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V. Chu

Bio: V. Chu is an academic researcher from Princeton University. The author has contributed to research in topics: Amorphous silicon & Amorphous solid. The author has an hindex of 24, co-authored 45 publications receiving 1758 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, the sub-band-gap optical absorption spectra of high-quality hydrogenated amorphous silicon (a•Si:H) films are shown to be dominated by surface and interface state absorption when measured by photothermal deflection spectroscopy (PDS), while spectra determined using the constant photocurrent method (CPM) are not.
Abstract: The sub‐band‐gap optical absorption spectra of high‐quality hydrogenated amorphous silicon (a‐Si:H) films are shown to be dominated by surface and interface state absorption when measured by photothermal deflection spectroscopy (PDS), while spectra determined using the constant photocurrent method (CPM) are not. For bulk defect states (both as‐deposited and light‐induced), the integrated subgap absorption is approximately twice as large for PDS as for CPM. Similarly, the conversion factor relating integrated subgap absorption with neutral dangling bond density is twice as large for CPM as PDS. This factor of 2 results from CPM seeing only transitions from below midgap into the conduction band while PDS sees transitions from the valence band into states above midgap as well.

152 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of hydrogen dilution on the optical, transport, and structural properties of amorphous and micro-crystalline silicon thin films deposited by hot-wire (HW) chemical vapor deposition and radio-frequency (RF) plasmaenhanced chemical vapor deblurring using substrate temperatures (Tsub) of 100 and 25
Abstract: The effect of hydrogen dilution on the optical, transport, and structural properties of amorphous and microcrystalline silicon thin films deposited by hot-wire (HW) chemical vapor deposition and radio-frequency (rf) plasma-enhanced chemical vapor deposition using substrate temperatures (Tsub) of 100 and 25 °C is reported. Microcrystalline silicon (μc-Si:H) is obtained using HW with a large crystalline fraction and a crystallite size of ∼30 nm for hydrogen dilutions above 85% independently of Tsub. The deposition of μc-Si:H by rf, with a crystallite size of ∼8 nm, requires increasing the hydrogen dilution and shows decreasing crystalline fraction as Tsub is decreased. The photoconductivity, defect density, and structure factor of the amorphous silicon films (a-Si:H) are strongly improved by the use of hydrogen dilution in the Tsub range studied. a-Si:H films with a photoconductivity-to-dark conductivity ratio above 105, a deep defect density below 1017 cm−3, an Urbach energy below 60 meV and a structure factor below 0.1 were obtained for rf films down to 25 °C (at growth rates ∼0.1–0.4 A/s) and for HW films down to 100 °C (at growth rates ∼10 A/s), using the appropriate hydrogen dilution. In the low Tsub range studied, the growth mechanism, film properties, and the amorphous to microcrystalline silicon transition depend on the flux of atomic hydrogen available. The properties of the films are compared to those of samples produced at 175 and 250 °C in the same reactors.

141 citations

Journal ArticleDOI
TL;DR: Mise en evidence experimentale d'une densite de defauts en equilibre thermique dans a-Si les defauts observes a la temperature ambiante etant dus, essentiellement, au gel durant le refroidissement.
Abstract: Mise en evidence experimentale d'une densite de defauts en equilibre thermique dans a-Si: H non dope, au dessus de 200°C, les defauts observes a la temperature ambiante etant dus, essentiellement, au gel durant le refroidissement; augmentation reversible de la densite de defauts par trempe rapide, diminution reversible par prevention du processus de generation des defauts (recombinaison des porteurs)

121 citations

Journal ArticleDOI
TL;DR: A flat microdevice which incorporates a thin-film amorphous silicon (a-Si:H) photodetector with an upper layer of functionalized SiO2 is used to quantify the density of both immobilized and hybridized DNA oligonucleotides labeled with a fluorophore, enabling on-chip electronic data acquisition.
Abstract: A flat microdevice which incorporates a thin-film amorphous silicon (a-Si:H) photodetector with an upper layer of functionalized SiO2 is used to quantify the density of both immobilized and hybridized DNA oligonucleotides labeled with a fluorophore. The device is based on the photoconductivity of hydrogenated amorphous silicon in a coplanar electrode configuration. Excitation, with near UV/blue light, of a single-stranded DNA molecule tagged with the fluorophore 1-(3-(succinimidyloxycarbonyl)benzyl)-4-(5-(4-methoxyphenyl)oxazol-2-yl) pyridinium bromide (PyMPO), results in the emission of visible light. The emitted light is then converted into an electrical signal in the photodetector, thus allowing the optoelectronic detection of the DNA molecules. The detection limit of the present device is of the order of 1 3 10 12 molecules/cm 2 and is limited by the efficiency of the filtering of the excitation light. A surface density of 33.5 6 4.0 pmol/cm 2 was measured for DNA covalently immobilized to the functionalized SiO2 thin film and a surface density of 3.7 6 1.5 pmol/cm 2 was measured for the complementary DNA hybridized to the bound DNA. The detection concept explored can enable on-chip electronic data acquisition, improving both the speed and the reliability of DNA microarrays.

