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우부성,김도진,김창수,Cun Xu Gao,김효진,홍순구,임영언 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.2I
Be-codoped GaMnAs layers were systematically grown via low-temperature molecular beam epitaxy with varying Mn and Be fluxes. Two Be fluxes to exhibit semiconducting and metallic resistivities were chosen, and the Mn fluxes were controlled so as to cover the range from solid solutions to precipitates. The structural, electrical, and magnetic properties were investigated for the as-grown and the annealed structures. Both the lightly and the heavily Be-codoped GaAs:(Mn,Be) films revealed ferromagnetism at room temperature due to precipitates of MnAs and MnGa. Beryllium preferably took the Ga sites through competition with Mn, and the pushed-out Mn atoms formed precipitates. Heavy codoping of Be, as well as heat treatments, facilitated the precipitation of MnGa rather than MnAs. The anomalous Hall-resistance originating from the precipitates was observed at room temperature only in the degenerately Be-codoped metallic GaAs:(Mn,Be) films. The observation was assisted by the high conductivity of the GaAs:Be matrix.
GaMnAs의 Be 병행 도핑에 의한 자기 수송 특성 연구
임완순,윤대식,우부성,고존서,김도진,임영언,김효진,김창수,김종오,Im W. S.,Yoon T. S.,Yu F. C.,Gao C. X.,Kim D. J.,Ibm Y. E.,Kim H. J.,Kim C. S.,Kim C. O. 한국재료학회 2005 한국재료학회지 Vol.15 No.1
Motivated by the enhanced magnetic properties of Mg-codoped GaMnN ferromagnetic semiconductors, Be-codoped GaMnAs films were grown via molecular beam epitaxy with varying Mn flux at a fixed Be flux. The structural, electrical, and magnetic properties were investigated. GaAs:(Mn,Be) films showed metallic behavior while GaAs:Mn films showed semiconducting behavior as determined by the temperature dependent resistivity measurements. The Hall-effect measurements with varying magnetic field showed clear anomalous Hall effect up to room temperature proving ferromagnetism and magnetotransport in the GaAs:(Mn,Be) films. Planar Hall resistance measurement also confirmed the properties. The dramatic enhancement of the Curie temperature in GaMnAs system was attributed to Be codoping in the GaMnAs films as well as MnAs precipitation.
이계진,강희수,김정애,우부성,김경현,김도진,김봉구,강영환,유승호,김창균,김창수,김효진,임영언 한국재료학회 2003 한국재료학회지 Vol.13 No.7
The room-temperature operating semiconductor GaMnN is known to be improved in its magnetic property when a highly conductive precipitate $Mn_3$GaN exists. Therefore, it is useful to investigate the behavior of the precipitate through heat treatments for further improvement of its magnetic property. Furthermore, neutron irradiation may further influence the behavior of the precipitates, and consequently, their effects on the magnetization. With the heat treatment, $Mn_3$GaN decomposed and a new phase of $Mn_3$Ga has generated. The kinetics was accelerated by neutron irradiation, which might generate defects that can help the decomposition of N and/or the formation of $Mn_3$Ga. The increase and decrease of the magnetization of the heat-treated GaMnN thin films were explained consistently by the behavior of the precipitates.
Be - codoped GaMnAs의 상온 강자성 및 자기 수송 특성
임완순(W. S. Im),우부성(F. C. Yu),고존서(C. X. Gao),김도진(D. J. Kim),김효진(H. J. Kim),임영언(Y. E. Ihm),김창수(C. S. Kim) 한국자기학회 2004 韓國磁氣學會誌 Vol.14 No.6
Be-codoped GaMnAs layers were systematically grown via molecular beam epitaxy with varying Mn- and Be-flux. Mn flux was controlled to cover from solid solution type GaMnAs to precipitated GaMnAs. Two Be flux were chosen to exhibit semiconducting and metallic resistivity in the grown layers. The structural, electrical, and magnetic properties of GaAs:(Mn,Be) were investigated. The lightly Be-codoped GaMnAs layers showed ferromagnetism at room temperature, but did not reveal magnetotransport due to small magneto-resistance and high resistance of the matrix. However, room temperature magnetotransport could be observed in the degenerate Be-codoped GaMnAs layers, and which was assisted by the high conductivity of the matrix. The Be-codoping has promoted segregation of new ferromagnetic phase of MnGa as well as MnAs.
p-Type GaN Growth from a Single GaN Precursor via Molecular Beam Epitaxy and Dopant Activation
Cunxu Gao,Chang Gyoun Kim,Chang Soo Kim,김도진,우부성,김효진,Young Eon Ihm 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.I
A study of GaN and p-GaN growths with doping of Mg, Be and Mn was undertaken using a single GaN precursor source via molecular beam epitaxy. Measurements of the changes in surface morphology and film resistivity with growth temperature and doping were carried out. Mg or Be acceptors were shown to improve the surface roughness of the films through forming of acceptor-nitrogen-hydrogen complexes. Thermal annealing for acceptor activation was performed in vacuum, Ar, and N$_2$ by using rapid thermal annealing. The environment of the activation annealing process was shown to affect the activation kinetics and the activation behaviors. A nitrogen ambient delayed the activation of the acceptors, but higher temperature promoted the activation process. The behaviors of the acceptor-nitrogen-hydrogen complexes were systematically examined through experimental set-ups and comparison with the behaviors in GaN:Mn film.