2019年JOS入选“中国科技期刊卓越行动计划”
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• ## Design, modelling and simulation of a floating gate transistor with a novel security feature

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This study proposes a new generation of floating gate transistors (FGT) with a novel built-in security feature. The new device has applications in guarding the IC chips against the current reverse engineering techniques, including scanning capacitance microscopy (SCM). The SCM measures the change in the C–V characteristic of the device as a result of placing a minute amount of charge on the floating gate, even in nano-meter scales. The proposed design only adds a simple processing step to the conventional FGT by adding an oppositely doped implanted layer to the substrate. This new structure was first analyzed theoretically and then a two-dimensional model was extracted to represent its C–V characteristic. Furthermore, this model was verified with a simulation. In addition, the C–V characteristics relevant to the SCM measurement of both conventional and the new designed FGT were compared to discuss the effectiveness of the added layer in masking the state of the transistor. The effect of change in doping concentration of the implanted layer on the C–V characteristics was also investigated. Finally, the feasibility of the proposed design was examined by comparing its I–V characteristics with the traditional FGT.

• ## Suppression of oxygen and carbon impurity deposition in the thermal system of czochralski monocrystalline silicon

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When preparing large monocrystalline silicon materials, severe carbon etching and silicide deposition often occur to the thermal system. Therefore, a suppression method that optimizes the upper insulation structure has been proposed. Assisted by the finite element method, we calculated temperature distribution and carbon deposition of heater and heat shield, made the rule of silicide and temperature distributing in the system, and we explained the formation of impurity deposition. Our results show that the optimized thermal system reduces carbon etching loss on heat components. The lowered pressure of the furnace brings a rapid decrease of silicide deposition. The increase of the argon flow rate effectively inhibits CO and back diffusion. The simulated results agree well with the experiment observations, validating the effectiveness of the proposed method.

• ## Mn doping effects on the gate-tunable transport properties of Cd3As2 films epitaxied on GaAs

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The Mn doping effects on the gate-tunable transport properties of topological Dirac semimetal Cd3As2 films have been investigated. Mn-doped Cd3As2 films are directly grown on GaAs(111)B substrates by molecular-beam epitaxy, during which the single crystal phase can be obtained with Mn concentration less than 2%. Shubnikov-de Haas oscillation and quantum Hall effect are observed at low temperatures, and electrons are found to be the dominant carrier in the whole temperature range. Higher Mn content results in smaller lattice constant, lower electron mobility and larger effective band gap, while the carrier density seems to be unaffected by Mn-doping. Gating experiments show that Shubnikov-de Haas oscillation and quantum Hall effect are slightly modulated by electric field, which can be explained by the variation of electron density. Our results provide useful information for understanding the magnetic element doping effects on the transport properties of Cd3As2 films.

• ## Metal–insulator transition in few-layered GaTe transistors

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Two-dimensional (2D) materials have triggered enormous interest thanks to their interesting properties and potential applications, ranging from nanoelectronics to energy catalysis and biomedicals. In addition to other widely investigated 2D materials, GaTe, a layered material with a direct band gap of ~1.7 eV, is of importance for applications such as optoelectronics. However, detailed information on the transport properties of GaTe is yet to be explored, especially at low temperatures. Here, we report on electrical transport measurements on few-layered GaTe field effect transistors (FETs) encapsulated by h-BN at different temperatures. We find that by tuning the carrier density, ambipolar transport was realized in GaTe devices, and an electrical-field-induced metal to insulator transition (MIT) was observed when it was hole doped. The mobilities of GaTe devices show a clear dependence on temperature and increase with the decrease of temperature, reaching ~1200 cm2V?1s?1 at 3 K. Our findings may inspire further electronic studies in devices based on GaTe.

• ## Gate-regulated transition temperatures for electron hopping behaviours in silicon junctionless nanowire transistors

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We investigate gate-regulated transition temperatures for electron hopping behaviours through discrete ionized dopant atoms in silicon junctionless nanowire transistors. We demonstrate that the localization length of the wave function in the spatial distribution is able to be manipulated by the gate electric field. The transition temperatures regulated as the function of the localization length and the density of states near the Fermi energy level allow us to understand the electron hopping behaviours under the influence of thermal activation energy and Coulomb interaction energy. This is useful for future quantum information processing by single dopant atoms in silicon.

