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Oh, Sooyeoun,Mastro, Michael A.,Tadjer, Marko J.,Kim, Jihyun Electrochemical Society 2017 ECS journal of solid state science and technology Vol.6 No.8
<P>Semiconductor materials ideal for solar-blind photodetectors (PDs) require an ultra-wide and direct bandgap to detect UV-C spectral wavelengths effectively. Using the mechanically exfoliated high-quality beta-Ga2O3 micro-flakes that have a direct bandgap of similar to 4.8 eV, we fabricated solar-blind PDs with a metal-semiconductor-metal (MSM) structure that can reduce the dark current, and then systemically investigated their photoresponse properties. The MSM devices with two Ni/Au Schottky contacts exhibited an extremely low dark current and high sensitivity (ratio of photocurrent to dark current > 10(3)) in UV-C wavelengths. In addition, they exhibited fast and stable on/off characteristics and high responsivity (1.68 A/W), with a superior rejection ratio when compared with the reported thin-film MSM solar-blind PDs, indicating the high potential of the quasi-two-dimensional beta-Ga2O3 for optoelectronic applications. (C) 2017 The Electrochemical Society. All rights reserved.</P>
Electromagnetic propagation in nanostructures
Michael A. Mastro,Charles R. Eddy Jr.,김지현,R. T. Holm 한양대학교 세라믹연구소 2008 Journal of Ceramic Processing Research Vol.9 No.1
Future integrated circuit technology will feature a fusion of optical and optoelectronic components with traditional electronic devices. Information can be rapidly transmitted as light in dielectric waveguides, photonic crystal guides and metallic nanoarrays. This paper presents a description of electromagnetic propagation in semiconductor and metallic nanostructures. Diffraction effects will dominate the propagation of light when the dimension of the cavity or device approaches its wavelength. The plasmonic effect circumvents this problem by propagating the light wave through highly localized conduction electrons in a noble metal [1]. Future integrated circuit technology will feature a fusion of optical and optoelectronic components with traditional electronic devices. Information can be rapidly transmitted as light in dielectric waveguides, photonic crystal guides and metallic nanoarrays. This paper presents a description of electromagnetic propagation in semiconductor and metallic nanostructures. Diffraction effects will dominate the propagation of light when the dimension of the cavity or device approaches its wavelength. The plasmonic effect circumvents this problem by propagating the light wave through highly localized conduction electrons in a noble metal [1].
Michael A. Mastro,김병재,정영훈,Jennifer K. Hite,Charles R. Eddy Jr.,김지현 한국물리학회 2011 Current Applied Physics Vol.11 No.3
Gallium nitride light emitting diodes were deposited on a sapphire substrate that was pre-patterned with an ordered two-dimensional structure. The size and arrangement of the substrate surface pattern was designed to increase the diffraction and extraction of light from the device as well as define the grain size and thus dislocation density of the GaN crystal. A close-packing of self-assembled SiO_2 nanospheres was used as the sacrificial etch mask. The etch process transferred a two-dimensional pattern into the sapphire substrate with a peak-to-peak dimension of approximately 250 nm. The distance was selected to match the emission wavelength in the crystal for optimal light scattering. Additionally, the dimensions of the crystal artificially defined the grain size of the GaN in contrast to the kinetically controlled grain size in a standard GaN on sapphire growth process.
Plasmonically enhanced emission from a group-III nitride nanowire emitter
Mastro, Michael A,Freitas Jr, Jaime A,Glembocki, Orest,Eddy Jr, Charles R,Holm, R T,Henry, Rich L,Caldwell, Josh,Rendell, Ronald W,Kub, Fritz,Kim, J IOP Pub 2007 Nanotechnology Vol.18 No.26
<P>The plasmonic response from a nanotextured silver coating was utilized to enhance the transfer of ultraviolet light generated in a group-III nitride nanowire emitter. A two-step approach was developed in a metal–organic chemical vapour deposition system to grow nanowires initially vertically by the vapour–liquid–solid mechanism and, subsequently, laterally by increasing the growth temperature and the group-V/III reactant ratio. This controllably produced a 20 nm GaN:Si core with a 200 nm outer-diameter AlGaN:Mg sheath structure. Solvothermal chemistry based on an ethylene glycol solvent was employed to deposit a silver coating that approximated a dense packing of metallic nanospheres. Nanoscale emission and plasmonically enhanced transfer of this energy were simulated to aid the development and understanding of this system.</P>
Group III-nitride radial heterojunction nanowire light emitters
Michael A. Mastro,Josh Caldwell,Mark Twigg,Blake Simpkins,Orest Glembocki,Ron T. Holm,Charles R. Eddy, Jr.,Fritz Kub,김홍렬,Jaehui Ahn,김지현 한양대학교 세라믹연구소 2008 Journal of Ceramic Processing Research Vol.9 No.6
Heterojunction nanowires were fabricated via a vapor-liquid-solid growth mechanism in a metal organic chemical vapor deposition system. The structure consisted of a n-type GaN:Si core surrounding by a distinct p-type AlGaN:Mg shell. Transmission electron microscopy revealed that the nanowires were free of extended defects. Photoluminescence measured a strong UV emission peak. Additionally, sources of mid-gap transitions are linked to surface states on the nanowire surface.
