Dark Current Values Research Articles

NEW INFRARED CAMERA OF THE CAUCASIAN MOUNTAIN OBSERVATORY OF THE SAI MSU: DESIGN, MAIN PARAMETERS AND RST LIGHT

The paper presents a prototype of an infrared photometer, made by the SAI of MSU on the base of a commercial infrared module Gavin-615A. The operating spectral range of the photometer is 3-5 µm. Studies of the photometer detector have shown that its parameters correspond to those declared by the manufacturer. Nonlinearity of the detector does not exceed ∼ 5% in the whole range of signals, coe cients of correction--function were determined. Additionally, we determined the readout noise RN = 1200 ± 210 e, conversioncoe cient GAIN = 520 ± 9 e/ADU, the BIAS = 960.5 ± 2.2 ADU, and dark current ≈ (9.3 ± 1.1) · 106-e /s,which consists of the sum of the detector dark current and radiation of the entrance window of the detector◦module. The value of dark current was measured at the window temperature of 6 C. Observations werestarted with the photometer at the 2.5-m telescope of the Causasian Mountain Observatory of MSU, the rst results are given in the paper. The unvignetted eld of view is 30'' . In the M band under good atmosphericconditions, an image quality is close to di raction limit. Images of a star with magnitude L = 7.96 and M = 6.78 were obtained with exposure of 20 seconds and a SNR∼10 ratio. It is shown that at high image quality with SNR=3 and exposure of 20 seconds it is possible to observe stars up to L ∼9m and M ∼8m . The main module of the photometer was also used for measurements of the sky background brightness.

Wide dynamic range photodiodes for microwave photonics and comunication systems

The influence of the design of high-speed photodiodes for microwave photonics and signal transmission systems on the diode dark current is studied experimentally. It is shown that Schottky barrier photodiodes demonstrate the lowest dark currents, excelling photodiodes of the pin design. Photodiodes of 25 micron mesa diameter with the dark current average value as low as 0.4 mA have been manufactured. It is shown the dark current value is controlled by the mesa side wall leakage.

Influence of silicon characteristics on the parameters of manufactured photonics cells

The paper investigates the influence of the electrophysical characteristics of silicon on the final parameters of photoelectronic elements using p-i-n photodiodes as an example. It has been found that photodiode samples made on the basis of silicon with a higher resistivity are more prone to the formation of inversion channels at the oxide-semiconductor interface. Also, the dark current and responsivity of such photodiodes reach saturation at a lower voltage. It has also been shown that silicon-based photodiodes with a longer lifetime of non-basic charge carriers have lower dark current values. It has been shown that products with crystallographic orientation [111] have a much lower density of surface dislocations after technological operations than in the case of silicon with orientation [100]. It was also found that materials with different crystallographic orientations have different phosphorus diffusion coefficients. It has been experimentally established that a silicon oxide film grows faster on the surface of crystallographic orientation silicon [111] than on the surface of crystallographic orientation silicon [100]. This is due to the difference in the surface density of silicon atoms inherent in different crystallographic planes.

InGaAs-Based MSM Photodetector: Researching Absorption Layer, Barrier Layer, and Digital Graded Superlattice Layer with 3D Simulation

The effects of absorption, barrier, and digital graded layer thickness on dark current and photocurrent in Metal Semiconductor Metal (MSM) photodetectors by using 3D Silvaco TCAD are reported. The photo-dark current ratio (Iphoto/Idark) is calculated using the photocurrent and dark current values obtained by simulation. In study A (absorption layer thickness variation) the photocurrent, dark current and photo-dark current ratio are increased with increased absorption layer thickness, and the dark current is 1.138x10-7 A levels. In Study B (barrier layer thickness variation), when the barrier layer is added to the absorption layer, the dark current is decreased to 1.56x10-11 A levels. It is reported that the photo-dark current ratio with increasing barrier layer thickness increases. In study C (digital graded superlattice layer thickness variation), the dark current increases, and photocurrent decreases with the increase of the digital graded superlattice layer thickness. However, the photo-dark current ratio with increasing digital graded superlattice layer thickness decreases. Furthermore, a similar trend of development is observed on photo-dark current with adding of the barrier layer and digital graded superlattice layer on the absorption layer. These findings demonstrate the importance of optimizing layer thickness in MSM photodetectors for improved device performance.

