Showing papers on "Depletion region published in 2018"
TL;DR: The distinctive WSe2 /SnS2 vdW heterostructure exhibits both ultrahigh photodetectivity of 1.29 × 1013 Jones (Iph /Idark ratio of ≈106 ) and photoresponsivity of 244 A W-1 at a reverse bias under the illumination of 550 nm light (3.77 mW cm-2 ).
Abstract: van der Waals (vdW) heterostructures based on atomically thin 2D materials have led to a new era in next-generation optoelectronics due to their tailored energy band alignments and ultrathin morphological features, especially in photodetectors. However, these photodetectors often show an inevitable compromise between photodetectivity and photoresponsivity with one high and the other low. Herein, a highly sensitive WSe2 /SnS2 photodiode is constructed on BN thin film by exfoliating each material and manually stacking them. The WSe2 /SnS2 vdW heterostructure shows ultralow dark currents resulting from the depletion region at the junction and high direct tunneling current when illuminated, which is confirmed by the energy band structures and electrical characteristics fitted with direct tunneling. Thus, the distinctive WSe2 /SnS2 vdW heterostructure exhibits both ultrahigh photodetectivity of 1.29 × 1013 Jones (Iph /Idark ratio of ≈106 ) and photoresponsivity of 244 A W-1 at a reverse bias under the illumination of 550 nm light (3.77 mW cm-2 ).
268 citations
TL;DR: A gold-induced NH4Cl-assisted vapor-based route is proposed and developed to achieve vertically aligned submicron Se crystals on lattice-matched (111)-oriented silicon substrates, based on which a high-performance large-area silicon-compatible photodetector is constructed.
Abstract: A gold-induced NH4Cl-assisted vapor-based route is proposed and developed to achieve vertically aligned submicron Se crystals on lattice-matched (111)-oriented silicon substrates, based on which a high-performance large-area silicon-compatible photodetector is constructed. Thanks to the energy band structure and the strongly asymmetrical depletion region, the fabricated Se/Si device maintains a similar wavelength cutoff to that of selenium devices before the IR region, along with a high-performance broadband photoresponse in the UV-to-visible region. The large-area photodetector maintains a very low leakage current under a −2 V bias, and a high on/off ratio of 103–104 is obtained with a high photocurrent of 62 nA at 500 nm. A photoresponse is clearly observed when the bias voltage is removed. The pulse response precisely provides a high response speed (τrise + τfall ≈ 1.975 ms), exceeding the fastest Se-based photodetectors in current reports. The enhanced photoelectric properties and the self-power photo...
192 citations
TL;DR: Strong depletion in a lateral p-n junction induced by local electronic doping at the surface of individual CH3 NH3 PbI3 perovskite nanosheets is reported and under visible optical excitation without electrical bias, the lateral diode demonstrates unprecedented photovoltaic conversion.
Abstract: A semiconductor p-n junction typically has a doping-induced carrier depletion region, where the doping level positively correlates with the built-in potential and negatively correlates with the depletion layer width. In conventional bulk and atomically thin junctions, this correlation challenges the synergy of the internal field and its spatial extent in carrier generation/transport. Organic-inorganic hybrid perovskites, a class of crystalline ionic semiconductors, are promising alternatives because of their direct badgap, long diffusion length, and large dielectric constant. Here, strong depletion in a lateral p-n junction induced by local electronic doping at the surface of individual CH3 NH3 PbI3 perovskite nanosheets is reported. Unlike conventional surface doping with a weak van der Waals adsorption, covalent bonding and hydrogen bonding between a MoO3 dopant and the perovskite are theoretically predicted and experimentally verified. The strong hybridization-induced electronic coupling leads to an enhanced built-in electric field. The large electric permittivity arising from the ionic polarizability further contributes to the formation of an unusually broad depletion region up to 10 µm in the junction. Under visible optical excitation without electrical bias, the lateral diode demonstrates unprecedented photovoltaic conversion with an external quantum efficiency of 3.93% and a photodetection responsivity of 1.42 A W-1 .
154 citations
TL;DR: Fundamental aspects of LSPR modulation through dynamic carrier density tuning in Sn-doped In2O3 (Sn:In 2O3) NCs are elucidated and potential applications in smart optoelectronics, catalysis and sensing are suggested.
