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Showing papers on "p–n junction published in 2012"


Journal ArticleDOI
TL;DR: Nanotextured p-InP photocathodes are employed in conjunction with a TiO2 passivation layer and a Ru cocatalyst to increase both Jsc and Eos values under H2 evolution conditions, and this work uses InP as a model material system to explore the role of surface nanotexturing on the PEC device performance.
Abstract: Water splitting by using sunlight for the production of hydrogen yields a storable product, which can be used as a fuel. There is considerable research into H2 generation, namely the reduction of protons to H2 in aqueous solution using semiconductor photocathodes. To maximize the photoelectrochemical (PEC) performance, the selection of the active materials and device configurations should be carefully considered. First, the short-circuit current density (Jsc) should be maximized by choosing materials with high optical absorption coefficients and low carrier recombination rates, both in the bulk and at the surface. The reflectance should be minimized by using surface nanotexturing to further improve light absorption. The onset potential (Eos) of the PEC device versus the reversible H /H2 redox potential should be maximized. Finally, the surface energy needs to be controlled to minimize the accumulation of gas bubbles on the surface of the photoelectrode. Light absorbers with band gaps in the range of 1.1–1.7 eV provide both a good match to the terrestrial solar spectrum and a significant fraction of the 1.23 eV free energy required to split water. Overpotentials associated with the electron transfer to (solvated) protons in aqueous solution should be minimized by improving carrier transport from semiconductor to electrolyte by decorating the semiconductor with cocatalysts, tuning band edges, and decreasing contact resistance. p-Type Si has been extensively investigated as a photocathode for photochemical hydrogen production. Planar Si has relatively low short-circuit current densities under AM1.5 G illumination, approximately 10 mAcm 2 (reference [9]), compared to what can be achieved in a pn junction solar cell (> 35 mAcm ). Nanostructuring and incorporation of cocatalysts have been used to raise the short-circuit current density to over 30 mAcm . A recent study using np Si radial junction microwires reported an Eos value of 0.54 V and an Jsc value of 15 mA, leading to an overall efficiency near 6%. The onset potential observed to date for p-Si photocathodes is less than half of the value required for overall water splitting (1.23 V). This low onset potential limits the performance of tandem or “Z-scheme” approaches, which would function without external bias, as it limits the potential overlap required for spontaneous water splitting. An ideal photocathode for use in a solar-driven hydrogen production system without bias should have both a high current density and a favorable open-circuit potential versus the reversible H/H2 redox couple. Herein, we employ nanotextured p-InP photocathodes in conjunction with a TiO2 passivation layer and a Ru cocatalyst to increase both Jsc and Eos values under H2 evolution conditions. InP has a number of attractive attributes as a photocathode: 1) Its band gap of 1.3 eV is well-matched to the solar spectrum; InP-based solar cells have achieved AM1.5 G efficiencies of up to 22%. 2) The conduction band edge of InP is slightly above the water reduction potential, thus electron transfer is favorable in this system. 3) The surface-recombination velocity of untreated InP is low (ca. 10 cms 1 for n-type and 10 cms 1 for p-type), which is particularly important for nonplanar devices with high surface areas, such as those explored in this study. For these reasons, InP has been studied previously as a photocathode for both water splitting and CO2 reduction. [18–20] Specifically, Heller and Vadimsky reported attractive PEC performances with current densities up to 28 mAcm 2 and conversion efficiencies of approximately 12% in InP photocathodes. Motivated by these results, we use InP as a model material system to elucidate the role of surface nanotexturing on the PEC device performance. We find that nanotextured InP photocathodes exhibit drastically enhanced performances compared to our planar cells that were processed using identical conditions. We examine the various effects of nanotexturing [*] M. H. Lee, K. Takei, J. Zhang, R. Kapadia, M. Zheng, J. Nah, J. W. Ager, Prof. A. Javey Material Sciences Division, Lawrence Berkeley National Laboratory Berkeley, CA 94720 (USA) E-mail: jwager@lbl.gov ajavey@berkeley.edu M. H. Lee, K. Takei, J. Zhang, R. Kapadia, M. Zheng, J. Nah, Prof. A. Javey Electrical Engineering and Computer Sciences University of California, Berkeley, CA 94720 (USA) M. H. Lee, T. S. Matthews, J. W. Ager, Prof. A. Javey Joint Center for Artificial Photosynthesis Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (USA)

246 citations


Journal ArticleDOI
TL;DR: A p-n junction photoanode has been fabricated by depositing p-type NiO nanoparticles on the n-type hematite thin film, which facilitates the extraction of accumulated holes fromHematite via the p-N junction, but also lowers the barrier for oxygen evolution reaction.

