above the top of the well. The resulting current varies exponentially with temperature and is expected to dominate at temperatures above 50 K. Thermally-assisted tunneling is the term used for the mechanism in which carriers are thermally excited into higher states below the top of the well, and then tunnel through the triangular tip of the barrier (under an applied electric field) into the continuum states on the other side of the barrier. Thermally-assisted tunneling becomes significant, compared to thermionic emission, at relatively high electric fields [46]. It is a thermally activated process except at very high electric fields. Temperature-independent tunneling refers to the process in which carriers tunnel from the densely occupied ground subband of one well into a neighboring well. The temperature-independent tunneling component of the dark current has many of the features of sequential resonant tunneling [47]. It is observed at temperatures that are low enough to suppress thermionic emission.
Definitions and Terminology
Published in Frank Vignola, Joseph Michalsky, Thomas Stoffel, Solar and Infrared Radiation Measurements, 2019
Frank Vignola, Joseph Michalsky, Thomas Stoffel
where Iout is the output current, Iph is the photocurrent generated by the incident light, Ish is the shunt resistance current, and the middle term is the result of the diode current (Is is the reverse diode current, e is the electron charge of 1.602 10–19 coulombs, V is the applied voltage in volts, k is the Boltzmann constant, and T is the absolute temperature of the photodiode in K). The shunt resistance current is an alternate path for the current to flow. Cells are designed with a large shunt resistance to minimize the loss. The diode current is the current that flows when there is no light incident on the device and is sometimes called the dark current. The circuitry for photodiodes is designed in a manner that minimizes the dark current.
Effect of Evanescent Waves on the Dark Current of Thermophotovoltaic Cells
Published in Nanoscale and Microscale Thermophysical Engineering, 2020
Dudong Feng, Eric J. Tervo, Shannon K. Yee, Zhuomin M. Zhang
where represent the concentrations of acceptors, donors, and intrinsic carriers, respectively, and and are the diffusion coefficient and relaxation time of electrons or holes in p or n regions, respectively. Equation (3) may be a proper approximation of the saturation current for a far-field TPV cell with a p-n junction structure. It has been applied for the analysis of near-field TPV systems by a number of researchers [11–14]. Nevertheless, the relation between the three components of saturation current is more complicated for a near-field TPV cell. In the scenario with an ideal photoconverter, only radiative recombination contributes to the dark current.
Effect of proton beam irradiation on the tracking efficiency of CMOS image sensors
Published in Radiation Effects and Defects in Solids, 2022
Jing Fu, Jie Feng, Yu-Dong Li, Lin Wen, Dong Zhou, Qi Guo
Dark-current noise refers to the output current generated by the device itself under no illumination, i.e. no input signal. The proton irradiation mainly induced oxide trap charges, interface states, and bulk defects into the CIS (17). With the increasing fluence, the number of defects increased, most of the pixels were affected, and the dark current increased simultaneously, implying a simultaneous increase in the background noise. Specifically, the dark current introduced by the bulk defects was difficult to eliminate via radiation hardening. Thus, the CIS dark current that results from the increase in the pixel gray value significantly impacts the measurement precision of the star tracker.
Natural sensitizers-mesoporous TiO2 hybrid nanomaterial for future optoelectronic applications
Published in Journal of Experimental Nanoscience, 2023
Nitasha Chaudhari, Swapnali Walake, Yogesh Hase, Paresh Nasikkar, Sandesh Jadkar, Yogesh Jadhav, Atul Kulkarni
Another key component of the photodetector is the photosensitivity parameter, which measures how current changes in relation to the dark current. The photosensitivity () is the difference in current (ΔI) when it is normalized to the dark current. The formula for the Photosensitivity (ξ) calculation is expressed as [47]