Abstract: Degenerately doped semiconductor nanocrystals (NCs) exhibit a localized surface plasmon resonance (LSPR) in the infrared range of the electromagnetic spectrum. Unlike metals, semiconductor NCs offer tunable LSPR characteristics enabled by doping, or via electrochemical or photochemical charging. Tuning plasmonic properties through carrier density modulation suggests potential applications in smart optoelectronics, catalysis and sensing. Here, we elucidate fundamental aspects of LSPR modulation through dynamic carrier density tuning in Sn-doped In2O3 (Sn:In2O3) NCs. Monodisperse Sn:In2O3 NCs with various doping levels and sizes were synthesized and assembled in uniform films. NC films were then charged in an in situ electrochemical cell and the LSPR modulation spectra were monitored. Based on spectral shifts and intensity modulation of the LSPR, combined with optical modelling, it was found that often-neglected semiconductor properties, specifically band structure modification due to doping and surface states, strongly affect LSPR modulation. Fermi level pinning by surface defect states creates a surface depletion layer that alters the LSPR properties; it determines the extent of LSPR frequency modulation, diminishes the expected near-field enhancement, and strongly reduces sensitivity of the LSPR to the surroundings.
121 citations
TL;DR: In this paper, a back-illuminated three-dimensional stacked single-photon avalanche diode (SPAD) was implemented in 45-nm CMOS technology for the first time.
Abstract: We present a high-performance back-illuminated three-dimensional stacked single-photon avalanche diode (SPAD), which is implemented in 45-nm CMOS technology for the first time. The SPAD is based on a P+/Deep N-well junction with a circular shape, for which N-well is intentionally excluded to achieve a wide depletion region, thus enabling lower tunneling noise and better timing jitter as well as a higher photon detection efficiency and a wider spectrum. In order to prevent premature edge breakdown, a P-type guard ring is formed at the edge of the junction, and it is optimized to achieve a wider photon-sensitive area. In addition, metal-1 is used as a light reflector to improve the detection efficiency further in backside illumination. With the optimized 3-D stacked 45-nm CMOS technology for back-illuminated image sensors, the proposed SPAD achieves a dark count rate of 55.4 cps/μm2 and a photon detection probability of 31.8% at 600 nm and over 5% in the 420–920 nm wavelength range. The jitter is 107.7 ps full width at half-maximum with negligible exponential diffusion tail at 2.5 V excess bias voltage at room temperature. To the best of our knowledge, these are the best results ever reported for any back-illuminated 3-D stacked SPAD technologies.
110 citations
01 Feb 2018
TL;DR: In this paper, a vertical GaTe-InSe van der Waals (vdWs) p-n heterojunction was fabricated by a PDMS-assisted transfer technique without etching.
Abstract: p–n junctions serve as the building blocks for fundamental semiconductor devices, such as solar cells, light-emitting diodes (LEDs) and photodetectors. With recent studies unveiling the excellent optoelectronic properties of two-dimensional (2D) semiconductors, they are considered to be superb candidates for high performance p–n junctions. Here, we fabricate a vertical GaTe–InSe van der Waals (vdWs) p–n heterojunction by a PDMS-assisted transfer technique without etching. The fabricated p–n heterojunction shows gate-tunable current-rectifying behavior with a rectification factor reaching 1000. In addition, it features fast photodetection under zero bias as well as a high power conversion efficiency (PCE). Under 405 nm laser excitation, the zero-biased photodetector shows a high responsivity of 13.8 mA W−1 as well as a high external quantum efficiency (EQE) of 4.2%. Long-term stability is also observed and a response time of 20 µs is achieved due to stable and fast carrier transit through the built-in electric field in the depletion region. Fast and efficient charge separation in the vertical 2D p–n junction paves the way for developing 2D photodetectors with zero dark current, high speed and low power consumption.
78 citations
TL;DR: In this paper, a p-n heterojunction at the illumination side with smooth band alignment and the absence of serious interface carrier recombination was constructed by inserting a layer of slightly doped p-type QDs with 1,2-ethanedithiol as ligands.
