Si PIN Photodiode Research Articles

Electrostatic Force-Assisted Transfer of Flexible Silicon Photodetector Focal Plane Arrays for Image Sensors.

Flexible photodetectors are pivotal in contemporary optoelectronic technology applications, such as data reception and image sensing, yet their performance and yield are often hindered by the challenge of heterogeneous integration between photoactive materials and flexible substrates. Here, we showcase the potential of an electrostatic force-assisted transfer printing technique for integrating Si PIN photodiodes onto flexible substrates. This clean and dry process eliminates the need for chemical etchants, making it a highly desirable method for manufacturing high-performance flexible photodetector arrays, expanding their widespread applications in electronic eyes, robotics, and human-machine interaction. As a demonstration, a 5 × 5 flexible Si photodetector focal plane array is constructed for imaging sensors and shaped into a convex semicylindrical form to achieve a π field of view with long-term mechanical and thermal stability. Such an approach provides a high yield rate and consistent performance, with the single photodetector demonstrating exceptional characteristics, including a responsivity of 0.61 A/W, a response speed of 39.77 MHz, a linear dynamic range of 108.53 dB, and a specific detectivity of 2.75 × 1012 Jones at an applied voltage of -3 V at 940 nm.

Design of a metasurface deflector for guided absorption enhancement in a Si PIN photodiode

We numerically demonstrated a surface-illuminated Si PIN photodiode (PD) structure with a metasurface composed of etched isosceles triangle pillars that can enhance sensitivity in the near-infrared wavelength range (NIR) by enabling directional scattering (DS) of photons. The metasurface is designed to act as a deflector to increase the absorption efficiency by extending the photon dwell time. This is particularly effective in thin intrinsic layers (i-layers) of silicon, surpassing the capabilities of conventional omnidirectional scattering gratings. Our results show a 3.5-fold increase in internal quantum efficiency over wavelengths above 0.9 µm compared to the structure without metasurface. The absorption enhancement brought about by directional scattering is not limited to thin i-layers; it can potentially improve a wide range of photodiode geometries and structures. Furthermore, the proposed structure, consisting of an all-Si layer and a simple geometric etching process, makes it compatible with foundry fabrication methods and opens up new possibilities for expanding applications of Si PDs.

New Crystal Photodiode Combination for Environmental Radiation Measurement

Here, a new design will be introduced to detect radiation in the environment with high efficiency. The designed structure consists of placing ZnS–Si APD and PIN photodiodes at the ends of conventional crystals such as NaI(Tl) and CsI(Tl). Since ZnS is transparent to photons with wavelengths between 340 and 10000 nm, photons coming from the crystals are absorbed directly in the depletion region and generate primary particles. With an increase in the number of generated primary particles, a stronger and cleaner signal is obtained. In the simulation work, the light generated by 30 keV–3 MeV gamma rays in the crystals was obtained using the Geant4 simulation code. The single-particle Monte Carlo technique was used to calculate the photodiode output signal for the crystal emission spectrum. The simulation results showed that the crystals and ZnS–Si photodiode structures formed a good combination. The high quantum efficiency and low excess noise factor make the ZnS–Si structure an excellent choice for scintillating light detection.

Segmented silicon-based solid-state detector with thin dead layer for superheavy element research

Silicon-based solid-state detectors (SSDs) are crucial for investigating the properties of superheavy elements (SHEs), since they measure the energy of SHEs and charged particles that are emitted as successive decay events of the SHEs. We have developed a segmented SSD for SHE studies using the new gas-filled recoil ion separators (GARIS-II and GARIS-III) at RIKEN. It is based on a back-illuminated Si PIN photodiode in which the irradiation is through the N+ layer. The detector is introduced as a side one for the GARIS focal plane detection system. To investigate the characteristics of the SSD, 241Am α particles were irradiated by automatically moving and rotating the α source for each segmented portion of the SSD. A Monte Carlo simulation was also performed to estimate the dead layer thickness of the segmented SSD.

