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  • 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, 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: Le, Thai Hung; Nguyen, Vu Nhan; Nguyen, Quang Bau (2012)

  • The impact of confined phonons on the nonlinear absorption coefficient (NAC) of a strong electromagnetic wave (EMW) by confined electrons in compositional superlattices is theoretically studied by using the quantum transport equation for electrons. The dependence of the NAC on the energy (), the amplitude (Eo) of external strong EMW, the temperature (T) of the system and the period (dA) of compositional superlattices is obtained in both case of confined and unconfined phonons. Two cases for the absorption: Close to the absorption threshold and far away from the absorption threshold (; and are the energy of optical phonon and the average energy of electrons, respectively) are considered. The analytic expressions are numerically evaluated, plotted and discussed for a specific of t...

  • Article


  • Authors: Dang, Dinh Toi; Nguyen, Quang Bau (2002)

  • By suggesting a simple density of localized states for amorphous materials and using the percolation method the analytical expression is obtained for describing qualitatively the observed variable-range hopping thermopower crossover from the Mott T l/2 -behaviour to the temperature-independent behaviour as the temperature increases. The crossover shows a profound manifestation of the Coulomb correlation along that observed in VRH conductivity crossover.

  • Article


  • Authors: Nguyen, Quoc Hung; Nguyen, Quang Bau (2002)

  • Based on the quantum kinetic equation for phonon, the amplification of sound (acoustic phonons) due to the absorption of laser radiation in cylindrical quantum wires with parabolic potential in the presence of m agnetic field is studied. Analytical expressions for the rate of acoustic phonons excitations, the conditions for the amplification of sound and the momentum conditions for electron to participate in the amplification of sound are obtained for the two cases: singlephoton absorption process and multiphoton absorption process. The differences between the two cases of singlephoton absorption and m ultiphoton absorption are discussed; the numerical computations and plots are carried out for a GaAs/GaAsAl quantum wire. The results are compared with bulk semiconductors and quant...

  • Article


  • Authors: Bui, Dinh Hoi; Pham, Thi Trang; Nguyen, Quang Bau (2013)

  • We consider a model of the Hall effect when a doped semiconductor superlattice (DSSL) with a periodical superlattice potential in the z-direction is subjected to a crossed dc electric field (EF) and magnetic field , in the presence of a laser radiation characterized by electric field (where and are the amplitude and the frequency of the laser radiation, respectively). By using the quantum kinetic equation for electrons and considering the electron - optical phonon interaction, we obtain analytical expressions for the Hall conductivity as well as the Hall coefficient (HC) with a dependence on B, , , , the temperature T of the system and the characteristic parameters of DSSL. The analytical results are computationally evaluated and graphically plotted for the GaAs:Si/GaAs:Be DSSL....

  • 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...