Abstract: Highly efficient PbS colloidal quantum dot (QD) solar cells based on an inverted structure have been missing for a long time. The bottlenecks are the construction of an effective p-n heterojunction at the illumination side with smooth band alignment and the absence of serious interface carrier recombination. Here, solution-processed nickel oxide (NiO) as the p-type layer and lead sulfide (PbS) QDs with iodide ligand as the n-type layer are explored to build a p-n heterojunction at the illumination side. The large depletion region in the QD layer at the illumination side leads to high photocurrent. Interface carrier recombination at the interface is effectively prohibited by inserting a layer of slightly doped p-type QDs with 1,2-ethanedithiol as ligands, leading to improved voltage of the device. Based on this graded device structure design, the efficiency of inverted structural heterojunction PbS QD solar cells is improved to 9.7%, one time higher than the highest efficiency achieved before.
78 citations
TL;DR: In this article, a broadband self-powered photodetector based on graphene/GaAs van der Waals heterojunction is reported, which achieved the maximum photocurrent responsivity of 210 µm/W−1 (increased by 38%) and detectivity of 2.98 µm /W−2 Jones (increases by 202%).
72 citations
TL;DR: In this paper, a continuous 2D analytical drain current model of double-gate (DG) heterojunction tunnel field effect transistors (HJTFETs) with a SiO2/HfO2 stacked gate-oxide structures is presented.
Abstract: A continuous 2-D analytical drain current model of double-gate (DG) heterojunction tunnel field-effect transistors (HJTFETs) with a SiO2/HfO2 stacked gate-oxide structures has been presented in this paper. The surface potential model has been developed by considering the effect of accumulation/inversion charges and depletion region at source/channel and drain/channel junctions. The electric field-dependent band-to-band tunneling generation rate has been derived from the surface potential model. The tangent line approximation method has been used to calculate the drain current of DG HJTFETs. The developed model is valid for all regions (subthreshold to strong accumulation/inversion region) of operation. The model has been developed for Si/Ge hetero and Si homojunction-based tunnel field-effect transistor devices. The model is also applicable for other structures such as III–V materials-based InAs/GaSb DG HJTFET and silicon-on-insulator-based HJTFET. The analytical model results are validated by 2-D ATLAS simulation data.
59 citations
TL;DR: A new CQD ink that is stable in nonpolar solvents is developed via a neutral donor ligand that functions as a phase-transfer catalyst that enables the realization of an efficient graded architecture that improves the built-in field and charge extraction.
Abstract: The best-performing colloidal-quantum-dot (CQD) photovoltaic devices suffer from charge recombination within the quasi-neutral region near the back hole-extracting junction. Graded architectures, which provide a widened depletion region at the back junction of device, could overcome this challenge. However, since today's best materials are processed using solvents that lack orthogonality, these architectures have not yet been implemented using the best-performing CQD solids. Here, a new CQD ink that is stable in nonpolar solvents is developed via a neutral donor ligand that functions as a phase-transfer catalyst. This enables the realization of an efficient graded architecture that, with an engineered band-alignment at the back junction, improves the built-in field and charge extraction. As a result, optimized IR CQD solar cells (Eg ≈ 1.3 eV) exhibiting a power conversion efficiency (PCE) of 12.3% are reported. The strategy is applied to small-bandgap (1 eV) IR CQDs to augment the performance of perovskite and crystalline silicon (cSi) 4-terminal tandem solar cells. The devices show the highest PCE addition achieved using a solution-processed active layer: a value of +5% when illuminated through a 1.58 eV bandgap perovskite front filter, providing a pathway to exceed PCEs of 23% in 4T tandem configurations with IR CQD PVs.
59 citations
TL;DR: This work employs a novel concept involving the modulation of the built-in potential within the QD layers for creating a new hybrid MoS2/PbS QDs phototransistor with consecutive type II junctions that improves the photoresponse and decreases the response times.
