A Schottky barrier rectifier was fabricated with a (100)-oriented <inline-formula> <tex-math notation="LaTeX">\beta </tex-math></inline-formula>-Ga 2 O 3 substrate grown by the edge-defined film-fed ...method. The Sn-doped <inline-formula> <tex-math notation="LaTeX">\beta </tex-math></inline-formula>-Ga 2 O 3 substrate had an effective donor concentration of approximately <inline-formula> <tex-math notation="LaTeX">2\times 10^{17} </tex-math></inline-formula> cm −3 . High performance parameters were obtained, such as a high forward current (421 A/cm 2 at 2 V), low ON-resistance (2.9 <inline-formula> <tex-math notation="LaTeX">\text{m}\Omega \cdot </tex-math></inline-formula>cm 2 ), and short reverse recovery time (20 ns). Furthermore, the dynamic behavior of the device is characterized through test on the half-wave rectification of ac voltages at different frequency. The diode worked well at 100 kHz. At the end of the letter, we discuss how Ga 2 O 3 Schottky rectifier can operate at high frequency.
AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) suffer from severe quantum confined Stark effect (QCSE) due to the strong polarization field in the quantum wells (QWs) grown on c-plane ...substrates. In this paper, we propose a novel DUV LED structure embedded with graded QWs in which the Al composition was linearly changed to screen the QCSE. A significant increase of the internal quantum efficiency and thus an enhancement of the light output power by nearly 67% can be achieved, attributing to the improvement of the electron-hole wave function overlap (Γ e-hh ) to 58.6% in the Increased-Al-composition graded QWs, as compared to the QW without grading (Γ e-hh = 40.4%) and reverse grading (Γ e-hh = 33.6%). Further investigations show that the grading profile of the Al composition in the QWs, including either linearly increases or decreases along the growth direction and the thickness of graded QWs, determine the polarization electrical field in the QWs and as a result, significantly affecting the performance of the devices. In the end, a careful optimization of the graded QWs is called. The proposed structure with such unique graded QWs provides us an effective solution to suppress the QCSE effect in the pursuit of high-performance DUV emitters.
Synaptic devices with bipolar analog resistive switching behavior are the building blocks for memristor-based neuromorphic computing. In this work, a fully complementary metal-oxide semiconductor ...(CMOS)-compatible, forming-free, and non-filamentary memristive device (Pd/Al₂O₃/TaO
/Ta) with bipolar analog switching behavior is reported as an artificial synapse for neuromorphic computing. Synaptic functions, including long-term potentiation/depression, paired-pulse facilitation (PPF), and spike-timing-dependent plasticity (STDP), are implemented based on this device; the switching energy is around 50 pJ per spike. Furthermore, for applications in artificial neural networks (ANN), determined target conductance states with little deviation (<1%) can be obtained with random initial states. However, the device shows non-linear conductance change characteristics, and a nearly linear conductance change behavior is obtained by optimizing the training scheme. Based on these results, the device is a promising emulator for biology synapses, which could be of great benefit to memristor-based neuromorphic computing.
Owing to the advantages of ultra-wide bandgap and rich material systems, gallium oxide (Ga2O3) has emerged as a highly viable semiconductor material for new researches. This article mainly focuses on ...the growth processes, material characteristics, and applications of Ga2O3. Compared with single crystals and the epitaxial growth of other wide-bandgap semiconductors, large-size and high-quality β-Ga2O3 single crystals can be efficiently grown with a low cost, making them highly competitive. Thanks to the availability of high-quality single crystals, epitaxial films, and rich material systems, high-performance semiconductor devices based on Ga2O3 go through a booming development in recent years. The defects and interfaces of Ga2O3 are comprehensively analyzed owing to their significant influence on practical applications. In this study, the two most common applications of Ga2O3 materials are introduced. The high breakdown electric field, high working temperature, and excellent Baliga's figure-of-merit of Ga2O3 represent an inspiring prospect for power electronic devices. In addition, the excellent absorption in deep-ultraviolet band provides new ideas for optoelectronic detectors and ensures the dramatic progress. Finally, the summary, challenges, and prospects of the Ga2O3 materials and devices are presented and discussed.
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Uniformity is one of the most severe challenges for resistive random access memory (RRAM). In this letter, a novel programming scheme with gate voltage ramping (GVR) is proposed to improve the ...uniformity of RRAM in a one transistor and one resistor structure. In traditional operation, the gate of the access transistor is biased with a constant voltage and a sweeping voltage is applied to the source or drain during the SET (from HRS to LRS) and RESET (from LRS to HRS) processes. With the GVR scheme, the gate voltage V G is ramped and the source/drain are kept constant. A tight distribution of HRS can be achieved using GVR. Analysis of power generation in the RESET process of the GVR scheme reveals positive feedback from joule heating, which helps to accelerate filament rupture and results in a tendency to achieve full RESET. The intermediate resistance states commonly observed are effectively eliminated.
