The differential cross-section for electronic Raman scattering in double semi-parabolic quantum wells of typical GaAs/AlxGa1-xAs is investigated numerically with the effective-mass approximation. The dependence of the...The differential cross-section for electronic Raman scattering in double semi-parabolic quantum wells of typical GaAs/AlxGa1-xAs is investigated numerically with the effective-mass approximation. The dependence of the differential cross-section on structural parameters such as the barrier width and the well widths is studied. Our results indicate that the electronic Raman scattering is affected by the geometrical size and can be negligible in the symmetric double-well case.展开更多
Within the framework of compact density matrix approach and iterative procedure, a detailed procedure for the calculation of the second-harmonic generation (SHG)susceptibility tensor is given in the electric-field-bia...Within the framework of compact density matrix approach and iterative procedure, a detailed procedure for the calculation of the second-harmonic generation (SHG)susceptibility tensor is given in the electric-field-biased parabolic and semi-parabolic quantum wells (QWs). The simple analytical formula for the SHG susceptibility in the systems is also deduced. Numerical results on typical AlGaAs/GaAs materials show that, for the same effective width,the SHG susceptibility in semi-parabolic QW is larger than that in parabolic QW due to the self-asymmetry of the semiparabolic QW, and the applied electric field can make the SHG susceptibilities in both systems enhance remarkably.Moreover, the SHG susceptibility is also related to the parabolic confinement frequency and the relaxation rate of the systems.展开更多
The optical conductivity of impurity-doped parabolic quantum wells in an applied electric field is investigated with the memory-function approach, and the analytic expression for the optical conductivity is derived. W...The optical conductivity of impurity-doped parabolic quantum wells in an applied electric field is investigated with the memory-function approach, and the analytic expression for the optical conductivity is derived. With characteristic parameters pertaining to GaAs/Ga1-xAlxAs parabolic quantum wells, the numerical results are presented.It is shown that, the smaller the well width, the larger the peak intensity of the optical conductivity, and the more asymmetric the shape of the optical conductivity; the optical conductivity is more sensitive to the electric field, the electric field enhances the optical conductivity; when the dimension of the quantum well increases, the optical conductivity increases until it reaches a maximum value, and then decreases.展开更多
Some realizable structures of double parabolic quantum wells（DPQWs） consisting of Al_xGa_（1-x）As/Al_yGa_（1-y）As are constructed to discuss theoretically the optical absorption due to the intersubband transition ...Some realizable structures of double parabolic quantum wells（DPQWs） consisting of Al_xGa_（1-x）As/Al_yGa_（1-y）As are constructed to discuss theoretically the optical absorption due to the intersubband transition of electrons for both symmetric and asymmetric cases with three energy levels of conduction bands. The electronic states in these structures are obtained using a finite element difference method. Based on a compact density matrix approach, the optical absorption induced by intersubband transition of electrons at room temperature is discussed. The results reveal that the peak positions and heights of intersubband optical absorption coefficients（IOACs） of DPQWs are sensitive to the barrier thickness, depending on Al component. Furthermore, external electric fields result in the decrease of peak, and play an important role in the blue shifts of absorption spectra due to electrons excited from ground state to the first and second excited states. It is found that the peaks of IOACs are smaller in asymmetric DPQWs than in symmetric ones. The results also indicate that the adjustable extent of incident photon energy for DPQW is larger than for a square one of a similar size. Our results are helpful in experiments and device fabrication.展开更多
The collective charge density excitations in a free-standing nanorod with a two-dimensional parabolic quantum well are investigated within the framework of Bohm-Pine＇s random-phase approximation in the two-subband mo...The collective charge density excitations in a free-standing nanorod with a two-dimensional parabolic quantum well are investigated within the framework of Bohm-Pine＇s random-phase approximation in the two-subband model.The new simplified analytical expressions of the Coulomb interaction matrix elements and dielectric functions are derived and numerically discussed.In addition,the electron density and temperature dependences of dispersion features are also investigated.We find that in the two-dimensional parabolic quantum well,the intrasubband upper branch is coupled with the intersubband mode,which is quite different from other quasi-one-dimensional systems like a cylindrical quantum wire with an infinite rectangular potential.In addition,we also find that higher temperature results in the intersubband mode（with an energy of 12 meV（～ 3 THz）） becoming totally damped,which agrees well with the experimental results of Raman scattering in the literature.These interesting properties may provide useful references to the design of free-standing nanorod based devices.展开更多
