Showing papers on "p–n junction published in 2016"

Controlled Generation of a p–n Junction in a Waveguide Integrated Graphene Photodetector

Abstract: With its electrically tunable light absorption and ultrafast photoresponse, graphene is a promising candidate for high-speed chip-integrated photonics. The generation mechanisms of photosignals in graphene photodetectors have been studied extensively in the past years. However, the knowledge about efficient light conversion at graphene p–n junctions has not yet been translated into high-performance devices. Here, we present a graphene photodetector integrated on a silicon slot-waveguide, acting as a dual gate to create a p–n junction in the optical absorption region of the device. While at zero bias the photothermoelectric effect is the dominant conversion process, an additional photoconductive contribution is identified in a biased configuration. Extrinsic responsivities of 35 mA/W, or 3.5 V/W, at zero bias and 76 mA/W at 300 mV bias voltage are achieved. The device exhibits a 3 dB bandwidth of 65 GHz, which is the highest value reported for a graphene-based photodetector.

Atomically thin lateral p–n junction photodetector with large effective detection area

Abstract: The widely used photodetector design based on atomically thin transition metal dichalcogenides (TMDs) has a lateral metal-TMD-metal junction with a fairly small, line shape photoresponsive active area at the TMD-electrode interface. Here, we report a highly efficient photodetector with extremely large photoresponsive active area based on a lateral junction of monolayer-bilayer WSe2. Impressively, the separation of the electron–hole pairs (excitons) extends onto the whole 1L–2L WSe2 junction surface. The responsivity of the WSe2 junction photodetector is over 3200 times higher than that of a monolayer WSe2 device and leads to a highest external quantum efficiency of 256% due to the efficient carrier extraction. Unlike the TMD p–n junctions modulated by dual gates or localized doping, which require complex fabrication procedures, our study establishes a simple, controllable, and scalable method to improve the photodetection performance by maximizing the active area for current generation.

In Situ Composition-Transforming Fabrication of BiOI/BiOIO3 Heterostructure: Semiconductor p–n Junction and Dominantly Exposed Reactive Facets

Abstract: We for the first time disclose the integrated effects of a semiconductor p–n heterojunction and dominantly exposed reactive facets that are enabled in a facile way. Unlike most of the reported semiconductor heterojunctions that are constructed by compositing the individual components, in this work, we report the composition–transformation fabricating BiOI/BiOIO3 heterostructure via an in situ reduction route by using thiourea as the reducing agent. This reducing process enables BiOIO3 dominant exposure of the {010} reactive facet, and the exposed percentage can be effectively tuned by monocontrolling the thiourea concentration. The photocatalysis and photoelectrochemical properties of samples are assessed by surveying the decomposition of methyl blue (MB) and photocurrent generation under simulated solar light or visible light illumination. The heterostructured BiOI/BiOIO3 nanocomposites unfold drastically strengthened photoreactivity, in which the MB degradation rate is over 85% for 1 h irradiation, and ...

High Performance Nanostructured Silicon–Organic Quasi p–n Junction Solar Cells via Low-Temperature Deposited Hole and Electron Selective Layer

Abstract: Silicon–organic solar cells based on conjugated polymers such as poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) on n-type silicon (n-Si) attract wide interest because of their potential for cost-effectiveness and high-efficiency. However, a lower barrier height (Φb) and a shallow built in potential (Vbi) of Schottky junction between n-Si and PEDOT:PSS hinders the power conversion efficiency (PCE) in comparison with those of traditional p–n junction. Here, a strong inversion layer was formed on n-Si surface by inserting a layer of 1, 4, 5, 8, 9, 11-hexaazatriphenylene hexacarbonitrile (HAT-CN), resulting in a quasi p–n junction. External quantum efficiency spectra, capacitance–voltage, transient photovoltage decay and minority charge carriers life mapping measurements indicated that a quasi p–n junction was built due to the strong inversion effect, resulting in a high Φb and Vbi. The quasi p–n junction located on the front surface region of silicon substrates improved the short wavelen...

