Planar Junctions Research Articles

Phase Signature of Topological Transition in Josephson Junctions.

Topological superconductivity holds promise for fault-tolerant quantum computing. While planar Josephson junctions are attractive candidates to realize this exotic state, direct phase measurements as the fingerprint of the topological transition are missing. By embedding two gate-tunable Al/InAs Josephson junctions in a loop geometry, we measure a π jump in the junction phase with an increasing in-plane magnetic field B_{∥}. This jump is accompanied by a minimum of the critical current, indicating a closing and reopening of the superconducting gap, strongly anisotropic in B_{∥}. Our theory confirms that these signatures of a topological transition are compatible with the emergence of Majorana bound states.

Wave Scattering by a Planar Junction Between Anomalously Reflecting Metasurface and Impedance Sheets

Metasurface technology has become one of the promising structures for controlling and manipulating of the phase and amplitude characteristics of the electromagnetic waves in recent years. For this reason, the determination of the exact diffracted fields is also crucial especially in the edge or discontinuity points of these types of materials. In the paper, the discontinuity problem by the junction between the layers of an anomalously reflecting metasurface and an impedance half-screen is taken into consideration. These two planar layers have a common edge discontinuity where the diffracted waves occur. The scattered waves from the structure are obtained by the novel technique of the method of transition boundary, which especially offers the relation between the diffracted and scattered geometrical optical waves at the transition boundaries. The diffracted wave expressions are derived by the technique of the method of transition boundary and the uniform wave expressions are obtained by the method of uniform geometrical theory of diffraction. The behaviors of the total wave and its components are analyzed numerically.

Directing Reaction Paths to Electrodeposit Cu-In-Se Films with Alternate Morphologies

Electrodeposition approach has been widely explored for CuInSe2 and its alloys as a low cost, scalable alternative to vacuum methods. Achieving device quality electrodeposited films of ternary compounds requires a profound knowledge of the intricate reaction mechanisms and the possible alternate paths that determine the film composition and electronic properties. Various studies of the Cu-In-Se (CISe) system have enabled unraveling the rather complicated reaction mechanisms and ultimately electrodeposit stoichiometric CuInSe2 [1-7].The complexity of the reaction mechanism for the ternary system CuSe system arises mainly from the multiple oxidation states of its component elements. Single step electrodeposition (SSE) from a Cu+/In3+/Se4+ electrolyte is challenging due to many competing chemical (C) and electrochemical (E) reactions that invariably create multiple solid phases, as partly illustrated in the Fig. 1R schematic. Experimental investigations reveal the simultaneous reduction of Cu2+ and Se4+ ions (E1 ) and chemical assimilation of In (C1 ) to form CuSe(In) within the first minute [6,7]. The CuSe(In) further reduces to Cu2Se and Se2- (E2 ). The Se2- ions may react with Se4+ ions to form Se0 (C2 ) or with In3+ ions to form In2Se3 (C3 ). Subsequent chemical reactions of In3+ ions with the Cu2Se, In2Se3 and Se2- reaction products form CuInSe2 (C4 ) and further CuIn3Se5 (C5 ) if sufficient flux of In3+ is available, Fig. 1R.The reactions leading to the formation of the CISe compounds are thermodynamically driven, which enables SSE of self-stabilized stoichiometries from a single solution, at a single potential, ED. Manipulation of process parameters (temperature, electrolyte composition, pH, mass transport and deposition potential) allows controlling the kinetics of competing reactions for SSE of stoichiometric CuInSe2, CuIn3Se5, or a mixture of the two compounds, Fig. 1M. A brief post-anneal enhances crystallinity without altering the film composition [7, 8]. Surface analytical microscopies and spectroscopies support the fortuitous formation of surprisingly ordered, interlinked, space-filling CISe nanocrystals forming interconnected network of sharp, abrupt 3-dimensional p-CuInSe2/n-CuIn3Se5 nanocrystalline homojunctions (NHJs). This approach generates CISe NHJ films with homogeneous composition on large foil, facilitating easy scale-up via roll-to-roll processing.Besides the processing advantages, the CISe NHJ films exhibit extraordinary electro-optical attributes that can potentially maximize spectral absorption and reduce recombination losses. The specific NHJ structure enables efficient separation and transport of free carriers, and essentially performs the same functions as standard planar pn junctions. The CISe nanocrystals are very different from colloidal nanocrystals, used in state-of-the-art bulk homojunction devices; they exhibit high doping densities, mixed conductivity and multiple bandgaps. These distinctive innate attributes of CISe films naturally create ordered morphology and facilitate interconnections between the nanocrystals to form optimum NHJ structures. The CISe pn NHJ layer can be directly inserted between 2 band-aligned contact electrodes to produce high performance practical 3G devices, Fig, 1L.The direct deposition of CISe pn NHJ resolves problems with current approaches for device fabrication based on conventional planar pn junctions, organic/colloidal bulk heterojunctions or inorganic ordered heterojunctions. The totality manifests a highly significant advance in semiconductor processing, providing a generally accessible, low-cost electrochemical method to fabricate high quality pn NHJs in simple flexible thin-film form factor with inorganic material systems. The films can be directly used for harvesting solar energy on a large scale for photoelectrochemical or photovoltaic applications and other devices applications, including light emitting diodes. References K. Mishra and K. Rajeshwar, J. Electroanal. Chem., 271 279 (1989).Pottier and G. Maurin, J. Appl. Electrochem. (1991).Massaccesi, S. Rouquette-Sanchez, J. Vedel, J. Electrochem. Soc., 140, 2540 (1993).Froment, M. C. Bernard, R. Cortes, B. Mokili, D. Lincot, J. Electrochem. Soc, 142 (1995) 2642.Thouin and J. Vedel, J. Electrochem. Soc. 142, 2996 (1995)Menezes, Mat. Res. Soc. Symp. Proc., S. Francisco, 426, 189 (1996).Li, S. S. Shaikh, S. Menezes, Thin Solid Films, 524, 20-25 (2012).Menezes and A. Samantilekke, Scientific Reports, https://rdcu.be/3AD7 (2018). Figure 1. Schematics of (R) Reaction Mechanism (M) SSE of p-CuInSe2/n-CuIn3Se5 NHJ thin film and (L) CISe NHJ device Figure 1

