2019年JOS入选“中国科技期刊卓越行动计划”
2020年11月JOS被EI数据库收录
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喜讯!半导体学报成功被EI收录!

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In Press articles are edited and published online ahead of issue. When the final article is assigned to volumes/issues, the Article in Press version will be removed and the final version will appear in the associated published volumes/issues.
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  • Structural and electrical characterization of Cu2ZnSnS4 ingot material grown by melting method

    S. Kerour, A. Bouloufa, M. Lasladj, K. Djessas, K. Medjnoun

    , Available online

    Abstract Full Text PDF

    In this work, a Cu2ZnSnS4 (CZTS) ingot is grown via a melting method, then cooled; the resulting molten stoichiometric mixture is sealed off in a quartz ampoule under vacuum. The CZTS powder chemical composition analyses are determined using Energy Dispersive Spectroscopy (EDS), and revealing the slightly Cu-rich and Zn-poor character of the ingot. Powder X-Ray Diffraction (XRD) analysis reveals a crystalline structure with a kesterite phase formation, and a preferred orientation of (112) plane. The lattice constants of the a- and c- axes, calculated based on the XRD analyses, are a = 5.40 Å and c = 10.84 Å. Based on Hall measurements at room temperature, we find that the crystal exhibits p-type conductivity, with a high concentration of 1018 cm–3, a resistivity of 1.7 Ω cm, and a mobility of 10.69 cm2V–1s–1. Activation energies are estimated based on an Arrhenius plot of conductivity versus 1/T, for a temperature range of 80–350 K, measuring 35 and 160 meV in low- and high-temperature regimes, respectively, which is attributed to complex defects (2CuZn+SnZn) and antisite defects (CuZn), respectively. The observed scattering mechanisms are attributed to ionized impurities and acoustic phonons at low and high temperatures, respectively. The extracted band-gap is 1.37 eV.

  • A 15 Gbps-NRZ, 30 Gbps-PAM4, 120 mA laser diode driver implemented in 0.15-µm GaAs E-mode pHEMT technology

    Ahmed Wahba, Lin Cheng, Fujiang Lin

    , Available online

    Abstract Full Text PDF

    This paper presents the design and testing of a 15 Gbps non-return-to-zero (NRZ), 30 Gbps 4-level pulse amplitude modulation (PAM4) configurable laser diode driver (LDD) implemented in 0.15-µm GaAs E-mode pHEMT technology. The driver bandwidth is enhanced by utilizing cross-coupled neutralization capacitors across the output stage. The output transmission-line back-termination, which absorbs signal reflections from the imperfectly matched load, is performed passively with on-chip 50-Ω resistors. The proposed 30 Gbps PAM4 LDD is implemented by combining two 15 Gbps-NRZ LDDs, as the high and low amplification paths, to generate PAM4 output current signal with levels of 0, 40, 80, and 120 mA when driving 25-Ω lasers. The high and low amplification paths can be used separately or simultaneously as a 15 Gbps-NRZ LDD. The measurement results show clear output eye diagrams at speeds of up to 15 and 30 Gbps for the NRZ and PAM4 drivers, respectively. At a maximum output current of 120 mA, the driver consumes 1.228 W from a single supply voltage of –5.2 V. The proposed driver shows a high current driving capability with a better output power to power dissipation ratio, which makes it suitable for driving high current distributed feedback (DFB) lasers. The chip occupies a total area of 0.7 × 1.3 mm2.

  • Heavily doped silicon: A potential replacement of conventional plasmonic metals

    Md. Omar Faruque, Rabiul Al Mahmud, Rakibul Hasan Sagor

    , Available online

    Abstract Full Text PDF

    The plasmonic property of heavily doped p-type silicon is studied here. Although most of the plasmonic devices use metal–insulator–metal (MIM) waveguide in order to support the propagation of surface plasmon polaritons (SPPs), metals that possess a number of challenges in loss management, polarization response, nanofabrication etc. On the other hand, heavily doped p-type silicon shows similar plasmonic properties like metals and also enables us to overcome the challenges possessed by metals. For numerical simulation, heavily doped p-silicon is mathematically modeled and the theoretically obtained relative permittivity is compared with the experimental value. A waveguide is formed with the p-silicon-air interface instead of the metal–air interface. Formation and propagation of SPPs similar to MIM waveguides are observed.