Flexible Photodiodes Based on Nitride Core/Shell p-n Junction Nanowires

Abstract: A flexible nitride p-n photodiode is demonstrated. The device consists of a composite nanowire/polymer membrane transferred onto a flexible substrate. The active element for light sensing is a vertical array of core/shell p–n junction nanowires containing InGaN/GaN quantum wells grown by MOVPE. Electron/hole generation and transport in core/shell nanowires are modeled within nonequilibrium Green function formalism showing a good agreement with experimental results. Fully flexible transparent contacts based on a silver nanowire network are used for device fabrication, which allows bending the detector to a few millimeter curvature radius without damage. The detector shows a photoresponse at wavelengths shorter than 430 nm with a peak responsivity of 0.096 A/W at 370 nm under zero bias. The operation speed for a 0.3 × 0.3 cm2 detector patch was tested between 4 Hz and 2 kHz. The −3 dB cutoff was found to be ∼35 Hz, which is faster than the operation speed for typical photoconductive detectors and which is c...

Properties of Plasmon-Induced Photoelectric Conversion on a TiO2/NiO p-n Junction with Au Nanoparticles

Abstract: We have successfully fabricated all-solid-state plasmonic photoelectric conversion devices composed of titanium dioxide (TiO2)/nickel oxide (NiO) p–n junctions with gold nanoparticles (Au-NPs) as prototype devices for a plasmonic solar cell. The characteristics of the crystal structures and the photoelectric properties of the all-solid-state devices were demonstrated. We observed that the crystalline structure of the NiO thin film and the interfacial structure of TiO2/Au-NPs/NiO changed significantly during an annealing treatment. Furthermore, the photoelectric conversion devices exhibited plasmon-induced photocurrent generation in the visible-wavelength region. The photocurrent may result from plasmon-induced charge separation. The photoelectric conversion properties via plasmon-induced charge separation were strongly correlated with the morphology of the TiO2/Au-NPs/NiO interface. The long-term stability of the plasmonic photoelectric conversion device was found to be very high because a stable photocur...

Sb2S3/Spiro-OMeTAD Inorganic–Organic Hybrid p–n Junction Diode for High Performance Self-Powered Photodetector

Abstract: Organic–inorganic hybrid diodes are very promising for solution processing, low cost, high performance optoelectronic devices. Here, we report a high quality p–n heterojunction diode composed of n-type inorganic Sb2S3 and p-type organic 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) with a rectification ratio of ∼102 at an applied bias of 1 V. On illumination with visible light (470 nm, 1.82 mW/cm2), the current value in our device becomes 8 × 102 times that of its dark value even at a zero bias condition. The estimated responsivity value at zero bias is 0.087 A/W which is so far the highest reported for any organic–inorganic hybrid photodiode, to the best of our knowledge. It also exhibits a fast photoresponse time of <25 ms (instrumental limit). More importantly, our device can also detect visible light with power density as low as 8 μW/cm2 with a photocurrent density of 1.2 μA/cm2 and a photocurrent to dark current ratio of more than 8. We also demonstrate that the...

On-chip photonic system using suspended p-n junction InGaN/GaN multiple quantum wells device and multiple waveguides

Abstract: We propose, fabricate, and characterize the on-chip integration of suspended p-n junction InGaN/GaN multiple quantum wells(MQWs) device and multiple waveguides on the same GaN-on-silicon platform. The integrated devices are fabricated via a wafer-level process and exhibit selectable functionalities for diverse applications. As the suspended p-n junction InGaN/GaN MQWs device operates under a light emitting diode(LED) mode, part of the light emission is confined and guided by the suspended waveguides. The in-plane propagation along the suspended waveguides is measured by a micro-transmittance setup. The on-chip data transmission is demonstrated for the proof-of-concept photonic integration. As the suspended p-n junction InGaN/GaN MQWs device operates under photodiode mode, the light is illuminated on the suspended waveguides with the aid of the micro-transmittance setup and, thus, coupled into the suspended waveguides. The guided light is finally sensed by the photodiode, and the induced photocurrent trace shows a distinct on/off switching performance. These experimental results indicate that the on-chip photonic integration is promising for the development of sophisticated integrated photonic circuits in the visible wavelength region.