Design, Fabrication and Characterization of 10kV/100A 4H-SiC PiN Power Rectifier

A 10kV/100A SiC PiN rectifier with MRM-JTE (multiple-ring modulated junction termination extension) is designed, fabricated and characterized. The optimized MRM-JTE achieves high breakdown capability and extends the optimal JTE dose window. A 100μm thick epitaxial SiC PiN rectifier with a doping concentration of 5×1014cm−3 has been fabricated using a standard TZ-JTE process. A 5.4V forward voltage drop is obtained at 100A forward current. Moreover, a measured breakdown voltage is up to 13.5kV corresponding to about 96% of the ideal parallel plane junction. The fabricated device exhibits a low RON,SP of 3.76mΩ·cm2 at 200A/cm2 , and a high BFOM of 48.5GW/cm2. In addition, the C-V characteristic and reverse recovery switch characteristic are also analyzed. In this paper, the successfully fabrication of high-voltage SiC PiN rectifier provides a further development for high-voltage high-power SiC power modules.

Anomalous proximity effect of planar topological Josephson junctions

The anomalous proximity effect in dirty superconducting junctions is one of most striking phenomena highlighting the profound nature of Majorana bound states and odd-frequency Cooper pairs in topological superconductors. Motivated by the recent experimental realization of planar topological Josephson junctions, we describe the anomalous proximity effect in a superconductor/semiconductor hybrid, where an additional dirty normal-metal segment is extended from a topological Josephson junction. The topological phase transition in the topological Josephson junction is accompanied by a drastic change in the low-energy transport properties of the attached dirty normal-metal. The quantization of the zero-bias differential conductance, which appears only in the topologically nontrivial phase, is caused by the penetration of the Majorana bound states and odd-frequency Cooper pairs into a dirty normal-metal segment. As a consequence, we propose a practical experiment for observing the anomalous proximity effect.

Ultrahigh-performance planar β-Ga2O3 solar-blind Schottky photodiode detectors

The low dark current, high responsivity and high specific detectivity could be preferably achieved in detectors based on junctions, owing to the efficient constraint of carriers. Compared with the other junctions, planar Schottky junctions have simple structures and technological demands and are easy integrated. Herein, in this work, we prepared the β -Ga2O3 thin film by metal-organic chemical vapor deposition method to construct planar Ti/ β -Ga2O3/Ni Schottky photodiode detectors with different on-state resistances. Fortunately, all the devices exhibit state-of-the-art performances, such as responsivity of 175–1372 A W−1, specific detectivity of 1014 Jones and external quantum efficiency of 85700%–671500%. In addition, the dependences of device performances on the on-state resistances indicate that the higher dark currents, photocurrents and photoresponsivities may well be obtained when on-state resistance is smaller, due to the less external power is used to overcome the impendence and condensance at the Ti/ β -Ga2O3 and Ni/ β -Ga2O3 interfaces, but contributing to higher electric current flow both in the dark and under illuminations.

