Junction Devices Research Articles

Impact of lifetime on the levelized cost of electricity from perovskite single junction and tandem solar cells

The calculated levelized cost of electricity for single junction and tandem devices show that when the time for perovskite devices to degrade to 85% of the original output (T85) is only 3 years, tandem device are economically favorable.

A floating gate negative capacitance MoS2 phototransistor with high photosensitivity.

Monolayer MoS2 exhibits interesting optoelectronic properties that have been utilized in applications such as photodetectors and light emitting diodes. For image sensing applications, improving the light sensitivity relies on achieving a low dark current that enables the detection weak light signals. Although previous reports on improving the detectivity have been explored with heterostructures and pn junction devices, some of these approaches lack CMOS compatibility processing and sufficient low dark current suppression. Steep slope transistors that overcome the Boltzmann tyranny can further enhance the performance in photodetectors by providing efficient extraction of photogenerated charges. Here, we report a monolayer MoS2 floating gate negative capacitance phototransistor with the integration of a hafnium-zirconium oxide ferroelectric capacitor. In this study, a SSmin of 30 mV dec-1, very low dark currents of 10-13-10-14 A, and a high detectivity of 7.2 × 1015 cm Hz1/2 W-1 were achieved under weak light illumination due to an enhancement in the photogating effect. In addition, its potential as an optical memory and as an optical synapse with excellent long-term potentiation characteristics in an artificial neural network was also explored. Overall, this device structure offers high photosensitivity to weak light signals for future low-powered optoelectronic applications.

Ferroelectric Devices for Intelligent Computing

Recently, transistor scaling is approaching its physical limit, hindering the further development of the computing capability. In the post-Moore era, emerging logic and storage devices have been the fundamental hardware for expanding the capability of intelligent computing. In this article, the recent progress of ferroelectric devices for intelligent computing is reviewed. The material properties and electrical characteristics of ferroelectric devices are elucidated, followed by a discussion of novel ferroelectric materials and devices that can be used for intelligent computing. Ferroelectric capacitors, transistors, and tunneling junction devices used for low-power logic, high-performance memory, and neuromorphic applications are comprehensively reviewed and compared. In addition, to provide useful guidance for developing high-performance ferroelectric-based intelligent computing systems, the key challenges for realizing ultrascaled ferroelectric devices for high-efficiency computing are discussed.

High-densities of free holes in homoepitaxial n-GaN induced by fluorine-plasma ion implantation

In this work, fluorine plasma ion implantation is used to induce high densities of free holes in homoepitaxial n-GaN for the first time, as evidenced by electroluminescence and p-n junction rectification. F+ ions implanted into the near-surface layer capture electrons from shallow bulk donors, bending the band upward until a high density of free holes is induced at the valence band maximum, and surface donors, depinning the Fermi level to form p-type ohmic contact. Free holes tunnel from the metal into states at the valence band maximum, where they form a conductive p-type channel, benefitting the development of GaN-based junction devices.

Electrical Transport and Current Conduction Mechanisms in ZnO/Si Heterojunction Diode

Abstract: The objective of this research is the relevant equations of electrical transport inside a junction device based on metallic oxides like zinc oxides retained on silicon substrate by spray pyrolysis process. Many characteristics, such as the heterojunction diode's non-ideal conduct, electronic conduction of electrons and gaps in the conduction and valence bands, charge carriers caught by trap centers, hopping conduction, and tunnel effect, are used in various conduction processes at electronic junctions. Poole-Frenkel (PF) emission, Schottky emissions, and trap aided tunneling are some of the other conduction mechanisms examined inside forward/reverse bias for ZnO/Si heterojunctions (TAT). This article also confirms, addresses, and elucidates the effect of temperature on the I-V properties of ZnO/Si.
 https://ecee.colorado.edu/~bart/book/book/chapter3/ch3_9.htm

Perpendicular Magnetic Anisotropy and Its Electric Field Manipulation in Magnetic Multilayered Heterostructures

