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  • Effect of inhomogeneous broadening on threshold current of GaN-based green laser diodes

    Yipeng Liang, Jianping Liu, Masao Ikeda, Aiqin Tian, Renlin Zhou, Shuming Zhang, Tong Liu, Deyao Li, Liqun Zhang, Hui Yang

    , Available online

    Abstract Full Text PDF

    The inhomogeneous broadening parameter and the internal loss of green LDs are determined by experiments and theoretical fitting. It is found that the inhomogeneous broadening plays an important role on the threshold current density of green LDs. The green LD with large inhomogeneous broadening even cannot lase. Therefore, reducing inhomogeneous broadening is a key issue to improve the performance of green LDs.

  • A novel design approach of charge plasma tunnel FET for radio frequency applications

    Shivendra Yadav, Alish Pamnani, Dheeraj Sharma, Anju Gedam, Atul Kumar, Neeraj Sharma

    , Available online

    Abstract Full Text PDF

    In this paper, the impact of extra electron source (EES) and dual metal gate engineering on conventional charge plasma TFET (CP-TFET) have been done for improving DC and analog/RF parameters. CP-TFET structure is upgraded to double source CP-TFET (DS-CP-TFET) by placing an EES below the source/channel junction for enhancing the device performance in terms of driving current and RF figures of merit (FOMs). But, in spite of these pros, the approach is having cons of higher leakage current similar to MOSFET and negative conductance (inherent nature of TFET). Both the issues have been resolved in the double source dual gate CP-TFET (DS-DG-CP-TFET) by gate workfunction engineering and drain underlapping respectively. Additionally, for getting the optimum performance of DS-DG-CP-TFET, the device sensitivity has been investigated in terms of position of EES, length of drain electrode and workfunction of gate electrode 1 (GE1).

  • Growth of oxidation-resistive silicene-like thin flakes and Si nanostructures on graphene

    Naili Yue, Joshua Myers, Liqin Su, Wentao Wang, Fude Liu, Raphael Tsu, Yan Zhuang, Yong Zhang

    , Available online

    Abstract Full Text PDF

    We report the growth of Si nanostructures, either as thin films or nanoparticles, on graphene substrates. The Si nanostructures are shown to be single crystalline, air stable and oxidation resistive, as indicated by the observation of a single crystalline Si Raman mode at around 520 cm–1, a STM image of an ordered surface structure under ambient condition, and a Schottky junction with graphite. Ultra-thin silicon regions exhibit silicene-like behavior, including a Raman mode at around 550 cm–1, a triangular lattice structure in STM that has distinctly different lattice spacing from that of either graphene or thicker Si, and metallic conductivity of up to 500 times higher than that of graphite. This work suggests a bottom-up approach to forming a Si nanostructure array on a large-scale patterned graphene substrate that can be used to fabricate nanoscale Si electronic devices.

  • Structural and optical studies on PVA capped SnS films grown by chemical bath deposition for solar cell application

    P Mallika Bramaramba Devi, G. Phaneendra Reddy, K. T. Ramakrishna Reddy

    , Available online

    Abstract Full Text PDF

    Tin monosulphide (SnS) thin films capped by PVA have been successfully deposited on glass substrates for cost effective photovoltaic device applications by a simple and low-cost wet chemical process, chemical bath deposition (CBD) at different bath temperatures varying in the range, 50–80 °C. X–ray diffraction analysis showed that the deposited films were polycrystalline in nature, showing orthorhombic structure with an intense peak corresponding to (040) plane of SnS. These observations were further confirmed by Raman analysis. FTIR spectra showed the absorption bands which corresponds to PVA in addition to SnS. The scanning electron microscopy and atomic force microscopy studies revealed that the deposited SnS films were uniform and nanostructured with an average particle size of 4.9 to 7.6 nm. The optical investigations showed that the layers were highly absorbing with the optical absorption coefficient ~105 cm–1. A decrease in optical band gap from 1.92 to 1.55 eV with an increase of bath temperature was observed. The observed band gap values were higher than the bulk value of 1.3 eV, which might be due to quantum confinement effect. The optical band gap values were also used to calculate particle size and the results are discussed.