Kim, Janghyuk,Mastro, Michael A.,Tadjer, Marko J.,Kim, Jihyun American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.35
<P>Layered materials separated from each bulk crystal can be assembled to form a strain-free heterostructure by using the van der Waals interaction. We demonstrated a heterostructure n-channel depletion-mode β-Ga<SUB>2</SUB>O<SUB>3</SUB> junction field-effect transistor (JFET) through van der Waals bonding with an exfoliated p-WSe<SUB>2</SUB> flake. Typical diode characteristics with a high rectifying ratio of ∼10<SUP>5</SUP> were observed in a p-WSe<SUB>2</SUB>/n-Ga<SUB>2</SUB>O<SUB>3</SUB> heterostructure diode, where WSe<SUB>2</SUB> and β-Ga<SUB>2</SUB>O<SUB>3</SUB> were obtained by mechanically exfoliating each crystal. Layered JFETs exhibited an excellent <I>I</I><SUB>DS</SUB>-<I>V</I><SUB>DS</SUB> output as well as <I>I</I><SUB>DS</SUB>-<I>V</I><SUB>GS</SUB> transfer characteristics with a high on/off ratio (∼10<SUP>8</SUP>) and low subthreshold swing (133 mV/dec). Saturated output currents were observed with a threshold voltage of −5.1 V and a three-terminal breakdown voltage of +144 V. Electrical performances of the fabricated heterostructure JFET were maintained at elevated temperatures with outstanding air stability. Our WSe<SUB>2</SUB>-Ga<SUB>2</SUB>O<SUB>3</SUB> heterostructure JFET paves the way to the low-dimensional high-power devices, enabling miniaturization of the integrated power electronic systems.</P> [FIG OMISSION]</BR>
Kim, Janghyuk,Mastro, Michael A.,Tadjer, Marko J.,Kim, Jihyun American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.25
<P>beta-gallium oxide (beta-Ga2O3) and hexagonal boron nitride (h-BN) heterostructure-based quasi-two-dimensional metal-insulator-semiconductor field-effect transistors (MISFETs) were demonstrated by integrating mechanical exfoliation of (quasi)-two-dimensional materials with a dry transfer process, wherein nanothin flakes of beta-Ga2O3 and h-BN were utilized as the channel and gate dielectric, respectively, of the MISFET. The h-BN dielectric, which has an extraordinarily flat and clean surface, provides a minimal density of charged impurities on the interface between beta-Ga2O3 and h-BN, resulting in superior device performances (maximum transconductance, on/off ratio, subthreshold swing, and threshold voltage) compared to those of the conventional back-gated configurations. Also, double-gating of the fabricated device was demonstrated by biasing both top and bottom gates, achieving the modulation of the threshold voltage. This heterostructured wide-band-gap nanodevice shows a new route toward stable and high-power nanoelectronic devices.</P>
Transparent conductive graphene electrode in GaN-based ultra-violet light emitting diodes
Kim, Byung-Jae,Mastro, Michael A.,Hite, Jennifer,Eddy, Charles R.,Kim, Jihyun The Optical Society 2010 Optics express Vol.18 No.22
<P>We report a graphene-based transparent conductive electrode for use in ultraviolet (UV) GaN light emitting diodes (LEDs). A few-layer graphene (FLG) layer was mechanically deposited. UV light at a peak wavelength of 368 nm was successfully emitted by the FLG layer as transparent contact to p-GaN. The emission of UV light through the thin graphene layer was brighter than through the thick graphene layer. The thickness of the graphene layer was characterized by micro-Raman spectroscopy. Our results indicate that this novel graphene-based transparent conductive electrode holds great promise for use in UV optoelectronics for which conventional ITO is less transparent than graphene.</P>
Nanostructured n-ZnO / thin film p-silicon heterojunction light-emitting diodes.
Ahn, Jaehui,Park, Hyunik,Mastro, Michael A,Hite, Jennifer K,Eddy, Charles R,Kim, Jihyun Optical Society of America 2011 Optics express Vol.19 No.27
<P>Electroluminescence (EL) was obtained from a p-Si (100) thin film/nanostructured n-ZnO heterojunction diode fabricated by a simple dielectrophoresis (DEP) method. The Si substrate was pre-patterned with electrodes and an insulating separation layer by a standard photolithographic process. ZnO nanostructures were formed by a simple solution chemistry and subsequently transferred to the pre-patterned substrate. Application of the DEP force at a frequency of 100 kHz and 6 V peak-to-peak voltage allowed precise positioning of the ZnO nanostructures at the edge of the metal electrodes. The physically formed p-Si (100) thin film/nanostructured n-ZnO heterojunction displayed multi-color emission from the ZnO near band edge as well as emission from defective states within the ZnO band gap.</P>
Kim, Janghyuk,Oh, Sooyeoun,Mastro, Michael A.,Kim, Jihyun The Royal Society of Chemistry 2016 Physical chemistry chemical physics Vol.18 No.23
<P>This study demonstrated the exfoliation of a two-dimensional (2D) beta-Ga2O3 nano-belt and subsequent processing into a thin film transistor structure. This mechanical exfoliation and transfer method produces beta-Ga2O3 nano-belts with a pristine surface as well as a continuous defect-free interface with the SiO2/Si substrate. This beta-Ga2O3 nano-belt based transistor displayed an on/off ratio that increased from approximately 10(4) to 10(7) over the operating temperature range of 20 degrees C to 250 degrees C. No electrical breakdown was observed in our measurements up to V-DS = +40 V and V-GS = -60 V between 25 degrees C and 250 degrees C. Additionally, the electrical characteristics were not degraded after a month-long storage in ambient air. The demonstration of high-temperature/high-voltage operation of quasi-2D beta-Ga2O3 nano-belts contrasts with traditional 2D materials such as transition metal dichalcogenides that intrinsically have limited temperature and power operational envelopes owing to their narrow bandgap. This work motivates the application of 2D beta-Ga2O3 to high power nano-electronic devices for harsh environments such as high temperature chemical sensors and photodetectors as well as the miniaturization of power circuits and cooling systems in nano-electronics.</P>