Electrical and Structural Properties of Chemically Deposited Photoconducting Films

In this study, we investigated the rise and decay of the chemically deposited quaternary metal sulfide thin films, which were deposited at different concentrations, temperatures, and deposition durations. On a glass substrate, films were deposited using a chemical bath deposition technique (CBD method). A graph plotted for the study of the rise and decay curves for these quaternary films was deposited. In addition to calculating the photocurrent and dark current values for the entire sample, the photoconductivity gain was also examined. There are reports and discussions about the X-ray diffraction pattern of our sample. The resulting films have thin-filmlike structures. This provides a unique outcome for photoconduction applications. Photoconducting gain ranges from 2.9 x 105 to 47.5 x 106are observed for various concentration, temperature, and deposition time combinations.

Metal–semiconductor–metal detectors ZnS/GaP for the ultraviolet and visible part of the spectrum with electrically tunable spectral photosensitivity

High-quality ZnS epitaxial layers grown on GaP semiconductor substrates by MOCVD method. Photodetectors of the visible and UV parts of the spectrum based on new interdigitated Schottky barrier metal–semiconductor–metal (MSM) contacts to semiconductor structure ZnS/GaP. The detectors exhibit low dark current values. The dependence of the characteristics of the spectral response of detectors on voltage has been established offsets. It was found that the long-wavelength response boundary of ZnS/GaP MSM detectors can shift from 355 to 450 nm when the bias voltage changes from 10 to 30 V. At the maximum photosensitivity wavelength of 450 nm, the ampere-watt sensitivity of the detector was 0.3 A/W at a bias voltage of 60 V, and the quantum efficiency was 82%.

Ultraviolet photodetectors based on ZnO nanowires with SiO2/ZnO multilayers

Ultraviolet photodetectors (UV PDs) have been a frequently studied focus of optoelectronic semiconductor devices because of their large range of applications. As one of the most famous materials in third-generation semiconductors, ZnO-based UV PDs have received a great deal of attention in various research areas. Due to the carrier transport channel and higher exciton bond energy, ZnO nanowires (NWs) have better photoelectron sensitivity under UV light than ZnO films. Here, well-organized ZnO NWs were fabricated on ZnO-seeded substrates via a hydrothermal method. Multilayers of double SiO2/ZnO(S/Z) layers were designed on the NWs, and the Schottky barrier was introduced by the close contact of the ZnO NWs and gold electrodes to improve the performance of ZnO UV PDs. Characteristics of the dark current, photocurrent, rise time, decay time, photo-to-current ratio (S), and responsivity values (Rs) of the PDs were studied. Furthermore, multilayer UV PDs were achieved on both Si and quartz substrates. S of the ZnO S/Z-based UV PDs fabricated on a silica substrate can reach 55.57, which is better than the values of ZnO UV PDs reported previously. Compared with silica-based UV PDs with S/Z layers, quartz-based UV PDs with S/Z layers show a higher performance of Rs, which reach 12.62 A/W. ZnO NWs with multilayers and the Schottky contact between ZnO NWs and Au are promising candidates in high-sensitivity UV PDs.