Thermal drift reduction in photodiode dosimeters with switching bias

The effect of temperature on dosimetric measurements is a major limitation of solid-state dosimeters. This is especially true for PIN photodiode dosimeters, where the dark current depends exponentially on temperature. To minimize this effect, a compensation method is presented that relies on the diode structure itself without the need for an external sensor or device. During irradiation, the photodiode is periodically switched from reverse to forward polarization to determine the temperature of the device. This measurement is based on the linear dependence between the temperature and the forward voltage of the diode when it is operated at constant current. An electronic circuit implementing this procedure was developed and used for experimental characterization of the response to radiation of the BPW34S Si PIN photodiode. The proposed procedure reduced the uncertainty due to thermal drift by a factor of 7.5. In addition, an average dose rate sensitivity of 12 ± 2 nC/cGy was measured, with a sensitivity degradation below 2% for the irradiation cycle of 21.4 Gy performed under a 6 MV photon beam. We have shown that a p-n junction can be successfully used to compensate for the temperature effect on the dosimetric measurement.

Commercial photodiodes and phototransistors as dosimeters of photon beams for radiotherapy.

The response to radiation typically used in radiotherapy treatments has been experimentally evaluated for three samples of two phototransistors (BPW85B and OP505A) and two PIN photodiodes types (VTB8440BH and BPW34S). To that end, a staggered irradiation cycle has been applied which included dose rate values from 0.81 to 4.87cGy/s, achieving a total absorbed dose of 21.4Gy. The samples have been irradiated with a linear accelerator and the relations between the induced photocurrent and the average and instantaneous dose rates, and between the accumulated charge and the absorbed dose, have been determined. The radiation-induced output currents were measured by means of an external interface of the devices to a previously designed readout unit. Experimental results of Si PIN photodiode BPW34S have shown a sensitivity of (13.9±0.5) nC/cGy, slight sensitivity dependence on dose rate, and a high linearity of the current with the average and instantaneous dose rate, requiring only 10V of reverse bias voltage. This device thermal drift has characterized and modeled for temperature effect compensation. Silicon PIN photodiode BPW34S, previously tested for X-rays and Co-60 gamma ray source, can also be a reliable candidate for dose rate and absorbed skin dose determination in typical radiotherapy treatments irradiations. A low sensitivity loss below 2% up to 21.4Gy has been measured, allowing its use as an affordable reusable skin dosimeter. Moreover, no significant difference has been observed between its response to dose-per-pulse and changing pulse repetition frequency in terms of sensitivity and dependence with dose-rate value.

Multi-Gigabit Spatial-Division Multiplexing Transmission Over Multicore Plastic Optical Fiber

Today, we are evident to the revolution of the automotive industry and its demand for high bandwidth sensor fusion. Multiple high bandwidth sensors are connected, generating tremendous amount of data to be transferred in real-time in harsh environment, i.e., multi-gigabit intra-vehicle networks. Plastic optical fiber (POF) is an attractive medium for these multi-gigabit intra-vehicle networks due to its inherent EM compatibility, galvanic isolation, low weight, high tolerance to mechanical vibrations, low bending loss, and easy handling. However, commercial off-the-shelf PMMA based POFs are bandwidth-length product limited. Here, we suggest increasing the spectral efficiency using spatial-division multiplexing (SDM). In this article, we have experimentally demonstrated a low cost and eye-safe 3 × 3 multiple-input multiple-output (MIMO) SDM system over a 15 meters multicore (MC) POF using commercial optical components, e.g., RC-LEDs and Si-PIN photodiodes. A 3 × 1 spot-based cores coupler spatial multiplexer was developed to couple the optical components with the MC-POF. This system achieved raw data rates of 1.5 Gb/s and 2.4 Gb/s using offline-processed MIMO equalization. The proposed system enables a flexible and scalable optical MIMO system that can meet the requirements of the automotive industry.