191 citations


Journal ArticleDOI
05 Oct 2012-ACS Nano
TL;DR: The performance of the photon sensor is much enhanced by the strain-induced piezopotential in the ZnO core through modulation of the Schottky barrier heights at the source and drain contacts.
Abstract: The piezo-phototronic effect is about the use of the piezoelectric potential created inside some materials for enhancing the charge carrier generation or separation at the metal-semiconductor contact or pn junction. In this paper, we demonstrate the impact of the piezo-phototronic effect on the photon sensitivity for a ZnO-CdS core-shell micro/nanowire based visible and UV sensor. CdS nanowire arrays were grown on the surface of a ZnO micro/nanowire to form a ZnO-CdS core-shell nanostructure by a facile hydrothermal method. With the two ends of a ZnO-CdS wire bonded on a polymer substrate, a flexible photodetector was fabricated, which is sensitive simultaneously to both green light (548 nm) and UV light (372 nm). Furthermore, the performance of the photon sensor is much enhanced by the strain-induced piezopotential in the ZnO core through modulation of the Schottky barrier heights at the source and drain contacts. This work demonstrates a new application of the piezotronic effect in photon detectors.

183 citations



Patent
29 Nov 2012
TL;DR: In this article, a power semiconductor device such as a diode and a thyristor with at least one pn junction between a pair of main surfaces is considered, where a first main electrode is formed on the surface of one of the main surfaces and a second main electrode has been formed on surface of the other surface.
Abstract: The present invention relates to a power semiconductor device such as a diode and thyristor. In a semiconductor device such as a diode and thyristor having at least one pn junction between a pair of main surfaces, a first main electrode is formed on the surface of one of the main surfaces and a second main electrode is formed on the surface of the other one of the main surfaces. A semiconductor lattice defect is formed such that its lattice defect density increases gradually in the direction from the first main electrode to the second main electrode. Since the distribution of carrier density in the conduction state can be flattened according to the invention, the reverse recovery charge can be reduced substantially without causing the ON-state voltage to increase.

158 citations


Journal ArticleDOI
TL;DR: In this paper, two types of p-n junction photodiodes were constructed, the photoactive p-layer was made from PbS NQDs and the transparent n-layer is fabricated from wide bandgap oxides (ZnO or TiO 2), and the spectral shape of the photoresponse exhibits a significant dependence on applied bias.
Abstract: Chemically synthesized nanocrystal quantum dots (NQDs) are promising materials for applications in solution-processable optoelectronic devices such as light emitting diodes, photodetectors, and solar cells. Here, we fabricate and study two types of p-n junction photodiodes in which the photoactive p-layer is made from PbS NQDs while the transparent n-layer is fabricated from wide bandgap oxides (ZnO or TiO 2). By using a p-n junction architecture we are able to significantly reduce the dark current compared to earlier Schottky junction devices without reducing external quantum efficiency (EQE), which reaches values of up to ∼80%. The use of this device architecture also allows us to significantly reduce noise and obtain high detectivity (>10 12 cm Hz 1/2 W -1) extending to the near infrared past 1 μm. We observe that the spectral shape of the photoresponse exhibits a significant dependence on applied bias, and specifically, the EQE sharply increases around 500-600 nm at reverse biases greater than 1 V. We attribute this behavior to a "turn-on" of an additional contribution to the photocurrent due to electrons excited to the conduction band from the occupied mid-gap states.

