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Two-Dimensional Materials in Photoconductive Detectors
Published in Sam Zhang, Materials for Devices, 2023
Yu Duan, Shuanglong Feng, Sam Zhang
Photodetectors play an essential role in the photoelectric system. Photodetectors convert light signals into electrical signals, which are processed by electronic circuits to realize light detection function.[1–3] Nowadays, photodetectors have been widely used in photoelectric display, imaging, environmental monitoring, optical communication, military, safety inspection, biomedicine, and many other fields.[4–7] According to the different detection bands, their functions are also different. For instance, deep ultraviolet light detectors are used for ultraviolet lithography and living cell detection. Visible range detectors are used in digital cameras and visual imaging, and infrared detectors are used in night vision, optical communication, and atmospheric quality inspection. Since the discovery of the photoelectric effect in 1887,[8] scientists have devoted themselves to exploring the interaction between light and semiconductor materials, which has laid the foundation for many theories of optoelectronic systems and become the key to modern industrial and scientific applications.
Optical Detection and Noise
Published in Chunlei Guo, Subhash Chandra Singh, Handbook of Laser Technology and Applications, 2021
The sensitivity of a photodetector can be defined in terms of the incident optical power required to achieve a given SNR. A figure of merit commonly used is the noise-equivalent power (NEP), defined as the mean optical power required to be incident on the detector to generate an SNR of unity. NEP in its most simple form, therefore, has units of watts and is specific to a particular detector, taking into account such parameters as the sensitive detection area A and the detection bandwidth Δf.
PHOTODETECTORS AND REPEATERS
Published in Glenn R. Elion, Herbert A. Elion, Fiber Optics in Communications Systems, 2020
Glenn R. Elion, Herbert A. Elion
Photodiodes are usually described by four basic quantities; response time, quantum efficiency, total noise equivalent power and responsivity. The response time is the transit time for electrons in the photodiode to transverse from the cathode to anode, typically from 0.2 to 5ns. Table XI lists the properties of various commercial PIN photodetectors. The quantum efficiency is the percentage of incident photons that liberate photodetector electrons. The responsivity is the average emitted current divided by the average incident power. Figure 20 shows the quantum efficiency and responsivity versus wavelength for typical PIN photodiodes. In avalanche photodiodes (APD) the two basic entities usually considered are the response speed and the multiplication or gain characteristics. The physical structure of avalanche diodes usually includes a guard ring to prevent excessive leakage at the junction edges and low breakdown voltages. Many APD devices are silicon based with antireflection coatings to provide quantum efficiencies near 90% with gains of several hundred. Table XII lists the properties of various commercially available APD devices.
Simulation study of front-illuminated GaN avalanche photodiodes with hole-initiated multiplication
Published in Cogent Engineering, 2020
Yangqian Wang, Yuliang Zhang, Yang A. Yang, Xing Lu, Xinbo Zou
Photodetectors are devices that can sense light or other electromagnetic radiations, playing an important role in many technologies from telecommunications to environmental sensing. III-N-based Avalanche Photodiodes (APDs) are of great interest for ultraviolet (UV) detection due to their low dark current density, high sensitivity, high optical gain, small size, and visible-blind characteristics. In this article, a novel APD device configuration and its working modes are studied to enhance III-N photodetector’s efficiency and sensitivity as well as to speed up the response of those APDs in a repetitive detection process.
Recent progress in three-dimensional flexible physical sensors
Published in International Journal of Smart and Nano Materials, 2022
Fan Zhang, Tianqi Jin, Zhaoguo Xue, Yihui Zhang
Photodetector is a class of widely used physical sensors, which detects light and transforms it into electrical signals. The detection mainly relies on the photoelectric effect, that is, electrically charged particles are emitted from a material when it absorbs light. Photodetectors with 3D geometric layout offer unique advantages in omnidirectional responses, multipolar detection, and enhanced photon detection efficiency, which have been explored for developing novel high-performance photodetectors. This subsection introduces the recent advances in this area.
Passive, active, and interactive drag-reduction technique to reduce friction and enhance the mixing intensity in rotating disk apparatus
Published in Chemical Engineering Communications, 2018
Hayder A. Abdulbari, Mohamad Amran Mohd Salleh, Musaab K. Rashed, M. Halim Shah Ismail
In this study, the lid contained transparent glass to allow the entry of the MicroPro laser beams into the container, and the traverse moved to allow the probe volume to travel between the top surface of the disk and the liquid container cover. The software controlling the movement was designed to automatically record the mean velocities at several points within the log region. MicroPro allows the traverse to auto-detect the surface of the rotating disk and to perform measurements in 30-μm increments starting from the surface. This feature enabled the measurement of 70 velocities within 2 mm above the disk surface. Figure 4 shows a simple sketch of the geometry, revealing the path of the laser and the measurement distance from the disk surface. During the measurements, a photodetector converts the optical signal into an electrical signal through a photoelectric mechanism. This photoelectric transition includes the conversion of the photon flux of the optical signal into an electron flux. The light scattered from the particles features a sinusoidal intensity variation with time. The frequency of this variation is a function of the particle’s velocity. Therefore, the information obtained from the frequency of the intensity variations caused by the movement of particles through the intersection volume is used to determine the velocity of the particles. The fringe spacing is a function of the wavelength of the incident beams and the angle between the beams, both of which are fixed for a single configuration. The variable in the determination of the particle velocity is the frequency of the intensity variations. Figure 5 shows the mechanism of MicroPro. Given that the spacing between the fringes is constant, the velocity of the particle or surface is proportional to the frequency of the reflected bursts. With the integral electronic traverse, the probe volume can be moved through the thickness of the boundary layer, providing a direct measurement of its velocity profile. The theory of laser Doppler velocimetry signals considers the time dependence of beat signals resulting from interference between two scattered light waves. These considerations yield the relationship between the measured signal frequency and the velocity of the particles as a function of the optical geometry and wavelength of the incident light beam. It is important to highlight that the velocity profile measurements were conducted in the present work from the top of the RDA container through the manufactured glass window because it is the only practical method to use the mini-LDV. Measuring the other velocity profiles over the entire disk surface was not practically possible due to the experimental setup geometrical complications.