Design and Optimization of an X-ray Detector Module for Air-Cargo Inspection

In this study, we developed an X-ray detector module (XDM) that includes two readout electronic units and a 64-channel data acquisition system for X-ray imaging systems. The readout electronic unit comprises eight X-ray sensor arrays (two CdWO4 scintillators and four Si-PIN photodiodes per detector array), 32 charge integrators, 32 sample-and-holds (S/H), 4 shift registers, and a buffer. The data acquisition system comprises line drivers and receivers, a multiplexer, an analog-to-digital converter, and a 32-kB static random-access memory. All the control signals for module operation are implemented in a field-programmable gate array. The module operates with a single 24 V DC supply and transfers each channel’s data to the host computer through an Ethernet port. We fabricated a 64-channel electronic module and evaluated its performance in terms of the relative offset and linearity. By connecting 14 XDMs, air-cargo container images were successfully acquired through X-ray irradiation at an energy of 6-MeV.

Impact Energy and Angular Dependence of L X-ray Emission from a Thick Polycrystalline Tungsten Element Induced by 15–25 keV Electrons

The impact energy and angular dependence of L X-rays of a thick polycrystalline tungsten (W; atomic number, Z = 74) target induced by 15–25 keV electrons has been measured at different angles varying from 15° to 75° at intervals of 5° using a Si PIN photodiode detector. The variation of measured relative intensity of Ll, Lα, Lβ and Lγ characteristic lines as a function of incidence angle is found to be anisotropic and the measured variation compares well with the PENELOPE simulation results. The angular variation of intensity ratio of Ll/Lα and Lβ/Lα shows anisotropic distribution, whereas the angular variation of the Lγ/Lα ratio exhibits almost isotropic distribution within the uncertainty of measurements. These measured ratios are found to be in good agreement with Monte Carlo (MC) calculations. The measured intensity ratios of Lβ/Lα and Lγ/Lα at a given incidence angle show a linear dependence with impact energy and exhibit good agreement with simulation results; however, the measured intensity ratio of Ll/Lα shows a non-linear variation with the impact energy and yields poor agreement with theoretical calculations.

A portable, low-cost and sensor-based detector on sweetness and firmness grades of kiwifruit

During storage, the sweetness of kiwifruit increases and its firmness decreases quickly. Since the sweetness is linked to consumers’ taste preference, and the firmness is regarded as the primary indicator of kiwifruit eating ripeness, detecting the sweetness and firmness are welcome by kiwifruit sellers, consumers and processors. To make the detected results intuitive and acceptable to more people, this study aimed to present a portable, low-cost, sensor-based grade detector on sweetness and firmness of kiwifruit. The detector consisted of a control/processing unit, a LED panel and driver unit, a light signal detection and amplifier unit, an input/output unit and a battery. Micro-controller of STM32 was used to do data collection and processing. The LED panel with nine LEDs at peak wavelengths of 800, 810, 850, 880, 900, 940, 970, 1000 and 1100 nm were used as light source. The reflected light from the kiwifruit was sensed by a Si PIN photodiode. The software of the detector was programmed by using C language. Kiwifruit varieties of 'Xuxiang' and 'Huayou' were used as samples, and their sweetness and firmness were divided into four grades. The model of support vector machine was established to determine kiwifruit grades. The validation experiment showed that the identification accuracies of the grade detector were 82.0% for sweetness and 74.0% for firmness of ‘Xuxiang’ variety, and 85.5% and 91.5% for sweetness and firmness of ‘Huayou’ variety, respectively. The detection time for one sample was less than 3 s.

