Characteristics Of Photodetectors Research Articles

Defects mediated optical emissions and efficient photodetection characteristics of sol–gel derived Ag-doped ZnO nanostructures for UV sensor

In the present work, defects mediated optical emission and efficient photodetection characteristics of ZnO:Ag (0, 2, 5, and 7 wt%) nanoparticles (NPs) synthesized by sol–gel method have been investigated for UV sensor. X-ray diffraction (XRD) patterns show the polycrystalline nature of ZnO NPs. The crystallite sizes corresponding to most intense peak (101) are found to be in the range of 10–20 nm. Effective enhancement of defect-mediated visible emissions is observed in Ag-doped ZnO NPs. Red-shift of UV peak in Ag-doped ZnO may be due the tensile strain upon Ag doping. Pure ZnO exhibits anomalous UV sensing, which is absent in ZnO NPs doped with Ag. The 7 wt% Ag-ZnO NPs is found to efficient UV photoresponsive. The results obtained by doping of Ag contents in the ZnO can be capable for making efficient and consistent prototype UV sensors.

High-performance self-powered photodetectors achieved through the pyro-phototronic effect in Si/SnOx/ZnO heterojunctions

Coupling together the pyroelectric effect and the photovoltaic effect is a novel method to significantly enhance the performance of photodetectors. In this work, we make use of this effect through a tri-layered heterojunction of n-Si/p-SnO x /n-ZnO, which takes advantage of the pyroelectric properties of the n-type ZnO film and the photovoltaic response of the n-type Si/p-type SnO x heterojunction. The photo-response of the device, with excitation from a 405 nm wavelength laser, is carefully investigated, and it is shown that the photodetector performance is improved with increased chopper frequency owing to the coupled photovoltaic-pyroelectric effect. The Al/Si/SnO x /ZnO/ITO device exhibits an optimum responsivity and detectivity of 36.7 mA/W and 1.5 × 10 11 Jones, respectively, with a laser power density of 36 mW/cm 2 and at a chopper frequency of 400 Hz. Ultrafast rise and fall times of 3 and 2 µs, respectively, were obtained. Moreover, by using a 650 nm wavelength laser source, the responsivity and detectivity were improved up to 64.1 mA/W and 2.4 × 10 11 Jones, respectively. The performance of these photodetectors is approximately twice as fast as other pyro-phototronic devices, and exhibits comparable photodetector characteristics when compared to perovskite/Si heterojunction and transition metal dichalcogenides lateral heterojunction devices. Therefore, by combining a pyroelectric ZnO film with a solar cell into one single structure, photodetectors based on the pyro-phototronic effect have been developed that demonstrate state-of-the-art performance. The devices show great promise for visible ultrafast photosensing. • Performance of the photodetectors are enhanced by coupling the photovoltaic and pyroelectric effects. • The pyro-phototronic effect is demonstrated for the first time in a n-p-n heterojunction. • An optimum responsivity and detectivity of 36.7 mA/W and 1.5 × 10 11 Jones were achieved at zero bias. • Ultrafast rise and fall times of 3 and 2 µs were achieved for Al/Si/SnO x /ZnO/ITO devices.

Optoelectronic performance characterization of MoS2 photodetectors for low frequency sensing applications

The specific advantages of implementing MoS2 and other layered semiconductors for optoelectronic biosensing and other relevant photodetection applications remain unclear. In this work, we investigate the photoresponsivity and noise characteristics of in-plane MoS2 photodetectors. This work indicates that MoS2 photodetectors exhibit lower noise equivalent power (NEP) and detectivity (D*) in comparison with commercial CdS photodetectors. In addition, the low-frequency NEP and D* values of MoS2 photodetectors exhibit a prominent dependence on the MoS2 photoactive layer thickness. We have identified the optimal MoS2 thickness in the range of 8–30 nm. We also study the photoresponse characteristics of optimized MoS2 photodetectors at several different wavelengths that are important for clinical colorimetry assays. Such an optimized photodetector shows a maximum photoresponsivity of 164.3 A/W and a minimum NEP of 3.99 × 10−17 W/Hz1/2 (and a D* of 5.01 × 1010 J) with relative variance less than 14%. This work provides a useful guideline for optimizing the photoresponse characteristics of MoS2-based optoelectronic devices, which is critical to practical low-frequency optoelectronic biosensing applications.