  • A complete small-signal HBT model including AC current crowding effect

    Jinjing Huang, Jun Liu

    , Available online

    doi: 10.1088/1674-4926/42/5/052401

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    An improved small-signal equivalent circuit of HBT concerning the AC current crowding effect is proposed in this paper. AC current crowding effect is modeled as a parallel RC circuit composed of Cbi and Rbi, with distributed base-collector junction capacitance also taken into account. The intrinsic portion is taken as a whole and extracted directly from the measured S-parameters in the whole frequency range of operation without any special test structures. An HBT device with a 2 × 20 μm2 emitter-area under three different biases were used to demonstrate the extraction and verify the accuracy of the equivalent circuit.

  • Morphology and crystalline property of an AlN single crystal grown on AlN seed

    Li Zhang, Haitao Qi, Hongjuan Cheng, Yuezeng Shi, Zhanpin Lai, Muchang Luo

    , Available online

    doi: 10.1088/1674-4926/42/5/052101

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    AlN single crystal grown by physical vapor transport (PVT) using homogeneous seed is considered as the most promising approach to obtain high-quality AlN boule. In this work, the morphology of AlN single crystals grown under different modes (3D islands and single spiral center) were investigated. It is proved that, within an optimized thermal distribution chamber system, the surface temperature of AlN seed plays an important role in crystal growth, revealing a direct relationship between growth mode and growth condition. Notably, a high-quality AlN crystal, with (002) and (102) reflection peaks of 65 and 36 arcsec at full width at half maximum (FWHM), was obtained grown under a single spiral center mode. And on which, a high-quality AlxGa1–xN epitaxial layer with high Al content (x = 0.54) was also obtained. The FWHMs of (002) and (102) reflection of AlxGa1–xN were 202 and 496 arcsec, respectively, which shows superiority over their counterpart grown on SiC or a sapphire substrate.

  • Fiber coupled high count-rate single-photon generated from InAs quantum dots

    Yao Chen, Shulun Li, Xiangjun Shang, Xiangbin Su, Huiming Hao, Jiaxin Shen, Yu Zhang, Haiqiao Ni, Ying Ding, Zhichuan Niu

    , Available online

    Abstract Full Text PDF

    In this work, we achieve high count-rate single-photon output in single-mode (SM) optical fiber. Epitaxial and dilute InAs/GaAs quantum dots (QDs) are embedded in a GaAs/AlGaAs distributed Bragg reflector (DBR) with a micro-pillar cavity, so as to improve their light emission extraction in the vertical direction, thereby enhancing the optical SM fiber’s collection capability (numerical aperture: 0.13). By tuning the temperature precisely to make the quantum dot exciton emission resonant to the micro-pillar cavity mode (Q ~1800), we achieve a fiber-output single-photon count rate as high as 4.73 × 106 counts per second, with the second-order auto-correlation g2(0) remaining at 0.08.

  • Photonic devices based on thin-film lithium niobate on insulator

    Shuai Yuan, Changran Hu, An Pan, Yuedi Ding, Xuanhao Wang, Zhicheng Qu, Junjie Wei, Yuheng Liu, Cheng Zeng, Jinsong Xia

    , Available online

    doi: 10.1088/1674-4926/42/4/041304

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    Lithium niobate on insulator (LNOI) is rising as one of the most promising platforms for integrated photonics due to the high-index-contrast and excellent material properties of lithium niobate, such as wideband transparency from visible to mid-infrared, large electro-optic, piezoelectric, and second-order harmonic coefficients. The fast-developing micro- and nano-structuring techniques on LNOI have enabled various structure, devices, systems, and applications. In this contribution, we review the latest developments in this platform, including ultra-high speed electro-optic modulators, optical frequency combs, opto-electro-mechanical system on chip, second-harmonic generation in periodically poled LN waveguides, and efficient edge coupling for LNOI.

