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2019年JOS入选“中国科技期刊卓越行动计划”
In Press
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• ## Strain-induced the dark current characteristics in InAs/GaSb type-II superlattice for mid-wave detector

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Type-II superlattice (T2SL) materials are a key element for infrared (IR) detectors. However, it is well known that the characteristics of the detectors with the T2SL layer are greatly affected by the strain developed during the growth process, which determines the performance of IR detectors. Therefore, great efforts have been made to properly control the strain effect and develop relevant analysis methods to evaluate the strain-induced dark current characteristics. In this work, we report the strain-induced dark current characteristics in InAs/GaSb T2SL MWIR photodetector. The overall strain of InAs/GaSb T2SL layer was analyzed by both high-resolution X-ray diffraction (HRXRD) and the dark current measured from the absorber layer at the elevated temperature (≥ 110 K), where the major leakage current component is originated from the reduced minority carrier lifetime in the absorber layer. Our findings indicate that minority carrier lifetime increases as the tensile strain on the InAs/GaSb T2SL is more compensated by the compressive strain through ‘InSb-like’ interface, which reduces the dark current density of the device. Specifically, tensile strain compensated devices exhibited the dark current density of less than 2 × 10–5 A/cm2 at 120 K, which is more than one order of magnitude lower value compared to that of the device without tensile strain relaxation.

• ## A review of flexible halide perovskite solar cells towards scalable manufacturing and environmental sustainability

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The perovskite material has many superb qualities which allow for its remarkable success as solar cells; flexibility is an emerging field for this technology. To encourage commercialization of flexible perovskite solar cells, two main areas are of focus: mitigation of stability issues and adaptation of production to flexible substrates. An in-depth report on stability concerns and solutions follows with a focus on Ruddlesden-Popper perovskites. Roll to roll processing of devices is desired to further reduce costs, so a review of flexible devices and their production methods follows as well. The final focus is on the sustainability of perovskite solar cell devices where recycling methods and holistic environmental impacts of devices are done.

• ## Nanofiber/nanowires-based flexible and stretchable sensors

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Nanofibers/nanowires with one-dimension (1D) nanostructure or well-patterned microstructure have shown distinctly advantages in flexible and stretchable sensor fields, owing to their remarkable tolerance against mechanical bending or stretching, outstanding electronic/optoelectronic properties, good transparency, and excellent geometry. Herein, latest summaries in the unique structure and properties of nanofiber/nanowire function materials and their applications for flexible and stretchable sensor are highlighted. Several types of high-performance nanofiber/nanowire-based flexible pressure and stretchable sensors are also reviewed. Finally, a conclusion and prospect for 1D nanofiber/nanowires-based flexible and stretchable sensors are also intensively discussed. This summary offers new insights for the development of flexible and stretchable sensor based 1D nanostructure in next-generation flexible electronics.

• ## Growth of aligned SnS nanowire arrays for near infrared photodetectors

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Aligned SnS nanowires arrays were grown via a simple chemical vapor deposition method. As-synthesized SnS nanowires are single crystals grown along the [111] direction. The single SnS nanowire based device showed excellent response to near infrared lights with good responsivity of 267.9 A/W, high external quantum efficiency of 3.12 × 104 % and fast response time. Photodetectors were built on the aligned SnS nanowire arrays, exhibiting a light on/off ratio of 3.6, and the response and decay time of 4.5 and 0.7 s, respectively, to 1064 nm light illumination.

• ## Flexible inorganic oxide thin-film electronics enabled by advanced strategies

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With the advent of human-friendly intelligent life, as well as increasing demands for natural and seamless human-machine interactions, flexibility and wearability are among the inevitable development trends for electronic devices in the future. Due to the advantages of rich physicochemical properties, flexible and stretchable inorganic oxide thin-film electronics play an increasingly important role in the emerging and exciting flexible electronic field, and they will act as a critical player in next-generation electronics. However, a stable strategy to render flexibility while maintaining excellent performance of oxide thin films is the most demanding and challenging problem, both for academic and industrial communities. Thus, this review focuses on the latest advanced strategies to achieve flexible inorganic oxide thin-film electronics. This review emphasizes the physical transferring strategies that are based on mechanical peeling and the chemical transferring strategies that are based on sacrificial layer etching. Finally, this review evaluates and summarizes the merits and demerits of these strategies toward actual applications, concluding with a future perspective into the challenges and opportunities for the next-generation of flexible inorganic oxide thin-film electronics.