Abstract: Phototransistors that are based on a hybrid vertical heterojunction structure of two-dimensional (2D)/quantum dots (QDs) have recently attracted attention as a promising device architecture for enhancing the quantum efficiency of photodetectors. However, to optimize the device structure to allow for more efficient charge separation and transfer to the electrodes, a better understanding of the photophysical mechanisms that take place in these architectures is required. Here, we employ a novel concept involving the modulation of the built-in potential within the QD layers for creating a new hybrid MoS2/PbS QDs phototransistor with consecutive type II junctions. The effects of the built-in potential across the depletion region near the type II junction interface in the QD layers are found to improve the photoresponse as well as decrease the response times to 950 μs, which is the faster response time (by orders of magnitude) than that recorded for previously reported 2D/QD phototransistors. Also, by implement...
TL;DR: In this article, a silver (Ag) mixed Cu2ZnSnS4 (ACZTS) based solar cell architecture was proposed to improve the efficiency of single junction kesterite solar cells.
Abstract: We propose a silver (Ag) mixed Cu2ZnSnS4 (ACZTS) based solar cell architecture to improve the efficiency of single junction Cu2ZnSnS4 (CZTS) solar cells The configuration exploits enhancement of depletion region using a CdS/ACZTS/CZTS architecture The doping concentration of different layers is adapted such that the primary absorber layer (ACZTS) may become fully depleted and CZTS acts as back surface field layer We analyze the prospect and performance of the proposed architecture through rigorous optoelectronic simulations We also study the role of the Schottky barrier at the back-contact interface of a conventional CZTS cell In this regard, we propose to use an Ohmic contact to increase the open circuit voltage by replacing the molybdenum (Mo) with indium tin oxide (ITO) We further optimize the ACZTS thickness and calculated a maximum obtainable efficiency of 1759% at 550 nm ACZTS with 940 mV open circuit voltage, 2465 mA cm−2 short circuit current and 7594% fill factor including the effects of Shockley-Read-Hall, radiative and surface recombination mechanisms The efficiency of the optimized cell is ∼66% higher than that of the existing best single junction kesterite cell We also vary the minority carrier life time (τc) and surface recombination velocity of back contact (SRVback) and report an ideal efficiency of 2214% with τc = 1 μs and SRVback = 1000 cm s−1 Finally, we replace the toxic CdS buffer layer with eco-friendly ZnS and observe a relative improvement of 1291% in the efficiency The concept proposed and analyses performed in this work advance the efficiency of single junction kesterite solar cells
TL;DR: In this article, a ferroelectric-semiconductor hybrid structure for photoelectrochemical applications was designed and fabricated, and the photocurrents of the hybrid photoanodes were enhanced by 60 ± 5% and 85 ± 15% with water oxidation and reduction respectively under the illumination of a monochromater (λ = 365nm).
13 Jun 2018
TL;DR: In this article, a flexible photodiode based on monolayer MoS2 lateral p-n homojunction with significant enhancement in photoresponsivity and detectivity was developed.
Abstract: Transition-metal dichalcogenides (TMDCs) have recently open a new perspective in electronics and optoelectronics due to their unique planar crystal structures and incredible physical characteristics. Strong in-plane piezoelectricity is their unique property owing to non-centrosymmetric structure, differing from other two dimension (2D) materials, such as graphene and black phosphorus. In this work, we develop a flexible photodiode based on monolayer MoS2 lateral p-n homojunction with significant enhancement in photoresponsivity and detectivity. Piezo-phototronic effect is used to achieve this enhancement by adjusting the barrier height and broadening depletion zone at p-n junction interface under external strain. The wider depletion zone benefits the separation and transport of photogenerated carriers, thus enhancing the photocurrent. When a 0.51% external static tensile strain was applied, the photoresponsivity and detectivity are improved up to 1162 A W−1 and 1.72 × 1012 Jones, with about 619% and 319% enhancement compared with strain-free state, respectively. Consequently, this work provides an effective strategy to utilize unavoidable external strain to improve TMDCs-based optoelectronic devices performance. At the same time, it has reference meaning to achieve flexible, low-consumption and high-performance 2D devices without electric gate-control.
TL;DR: In this article, a simple ultrasound-assisted method was used for fabrication of Au/(ZnO-PVA)/n-Si structures and the measured capacitance and conductance have a strong function of frequency and voltage in depletion and accumulation regions.