Improved Photoresponse Characteristics of a ZnO-Based UV Photodetector by the Formation of an Amorphous SnO2 Shell Layer

Although ZnO nanostructure-based photodetectors feature a well-established system, they still present difficulties when being used in practical situations due to their slow response time. In this study, we report on how forming an amorphous SnO2 (a-SnO2) shell layer on ZnO nanorods (NRs) enhances the photoresponse speed of a ZnO-based UV photodetector (UV PD). Our suggested UV PD, consisting of a ZnO/a-SnO2 NRs core–shell structure, shows a rise time that is 26 times faster than a UV PD with bare ZnO NRs under 365 nm UV irradiation. In addition, the light responsivity of the ZnO/SnO2 NRs PD simultaneously increases by 3.1 times, which can be attributed to the passivation effects of the coated a-SnO2 shell layer. With a wide bandgap (~4.5 eV), the a-SnO2 shell layer can successfully suppress the oxygen-mediated process on the ZnO NRs surface, improving the photoresponse properties. Therefore, with a fast photoresponse speed and a low fabrication temperature, our as-synthesized, a-SnO2-coated ZnO core–shell structure qualifies as a candidate for ZnO-based PDs.

The Effect of Annealing Ambience on the Material and Photodetector Characteristics of Sputtered ZnGa2O4 Films.

Spinel ZnGa2O4 films were grown on c-plane sapphire substrates at the substrate temperature of 400 °C by radio-frequency magnetron sputtering. Post thermal annealing was employed at the annealing temperature of 700 °C in order to enhance their crystal quality. The effect of thermal annealing on the microstructural and optoelectronic properties of ZnGa2O4 films was systematically investigated in various ambiences, such as air, nitrogen, and oxygen. The X-ray diffraction patterns of annealed ZnGa2O4 films showed the crystalline structure to have (111) crystallographic planes. Transmission electron micrographs verified that ZnGa2O4 film annealed under air ambience possesses a quasi-single-crystalline structure. This ZnGa2O4 film annealed under air ambience exhibited a smooth surface, an excellent average transmittance above 82% in the visible region, and a wide bandgap of 5.05 eV. The oxygen vacancies under different annealing ambiences were revealed a substantial impact on the material and photodetector characteristics by X-ray photoelectron spectrum investigations. ZnGa2O4 film exhibits optimal performance as a metal-semiconductor-metal photodetector when annealed under air ambience. Under these conditions, ZnGa2O4 film exhibits a higher photo/dark current ratio of ~104 order, as well as a high responsivity of 2.53 A/W at the bias of 5 V under an incident optical light of 240 nm. These results demonstrate that quasi-single-crystalline ZnGa2O4 films have significant potential in deep-ultraviolet applications.

Polyimide photodevices without a substrate by electron-beam irradiation

Despite the insulating properties of polyimide (PI), this study implemented an optoelectronic device comprising only PI. To realize suitable photocharacteristics of the PI photodetector, the PI-coated glass substrate was irradiated with an electron beam to transform the optical and electrical characteristics of PI from lower light absorption and insulation to relatively higher light absorption and conductive properties; the substrate was then removed. With the optimization of the electron-beam irradiation treatment conditions, detectivity of 6.38 × 1010 Jones was exhibited for the PI photodetector at 1 V under laser illumination at a wavelength of 450 nm. Furthermore, the mechanical characteristics of the free-standing PI photodetector under cyclic bending tests suggested a reduction of less than 25% after 1,000 cycles of bending. This demonstrates an innovative approach to the design of stable, flexible PI photodevices through elimination of a separate substrate.