"Understanding of underlying physics related to the Perpendicular Magnetic Anisotropy (PMA) in magnetic heterostructures represents a major issue for its exploit in random-access memory (MRAM) devices. Using ab-initio analysis, we reveal some basic aspects related to the anatomy of PMA and its variation with electric field in various X/Fe/MgO(001) multilayer configurations (X=Cr, Au, V, Ag, Pt, Pd,…) compatible with standard experimental architectures of magnetic tunnel junction devices. Our study quantifies and underlines the significant role of the Rashba interfacial field on PMA. We explain and correlate the sign, the magnitude, and the electric field dependence of the PMA, the Rashba coefficient R and the Dzyaloshinskii–Moriya (DMI) asymmetric exchange interaction parameter. Moreover, when varying the Fe thickness in X/Fe/MgO(001) systems, we observe oscillations of PMA with the number of Fe monolayers, explained within the framework of quantum wells of the 1 Bloch symmetry electrons in Fe. Further atomistic micromagnetic simulations including different Fe layer thicknesses and the corresponding PMA predict macroscopic magnetization characteristics in realistic experimental systems. Keywords: perpendicular magnetic anisotropy, electric field control of PMA, magnetic tunnel junctions, magnetic multilayer heterostructures, atomistic magnetic simulations. "

Atomic-Scale Modification of Oxidation Phenomena on the Ge(100) Surface by Si Alloying.

Properties of Ge oxides are significantly different from those of widely used Si oxides. For example, the instability of GeO x at device junctions causes electronic defect levels that degrade the performance of Ge-containing devices (e.g., transistors and infrared detectors). Therefore, the passivating Si layers have been commonly used at Ge interfaces to reduce the effects of Ge oxide instability and mimic the successful strategy of Si oxidation. To contribute to the atomic-scale knowledge and control of oxidation of such Si-alloyed Ge interfaces (O/Si/Ge), we present a synchrotron radiation core-level study of O/Si/Ge, which is combined with scanning probe microscopy measurements. The oxidation processes and electronic properties of O/Si/Ge(100) are examined as functions of Si amount and oxidation doses. In particular, the incorporation of Si into Ge is shown to cause the strengthening of Ge-O bonds and the increase of incorporated oxygen amount in oxide/Ge junctions, supporting that the method is useful to decrease the defect-level densities.

Strategic fabrication of efficient photo-responsive semiconductor electronic diode-devices by Bovine Serum Albumin protein-based Cu(II)-metallohydrogel scaffolds

Bovine Serum Albumin protein-based two fascinating functional self-healing Cu(II) metallohydrogel scaffolds (MD1 and MD2) have been studied for the development of metal-semiconductor junction based Schottky diode device. Multiple metal-semiconductor (MS) junction devices, offering the sandwich-like configuration of Indium tin oxide (ITO)/ metallogel/Aluminium (Al), have been made-up to investigate the electrical properties of the synthesized metallohydrogel materials. Optical characterizations including optical band gap measurement have been carried out using Tauc's equation for both the metallohydrogels. The current-voltage (I-V) characteristics of just made-up devices are studied under irradiation and non- irradiation conditions to explore the electrical features through investigating the charge transport phenomenon. The electrical conductivity gets estimated as 3.13 × 10−5 S.m−1 and 2.69 × 10−5 S.m−1 for MD1 and MD2 under dark condition, and 11.06 × 10−5 S.m−1 and 5.99 × 10−5 S.m−1 for MD1 and MD2, respectively, in photo-irradiation. The measured optical and electrical properties of MD1 and MD2 metallohydrogels are thoroughly investigated and the data indicates that MD1 and MD2 metallohyrogels are semiconducting in nature with excellent photo-responsive behaviour. Moreover, the representative I − V characteristic of the MD1 and MD2 metallohydrogels at both irradiation and non-irradiation conditions represents the nonlinear rectifying behaviour, a typical signature for Schottky diode (SD).