138 citations


Journal ArticleDOI
TL;DR: The interdigitated diode is shown to outperform the lateral diode in achieving a low VπLπ of 0.62 V∙cm with comparable propagation loss at the expense of a higher depletion capacitance.
Abstract: Carrier-depletion based silicon modulators with lateral and interdigitated PN junctions are compared systematically on the same fabrication platform. The interdigitated diode is shown to outperform the lateral diode in achieving a low VπLπ of 0.62 V∙cm with comparable propagation loss at the expense of a higher depletion capacitance. The low VπLπ of the interdigitated PN junction is employed to demonstrate 10 Gbit/s modulation with 7.5 dB extinction ration from a 500 µm long device whose static insertion loss is 2.8 dB. In addition, up to 40 Gbit/s modulation is demonstrated for a 3 mm long device comprising a lateral diode and a co-designed traveling wave electrode.

132 citations


Journal ArticleDOI
TL;DR: In this article, a type of pn-junction not formed by impurity-doping was proposed by grading the Al composition in an AlGa1−xN thin film, resulting in alternating p and n conducting regions due to polarization charge.
Abstract: We propose a type of pn-junction not formed by impurity-doping, but rather by grading the Al composition in an AlxGa1−xN thin film, resulting in alternating p and n conducting regions due to polarization charge. By linearly grading AlxGa1−xN from 0% to x (x ≤ 30%) and back to 0% Al, a polarization induced pn-junction is formed, even in the absence of any impurity doping. X-ray diffraction reciprocal space maps are used to determine the strain state of the different graded composition samples. Polarization induced doping also provides a solution to the problem of p-type doping efficiency for III-nitrides.

131 citations


Journal ArticleDOI
TL;DR: Finite-element modeling of axial and radial Si NW p-n junctions with total diameters of ~240 nm and donor/acceptor doping levels ranging from 10(16) to 10(20) cm(-3) is presented, and it is expected that insights from finite element modeling will serve as a powerful method to guide the design of advanced nanoscale structures.
Abstract: Semiconductor nanowires (NWs) are a developing platform for electronic and photonic technologies, and many demonstrated devices utilize a p-type/n-type (p–n) junction encoded along either the axial or radial directions of the wires. These miniaturized junctions enable a diverse range of functions, from sensors to solar cells, yet the physics of the devices has not been thoroughly evaluated. Here, we present finite-element modeling of axial and radial Si NW p–n junctions with total diameters of ∼240 nm and donor/acceptor doping levels ranging from 1016 to 1020 cm–3. We evaluate the photovoltaic performance of horizontally oriented NWs under 1 sun illumination and compare simulated current–voltage data to experimental measurements, permitting detailed analysis of NW performance, limitations, and prospect as a technology for solar energy conversion. Although high surface-to-volume ratios are cited as detrimental to NW performance, radial p–n junctions are surprisingly insensitive to surface recombination, wi...

124 citations


Journal ArticleDOI
TL;DR: Estimating the surface recombination velocities clearly indicates a nonabrupt p-n junction, which is in essential agreement with the model of delayed dopant incorporation in the Au-assisted vapor-liquid-solid mechanism.
Abstract: Axial GaAs nanowire p–n diodes, possibly one of the core elements of future nanowire solar cells and light emitters, were grown via the Au-assisted vapor–liquid–solid mode, contacted by electron beam lithography, and investigated using electron beam induced current measurements. The minority carrier diffusion lengths and dynamics of both, electrons and holes, were determined directly at the vicinity of the p–n junction. The generated photocurrent shows an exponential decay on both sides of the junction and the extracted diffusion lengths are about 1 order of magnitude lower compared to bulk material due to surface recombination. Moreover, the observed strong diameter-dependence is well in line with the surface-to-volume ratio of semiconductor nanowires. Estimating the surface recombination velocities clearly indicates a nonabrupt p–n junction, which is in essential agreement with the model of delayed dopant incorporation in the Au-assisted vapor–liquid–solid mechanism. Surface passivation using ammonium s...