Photoelectric Characteristics and Applications of Quantum Effect Photodetector

This paper introduces the photon storage and current oscillation characteristics of a quantum effect photodetector and studies the high-sensitivity characteristics of the detector based on device model. The photodetector adopts AlAs/GaAs/AlAs double-barrier structure, and there is an InAs quantum dots and In0.15Ga0.85 As quantum well in the GaAs wide well. In the bias voltage range of −1.5 ∼ 1 V, the dark current is about 0.1 pA, when the device is biased at −1.15 V, and the dark current of the device is 4.86 × 10−15 A. Under 632.8 nm laser irradiation, when the optical power is 0.01 pW, the current responsivity is 5.69 × 107 A/W, which has a large photoconductive gain. After the readout circuit and the photodetector are docked and packaged, it is found that the response voltage has a linear relationship with the integration time and the irradiation power. Based on the 1 × 64 quantum dots photodetector array and readout circuit, a miniature quantum dots spectrometer was developed and the high-sensitivity characteristics of the photodetector were verified.

High Performance Organic Phototransistor Doped With MXene

Organic phototransistors have attracted tremendous attentions due to their light weight and good compatibility with flexible substrates. However, developing organic phototransistors with high performance over the broadband spectrum still remains great challenge. In this study, high-performance broadband phototransistor is developed with organic materials/MXene, which exhibits improved mobility and outstanding photodetection characteristics. The combination of MXene and organic semiconductor materials provides a promising way to prepare high-performance OPT with broadband detection.

Performance Improvement of Co-Sputtering AlGaZnO Solar-Blind Photodetectors

The author reported the AlGaZnO photodetector characteristics with various AGO:ZnO co-sputtering power ratio. It was found the optimized on/off ratio and responsivity were about 3.64 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> and 0.15 A/W, respectively, at the 10 V applied bias, and with AGO:ZnO power ratio of 80 W:50 W. The UV to visible rejection ratio was 8.08 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , indicated the significant response under UV illumination. The on/off ratio and responsivity could further be improved to 4.2 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> and 0.44 A/W, respectively, by annealed at 300°C for an hour, to decrease the defect in the AGZO film. Besides, the photoresponse of the AGZO photodetectors also showed a repeatable and stable switching characteristic. These results indicate the performance of AGZO photodetector were good, and can be a good candidate for low cost, fast fabricated solar-blind application.

The effect of oxygen annealing on characteristics of β-Ga2O3 solar-blind photodetectors on SiC substrate by ion-cutting process

In this work, a high quality (2̅01) β-Ga2O3 single-crystalline film was transferred to the 4H-SiC substrate by ion-cutting technique, on which the metal-semiconductor-metal (MSM) solar-blind photodetectors (PDs) were fabricated. The effect of the oxygen annealing on the performance of PDs has been systematically studied. The PD fabricated on the as-transferred film exhibits a high responsivity (R) of 2.24 A/W with a large external quantum efficiency of 1.21 × 103%, and an ultrahigh responsivity rejection ratio (R240nm/R350nm) of 1.02 × 105. In comparison, the PD based on the β-Ga2O3 film annealed in oxygen atmosphere exhibits a reduced dark current of 0.6 nA at the bias of 5 V, a fast decay time of 41 ms but a relatively reduced internal gain. It is resulted from the increased Schottky barrier height and the suppression of persistent photoconductivity effect due to the reduced density of surface oxygen vacancies and defects upon annealing. These results would promote a better understanding of dark current and responsivity of PDs modulated by oxygen annealing.

Investigation of the characteristics of matrix multi-element avalanche photodetectors operating in the photon counting mode

At present, matrix multi-element avalanche photodetectors operating in the photon counting mode are widely used for detecting optical radiation. However, the char-acteristics of matrix multi-element avalanche photodetectors operating in this mode are currently insufficiently studied. Prototypes of Si-photomultiplier tubes (Si-PMTs) with a p+–p–n+ structure produced by JSC Integral (Republic of Belarus), as well as serially produced silicon photomultipliers Ketek PM 3325 and ON Semi FC 30035 have been used as objects of research. This article presents the research results of characteristics in the photon counting mode of the specified photodetec-tors. The dependences of the specific amplitude sensitivity ratio on the wavelength of optical radiation, the temperature, the supply voltage of the matrix multi-element avalanche photodetector are determined.