Oscillations of photonic heat current through parallel-coupled double circular mesoscopic Josephson junction devices

Oscillations of photonic heat current through parallel-coupled double circular mesoscopic Josephson junction devices

Exotic Spintronic Properties of Transition‐Metal Monolayers on Graphyne

AbstractThe recent discovery of 2D magnetic materials, which are compounds of transition metals (TM) with other elements, has opened new avenues for basic research on low‐dimensional magnetism and potential applications in spintronics. To further explore new 2D magnets of pure TM is an interesting topic. Based on the first‐principles calculations, here a strategy of obtaining monolayer TM magnets, i.e., depositing TM atoms on graphyne (Gy), which has proper hexagonal hollow geometry, is proposed. It is found that a TM monolayer with perfect hexagonal geometry can be formed on Gy. The TM monolayer exhibits a wealth of physical properties in dependence of TM species, such as ferromagnetic and anti‐ferromagnetic ground states, as well as intriguing semimetal and half‐metal characteristics. It is also found that the half‐metal characteristics make the monolayer TM have great potential applications in horizontal magnetic tunnel junction (MTJ) devices, where the tunneling magnetoresistance can reach as high as 850 000%. These results provide a new framework for obtaining 2D magnets with outstanding spintronic properties.

High‐Accuracy and Broadband Wavelength Sensor with Detection Region Ranging from Deep Ultraviolet to Near Infrared Light

AbstractIn this paper, a broadband wavelength sensor which is composed of two horizontally stacked photodetectors is reported. The top part is a monolayer graphene (MLG)/thin Si/MLG heterojunction device and the bottom part is a MLG/Ge Schottky junction device. Owing to the thin thickness of the Si and the wavelength‐dependent absorption coefficients of both Si and Ge, the two photodetectors exhibit sharp contrast in photon‐generation rate when illuminated with different wavelengths of light. This distinction in photon generation leads to completely different evolution in photocurrent, and the corresponding relationship between the photocurrent ratio and wavelength can be easily expressed as a monotonic function, via which the wavelength in a broad range from deep ultraviolet (265 nm) to near infrared light (1550 nm) can be easily calculated. Notably, the average relative error and the average absolute error of the wavelength sensor are estimated to be 2.1% and 2.3 nm, respectively, which are much better than previously reported values.

High-Switching-Frequency SiC Power Converter for High-Speed Switched Reluctance Machine

This article reports design and testing of silicon carbide) devices-based three-phase asymmetric H-bridge converter capable of switching at 50 kHz and intended to drive high-speed switched reluctance machine. Electromagnetic designs of a 7.5-kW, 30 000-r/min and a 20-kW, 50 000-r/min Switched reluctance machine are presented. The 30 000-r/min machine is fabricated and characterized. A machine model is obtained from the measured characteristics. Based on the machine model, as well as drive operating variables and device data-sheet parameters, two methods are proposed for evaluating the losses in the power devices. The first method relies on machine model to obtain machine current and converter duty ratio, and thereby estimate the device losses. A second simplified method provides closed-form expressions for device losses. The proposed analytical expressions relate the machine characteristics such as inductance and saturation current with converter losses. The estimated loss is further used to predict device junction temperature. The power converter and device ratings are chosen so that the converter is suitable for both machines. The capacitor selection and sizing are discussed. Further, the power converter architecture and other subsystems of the converter are described. Test results are presented for the asymmetric H-bridge converter at 800 V dc bus voltage, 50 A of load current, and 50 kHz of switching frequency. Thermal image is presented for validation of estimated heat-sink temperature. The predicted heat-sink temperature is found to agree well with the measured temperature. The power converter is used to operate the 30 000-r/min machine at various speeds.