  • Substrates and interlayer coupling effects on Mo1?xWxSe2 alloys

    Fang Liang, Hejun Xu, Zuoyuan Dong, Yafeng Xie, Chen Luo, Yin Xia, Jian Zhang, Jun Wang, Xing Wu

    , Available online

    Abstract Full Text PDF

    Two-dimensional (2D) transition metal dichalcogenides alloys are potential materials in the application of photodetectors over a wide spectral range due to their composition-dependent bandgaps. The study of bandgap engineering is important for the application of 2D materials in devices. Here, we grow the Mo1?xWxSe2 alloys on mica, sapphire and SiO2/Si substrates by chemical vapor deposition (CVD) method. Mo1?xWxSe2 alloys are grown on the mica substrates by CVD method for the first time. Photoluminescence (PL) spectroscopy is used to investigate the effects of substrates and interlayer coupling force on the optical bandgaps of as-grown Mo1?xWxSe2 alloys. We find that the substrates used in this work have an ignorable effect on the optical bandgaps of as-grown Mo1?xWxSe2. The interlayer coupling effect on the optical bandgaps of as-grown Mo1?xWxSe2 is larger than the substrates effect. These findings provide a new way for the future study of the growth and physical properties of 2D alloy materials.

  • A novel 4H-SiC trench MOSFET with double shielding structures and ultralow gate-drain charge

    Xiaorong Luo, Tian Liao, Jie Wei, Jian Fang, Fei Yang, Bo Zhang

    , Available online

    Abstract Full Text PDF

    A new ultralow gate–drain charge (QGD) 4H-SiC trench MOSFET is presented and its mechanism is investigated by simulation. The novel MOSFET features double shielding structures (DS-MOS): one is the grounded split gate (SG), the other is the P+ shielding region (PSR). Both the SG and the PSR reduce the coupling effect between the gate and the drain, and transform the most part of the gate–drain capacitance (CGD) into the gate–source capacitance (CGS) and drain–source capacitance (CDS) in series. Thus the CGD is reduced and the proposed DS-MOS obtains ultralow QGD. Compared with the double-trench MOSFET (DT-MOS) and the conventional trench MOSFET (CT-MOS), the proposed DS-MOS decreases the QGD by 85% and 81%, respectively. Moreover, the figure of merit (FOM), defined as the product of specific on-resistance (Ron, sp) and QGD (Ron, spQGD), is reduced by 84% and 81%, respectively.

  • Broadband absorption of graphene from magnetic dipole resonances in hybrid nanostructure

    Xiaowei Jiang

    , Available online

    Abstract Full Text PDF

    As emerging new material, graphene has inspired great research interest. However, most of the studies focused on how to improve the absorption efficiency of graphene, but payed little attention on broadening absorption bandwidth while ensuring high absorption efficiency. In this work, we proposed a hybrid nanostructure, which not only can improve absorption efficiency but also can increase absorption bandwidth. The proposed hybrid nanostructure consists of a monolayer graphene sandwiched between three Ag gratings with different widths and a SiO2 spacer on a Ag substrate, these three gratings and substrate can excite three independent magnetic dipole resonances. In our calculations, we numerically demonstrate the proposed hybrid structure can achieve graphene absorption bandwidth of 0.311 μm in near-infrared region with absorption exceeding 30% . We also studied absorption peaks dependence on gratings widths and SiO2 spacer thickness, and explained the results using physical mechanism. Our research can provide a theoretical guidance for future device preparation.

  • Multi-channel 28-GHz millimeter-wave signal generation on a silicon photonic chip with automated polarization control

    Ruiyuan Cao, Yu He, Qingming Zhu, Jingchi Li, Shaohua An, Yong Zhang, Yikai Su

    , Available online

    Abstract Full Text PDF

    We propose and experimentally demonstrate an integrated silicon photonic scheme to generate multi-channel millimeter-wave (MMW) signals for 5G multi-user applications. The fabricated silicon photonic chip has a footprint of 1.1 × 2.1 mm2 and integrates 7 independent channels each having on-chip polarization control and heterodyne mixing functions. 7 channels of 4-Gb/s QPSK baseband signals are delivered via a 2-km multi-core fiber (MCF) and coupled into the chip with a local oscillator (LO) light. The polarization state of each signal light is automatically adjusted and aligned with that of the LO light, and then 7 channels of 28-GHz MMW carrying 4-Gb/s QPSK signals are generated by optical heterodyne beating. Automated polarization-control function of each channel is also demonstrated with ~7-ms tuning time and ~27-dB extinction ratio.

