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  • Article


  • Authors: Nguyen, Quang Bau; Cao, Thi Vi Ba; Do, Tuan Long (2017)

  • Based on the quantum kinetic equation method, the influence of confined optical phonons and laser radiation on the Radioelectric effect in a cylindrical semiconductor quantum wire with parabolic potential subjected to a dc electric field and a linearly polarized electromagnetic wave has been theoretically studied. The obtained analytical expression of the Radioelectric field (REF) depends on frequencies and amplitudes of the external electromagnetic waves, the quantum wire parameters, the temperature of the system, and especially the quantum numbers (n and m) which characterize the phonon confinement. Numerical calculations for the GaAs/GaAsAl quantum wire show the strongly impact of the confined optical phonons as well as the laser radiation on the REF magnitude and posture. The RE...

  • Article


  • Authors: Cao, Thi Vi Ba; Tran, Hai Hung; Doan, Minh Quang; Nguyen, Quang Bau (2017)

  • The Ettingshausen coefficient (EC) in a Rectangular quantum wire with an infinite potential (RQWIP)in the presence of an Electromagnetic wave (EMW) is calculated by using a quantum kinetic equation for electrons. Considering the case of the electron - optical phonon interaction, we have found the expressions of the kinetic tensors . From the kinetic tensors, we have also obtained the analytical expression of the EC in the RQWIP in the presence of EMW as function of the frequency and the intensity of the EMW, of the temperature of system, of the magnetic field and of the characteristic parameters of RQWIP. The theoretical results for the EC are numerically evaluated, plotted and discussed for a specific RQWIP GaAs/GaAsAL. We also compared received EC with those for normal bulk semi...

  • Article


  • Authors: Nguyen, Quang Bau (2006)

  • Analytic expressions for the obsorption coefficient of a weak Electromag­netic Wave (EMW) by free carriers for the case electron-optical phonon scattering in 2 dimensional system (quantum wells and doped superlattices) are calculated by the KuboMori method in two cases: the absence of a magnetic field and the pres­ence of a magnetic field applied perpendicular to its barriers, A different dependence of the absorption coefficient on the temperature T of system, the electromagnetic wave frequency , the cyclotron frequency n (when a magnetic field is present) and characteristic parameters of a 2 dimensional system in comparision with normal semi­conductors are obtained. The analytic expressions are numerically evaluated plotted and discussed for a specific 2 dimensional system (AlAs/...

  • Article


  • Authors: Nguyen, Quang Bau; Dao, Thu Hang; Doan, Minh Quang; Nguyen, Thi Thanh Nhan (2017)

  • We have studied magneto-thermoelectric effects in quantum well in the presence of electromagnetic wave. The analytic expression for Ettingshausen coefficient (EC) in the Quantum Well with parabolic potential (QWPP) in the presence of Electromagnetic wave (EMW) is calculated by using the quantum kinetic equation for electrons. The dependence of EC on the frequency, the amplitude of EMW, the Quantum Well parameters and the temperature are obtained. The results are numerically calculated, plotted, and discussed for GaAs/GaAsAl Quantum Well to clearly show the dependence of EC on above parameters and the results in this case are compared with the case in the bulk semiconductors. We realize that as the temperature increases, the EC decreases. The results show appearance of the Shubnikov–...

  • Article


  • Authors: Nguyen, Thi Thanh Ha; Nguyen, Anh Dung; Nguyen, Quang Bau; Pham, Khac Hung (2016)

  • We have studied the diffusion mechanism in network-forming liquids via molecular dynamics simulation. Two models of silica liquid at temperatures of 2600 and 3500 K have been constructed. The motion of atoms is analyzed through reactions SiOx®SiOx±1, OSiy®OSiy±1 and coordination cells. It was shown that the reactions happen not randomly in the space, but they occur more frequently with some coordination cells and bonds Si-O. This effect enhances upon lowering the temperature. The number of reactions happening in the coordination cells is strongly correlated with the mobility of CC atom. We found that there are large rigid clusters which compose of immobile atoms and exist for long time. Further, the dynamics heterogeneity (DH) is determined via sets of: (1) most mobile or immobile a...

  • Article


  • Authors: Nguyen, Thi Thanh Ha; Nguyen, Quang Bau; Pham, Khac Hung (2012)

  • In this paper, we numerically study the diffusion mechanism at atomic level in silica liquid via molecular dynamics simulation. The model consisting of 1998 particles and using the BKS potential has been constructed at the temperature from 2600 to 4500 K. Furthermore, we track the evolution of network units with x=4, 5 and 6 over different time. The simulation shows that the diffusivity depends strongly not only on the rate of the exchanging the coordinated oxygens, but also on the correlation effect. This effect is caused by the specific distribution of the exchanging coordinated oxygens (ECO) through the space which leads to spatially heterogeneous dynamics in the liquid. Analyzing the temperature dependence of the correlation coefficient F we found that the slowdown in dynamics n...

  • Article


  • Authors: Le, Thai Hung; Nguyen, Quang Bau; Pham, Ngoc Thang (2017)

  • The Transverse Hall effect (THE) has been theoretical studied in a quantum well (QW) with high infinite potential subjected to a crossed dc electric field and a magnetic field (MF) which is oriented perpendicularly to the confinement direction in the present of an intense electromagnetic wave (EMW). The analytical expression of the transverse hall coefficient (THC) which depends not only on the parameters of the system but especially on the quantum number m characterizing confined phonons, is obtained by using the quantum kinetic equation method for confined electrons - confined optical phonons interaction. The analytic expression of THC is numerically evaluated, plotted and discussed for a specific case of the AlAs/GaAs/AlAs QW. Results show the THC depends strong nonlinearly on th...

  • Article


  • Authors: Nguyen, Quang Bau; Do, Tuan Long (2016)

  • Based on the quantum kinetic equation method, the Hall effect in doped semiconductor superlattices (DSSL) has been theoretically studied under the influence of confined LO-phonons and the laser radia-tion. The analytical expression of the Hall conductivity tensor, the magnetoresistance and the Hall co-efficient of aGaAs:Si/GaAs:BeDSSL is obtained in terms of the external fields, lattice period and doping concentration. The quantum numbers N, n, m were varied in order to characterize the effect of electron and LO-phonon confinement. Numerical evaluations showed that LO-phonon confinement enhanced the probability of electron scattering, thus increasing the number of resonance peaks in the Hall conductivity tensor and decreasing the magnitude of the magnetoresistance as well as the Ha...