Unified Formula for Stationary Josephson Current in Planar Graphene Junctions

The stationary Josephson current in a ballistic graphene system is theoretically studied with focus on a planar junction consisting of a monolayer graphene sheet on top of which a pair of superconducting electrodes is deposited. To characterize such a planar junction, we employ two parameters: the coupling strength between the graphene sheet and the superconducting electrodes, and a potential drop induced in the graphene sheet by direct contact with the electrodes. We derive a general formula for the Josephson current by taking these parameters into account in addition to other basic parameters, such as temperature and chemical potential. The resulting formula applies to a wide range of parameters and reproduces previously reported results in certain limits.

Depth-dependent EBIC microscopy of radial-junction Si micropillar arrays

Recent advances in fabrication have enabled radial-junction architectures for cost-effective and high-performance optoelectronic devices. Unlike a planar PN junction, a radial-junction geometry maximizes the optical interaction in the three-dimensional (3D) structures, while effectively extracting the generated carriers via the conformal PN junction. In this paper, we report characterizations of radial PN junctions that consist of p-type Si micropillars created by deep reactive-ion etching (DRIE) and an n-type layer formed by phosphorus gas diffusion. We use electron-beam induced current (EBIC) microscopy to access the 3D junction profile from the sidewall of the pillars. Our EBIC images reveal uniform PN junctions conformally constructed on the 3D pillar array. Based on Monte-Carlo simulations and EBIC modeling, we estimate local carrier separation/collection efficiency that reflects the quality of the PN junction. We find the EBIC efficiency of the pillar array increases with the incident electron beam energy, consistent with the EBIC behaviors observed in a high-quality planar PN junction. The magnitude of the EBIC efficiency of our pillar array is about 70% at 10 kV, slightly lower than that of the planar device (≈ 81%). We suggest that this reduction could be attributed to the unpassivated pillar surface and the unintended recombination centers in the pillar cores introduced during the DRIE processes. Our results support that the depth-dependent EBIC approach is ideally suitable for evaluating PN junctions formed on micro/nanostructured semiconductors with various geometry.

Quantum transport of planar Josephson junctions with Majorana bound states

We investigate the transport features of a planar Josephson junction which was recently proposed and verified as a host of Majorana bound states (MBSs). With finite phase difference, MBSs can be gapped from the excited states at moderate Zeeman field. A considerable amount of current density develops at the stripe edges due to the presence of the MBSs. More interestingly, we note that in detecting MBSs via scanning tunneling spectroscopy (STM), a conductance minimum is observed at the peak position of the MBS local density of states. We ascribe this discrepancy to the fact that the penetration of the pair potential decays away the superconducting/normal interface. These results are instructive in not only for identifying MBSs in planar Josephson junction via STM measurement, but also for the detection of MBSs in platforms with nonuniform pair potentials.

How to measure the Majorana polarization of a topological planar Josephson junction

We analyze the topological superconductivity and investigate the spectroscopic properties manifested by the zero-energy modes, induced in a metallic strip embedded into a Josephson-type junction. Focusing on the Majorana polarization of such quasiparticles, we propose feasible means for its empirical detection, using the spin-selective Andreev reflection method. Our study reveals a gradual development of a transverse gradient of the Majorana polarization across the metallic strip upon increasing its width. We also inspect the spatial profile and polarization of the Majorana quasiparticles in the presence of a strong electrostatic impurity. We show that, depending on its position, such a defect can lead to a substantial localization of the Majorana mode.

Programmable Organic-Free Negative Differential Resistance Memristor Based on Plasmonic Tunnel Junction.

A novel negative differential resistance (NDR) phenomenon is reported herein based on planar plasmonic tunnel junction, resulting from plasmon-assisted long-range electron tunneling (P-tunneling) and electronic caching effect of Au@SiO2 nanoparticles. The tunnel junction is made of shell-insulated Au@SiO2 nanoparticle nanomembrane, in which SiO2 shells act as a tunable tunneling barrier, while the Au core not only support the plasmonic effect to enable P-tunneling, but also act as electronic caches to render NDR responses. The NDR peak voltage and current can be programmably controlled by varying the thickness of SiO2 shell and the size of Au core to tune barrier level for electron transport. In addition, light induced plasmonic effect can be further managed to regulate the NDR behavior by fine-tuning P-tunneling. The phenomenon is exploited for robust use as memristors. The work provides a new mechanism for the generation of NDR effect and may open a way for the development of robust and new conceptual nanoelectronic devices.

