Browsing by Author "Zhu, Yan"

Now showing 1 - 7 of 7
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    Design, fabrication, and analysis of p-channel arsenide/antimonide hetero-junction tunnel transistors
    Rajamohanan, Bijesh; Mohata, Dheeraj K.; Zhu, Yan; Hudait, Mantu K.; Jiang, Zhengping; Hollander, Matthew; Klimeck, Gerhard; Datta, Suman (American Institute of Physics, 2014-01-23)
    In this paper, we demonstrate InAs/GaSb hetero-junction (hetJ) and GaSb homo-junction (homJ) p-channel tunneling field effect transistors (pTFET) employing a low temperature atomic layer deposited high-kappa gate dielectric. HetJ pTFET exhibited drive current of 35 mu A/mu m in comparison to homJ pTFET, which exhibited drive current of 0.3 mu A/mu m at V-DS = -0.5V under DC biasing conditions. Additionally, with pulsing of 1 mu s gate voltage, hetJ pTFET exhibited enhanced drive current of 85 mu A/mu m at V-DS = -0.5 V, which is the highest reported in the category of III-V pTFET. Detailed device characterization was performed through analysis of the capacitance-voltage characteristics, pulsed current-voltage characteristics, and x-ray diffraction studies. (C) 2014 AIP Publishing LLC.
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    Energy band alignment of atomic layer deposited HfO2 oxide film on epitaxial (100)Ge, (110)Ge, and (111)Ge layers
    Hudait, Mantu K.; Zhu, Yan (American Institute of Physics, 2013-03-21)
    Crystallographically oriented epitaxial Ge layers were grown on (100), (110), and (111) A GaAs substrates by in situ growth process using two separate molecular beam epitaxy chambers. The band alignment properties of atomic layer hafnium oxide (HfO2) film deposited on crystallographically oriented epitaxial Ge were investigated using x-ray photoelectron spectroscopy (XPS). Valence band offset, DEv values of HfO2 relative to (100) Ge, (110) Ge, and (111) Ge orientations were 2.8 eV, 2.28 eV, and 2.5 eV, respectively. Using XPS data, variation in valence band offset, Delta E-V(100)Ge > Delta E-V(111)Ge > Delta E-V(110)Ge, was obtained related to Ge orientation. Also, the conduction band offset, DEc relation, Delta E-c(110)Ge > Delta E-c(111)Ge > Delta E-c(100)Ge related to Ge orientations was obtained using the measured bandgap of HfO2 on each orientation and with the Ge bandgap of 0.67 eV. These band offset parameters for carrier confinement would offer an important guidance to design Ge-based p-and n- channel metal-oxide field-effect transistor for low-power application. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4795284]
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    Heterogeneous Integration of Epitaxial Ge on Si using AlAs/GaAs Buffer Architecture: Suitability for Low-power Fin Field-Effect Transistors
    Hudait, Mantu K.; Clavel, Michael B.; Goley, Patrick S.; Jain, Nikhil; Zhu, Yan (Nature Publishing Group, 2014-11-07)
    Germanium-based materials and device architectures have recently appeared as exciting material systems for future low-power nanoscale transistors and photonic devices. Heterogeneous integration of germanium (Ge)-based materials on silicon (Si) using large bandgap buffer architectures could enable the monolithic integration of electronics and photonics. In this paper, we report on the heterogeneous integration of device-quality epitaxial Ge on Si using composite AlAs/GaAs large bandgap buffer, grown by molecular beam epitaxy that is suitable for fabricating low-power fin field-effect transistors required for continuing transistor miniaturization. The superior structural quality of the integrated Ge on Si using AlAs/GaAs was demonstrated using high-resolution x-ray diffraction analysis. High-resolution transmission electron microscopy confirmed relaxed Ge with high crystalline quality and a sharp Ge/AlAs heterointerface. X-ray photoelectron spectroscopy demonstrated a large valence band offset at the Ge/AlAs interface, as compared to Ge/GaAs heterostructure, which is a prerequisite for superior carrier confinement. The temperature-dependent electrical transport properties of the n-type Ge layer demonstrated a Hall mobility of 370 cm2/Vs at 290 K and 457 cm2/Vs at 90 K, which suggests epitaxial Ge grown on Si using an AlAs/ GaAs buffer architecture would be a promising candidate for next-generation high-performance and energy-efficient fin field-effect transistor applications.