Plasmon‐Induced Pyro‐Phototronic Effect Enhancement in Self‐Powered UV–Vis Detection with a ZnO/CuO p–n Junction Device

AbstractIt is important to detect light of low power density sensitively and fast for the application of optical communication, environmental monitoring, astronomy, and national securities. However, ZnO‐based photodetectors exhibit long decay time owing to the persistent photoconductivity (PPC) and are hard to detect light with low power density efficiently. Here, a practical strategy is utilized to improve the performance of ZnO‐based photodetectors by coupling the pyroelectric effect of ZnO with localized surface plasmon resonance (LSPR) of Au nanoparticles subtly. Hence, a self‐powered photodetector is demonstrated, which is integrated with ZnO/CuO core–shell nanorods and Au nanoparticles to detect UV to vis light. This self‐powered photodetector achieves fast and sensitive detection of UV when power density is 68 nW cm−2. The performance is significantly improved than the photodetectors without Au nanoparticles. The optimal responsivity and detectivity under the same power density of UV at 325 nm are 1.4 × 10−4 A W−1 and 3.3 × 1011 Jones. Response/recovery time is remarkably shortened to ≈10 ms. The results indicate that the material configurations and design concept make the device applicable for self‐powered, high‐performance photodetectors, and provide further promoted understanding of LSPR enhanced performance of photodetectors.

Large Dzyaloshinskii-Moriya interaction and room-temperature nanoscale skyrmions in CoFeB/MgO heterostructures

Magnetic skyrmions in heavy metal (HM)/CoFeB/MgO structures are of particular interest for skyrmion-based magnetic tunnel junction (MTJ) devices because of their reliable generation, stability, and readout through purely electrical methods. To optimize the properties, such as stability, a strong Dzyaloshinskii-Moriya interaction (DMI) is required at room temperature. Here, using first-principles calculations, we demonstrate that huge DMI can be obtained in Ir/CoFe structures with an Fe-terminated configuration. Moreover, Brillouin light-scattering measurements show that indeed Ta/Ir/Co 20 Fe 60 B 20 /MgO thin films with perpendicular magnetic anisotropy exhibit a large DMI value (1.13 mJ/m 2 ) when the thickness of the CoFeB layer is 1.1 nm, which can be attributed to the smooth and Fe-rich interface between Ir and CoFeB layers. Furthermore, we observe stable sub-100 nm magnetic skyrmions at room temperature in the Ir/CoFeB/MgO systems by magnetic force microscope. This work paves the way for promoting the application of skyrmions in CoFeB/MgO-based perpendicular anisotropy MTJ structures. Large DMI in Ir/CoFeB/MgO thin films with perpendicular magnetic anisotropy First-principles calculations combined with Brillouin light-scattering methods Significant role of interfacial configuration on the regulation of DMI Sub-100 nm room-temperature magnetic skyrmions in Ir/CoFeB/MgO multilayers Chen et al. observe a large Dzyaloshinskii-Moriya interaction, combined with the evidence of sub-100-nm room-temperature skyrmions in Ir/CoFeB/MgO structures. This material stack may provide a platform to realize skyrmionics, especially the nucleation and electrical detection of skyrmions in perpendicular anisotropy-based magnetic tunnel junctions.

Cation exchange synthesis of porous Cd1‐xZnxS twinned nanosheets for visible light highly active H2 evolution

AbstractEfficient charge separation is critical for the enhancement of photocatalytic activity for hydrogen generation. The porous Cd1‐xZnxS nanosheets with twinned phase junctions were synthesized by the cation‐exchange approach of inorganic‐organic hybrid ZnS‐diethylenetriamine nanoflakes with cadmium ions. With the synergy of the phase junctions induced by nano twins and porous structure, the hydrogen evolution average rate over the optimal sample Cd0.5Zn0.5S photocatalyst reaches 14.44 mmol h−1 g−1 without noble metal loading under visible light irradiation, corresponding to apparent quantum efficiency of 37.3% at 420 nm and solar‐to‐hydrogen energy conversion efficiency of 3.46%. On the one hand, twin‐induced phase junctions can improve the separation efficiency of photoelectron‐hole pairs, on the other hand, the large specific surface area ascribed to the porous nanosheet can effectively improve the light absorption capacity of photocatalysis, and provide more surface active sites. This study could provide a facile approach to design and fabricate advanced materials with porous twinned phase junctions for photocatalytic applications and optoelectronic devices.

