Junction Photodetectors Research Articles

Vertical α/β-Ga2O3 phase junction nanorods array with graphene-silver nanowire hybrid conductive electrode for high-performance self-powered solar-blind photodetectors

Gallium oxide semiconductor, with a bandgap energy of 4.9 eV, is regarded as a hopeful candidate for next-generation solar-blind photodetectors. However, the construction of photodetector based on Ga2O3 pn junction is still challengeable due to immature doping technology of p-Ga2O3. By considering the small lattice mismatch (＜3%) and similar band gap structure of α-Ga2O3 and β-Ga2O3, a well-designed solar-blind photodetector was built, based on vertical α/β-Ga2O3 junction nanorod arrays (NRAs) with a graphene-silver nanowires (Ag NWs) hybrid top electrode. Thanks to the high conductivity and optical transmittance of graphene-Ag NWs top electrode, the photodetector based on α/β-Ga2O3 junction NARs displayed excellent photoelectric performance. Meanwhile, the matched band structure of Π type formed at the interface of α/β-Ga2O3 junction promoted the automatic separation of photogenerated carriers and their transfer to the corresponding electrodes. A fast photoresponse time of 0.54 s, a high light-to-dark ratio about 2000, and a high rejection ratio (R254/R365) of 2.7 × 103 under the zero bias, were realized. The excellent photoelectrical performance of α/β-Ga2O3 junction photodetector even in vacuum environment forecasts its potential application in some low air density fields, such as missile early warning and tracking and ozone hole monitoring.

Probing bias and power dependency of high-performance broadband Mg/ZnSnP2/Sn back-to-back Schottky junction photodetectors

Two non-identical Mg/ZnSnP2 and ZnSnP2/Sn Schottky diodes connected in coplanar back-to-back configuration are fabricated on p-type silicon (100) substrate for photodetection in the UV-VIS-NIR spectral region. A detailed study of the power and bias dependent responsivity, detectivity, and response and recovery speed of the devices is reported. The responsivity and detectivity were found to be 0.2 A W-1 and 4.62 × 1012 Jones for the Mg/ZnSnP2 and 0.03 A W-1 and 1.62 × 1011 Jones for the Sn/ZnSnP2 junctions, respectively when they were operated without bias. However, under a reverse bias of 2.5 V, these values changed to 4.7 A W-1 and 1.19 × 1012 Jones in the case of Mg/ZnSnP2 and 12.7 A W-1 and 4.78 × 1011 Jones for Sn/ZnSnP2 junctions, respectively. The photocurrents associated with both the junctions were increased superlinearly with illumination power which is correlated to the conversion of the existing traps within the forbidden energy gap to the recombination centers. The response and recovery speed of the photodetectors were also studied under variable bias and illumination power. Under an incident power of 0.34 mW, the rise and decay times for the Mg/ZnSnP2 and Sn/ZnSnP2 junctions were 200 μs, 2300 μs and 390 μs, 240 μs, respectively at 2.5 V. The Mg/ZnSnP2 showed an anomalous bias dependent secondary decay channel which disappeared at self-powered configuration. The frequency-dependent capacitance in the dark and illumination power-dependent capacitance of the structure were also performed to understand the presence of defect states and the capture of photogenerated carriers by the traps and recombination centers.

Self-driven all-inorganic perovskite microplatelet vertical Schottky junction photodetectors with a tunable spectral response

An all-inorganic perovskite self-driven vertical Schottky junction photodetector with a tunable spectral response is reported.

Ultrasensitive Fiber-Based ZnO Nanowire Network Ultraviolet Photodetector Enabled by the Synergism between Interface and Surface Gating Effects.

A flexible UV photodetector with a high on/off ratio is extremely important for environmental sensing, optical communication, and flexible optoelectronic devices. In this work, a flexible fiber-based UV photodetector with an ultrahigh on/off ratio is developed by utilizing the synergism between interface and surface gating effects on a ZnO nanowire network structure. The synergism between two gating effects is realized by the interplay between surface band bending and the Fermi level through the nanowire network structure, which is proved through the control experiments between the ZnO micro/nanowire photodetector and micro/nanowire junction photodetector, and the corresponding Kelvin probe force microscopy (KPFM) measurements. The on/off ratio of the fiber-based ZnO nanowire network UV photodetector reaches 1.98 × 108 when illuminated by 1.0 mW cm-2 UV light, which is 20 times larger than the largest reported result under the same UV illumination. This new UV sensor also has a high resolution to UV light intensity change in the nW cm-2 range. Furthermore, when the fiber-based photodetector is curved, it still shows excellent performance as above. This work gives a new effective route for the development of a high-performance UV photodetector or other optoelectronic detection devices.