21 Feb 2018
TL;DR: In this paper, a tunneling barrier device made of 20 nm thick Sb2Te3 layer deposited onto 500 nm thick CdS is designed and characterized by means of x-ray diffraction and impedance spectroscopy techniques.
Abstract: In the current work, a tunneling barrier device made of 20 nm thick Sb2Te3 layer deposited onto 500 nm thick CdS is designed and characterized. The design included a Yb metallic substrate and Ag point contact of area of 10−3 cm2. The heterojunction properties are investigated by means of x-ray diffraction and impedance spectroscopy techniques. It is observed that the coating of the Sb2Te3 onto the surface of CdS causes a further deformation to the already strained structure of hexagonal CdS. The designed energy band diagram for the CdS/Sb2Te3 suggests a straddling type of heterojunction with an estimated conduction and valence band offsets of 0.35 and 1.74 eV, respectively. In addition, the analysis of the capacitance-voltage characteristic curve revealed a depletion region width of 14 nm. On the other hand, the capacitance and conductivity spectra which are analyzed in the frequency domain of 0.001–1.80 GHz indicated that the conduction in the device is dominated by the quantum mechanical tunneling in the region below 0.26 GHz and by the correlated barrier hopping in the remaining region. While the modeling of the conductivity spectra allowed investigation of the density of states near Fermi levels and an average scattering time of 1.0 ns, the capacitance spectra exhibited resonance at 0.26 GHz followed by negative differential capacitance effect in the frequency domain of 0.26–1.8 GHz. Furthermore, the evaluation of the impedance and reflection coefficient spectra indicated the usability of these devices as wide range low pass filters with ideal values of voltage standing wave ratios.
TL;DR: A buried metal layer (BML) of appropriate workfunction is used to create a Schottky junction at the bottom of Si device layer, whereas the source–channel–drain path is junctionless and hence named the buried-metal-soI-lateral JLT (BM-SOI-LJLT).
Abstract: In this letter, we propose a novel structure of an n-channel silicon-on-insulator junctionless transistor (SOI-JLT) with improved ${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}}$ ratio and scalability. A buried metal layer (BML) of appropriate workfunction ( $\phi _{\text {BM}}$ ) is used to create a Schottky junction at the bottom of Si device layer, whereas the source–channel–drain path is junctionless and hence named the buried-metal-SOI-lateral JLT (BM-SOI-LJLT). The BML-induced bottom depletion layer combined with the depletion region due to top gate results in a perfect volume depletion in OFF state. A 2-D calibrated simulation has shown an ${I} _{ \mathrm{\scriptscriptstyle ON}}/{I} _{ \mathrm{\scriptscriptstyle OFF}}$ ratio of ~108 in BM-SOI-LJLT compared to ~2 in the conventional SOI-JLT at $\phi _{\text {BM}}$ of 5.1 eV and a gate length of 20 nm. Furthermore, the lateral band-to-band tunneling parasitic leakage is significantly lower in the BM-SOI-LJLT and does not degrade its ${I} _{ \mathrm{\scriptscriptstyle ON}}/{I} _{ \mathrm{\scriptscriptstyle OFF}}$ ratio. Furthermore, high vertical field due to the Schottky junction minimizes the lateral coupling between the source and drain field lines and thus improves the short-channel-effect suppression and scalability of the proposed device.
TL;DR: In this paper, a self-powered ultraviolet photodetector based on n-GaN and p-NiO was fabricated through thermal oxidation, which has a larger turn-on voltage and a smaller dark current because of the relatively higher effective barrier height.
TL;DR: This study provides new guidelines for flexible optoelectronic devices by demonstrating a heterostructure composed of few-layer ReS2 and WSe2 that exhibits a p-n junction and ann junction in different gate-bias regimes and identifies three carrier-transfer mechanisms.
