Absorption Coefficient of Weak Electromagnetic Waves Caused by Confined Electrons in Quantum Wires

Nguyen Quang BAu,Tran Cong PHONG,Le DINH 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.II

The quantum theory of the absorption of weak electromagnetic waves (EMWs) caused by confined electrons in quantum wires has been studied based on Kubo's linear response theory and Mori's projection operator method. Analytical expressions for the absorption coefficients of weak EMWs in quantum wires with electron-acoustic phonon and electron-optical phonon scattering mechanisms are obtained. The dependence of the absorption coefficient of a weak EMW on its frequency $\omega$ as system temperature $T$, and the parameters charactering the sample are analyzed. Numerical calculations have been done, and the results are discussed for a typical wire of GaAs/GaAsAl.

The Nonlinear Absorption Coefficient of Strong Electromagnetic Waves Caused by Electrons Confined in Quantum Wires

Nguyen Quang Bau,Hoang Dinh Trien 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.1

Analytic expressions for the nonlinear absorption coefficient of a strong electromagnetic wave caused by electrons confined in cylindrical quantum wires are calculated by using the quantum kinetic equation for electrons. The problem is considered for electron-phonon scattering mechanisms (electron-optical phonon scattering and electron-acoustic phonon scattering) in the absence of an external magnetic field and for electron-optical phonon scattering in the presence of an external magnetic field. The dependence of the nonlinear absorption coefficient on the intensity E0 and the frequency of the external strong electromagnetic wave, the temperature T of the system, the radius of the wires R, and the cyclotron frequency wc (for the case of the presence of an external magnetic field) is obtained. The analytic expressions are numerically calculated and discussed for GaAs/GaAsAl quantum wires. The results are compared with those for normal bulk semiconductors and quantum wells to show the differences.

The Nonlinear Absorption Coeffcient of a Strong Electromagnetic Wave Caused by Confined Electrons in Quantum Wells

Bau Quang Nguyen,Hung Manh Do,Ngoe Bich Nguyen 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.2

Analytic expressions for the nonlinear absorption coefficient of a strong electromagnetic wave (laser radiation) caused by confined electrons for the case of electron - optical phonon scattering and electron - acoustic phonon scattering in quantum wells are calculated by using the quantum kinetic equation for electrons. The problem is also considered for both the absence and the presence of an external magnetic field. The dependence of the nonlinear absorption coefficient on the intensity and the frequency of the external strong electromagnetic wave, the temperature T of the system and the cyclotron frequency for case of an external magnetic field is obtained. The analytic expressions are numerically evaluated, plotted and discussed for a specific quantum well AlAs/GaAs/ AlAs. The computations show that the nonlinear absorption coefficient in quantum wells is much more greater than to is in normal bulk semiconductor. The appearance of an external magnetic field causes surprising changes in the nonlinear absorption. All the results are compared with those for the normal bulk semiconductors to show the difference.

Negative Absorption Coefficient of a Weak Electromagnetic Wave Caused by Electrons Confined in Rectangular Quantum Wires in the Presence of Laser Radiation

Nguyen Quang Bau,Thi Thanh Nhan,Nguyen Vu Nhan 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.4

Analytic expressions for the absorption coefficient (ACF) of a weak electromagnetic wave (EMW)caused by electrons confined in rectangular quantum wires (RQWs) in the presence of laser radiationare calculated using the quantum kinetic equation for electrons in the case of electron-optical phononscattering. The dependence of the ACF of a weak EMW on the intensity E01 and the frequency 1 of the external laser radiation, the intensity E02 and the frequency2 of the weak EMW, thetemperature T of the system and the size L (Lx and Ly) of the RQWs is obtained. The resultsare numerically calculated and discussed for GaAs/GaAsAl RQWs. The numerical results showthat the ACF of a weak EMW in RQWs can have negative values. Thus, in the presence of laserradiation, under proper conditions, a weak EMW is increased. This is different from the similarproblem in bulk semiconductors and from the case without laser radiation

Influence of a Strong Electromagnetic Wave (Laser Radiation) on the Hall Effect in Quantum Wells with a Parabolic Potential

Nguyen Quang Bau,Bui Dinh Hoi 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.1