Fabrication and characterization of Si-PIN photodiodes

In this work, characteristics of silicon-based p$^{+\, }$type, intrinsic (I), n$^{-}$ type (Si-PIN) photodiodes with active area of 3.5 $\times $ 3.5 mm$^{2}$, 5.0 $\times $ 5.0 mm$^{2}$, or 7.0 $\times $ 7.0 mm$^{2}$ and their possible usage in optoelectronics were studied. The devices were fabricated in the Radiation Detector Application and Research Center (NURDAM) of Bolu Abant Izzet Baysal University, Turkey. To acquire the device specifications, the current-voltage (I-V) and the capacitance-voltage (C-V) measurements were carried out in the photoconductive mode. Quantum efficiency and spectral responsivity measurements were performed in the photovoltaic mode. Both measurements were carried out in a dark environment at room temperature. The measured values of the dark current (I$_{dc})$ and the capacitance of photodiodes were -6.97 to -19.10 nA and 23 to 61 pF at -5 V, respectively. The quantum efficiency measurements of the devices increased up to 66%. P responsivity was found to be 0.436 $\pm $ 1 mA/W at 820 nm. The results indicate that the I$_{dc}$ current and the performance of the devices were improved. Therefore, the devices can be utilized for optoelectronics applications and commercial usage.

Spectral energy and angular distributions of bremsstrahlung radiation produced by 3.5 keV electrons in scattering with a free SF6 molecule

Absolute double differential cross sections (DDCS) of bremsstrahlung (BS) radiation produced by 3.5 keV electrons in scattering with a free SF6 molecule were measured by using a Si-PIN photodiode detector in the angular detection range of 45°−110° relative to the direction of incident electrons. Angular distributions of the BS photons are found to be anisotropic. The experimental DDCS spectra are compared with the theoretical calculations obtained from atomic-field BS formulations of Kissel–Quarles–Pratt (KQP) using the “additivity hypothesis”. A fair agreement is observed between the measured results and those obtained from the KQP calculations for both the energy and the angular spectral distributions of BS radiation. The measured anisotropy of bremsstrahlung radiation is reproduced reasonably well by a modified Sommerfeld formula, if the relative velocity β is chosen to be half of the incident electron velocity β0. The measured anisotropy may be described by a parameter P, which is compared with the degree of polarisation obtained from theoretical calculations. Further, it is noted that the molecular weight, geometry and the number of constituent atoms present in the considered molecule do not seem to influence the usefulness of “additivity hypothesis”. In conclusion, the present results have once again corroborated the validity of “additivity hypothesis” for predicting the spectral distributions of molecular bremsstrahlung produced by keV-electrons.

Experimental evidence of molecular coherence effects in the bremsstrahlung radiation processes

The first experimental evidence of Young-type interferences is presented in bremsstrahlung (BS) processes by measuring the double differential cross sections (DDCS) of BS photons emitted from a two-centre N2 molecule under impact of 4.0 keV electrons. The spectra were recorded for emission of photons in the angular range of 45°–120° and the energy range of 2.0–3.8 keV using a Si PIN photodiode detector (FWHM = 165 eV at 5.9 keV). The measured variation of DDCS ratio of N2 to Ar as a function of photon energy shows no obvious signature of interference structure. However, the measured angular distribution of the intensity ratio of BS photons of N2 to Ar is found to exhibit the noticeable oscillations. Furthermore, a clear oscillatory structure is observed in the angular distribution of BS photons if the intensity of photons emitted from N2 molecules at angle θ to the intensity of photons emitted at angle 90°, i.e. I(θ)/I(90°) is plotted as a function of emission angle. Noting the fact that, only one theoretical work on coherence effects in BS processes under low-energy electron impact with homonuclear diatomic molecules is reported in the literature by Borie et al (1970 Phys. Rev. A 2 1443) which fails to explain the observed oscillations and shows orders of magnitude difference in the amplitude and mismatch in the shape of oscillations. The presence of observed oscillations is suggested to arise due to coherent superposition of BS photons of a given energy emitted in scattering of 4.0 keV electrons with a two-centre N2 molecule. Strong disagreement between our measurements and the calculations from Borie et al theory clearly suggests that a more refined and adequate theoretical model together with additional experimental investigations are needed to verify the present observations.

