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RISS 인기검색어
- 검색키워드
- 주제어 : Valley polarization (검색결과 6 건)
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김동학,임대영 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.10
We study the effects of charged defects and impurities on the optical properties and the valley polarization in monolayer MoS2. Both the defects generated by vacuum annealing and the impurities introduced by AuCl3 chemical doping dramatically increase the photoluminescence (PL) intensity. This is due to a p-doping effect, which increases the exciton lifetime by suppressing the non-radiative trionic decay in the n-type, as-exfoliated monolayer MoS2. The PL from vacuum-annealed MoS2 can be controlled reversibly. It decreases upon laser irradiation or pumping in a vacuum due to the desorption of air molecules adsorbed at S-vacancy sites and recovers slowly with the re-adsorption of air molecules. Both the vacuum annealing and the AuCl3 doping reduce the valley polarization significantly. A systematic study on the PL and the circular polarization reveals that the reduction in the circular polarization cannot be explained by the increased exciton lifetime alone. The valley polarization almost recovers to its pre-annealing value after pumping in a vacuum, indicating that S-vacancies with ‘charged’ air molecules affect the valley properties more strongly than neutral ones. The valley polarization decrease is more significant at high temperatures, which excludes the increased intervalley scattering due to defects or impurities as its main origin. Relaxation of the valley-contrasting optical selection rule due to defects or impurities, which was reported recently, seems to explain our experimental results better.
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Excitonic Valley Polarization and Coherence in Few-layer MoS2
김동학,신민주,임대영 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.5
We study the excitonic valley polarization and coherence in few-layer MoS2 by using circularandlinear-polarization-resolved photoluminescence. The valley polarization is largest in monolayerMoS2 and decreases with increasing number of layers or temperature. Contrary to the valleypolarization, the linear polarization is negligibly small in monolayer MoS2 and increases with increasingnumber of layers or temperature. The temperature-dependent valley depolarization canbe explained by the exciton center-of-mass momentum-dependent electron-hole exchange interaction. The valley decoherence in few-layer MoS2 is much faster than the valley depolarization at lowtemperature and is steady against increasing temperature or photoexcitation intensity, indicatingthat the decoherence process does not involve phonon or carrier-carrier scattering. The dominantvalley decoherence has a pure dephasing origin and cannot be explained by the valley-depolarizinge-h exchange interaction.
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The electrical and valley properties of monolayer MoSe2
김동학,임대영 한국물리학회 2017 Current Applied Physics Vol.17 No.2
We studied the electrical, optical and valley properties of monolayer MoSe2. The measured PL circular polarization of monolayer MoSe2 was negligibly small, compared with the more-than 60% circular polarization of monolayer MoS2. Doping-dependent PL measurement and Kelvin probe microscopy show that the small circular polarization because of its longer exciton lifetime in monolayer MoSe2. Furthermore, it is found that the longer exciton lifetime is due to the nearly intrinsic electrical property of monolayer MoSe2, where non-radiative trion decay, which is the dominant exciton decay mechanism in n-type monolayer MoS2, is minimized due to the low density of excess electrons (holes). We believe that S and Se vacancies play an important role in determining the Fermi level position for these materials. Our experimental results show that monolayer MoSe2 can be a better valleytronics material than monolayer MoS2 in spite of its small circular polarization.
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The electrical and valley properties of monolayer MoSe<sub>2</sub>
Kim, Dong Hak,Lim, D. Elsevier 2017 Current Applied Physics Vol.17 No.2
<P>We studied the electrical, optical and valley properties of monolayer MoSe2. The measured PL circular polarization of monolayer MoSe2 was negligibly small, compared with the more-than 60% circular polarization of monolayer MoSe2. Doping-dependent PL measurement and Kelvin probe microscopy show that the small circular polarization because of its longer exciton lifetime in monolayer MoSe2. Furthermore, it is found that the longer exciton lifetime is due to the nearly intrinsic electrical property of monolayer MoSe2, where non-radiative trion decay, which is the dominant exciton decay mechanism in n-type monolayer MoSe2, is minimized due to the low density of excess electrons (holes). We believe that S and Se vacancies play an important role in determining the Fermi level position for these materials. Our experimental results show that monolayer MoSe2 can be a better valleytronics material than monolayer MoSe2 in spite of its small circular polarization. (C) 2016 Elsevier B.V. All rights reserved.</P>
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Soufi ane Derrouiche,Benyounes Bouazza,Choukria Sayah 한국전기전자재료학회 2018 Transactions on Electrical and Electronic Material Vol.19 No.4
In this work, we present a study of the characterization of the existence and absence of polar and inter-valley scatteringmechanisms in In 0.53 Ga 0.47 As through analysis of the stationary and non-stationary curves of charge-carrier energy. Theabsence of polar scattering mechanisms is determined from the observation of a marked increase in carrier energy on thestationary curve of charge carriers energy as a function of applied electric fi eld whose a dramatic and fastly increase of chargecarriers energy is registered in their absence. In contrast, the absence of inter-valley scattering mechanisms is determined bythe presence of an increase in carrier energy on the non-stationary curve as a function of applied electric fi eld.
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