Based on the quantum kinetic equation for electrons, we theoretically study the influence of an electromagnetic wave (EMW) on the Hall effect in a quantum well (QW) with a parabolic potential V (z) = m!zz2/2 (where m and !z are the effective mass of electron and the confinement frequency of QW, respectively) subjected to a crossed dc electric field E~1 = (0, 0,E1) and magnetic field ~B = (0,B, 0) in the presence of a strong EMW characterized by electric field ~E = (E0 sin t, 0, 0)(where E0 and are the amplitude and the frequency of EMW, respectively). We obtain analytic expressions for the components zz and xz of the Hall conductivity as well as a Hall coefficient with a dependence on B, E1, E0, , temperature T of the system and the characteristic parameters of QW. The results are numerically evaluated and graphed for a specific quantum well, GaAs/AlGaAs,to show clearly the dependence of the Hall conductivity and the Hall coefficient on above parameters. The influence of the EMW is interpreted by using the dependences of the Hall conductivity and the Hall coefficient on the amplitude E0 and the frequency of EMW and by using the dependences on the magnetic field B and the dc electric field E1 as in the ordinary Hall effect.

Calculations of the Acoustoelectric Current in a Quantum Well by Using a Quantum Kinetic Equation

Nguyen Quang Bau,Nguyen Van Hieu,NguyenVuNhan 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.12

An analytic expression for the acoustoelectric current (AC) <i>j</i>^ac induced by electron-external acoustic wave interactions and electron-internal acoustic wave (internal phonons) scattering in a quantum well (QW) is calculated by using the quantum kinetic equation for electrons. The physical problem is investigated in the region <i>ql</i> ≫ 1 (where q is the acoustic wave number and <i>l</i> is the electrons mean free path). The dependence of the AC <i>j</i>^ac on the external acoustic wave frequency ω_q, the width of the QW <i>L</i> and the temperature <i>T</i> for a specific QW of AlGaAs/GaAs/AlGaAs is achieved by using a numerical method. The computational results show that the dependence of the AC <i>j</i>^ac on the temperature <i>T</i>, the external acoustic wave frequency ω_q, the width of the QW <i>L</i> is non-monotonic and that the peaks can be attributed to transitions between mini-bands <i>n</i> → <i>n</i>0. The dependence of the AC <i>j</i>^ac on the temperature <i>T</i> and the Fermi energy ε_F is obtained, and a maximum of the AC <i>j</i>^ac for ε_F = 0.038 eV and ω_q = 3 × 10¹¹ s⁻¹ seen at <i>T</i> = 50 K, which agrees with the experimental results for AlGaAs/GaAs/AlGaAs QWs. All these results are compared with those for normal bulk semiconductors and superlattices to show the differences. Finally, the quantum theory of the acoustoelectric effect in a quantum well is newly developed.

Study of the Quantum Magneto-Thermoelectric Effect in the Two-Dimensional Compositional Superlattice GaAs/AlGaAs under the influence of an Electromagnetic Wave by Using the Quantum Kinetic Equation

Nguyen Quang Bau,Dao Thu Hang,Do Tuan Long 한국물리학회 2019 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.75 No.12

The quantum magneto-thermoelectric effect in a two-dimensional compositional superlattice under the influence of an electromagnetic wave (EMW) in two cases is investigated. Two cases of the electron scattering mechanism are considered: the electron-acoustic phonon scattering and electron-optical phonon scattering. Analytical expressions for the quantum Ettingshausen coefficient (EC), the thermopower tensor, the thermoelectric tensor and the kinetic tensor are obtained by using a quantum kinetic equation. These expressions are numerically solved for the two-dimensional compositional superlattice GaAs/AlGaAs and the results are discussed. The results show that in the case of electron-acoustic phonon scattering, the Shubnikov-de Haas oscillations appear when we examine the dependences of the quantum EC, the thermopower tensor and the thermoelectric tensor on the magnetic field. In the case of electron-optical phonon scattering, resonance peaks that satisfy the condition of the inter-subband magneto-phonon resonance appear. In the two cases, the superlattice period (a parameter specific to the material) strongly affects the quantum magneto-thermoelectric effect. When the superlattice period is small, quantum EC oscillations (in the case of electron-acoustic phonon interaction) and quantum EC resonance peaks (in the case of electron-optical phonon interaction) appear. However, when the superlattice period is large, these oscillations and resonance peaks are not observed. Especially, the influence of electromagnetic waves on the quantum magneto-thermoelectric effect is also clarified. The quantum theory of the magneto-thermoelectric effect has been studied from low temperature to high temperature. This overcomes the limitations of the Boltzmann kinetic equation which was studied at high temperature. The results are new and can serve as a basis for further development of the theory of quantum magneto-thermoelectric effects in low-dimensional semiconductor systems.