Fourier analysis of spectral characteristics of a matrix photodetector in the frequency and time domain

The purpose of this paper is to research the frequency and time characteristics of the photo-detector using the direct and inverse Fourier transform. The spectral characteristics of the matrix photodetector were selected as the object of research. For the channels of the trans-ducer it was found that the frequency spectrum consists of two elementary bands in the form of Gaussian curves. It was revealed that the spectra have super-broadband properties. The impulse (time) characteristic of the spectra is described by the equation in an analytical form, which is in good agreement with the calculation. The rise time of the transient response is 1.8–2.9 fs. The process of absorption of light is significantly influenced by dielectric relaxa-tion of the charge. The results obtained provide important information on the properties of the photodetector in the frequency and time domain.

Fabrication and properties of a solar-blind ultraviolet photodetector based on Si-doped β-Ga2O3 film grown on p-Si (111) substrate by MOCVD

A solar-blind ultraviolet photodetector based on p-Si/n-β-Ga2O3:Si heterojunction, using the Si-doped β-Ga2O3 as the n-type layer, was fabricated successfully by metal-organic chemical vapor deposition (MOCVD). The current-voltage and photoresponse characteristics of photodetector were investigated. The fabricated p-Si/n-β-Ga2O3:Si heterojunction photodetector exhibited typical rectification behavior and good solar-blind ultraviolet photoresponse. Sensitive photodetection of current at the reverse bias voltage and stable on-off switching performance were achieved. The photodetector showed a responsivity of 3.76 A/W and a photo-to-dark current ratio of 37.9 under 254 nm illumination. The rise time constants (τr1, τr2) and the decay time constants (τd1, τd2) of the photodetector under 254 nm illumination at the reverse voltage of − 20 V were estimated to be (0.30 s, 0.76 s) and (0.15 s, 6.15 s), respectively. The fabricated p-Si/n-β-Ga2O3:Si heterojunction photodetector displayed relatively faster response speed compared to the reported photodetectors based on p-Si/undoped β-Ga2O3 heterojunction. The results indicate that photodetectors based on p-Si/n-β-Ga2O3:Si heterojunction have potential development for the high-performance solar-blind ultraviolet photodetectors.

Ambient stability improvement of CQD photodetectors by low-temperature deposited graphene encapsulation

In this work, we have investigated the ambient stability improvement of colloidal quantum dots (CQD) photodetectors by graphene encapsulation. The low temperature deposited graphene is performed to act as an isolating membrane between PbS CQDs and the ambient environment. The oxidization of PbS CQDs can be significantly inhibited with a graphene isolating membrane. In addition, the optoelectronic characteristics of PbS CQDs-based photodetectors encapsulated by graphene are well maintained even exposed in ambient for a month. This work paves the way for the fabrication and application of the air-stable CQDs.

Modulation characteristics of uncooled graphene photodetectors

We report on the modulation characteristics of the uncooled terahertz (THz) and infrared (IR) detectors using uniform graphene layers (GLs) and perforated graphene layers (PGL). Our analysis shows that the PGL detectors could have more than an order of magnitude smaller dark current compared to more conventional GL reversed biased photodetectors operating in the same frequency range. The modulation mechanism for the simulated photodetectors is the variation of the density and effective temperature of the two-dimensional electron–hole plasma with the varying intensity of the THz or IR radiation. Our simulations predict a reasonable modulation depth up to the modulation frequencies of 50 GHz for the impinging radiation frequencies up to the mid-IR range.