Dark Current Measurement and Noise Correction Method for LWIR QWIP Detection System Based on Focal-Plane Temperature

The performance of long-wave infrared (LWIR) quantum well (QWIP) detection systems is seriously affected by the dark current of the detectors. Tiny variations in the focal-plane temperature of the devices cause fluctuations in the dark current, which in turn generate temporal noise. It is difficult to measure the dark current accurately after the detector assembly is packaged. To address the above problems, a QWIP dark current measurement method based on focal-plane temperature is proposed, as well as a method to reduce dark current noise. First, the response model of the LWIR QWIP detection system was established, and the dark current model was introduced. Then, the detection system components were introduced, chiller calibration experiments were carried out, and the dark current values of the QWIP at different temperatures were measured by combining the system design and parameters. Next, the dark current noise correction method was proposed, the target data were collected, and experiments were carried out to correct them. Finally, after the calculation, the temporal noise was reduced by 57.69% after the correction, which is proof of a significant effect. This method can obtain the real-time dark current value by collecting the focal-plane temperature data, and reduce the dark current temporal noise (difficult to eliminate using conventional methods), which is beneficial for promoting the application of QWIPs in LWIR remote sensing detection.

All-Oxide Transparent Photodetector Array for Ultrafast Response through Self-Powered Excitonic Photovoltage Operation.

Can photodetectors be transparent and operate in self-powered mode? Is it possible to achieve invisible electronics, independent of the external power supply system, for on-site applications? Here, a ZnO/NiO heterojunction-based high-functional transparent ultraviolet (UV) photodetector operating in the self-powered photovoltaic mode with outstanding responsivity and detectivity values of 6.9 A W-1 and 8.0 × 1012 Jones, respectively, is reported. The highest IUV /Idark value of 8.9 × 104 is attained at a wavelength of 385nm, together with a very small dark current value of 9.15 × 10-12 A. A large-scale sputtering method is adopted to deposit the heterostructure of n-ZnO and p-NiO sequentially. This deposition instinctively forms an abrupt junction, resulting in a high-quality heterojunction device. Moreover, developing a ZnO/NiO-heterojunction-based 4 × 5 matrix array with an output photovoltage of 4.5V is preferred for integrating photodetectors into sensing and imaging systems. This transparent UV photodetector exhibits the fastest photo-response time (83ns) reported for array configurations, which is achieved using an exciton-induced photovoltage based on a neutral donor-bound exciton. Overall, this study provides a simple method for achieving a high-performance large-scale transparent UV photodetector with a self-powered array configuration.

A study on GaN-based betavoltaic batteries

In this paper, a GaN-based betavoltaic epitaxial structure was grown by metal–organic chemical vapor deposition and a p-type ohmic contact was studied for different Ni/Au metal thickness ratios, temperature dependent in N2:O2 (1:1) gas atmosphere and different surface treatments for this epitaxial structure. Transfer length method measurements were done after each different process condition in order to check specific contact resistivities. GaN-based betavoltaic batteries were fabricated and a scanning electron microscope (SEM) was used as an electron source to test these devices. For this purpose, devices connected to a printed circuit board were exposed to an electron current of 1.5 nA with 17 keV energy in the SEM. For 1 × 1 mm2 devices, a dark current value of 2.8 pA at 0 V, fill factor of 0.35, maximum power conversion efficiency of 3.92%, and maximum output power of 1 µW were obtained.

Simulation Study of Vertical p–n Junction Photodiodes’ Optical Performance According to CMOS Technology

CMOS photodiodes have been widely reported in microsystem applications. This article presents the design and numerical simulation of p–n junction photodiodes, using COMSOL Multiphysics, for three CMOS technologies (0.18 μm, 0.35 μm and 0.7 μm) and three different p–n junction structures: n+/p-substrate, p+/n-well and n-well/p-substrate. For these simulations, the depth junctions and dopant concentrations were set according to the different technologies. Then, each photodiode was spectrophotometrically characterized regarding the current, responsivity and quantum efficiency. The obtained numerical results show that the 0.18 and 0.35 μm CMOS technologies are those with the highest peak of efficiency when visible spectral ranges are needed, comparative to the 0.7 µm technology. Furthermore, the three most common p–n vertical junction photodiode structures were compared. The n+/p-substrate junction photodiode appears to be the one with the highest quantum efficiency in the visible range, which is in agreement with the literature. It can be concluded that the photodiodes’ characteristic curves and dark current values are consistent with reports in the literature. Therefore, this numerical approach allows to predict the photodiodes’ performance, helping to select the best structural design for each required application, before their microfabrication.