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    Identification of a Novel Hepacivirus in Southeast Asian Shrew (Crocidura fuliginosa) from Yunnan Province, China
    Guo, Ling; Li, Bei; Han, Peiyu; Dong, Na; Zhu, Yan; Li, Fuli; Si, Haorui; Shi, Zhengli; Wang, Bo; Yang, Xinglou; Zhang, Yunzhi (MDPI, 2023-11-28)
    The genus Hepacivirus contains single-stranded positive-sense RNA viruses belonging to the family Flaviviridae, which comprises 14 species. These 14 hepaciviruses have been found in different mammals, such as primates, dogs, bats, and rodents. To date, Hepacivirus has not been reported in the shrew genus of Crocidura. To study the prevalence and genetic evolution of Hepacivirus in small mammals in Yunnan Province, China, molecular detection of Hepacivirus in small mammals from Yunnan Province during 2016 and 2017 was performed using reverse-transcription polymerase chain reaction (RT-PCR). Our results showed that the overall infection rate of Hepacivirus in small mammals was 0.12% (2/1602), and the host animal was the Southeast Asian shrew (Crocidura fuliginosa) (12.5%, 2/16). Quantitative real-time PCR showed that Hepacivirus had the highest viral RNA copy number in the liver. Phylogenetic analysis revealed that the hepaciviruses obtained in this study does not belong to any designated species of hepaciviruses and forms an independent clade. To conclude, a novel hepacivirus was identified for the first time in C. fuliginosa specimens from Yunnan Province, China. This study expands the host range and viral diversity of hepaciviruses.
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    In situ accurate control of 2D-3D transition parameters for growth of low-density InAs/GaAs self-assembled quantum dots
    Li, Mi-Feng; Yu, Ying; He, Ji-Fang; Wang, Li-Juan; Zhu, Yan; Shang, Xiang-jun; Ni, Hai-Qiao; Niu, Zhi-Chuan (2013-02-18)
    A method to improve the growth repeatability of low-density InAs/GaAs self-assembled quantum dots by molecular beam epitaxy is reported. A sacrificed InAs layer was deposited firstly to determine in situ the accurate parameters of two- to three-dimensional transitions by observation of reflection high-energy electron diffraction patterns, and then the InAs layer annealed immediately before the growth of the low-density InAs quantum dots (QDs). It is confirmed by micro-photoluminescence that control repeatability of low-density QD growth is improved averagely to about 80% which is much higher than that of the QD samples without using a sacrificed InAs layer.