120 citations


Journal ArticleDOI
Zhe Jiang1, Quan Qing1, Ping Xie1, Ruixuan Gao1, Charles M. Lieber1 
TL;DR: It is demonstrated that p-n diode devices can serve as a new and powerful family of highly localized biosensor probes that provide substantial opportunity in areas ranging from bio/chem sensing and nanoscale photon detection to three-dimensional recording from within living cells and tissue.
Abstract: Semiconductor nanowires and other semiconducting nanoscale materials configured as field-effect transistors have been studied extensively as biological/chemical (bio/chem) sensors. These nanomaterials have demonstrated high-sensitivity from one- and two-dimensional sensors, although the realization of the ultimate pointlike detector has not been achieved. In this regard, nanoscale p-n diodes are attractive since the device element is naturally localized near the junction, and while nanowire p-n diodes have been widely studied as photovoltaic devices, their applications as bio/chem sensors have not been explored. Here we demonstrate that p-n diode devices can serve as a new and powerful family of highly localized biosensor probes. Designed nanoscale axial p-n junctions were synthetically introduced at the joints of kinked silicon nanowires. Scanning electron microscopy images showed that the kinked nanowire structures were achieved, and electrical transport measurements exhibited rectifying behavior with well-defined turn-on in forward bias as expected for a p-n diode. In addition, scanning gate microscopy demonstrated that the most sensitive region of these nanowires was localized near the kinked region at the p-n junction. High spatial resolution sensing using these p-n diode probes was carried out in aqueous solution using fluorescent charged polystyrene nanobeads. Multiplexed electrical measurements show well-defined single-nanoparticle detection, and experiments with simultaneous confocal imaging correlate directly the motion of the nanobeads with the electrical signals recorded from the p-n devices. In addition, kinked p-n junction nanowires configured as three-dimensional probes demonstrate the capability of intracellular recording of action potentials from electrogenic cells. These p-n junction kinked nanowire devices, which represent a new way of constructing nanoscale probes with highly localized sensing regions, provide substantial opportunity in areas ranging from bio/chem sensing and nanoscale photon detection to three-dimensional recording from within living cells and tissue.

Journal ArticleDOI
TL;DR: P polarization-induced conductivity without impurity doping provides a solution to the problem of conductivity uniformity in nanowires and nanoelectronics and opens a new field of polarization engineering in nanostructures that may be applied to other polar semiconductors.
Abstract: Almost all electronic devices utilize a pn junction formed by random doping of donor and acceptor impurity atoms We developed a fundamentally new type of pn junction not formed by impurity-doping, but rather by grading the composition of a semiconductor nanowire resulting in alternating p and n conducting regions due to polarization charge By linearly grading AlGaN nanowires from 0% to 100% and back to 0% Al, we show the formation of a polarization-induced pn junction even in the absence of any impurity doping Since electrons and holes are injected from AlN barriers into quantum disk active regions, graded nanowires allow deep ultraviolet LEDs across the AlGaN band-gap range with electroluminescence observed from 34 to 5 eV Polarization-induced p-type conductivity in nanowires is shown to be possible even without supplemental acceptor doping, demonstrating the advantage of polarization engineering in nanowires compared with planar films and providing a strategy for improving conductivity in wide-band

Journal ArticleDOI
TL;DR: In this paper, an enhanced interband tunnel injection of holes into a PN junction with a specific resistivity of 1.2 X 10-4 −4 −Omega cm2 is demonstrated.
Abstract: Enhanced interband tunnel injection of holes into a PN junction is demonstrated using P-GaN/InGaN/N-GaN tunnel junctions with a specific resistivity of 1.2 X 10-4 {\Omega} cm2. The design methodology and low-temperature characteristic of these tunnel junctions is discussed, and insertion into a PN junction device is described. Applications of tunnel junctions in III-nitride optoelectronics devices are explained using energy band diagrams. The lower band gap and polarization fields reduce tunneling barrier, eliminating the need for ohmic contacts to p-type GaN. This demonstration of efficient tunnel injection of carriers in III-Nitrides can lead to a replacement of existing resistive p-type contact material in light emitters with tunneling contact layers, requiring very little metal footprint on the surface, resulting in enhanced light extraction from top emitting emitters.