Back-to-back Schottky junction photodetectors based on CVD grown CsPbBr3 microcrystalline striped films

In recent years, a new type of lead halide perovskite has attracted a lot of attention for next-generation photodetectors (PDs) with high responsivity, good detectivity, and fast photoresponse speed. Specifically, cesium based all-organic perovskites exhibit better photostability and therefore have achieved increasing success in PDs recently. For reducing the leak current and increasing the response speed of photoconductive PDs, back-to-back Schottky junction PD is designed and fabricated through a direct growth approach of CsPbBr3 microcrystal (MC) films on indium tin oxide (ITO) electrodes by the chemical vapor deposition (CVD) method. Due to the enhanced Schottky barrier height and threshold voltage between CsPbBr3 and ITO electrodes, the PD exhibits the on/off ratio of up to 104, peak responsivity of 3.9 AW−1, detectivity of 3.8 × 1012, and fast response speed of 0.22 ms (rise time) and 0.45 ms (decay time). In addition, the stability of PD is also enhanced by the high crystal quality of CVD grown CsPbBr3 MCs.

Self‐Powered Photodetectors Based on 2D Materials

AbstractSelf‐powered photodetectors are considered as a new type of photodetectors enabling self‐powered photodetection without external power. The excellent photoresponsivity, fast photoresponse rate, low dark current, and large light on/off ratio of these photodetectors have attracted wide interest among scholars. 2D materials are widely used in self‐powered photodetectors due to their excellent optical and electrical properties, unique 2D structures, and their capabilities to exhibit excellent photodetection performance. According to the self‐driving mechanism of 2D material‐based self‐powered photodetectors, they are divided into three categories: p–n junction photodetectors, Schottky junction photodetectors, and photoelectrochemical photodetectors. From these three perspectives, the research progress of 2D material‐based self‐powered photodetectors is summarized in detail here. Research reports indicate that 2D material‐based self‐powered photodetectors have excellent self‐powered photoresponse behavior, good light on/off characteristics, and wideband spectral response ranges. The excellent photoresponse performance of 2D material‐based self‐powered photodetectors facilitates their potential applications in the field of optoelectronic devices. In particular, self‐powered photodetectors have great potential as novel emerging self‐driven optoelectronic devices. Finally, directions for the further development of 2D material‐based self‐powered photodetectors are anticipated.

Interface Defect Engineering for Improved Graphene-Oxide-Semiconductor Junction Photodetectors

The deeply depleted graphene-oxide-semiconductor (D2GOS) junction detector provides an effective architecture for photodetection, enabling direct readout of photogenerated charge. Because of an inh...

Visible and infrared photocurrent enhancement in a graphene-silicon Schottky photodetector through surface-states and electric field engineering

The design of efficient graphene-silicon (GSi) Schottky junction photodetectors requires detailed understanding of the spatial origin of the photoresponse. Scanning-photocurrent-microscopy (SPM) studies have been carried out in the visible wavelengths regions only, in which the response due to silicon is dominant. Here we present comparative SPM studies in the visible ( nm) and infrared ( nm) wavelength regions for a number of GSi Schottky junction photodetector architectures, revealing the photoresponse mechanisms for silicon and graphene dominated responses, respectively, and demonstrating the influence of electrostatics on the device performance. Local electric field enhancement at the graphene edges leads to a more than ten-fold increased photoresponse compared to the bulk of the graphene-silicon junction. Intentional design and patterning of such graphene edges is demonstrated as an efficient strategy to increase the overall photoresponse of the devices, leading to a more than two-fold responsivity enhancement under global illumination to 5 10−6 A W−1 at a wavelength of 1650 nm for the patterned device compared to the unpatterned device. Complementary simulations and modeling illuminate observed effects and highlight the importance of considering graphene’s shape and pattern and device geometry in the device design.

Multilayered PdSe2/Perovskite Schottky Junction for Fast, Self-Powered, Polarization-Sensitive, Broadband Photodetectors, and Image Sensor Application.