• ## Recent advancements in flexible humidity sensors

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doi: 10.1088/1674-4926/41/4/040401

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• ## 4H-SiC trench MOSFET with an integrated Schottky barrier diode and L-shaped P+ shielding region

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A novel 4H-SiC trench MOSFET is presented and investigated by simulation in this paper. The device features an integrated Schottky barrier diode and an L-shaped P+ shielding region beneath the gate trench and aside one wall of the gate trench (S-TMOS). The integrated Schottky barrier diode works as a free-wheeling diode in reverse recovery and reverse conduction, which significantly reduces reverse recovery charge (Qrr) and reverse turn-on voltage (VF). The L-shaped P+ region effectively shields the coupling of gate and drain, resulting in a lower Gate-Drain capacitance (Cgd) and Gate-Drain charge (Qgd). Compared with that of conventional SiC trench MOSFET(C-TMOS), the VF and Qrr of S-TMOS has reduced by 44% and 75%, respectively, with almost the same forward output current and reverse breakdown voltage. Moreover, the S-TMOS reduces Qgd and Cgd by 32% and 22%, respectively, in comparison with C-TMOS.

• ## An 18-bit sigma–delta switched-capacitor modulator using 4-order single-loop CIFB architecture

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Oversampling sigma–delta (Σ–Δ) analog-to-digital converters (ADCs) are currently one of the most widely used architectures for high-resolution ADCs. The rapid development of integrated circuit manufacturing processes has allowed the realization of a high resolution in exchange for speed. Structurally, the Σ–Δ ADC is divided into two parts: a front-end analog modulator and a back-end digital filter. The performance of the front-end analog modulator has a marked influence on the entire Σ–Δ ADC system. In this paper, a 4-order single-loop switched-capacitor modulator with a CIFB (cascade-of-integrators feed-back) structure is proposed. Based on the chosen modulator architecture, the ASIC circuit is implemented using a Chartered 0.35 μm CMOS process with a chip area of 1.72 × 0.75 mm2. The chip operates with a 3.3-V power supply and a power dissipation of 22 mW. According to the results, the performance of the designed modulator has been improved compared with a mature industrial chip and the effective number of bits (ENOB) was almost 18-bit.

• ## Defect levels in d-electron containing systems: comparative study of CdTe using LDA and LDA + U

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The defect properties in d-electron containing materials will be strongly influenced by the non-negligible on-site Coulomb interactions. However, this has been omitted in the current widely adopted standard first-principles calculations, such as LDA, leading to a large deviation of calculated results. Therefore, as a comparative case study, in this paper the defects of CdTe are investigated by first-principles calculations including standard LDA and LDA + U, and we find that LDA + U gives more accurate formation energies of the neutral point defects than the standard LDA. The same trend can be found in transition energies of the charged state defects as well. These comparative analyses show that LDA + U gives better results for the defects of CdTe than the standard LDA and requires less computing resource than LAPW, indicating it should have huge potential to model supercells with large number of atoms and strong electron interactions. Moreover, a new anion interstitial defect structure is found to be more stable than the well-known tetrahedron central anion interstitial defect structure \begin{document}${\rm{Te}}_i^a$\end{document}.

• ## A high performance adaptive on-time controlled valley-current-mode DC–DC buck converter

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This paper presents an AOT-controlled (adaptive-on-time, AOT) valley-current-mode buck converter for portable application. The buck converter with synchronous rectifier not only uses valley-current-mode control but also possesses hybrid-mode control functions at the same time. Due to the presence of the zero-current detection circuit, the converter can switch freely between the two operating modes without the need for an external mode selection circuit, which further reduces the design difficulty and chip area. The converter for the application of high power efficiency and wide current range is used to generate the voltage of 0.6–3.0 V with a battery source of 3.3–5.0 V, while the load current range is 0.05–2 A. The circuit can work in continuous conduction mode with constant frequency in high load current range. In addition, a stable output voltage can be obtained with small voltage ripple. In pace with the load current decreases to a critical value, the converter transforms into the discontinuous conduction mode smoothly. As the switching period increases, the switching loss decreases, which can significantly improve the conversion efficiency. The proposed AOT controlled valley current mode buck converter is integrated with standard 0.18 μm process and the simulation results show that the converter provides well-loaded regulations with power efficiency over 95%. When the circuit switches between the two conduction modes drastically, the response time can be controlled within 30 μs. The undershoot voltage is controlled within 25 mV under a large current hopping range.