Journal ArticleDOI
TL;DR: In this article, an external stressor technique was employed to introduce a 0.76% bi-axial tensile strain in the active region of a vertical PN junction.
Abstract: We demonstrate room-temperature electroluminescence (EL) from light-emitting diodes (LED) on highly strained germanium (Ge) membranes. An external stressor technique was employed to introduce a 0.76% bi-axial tensile strain in the active region of a vertical PN junction. Electrical measurements show an on-off ratio increase of one order of magnitude in membrane LEDs compared to bulk. The EL spectrum from the 0.76% strained Ge LED shows a 100nm redshift of the center wavelength because of the strain-induced direct band gap reduction. Finally, using tight-binding and FDTD simulations, we discuss the implications for highly efficient Ge lasers.

Journal ArticleDOI
TL;DR: It is found that GeO₂ surface passivation can effectively suppress the dark current of a germanium photodetector in conjunction with gas-phase doping, and it is obtained extremely low values of Jbulk and Jsurf.
Abstract: We have investigated the dark current of a germanium (Ge) photodetector (PD) with a GeO2 surface passivation layer and a gas-phase-doped n+/p junction. The gas-phase-doped PN diodes exhibited a dark current of approximately two orders of magnitude lower than that of the diodes formed by a conventional ion implantation process, indicating that gas-phase doping is suitable for low-damage PN junction formation. The bulk leakage (Jbulk) and surface leakage (Jsurf) components of the dark current were also investigated. We have found that GeO2 surface passivation can effectively suppress the dark current of a Ge PD in conjunction with gas-phase doping, and we have obtained extremely low values of Jbulk of 0.032 mA/cm2 and Jsurf of 0.27 μA/cm.

Journal ArticleDOI
TL;DR: It is shown that the CZTS-fullerene interface could dissociate photogenerated excitons due to the depletion region formed at the pn-junction and compared it with the parameters of devices based on the components of the heterojunction.
Abstract: A heterojunction between a layer of CZTS nanoparticles and a layer of fullerene derivatives forms a pn-junction. We have used such an inorganic–organic hybrid pn-junction device for solar cell applications. As routes to optimize device performance, interdot separation has been reduced by replacing long-chain ligands of the quantum dots with short-chain ligands and thickness of the CZTS layer has been varied. We have shown that the CZTS–fullerene interface could dissociate photogenerated excitons due to the depletion region formed at the pn-junction. From capacitance–voltage characteristics, we have determined the width of the depletion region, and compared it with the parameters of devices based on the components of the heterojunction. The results demonstrate solar cell applications based on nontoxic and earth-abundant materials.

Journal ArticleDOI
TL;DR: In this article, an external stressor technique was employed to introduce a 0.76% bi-axial tensile strain in the active region of a vertical PN junction.
Abstract: We demonstrate room-temperature electroluminescence (EL) from light-emitting diodes (LEDs) on highly strained germanium (Ge) membranes. An external stressor technique was employed to introduce a 0.76% bi-axial tensile strain in the active region of a vertical PN junction. Electrical measurements show an on-off ratio increase of one order of magnitude in membrane LEDs compared to bulk. The EL spectrum from the 0.76% strained Ge LED shows a 100 nm redshift of the center wavelength because of the strain-induced direct band gap reduction. Finally, using tight-binding and finite-difference time domain simulations, we discuss the implications for highly efficient Ge lasers.

Journal ArticleDOI
TL;DR: In this paper, the authors consider a junction between surface p and surface n on an ideal topological insulator in which carrier type and density in two adjacent regions are locally controlled by composition graded doping or electrical gating.
Abstract: We consider a junction between surface $p$ type and surface $n$ type on an ideal topological insulator in which carrier type and density in two adjacent regions are locally controlled by composition graded doping or electrical gating. Such junction setting on topological insulators are fundamental for possible device application. A single gapless chiral edge state localized along the junction interface appears in the presence of an external magnetic field, and it can be probed by scanning tunneling microscopy and transport measurements. We propose to realize this topological p-n junction in (Bi${}_{1\ensuremath{-}x}$Sb${}_{x}$)${}_{2}$Te${}_{3}$, which has insulating bulk properties and a tunable surface state across the Dirac cone.