• ## Photodetectors based on 2D material/Si heterostructure

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doi: 10.1088/1674-4926/41/8/080401

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• ## Contact engineering for two-dimensional semiconductors

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Two-dimensional (2D) layered materials, including graphene, black phosphorus (BP) and transition metal dichalcogenide (TMD) such as molybdenum disulfide (MoS2), tungsten diselenide (WSe2), have attracted increasing attention for the application in electronic and optoelectronic devices. Contacts, which are the communication links between these 2D materials and external circuitry, have significant effects on the performance of electronic and optoelectronic devices. However, the performance of devices based on 2D semiconductors (SCs) is often limited by the contacts. Here, we provide a comprehensive overview of the basic physics and role of contacts in 2D SCs, elucidating Schottky barrier nature and Fermi level pinning effect at metal/2D SCs contact interface. The progress of contact engineering, including traditional metals contacts and metallic 2D materials contacts, for improving the performance of 2D SCs based devices is presented. Traditional metal contacts, named 3D top and edge contacts, are discussed briefly. Meanwhile, methods of building 2D materials contacts (2D top contact and 2D edge contact) are discussed in detail, such as chemical vapor deposition (CVD) growth of 2D metallic material contacts, phase engineered metallic phase contacts and intercalation induced metallic state contacts. Finally, the challenges and opportunities of contact engineering for 2D SCs are outlined.

• ## Charge transport and quantum confinement in MoS2 dual-gated transistors

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Semiconductive two dimensional (2D) materials have attracted significant research attention due to their rich band structures and promising potential for next-generation electrical devices. In this work, we investigate the MoS2 field-effect transistors (FETs) with a dual-gated (DG) architecture, which consists of symmetrical thickness for back gate (BG) and top gate (TG) dielectric. The thickness-dependent charge transport in our DG-MoS2 device is revealed by a four-terminal electrical measurement which excludes the contact influence, and the TCAD simulation is also applied to explain the experimental data. Our results indicate that the impact of quantum confinement effect plays an important role in the charge transport in the MoS2 channel, as it confines charge carriers in the center of the channel, which reduces the scattering and boosts the mobility compared to the single gating case. Furthermore, temperature-dependent transfer curves reveal that multi-layer MoS2 DG-FET is in the phonon-limited transport regime, while single layer MoS2 shows typical Coulomb impurity limited regime.

• ## Growth of large-scale two-dimensional insulator Na2Ta4O11 through chemical vapor deposition

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The insulator Na2Ta4O11 has been considered as a potential photocatalyst. However, little attention has been given to the synthesis of Na2Ta4O11 nanoparticles, let alone the growth of two-dimensional (2D) layered Na2Ta4O11 flake, which may bring innovative properties and promising applications. Here, the 2D thin-layer Na2Ta4O11 flake was first produced by chemical vapor deposition (CVD) method, with the smallest thickness reported currently. We have also synthesized 2D Na2Ta4O11 flake over 100 μm, which was the largest value over the 2D level reported to date. Our work proposed novel strategies to synthesize other 2D metal oxide material and endow the Na2Ta4O11 more properties and applications.

• ## Silicon photonic transceivers for application in data centers

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Global data traffic is growing rapidly, and the demand for optoelectronic transceivers applied in data centers (DCs) is also increasing correspondingly. In this review, we first briefly introduce the development of optoelectronics transceivers in DCs, as well as the advantages of silicon photonic chips fabricated by complementary metal oxide semiconductor process. We also summarize the research on the main components in silicon photonic transceivers. In particular, quantum dot lasers have shown great potential as light sources for silicon photonic integration—whether to adopt bonding method or monolithic integration—thanks to their unique advantages over the conventional quantum-well counterparts. Some of the solutions for high-speed optical interconnection in DCs are then discussed. Among them, wavelength division multiplexing and four-level pulse-amplitude modulation have been widely studied and applied. At present, the application of coherent optical communication technology has moved from the backbone network, to the metro network, and then to DCs.

• ## Non-volatile optical memory in vertical van der Waals heterostructures

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Emulating synaptic plasticity in an artificial neural network is crucial to mimic the basic functions of the human brain. In this work, we report a new optoelectronic resistive random access memory (ORRAM) in a three-layer vertical heterostructure of graphene/CdSe quantum dots (QDs)/graphene, which shows non-volatile multi-level optical memory under optical stimuli, giving rise to light-tunable synaptic behaviors. The optical non-volatile storage time is up to ~450 s. The device realizes the function of multi-level optical storage through the interlayer changes between graphene and QDs. This work highlights the feasibility for applying two-dimensional (2D) materials in ORRAM and optoelectronic synaptic devices towards artificial vision.