Group‐10 transition metal dichalcogenides (TMDs) with distinct optical and tunable electrical properties have exhibited great potential for various optoelectronic applications. Herein, a self‐powered photodetector is developed with broadband response ranging from deep ultraviolet to near‐infrared by combining FA1− xCsxPbI3 perovskite with PdSe2 layer, a newly discovered TMDs material. Optoelectronic characterization reveals that the as‐assembled PdSe2/perovskite Schottky junction is sensitive to light illumination ranging from 200 to 1550 nm, with the highest sensitivity centered at ≈800 nm. The device also shows a large on/off ratio of ≈104, a high responsivity (R) of 313 mA W−1, a decent specific detectivity (D*) of ≈1013 Jones, and a rapid response speed of 3.5/4 µs. These figures of merit are comparable with or much better than most of the previously reported perovskite detectors. In addition, the PdSe2/perovskite device exhibits obvious sensitivity to polarized light, with a polarization sensitivity of 6.04. Finally, the PdSe2/perovskite detector can readily record five “P,” “O,” “L,” “Y,” and “U” images sequentially produced by 808 nm. These results suggest that the present PdSe2/perovskite Schottky junction photodetectors may be useful for assembly of optoelectronic system applications in near future.

2D Carbon Material/Silicon Heterojunctions for Fast Response Self-Powered Photodetector

Photodetectors (PDs) based on single-walled carbon nanotube film/silicon and graphene/silicon heterojunctions have been realized for fast applications. We investigated the response of the PDs to femtosecond pulsed laser using a three-electrode configuration for photoconductive operations. Both junction PDs exhibit rise times of some nanoseconds, detecting light from ultraviolet (275[Formula: see text]nm) to infrared (1150[Formula: see text]nm). Applying a gate voltage [Formula: see text], the rise time decreases down to about 1[Formula: see text]ns, making our devices comparable to most commercial PDs.

High‐Responsivity Near‐Infrared Photodetector Using Gate‐Modulated Graphene/Germanium Schottky Junction

AbstractA high‐responsivity near‐infrared photodetector is demonstrated using a transparent ZnO top gate‐modulated graphene/Ge Schottky junction. The responsivity of a graphene/Ge junction photodetector characterized with a scanning photocurrent microscopy system is improved to 0.75 A W−1. This result is 5 to 35 times higher than the previously reported graphene/Ge photodetectors that did not use gate modulation. The detectivity is also improved to 2.53 × 109 cm Hz1/2 W−1 at Vg = −10 V from 0.43 × 109 cm Hz1/2 W−1 at Vg = 0 V. The performance of this gate‐modulated graphene/Ge Schottky junction base infrared (IR) detector is comparable to a commercially available IR photodetector, but the fabrication process is much simpler and compatible with glass or flexible substrates.

Metal-Catalyst-Free Growth of Patterned Graphene on SiO2 Substrates by Annealing Plasma-Induced Cross-Linked Parylene for Optoelectronic Device Applications.

A metal-catalyst-free method for the direct growth of patterned graphene on an insulating substrate is reported in this paper. Parylene N is used as the carbon source. The surface molecule layer of parylene N is cross-linked by argon plasma bombardment. Under high-temperature annealing, the cross-linking layer of parylene N is graphitized into nanocrystalline graphene, which is a process that transforms organic to inorganic and insulation to conduction, while the parylene N molecules below the cross-linking layer decompose and vaporize at high temperature. Using this technique, the direct growth of a graphene film in a large area and with good uniformity is achieved. The thickness of the graphene is determined by the thickness of the cross-linking layer. Patterned graphene films can be obtained directly by controlling the patterns of the cross-linking region (lithography-free patterning). Graphene-silicon Schottky junction photodetectors are fabricated using the as-grown graphene. The Schottky junction shows good performance. The application of direct-grown graphene in optoelectronics is achieved with a great improvement of the device fabrication efficiency compared with transferred graphene. When illuminated with a 792 nm laser, the responsivity and specific detectivity of the detector measured at room temperature are 275.9 mA/W and 4.93 × 109 cm Hz1/2/W, respectively.