Energy levels of a donor impurity in the ZnO parabolic quantum well under the magnetic field are investigated using the variational method.The binding energy of the ground state,the energies of 2p±state and 1 s→...Energy levels of a donor impurity in the ZnO parabolic quantum well under the magnetic field are investigated using the variational method.The binding energy of the ground state,the energies of 2p±state and 1 s→2p±transition energies of a hydrogenic donor in the ZnO parabolic quantum well are numerically calculated as a function of the strength of magnetic field for different parabolic potential fields.The results show that the external magnetic field has an obvious influence on the binding energies and the 1 s→2p±transition energies of a hydrogenic donor.The Is to 2p±transition energy increases linearly with the strength of magnetic field,but the Is to 2p;transition energy decreases when the strength of magnetic field increases for the small field strength. Compared to the GaAs parabolic well,the donors are more tightly bound to the ZnO parabolic well and the influence of external magnetic field on the binding energy of a donor is much stronger in the ZnO parabolic well.展开更多
We study the multisubband electron mobility in a barrier delta doped AlχGal-χAs parabolic quantum well structure under the influence of an applied electric field perpendicular to the interface plane. We consider the...We study the multisubband electron mobility in a barrier delta doped AlχGal-χAs parabolic quantum well structure under the influence of an applied electric field perpendicular to the interface plane. We consider the alloy fraction χ = 0.3 for barriers and vary x from 0.0 to 0.1 for the parabolic well. Electrons diffuse into the well and confine within the triangular like potentials near the interfaces due to Coulomb interaction with ionized donors. The parabolic structure potential, being opposite in nature, partly compensates the Coulomb potential. The external electric field further amends the potential structure leading to an asymmetric potential profile. Accordingly the energy levels, wave functions and occupation of subbands change. We calculate low temperature electron mobility as a function of the electric field and show that when two subbands are occupied, the mobility is mostly dominated by ionised impurity scattering mediated by intersubband effects. As the field increases transition from double subband to single subband occupancy occurs. A sudden enhancement in mobility is obtained due to curtailment of intersubband effects. Thereafter the mobility is governed by both impurity and alloy disorder scatterings. Our analysis of mobility as a function of the electric field for different structural parameters shows interesting results.展开更多
基金Project supported by the Shiraz University of Technology, Iran
文摘The differential cross-section for electronic Raman scattering in double semi-parabolic quantum wells of typical GaAs/AlxGa1-xAs is investigated numerically with the effective-mass approximation. The dependence of the differential cross-section on structural parameters such as the barrier width and the well widths is studied. Our results indicate that the electronic Raman scattering is affected by the geometrical size and can be negligible in the symmetric double-well case.
文摘Within the framework of compact density matrix approach and iterative procedure, a detailed procedure for the calculation of the second-harmonic generation (SHG)susceptibility tensor is given in the electric-field-biased parabolic and semi-parabolic quantum wells (QWs). The simple analytical formula for the SHG susceptibility in the systems is also deduced. Numerical results on typical AlGaAs/GaAs materials show that, for the same effective width,the SHG susceptibility in semi-parabolic QW is larger than that in parabolic QW due to the self-asymmetry of the semiparabolic QW, and the applied electric field can make the SHG susceptibilities in both systems enhance remarkably.Moreover, the SHG susceptibility is also related to the parabolic confinement frequency and the relaxation rate of the systems.
文摘The optical conductivity of impurity-doped parabolic quantum wells in an applied electric field is investigated with the memory-function approach, and the analytic expression for the optical conductivity is derived. With characteristic parameters pertaining to GaAs/Ga1-xAlxAs parabolic quantum wells, the numerical results are presented.It is shown that, the smaller the well width, the larger the peak intensity of the optical conductivity, and the more asymmetric the shape of the optical conductivity; the optical conductivity is more sensitive to the electric field, the electric field enhances the optical conductivity; when the dimension of the quantum well increases, the optical conductivity increases until it reaches a maximum value, and then decreases.