Data retention is one crucial reliability aspect of resistive random access memory (RRAM). The retention failure mechanism of the low-resistance state (LRS) for conductive bridge RAM is generally ...originated from the lateral diffusion of metal ions/atoms from the filament to its surrounding medium. In this letter, we proposed an effective method to improve the LRS retention by controlling the formation of the single filament. For a certain LRS, the effective surface area for metal ions/atoms diffusion in single filament is less than that of multi-filament. Thus, better LRS retention characteristics can be achieved by reducing the metal species diffusion. The validity of this method is verified by the superior retention characteristics of the LRS programmed by current mode, in comparison with voltage programming mode. The former tends to generate a single filament, while the later grows multi-filament. This letter provides a possible way to enhance the retention characteristics of RRAM.
In resistive random access memories, modeling conductive filament growing dynamics is important to understand the switching mechanism and variability. In this paper, a universal Monte Carlo simulator ...is developed based on a cell switching model and a tunneling-based transport model. Driven by external electric field, the growing process of the nanoscale filament occurring in the gap region is actually dominated by cells' conductive/insulating switching, modeled through a phenomenological physics-based probability function. The electric transport through the partially formed CF is considered as current tunneling in the framework of the Quantum Point Contact model, and the potential barrier is modulated during cells' evolution. To demonstrate the validity and universality of our simulator, various operation schemes are simulated, with the simulated I - V characteristics well explaining experimental observations. Furthermore, the statistical analyses of simulation results in terms of Weibull distribution and conductance evolution also nicely track previous experimental results. Representing a simulation scale that links atomic-scale simulations to compact modeling, our simulator has the advantage of being much faster comparing with other atomic-scale models. Meanwhile, our simulator shows good universality since it can be applied to various operation signals, and also to different electrodes and dielectric layers dominated by different switching mechanisms.
Resistive random access memory (RRAM) is a promising emerging nonvolatile memory which offer high density integration in the form of cross-bar array design. Selector devices are a vital requirement ...to suppress the cross-talk issue. In this letter, we are going to demonstrate the coexistence of resistive switching (RS) and threshold switching (TS) in an ultrathin 2-nm Aluminium oxide (AlOx)-based crossbar RRAM devices. Depending on current level the device itself can switch from TS to RS mode with a nonlinearity of > 10 2 . Stable TS of > 10 3 cycles has been achieved at 10 nA. Achievements of this letter offers the usability of 2-nm AlOx RRAM devices as a selector and as a memory device for high density crossbar array integration.
In this letter, we present the characterization and modeling of the reset statistics of Pt/NiO/W resistive random access memories. The experimental observations show that the Weibull slopes of both V ...reset and I reset cumulative distributions increase linearly with 1/ R on . The value of V reset63% is roughly independent of R on while I reset63% increases with 1/ R on . Fully analytical cell-based models based on the thermal dissolution of conductive filament are proposed for the reset switching statistical distributions, which can account for the experimental results with a remarkable agreement.
The use of graphene electrodes with hydrogenated edges for solid‐state nanopore‐based DNA sequencing is proposed, and molecular dynamics simulations in conjunction with electronic transport ...calculations are performed to explore the potential merits of this idea. The results of the investigation show that, compared to the unhydrogenated system, edge‐hydrogenated graphene electrodes facilitate the temporary formation of H‐bonds with suitable atomic sites in the translocating DNA molecule. As a consequence, the average conductivity is drastically raised by about 3 orders of magnitude while exhibiting significantly reduced statistical variance. Furthermore, the effect of the distance between opposing electrodes is investigated and two regimes identified: for narrow electrode separation, the mere hindrance due to the presence of protruding hydrogen atoms in the nanopore is deemed more important, while for wider electrode separation, the formation of H‐bonds becomes the dominant effect. Based on these findings, it is concluded that hydrogenation of graphene electrode edges represents a promising approach to reduce the translocation speed of DNA through the nanopore and substantially improve the accuracy of the measurement process for whole‐genome sequencing.
DNA sequencing with graphene nano‐electrodes shows great promise because the atomically thin graphene could electrically couple to one nucleobase at a time. Through a combination of molecular dynamics simulations and electronic transport calculations, it is found that hydrogenation of the graphene edges can lead to the formation of H‐bonds with DNA, resulting in higher conductivity and less statistical signal distribution.
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