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상온 강자성 (Ga,Mn)N 박막을 이용한 질화물계 스핀 발광소자의 스핀편극된 빛의 발광
함문호,명재민,Ham, Moon-Ho,Myoung, Jae-Min 한국전기전자재료학회 2005 전기전자재료학회논문지 Vol.18 No.11
We investigated the fabrication and characteristics of the nitride-based spin-polarized LEDs with room-temperature ferromagnetic (Ga,Mn)N layer as a spin injection source. The (Ga,Mn)N thin films having room-temperature ferromagnetic ordering were found to exhibit the negative MR and anomalous Hall resistance up to room temperature, revealing the existence of spin-polarized electrons in (Ga,Mn)N films at room temperature. The electrical characteristics in the spin LEDs did not degraded in spite of the insertion of the (Ga,Mn)N layer into the LED structure. In EL spectra of the spin LEDs, it is confirmed that the devices produce intense EL emission at 7 K as well as room temperature. These results are expected to open up new opportunities to realize room-temperature operating semiconductor spintronic devices.
Engineering carbon nanomaterials for nanoelectronics
함문호 한국공업화학회 2016 한국공업화학회 연구논문 초록집 Vol.2016 No.0
Carbon nanostructures such as graphene and carbon nanotubes (CNTs) have unique physical and electrical properties. There is currently interest in taking advantage of these properties for future electronic applications. In this talk, I first present a modified chemical vapor deposition (CVD) technique for the production of large-area, high-quality continuous monolayer graphene films from benzene on Cu at 100-300 °C at ambient pressure. In this method, we extended the graphene growth step in the absence of residual oxidizing species by introducing pumping and purging cycles prior to growth. Next, I introduce well-dispersed CNTs in lithium-doped ZnO (LiZnO) for facilitating high-mobility, low-cost metal-oxide-based thin-film transistors (TFTs), using a simple, wet-chemical functionalization method. The crucial role of surface functionalization of CNTs is clarified with the demonstration of LiZnO TFTs with a field-effect mobility of 28.6 ㎠/Vs and an on/off current ratio of 9.3 × 10(6).
Patterning graphene for electronics and sensors
함문호 한국공업화학회 2014 한국공업화학회 연구논문 초록집 Vol.2014 No.1
Graphene, a 2-dimensional carbon nanostructure, has unique electrical and optical properties. There is currently interest in taking advantage of these properties for electronic applications. In this talk, I will explore graphene for high-efficient electronic and sensor applications. I first demonstrate the field-effect transistor (FET) characteristics and photoelectric properties of graphene nanoribbon (GNR) arrays having 9-12 nm ribbon widths which were fabricated using a cylindrical PS-b-PDMS block copolymer (BCP) as a lithographic mask to pattern graphene monolayer sheets grown by chemical vapor deposition (CVD) and transferred onto heavily p-doped Si substrates coated with a 300 nm-thick SiO<sub>2</sub> layer. GNR array FETs exhibited higher on/off ratio and photocurrent when compared to pristine graphene FETs. The reactivity of CVD graphene supported on different substrates and reactivity imprint lithography for graphene are also discussed.
Ferromagnetic Properties in Diluted Magnetic Semiconductors (Al,Mn)N grown by PEMBE
함문호,명재민 한국전기전자재료학회 2006 Transactions on Electrical and Electronic Material Vol.7 No.1
We present the structural, magnetic, and electrical properties in the (Al,Mn)N films with various Mn concentrations grown by plasma-enhanced molecular beam epitaxy. X-ray diffraction analyses reveal that the (Al,Mn)N films have the wurtzite structure without secondary phases. All (Al,Mn)N films showed the ferromagnetic ordering. Particularly, (Al1-x Mnx)N film with x = 0.028 exhibited the highest magnetic moment per Mn atom at room temperature. Since all the films exhibit the insulating characteristics, the origin of ferromagnetism in (Al,Mn)N might be attributed to either indirect exchange interaction caused by virtual electron excitations from Mn acceptor level to the valence band within the samples or a percolation of bound magnetic polarons arisen from exchange interaction of localized carriers with magnetic impurities in a low carrier density regime.
Controlled Formation of Oxide Shells from GaN Nanowires: Poly- to Single-Crystal
함문호,Sanghun Lee,명재민,이웅 대한금속·재료학회 2011 ELECTRONIC MATERIALS LETTERS Vol.7 No.3
One-dimensional nanocable heterostructures consisting of GaN nanowire cores and Ga_2O_3 shells were prepared by thermal oxidation of single-crystal GaN nanowires in an oxygen atmosphere. Morphologically uniform GaN/Ga_2O_3 core/shell nanocable structures with single-crystal oxide shells can be obtained in a controllable manner by varying the oxygen pressure and oxidation time. Although the thickness of the oxide shell can be controlled by varying the oxidation time and oxygen pressure, the crystallinity of the oxide shell evolves from a single crystal to a polycrystal as the oxygen pressure is increased. This behavior implies that the process can be understood in terms of the competition between the diffusion of oxygen through the growing oxide layer and the reaction at the GaN/Ga_2O_3 interface.
고속 회전체용 가스 포일 스러스트 베어링의 하중지지력 및 마찰손실 해석을 위한 유체-구조 연성해석
최문호(Moo Ho Choi),이준호(Jun Ho Lee),함진기(Jin Ki Ham) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11
A novel fluid-solid interaction (FSI) model was developed to evaluate load carrying capacity (LCC) and frictional power loss for gas-lubricated, compliant surface radial foil thrust bearings. The FSI model consists of coupled hydrodynamic and static structure analysis model. The hydrodynamic model received pressure distribution and film thickness onto the deformed thrust bearing surface. Then the hydrodynamic analysis code solved compressible Reynolds equation using finite element method to obtain iterative solution of periodic pressure distribution. The hydrodynamic analysis model was verified by comparing the solution with those obtained by computational fluid dynamics package in the rigid bearing surface. The structural analysis was conducted with commercial finite element analysis package considering the present state-of-the-art techniques used in foil bearing analysis. The analysis model in this research was compared with previous experimental data and correlations taken at a fixed film thickness and a rigid bearing. Then the correlations were modified in order to express the LCC and the power loss considering the periodic pressure distribution and the deformation of the top foil.
ALD법으로 성장한 HfO<sub>2</sub> 박막의 열처리에 따른 특성변화
이재웅,함문호,맹완주,김형준,명재민,Lee, J.W.,Ham, M.H.,Maeng, W.J.,Kim, H.,Myoung, J.M. 한국재료학회 2007 한국재료학회지 Vol.17 No.2
The effects of post-annealing of high-k $HfO_2$ thin films grown by atomic layer deposition method were investigated by the annealing treatments of $400-600^{\circ}C$. $Pt/HfO_2/p-Si\;MOS$ capacitor structures were fabricated, and then the capacitance-voltage and current-voltage characteristics were measured to analyze the electrical characteristics of dielectric layers. The X-ray diffraction analyses revealed that the $500^{\circ}C-annealed\;HfO_2$ film remained to be amorphous, and the $600^{\circ}C-annealed\;HfO_2$ film was crystallized. The annealing treatment at $500^{\circ}C$ resulted in the highest capacitance and the lowest leakage current due to the reduction of defects in the $HfO_2$ films and non-crystallization. Our results suggest that post-annealing treatments are a critical factor in improving the characteristics of gate dielectric layer.