Doped Two-dimensional Semiconductor Superlattice: Photo-stimulated Quantum Thermo-magnetoelectric Effects under the Influence of a Confined Phonon

Bau Nguyen Quang,Quynh Nguyen Thi Lam,Ba Cao Thi Vi,Hung Le Thai 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.77 No.12

Photo-stimulated quantum thermo-magnetoelectric effects in doped two-dimensional semiconductor superlattices, including the photo-stimulated quantum Ettingshausen effect and the photo-stimulated quantum Peltier effect, have been theoretically studied by using the quantum kinetic equation method. In this work, we assume that the electron-confined acoustic phonon scattering is essential. Moreover, the presence of the laser radiation (LR) is also taken into account to determine the influence of confined phonons on the aforementioned effects. We have defined the analytical expressions for the kinetic tensors and the Ettingshausen and the Peltier coefficients, presented the numerically calculated the theoretical results for the GaAs:Si/GaAs:Be doped semiconductor superlattice and compared them with these for the case of an unconfined acoustic phonon. The results obtained indicated that the formulas for the kinetic tensors, the Ettingshausen coefficient (EC) and the Peltier coefficient (PC) contain the quantum number m specifying the confinement of a phonon and approach the results for an unconfined phonon as m goes to zero. We found that the kinetic tensors, the EC and the PC oscillate with changing magnetic field and that the confinement of a phonon causes a shift of the peaks in these oscillations to lower energy. The dependences of both EC and PC on the temperature were found to be nonlinear. Moreover, all the coefficients level off when the temperature was less than 4.5 K or greater than 5.5 K. The EC also depended on the doping concentration in a nonlinear way and reaches a positive constant value when the semiconductor superlattice was doped with a high concentration. Most of the numerical results showed that the magnitude of the tensors, the EC as well as the PC, within a confined acoustic phonon varie significantly in comparison with the unconfined phonon case. This means that the confinement of the phonon affects the thermo-magnetoelectric effect quantitatively and qualitatively. These results contribute to completing the theory of the thermo-magnetoelectric effects in the low-dimensional semiconductor systems.

Parametric Resonance of Acoustic and Optical Phonons in a Quantum Well

Tran Cong Phong,Nguyen Quang Bau 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.5

The parametric resonance of acoustic and optical phonons in a quantum well in the presence of an external electromagnetic eld is theoretically predicted by using a set of quantum transport equations for the phonons. Dispersions of the resonant phonon frequency and the threshold amplitude of the field for parametric amplication of the acoustic phonons are obtained. If they are obtained, then they are also estimated for realistic semiconductor models.

Theoretical study of photo-stimulated thermo-magnetoelectric effects in two-dimensional compositional superlattices using quantum kinetic equation

Ba Cao Thi Vi,Bau Nguyen Quang,Quynh Nguyen Thi Lam,Nam Nguyen Dinh,Long Do Tuan 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.81 No.8

Two scattering mechanisms, including the confned electron (CE)–confned acoustic phonon (CAP) scattering and the CE–confned optical phonon (COP) scattering, have been considered in the theoretical problem of photo-stimulated thermomagnetoelectric efects (TME) occurring in two-dimensional compositional semiconductor superlattices (CSS). The quantum kinetic equation (QKE) method is applied to calculate the characteristic quantities of two typical photo-stimulated TME, namely, the Ettingshausen efect (EE) and the Peltier efect (PE). The obtained analytical results show that the external felds (the magnetic feld B, the dc electric feld E, the frequency 휔 and the amplitude E0 of the laser radiation), the period of superlattice d as well as the temperature of the systems T are quantities that govern the quantum Ettingshausen coefcient (qEC) and the quantum Peltier coefcient (qPC).The presence of m-quantum number specifying phonon confnement in the analytical expression of the qEC and the qPC is as a demonstration for the infuence of size efect on both the EE and the PE. The results are numerically estimated and graphed for the GaAs∕Al0.25Ga0.75As CSS to indicate the dependence of the qEC and the qPC on aforementioned quantities. Moreover, the confned phonons contribute to the magneto-phonon-photon resonance condition (MPPRC) in CSS. Therefore, the behaviors of the photo-stimulated TME within phonon confnement are diferent from the case of bulk phonons. Due to the confnement of an acoustic phonon, the Shubnikov–de Hass oscillations are observed with the changes in the amplitude and the posture when investigating the dependence of the qEC and the qPC on the magnetic feld and the frequency of the laser radiation (LR). Meanwhile, resonance peaks of these coefcients are relocated under the infuence of a COP. Besides, the confnement of phonons causes the changes in the magnitude of both the qEC and the qPC compared to the case of unconfned phonons. The obtained results hold true for all temperatures and contribute to perfecting the theory of the quantum TME in the low-dimensional semiconductor systems (LDSS).