• ## 1064 nm InGaAsP multi-junction laser power converters

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Laser photovoltaic devices converting 1064 nm light energy into electric energy present a promising prospect in wireless energy transmission due to the commercial availability of high power 1064 nm lasers with very small divergence. Besides their high conversion efficiency, a high output voltage is also expected in a laser energy transmission system. Meanwhile, 1064 nm InGaAsP multi-junction laser power converters have been developed using p+-InGaAs/n+-InGaAs tunnel junctions to connect sub-cells in series to obtain a high output voltage. The triple-junction laser power converter structures are grown on p-type InP substrates by metal-organic chemical vapor deposition (MOCVD), and InGaAsP laser power converters are fabricated by conventional photovoltaic device processing. The room-temperature IV measurements show that the 1 × 1 cm2 triple-junction InGaAsP laser power converters demonstrate a conversion efficiency of 32.6% at a power density of 1.1 W/cm2, with an open-circuit voltage of 2.16 V and a fill factor of 0.74. In this paper, the characteristics of the laser power converters are analyzed and ways to improve the conversion efficiency are discussed.

• ## Numerical study of mono-crystalline silicon solar cells with passivated emitter and rear contact configuration for the efficiency beyond 24% based on mass production technology

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Mono-crystalline silicon solar cells with a passivated emitter rear contact (PERC) configuration have attracted extensive attention from both industry and scientific communities. A record efficiency of 24.06% on p-type silicon wafer and mass production efficiency around 22% have been demonstrated, mainly due to its superior rear side passivation. In this work, the PERC solar cells with a p-type silicon wafer were numerically studied in terms of the surface passivation, quality of silicon wafer and metal electrodes. A rational way to achieve a 24% mass-production efficiency was proposed. Free energy loss analyses were adopted to address the loss sources with respect to the limit efficiency of 29%, which provides a guideline for the design and manufacture of a high-efficiency PERC solar cell.

• ## First principles study of the electronic structure and photovoltaic properties of β-CuGaO2 with MBJ + U approach

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Based on the density functional theory, the energy band and electronic structure of β-CuGaO2 are calculated by the modified Becke-Johnson plus an on-site Coulomb U (MBJ + U) approach in this paper. The calculated results show that the band gap value of β-CuGaO2 obtained by the MBJ + U approach is close to the experimental value. The calculated results of electronic structure indicate that the main properties of the material are determined by the bond between Cu-3d and O-2p energy levels near the valence band of β-CuGaO2, while a weak anti-bond combination is formed mainly by the O-2p energy level and Ga-4s energy level near the bottom of the conduction band of β-CuGaO2. The β-CuGaO2 thin film is predicted to hold excellent photovoltaic performance by analysis of the spectroscopic limited maximum efficiency (SLME) method. At the same time, the calculated maximum photoelectric conversion efficiency of the ideal CuGaO2 solar cell is 32.4%. Relevant conclusions can expand β-CuGaO2 photovoltaic applications.

• ## Recent progress of morphable 3D mesostructures in advanced materials

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Soft robots complement the existing efforts of miniaturizing conventional, rigid robots, and have the potential to revolutionize areas such as military equipment and biomedical devices. This type of system can accomplish tasks in complex and time-varying environments through geometric reconfiguration induced by diverse external stimuli, such as heat, solvent, light, electric field, magnetic field, and mechanical field. Approaches to achieve reconfigurable mesostructures are essential to the design and fabrication of soft robots. Existing studies mainly focus on four key aspects: reconfiguration mechanisms, fabrication schemes, deformation control principles, and practical applications. This review presents a detailed survey of methodologies for morphable mesostructures triggered by a wide range of stimuli, with a number of impressive examples, demonstrating high degrees of deformation complexities and varied multi-functionalities. The latest progress based on the development of new materials and unique design concepts is highlighted. An outlook on the remaining challenges and open opportunities is provided.

• ## Tubular/helical architectures construction based on rolled-up AlN nanomembranes and resonance as optical microcavity

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Aluminum nitride (AlN) has attracted a great amount of interest due to the fact that these group III–V semiconductors present direct band gap behavior and are compatible with current micro-electro-mechanical systems. In this work, three dimensional (3D) AlN architectures including tubes and helices were constructed by rolling up AlN nanomembranes grown on a silicon-on-insulator wafer via magnetron sputtering. The properties of the AlN membrane were characterized through transmission electron microscopy and X-ray diffraction. The thickness of AlN nanomembranes could be tuned via the RIE thinning method, and thus micro-tubes with different diameters were fabricated. The intrinsic strain in AlN membranes was investigated via micro-Raman spectroscopy, which agrees well with theory prediction. Whispering gallery mode was observed in AlN tubular optical microcavity in photoluminescence spectrum. A postprocess involving atomic layer deposition and R6G immersion were employed on as-fabricated AlN tubes to promote the Q-factor. The AlN tubular micro-resonators could offer a novel design route for Si-based integrated light sources. In addition, the rolled-up technology paves a new way for AlN 3D structure fabrication, which is promising for AlN application in MEMS and photonics fields.