Abrupt degenerately-doped silicon nanowire tunnel junctions

We have confirmed the presence of narrow, degenerately-doped axial silicon nanowire (SiNW) p-n junctions via off-axis electron holography (EH). SiNWs were grown via the vapor-solid-liquid (VLS) mechanism using gold (Au) as the catalyst, silane (SiH4), diborane (B2H6) and phosphine (PH3) as the precursors, and hydrochloric acid (HCl) to stabilize the growth. Two types of growth were carried out, and in each case we explored growth with both n/p and p/n sequences. In the first type, we abruptly switched the dopant precursors at the desired junction location, and in the second type we slowed the growth rate at the junction to allow the dopants to readily leave the Au catalyst. We demonstrate degenerately-doped p/n and n/p nanowire segments with abrupt potential profiles of 1.02 ± 0.02 and 0.86 ± 0.3 V, and depletion region widths as narrow as 10 ± 1 nm via EH. Low temperature current-voltage measurements show an asymmetric curvature in the forward direction that resemble planar gold-doped tunnel junctions, where the tunneling current is hidden by a large excess current. The results presented herein show that the direct VLS growth of degenerately-doped axial SiNW p-n junctions is feasible, an essential step in the fabrication of more complex SiNW-based devices for electronics and solar energy.

High‐Responsivity Graphene/4H‐SiC Ultraviolet Photodetector Based on a Planar Junction Formed by the Dual Modulation of Electric and Light Fields

AbstractUltraviolet (UV) photodetectors have been fabricated on a graphene/4H‐SiC wafer. In this device, the electrical doping in the graphene layer, under the gate, is realized by changing the gate voltage while the optical doping in the graphene layer outside the gate region is realized through the photogenerated carrier injection from SiC, by laser excitation at 325 nm. This kind of dual modulation of optical and electric fields ultimately results in the formation of a planar n–p–n or n–n–n junction in the graphene layer. The photoresponse results demonstrate that the planar n–p–n junction is formed at the negative gate voltage, and facilitates negative photoconductivity. The n–n–n junction is formed at the positive gate voltage and facilitates normal photoconductivity. The maximum responsivity, which is attributable to the high photoconductive gain in the planar n–n–n junction, is 254.1A W−1, at drain‐source voltage of −3 V and gate‐source voltage of 3 V. Based on these results, the estimated lifetime of the electrons in the graphene channel extends greatly to more than four orders of magnitude longer than that in the isolated graphene. The above results prove that this graphene/4H‐SiC combined structure possesses great potential in practical UV‐detection applications.

Plasmonic-enhanced light emission from a waveguide-integrated tunnel junction

Light emission from inelastic electron tunneling has been demonstrated for 40 years. The ultrafast response rate and the ultracompact footprint make it promising for high-speed miniaturized light sources. But the application of the tunnel junction is limited by extremely low external quantum efficiency due to the low proportion of inelastic tunneling electron and wave vector mismatch between surface plasmons and photon emission. Here, we present a plasmonic-enhanced metal-insulator-semiconductor (MIS) junction coupled to a silicon waveguide with a coplanar electrode connected to a nanoantenna. The proposed tunnel junction can be fabricated using existing semiconductor planar processes to achieve controllable barrier thickness and quality for vertical current injection. Finally, an electrically driven light source with a radiation power nearly 8000 times higher than the spontaneous emission power in free space is shown to be achievable with the new structure at an operating wavelength of 1.31 µm. It is 510-fold higher than that of typical planar MIS junctions.

Line Waves in Non-Hermitian Metasurfaces

Planar junctions between reactive surface impedances with dual character (capacitive/inductive) can sustain line waves localized both in-plane and out-of-plane around the discontinuity, which propa...