  • Organic perovskites

    Chuantian Zuo, Liming Ding

    , Available online

    doi: 10.1088/1674-4926/42/4/040201

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  • High-frequency characterization of high-speed modulators and photodetectors in a link with low-speed photonic sampling

    Mengke Wang, Shangjian Zhang, Zhao Liu, Xuyan Zhang, Yutong He, Yangxue Ma, Yali Zhang, Zhiyao Zhang, Yong Liu

    , Available online

    doi: 10.1088/1674-4926/42/4/042303

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    We propose a low-speed photonic sampling for independent high-frequency characterization of a Mach–Zehnder modulator (MZM) and a photodetector (PD) in an optical link. A low-speed mode-locked laser diode (MLLD) provides an ultra-wideband optical stimulus with scalable frequency range, working as the photonic sampling source of the link. The uneven spectrum lines of the MLLD are firstly characterized with symmetric modulation within the interesting frequency range. Then, the electro-optic modulated signals are down-converted to the first Nyquist frequency range, yielding the self-referenced extraction of modulation depth and half-wave voltage of the MZM without correcting the responsivity fluctuation of the PD in the link. Finally, the frequency responsivity of the PD is self-referenced measured under null modulation of the MZM. As frequency responses of the MZM and the PD can be independently obtained, our method allows self-referenced high-frequency measurement for a high-speed optical link. In the proof-of-concept experiment, a 96.9 MS/s MLLD is used for measuring a MZM and a PD within the frequency range up to 50 GHz. The consistency between our method and the conventional method verifies that the ultra-wideband and self-referenced high-frequency characterization of high-speed MZMs and PDs.

  • Orthogonally polarized RF optical single sideband generation with integrated ring resonators

    Mengxi Tan, Xingyuan Xu, Jiayang Wu, Thach G. Nguyen, Sai T. Chu, Brent E. Little, Arnan Mitchell, Roberto Morandotti, David J. Moss

    , Available online

    doi: 10.1088/1674-4926/42/4/041305

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    We review recent work on narrowband orthogonally polarized optical RF single sideband generators as well as dual-channel equalization, both based on high-Q integrated ring resonators. The devices operate in the optical telecommunications C-band and enable RF operation over a range of either fixed or thermally tuneable frequencies. They operate via TE/TM mode birefringence in the resonator. We achieve a very large dynamic tuning range of over 55 dB for both the optical carrier-to-sideband ratio and the dual-channel RF equalization for both the fixed and tunable devices.

  • Monolithic DWDM source with precise channel spacing

    Lianping Hou, Song Tang, John H. Marsh

    , Available online

    doi: 10.1088/1674-4926/42/4/042301

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    We report a low-cost manufacturing approach for fabricating monolithic multi-wavelength sources for dense wavelength division multiplexing (DWDM) systems that offers high yield and eliminates crystal regrowth and selective area epitaxy steps that are essential in traditional fabrication methods. The source integrates an array of distributed feedback (DFB) lasers with a passive coupler and semiconductor optical amplifier (SOA). Ridge waveguide lasers with sampled Bragg side wall gratings have been integrated using quantum well intermixing to achieve a fully functional four-channel DWDM source with 0.8 nm wavelength spacing and residual errors < 0.13 nm. The output power from the SOA is > 10 mW per channel making the source suitable for use in passive optical networks (PONs). We have also investigated using multisection phase-shifted sampled gratings to both increase the effective grating coupling coefficient and precisely control the channel lasing wavelength spacing. An 8-channel DFB laser array with 100 GHz channel spacing was demonstrated using a sampled grating with two π-phase-shifted sections in each sampling period. The entire array was fabricated by only a single step of electron beam lithography.

  • Beyond the 100 Gbaud directly modulated laser for short reach applications

    Jianou Huang, Chao Li, Rongguo Lu, Lianyan Li, Zizheng Cao

    , Available online

    doi: 10.1088/1674-4926/42/4/041306

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    It is very attractive to apply a directly modulated laser (DML)-based intensity-modulation and direct-detection (IM/DD) system in future data centers and 5G fronthaul networks due to the advantages of low cost, low system complexity, and high energy efficiency, which perfectly match the application scenarios of the data centers and 5G fronthaul networks, in which a large number of high-speed optical interconnections are needed. However, as the data traffic in the data centers and 5G fronthaul networks continues to grow exponentially, the future requirements for data rates beyond 100 Gbaud are challenging the existing DML-based IM/DD system, and the main bottleneck is the modulation bandwidth of the DML. In this paper, the data rate demands and technical standards of the data centers and 5G fronthaul networks are reviewed in detail. With the modulation bandwidth requirements, the technical routes and achievements of recent DMLs are reviewed and discussed. In this way, the prospects, challenges, and future development of DMLs in the applications of future data centers and 5G fronthaul networks are comprehensively explored.