Journal ArticleDOI
TL;DR: In this paper, theoretical results on transport properties of B-and N-doped aGNR p-n junction were presented on the basis of density functional theory and nonequilibrium Green's function technique, which revealed that the voltage rectifying efficiency can be highly enhanced by forming a tandem diode by connecting two single diodes in series.
Abstract: On the basis of density functional theory and nonequilibrium Green’s function technique, we have presented theoretical results on transport properties of B- and N-doped aGNR p–n junction. The current–voltage characteristic of this system indicates robust negative differential resistance (NDR) behavior of it. Meanwhile, that p–n junction diode can be utilized as a highly efficient voltage rectifier. The calculations also reveal that the voltage rectifying efficiency can be highly enhanced by forming a tandem diode by connecting two single diodes in series. The variation of transport properties on the width of aGNR is also investigated. The NDR phenomena as well as the rectifying property can be well explained on the basis of relative shifting of discrete energy states of the conjugate system with applied bias, which in turn explains very strong coupling between the p and n regions of the diode.

Journal ArticleDOI
15 Jun 2012
TL;DR: The structural, optical, and electronic characteristics of the CTS make it great potential as bottom cell absorber material for low-cost thin film tandem solar cell application.
Abstract: Photovoltaic properties of narrow-bandgap Cu(2)SnS(3) (CTS) are studied for the first time by employing a superstrate solar cell structure of fluorine-doped tin oxide (FTO) glass/TiO(2)/In(2)S(3)/CTS/Mo. The structural, optical, and electronic characteristics of the CTS make it great potential as bottom cell absorber material for low-cost thin film tandem solar cell application. Furthermore, by inserting a thin low temperature deposited In(2)S(3) layer between the In(2)S(3) buffer layer and the CTS absorber layer, an enhancement in the performance of the solar cell can be achieved, leading to about 75% improvement (η=1.92%) over the unmodified device (η=1.10%).

Journal ArticleDOI
TL;DR: In this article, a 1D α-MoO3/CuO p-n junction nanocomposite has been synthesized via a simple method, which exhibits great enhanced H2S gas sensing properties.
Abstract: One-dimensional (1D) α-MoO3/CuO nanocomposite has been synthesized via a simple method. This nanocomposite consists of n-type α-MoO3 nanorods decorated with p-type CuO nanoparticles, leading to the formation of p–n junctions at their interfaces. The p–n junction nanocomposite exhibits great enhanced H2S gas sensing properties, compared to pristine α-MoO3 nanorods. The sensor response of this nanocomposite is up to 272.0–10 ppm H2S gas at the optimal working temperature (270 °C), which is 53.3 times higher than that of α-MoO3 nanorods. More importantly, even at 100 °C, α-MoO3/CuO p–n junction nanocomposite still has very strong response to 5 ppm H2S gas. In addition, the nanocomposite sensors have a very good selectivity to H2S gas. Such enhanced H2S sensing performances are attributed to the disappearance of p–n junctions, which can be proved by the fact that crystalline CuO nanoparticles are converted into amorphous CuS ones after the nanocomposite is exposed to H2S gas.

Journal ArticleDOI
TL;DR: APTES andPFES were used to modify the interface between transferred CVD graphene films and its supporting dielectric to create n-type and p-type graphene, respectively, resulting in thermally stable graphene p-n junctions for temperatures up to 200 °C.
Abstract: 3-Aminopropyltriethoxysilane (APTES) and perfluorooctyltriethoxysilane (PFES) were used to modify the interface between transferred CVD graphene films and its supporting dielectric to create n-type and p-type graphene, respectively. A graphene p–n junction was obtained by patterning both modifiers on the same dielectric and verified through the creation of a field effect transistor (FET). Characteristic I–V curves indicate the presence of two separate Dirac points which confirms an energy separation of neutrality points within the complementary regions. This method minimizes doping-induced defects and results in thermally stable graphene p–n junctions for temperatures up to 200 °C.

