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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>
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>
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>
Rechargeable zinc oxide / carbon nano-structures
M. A. Mastro,M. J. Tadjer,F. J. Kub,K. D. Hobart,C. R. Eddy, Jr,김지현,M.R. Papantonakis 한양대학교 세라믹연구소 2010 Journal of Ceramic Processing Research Vol.11 No.1
A simple solution growth process was employed to deposit ZnO nanowires on carbon nanotubes and nano-structured carbon paper. Vertical ZnO nanowires formed on the carbon paper with a hexagonal orientation. On the carbon nanotubes, the ZnO nanowires and platelets integrated as an agglomerated sphere. Electric charge flow was measured in both structures upon probe contact, and would decay over several hours. A mechanical perturbation was found to recharge the structure, which was attributed to the piezoelectric ZnO nanowires. Continuous as well as intermittent vibration coupled with an electrochemical storage mechanism to create a perpetual current source.
S. Amari,F. Dahmane,S. Bin Omran,B. Doumi,I. E. Yahiaoui,A. Tadjer,R. Khenata 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.69 No.9
In this study, the structural, magnetic and electronic properties of the Co2FeGe1−xSix (x = 0, 0.5, 1) Heusler compounds have been calculated using the full-potential linearized augmented plane-wave method based on the spin density functional theory within the generalized gradient approximation of Perdew-Burke-Ernzerhof. In order to take into account the correlation effects, we have also performed GGA + U calculations, where the Hubbard on-site Coulomb interaction correction U is calculated by using the constraint local density approximation for the Co and the Mn atoms. The Cu2MnAl-type structure is found to be energetically more favorable than the Hg2CuTitype structure for both the Co2FeSi and the Co2FeGe compounds. The calculated atomic resolved densities of states of Co2FeSi and Co2FeGe indicate nearly half-metallic behaviors with small spindown electronic densities of states at the Fermi level. This behavior is corrected by including the Hubbard Coulomb energy U term. The Coulomb exchange correlation U confirms the halfmetallic property in both the Co2FeSi and the Co2FeGe compounds. We also discuss the electronic structures, the total and the partial densities of states, and the local magnetic moments. The Co2FeGe0.5Si0.5 compound shows a nearly half-metallic behavior with a small spin-down electronic density of states at the Fermi level in both the GGA and GGA+U approximations.
Power Electronic Materials Research to Enable Next Generation GaN Power Switches
Charles R. “Chip” Eddy,N. Nepal,V.R. Anderson,C.R. English,N.Y. Garces,V.D. Wheeler,B.N. Feigelson,J.D. Greenlee,M.J. Tadjer,A.D. Koehler,T.J. Anderson,T.I. Feygelson,B.B. Pate,M.A. Mastro,F.J. Kub,K. 한국진공학회 2017 한국진공학회 학술발표회초록집 Vol.2017 No.8