Electrostatically tunable lateral MoTe2 p-n junction for use in high-performance optoelectronics.

Abstract: Because of their ultimate thickness, layered structure and high flexibility, pn junctions based on layered two-dimensional semiconductors have been attracting increasing attention recently. In this study, for the first time, we fabricated lateral pn junctions (LPNJs) based on ultrathin MoTe2 by introducing two separated electrostatic back gates, and investigated their electronic and photovoltaic performance. Pn, np, nn, and pp junctions can be easily realized by modulating the conductive channel type using gate voltages with different polarities. Strong rectification effects were observed in the pn and np junctions and the rectification ratio reached ∼5 × 10(4). Importantly, we find a unique phenomenon that the parameters for MoTe2 LPNJs experience abrupt changes during the transition from p to n or n to p. Furthermore, a high performance photovoltaic device with a filling factor of above 51% and electrical conversion efficiency (η) of around 0.5% is achieved. Our findings are of importance to comprehensively understand the electronic and optoelectronic properties of MoTe2 and may further open up novel electronic and optoelectronic device applications.

A CuO–ZnO nanostructured p–n junction sensor for enhanced N-butanol detection

Abstract: Herein, a novel CuO–ZnO nanostructured p–n junction composite is prepared via the hydrothermal method. It is composed of a ZnO two dimensional (2-D) porous nanosheet assembly and leaf-like 2-D CuO nanoplates. Then, its gas sensing performance toward n-butanol is studied. The 2-D/2-D CuO–ZnO composite sensor shows 2.7 times higher sensitivity than that of pure ZnO at 220 °C. Moreover, its response to n-butanol is 3.5–84 times higher than those for other target gases. This reveals an excellent selectivity toward n-butanol. Its detection limit for n-butanol is calculated to be 0.4 ppm, indicating a potential advantage in low concentration detection. The significant enhancement of the composite's sensing performance can be firstly attributed to the p–n junction, which brings electronic sensitization for the composite sensor. Moreover, the porous structure and the open 2-D/2-D heterostructure also contribute to the sensing performance of the composite. These allow the gas molecules to diffuse rapidly, making chemisorption and surface reactions on the p–n junction more easy.

In-plane topological p-n junction in the three-dimensional topological insulator Bi 2−x Sb x Te 3−y Se y

Abstract: A topological p-n junction (TPNJ) is an important concept to control spin and charge transport on a surface of three-dimensional topological insulators (3D-TIs). Here we report successful fabrication of such TPNJ on a surface of 3D-TI Bi2−xSbxTe3−ySey thin films and experimental observation of the electrical transport. By tuning the chemical potential of n-type topological Dirac surface of Bi2−xSbxTe3−ySey on its top half by using tetrafluoro-7,7,8,8-tetracyanoquinodimethane as an organic acceptor molecule, a half surface can be converted to p-type with leaving the other half side as the opposite n-type, and consequently TPNJ can be created. By sweeping the back-gate voltage in the field effect transistor structure, the TPNJ was controlled both on the bottom and the top surfaces. A dramatic change in electrical transport observed at the TPNJ on 3D-TI thin films promises novel spin and charge transport of 3D-TIs for future spintronics. Dirac cone surface states rectify an ultralow dissipative spin and charge current, but it is yet to be confirmed in devices. Here, Tuet al. observe p-type electrical transport on one half surface and n-type on the other in Bi2−xSbxTe3−ySeythin films, realizing a topological p-n junction.

High resolution scanning optical imaging of a frozen polymer p-n junction

Abstract: Semiconductor homojunctions such as p-n or p-i-n junctions are the building blocks of many semiconductor devices such as diodes, photodetectors, transistors, or solar cells. The determination of junction depletion width is crucial for the design and realization of high-performance devices. The polymer analogue of a conventional p-n or p-i-n junction can be created by in situ electrochemical doping in a polymer light-emitting electrochemical cell (LEC). As a result of doping and junction formation, the LECs possess some highly desirable device characteristics. The LEC junction, however, is still poorly understood due to the difficulties of characterizing a dynamic-junction device. Here, we report concerted optical-beam-induced-current (OBIC) and scanning photoluminescence (PL) imaging studies of planar LECs that have been frozen to preserve the doping profile. By optimizing the cell composition, the electrode work function, and the turn-on conditions, we realize a long, straight, and highly emissive p-n ju...