Structure, morphology, and photoresponse characteristics dependence on substrate nature of grown π-SnS films using chemical bath deposition

Thin films suffer from insufficient strength and cannot be made self-holding. Hence, more convenient fabrication process onto proper holding substrate material is needed to achieve well-matching with the film material. This research work aims to investigation of the influence of the substrate nature on the evolution of the structure, morphology and photoresponse characteristics of tin monosulfide (π-SnS) films. The π-SnS films have been deposited through the simple and cost-effective chemical bath deposition technique onto PET, glass, and n-type Si wafer substrates. X-ray diffraction and Raman analyses confirm that the films crystallize within a cubic structure of SnS phase with polycrystalline nature. Field emission scanning electron microscopy observations reveal that the surfaces of PET and Si substrates are covered with irregular spherical grains with the presence of some nanoflakes. Conversely, the surface of the glass substrate is found to be entirely covered with high-density assembled nanoflakes. The dark current value has been found to increase significantly from pA up to μA; at 3 V bias voltage, the dark current values are 55 pA, 850 pA, and 3.5 μA for the photodetectors based on PET, glass, and Si substrates, respectively. Moreover, upon the near-infrared illumination at 750 nm, the fabricated photodetectors demonstrate good sensitivity and photoresponse time; at 3 V bias voltage, the sensitivity values are found to be 2591, 697, and 2982 for photodetectors onto PET, glass, and Si substrates, respectively. The obtained results demonstrate the critical role of substrate nature on the characteristics of the as-grown π-SnS films.

Optimization of the profile and material of wire contacts for an IR photodetector

The study is devoted to the influence of the choice of geometry and materials of wire contacts on the reflection coefficient and thermal characteristics of the photodetector and the quality of the device design. The process of diffusion of materials of wire contacts and contact pads on a photodetector crystal is investigated. The studies were carried out on samples that are rather small in size (250x250x400 um). During the experiment, 4 main types of loop geometry were selected (main loop, reverse loop, double reverse loop, long loop). The loops were formed using a gold wire 25 μm in diameter. The quality of microwelds was investigated in 3 ways: shear and pull-off tests, optical observation using a scanning electron microscope (SEM), and contact resistance measurement. The aim of the work is to create a high-quality design of an IR photodetector, which allows achieving a high sensitivity (at least 0.5 A / W), a large dynamic range (at least 40 dB) and low indicators of dark current values. The developed technology ensures high quality of the photodetector design. Due to the low costs of this technological process (wire material, the number of operations required for installation), relative to other technologies, which allows maintaining high performance in the technical component of the photodetector, the installation method may be of practical interest in production.

Observation of negative photoconductivity at bandgap and super bandgap excitations in GaN nanorods

We report on the surprising observation of negative photoconductivity (NPC) in GaN nanorods (NRs) by bandgap and super bandgap excitations. A metal-semiconductor-metal (MSM) type of device configuration using Ni/Au as an electrode at both ends, has been used to study the NPC phenomenon. On exposing the device to the light sources with 363 nm (bandgap excitation) and 250 nm (super bandgap excitation) wavelengths, NPC with a drop of approximately 50 and 60% was observed, respectively. To explain this phenomenon, a model of trapping of photogenerated electrons by the trap states is proposed. Interestingly, a significant drop in the illumination current is observed at low values of power density (up to 3 μW/mm2) of the incident light. It has been interpreted that on increasing the power density, the density of trapped electrons starts approaching the density of available trap states. The de-trapping process is observed to be very slow as the illumination current reached the dark current value in nearly 2 h after switching off the incident light. The observation of NPC and saturation of trap states with high intensity of incident light are also validated by Kelvin Probe Force Microscopy (KPFM) characterization performed in the dark and on illumination with varying intensity of the incident light. Furthermore, on increasing the temperature from room temperature (RT) to 300 °C, the NPC was found to reduce to almost zero, which indicates the de-trapping of trapped electrons on increasing the temperature.