  • Realizing super-long Cu2O nanowires arrays for high-efficient water splitting applications with a convenient approach

    Nasori Nasori, Tianyi Dai, Xiaohao Jia, Agus Rubiyanto, Dawei Cao, Shengchun Qu, Zhanguo Wang, Zhijie Wang, Yong Lei

    , Available online

    Abstract Full Text PDF

    Nanowire (NW) structures is an alternative candidate for constructing the next generation photoelectrochemical water splitting system, due to the outstanding optical and electrical properties. NW photoelectrodes comparing to traditional semiconductor photoelectrodes shows the comparatively shorter transfer distance of photo-induced carriers and the increase amount of the surface reaction sites, which is beneficial for lowering the recombination probability of charge carriers and improving their photoelectrochemical (PEC) performances. Here, we demonstrate for the first time that super-long Cu2O NWs, more than 4.5 μm, with highly efficient water splitting performance, were synthesized using a cost-effective anodic alumina oxide (AAO) template method. In comparison with the photocathode with planar Cu2O films, the photocathode with Cu2O NWs demonstrates a significant enhancement in photocurrent, from –1.00 to –2.75 mA/cm2 at –0.8 V versus Ag/AgCl. After optimization of the photoelectrochemical electrode through depositing Pt NPs with atomic layer deposition (ALD) technology on the Cu2O NWs, the plateau of photocurrent has been enlarged to –7 mA/cm2 with the external quantum yield up to 34% at 410 nm. This study suggests that the photoelectrode based on Cu2O NWs is a hopeful system for establishing high-efficiency water splitting system under visible light.

  • Design and analysis of a NMOS triggered LIGBT structure for electrostatic discharge protection

    Li Tian, Jianbing Cheng, C. R. Zhang, L. Shen, Lei Wang

    , Available online

    Abstract Full Text PDF

    A novel NMOS triggered LIGBT (NTLIGBT) structure is proposed for electrostatic discharge (ESD) protection in this paper. The structure utilizes internal NMOS to trigger SCR-like structure in LIGBT. The trigger voltage is significantly reduced because the embedded NMOS causes N+-drain/P-body junction being apt to avalanche breakdown. At the same time, the new parasitic PNP transistor including the newly added P+-region as a collector forms another path to bleed ESD current and then the conductivity modulation in the LIGBT is weakened. As a result, the holding voltage is increased. So, the proposed NTLIGBT structure has a narrow ESD design window. The simulation results show an improvement of 71.5% in trigger voltage and over 50% in holding voltage comparing with the conventional LIGBT structure.

  • Semiconductor-based terahertz frequency combs

    Hua Li

    , Available online

    doi: 10.1088/1674-4926/40/5/050402

    Abstract Full Text PDF Get Citation

  • Effects of V-pits covering layer position on the optoelectronic performance of InGaN green LEDs

    Chen Xu, Changda Zheng, Xiaoming Wu, Shuan Pan, Xingan Jiang, Junlin Liu, Fengyi Jiang

    , Available online

    doi: 10.1088/1674-4926/40/5/050801

    Abstract Full Text PDF Get Citation

    The impact of the V-pits covering layer (VCL) position on the optoelectronic performance of InGaN-based green light-emitting diodes (LEDs) was investigated. It is found that earlier covering of V-pits will hinder the hole injection via the sidewall of V-pits, and then result in less quantum wells (QWs) participating in radioluminescence. The current-voltage characteristics show that the LEDs with earlier covering of V-pits have higher operating voltage at room temperature, and a more dramatic voltage rise with the reduction of temperature. Meanwhile, more manifested emission of sidewall QWs and deeper QWs near to n-type layer was observed at cryogenic temperatures, owing to the earlier V-pits covering leading to more holes being injected via the sidewall of V-pits, which have higher kinetic energy and could transport to deeper QWs.