Abstract: Two-dimensional transition-metal dichalcogenides (TMDCs) are notable materials owing to their flexibility, transparency, and appropriate bandgaps. Because of their unique advantages, TMDC p–n diodes have been studied for next-generation electronics and optoelectronics. However, their efficiency must be increased for commercialization. In this study, we demonstrated a heterostructure composed of few-layer ReS2 and WSe2. This few-layer ReS2/WSe2 heterostructure exhibits a p–n junction and an n–n junction in different gate-bias regimes. In the p–n junction regime, the heterostructure shows outstanding rectification behavior. Additionally, we identify three carrier-transfer mechanisms − direct tunneling, Fowler–Nordheim tunneling, and the space charge region − depending on the drain bias. Furthermore, the photovoltaic effect is observed in this few-layer ReS2/WSe2 heterostructure. As a result, a high fill factor (≈ 0.56), power conversion (≈ 1.5%), and external quantum efficiency (≈ 15.3%) were obtained. This study provides new guidelines for flexible optoelectronic devices.
TL;DR: Finite element simulations of device models provide a detailed understanding of how the electrostatics affect charge transport in nanowire/vdW heterojunctions and inform the design of future vdW heter Mojunction photodetectors and transistors.
Abstract: Layered two-dimensional (2-D) semiconductors can be combined with other low-dimensional semiconductors to form nonplanar mixed-dimensional van der Waals (vdW) heterojunctions whose charge transport behavior is influenced by the heterojunction geometry, providing a new degree of freedom to engineer device functions. Toward that end, we investigated the photoresponse of Si nanowire/MoS2 heterojunction diodes with scanning photocurrent microscopy and time-resolved photocurrent measurements. Comparison of n-Si/MoS2 isotype heterojunctions with p-Si/MoS2 heterojunction diodes under varying biases shows that the depletion region in the p–n heterojunction promotes exciton dissociation and carrier collection. We measure an instrument-limited response time of 1 μs, which is 10 times faster than the previously reported response times for planar Si/MoS2 devices, highlighting the advantages of the 1-D/2-D heterojunction. Finite element simulations of device models provide a detailed understanding of how the electrost...
TL;DR: The SPCM revealed the presence of the depletion layer at the heterojunction, whereas graphene provided an excellent electrical contact for the MoS2 layer without resulting in a rectifying behavior, even if they were anchored within a very short range.
Abstract: We demonstrated imaging of the depletion layer in a MoS2/graphene heterojunction fabricated by chemical vapor deposition and obtained their transport parameters such as diffusion length, lifetime, and mobility by using scanning photocurrent microscopy (SPCM). The device exhibited a n-type operation, which was determined by the MoS2 layer with a lower mobility. The SPCM revealed the presence of the depletion layer at the heterojunction, whereas graphene provided an excellent electrical contact for the MoS2 layer without resulting in a rectifying behavior, even if they were anchored within a very short range. The polarity of the photocurrent signal switched when we applied a drain–source bias voltage, from which we extracted the potential barrier at the junction. More importantly, a bias-dependent SPCM allowed us to simultaneously record the diffusion lengths of both majority and minority carriers for the respective MoS2 and graphene layers. By combining the diffusion lengths with the lifetimes measured by ...
01 Dec 2018
TL;DR: In this article, homoepitaxial GaN p-n junction diodes with novel beveled-mesa structures were fabricated, which showed the breakdown voltages of 180 −480 V, small leakage currents, and excellent avalanche capabilities.
Abstract: We report homoepitaxial GaN p-n junction diodes with novel beveled-mesa structures. The n-layers and p-layers, the doping concentrations of which are comparable, were prepared. We found that electric field crowding does not occur in the structure using TCAD simulation. The fabricated devices showed the breakdown voltages of 180–480 V, small leakage currents, and excellent avalanche capabilities. The breakdown voltages increased at elevated temperature. At the breakdown, nearly uniform luminescence in the entire p-n junctions was observed in all the devices. These results are strong evidences that the uniform avalanche breakdowns occurred in the devices. We carefully characterized the depletion layer width at the breakdown, and the parallel-plane breakdown electric fields of 2.8-3.5 MV/cm were obtained, which are among the best of the reported non-punch-through GaN vertical devices.
09 Feb 2018
TL;DR: In this article, a heterostructured white-light photodetector was fabricated by the sequential deposition of zinc oxide (ZnO), bismuth ferrite (BFO), and poly(3,4-ethylenedioxythiophene)/polystyrene sulfonate (PEDOT:PSS) onto a flexible poly(ethylene terephthalate) (PET) substrate.