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    Microfluidic Technology for Low-Input Epigenomic Analysis
    Zhu, Yan (Virginia Tech, 2018-05-25)
    Epigenetic modifications, such as DNA methylation and histone modifications, play important roles in gene expression and regulation, and are highly involved in cellular processes such as stem cell pluripotency/differentiation and tumorigenesis. Chromatin immunoprecipitation (ChIP) is the technique of choice for examining in vivo DNA-protein interactions and has been a great tool for studying epigenetic mechanisms. However, conventional ChIP assays require millions of cells for tests and are not practical for examination of samples from lab animals and patients. Automated microfluidic chips offer the advantage to handle small sample sizes and facilitate rapid reaction. They also eliminate cumbersome manual handling. In this report, I will talk about three different projects that utilized microfluidic immunoprecipitation followed by next genereation sequencing technologies to enable low input and high through epigenomics profiling. First, I examined RNA polymerase II transcriptional regulation with microfluidic chromatin immunoprecipitation followed by next generation sequencing (ChIP-seq) assays. Second, I probed the temporal dynamics in the DNA methylome during cancer development using a transgenic mouse model with microfluidic methylated DNA immunoprecipitation followed by next generation sequencing (MeDIP-seq) assays. Third, I explored negative enrichment of circulating tumor cells (CTCs) followed by microfluidic ChIP-seq technology for studying temporal dynamic histone modification (H3K4me3) of patient-derived tumor xenograft on an immunodeficient mouse model during the course of cancer metastasis. In the first study, I adapted microfluidic ChIP-seq devices to achieve ultrahigh sensitivity to study Pol2 transcriptional regulation from scarce cell samples. I dramatically increased the assay sensitivity to an unprecedented level (~50 K cells for pol2 ChIP-seq). Importantly, this is three orders of magnitude more sensitive than the prevailing pol2 ChIP-seq assays. I showed that MNase digestion provided better ChIP-seq signal than sonication, and two-steps fixation with MNase digestion provided the best ChIP-seq quality followed by one-step fixation with MNase digestion, and lastly, no fixation with MNase digestion. In the second study, I probed dynamic epigenomic changes during tumorigenesis using mice often require profiling epigenomes using a tiny quantity of tissue samples. Conventional epigenomic tests do not support such analysis due to the large amount of materials required by these assays. In this study, I developed an ultrasensitive microfluidics-based methylated DNA immunoprecipitation followed by next-generation sequencing (MeDIP-seq) technology for profiling methylomes using as little as 0.5 ng DNA (or ~100 cells) with 1.5 h on-chip process for immunoprecipitation. This technology enabled me to examine genome-wide DNA methylation in a C3(1)/SV40 T-antigen transgenic mouse model during different stages of mammary cancer development. Using this data, I identified differentially methylated regions and their associated genes in different periods of cancer development. Interestingly, the results showed that methylomic features are dynamic and change with tumor developmental stage. In the last study, I developed a negative enrichment of CTCs followed by ultrasensitive microfluidic ChIP-seq technology for profiling histone modification (H3K4Me3) of CTCs to resolve the technical challenges associated with CTC isolation and difficulties related with tools for profiling whole genome histone modification on tiny cell samples.
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    Mixed As/Sb and tensile strained Ge/InGaAs heterostructures for low-power tunnel field effect transistors
    Zhu, Yan (Virginia Tech, 2014-05-02)
    Reducing supply voltage is a promising way to address the power dissipation in nano-electronic circuits. However, the fundamental lower limit of subthreshold slope (SS) within metal-oxide-semiconductor field-effect transistors (MOSFETs) is a major obstacle to further scaling the operation voltage without degrading ON/OFF-ratio in today's integrated circuits. Tunnel field-effect transistors (TFETs) benefit from steep switching characteristics due to the quantum-mechanical tunneling injection of carriers from source to channel, rather than by conventional thermionic emission in MOSFETs. TFETs based on group III-V compound semiconductor and Ge heterostructures further improve the ON-state current and reduce SS due to the low bandgap energies and smaller carrier tunneling mass. The mixed arsenide/antimonide (As/Sb) InxGa1-xAs/GaAsySb1-y and Ge/InxGa1-xAs heterostructures allow a wide range of bandgap energies and various band alignments depending on the alloy compositions in the source and channel materials. Band alignments at source/channel heterointerface can be well modulated by carefully controlling the compositions of the InxGa1-xAs or GaAsySb1-y. In particular, this research systematically investigate the development and optimization of low-power TFETs using mixed As/Sb and Ge/InxGa1-xAs based heterostructures including: basic working principles, design considerations, material growth, interface engineering, material characterization, band alignment determination, device fabrication, device performance investigation, and high-temperature reliability. A comprehensive study of TFETs using mixed As/Sb and Ge/InxGa1-xAs based heterostructures shows superior structural properties and distinguished device performances, both of which indicate the mixed As/Sb and Ge/InxGa1-xAs based TFET as a promising option for high performance, low standby power and energy efficient logic circuit application.