  • Photonic radio frequency channelizers based on Kerr optical micro-combs

    Mengxi Tan, Xingyuan Xu, Jiayang Wu, Thach G. Nguyen, Sai T. Chu, Brent E. Little, Roberto Morandotti, Arnan Mitchell, David J. Moss

    , Available online

    doi: 10.1088/1674-4926/42/4/041302

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    We review recent work on broadband RF channelizers based on integrated optical frequency Kerr micro-combs combined with passive micro-ring resonator filters, with microcombs having channel spacings of 200 and 49 GHz. This approach to realizing RF channelizers offers reduced complexity, size, and potential cost for a wide range of applications to microwave signal detection.

  • Preface to the Special Issue on Semiconductor Optoelectronic Integrated Circuits

    Wei Wang, Lingjuan Zhao, Dan Lu, Jianping Yao, Weiping Huang, Yong Liu, Brent Little

    , Available online

    doi: 10.1088/1674-4926/42/4/040101

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  • Blue perovskite LEDs

    Mengqi Zhang, Chuantian Zuo, Jianjun Tian, Liming Ding

    , Available online

    doi: 10.1088/1674-4926/42/7/070201

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  • Compact SPAD pixels with fast and accurate photon counting in the analog domain

    Zhiqiang Ma, Zhong Wu, Yue Xu

    , Available online

    Abstract Full Text PDF

    A compact pixel for single-photon detection in the analog domain is presented. The pixel integrates a single-photon avalanche diode (SPAD), a passive quenching & active recharging circuit (PQARC), and an analog counter for fast and accurate sensing and counting of photons. Fabricated in a standard 0.18 µm CMOS technology, the simulated and experimental results reveal that the dead time of the PQARC is about 8 ns and the maximum photon-counting rate can reach 125 Mcps (counting per second). The analog counter can achieve an 8-bit counting range with a voltage step of 6.9 mV. The differential nonlinearity (DNL) and integral nonlinearity (INL) of the analog counter are within the ± 0.6 and ± 1.2 LSB, respectively, indicating high linearity of photon counting. Due to its simple circuit structure and compact layout configuration, the total area occupation of the presented pixel is about 1500 μm2, leading to a high fill factor of 9.2%. The presented in-pixel front-end circuit is very suitable for the high-density array integration of SPAD sensors.

  • Low-bandgap Sn–Pb perovskite solar cells

    Rui He, Chuantian Zuo, Shengqiang Ren, Dewei Zhao, Liming Ding

    , Available online

    doi: 10.1088/1674-4926/42/6/060202

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  • Surface-enhanced Raman spectroscopy chips based on two-dimensional materials beyond graphene

    Enqing Zhang, Zhengkun Xing, Dian Wan, Haoran Gao, Yingdong Han, Yisheng Gao, Haofeng Hu, Zhenzhou Cheng, Tiegen Liu

    , Available online

    Abstract Full Text PDF

    Surface-enhanced Raman spectroscopy (SERS) based on two-dimensional (2D) materials has attracted great attention over the past decade. Compared with metallic materials, which enhance Raman signals via the surface plasmon effect, 2D materials integrated on silicon-based substrates are ideal for use in the fabrication of plasmon-free SERS chips, with the advantages of outstanding fluorescence quenching capability, excellent biomolecular compatibility, tunable Fermi levels, and potentially low-cost material preparation. Moreover, recent studies have shown that the limits of detection of 2D-material-based SERS may be comparable with those of metallic substrates, which has aroused significant research interest. In this review, we comprehensively summarize the advances in SERS chips based on 2D materials. As several excellent reviews of graphene-enhanced Raman spectroscopy have been published in the past decade, here, we focus only on 2D materials beyond graphene, i.e., transition metal dichalcogenides, black phosphorus, hexagonal boron nitride, 2D titanium carbide or nitride, and their heterostructures. We hope that this paper will serve as a useful reference for researchers specializing in 2D materials, spectroscopy, and diverse applications related to chemical and biological sensing.