Abstract: A heterostructured white-light photodetector was fabricated by the sequential deposition of zinc oxide (ZnO), bismuth ferrite (BFO), and poly(3,4-ethylenedioxythiophene)/polystyrene sulfonate (PEDOT:PSS) onto a flexible poly(ethylene terephthalate) (PET) substrate. Central to this unique structure is an n+–n junction at the ZnO–BFO interface, which allows the device to drive unusually large currents. The intrinsic BFO electric field, arising from the depletion region within the ferroelectric material, is reduced through the combined effect of two barrier fields formed at the BFO–Au and ZnO–BFO interfaces. The combination of these three fields reduces parasitic recombination and causes photoexcited electron–hole pairs to drift to the electrodes. The photocurrent sensitivity and photocurrent gain were determined to be 0.04 A/W and 105, respectively. The decay time extracted from the photoresponse curve was 6 s, whereby the photocurrent drops by a factor of 30. In addition, the device exhibits good flexibili...
TL;DR: In this paper, bipolar resistive switching of the metal-insulator-semiconductor (MIS) capacitor-like structures with the inert Au top electrode and Si3N4 dielectric nanolayer was investigated.
TL;DR: In this paper, the photoresponse of a lateral 2D transition-metal dichalcogenide (TMD) heterostructure using tip-enhanced photoluminescence (TEPL) with nanoscale spatial resolution and with picoscale tip-sample distance dependence was investigated.
Abstract: Lateral two-dimensional (2D) transition-metal dichalcogenide (TMD) heterostructures have recently attracted wide attention as promising materials for optoelectronic nanodevices. Due to the nanoscale width of lateral heterojunctions, the study of their optical properties is challenging and requires using subwavelength optical characterization techniques. We investigated the photoresponse of a lateral 2D $\mathrm{WS}{\mathrm{e}}_{2}/\mathrm{MoS}{\mathrm{e}}_{2}$ heterostructure using tip-enhanced photoluminescence (TEPL) with nanoscale spatial resolution and with picoscale tip-sample distance dependence. We demonstrate the observation of quantum plasmonic effects in 2D heterostructures on a nonmetallic substrate, and we report the nano-optical measurements of the lateral 2D TMD heterojunction width of $\ensuremath{\sim}150$ nm and the charge tunneling distance of $\ensuremath{\sim}20$ pm. Controlling the plasmonic tip location allows for both nano-optical imaging and plasmon-induced hot-electron injection into the heterostructure. By adjusting the tip-sample distance, we demonstrated the controllability of the hot-electron injection via the competition of two quantum plasmonic photoluminescence (PL) enhancement and quenching mechanisms. The directional charge transport in the depletion region leads to the increased hot-electron injection, enhancing the $\mathrm{MoS}{\mathrm{e}}_{2}$ PL signal. The properties of the directional hot-electron injection in the quantum plasmonic regime make the lateral 2D $\mathrm{MoS}{\mathrm{e}}_{2}/\mathrm{WS}{\mathrm{e}}_{2}$ heterostructures promising for quantum nanodevices with tunable photoresponse.
TL;DR: In this paper, a planar solar cell comprising ITO(glass)/PEDOT:PSS/CH3NH3PbI3-xClx/PC60BM/PEI/Ag with a maximum power conversion efficiency (PCE) of 15.4%.
19 Sep 2018
TL;DR: A new boundary condition is proposed, which sets a total current density via an equation expressing the potential gradient as an explicit function of i, and for the first time, the distributions of concentrations, space charge density and current density along the distance to an ion-exchange membrane surface are computed as functions of time in galvanostatic mode.