Extraordinarily high ultraviolet photodetection by defect tuned phosphorus doped ZnO thin film on flexible substrate

Phosphorus (P) doped zinc oxide (ZnO) thin film has skillfully been deposited on flexible substrate using radio frequency sputtering technique at room temperature under controlled oxygen ambient to tune its point defects. P doped ZnO film shows a very high ultraviolet (UV) photosensitivity with responsivity and detectivity values of 23.5 mA/W and 1.86×1013 Jones respectively as compared to the values of 0.073 mA/W and 2.56×1010 Jones respectively for pristine ZnO. Incorporation of P dopant under controlled oxygen ambient results in a very low dark current value due to acceptor-donor compensation leading to an unprecedentedly ultra-high photo-to-dark current ratio of 2.15×105 under 350 nm illumination. A photosensitivity under repetitive flat and bending conditions has been attained. Further, photoresponse towards a low intensity UV illumination of power 29 μW/cm2 has been noted with a photo-to-dark current ratio of 3.88×103 indicating an excellent photodetection efficiency of the P doped ZnO film.

Carbon dopants carriers facilitators as agents for improving hole extraction efficiency of cobalt tetraoxide nanoparticles employed in fabrication of photodetectors

(CH3NH3)3Bi2I9 perovskites have attracted enormous attention due to their lower toxic and more stable nature than CH3NH3PbI3 counterparts. However, higher bandgap and lower carrier mobility hinder the application of (CH3NH3)3Bi2I9 in optoelectronics. Hence, we employed carbon doping of Co3O4 hole extractors to reduce the bandgap of (CH3NH3)3Bi2I9, minimize non – radiative recombination rate and improve surface morphology of the (CH3NH3)3Bi2I9 particles. Consequently, photodetectors based on carbon-doped Co3O4 display reduced internal resistance, high photocurrent and low dark current values. The fabricated photodetectors display high responsivity (1.56 × 106 μA/W), high detectivity (5.74 × 1012 Jones), high sensitivity (8.23 × 103) and fast optical switching times (< 10 ms) values under device testing conditions of 2.0 V bias voltage, 10 mW/cm2 power intensity of solar illumination and ambient room conditions. The linearity and stability of the photodetectors over wide range of light intensities and 100 optical switching cycles were also demonstrated respectively.

Improvement of Photoelectrochemical Properties of WO3 Photoelectrode Fabricated by Using H2O2 Additive

In this study, we deposited a WO3 thin-film photoelectrode on a fluorine-doped tin oxide (FTO) substrate using a spin-coating method, and we investigated the photocurrent density and dark current density of the WO3 photoelectrode with various amounts of H2O2 additive. The morphological, structural, optical, electrical and photoelectrochemical properties of the WO3 photoelectrode with various amounts of H2O2 additive were analyzed using FE-SEM, XRD, UV-vis spectroscopy, EIS and a three-electrode potentiostat/galvanostat system, respectively. The amount of H2O2 additive has a large influence on the thickness of the WO3 photoelectrode, XRD (100) peak intensity, light absorption, optical energy bandgap, flat-band potential, donor density value, etc., and thus has a large influence on photoelectrochemical properties. Specifically, the H2O2 additive had a large influence on the growth of the WO3 photoelectrode, and the photocurrent density and dark current density characteristics of the WO3 photoelectrode grown to a uniform and thick thickness were largely improved. As a result, the WO3 photoelectrode fabricated with 0.2 mL of added H2O2 exhibited a high photocurrent density value of 1.17 mA/cm&lt;sup&gt;2&lt;/sup&gt;, which was about 23 times higher than that of the WO3 photoelectrode fabricated without H2O2 additive, and had a dark current density value of a low 0.04 mA/cm&lt;sup&gt;2&lt;/sup&gt;, which was a reduction of about 87%.