Optimized front TCO and metal grid electrode for module‐integrated perovskite–silicon tandem solar cells

AbstractTo unlock the full potential of perovskite–silicon tandem solar cells with >30% efficiency at presumably low cost, the transparent conductive oxides (TCOs) and metal grid at the front side need to be adapted compared to classical silicon heterojunction (SHJ) solar cells. By means of optical and electrical modelling, we consider the main aspects to optimize the front electrode for the tandem case, where in contrast to silicon single junction devices, there are (i) different optical properties including a lower refractive index of the perovskite absorber (ii) about half the current, thus quarter the resistive power losses for the same series resistance contribution (iii) lateral transport at the front needs to be provided solely by the front TCO layer and (iv) lower thermal stability of the perovskite, which affects TCO deposition conditions and results in a less efficient sintering of the silver screen printing pastes. This study concludes that compared to silicon heterojunction cells, the thickness of the front TCO should be reduced from 75 nm to around 20 nm, resulting in less parasitic absorption and a potential cost reduction of 1.46 €ct/cell for ITO. We investigate the impact of different front metallization including plating and silver screen printing and showcase that for multi‐wire interconnection concepts, the number of wires can be reduced from 18 wires to 9 or even less depending on the front metallization. Finally, we give an outlook on the silver consumption and levelized cost of electricity.

(Invited) Vertically Stacked Junction Devices Fabricated Using Single-Crystal Graphene on SiC Substrate

Graphene is a potential post-silicon nanomaterial because of its tremendous properties. Single-crystal graphene epitaxially grown on a SiC substrate is the most promising candidate for future electron devices. Single-crystal graphene with a 100 mm2 size has been successfully fabricated using a high-temperature rapid thermal annealing system [1]. In this study, two types of stacked graphene devices using graphene on SiC are demonstrated. The first device is a bi-crystal system consisting of two graphene samples as shown in Fig. 1 (a). These samples are directly bonded in a face-to-face manner. Contact pins are attached to the graphene surface for ohmic contact. The electrical characteristics of the stacked graphene junction were ohmic at a low bias voltage below 20 V. The linear characteristic at a low bias voltage is attributed to the linear dispersion relation in the band structure of graphene, Dirac cone. At a high bias voltage, the conductance of the graphene junction drastically increased. This nonlinear behavior originates from a semi-metallic property far from the Dirac point. Thermal imaging results indicated that electrical power was directly converted to infrared radiation. The radiation efficiency was estimated to be approximately 10%, which was high compared to that of a previously reported graphene blackbody emitter. The infrared emission spectrum measured using FT-IR was blackbody-like [2]. The peak wavelength of the measured spectrum was almost constant at 10.2 µm with changing applied power. The estimated junction voltage was approximately 5 V at a bias voltage of 80 V. Hot electrons were injected to the graphene layer. The results suggested that infrared emissions from the graphene–graphene stacked junction could be attributed to a nonthermal emission mechanism, such as phonon–plasmon coupling. The other vertically stacked graphene junction is a tunneling diode as shown in Fig. 1 (b). An insulative layer is sandwiched between two graphene samples. A structured water layer [3] formed by deionized water treatment on the epitaxial graphene sample acts as a tunneling barrier. Nonlinear I–V characteristics were observed. The dynamic range of the current change reached the sixth order of magnitude. The estimated thickness of the structured water layer was approximately 0.5 nm. As the tunneling barrier was sufficiently thin, a direct tunneling phenomenon could be observed in a low bias regime. In a high bias regime, the Fowler–Nordheim tunneling phenomenon was observed. A sandwich structure of a vertically stacked graphene junction with a sub-nm-thick structured water layer was constructed through simple water treatment and a direct bonding technique [4]. [1] T. Aritsuki, et al., Jpn. J. Appl. Phys. 55 (2016) 06GF03. [2] N. Murakami, et al., Jpn. J. Appl. Phys. 60 (2021) SCCD01. [3] M. Kitaoka, et al., Jpn. J. Appl. Phys. 56 (2017) 085102. [4] J. Du, et al., Jpn. J. Appl. Phys. 58 (2019) SDDE01. Figure 1