Abstract: The use of the Nernst⁻Planck and Poisson (NPP) equations allows computation of the space charge density near solution/electrode or solution/ion-exchange membrane interface. This is important in modelling ion transfer, especially when taking into account electroconvective transport. The most solutions in literature use the condition setting a potential difference in the system (potentiostatic or potentiodynamic mode). However, very often in practice and experiment (such as chronopotentiometry and voltammetry), the galvanostatic/galvanodynamic mode is applied. In this study, a depleted stagnant diffusion layer adjacent to an ion-exchange membrane is considered. In this article, a new boundary condition is proposed, which sets a total current density, i, via an equation expressing the potential gradient as an explicit function of i. The numerical solution of the problem is compared with an approximate solution, which is obtained by a combination of numerical solution in one part of the diffusion layer (including the electroneutral region and the extended space charge region, zone (I) with an analytical solution in the other part (the quasi-equilibrium electric double layer (EDL), zone (II). It is shown that this approach (called the "zonal" model) allows reducing the computational complexity of the problem tens of times without significant loss of accuracy. An additional simplification is introduced by neglecting the thickness of the quasi-equilibrium EDL in comparison to the diffusion layer thickness (the "simplified" model). For the first time, the distributions of concentrations, space charge density and current density along the distance to an ion-exchange membrane surface are computed as functions of time in galvanostatic mode. The calculation of the transition time, τ, for an ion-exchange membrane agree with an experiment from literature. It is suggested that rapid changes of space charge density, and current density with time and distance, could lead to lateral electroosmotic flows delaying depletion of near-surface solution and increasing τ.
02 Nov 2018
TL;DR: Gu et al. as discussed by the authors investigated a graphene-silicon p-i-n photodiode defined in a foundry processed planar photonic crystal waveguide structure, achieving visible-near-infrared, zero-bias, and ultrafast photodetection.
Abstract: Sufficiently large depletion region for photocarrier generation and separation is a key factor for two-dimensional material optoelectronic devices, but only a few device configurations have been explored for a deterministic control over the space charge region area in graphene with convincing scalability. Here we investigate a graphene-silicon p-i-n photodiode defined in a foundry processed planar photonic crystal waveguide structure, achieving visible—near-infrared, zero-bias, and ultrafast photodetection. Graphene is electrically contacting to the wide intrinsic region of silicon and extended to the p an n doped region, functioning as the primary photocarrier conducting channel for electronic gain. Graphene significantly improves the device speed through ultrafast out-of-plane interfacial carrier transfer and the following in-plane built-in electric field assisted carrier collection. More than 50 dB converted signal-to-noise ratio at 40 GHz has been demonstrated under zero bias voltage, the quantum efficiency could be further amplified by hot carrier gain on graphene-i Si interface and avalanche process on graphene-doped Si interface. With the device architecture fully defined by nanomanufactured substrate, this work demonstrates post-fabrication-free two-dimensional material active silicon photonic devices. A hybrid optoelectronic junction design with graphene on silicon enables high quantum efficiency and ultrafast response. A team led by T. Gu at the University of Delaware developed a device configuration based on an in-plane p-i-n junction made of graphene on a silicon photonic crystal waveguide. The photonic crystal is used to enhance the photoresistivity, whereas graphene plays the role of electrical contact to the intrinsic region of silicon whilst also extending to the p- and n-doped regions, and acts as photocarrier conducting channel. The carrier transport channel is dominated by drift-current, which is instrumental to high external quantum efficiency. The latter is improved eight times on average over the visible range, if compared to a control device based on bare silicon.
TL;DR: In this article, the authors investigated light-soaking effects in inverted organic photovoltaic (OPV) devices with zinc oxide (ZnO) and aluminum doped ZnO (AZO) electron transport layers (ETL), which is important for the development of low-cost and stable solar cells.
Abstract: This paper investigates light-soaking effects in inverted organic photovoltaic (OPV) devices with zinc oxide (ZnO) and aluminum doped ZnO (AZO) electron transport layers (ETL), which is important for the development of low-cost and stable solar cells. The samples demonstrated high solar harvesting properties with power conversion efficiency up to 3.9%. Air-stability tests of up to 150 days were performed on devices with different Al doping levels. The devices maintained higher than 60% of the initial PCE after 50 days of open-air exposure. The light-soaking mechanism was investigated with experiments and simulations and shown to be eliminated when the Al fraction of the AZO is higher than 4%. The simulated band diagram of the OPV devices indicates that the low carrier density in the ZnO layer by virtue of depletion is the main reason of the light-soaking effect. Doping the ZnO layer as well as exposing the devices under UV irradiation will introduce additional free carriers into the ETL and reduce the width of the depletion region at both sides of the ETL.