Comprehensive Pyro‐Phototronic Effect Enhanced Ultraviolet Detector with ZnO/Ag Schottky Junction

AbstractAs a coupling effect of pyroelectric and photoelectric effect, pyro‐phototronic effect has demonstrated an excellent tuning role for fast response p–n junction photodetectors (PDs). Here, a comprehensive pyro‐phototronic effect is utilized to design and fabricate a self‐powered and flexible ultraviolet PD based on the ZnO/Ag Schottky junction. By using the primary pyroelectric effect, the maximal transient photoresponsivity of the self‐powered PDs can reach up to 1.25 mA W−1 for 325 nm illumination, which is improved by 1465% relative to that obtained from the steady‐state signal. The relative persistent secondary pyroelectric effect weakens the height of Schottky barrier, leading to a reduction of the steady‐state photocurrent with an increase in the power density. When the power density is large enough, the steady‐state photocurrent turns into a reverse direction. The corresponding tuning mechanisms of the comprehensive pyro‐phototronic effect on transient and steady‐state photocurrent are revealed based on the bandgap diagrams. The results may help us to further clarify the mechanism of the pyro‐phototronic effect on the photocurrent and also provide a potential way to optimize the performance of self‐powered PDs.

Visible-Light-Responsive High-Detectivity Organic Photodetectors with a 1 μm Thick Active Layer.

Organic photodetectors (OPDs) are attracting attention for use in flexible and portable electronic applications such as image sensors, remote sensing, optical communications, and medical sensors because of their strong photon responsivity in thin films over a broad range of wavelengths. In particular, the efficient photon-to-current conversion of OPDs under visible light allows their use in indirect X-ray detectors using scintillators to convert X-rays to visible light. The polymer poly(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2- b:4,5- b']dithiophene- co-5-(2-hexyldecyl)-1,3-bis(6-octylthieno[3,2- b]thiophen-2-yl)-4 H-thieno[3,4- c]pyrrole-4,6(5 H)-dione) (PBDTT-8ttTPD) shows strong absorption bands in the region of 500-650 nm, as well as high hole mobility, which provides excellent photoresponsivity and photon-to-current conversion efficiency. A p-n junction photodetector was fabricated by blending PBDTT-8ttTPD and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) and varying the thickness of the active layer (260-1100 nm). The PBDTT-8ttTPD:PC71BM-based OPDs show promising photodetecting properties having a low dark current of 3.72 × 10-9 A cm-2 and high responsivity of 0.39 A W-1 because of the well-controlled morphology, high molar absorption coefficient, and excellent carrier mobility of the PBDTT-8ttTPD:PC71BM layer. Consequently, the specific detectivity of the PBDTT-8ttTPD-based OPD devices was 1.13 × 1013 Jones at -2 V on irradiation with a light-emitting diode (530 nm wavelength) with a power density of 55.6 μW cm-2.

Flexible Vertical p-n Diode Photodetectors with Thin N-type MoSe2 Films Solution-Processed on Water Surfaces.

Two-dimensional (2D) nanosheets of transition metal dichalcogenides (TMDs) are of significant interest for potential photoelectronic applications. However, the fabrication of solution-processed arrays of mechanically flexible thin TMD films-based vertical type p-n junction photodetectors over a large area is a great challenge. Our method is based on controlled solvent evaporation of MoSe2 suspension spread on water surface. Single or few-layered MoSe2 nanosheets modified with the dispersant amine-terminated poly(styrene) (PS-NH2) were homogeneously deposited and stacked on water upon solvent evaporation, giving rise to uniform MoSe2/PS-NH2 composite films that can be readily transferred onto other substrates. A p-n junction vertical diode of Al/p-type Si/p-type poly(9,9-di- n-octylfluorenyl-2,7-diyl)/n-type MoSe2 composite/Au stacked from bottom to top exhibited characteristic rectifying current behavior upon voltage sweep with a rectification ratio of 103. Subsequent illumination of near-infrared light on the device resulted in a substantially enhanced dark current of approximately 103 times greater than that of the nonexposed device. The photodetection performance, that is, switching time, responsivity, and detectivity, were 100.0 ms, 2.5 AW-1, and 2.34 × 1014, respectively. Furthermore, the performance of mechanically flexible photodetectors devices was comparable with that of the devices fabricated on the hard Si substrate even after 1000 bending cycles at a bending diameter of 7.2 mm.

WSe2/Au vertical Schottky junction photodetector with low dark current and fast photoresponse

Atomically thin two-dimensional materials including graphene, transition metal dichalcogenides, black phosphorus and so forth have been considered as promising channel medias for electronic and optoelectronic devices in the past few years. However, the poor photoresponse time and the large dark current are the two major issues which greatly block their applications. Here, we report a vertical Au–WSe2–ITO (indium tin oxide) Schottky junction photodetector with a broadband photoresponse from 550–950 nm and a stable photovoltaic responsivity of ∼0.1 A W−1. The fast photoresponse of ∼50 μs and low dark current of ∼1 pA are achieved at the vertical Au–WSe2–ITO photodetector. These results indicate that metal contact to a 2D material-based vertical Schottky junction can achieve an excellent photoelectric response.