Angular and impact energy dependence of intensity ratio of Kα,β x-rays to underneath bremsstrahlung radiation emitted from 15 to 25 keV electrons incident on a pure thick Cu (Z=29) target

We present new results on angular and impact energy dependence of the relative intensity ratios of Kα and Kβ characteristic (CS) x-ray lines to their respective underneath bremsstrahlung (BS) radiation produced from 15-25 keV electrons incident on a thick polycrystalline pure target of Cu (Z = 29). The angular distributions of relative intensity ratios were carried out by measuring the radiations emitted at incidence angle θi that varied from 15° to 75° in reflection geometry mode of the target. The x-rays emerging from the target surface were detected by an energy dispersive Si PIN photodiode detector. The magnitude of relative intensity ratio of Kα/BS is found to be larger than that of Kβ/BS by a factor of about 5.11, 5.24 and 5.49 for 15 keV, 20 keV and 25 keV impact energy, respectively measured, for example, at θi = 15°. However, the intensity ratio of a given characteristic line to its underneath BS increases on average by a factor of about 2.2 in varying the impact energy from 15 keV to 25 keV measured at different angles. The experimental results on angular and impact energy dependence are compared with the corresponding results obtained from Monte-Carlo simulations using the PENELOPE code. The overall agreement between experiment and theory is found to be satisfactory within the uncertainty of measurements.

Excess Loss in Homodyne Detection Originating from Distributed Photocarrier Generation in Photodiodes

The distributed absorption of photons in photodiodes induces an excess noise in continuous-wave photodetection above the transit-time roll-off frequency. We show that it can be treated as a frequency-dependent excess optical loss in homodyne detection. This places a limit on the bandwidth of high-accuracy homodyne detection, even if an ideal photodetector circuit is available. We experimentally verify the excess loss in two ways; a comparison of signal gain and shot-noise gain of one-port homodyne detection, and a balanced homodyne detection of squeezed light at 500 MHz sideband. These results agree with an analytic expression we develop, where the randomness of the photoabsorption is directly modeled by an intrusion of vacuum field. At 500 MHz, we estimate the excess loss at 14% for a Si-PIN photodiode with 860 nm incident light, while the numerical simulation predicts much smaller excess loss in InGaAs photodiodes with 1550 nm light.

X-ray detector based on Mn doped MgAl2O4 and Si photodiode.

Luminescence properties of Mn doped MgAl2O4 crystals connected with the Si PIN photodiode (PD) have been evaluated for X-ray detector applications. Mn doped MgAl2O4 crystals emit green colored luminescence peaking at around λ = 520 nm with CuKα irradiation. The intensity of the output signal from Si PD increases linearly with the X-ray intensity of CuKα generated with the X-ray tube at a current from 2 mA to 40 mA. The intensity of the X-ray excited luminescence is strongest in the specimen with 3.0 mol. % Mn. Afterglow luminescence is weak in the specimen with 2.0 mol. % Mn. Mn doped MgAl2O4 crystals connected with the Si PD is considered to be a useful X-ray detector.

Measurement of the angular distribution of thick target bremsstrahlung produced by 10–25 keV electrons incident on Ti and Cu targets

Angular distributions of bremsstrahlung photons produced by 10–25 keV electrons incident on thick Ti (Z = 22) and Cu (Z = 29) targets using a Si-PIN photodiode detector have been measured and new results are reported. The incidence angle, defined as the angle between the direction of the incident electrons and the normal of the target surface, varied between 15° and 75°. The intensity of the bremsstrahlung radiation, differential in angle and energy, that is, the double differential bremsstrahlung yield, was obtained by varying the incidence angle, while the photon detector was kept fixed perpendicular to the electron beam direction in reflection geometry. The experimental bremsstrahlung yields were normalized so that the values measured at 45° coincide with the results of Monte Carlo simulations. For the other incidence angles, the measured yields are found to be in good agreement with simulation results, within the experimental uncertainties. Our results suggest that the bremsstrahlung radiation emerging from the considered electron-target collision reactions is anisotropic in general; a relatively larger anisotropy is observed for all energy photons produced by high-energy electrons compared to that by low energy electrons. Furthermore, there is an indication of a weak dependence of the angular variation of the bremsstrahlung yield on atomic number (Z) of the bombarded targets.