基金Project supported by the National Natural Science Foundation of China(Grant No.61274098)
文摘Some realizable structures of double parabolic quantum wells（DPQWs） consisting of Al_xGa_（1-x）As/Al_yGa_（1-y）As are constructed to discuss theoretically the optical absorption due to the intersubband transition of electrons for both symmetric and asymmetric cases with three energy levels of conduction bands. The electronic states in these structures are obtained using a finite element difference method. Based on a compact density matrix approach, the optical absorption induced by intersubband transition of electrons at room temperature is discussed. The results reveal that the peak positions and heights of intersubband optical absorption coefficients（IOACs） of DPQWs are sensitive to the barrier thickness, depending on Al component. Furthermore, external electric fields result in the decrease of peak, and play an important role in the blue shifts of absorption spectra due to electrons excited from ground state to the first and second excited states. It is found that the peaks of IOACs are smaller in asymmetric DPQWs than in symmetric ones. The results also indicate that the adjustable extent of incident photon energy for DPQW is larger than for a square one of a similar size. Our results are helpful in experiments and device fabrication.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.60976008,61006004,61076001,and 10979507)the National Basic Research Program of China(Grant No.A000091109-05)the National High Technology Research and Development Program of China(Grant No.2011AA03A101)
文摘The collective charge density excitations in a free-standing nanorod with a two-dimensional parabolic quantum well are investigated within the framework of Bohm-Pine＇s random-phase approximation in the two-subband model.The new simplified analytical expressions of the Coulomb interaction matrix elements and dielectric functions are derived and numerically discussed.In addition,the electron density and temperature dependences of dispersion features are also investigated.We find that in the two-dimensional parabolic quantum well,the intrasubband upper branch is coupled with the intersubband mode,which is quite different from other quasi-one-dimensional systems like a cylindrical quantum wire with an infinite rectangular potential.In addition,we also find that higher temperature results in the intersubband mode（with an energy of 12 meV（～ 3 THz）） becoming totally damped,which agrees well with the experimental results of Raman scattering in the literature.These interesting properties may provide useful references to the design of free-standing nanorod based devices.
基金Project supported by the National Natural Science Foundation of China(No.10647006)the Youth Science Foundation of Lanzhou University of Technology,China(No.QN200805)
文摘Energy levels of a donor impurity in the ZnO parabolic quantum well under the magnetic field are investigated using the variational method.The binding energy of the ground state,the energies of 2p±state and 1 s→2p±transition energies of a hydrogenic donor in the ZnO parabolic quantum well are numerically calculated as a function of the strength of magnetic field for different parabolic potential fields.The results show that the external magnetic field has an obvious influence on the binding energies and the 1 s→2p±transition energies of a hydrogenic donor.The Is to 2p±transition energy increases linearly with the strength of magnetic field,but the Is to 2p;transition energy decreases when the strength of magnetic field increases for the small field strength. Compared to the GaAs parabolic well,the donors are more tightly bound to the ZnO parabolic well and the influence of external magnetic field on the binding energy of a donor is much stronger in the ZnO parabolic well.
文摘We study the multisubband electron mobility in a barrier delta doped AlχGal-χAs parabolic quantum well structure under the influence of an applied electric field perpendicular to the interface plane. We consider the alloy fraction χ = 0.3 for barriers and vary x from 0.0 to 0.1 for the parabolic well. Electrons diffuse into the well and confine within the triangular like potentials near the interfaces due to Coulomb interaction with ionized donors. The parabolic structure potential, being opposite in nature, partly compensates the Coulomb potential. The external electric field further amends the potential structure leading to an asymmetric potential profile. Accordingly the energy levels, wave functions and occupation of subbands change. We calculate low temperature electron mobility as a function of the electric field and show that when two subbands are occupied, the mobility is mostly dominated by ionised impurity scattering mediated by intersubband effects. As the field increases transition from double subband to single subband occupancy occurs. A sudden enhancement in mobility is obtained due to curtailment of intersubband effects. Thereafter the mobility is governed by both impurity and alloy disorder scatterings. Our analysis of mobility as a function of the electric field for different structural parameters shows interesting results.