Gate-Controlled Graphene-Silicon Schottky Junction Photodetector.

Various photodetectors showing extremely high photoresponsivity have been frequently reported, but many of these photodetectors could not avoid the simultaneous amplification of dark current. A gate-controlled graphene-silicon Schottky junction photodetector that exhibits a high on/off photoswitching ratio (≈104 ), a very high photoresponsivity (≈70 A W-1 ), and a low dark current in the order of µA cm-2 in a wide wavelength range (395-850 nm) is demonstrated. The photoresponsivity is ≈100 times higher than that of existing commercial photodetectors, and 7000 times higher than that of graphene-field-effect transistor-based photodetectors, while the dark current is similar to or lower than that of commercial photodetectors. This result can be explained by a unique gain mechanism originating from the difference in carrier transport characteristics of silicon and graphene.

Towards a novel single-LED pulse oximeter based on a multispectral sensor for IoT applications

Pulse oximetry is one of the most commonly employed monitoring modalities in critical care setting. Conventional pulse oximeters use two leds at different wavelengths and a photodiode to estimate blood oxygen saturation noninvasively, based in the difference of absorption coefficients between hemoglobin and deoxyhemoglobin. Nevertheless, factors such as low oxygen saturations or led wavelength displacement, modify differently the expected light absorbance for both LEDs. To address this issue, we propose a novel approach combining a single led and a Buried Quad Junction photodetector, i.e. a multispectral sensor. With this fundamental modification of the pulse oximetry principle, we reduce the modifying effects introduced by the aforementioned sources of inaccuracy by using a single led. Results from in vivo measurements, show that the three tests of the proposed system's precision falls within the commercial tolerance of 4% SpO2%.

P3HT–graphene bilayer electrode for Schottky junction photodetectors

We have investigated the effect of a poly (3-hexylthiophene-2.5-diyl)(P3HT)–graphene bilayer electrode on the photoresponsivity characteristics of Si-based Schottky photodetectors. P3HT, which is known to be an electron donor and absorb light in the visible spectrum, was placed on CVD grown graphene by dip-coating method. The results of the UV–vis and Raman spectroscopy measurements have been evaluated to confirm the optical and electronic modification of graphene by the P3HT thin film. Current–voltage measurements of graphene/Si and P3HT–graphene/Si revealed rectification behavior confirming a Schottky junction formation at the graphene/Si interface. Time-resolved photocurrent spectroscopy measurements showed the devices had excellent durability and a fast response speed. We found that the maximum spectral photoresponsivity of the P3HT–graphene/Si photodetector increased more than three orders of magnitude compared to that of the bare graphene/Si photodetector. The observed increment in the photoresponsivity of the P3HT–graphene/Si samples was attributed to the charge transfer doping from P3HT to graphene within the spectral range between near-ultraviolet and near-infrared. Furthermore, the P3HT–graphene electrode was found to improve the specific detectivity and noise equivalent power of graphene/Si photodetectors. The obtained results showed that the P3HT–graphene bilayer electrodes significantly improved the photoresponsivity characteristics of our samples and thus can be used as a functional component in Si-based optoelectronic device applications.

Large-area synthesis and photoelectric properties of few-layer MoSe2 on molybdenum foils

Compared with MoS2 and WS2, selenide analogs have narrower band gaps and higher electron mobilities, which make them more applicable to real electrical devices. In addition, few-layer metal selenides have higher electrical conductivity, carrier mobility and light absorption than the corresponding monolayers. However, the large-scale and high-quality growth of few-layer metal selenides remains a significant challenge. Here, we develop a facile method to grow large-area and highly crystalline few-layer MoSe2 by directly selenizing the Mo foil surface at 550 °C within 60 min under ambient pressure. The atomic layers were controllably grown with thicknesses between 3.4 and 6 nm, which just met the thickness range required for high-performance electrical devices. Furthermore, we fabricated a vertical p–n junction photodetector composed of few-layer MoSe2 and p-type silicon, achieving photoresponsivity higher by two orders of magnitude than that of the reported monolayer counterpart. This technique provides a feasible approach towards preparing other 2D transition metal dichalcogendes for device applications.