  • Waveguide external cavity narrow linewidth semiconductor lasers

    Chanchan Luo, Ruiying Zhang, Bocang Qiu, Wei Wang

    , Available online

    doi: 10.1088/1674-4926/42/4/041308

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    Narrow linewidth light source is a prerequisite for high-performance coherent optical communication and sensing. Waveguide-based external cavity narrow linewidth semiconductor lasers (WEC-NLSLs) have become a competitive and attractive candidate for many coherent applications due to their small size, volume, low energy consumption, low cost and the ability to integrate with other optical components. In this paper, we present an overview of WEC-NLSLs from their required technologies to the state-of-the-art progress. Moreover, we highlight the common problems occurring to current WEC-NLSLs and show the possible approaches to resolving the issues. Finally, we present the possible development directions for the next phase and hope this review will be beneficial to the advancements of WEC-NLSLs.

  • Four-wave mixing in silicon-nanocrystal embedded high-index doped silica micro-ring resonator

    Yuhua Li, Xiang Wang, Roy Davidson, Brent E. Little, Sai Tak Chu

    , Available online

    doi: 10.1088/1674-4926/42/4/042302

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    A nonlinear integrated optical platform that allows the fabrication of waveguide circuits with different material composition, and at small dimensions, offers advantages in terms of field enhancement and increased interaction length, thereby facilitating the observation of nonlinear optics effects at a much lower power level. To enhance the nonlinearity of the conventional waveguide structure, in this work, we propose and demonstrate a microstructured waveguide where silicon rich layer is embedded in the core of the conventional waveguide in order to increase its nonlinearity. By embedding a 20 nm thin film of silicon nanocrystal (Si-nc), we achieve a twofold increase of the nonlinear parameter, γ. The linear relationship between the four-wave mixing conversion efficiency and pump power reveals the negligible nonlinear absorption and small dispersion in the micro-ring resonators. This simple approach of embedding an ultra-thin Si-nc layer into conventional high-index doped silica dramatically increases its nonlinear performance, and could potentially find applications in all-optical processing functions.

  • Recent progress in integrated electro-optic frequency comb generation

    Hao Sun, Mostafa Khalil, Zifei Wang, Lawrence R. Chen

    , Available online

    doi: 10.1088/1674-4926/42/4/041301

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    Optical frequency combs have emerged as an important tool enabling diverse applications from test-and-measurement, including spectroscopy, metrology, precision distance measurement, sensing, as well as optical and microwave waveform synthesis, signal processing, and communications. Several techniques exist to generate optical frequency combs, such as mode-locked lasers, Kerr micro-resonators, and electro-optic modulation. Important characteristics of optical frequency combs include the number of comb lines, their spacing, spectral shape and/or flatness, and intensity noise. While mode-locked lasers and Kerr micro-resonators can be used to obtain a large number of comb lines compared to electro-optic modulation, the latter provides increased flexibility in tuning the comb spacing. For some applications in optical communications and microwave photonics, a high degree of integration may be more desirable over a very large number of comb lines. In this paper, we review recent progress on integrated electro-optic frequency comb generators, including those based on indium phosphide, lithium niobate, and silicon photonics.

  • Latest advances in high-performance light sources and optical amplifiers on silicon

    Songtao Liu, Akhilesh Khope

    , Available online

    doi: 10.1088/1674-4926/42/4/041307

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    Efficient light generation and amplification has long been missing on the silicon platform due to its well-known indirect bandgap nature. Driven by the size, weight, power and cost (SWaP-C) requirements, the desire to fully realize integrated silicon electronic and photonic integrated circuits has greatly pushed the effort of realizing high performance on-chip lasers and amplifiers moving forward. Several approaches have been proposed and demonstrated to address this issue. In this paper, a brief overview of recent progress of the high-performance lasers and amplifiers on Si based on different technology is presented. Representative device demonstrations, including ultra-narrow linewidth III–V/Si lasers, fully integrated III–V/Si/Si3N4 lasers, high-channel count mode locked quantum dot (QD) lasers, and high gain QD amplifiers will be covered.