Training of quantized deep neural networks using a magnetic tunnel junction-based synapse

Quantized neural networks (QNNs) are being actively researched as a solution for the computational complexity and memory intensity of deep neural networks. This has sparked efforts to develop algorithms that support both inference and training with quantized weight and activation values, without sacrificing accuracy. A recent example is the GXNOR framework for stochastic training of ternary and binary neural networks (TNNs and BNNs, respectively). In this paper, we show how magnetic tunnel junction (MTJ) devices can be used to support QNN training. We introduce a novel hardware synapse circuit that uses the MTJ stochastic behaviour to support the quantize update. The proposed circuit enables processing near memory (PNM) of QNN training, which subsequently reduces data movement. We simulated MTJ-based stochastic training of a TNN over the MNIST, SVHN, and CIFAR10 datasets and achieved an accuracy of , and , respectively (less than degradation compared to the GXNOR algorithm). We evaluated the synapse array performance potential and showed that the proposed synapse circuit can train TNNs in situ, with for feedforward and for weight update.

Ferroelectricity of pure HfOx in metal-ferroelectric-insulator-semiconductor stacks and its memory application

Ferroelectricity in hafnium oxide (HfOx) and its various applications have been rigorously investigated in recent years. In particular, most studies have focused on a non-centrosymmetric ferroelectric phase that is developed via the injection of external ions into HfOx. However, the drawbacks of doped HfOx, such as serious dopant variation and thermal instability, have hindered its commercialization in low-power logic and memory applications. In this study, we demonstrated the ferroelectricity of pure HfOx without additional ion doping in metal-ferroelectric-insulator-semiconductor (MFIS) stacks. We experimentally confirmed that variation-resistant and thermally stable ferroelectric pure HfOx could be achieved with remarkable polarization by controlling the oxygen vacancies inside pure HfOx and the thermal quenching process for orthorhombic phase transition. Furthermore, to verify the feasibility of the ferroelectric pure HfOx in memory devices, the modulation of tunneling resistance was measured using MFIS ferroelectric tunnel junction (FTJ) devices, revealing that the tunneling current was adjustable over a 2-order current range via the polarization of the pure HfOx, implying that multiple current states could be obtained for multilevel memory operations.

Electrostatically Doped Schottky barrier tunnel field effect transistor

ABSTRACT This work reports a novel steep switching device architecture, electrosatically doped asymmetric schottky barrier tunnel field effect transistor (ED-SB-TFET) investigated by calibrated exhaustive 2D TCAD device simulation. This work deploys the concept of work-function engineering of the drain electrode along with the PtSi 5 source. The tactical use of a spacer along with the incorporation of high-K gate dielectrics enabled improvised switching ratio as well as sub-threshold slope (SS) reduction. The proposed ED-SB-TFET demonstrates a substantial reduction in the ambipolar current (Iamb ), steeper SS, magnificent boost in drive current and higher scalability. This concept of electrostatic doping in schottky junction device facilitates easy fabrication technology as it does not need ion implantation/diffusion to realise the ultra-sharp source/drain doping profile. Further, the reported structure offers extreme resilience for random dopant fluctuations (RDFs), process variations, doping control issues, and bulk trap-assisted tunnelling (TAT) induced degradation. In addition to this, the analog and RF performance parameters have also been investigated. Our study establishes ED-SB-TFET as a promising candidate for low power futuristic switching applications.