Experimental Realization of a Topological p-n Junction by Intrinsic Defect Grading.

Abstract: A Bi2Te3 single crystal is grown with the modified Bridgman technique. The crystal has a nominal composition with a Te content of 61 mol% resulting in the existence of two distinct regions, p- and n-doped, respectively; color-coded tunneling spectra are taken over 60 nm at the transition region.

Barrier inhomogeneities limited current and 1/f noise transport in GaN based nanoscale Schottky barrier diodes.

Abstract: The electrical behaviour of Schottky barrier diodes realized on vertically standing individual GaN nanorods and array of nanorods is investigated. The Schottky diodes on individual nanorod show highest barrier height in comparison with large area diodes on nanorods array and epitaxial film which is in contrast with previously published work. The discrepancy between the electrical behaviour of nanoscale Schottky diodes and large area diodes is explained using cathodoluminescence measurements, surface potential analysis using Kelvin probe force microscopy and 1ow frequency noise measurements. The noise measurements on large area diodes on nanorods array and epitaxial film suggest the presence of barrier inhomogeneities at the metal/semiconductor interface which deviate the noise spectra from Lorentzian to 1/f type. These barrier inhomogeneities in large area diodes resulted in reduced barrier height whereas due to the limited role of barrier inhomogeneities in individual nanorod based Schottky diode, a higher barrier height is obtained.

Photocurrent enhancement of graphene phototransistors using p–n junction formed by conventional photolithography process

Abstract: A p–n junction was developed in a graphene transistor by a simple photolithography process used in typical semiconductor processes. The p- and n-type regions were formed by coating photoresist on part of the graphene channel and immersion of the uncovered graphene region in alkali developer, respectively. A 3-fold enhancement of the photocurrent was observed at the maximum field effect mobility. It is therefore important to maximize the field effect mobility by doping to maximize the photocurrent. The results obtained here are an important step toward the production of high-sensitivity graphene-based phototransistors compatible with conventional industrial procedures.

Microwave Photodetection in an Ultraclean Suspended Bilayer Graphene p–n Junction

Abstract: We explore the potential of bilayer graphene as a cryogenic microwave photodetector by studying the microwave absorption in fully suspended clean bilayer graphene p–n junctions in the frequency range of 1–5 GHz at a temperature of 8 K. We observe a distinct photocurrent signal if the device is gated into the p–n regime, while there is almost no signal for unipolar doping in either the n–n or p–p regimes. Most surprisingly, the photocurrent strongly peaks when one side of the junction is gated to the Dirac point (charge-neutrality point CNP), while the other remains in a highly doped state. This is different to previous results where optical radiation was used. We propose a new mechanism based on the phototermal effect explaining the large signal. It requires contact doping and a distinctly different transport mechanism on both sides: one side of graphene is ballistic and the other diffusive. By engineering partially diffusive and partially ballistic devices, the photocurrent can drastically be enhanced.

Spatial Control of Laser-Induced Doping Profiles in Graphene on Hexagonal Boron Nitride

Abstract: We present a method to create and erase spatially resolved doping profiles in graphene-hexagonal boron nitride heterostructures. The technique is based on photoinduced doping by a focused laser beam and does neither require masks nor photoresists. This makes our technique interesting for rapid prototyping of unconventional electronic device schemes, where the spatial resolution of the rewritable, long-term stable doping profiles is limited by only the laser spot size (≈600 nm) and the accuracy of sample positioning. Our optical doping method offers a way to implement and to test different, complex doping patterns in one and the very same graphene device, which is not achievable with conventional gating techniques.