93 citations

Journal ArticleDOI
TL;DR: The covalent immobilization of DNA, followed by DNA hybridization, and of the surface adsorption of oligonucleotides and proteins were detected electronically by the a-Si:H ISFET.

85 citations


Cited by
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Journal ArticleDOI
TL;DR: The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielectrics for gate formation, and passivation are discussed in this article.
Abstract: Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics, solar blind UV photodetectors, solar cells, and sensors with capabilities beyond existing technologies due to its large bandgap. It is usually reported that there are five different polymorphs of Ga2O3, namely, the monoclinic (β-Ga2O3), rhombohedral (α), defective spinel (γ), cubic (δ), or orthorhombic (e) structures. Of these, the β-polymorph is the stable form under normal conditions and has been the most widely studied and utilized. Since melt growth techniques can be used to grow bulk crystals of β-GaO3, the cost of producing larger area, uniform substrates is potentially lower compared to the vapor growth techniques used to manufacture bulk crystals of GaN and SiC. The performance of technologically important high voltage rectifiers and enhancement-mode Metal-Oxide Field Effect Transistors benefit from the larger critical electric field of β-Ga2O3 relative to either SiC or GaN. However, the absence of clear demonstrations of p-type doping in Ga2O3, which may be a fundamental issue resulting from the band structure, makes it very difficult to simultaneously achieve low turn-on voltages and ultra-high breakdown. The purpose of this review is to summarize recent advances in the growth, processing, and device performance of the most widely studied polymorph, β-Ga2O3. The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielectrics for gate formation, and passivation are discussed. Areas where continued development is needed to fully exploit the properties of Ga2O3 are identified.

1,535 citations

Journal ArticleDOI
TL;DR: In this article, the authors present several classes of inorganic semiconductor materials that can be used to form high-performance thin-film transistors for large area, flexible electronics.
Abstract: This article reviews several classes of inorganic semiconductor materials that can be used to form high-performance thin-film transistors (TFTs) for large area, flexible electronics. Examples ranging from thin films of various forms of silicon to nanoparticles and nanowires of compound semiconductors are presented, with an emphasis on methods of depositing and integrating thin films of these materials into devices. Performance characteristics, including both electrical and mechanical behavior, for isolated transistors as well as circuits with various levels of complexity are reviewed. Collectively, the results suggest that flexible or printable inorganic materials may be attractive for a range of applications not only in flexible but also in large-area electronics, from existing devices such as flat-panel displays to more challenging (in terms of both cost and performance requirements) systems such as large area radiofrequency communication devices, structural health monitors, and conformal X-ray imagers.

813 citations

Book
28 Aug 2000
TL;DR: The state of the art and research issues that need to be resolved in order to make sensitive skin a reality are surveyed.
Abstract: Sensitive skin is a large-area, flexible array of sensors with data processing capabilities, which can be used to cover the entire surface of a machine or even a part of a human body. Depending on the skin electronics, it endows its carrier with an ability to sense its surroundings via the skin’s proximity, touch, pressure, temperature, chemical/biological, or other sensors. Sensitive skin devices will make possible the use of unsupervised machines operating in unstructured, unpredictable surroundings—among people, among many obstacles, outdoors on a crowded street, undersea, or on faraway planets. Sensitive skin will make machines “cautious” and thus friendly to their environment. This will allow us to build machine helpers for the disabled and elderly, bring sensing to human prosthetics, and widen the scale of machines’ use in service industry. With their ability to produce and process massive data flow, sensitive skin devices will make yet another advance in the information revolution. This paper surveys the state of the art and research issues that need to be resolved in order to make sensitive skin a reality. The paper is partially based on the report of the Sensitive Skin Workshop conducted jointly by the National Science Foundation (NSF) and Defense Advanced Research Projects Agency (DARPA) in October 1999 in Arlington, VA, of which the three co-authors were the co-chairs [1].

530 citations

Journal ArticleDOI
TL;DR: A copolymer comprising 1,4-diketopyrrolo[3,4c]pyrrole (DPP) and thieno[ 3,2-b]thiophene moieties, PDBT-co-TT, shows high hole mobility of up to 0.94 cm2 V-1 s-1 in organic thin-film transistors.
Abstract: A copolymer comprising 1,4-diketopyrrolo[3,4-c]pyrrole (DPP) and thieno[3,2-b]thiophene moieties, PDBT-co-TT, shows high hole mobility of up to 0.94 cm2 V-1 s-1 in organic thin-film transistors. The strong intermolecular interactions originated from π-π stacking and donor-acceptor interaction lead to the formation of interconnected polymer networks having an ordered lamellar structure, which have established highly efficient pathways for charge carrier transport.

515 citations