Journal ArticleDOI
TL;DR: In this paper, the CdS/CIGS p-n junction region in thin-film solar cells using atom probe tomography was studied. And the experimental findings demonstrate the capability of atom probe-tomography in studying buried interfaces and yield vital information for understanding and modeling the pn junction band structure in Cu(In,Ga)Se2 solar cells.
Abstract: In this work we study the CdS/Cu(In,Ga)Se2 p-n junction region in Cu(In,Ga)Se2 thin-film solar cells using atom probe tomography. A Cu-, Ga-depleted, and Cd-doped region of about 1 nm thickness is detected at the Cu(In,Ga)Se2 side of the CdS/Cu(In,Ga)Se2 interface. Furthermore, Cd is also found to be enriched at Cu(In,Ga)Se2 grain boundaries connected to the CdS layer. Na and O impurities decorate the CdS/CIGS interface, where Na-rich clusters are preferentially located in CdS regions abutting to Cu(In,Ga)Se2 grain boundaries. The experimental findings of this work demonstrate the capability of atom probe tomography in studying buried interfaces and yield vital information for understanding and modeling the p-n junction band structure in Cu(In,Ga)Se2 solar cells.

Journal ArticleDOI
TL;DR: The degree of surface passivation achieved in this paper is comparable to or better than that achieved for nanowires in prior studies at significantly larger diameters, and it is suggested that the dramatically improved surface recombination velocities may result from the reduced sidewall reactions and deposition in the authors' cold wall CVD reactor.
Abstract: VLS-grown semiconductor nanowires have emerged as a viable prospect for future solar-based energy applications. In this paper, we report highly efficient charge separation and collection across in situ doped Si p–n junction nanowires with a diameter <100 nm grown in a cold wall CVD reactor. Our photoexcitation measurements indicate an internal quantum efficiency of ∼50%, whereas scanning photocurrent microscopy measurements reveal effective minority carrier diffusion lengths of ∼1.0 μm for electrons and 0.66 μm for holes for as-grown Si nanowires (dNW ≈ 65–80 nm), which are an order of magnitude larger than those previously reported for nanowires of similar diameter. Further analysis reveals that the strong suppression of surface recombination is mainly responsible for these relatively long diffusion lengths, with surface recombination velocities (S) calculated to be 2 orders of magnitude lower than found previously for as-grown nanowires, all of which used hot wall reactors. The degree of surface passiva...

Journal ArticleDOI
TL;DR: In this article, the junction resistance of a tilted interface probed with separate split gates is shown to increase with tilt, in agreement with recent experimental evidence, showing that the tilt dependence arises because of the misalignment between modal density and the anisotropic transmission lobe oriented perpendicular to the tilt.
Abstract: Electrons in graphene follow unconventional trajectories at $p$-$n$ junctions, driven by their pseudospintronic degree of freedom. The prominent angular dependence of transmission is significant, capturing the chiral nature of the electrons and culminating in unit transmission at normal incidence (Klein tunneling). We theoretically show that such chiral tunneling can be directly observed from the junction resistance of a tilted interface probed with separate split gates. The junction resistance is shown to increase with tilt, in agreement with recent experimental evidence. The tilt dependence arises because of the misalignment between modal density and the anisotropic transmission lobe oriented perpendicular to the tilt. A critical determinant is the presence of specular edge scattering events that can completely reverse the angle dependence. The absence of such reversals in the experiments indicates that these edge effects are not overwhelmingly deleterious, making the premise of transport governed by electron ``optics'' in graphene an exciting possibility.