  • Hybrid material integration in silicon photonic integrated circuits

    Swapnajit Chakravarty, Min Teng, Reza Safian, Leimeng Zhuang

    , Available online

    doi: 10.1088/1674-4926/42/4/041303

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    Hybrid integration of III–V and ferroelectric materials is being broadly adopted to enhance functionalities in silicon photonic integrated circuits (PICs). Bonding and transfer printing have been the popular approaches for integration of III–V gain media with silicon PICs. Similar approaches are also being considered for ferroelectrics to enable larger RF modulation bandwidths, higher linearity, lower optical loss integrated optical modulators on chip. In this paper, we review existing integration strategies of III–V materials and present a route towards hybrid integration of both III–V and ferroelectrics on the same chip. We show that adiabatic transformation of the optical mode between hybrid ferroelectric and silicon sections enables efficient transfer of optical modal energies for maximum overlap of the optical mode with the ferroelectric media, similar to approaches adopted to maximize optical overlap with the gain section, thereby reducing lasing thresholds for hybrid III–V integration with silicon PICs. Preliminary designs are presented to enable a foundry compatible hybrid integration route of diverse functionalities on silicon PICs.

  • 18.69% PCE from organic solar cells

    Ke Jin, Zuo Xiao, Liming Ding

    , Available online

    doi: 10.1088/1674-4926/42/6/060502

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  • Oscillation neuron based on a low-variability threshold switching device for high-performance neuromorphic computing

    Yujia Li, Jianshi Tang, Bin Gao, Xinyi Li, Yue Xi, Wanrong Zhang, He Qian, Huaqiang Wu

    , Available online

    doi: 10.1088/1674-4926/42/6/064101

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    Low-power and low-variability artificial neuronal devices are highly desired for high-performance neuromorphic computing. In this paper, an oscillation neuron based on a low-variability Ag nanodot (ND) threshold switching (TS) device with low operation voltage, large on/off ratio and high uniformity is presented. Measurement results indicate that this neuron demonstrates self-oscillation behavior under applied voltages as low as 1 V. The oscillation frequency increases with the applied voltage pulse amplitude and decreases with the load resistance. It can then be used to evaluate the resistive random-access memory (RRAM) synaptic weights accurately when the oscillation neuron is connected to the output of the RRAM crossbar array for neuromorphic computing. Meanwhile, simulation results show that a large RRAM crossbar array (> 128 × 128) can be supported by our oscillation neuron owing to the high on/off ratio (> 108) of Ag NDs TS device. Moreover, the high uniformity of the Ag NDs TS device helps improve the distribution of the output frequency and suppress the degradation of neural network recognition accuracy (< 1%). Therefore, the developed oscillation neuron based on the Ag ND TS device shows great potential for future neuromorphic computing applications.

  • GIWAXS: A powerful tool for perovskite photovoltaics

    Chenyue Wang, Chuantian Zuo, Qi Chen, Liming Ding

    , Available online

    doi: 10.1088/1674-4926/42/6/060201

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  • Dithieno[3',2':3,4;2'',3'':5,6]benzo[1,2-c][1,2,5]oxadiazole-based polymer donors with deep HOMO levels

    Xiongfeng Li, Jingui Xu, Zuo Xiao, Xingzhu Wang, Bin Zhang, Liming Ding

    , Available online

    doi: 10.1088/1674-4926/42/6/060501

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  • Defect engineering on all-inorganic perovskite solar cells for high efficiency

    Bingcheng Yu, Chuantian Zuo, Jiangjian Shi, Qingbo Meng, Liming Ding

    , Available online

    doi: 10.1088/1674-4926/42/5/050203

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  • Drop-coating produces efficient CsPbI2Br solar cells

    Hanrui Xiao, Chuantian Zuo, Fangyang Liu, Liming Ding

    , Available online

    doi: 10.1088/1674-4926/42/5/050502

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  • Fiber-like solar cells

    Xing Fan, Dechun Zou, Liming Ding

    , Available online

    doi: 10.1088/1674-4926/42/5/050202

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  • Magnetic quantum oscillation in a monolayer insulator

    Xin Lu

    , Available online

    doi: 10.1088/1674-4926/42/6/060401

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  • WO3 passivation layer-coated nanostructured TiO2: An efficient defect engineered photoelectrode for dye sensitized solar cell