Flexible and high-performance broadband nanoflowers tin sulfide photodetector

A significant prerequisite for the development of a high-performance photodetector remains its low dark current value, because it promotes sensitivity and signal-to-noise ratio, in addition to low detectability light power density. Nevertheless, the fabricated photodetectors, which are based on deposited tin sulfide (SnS) films onto a flexible (PET at pH 5) and glass substrates, exhibited relatively high dark current values around (0.2 µA) and (several µA), respectively. This study proposes a novel approach for a better control of the photoresponse characteristics of nanostructured SnS film which resulted from reducing the deposition growth rate by adjusting the pH of the reaction solution to 5.8. The film was deposited onto a flexible substrate of polyethylene terephthalate (PET) using an inexpensive chemical bath deposition method. The as-fabricated photodetector exhibited a low dark current value approximately (~ 24 nA) at 5 V bias voltage and a good response in a broad range covering the UV up to the near-infrared. Besides, light-emitting diodes (380, 530, 750, and 850 nm) were used to investigate the photoresponse characteristics of the photodetector. The latter manifested fast photoresponse times (rise and decay) and good sensitivity for all used illumination wavelengths. Furthermore, under various illumination power densities of 850 nm, the photocurrent manifested a good dependence upon power density. Based on the obtained excellent photoresponse characteristics, this photodetector is promising for the photoelectronic flexible device in the UV–Vis–NIR range.

Major role of intrinsic defects in optical and electrical properties adopting a highly defect-controlled photoconductivity in spin-coated α-MoO3 thin films gained after UV illumination

Spin-coated MoO3 thin films were subsequently subjected to later thermal treatment (LTT) at different temperatures. The x-ray diffraction (XRD) results corroborated that the produced films crystallise in their α-phase with layer structure featured by preferential orientations along the (0k0) planes, and it was also revealed that the thermal energy gained by the later heat treatment plays a major role in enhancing crystallinity enlarging crystallite size. The optical spectroscopic analysis showed that in the visible and near-infrared regions, the average transmission of the film samples remarkably increases with increasing the LTT temperature, whereas the films prepared at 625 °C exhibits an average optical transmission of 79.92%. The optical bandgaps of the film samples were calculated to be of comparable values to the bulk one of α-MoO3 when increasing the LTT temperature from 375 to 525 °C, but it was found to be little greater than the bulk value by further increase in the LTT temperature. The DC electrical results revealed that raising the LTT temperature significantly enhances the electrical resistivity of the film samples, chiefly over the low working-temperatures. These results ascertained the realization of more than one conduction mechanism with different activation energies for the same film, and ramarkable upswings in activation energies were observed by increasing the LTT temperature. The photoconductivity (PC) analysis indicated the occurrence of various trapping processes associated with different photoexcitation energies. The PC analysis also corroborated that the highly resistive thin films exhibit much greater sensitivity to UV illumination compared with the remaining films, whereas the film prepared at the LTT temperature 625 °C presents the higher illumination current at the steady state condition exceeding the dark current value by a factor of 66.01.

The Influence of the Conditions of Getter Formation in High-Resistivity Silicon on the Characteristics of PIN Photodiodes

The influence of the conditions of gettering in high-resistivity silicon during fabrication of PIN photodiodes on reverse dark currents has been studied. It is shown that gettering using a combination of phosphorus ion implantation and deposition of a polysilicon film with subsequent doping of the substrate rear side with phosphorus at temperatures below 900°C leads to low values of the reverse dark current and increases the nonequilibrium carrier lifetime.