Scalability of dark current in silicon PIN photodiode**Project supported by the National Key Research and Development Program of China (Grant No. 2017YFF0104801) and the National Natural Science Foundation of China (Grant Nos. 61335004, 61675046, and 61505003).

The mechanism for electrical conduction is investigated by the dark temperature-dependent current–voltage characteristics of Si PIN photodiodes with different photosensitive areas. The characteristic tunneling energy E00 can be obtained to be 1.40 meV, 1.53 meV, 1.74 meV, 1.87 meV, and 2.01 meV, respectively, for the photodiodes with L = 0.25 mm, 0.5 mm, 1 mm, 1.5 mm, and 2 mm by fitting the ideality factor n versus temperature curves according to the tunneling-enhanced recombination mechanism. The trap-assisted tunneling-enhanced recombination in the i-layer plays an important role in our device, which is consistent with the experimental result that area-dependent leakage current is dominant with the side length larger than 1 mm of the photosensitive area. Our results reveal that the quality of the bulk material plays an important role in the electrical conduction mechanism of the devices with the side length larger than 1 mm of the photosensitive area.

Angular dependence of Kβ/Kα intensity ratios of thick Ti and Cu pure elements from 10–25 keV electron bombardment

Measurements yielding the first results on angular dependence of Kβ/Kα X-ray intensity ratios of thick Ti (Z = 22) and Cu (Z = 29) targets induced by 10–25 keV electrons are presented. The measurements were done by rotating the target surface around the electron beam direction in the angular detection range 105° ≤ θ ≤ 165° in the reflection mode using an energy dispersive Si PIN photodiode detector. The measured angular dependence of Kβ/Kα intensity ratios is shown to be almost isotropic for Ti and Cu targets for the range of detection angles, 105° ≤ θ ≤ 150°, while there is a very weak increase beyond 150° for both targets. No dependence of Kβ/Kα intensity ratios on impact energy is observed; while on average, the value of the Kβ/Kα X-ray intensity ratio for Cu is larger by about 8% than that for Ti, which indicates a weak Z-dependence of the target. The experimental results are compared with those obtained from PENELOPE MC calculations and from the Evaluated Atomic Data Library (EADL) ratios. These results on Kβ/Kα X-ray intensity ratios are found to be in reasonable agreement in the detection angle range 105° ≤ θ ≤ 150° to within uncertainties, whereas the simulation and experimental results show a very slight increase in the intensity ratio with θ as the latter attains higher values. The results presented in this work provide a direct check on the accuracy of PENELOPE at oblique incidence angles for which there has been a lack of measurements in the literature until now.

The development of $$^{222}\hbox {Rn}$$222Rn detectors for JUNO prototype

The radioactive noble gas $^{222}$Rn, which can be dissolved in water, is an important background source for JUNO. In this paper, based on the water system of JUNO prototype, two kinds of high sensitivity radon detectors have been proposed and developed. The sensitivity of Si-PIN Rn detector, which uses a Si-PIN photodiode to detect the $\alpha$ from $^{214}$Po decay, is $\sim$9.0~mBq/m$^3$. The sensitivity of LS Rn detector, which uses liquid scintillator to detect the coincident signals of $\beta$ from $^{214}$Bi decay and $\alpha$ from $^{214}$Po decay, is $\sim$64.0~mBq/m$^3$. Both of the two kinds of Rn detector have the potential to be developed as an online Rn concentration monitoring equipment for JUNO veto detector.