Persistent currents and spin torque caused by percolated quantum spin Hall state

Motivated by recent experiments, we investigate the quantum spin Hall state in 2D topological insulator/ferromagnetic metal planar junctions by means of a tight-binding model and linear response theory. We demonstrate that whether the edge state Dirac cone is submerged into the ferromagnetic subbands and the direction of the magnetization dramatically affect (i) how the edge state percolates into the ferromagnet, and (ii) the spin-momentum locking of the edge state. Laminar flows of room temperature persistent charge and spin currents near the interface are uncovered. In addition, the current-induced spin polarization at the edge of the 2D topological insulator is found to be dramatically enhanced near the impurities. The current-induced spin polarization in the ferromagnet is mainly polarized in the out-of-plane direction ${\hat{\bf z}}$, rendering a current-induced spin torque that is predominantly field-like $\propto {\bf S}\times{\hat{\bf z}}$.

185 Altered Celsr1 adhesion disrupts planar cell polarity and junction asymmetry

Collective polarization of cells along a tissue plane, referred to as planar cell polarity (PCP), is fundamental to embryonic development and tissue organization in complex, multicellular organisms. The ordered alignment of body hairs along the mammalian skin is an excellent example of PCP. PCP is regulated by the asymmetric localization of core PCP components at cell junctions bridged by atypical cadherin Celsr1. The goal of this work is to elucidate how Celsr1 mediates extracellular adhesion to coordinate functional PCP and how these activities are altered by the PCP-disrupting mutation Crash (Crsh).

Field cooled annular Josephson tunnel junctions

We investigate the physics of planar annular Josephson tunnel junctions quenched through their transition temperature in the presence of an external magnetic field. Experiments carried out with long Nb/Al-AlOx/Nb annular junctions showed that the magnetic flux trapped in the high-quality doubly-connected superconducting electrodes forming the junction generates a persistent current whose associated magnetic field affects the both the static and dynamics properties of the junctions. More specifically, the field trapped in the hole of one electrode combined with a d.c. bias current induces a viscous flow of dense trains of Josephson vortices which manifests itself through the sequential appearance of displaced linear slopes, Fiske step staircases and Eck steps in the junction’s current-voltage characteristic. Furthermore, a field shift is observed in the first lobe of the magnetic diffraction pattern. The effects of the persistent current can be mitigated or even canceled by an external magnetic field perpendicular to the junction plane. The radial field associated with the persistent current can be accurately modeled with the classical phenomenological sine-Gordon model for extended one-dimensional Josephson junctions. Extensive numerical simulations were carried out to disclose the basic flux-flow mechanism responsible for the appearance of the magnetically induced steps and to elucidate the role of geometrical parameters. It was found that the imprint of the field cooling is enhanced in confocal annular junctions which are the natural generalization of the well studied circular annular junctions.

High-frequency diffraction contribution by planar metallic–DNG metamaterial junctions

AbstractThe plane wave diffraction by a planar junction consisting of a thick metallic sheet and a lossy double-negative metamaterial slab is studied by using the Uniform Asymptotic Physical Optics approach. This approach assumes the radiation integral as a starting point and uses the physical optics surface currents as sources to be integrated. The integral is manipulated by taking advantage of useful approximations and evaluations, and re-formulated in order to apply an asymptotic procedure able to generate a closed-form approximate solution in the framework of the Uniform Geometrical Theory of Diffraction. Accordingly, advantages and drawbacks result from the application of the proposed solution. The jumps of the geometrical optics field are compensated. Implementation and handling of the computer code are facilitated by the evaluation of well-known functions and parameters. No differential/integral equations or special functions must be computed.

Fluoroaromatic Cation‐Assisted Planar Junction Perovskite Solar Cells with Improved VOC and Stability: The Role of Fluorination Position

The notoriously poor stability of organic–inorganic hybrid perovskite solar cells is a crucial issue restricting the commercial application of such burgeoning technology. Passivation of bulk perovskite absorber by fluorinated aromatic ammonium salt via low‐dimensional perovskites has been proved to be an effective way of improving stability and efficiency. Herein, the influence of fluorination position (ortho‐, meso‐, and para‐) on the aromatic moiety is studied in terms of their dipole moments and the ability to reduce defect density, extend carrier lifetimes, and assist charge transfer. In addition to the improved power conversion efficiency (PCE) from 19.17% to above 20%, the device treated with 2‐(o‐fluorophenyl)ethylamine iodide exhibits a remarkable open‐circuit voltage (VOC) of 1.21 V. While the 2‐(p‐fluorophenyl)ethylamine iodide‐treated device shows only 1% loss of its initial value under ambient atmosphere (with RH of 10–30%) without encapsulation for 1440 h storage. The molecular structure of fluorinated aromatic cations plays multiple roles in passivating the interface of the perovskite device.