  • Research for radiation-hardened high-voltage SOI LDMOS

    Yanfei Li, Shaoli Zhu, Jianwei Wu, Genshen Hong, Zheng Xu

    , Available online

    doi: 10.1088/1674-4926/40/5/050401

    Abstract Full Text PDF Get Citation

    Based on the silicon-on-insulator (SOI) technology and radiation-hardened silicon gate (RSG) process, a radiation-hardened high-voltage lateral double-diffused MOSFET (LDMOS) device is presented in this paper. With the gate supply voltage of 30 V, the LDMOS device has a gate oxide thickness of 120 nm, and the RSG process is effective in reducing the total ionizing dose (TID) radiation-induced threshold voltage shift. The p-type ion implantation process and gate-enclosed layout topology are used to prevent radiation-induced leakage current through a parasitic path under the bird's beak and at the deep trench corner, and the device is compatible with high-voltage SOI CMOS process. In the proposed LDMOS, the total ionizing dose radiation degradation for the ON bias is more sensitive than the OFF bias. The experiment results show that the SOI LDMOS has a negative threshold voltage shift of 1.12 V, breakdown voltage of 135 V, and off-state leakage current of 0.92 pA/μm at an accumulated dose level of 100 krad (Si).

  • Colloidal quantum dot lasers and hybrid integrations

    Jianjun Chen

    , Available online

    doi: 10.1088/1674-4926/40/5/050401

    Abstract Full Text PDF Get Citation

  • Precision photonics integration for future large-scale photonic integrated circuits

    Xiangfei Cheng

    , Available online

    doi: 10.1088/1674-4926/40/5/050301

    Abstract Full Text PDF Get Citation

    Since the proposal of the concept of photonic integrated circuits (PICs), tremendous progress has been made. In 2005, Infinera Corp. rolled out the first commercial PICs, in which hundreds of optical functions were integrated onto a small form factor chip for wavelength division multiplexing (WDM) systems[1], then a monolithically integrated 10 × 10 Gb/s WDM chip has been demonstrated, the channel number is ten[2]. Like ICs, large-scale PICs (LS-PICs) will be sure to be pursued. However, there are still some general challenges associated with LS-PICs. The challenges for III–V (mainly InP) PICs is the semiconductor process, which is not mature for LS-PICs. Up to now, the channel number in commercial III–V WDM PICs by Infinera is still about ten or less. For silicon photonics, the challenge is the silicon based light source. The low cost and mature solution for silicon lasers is still unavailable and only 4 × 25 Gb/s PICs are deployed by Intel Corp. after 18-year R&D investment. Thus it is still unavailable for practical LS-PICs in the present times.

  • Growth properties of gallium oxide on sapphire substrate by plasma-assisted pulsed laser deposition

    Congyu Hu, Katsuhiko Saito, Tooru Tanaka, Qixin Guo

    , Available online

    Abstract Full Text PDF

    Gallium oxide was deposited on a c-plane sapphire substrate by oxygen plasma-assisted pulsed laser deposition (PLD). An oxygen radical was generated by an inductive coupled plasma source and the effect of radio frequency (RF) power on growth rate was investigated. A film grown with plasma assistance showed 2.7 times faster growth rate. X-ray diffraction (XRD) and Raman spectroscopy analysis showed β-Ga2O3 films grown with plasma assistance at 500 °C. The roughness of the films decreased when the RF power of plasma treatment increased. Transmittance of these films was at least 80% and showed sharp absorption edge at 250 nm which was consistent with data previously reported.

  • Optimization of erase time degradation in 65 nm NOR flash memory chips

    Jing Liu, Yuanlu Xie, Changxing Huo, Hongyang Hu, Kun Zhang, Jinshun Bi, Ming Liu

    , Available online

    Abstract Full Text PDF

    Reliability issues of flash memory are becoming increasingly significant with the shrinking of technology nodes. Among them, erase time degradation is an issue that draws the attention of academic and industry researchers. In this paper, causes of the " erase time degradation” are exhaustively analyzed, with proposals for its improvement presented, including a low stress program/erase scheme with a staircase pulse and disturb-immune array bias condition. Implementation of the optimized circuit structure is verified in a 128 Mb SPI NOR Flash memory chip, which is fabricated on a SMIC 65 nm ETOX process platform. Testing results indicate a degradation of the sector erase time from 10.67 to 104.9 ms after 105 program/erase cycles, which exhibits an improvement of approximately 100 ms over conventional schemes.

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