    Arya Babu, Arya Vasanth, Shantikumar Nair, Mariyappan Shanmugam

    , Available online

    Abstract Full Text PDF

    Major loss factors for photo-generated electrons due to the presence of surface defects in titanium dioxide (TiO2) were controlled by RF-sputtered tungsten trioxide (WO3) passivation. X-ray photoelectron spectroscopy assured the coating of WO3 on the TiO2 nanoparticle layer by showing Ti 2p, W 4f and O 1s characteristic peaks and were further confirmed by X-ray diffraction studies. The coating of WO3 on the TiO2 nanoparticle layer did not affect dye adsorption significantly. Dye sensitized solar cells (DSSCs) fabricated using WO3-coated TiO2 showed an enhancement of ~10% compared to DSSCs fabricated using pristine TiO2-based photo-electrodes. It is attributed to the WO3 passivation on TiO2 that creates an energy barrier which favored photo-electron injection by tunneling but blocked reverse electron recombination pathways towards holes available in highest occupied molecular orbital of the dye molecules. It was further evidenced that there is an optimum thickness (duration of coating) of WO3 to improve the DSSC performance and longer duration of WO3 suppressed photo-electron injection from dye to TiO2 as inferred from the detrimental effect in short circuit current density values. RF-sputtering yields pinhole-free, highly uniform and conformal coating of WO3 onto any area of interest, which can be considered for an effective surface passivation for nanostructured photovoltaic devices.

  • Intramolecular spatial charge transfer enhances TADF efficiency

    Baoyi Ren, Chuantian Zuo, Yaguang Sun, Liming Ding

    , Available online

    doi: 10.1088/1674-4926/42/5/050201

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  • Determination of trap density-of-states distribution of nitrogen-doped ultrananocrystalline diamond/hydrogenated amorphous carbon composite films

    Mahmoud Shaban

    , Available online

    Abstract Full Text PDF

    Thin films comprising nitrogen-doped ultrananocrystalline diamond/hydrogenated amorphous-carbon (UNCD/a-C:H) composite films were experimentally investigated. The prepared films were grown on Si substrates by the coaxial arc plasma deposition method. They were characterized by temperature-dependent capacitance-frequency measurements in the temperature and frequency ranges of 300–400 K and 50 kHz–2 MHz, respectively. The energy distribution of trap density of states in the films was extracted using a simple technique utilizing the measured capacitance-frequency characteristics. In the measured temperature range, the energy-distributed traps exhibited Gaussian-distributed states with peak values lie in the range: 2.84 × 1016–2.73 × 1017 eV–1 cm–3 and centered at energies of 120–233 meV below the conduction band. These states are generated due to a large amount of sp2-C and π-bond states, localized in GBs of the UNCD/a-C:H film. The attained defect parameters are accommodating to understand basic electrical properties of UNCD/a-C:H composite and can be adopted to suppress defects in the UNCD-based materials.

  • Efficient and photostable CsPbI2Br solar cells realized by adding PMMA

    Yanbo Shang, Zhimin Fang, Wanpei Hu, Chuantian Zuo, Bairu Li, Xingcheng Li, Mingtai Wang, Liming Ding, Shangfeng Yang

    , Available online

    doi: 10.1088/1674-4926/42/5/050501

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  • Modeling the photon counting and photoelectron counting characteristics of quanta image sensors

    Bowen Liu, Jiangtao Xu

    , Available online

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    A signal chain model of single-bit and multi-bit quanta image sensors (QISs) is established. Based on the proposed model, the photoresponse characteristics and signal error rates of QISs are investigated, and the effects of bit depth, quantum efficiency, dark current, and read noise on them are analyzed. When the signal error rates towards photons and photoelectrons counting are lower than 0.01, the high accuracy photon and photoelectron counting exposure ranges are determined. Furthermore, an optimization method of integration time to ensure that the QIS works in these high accuracy exposure ranges is presented. The trade-offs between pixel area, the mean value of incident photons, and integration time under different illuminance level are analyzed. For the 3-bit QIS with 0.16 e-/s dark current and 0.21 e- r.m.s. read noise, when the illuminance level and pixel area are 1 lux and 1.21 μm2, or 10 000 lux and 0.21 μm2, the recommended integration time is 8.8 to 30 ms, or 10 to 21.3 μs, respectively. The proposed method can guide the design and operation of single-bit and multi-bit QISs.

  • A review of manufacturing technologies for silicon carbide superjunction devices

    Run Tian, Chao Ma, Jingmin Wu, Zhiyu Guo, Xiang Yang, Zhongchao Fan

    , Available online

    Abstract Full Text PDF

    Superjunction technology is believed to reach the optimal specific on-resistance and breakdown voltage trade-off. It has become a mainstream technology in silicon high-voltage metal oxide semiconductor field effect transistor devices. Numerous efforts have been conducted to employ the same concept in silicon carbide devices. These works are summarized here.