• ## Modelling and optical response of a compressive-strained AlGaN/GaN quantum well laser diode

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The effects of the quantum well (QW) width, carrier density, and aluminium (Al) concentration in the barrier layers on the optical characteristics of a gallium nitride (GaN)-based QW laser diode are investigated by means of a careful modelling analysis in a wide range of temperatures. The device’s optical gain is calculated by using two different band energy models. The first is based on the simple band-to-band model that accounts for carrier transitions between the first levels of the conduction band and valence band, whereas the second assumes the perturbation theory (k.p model) for considering the valence intersubband transitions and the relative absorption losses in the QW. The results reveal that the optical gain increases with increasing the n-type doping density as well as the Al molar fraction of the AlxGa1–xN layers, which originate the GaN compressive-strained QW. In particular, a significant optical gain on the order of 5000 cm–1 is calculated for a QW width of 40 ? at room temperature. In addition, the laser threshold current density is of few tens of A/cm2 at low temperatures.

• ## A review on performance comparison of advanced MOSFET structures below 45 nm technology node

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CMOS technology is one of the most frequently used technologies in the semiconductor industry as it can be successfully integrated with ICs. Every two years the number of MOS transistors doubles because the size of the MOSFET is reduced. Reducing the size of the MOSFET reduces the size of the channel length which causes short channel effects and it increases the leakage current. To reduce the short channel effects new designs and technologies are implemented. Double gate MOSFET design has shown improvement in performance as amplifiers over a single MOSFET. Silicon-based MOSFET design can be used in a harsh environment. It has been used in various applications such as in detecting biomolecules. The increase in number of gates increases the current drive capability of transistors. GAA MOSFET is an example of a quadruple gate around the four sides of channel that increases gate control over the channel region. It also increases effective channel width that improves drain current and reduces leakage current keeping short channel effects under limit. Junctionless MOSFET operates faster and uses less power with increase in ON-state current leading to a good value of ION/IOFF ratio. In this paper, several gate and channel engineered MOSFET structures are analyzed and compared for sub 45 nm technology node. A comparison among different MOSFET structures has been made for subthreshold performance parameters in terms of IOFF, subthreshold slope and DIBL values. The analog/RF performance is analyzed for transconductance, effective transistor capacitances, stability factor and critical frequency. The paper also covers different applications of advance MOSFET structures in analog/digital or IoT/ biomedical applications.

• ## Characteristics and techniques of GaN-based micro-LEDs for application in next-generation display

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Due to the excellent optoelectronic properties, fast response time, outstanding power efficiency and high stability, micro-LED plays an increasingly important role in the new generation of display technology compared with LCD and OLED display. This paper mainly introduces the preparation methods of the GaN-based micro-LED array, the optoelectronic characteristics, and several key technologies to achieve full-color display, such as transfer printing, color conversion by quantum dot and local strain engineering.

• ## A 0.1–1.5 GHz multi-octave quadruple-stacked CMOS power amplifier

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In this letter, we design and analyze 0.1–1.5 GHz multi-octave quadruple-stacked CMOS power amplifier (PA) in 0.18 μm CMOS technology. By using two-stage quadruple-stacked topology and feedback technology, the proposed PA realizes an ultra-wideband CMOS PA in a small chip area. Wideband impedance matching is achieved with smaller chip dimension. The effects of feedback resistors on the RF performance are also discussed for this stacked-FET PA. The PA shows measured input return loss (< –10.8 dB) and output return loss (< –9.6 dB) in the entire bandwidth. A saturated output power of 22 dBm with maximum 20% power added efficiency (PAE) is also measured with the drain voltage at 5 V. The chip size is 0.44 mm2 including all pads.

• ## Skin-inspired electronics: emerging semiconductor devices and systems

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Current electronics are driven by advanced microfabrication for fast and efficient information processing. In spite of high performance, these wafer-based devices are rigid, non-degradable, and unable to autonomous repair. Skin-inspired electronics have emerged as a new class of devices and systems for next-generation flexible and wearable electronics. The technology gains inspiration from the structures, properties, and sensing mechanisms of the skin, which may find a broad range of applications in cutting-edge fields such as healthcare monitoring, human-machine interface, and soft robotics/prostheses. Practical demands have fueled the development of electronic materials with skin-like properties in terms of stretchability, self-healing capability, and biodegradability. These materials provide the basis for functional sensors with innovative and biomimetic designs. Further system-level integrations and optimizations enable new forms of electronics for real-world applications. This review summarizes recent advancements in this active area and speculates on future directions.