• ## Effect of microstructure of Au80Sn20 solder on the thermal resistance TO56 packaged GaN-based laser diodes

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Au80Sn20 alloy is a widely used solder for laser diode packaging. In this paper, the thermal resistance of GaN-based blue laser diodes packaged in TO56 cans were measured by the forward voltage method. The microstructures of Au80Sn20 solder were then investigated to understand the reason for the difference in thermal resistance. It was found that the microstructure with a higher content of Au-rich phase in the center of the solder and a lower content of (Au,Ni)Sn phase at the interface of the solder/heat sink resulted in lower thermal resistance. This is attributed to the lower thermal resistance of Au-rich phase and higher thermal resistance of (Au,Ni)Sn phase.

• ## Comparative study of various methods for extraction of multi- quantum wells Schottky diode parameters

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In this work, forward current voltage characteristics for multi-quantum wells Al0.33Ga0.67As Schottky diode were measured at temperature ranges from 100 to 300 K. The main parameters of this Schottky diode, such as the ideality factor, barrier height, series resistance and saturation current, have been extracted using both analytical and heuristics methods. differential evolution (DE), particle swarm optimization (PSO) and artificial bee colony (ABC) have been chosen as candidate heuristics algorithms, while Cheung technic was selected as analytical extraction method. The obtained results show clearly the high performance of DE algorithms in terms of parameters accuracy, convergence speed and robustness.

• ## Nanoflower ZnO thin-film grown by hydrothermal technique based Schottky diode

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This paper reports the realization of planar Schottky diodes based on nanorod ZnO thin film. The nanorod ZnO thin film was fabricated by hydrothermal technique on boron doped p-type Si (100) substrate. The Ag//ZnO/Al planar diode operating with voltage bias from –3 to 3 V. The IV characteristics clearly indicate that the devices have rectifying performance. The thermionic emission theory governs the current across the studied Schottky diode. The device achieved a turn-on voltage of 0.9 V, barrier height 0.69 eV and saturation current of 1.2 × 10–6 A. The diode shows a very large ideality factor (n > > 2) which is attributed to high interface trap concentration. The surface topology was investigated by scanning electron microscope (SEM). The structural properties of the nanostructured ZnO thin film were characterized by X-ray diffraction (XRD). The SEM images reveal that the ZnO nanorods grow perpendicular to the substrate with uniformity and high density. The XRD pattern illustrates the dominant peak appearing at (002). This intense peak indicates the c-axis orientated phase of the wurtzite ZnO structure. It demonstrates that the crystals grow uniformly perpendicular to the substrate surface in good agreement with the SEM images.

• ## Design of CMOS active pixels based on finger-shaped PPD

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To improve the full-well capacity and linear dynamic range of CMOS image sensor, a special finger-shaped pinned photodiode (PPD) is designed. In terms of process, the first N-type ion implantation of the PPD N buried layer is extended under the transfer gate, thereby increasing the PPD capacitance. Based on TCAD simulation, the width and spacing of PPD were precisely adjusted. A high full-well capacity pixel design with a pixel size of 6 × 6 μm2 is realized based on the 0.18 μm CMOS process. The simulation results indicate that the pixel with the above structure and process has a depletion depth of 2.8 μm and a charge transfer efficiency of 100%. The measurement results of the test chip show that the full-well capacity can reach 68650e. Compared with the conventional structure, the proposed PPD structure can effectively improve the full well capacity of the pixel.

• ## Study of electrophysical properties of metal–semiconductor contact by the theory of complex systems

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The purpose of this work is to analyze the electrical properties of the metal–semiconductor contact (MSC) in the framework of the theory of complex systems. The effect of inhomogeneity of the different microstructures: polycrystalline, monocrystalline, amorphous metal–semiconductor contact surface is investigated, considering a Schottky diode (SD) as a parallel connection of numerous subdiodes. It has been shown that the polycrystallinity of the metal translates a homogeneous contact into a complex system, which consists of parallel connected numerous elementary contacts having different properties and parameters.

• ## 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 date–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.

• ## 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}.

• ## 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.