Efficient energy harvesting of a GaN p–n junction piezoelectric generator through suppressed internal field screening

Abstract: A high-efficiency GaN-based thin film piezoelectric energy harvester was demonstrated by suppressed screening of a piezoelectric field with the aid of a p–n diode junction. Piezoelectric field screening was effectively controlled by the deposition of highly resistive p-type GaN. The semi-intrinsic property of Mg-doped GaN and improved junction quality successfully suppressed internal screening, which resulted in a significantly enhanced output voltage up to 8.1 V and a maximum output current density of 3.0 μA cm−2. The energy-harvesting capabilities of the device were evaluated by charging a commercial capacitor, and self-powered light-emitting diode operation was demonstrated using the fabricated generator.

Flexible Transparent Field‐Effect Diodes Fabricated at Low‐Temperature with All‐Oxide Materials

Abstract: DOI: 10.1002/aelm.201500486 of our knowledge, the first flexible and fully transparent fieldeffect diode (FED) fabricated at low-temperature with all oxide materials, using diode-connected thin-film transistor architecture. Conventional thin-film transistors were also fabricated at the same time as reference. The diodes exhibited a high rectification ratio of 5 × 108 and low leakage current of 1 pA, same as the on/off ratio and off current in the referenced TFT. Technology computer aided design (TCAD) simulation was employed to explore its working mechanism. Finally, a singlestage rectifier was demonstrated by applying this unique FED to rectify alternating current (AC) signals with different amplitudes and frequencies. For ease of understanding, a conceptualized schematic of FED is shown in Figure 1a. The device is two-terminal contacted, with dielectric and channel layers stacked inside. A lowtemperature (≤100 °C) process (Figure 1b) was used to fabricate the devices. (Details of the fabrication process can be found in Experimental Section.) During the same process, a conventional TFT was fabricated as well to serve as reference (see the top view in Figure 1c). Both of the devices on polyethylene naphthalate (PEN) and glass substrates are optically transparent, with the whole devices (including the substrates) exhibiting a transmittance over 80% in full visible spectral range (Figure 1d). The referenced TFT adopted a staggered bottom-gate structure, with channel width/length (W/L) of 300/20 μm. Figure 2a shows the transfer characteristics of referenced TFT on PEN substrates (IDS–VGS, DS denotes drain to source and GS gate to source). An on/off current ratio of 5 × 108 was obtained by operating the TFT at VDS = 3 V and VGS = ±20 V. The fieldeffect mobility (μeff) of 11.56 cm2 V−1 s−1 was calculated from the linear region. The SS was determined to be 0.53 V dec−1, calculated using the minimum value of 1/(∂log(IDS)/∂VGS) versus VGS plot. The turn-on voltage (VON) was read out to be ≈0 V from the transfer curve. Gate oxide capacitance (Cox) of 1.5 × 10−7 F cm−2 was extracted from capacitance–voltage (C–V) measurement curve (not shown here). Figure 2b shows the IDS–VDS output characteristics at VGS = 5–10 V, which exhibits typical square-law behavior. It should be noted that good ohmic contact was formed at the interface of indium tin oxide/zinc oxide (ITO/ZnO), so no rectifying property was expected from source and drain contacts. These properties in referenced TFT are important, as the field-effect diode has the identical material quality and will follow the same field-effect principles. Devices on glass substrates have similar characteristics with those on PEN, so, to avoid repetition, the electrical characteristics in this paper are all carried out on the PEN devices. Figure 2c shows the current–voltage (I–V) characteristics of FED in flat and bent states, respectively (see Figure 2d). A high rectification ratio of 5 × 108 was obtained at V = ±20 V, which is much higher than most of the reported Schottky and pn junction Flexible and transparent electronics[1–3] have gained momentum in the last decade, owing to their great potential in future technological applications.[4–6] Most of the researches, concerning about inorganic semiconductors, have been generally involved in metal oxide semiconductors, as they are optically transparent and compatible with low temperature process. Flexible and transparent oxide thin-film transistors (TFTs), as key devices for realizing next generation circuits, have been extensively studied both on glass and plastic substrates during these years.[7–9] High performances with field-effect mobility more than 10 cm2 V−1 s−1, on/off current ratio more than 108, and subthreshold swing (SS) less than 0.5 V dec−1 were obtained.[7–9] Besides TFTs, thin-film diodes (TFDs) are important components to achieve electronic circuits, especially for energy conversion[10,11] and selective switching.[12,13] However, few researches have focused on flexible or transparent diodes. The limited reports can be categorized into 4 types: (1) pn heterojunction diode.[14–19] As most of the widebandgap semiconductors are n-type conductive, a proper p-type wide-bandgap material must be chosen wisely to form a large built-in potential barrier. (2) Schottky junction diode.[20–23] The electron affinities (χ) of most wide-bandgap materials are more than 4 eV, thus only a small Schottky barrier height could be formed with non-noble metals. (3) Metal-insulatesemiconductor diode.[24] As in Schottky diode, a large difference between metal work function (ΦM) and semiconductor affinity (χ) is needed to achieve a large rectification ratio. (4) Metal-insulator-metal (MIM) diode.[25,26] Actually, it is not easy for MIM diodes to be applied in transparent circuits because of the difficulties to find two kinds of transparent electrodes with large work function difference. (5) Self-switching diode.[27] Besides small rectification ratio, this kind of device involves nanofabrication, which may bring high costs and challenges in technology compatibility. Diode-connected field-effect transistor/bipolar junction transistor, with drain/collector and gate/base electrodes shorted, is widely used in integrated circuits to serve as passive load.[28] Because of its asymmetric current–voltage characteristics,[29,30] diode-connected transistor is also used as rectification device in energy harvest systems.[31,32] This paper reports, to the best www.MaterialsViews.com www.advelectronicmat.de

