Zhang L.,Guangzhou Panyu Polytechnic
Physica Status Solidi (B) Basic Research | Year: 2012
By employing the two-parameter variational approach, the binding energies of bound polarons in a quasi-one-dimensional wurtzite nanowire (NW) are investigated. Two types of polar optical phonon modes, i.e., the interface optical (IO) and quasi-confined (QC) phonon modes of wurtzite NWs are taken in account. The results reveal that the phonon contribution to binding energy of bound polaron in GaN NWs reaches ∼370meV. The quite large contribution of phonon modes to the total binding energy is mainly ascribed to the very strong electron-phonon coupling constant in GaN materials. Moreover, the IO modes plays more important role to the binding energies of bound polaron as the NW radius is small, while the QC modes dominates as the NW radius is relatively large. The calculated results of impurity binding energy are quite consistent with the recent experimental measurement. The numerical results also show that the two-parameter variational approach is necessary and suitable for the description of impurity states in wurtzite GaN NW structures. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Changhui C.,Guangzhou Panyu Polytechnic
RISTI - Revista Iberica de Sistemas e Tecnologias de Informacao | Year: 2016
With the emergence of a large number of multimedia applications on the Internet, the higher requirements for the quality of network services are put forward. At present, most of the existing Quality of Service (QoS ) flow control methods have low utilization rate of network resources, poor reliability, coarse grain size, difficult implementation and poor scalability. Therefore, a QoS flow control method based on the OpenFlow technology is proposed in this paper. The separation new ideas of control layer and data layer that proposed by the software defined network (SDN) are referenced on the basis of the brief introduction of QoS, OpenFlow technology and Open vswitch, and the adaptive multi constrained QoS routing technology is used to design the QoS flow control method based on the OpenFlow technology. The experimental results show that this method can improve the flexibility and reliability of QoS control, and realize the efficient utilization of network resources and the fine granularity of traffic flow control. The QoS flow control method based on OpenFlow fully plays the advantage of SDN network, and realizes the reliable transmission and fine granularity control of QoS flow, so as to achieve the efficient utilization of network resources.
Zhang L.,Guangzhou Panyu Polytechnic
Physica Status Solidi (B) Basic Research | Year: 2011
The polar optical phonon states of four types of phonon modes including the interface optical (IO) modes, the propagating (PR) modes, the quasi-confined (QC) phonon modes in well-layer material (QCw), and the QC phonon modes in barrier-layer material (QCB) in a wurtzite GaN/AlxGa1-xN superlattice (SLs) are investigated within the dielectric continuum model framework. The analytical phonon states of the four types of modes and their dispersive equations in the wurtzite GaN/AlxGa1-xN SL structures are obtained. Numerical calculations on the dispersive spectra of phonon modes and the quantum size effect are performed for a wurtzite GaN/Al0.15Ga0.85N SL. Results reveal that dispersive curves of phonon modes in SLs form a series of frequency bands. The behaviors of QCw modes reducing to PR and IO modes are observed clearly. With the increase of well-layer GaN width d1 of the SLs, the dispersion of the QCB modes become weaker and weaker, and their frequency bands become narrower and narrower. But the PR, IO, and the QCw phonon modes become more dispersive, and the frequency bands of these modes become wider and wider as d1 increases. The present theoretical scheme and numerical results are quite useful for analyzing the dispersive spectra of full phonon modes and their polaronic effect in wurtzite GaN/AlGaN SL structures. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Zhang L.,Guangzhou Panyu Polytechnic
Physica Status Solidi (B) Basic Research | Year: 2010
Based on the macroscopic dielectric continuum model, the interface-optical-propagating (IO-PR) mixing phonon modes of a quasi-zero-dimensional wurtzite cylindrical quantum dot (QD) structure are derived and studied. The analytical phonon states of IO-PR mixing modes are given. It is found that there are two types of IO-PR mixing phonon modes, i.e., the ρ-IO/z-PR mixing modes and the z-IO/ρ-PR mixing modes, existing in wurtzite QDs. Each IO-PR mixing mode also has symmetrical and antisymmetrical forms. Via a standard procedure of field quantization, the Fröhlich Hamiltonians of the electron-(IO-PR) mixing phonon interaction are obtained. The orthogonal relations of polarization eigenvectors for these IO-PR mixing modes are also displayed. Numerical calculations for a wurtzite GaN cylindrical QD are focused on the quantum size effect and the dielectric effect on the dispersive properties of IO-PR mixing modes. The results reveal that both the radial-direction size and the axial-direction size as well as the dielectric matrix have great influence on the dispersive frequencies of the IO-PR mixing phonon modes. The limiting features of dispersive curves of these phonon modes are discussed in depth. The phonon modes' "reducing" behavior of wurtzite quantum confined structures has been found in the systems. Moreover, the behaviors that the IO-PR mixing phonon modes in wurtzite QDs reduce to the IO modes and the PR modes in wurtzite quantum well and quantum wire systems are analyzed deeply from the viewpoints of both physics and mathematics. These results show that the present theories of polar mixing phonon modes in wurtzite cylindrical QDs are consistent with the phonon mode theories in wurtzite quantum wells and quantum wire systems. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Zhang L.,Guangzhou Panyu Polytechnic |
Shi J.J.,Peking University
Journal of Applied Physics | Year: 2013
Based on the surface optical phonon states and their electron-phonon coupling functions obtained recently, the surface polaronic exciton states in a quasi-one-dimensional (Q1D) wurtzite nanowire (NW) are investigated by using the variational method and Lee-Low-Pines transform. In order to reflect the different confined features of Q1D wurtzite NWs in axial and radial directions and anisotropy of wurtzite nitride crystals, a two-parameter variational approach is proposed and applied to describe the polaronic exciton states in the NWs. Numerical calculations are performed for GaN NWs. The quantum size effects on the binding energies of polaronic exciton and the contributions of surface phonon modes are analyzed in detail. Our results show that the binding energy of polaronic exciton and surface phonon contribution in the wurtzite GaN NWs reaches 190 and 95 meV, respectively, which are one or two orders of magnitude larger than those in cubic GaAs-based quantum wells and NWs with the same radius. This is mainly ascribed to the strong electron-phonon interaction, the large effective masses of carriers and relatively small dielectric constants in GaN material. The numerical results also show that the two-parameter variational approach is reasonable and necessary for the description of polaronic exciton states in Q1D wurtzite GaN NWs. Moreover, the behaviors of the two variational parameters for the polaronic exciton states are quite different from those for the bound polaron states in Q1D wurtzite NWs. © 2013 American Institute of Physics.