Fabrication and characterization of InN-based metal-semiconductor-metal infrared photodetectors prepared using sol–gel spin coated technique

We report on the growth and characterization of undoped indium nitride (InN) thin films grown on a silicon substrate. The InN thin films were grown on aluminium nitride (AlN) template with gallium nitride (GaN) nucleation layer using a relatively simple and low-cost sol–gel spin coating method. The crystalline structure and optical properties of the deposited films were investigated. X-ray diffraction and Raman results revealed that InN thin films with wurtzite structure were successfully grown. For InN thin film grown on a substrate with the GaN nucleation layer, its strain and dislocation density are lower than that of the substrate with the AlN nucleation layer. From the ultra-violet-visible diffuse reflectance spectrum analysis, the energy bandgap of the InN thin films with the GaN layer was 1.70 eV. The potential application of the sol–gel spin-coated InN thin films was also explored. Metal–semiconductor–metal (MSM) infrared (IR) photodetectors were fabricated by depositing the platinum contacts using two interdigitated electrodes metal mask on the samples. The finding shows that the device demonstrates good sensitivity and repeatability towards IR excitation at a wavelength of 808 nm. The photodetector characteristics at dark and photocurrent conditions such as Schottky barrier height (SBH) and ideality factor are determined. Upon exposure to the IR source at 3V applied bias, InN/AlN/Si device configuration displays rapid rise time of 0.85 s and decay time of 0.78 s, while InN/GaN/AlNSi demonstrates slow rise time of 7.45 s and decay time of 13.75 s.

Signal-to-noise characteristics of graphene photodetectors based on photothermoelectric effect

A sensor using the photothermoelectric effect of graphene is anticipated as a candidate for infrared sensors that can operate at room temperature with fast response and high sensitivity. We investigate photothermoelectric detection and the signal-to-noise characteristics of a sensor with a simple metal–graphene–metal structure numerically and analytically and obtain an analytical expression giving the ideal value of specific detectivity D∗ for a sensor having an ideal potential distribution. It is found that the optimal sensor length is approximately three times longer than the cooling length and that the value of D∗ for such a sensor with typical cooling length is estimated to be as large as 106 cmHz/W. The sensor performance can be greatly enhanced by employing light-confining structures such as cavities and plasmon antennas, achieving D∗ above 108 cmHz/W.

Effect of Pt-doped on the photocurrent of MSM photodetector

This article report the fabrication and characteristics of MSM photo detector by compare between non-doped and doped platinum (Pt) atom. Fabrication process has same but different in Pt doping process for atom doping and diffusion process. The metal finger width 2um with 50 um spacing between metal contact. At bias voltage 10 voltage show higher capacitance-voltage and photocurrent increase after doped with Pt atom. By experiment shows photocurrent increase around 4 times from 45.98 to 197.22 uA at bias 10 voltage by photoluminescence 25,000 lux.

MoS2/h-BN/Graphene Heterostructure and Plasmonic Effect for Self-Powering Photodetector: A Review.

A photodetector converts optical signals to detectable electrical signals. Lately, self-powered photodetectors have been widely studied because of their advantages in device miniaturization and low power consumption, which make them preferable in various applications, especially those related to green technology and flexible electronics. Since self-powered photodetectors do not have an external power supply at zero bias, it is important to ensure that the built-in potential in the device produces a sufficiently thick depletion region that efficiently sweeps the carriers across the junction, resulting in detectable electrical signals even at very low-optical power signals. Therefore, two-dimensional (2D) materials are explored as an alternative to silicon-based active regions in the photodetector. In addition, plasmonic effects coupled with self-powered photodetectors will further enhance light absorption and scattering, which contribute to the improvement of the device’s photocurrent generation. Hence, this review focuses on the employment of 2D materials such as graphene and molybdenum disulfide (MoS2) with the insertion of hexagonal boron nitride (h-BN) and plasmonic nanoparticles. All these approaches have shown performance improvement of photodetectors for self-powering applications. A comprehensive analysis encompassing 2D material characterization, theoretical and numerical modelling, device physics, fabrication and characterization of photodetectors with graphene/MoS2 and graphene/h-BN/MoS2 heterostructures with plasmonic effect is presented with potential leads to new research opportunities.

Solution-Processed Black-Si/Cu2ZnSnS4 Nanocrystal Heterojunctions for Self-Powered Broadband Photodetectors and Photovoltaic Devices

We report, for the first time, the fabrication of n-black Si (B–Si)/p-Cu2ZnSnS4 nanocrystal (CZTS NC) heterojunctions to demonstrate their photodetection and photovoltaic characteristics. Inks with...