  • Recent progress of physical failure analysis of GaN HEMTs

    Xiaolong Cai, Chenglin Du, Zixuan Sun, Ran Ye, Haijun Liu, Yu Zhang, Xiangyang Duan, Hai Lu

    , Available online

    Abstract Full Text PDF

    Gallium nitride (GaN)-based high-electron mobility transistors (HEMTs) are widely used in high power and high frequency application fields, due to the outstanding physical and chemical properties of the GaN material. However, GaN HEMTs suffer from degradations and even failures during practical applications, making physical analyses of post-failure devices extremely significant for reliability improvements and further device optimizations. In this paper, common physical characterization techniques for post failure analyses are introduced, several failure mechanisms and corresponding failure phenomena are reviewed and summarized, and finally device optimization methods are discussed.

  • A crossover from Efros–Shklovskii hopping to activated transport in a GaAs two-dimensional hole system at low temperatures

    S. Dlimi, A. El kaaouachi, L. Limouny, B. A. Hammou

    , Available online

    Abstract Full Text PDF

    In this paper, we discuss low-temperature hopping-conductivity behavior in the insulating phase, in the absence of a magnetic field. We conduct a theoretical study of the crossover from hopping to activated transport in a GaAs two-dimensional hole system at low temperatures, finding that a crossover takes place from the Efros-Shklovskii variable-range hopping (VRH) regime to an activated regime in this system. This conductivity behavior in p-GaAs quantum wells is qualitatively consistent with the laws laid down in theories of localized electron interactions. Given sufficiently strong interactions, the holes in the localized states are able to hop collectively.

  • Facile fabrication of heterostructure with p-BiOCl nanoflakes and n-ZnO thin film for UV photodetectors

    Longxing Su, Weixin Ouyang, Xiaosheng Fang

    , Available online

    Abstract Full Text PDF

    Herein, high-quality n-ZnO film layer on c-sapphire and well-crystallized tetragonal p-BiOCl nanoflakes on Cu foil are prepared, respectively. According to the absorption spectra, the bandgaps of n-ZnO and p-BiOCl are confirmed as ~3.3 and ~3.5 eV, respectively. Subsequently, a p-BiOCl/n-ZnO heterostructural photodetector is constructed after a facile mechanical bonding and post annealing process. At –5 V bias, the photocurrent of the device under 350 nm irradiation is ~800 times higher than that in dark, which indicates its strong UV light response characteristic. However, the on/off ratio of In–ZnO–In photodetector is ~20 and the Cu–BiOCl–Cu photodetector depicts very weak UV light response. The heterostructure device also shows a short decay time of 0.95 s, which is much shorter than those of the devices fabricated from pure ZnO thin film and BiOCl nanoflakes. The p-BiOCl/n-ZnO heterojunction photodetector provides a promising pathway to multifunctional UV photodetectors with fast response, high signal-to-noise ratio, and high selectivity.

  • 3.3 kV 4H-SiC DMOSFET with a source-contacted dummy gate for high-frequency applications

    Kyuhyun Cha, Kwangsoo Kim

    , Available online

    Abstract Full Text PDF

    In this paper, a 4H-SiC DMOSFET with a source-contacted dummy gate (DG-MOSFET) is proposed and analyzed through Sentaurus TCAD and PSIM simulations. The source-contacted MOS structure forms fewer depletion regions than the PN junction. Therefore, the overlapping region between the gate and the drain can be significantly reduced while limiting RON degradation. As a result, the DG-MOSFET offers an improved high-frequency figure of merit (HF-FOM) over the conventional DMOSFET (C-MOSFET) and central-implant MOSFET (CI-MOSFET). The HF-FOM (RON × QGD) of the DG-MOSFET was improved by 59.2% and 22.2% compared with those of the C-MOSFET and CI-MOSFET, respectively. In a double-pulse test, the DG-MOSFET could save total power losses of 53.4% and 5.51%, respectively. Moreover, in a power circuit simulation, the switching power loss was reduced by 61.9% and 12.7% in a buck converter and 61% and 9.6% in a boost converter.

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