Method to improve the linearity of the silicon Mach-Zehnder optical modulator by doping control

Abstract: We optimize the linearity performance of silicon carrier-depletion Mach-Zehnder optical modulator through controlling the doping concentration. The optical field distribution in the waveguide is a Gaussian-like distribution. As the doping concentration increases, the dynamic depletion width of the PN junction under the same modulation signal will decrease, and the integration width of the overlap between the Gaussian-like optical field distribution and the depletion region will become smaller. Therefore the modulated signal has less nonlinear components. Our simulation results proved this analysis. We also fabricated different devices with different doping concentrations. By adopting a ten times doping concentration, the spurious free dynamic range (SFDR) for third-order intermodulation distortion (TID) increases from 109.2 dB.Hz2/3 to 113.7 dB.Hz2/3 and the SFDR for second harmonic distortion (SHD) increases from 87.6 dB.Hz1/2 to 97.5 dB.Hz1/2 at a driving frequency of 2 GHz. When the driving frequency is 20 GHz, the SFDRs for TID and SHD distortions are 110.3 dB.Hz2/3 and 96 dB.Hz1/2, respectively.

THz Detection Using p + /n-Well Diodes Fabricated in 45-nm CMOS

Abstract: Electronic-detection up to $\sim 0.9$ THz using p+/n-well junction diodes in a 45-nm bulk CMOS process is demonstrated. Because the 1/f noise corner frequency is $\sim 1$ kHz instead of $\sim 10$ MHz common to Schottky and diode-connected nMOS transistor detectors, despite lower responsivity, detectors using a p+/n-well diode with an optimized transit time achieve competitive noise equivalent power (NEP) while exhibiting smaller variations. The junction diode has a measured zero-bias cutoff frequency ( $f_{T}$ ) of $\sim 1.8$ THz. The direct-antenna matched structure can reach a peak optical responsivity ( $R_{v}$ ) of 558 V/W at 0.781 THz with a minimum optical NEP of 56 pW/Hz0.5 at a modulation frequency of 100 kHz.

Integrated p–n junction InGaN/GaN multiple-quantum-well devices with diverse functionalities

Abstract: We propose, fabricate, and demonstrate integrated p–n junction InGaN/GaN multiple-quantum-well devices with diverse functionalities on a GaN-on-silicon platform. Suspended devices with a common n-contact are realized using a wafer-level process. For the integrated devices, part of the light emitted by a light-emitting diode (LED) is guided in-plane through a suspended waveguide and is sensed by another photodiode. The induced photocurrent is tuned by the LED. The integrated devices can act as two independent LEDs to deliver different signals simultaneously for free-space visible light communication. Furthermore, the suspended devices can be used as two separate photodiodes to detect incident light with a distinct on/off switching performance.