Journal ArticleDOI
TL;DR: In this paper, the authors used detector stacking methods to increase thermal neutron detection efficiency, along with the current process to backfill 6LiF into the silicon microstructures, achieving over 42% intrinsic thermal neutrion detection efficiency.
Abstract: Silicon diodes with large aspect ratio trenched microstructures, backfilled with 6LiF, show a dramatic increase in thermal neutron detection efficiency beyond that of conventional thin-film coated planar devices. Described in this work are advancements in the technology using detector stacking methods to increase thermal neutron detection efficiency, along with the current process to backfill 6LiF into the silicon microstructures. The highest detection efficiency realized thus far is over 42% intrinsic thermal neutron detection efficiency by device-stacking methods. The detectors operate as conformally diffused pn junction diodes each having 1 cm2 area. Two individual devices were mounted back-to-back with counting electronics coupling the detectors together into a single dual-detector device. The solid-state silicon device was operated at 3 V and utilized simple signal amplification and counting electronic components that have been adjusted from previous work for slow charge integration time. The intrinsic detection efficiency for normal-incident 0.0253 eV neutrons was found by calibrating against a 3He proportional counter.

Journal ArticleDOI
TL;DR: In this article, a unique non-radiative p-n-p junction structure was proposed to provide high current conduction with high mobility in organic semiconductor devices, which can be very useful for many practical organic device applications.

Journal ArticleDOI
TL;DR: In this article, an all-silicon photodetector integrated in a silicon-on-insulator waveguide for the telecom regime is proposed, based on internal photoemission from electrically floating metal silicide nanoparticles (NPs) embedded in the space charge region of a Si p-n junction.
Abstract: An all-silicon photodetector integrated in a silicon-on-insulator waveguide for the telecom regime is proposed. The device is based on internal photoemission from electrically floating metal silicide nanoparticles (NPs) embedded in the space charge region of a Si p-n junction. Numerical simulation indicates that the light absorption could be enhanced if localized surface plasmon resonances are excited on the metal silicide nanoparticles, thus enabling to shrink the detector’s footprint to a submicron scale. A proof-of-concept detector fabricated using standard silicon complementary metal-oxide-semiconductor technology exhibits a peak responsivity of ∼30 mA/W at 5-V reverse bias and a 3-dB bandwidth of ∼6 GHz. It is expected that the overall performance would be significantly improved by optimization of both the detector’s configuration and the fabrication parameters.

Journal ArticleDOI
TL;DR: This work presents a clear path toward engineering dead space effects in thin 3D-confined multiplication regions for high performance avalanche detectors for applications in telecommunications, sensing and single photon detection.
Abstract: We demonstrate a nanopillar (NP) device structure for implementing plasmonically enhanced avalanche photodetector arrays with thin avalanche volumes (∼ 310 nm × 150 nm × 150 nm). A localized 3D electric field due to a core–shell PN junction in a NP acts as a multiplication region, while efficient light absorption takes place via surface plasmon polariton Bloch wave (SPP-BW) modes due to a self-aligned metal nanohole lattice. Avalanche gains of ∼216 at 730 nm at −12 V are obtained. We show through capacitance–voltage characterization, temperature-dependent breakdown measurements, and detailed device modeling that the avalanche region is on the order of the ionization path length, such that dead-space effects become significant. This work presents a clear path toward engineering dead space effects in thin 3D-confined multiplication regions for high performance avalanche detectors for applications in telecommunications, sensing and single photon detection.

Journal ArticleDOI
TL;DR: In this paper, a diamond lateral p-n junction diodes were fabricated by selective growth of n+type diamond and evaluated their structural and electrical properties at room temperature to 773 K.
Abstract: We fabricated diamond lateral p–n junction diodes by selective growth of n+-type diamond and evaluated their structural and electrical properties. The phosphorus-doped n+ diamond was selectively grown by microwave chemical vapor deposition at the side of a boron-doped p-type layer to form lateral p–n junction diodes. No distinct defects are observed at the interface of the p–n junction diode by cross-sectional transmission electron microscopy, implying the good homoepitaxial growth of the n-type diamond. Electron beam induced-current measurements directly confirmed the existence of the depletion layer in p–n junction diode. The electrical properties of the lateral p–n junction diodes were investigated at room temperature to 773 K. The devices show normal diode characteristics at all temperatures. A very low leakage current <10−14 A in the reverse bias was obtained at room temperature, resulting in a high rectification ratio of 108. Although the rectification ratio decreases with increasing temperature, it possesses 106 even at 573 K. A breakdown voltage was examined to be more than 100 V.