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46. The Nonlinear Acoustoelectric Effect in a Cylindrical Quantum
Wire with a Infinite Potential
Nguyen Van Nghia (1), Tran Thi Thu Huong (2), Nguyen
Quang Bau (2)
(1) Department of physics, Water Resources University, 175 Tay Son,
Dong Da, Ha Noi
(2) Department of physics, Hanoi National University, 334 Nguyen
Trai, Thanh Xuan, Ha Noi
The nonlinear acoustoelectric effect in a cylindrical quantum wire
with a infinite potential is investigated by using Boltzmann kinetic
equation for an acoustic wave whose wavelength λ = 2π/q is smaller
than the mean free path l of the electrons and hypersound in the
region ql >> 1, (where q is the acoustic wave number). The analytic
expression for the acoustoelectric current I is calculated in the case:
relaxation time of momentum is constant approximation and
degenerates electrons gas. The nonlinear dependence of the
expression for the acoustoelectric current I on the acoustic wave
numbers q and on the intensity of constant electric field E are
obtained. Numerical computations are performed for AlGaAs/GaAs
cylindrical quantum wire with a infinite potential. The results are
compared with the normal bulk semiconductors and the
superlattices to show the values of the acoustoelectric current I in
the cylindrical quantum wire are different than they are in the
normal bulk semiconductors and the superlattices.
Báo cáo Treo
Hội nghị Vật lý lý thuyết toàn quốc lần thứ 35
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47. The Dependence of the Parametric Transformation Coefficient of
Confined Acoustic and Confined Optical Phonons in the Rectangular
Quantum Wire
Luong Van Tung (1), Ngo Thi Thanh Ha (2), Nguyen Thi
Thanh Nhan (2), Le Thi Thu Phuong (2), Nguyen Quang
Bau (2)
(1) Department of Physics, Dong Thap University, 783-Pham Huu
Lau, Dong Thap, Viet Nam (2) Hanoi University of Science, 334
Nguyen Trai, Thanh Xuan, Ha Noi
The parametric transformation of confined acoustic and confined
optical phonons in a rectangular quantum wire is theoretically
studied by using a set of quantum kinetic equations for phonons.
The analytic expression of parametric transformation coefficient of
confined acoustic and confined optical phonons in a rectangular
quantum wire is obtained. The dependence of the parametric
transformation coefficient on the temperature T is numerically
evaluated, plotted and discussed for a specific quantum wire
GaAs/GaAsAl. All the results are compared with those for the
unconfined phonons to show the difference.
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Báo cáo Treo
48. Rate of Phonon Excitation and Conditions for Phonon
Generation in Cylindrical Quantum Wires
Tran Cong Phong (1,2), Le Thi Thu Phuong (1), Tran Dinh
Hien (1)
(1) Department of Physics, Hue University's College of Education, 32
Le Loi, Hue, Vietnam;
(2) National Education Union of Vietnam, 02 Trinh Hoai Duc, Dong
Da, Ha noi, Vietnam
Phonon generation via the Cerenkov effect in cylindrical quantum
wires (CQW) is theoretically studied based on the quantum kinetic
equation for phonon population operator. Both electrons and
phonons are confined in the CQW. Analytical expressions for the
rate of change of the phonon population and conditions for phonon
generation are obtained. Numerical results for GaAs/AlAs
cylindrical quantum wires show that the amplitude of the laser field
Tp. Hồ Chí Minh, 02-06/8/2010
must satisfy additional conditions that are different in comparison
with those of the other works. The differences between the
generation of acoustic phonon and longitudinal optical phonon are
considered. Comparisons between two cases of confined phonons
and bulk phonons are discussed.
Báo cáo Treo
49. Độ linh động và điện trở của khí điện tử trong giếng lượng tử
SiGe/Si/SiGe ở nhiệt độ khác không
Vo Van Tai and Nguyen Quoc Khanh
Trường Đại học KHTN TP HCM, 227 Nguyễn Văn Cừ, Quận 5, TP
Hồ Chí Minh
Chúng tôi đã tính độ linh động và điện trở của khí điện tử giả hai
chiều trong giếng lượng tử Si ở nhiệt độ khác không cho cả hai
trường hợp có hoặc không có từ trường song song. Mật độ hạt, bề
dày lớp và nhiệt độ được chọn sao cho tán xạ tạp chất và bề mặt
nhám là các cơ chế chủ yếu. Các kết quả của chúng tôi có dáng điệu
phù hợp với các kết quả thực nghiệm. Chúng tôi chỉ ra rằng đối với
từ trường quanh giá trị bão hòa điện trở hầu như không phụ thuộc
nhiệt độ.
Báo cáo Treo
50. Two Band Model for Diluted Magnetic Semiconductors: Study of
the Ferromagnetic Transition Temperature
Vu Kim Thai and Hoang Anh Tuan
Institute of Physics, Vietnam Academy of Science and Technology, 10
Dao Tan, Ba Dinh, Ha Noi
The ferromagnetic transition temperature (Tc) of a two band model
for diluted magnetic semiconductors (DMS) is calculated by using
the coherent potential approximation (CPA). It is shown that Tc is
strongly parameter dependent such as density of the carriers,
magnetic coupling constants, and the hopping terms. The maximal
Tc of the two band model is found when both impurity bands fully
overlap and this value is approximately twice larger than the highest
Tc obtained in the single band model.
Báo cáo Treo
51. Density Functional Based Tight Binding Study on Wurzite Coreshell
Nanowires Heterostructures ZnO/ZnS.
N.T. Thuong, N.V. Minh, N.N. Tuan, V.N. Tuoc
Hanoi University of Technology, 1 Dai Co Viet, Hai Ba Trung, Ha
Noi
We present a Density Functional Based Tight Binding study on
the structural and electronic structure of II-VI wurtzite coreshell,
core- multi-shell ZnO/ZnS hexagonal unsaturated
nanowires of circular and hexagonal cross section shapes and
examine the dependence of interface stress and formation
energy on nanowire lateral size with diameter range from 20Å
upto 40Å. Wire’s Young’s modulus along the axial growth
direction have been estimated. Also the tensile test have been
applied for various wires to show the diameter dependence’s of
their mechanical properties. The electronic properties of these
heterostructure nanowire (e.g. Projected Band Structure,
Density of State, charge transfer via Mulliken population
analysis) also exhibit wire’s diameter dependence behaviors.
Báo cáo Treo
52. Electron Scattering from Polarization Charges Bound on a
Rough Interface of Uniformly-Doped ZnO/Zn1‐xMgxO
Heterostructure
Le Tuan (1) and Nguyen Thanh Tien (2)
(1) Institute of Engineering Physics, Hanoi University of Science and
Technology, 1 Dai Co Viet Road, Hanoi, Vietnam (2) College of
Science, Can Tho University, 3-2 Road, Can Tho City, Vietnam
We present a theory of polarization surface roughness (PSR)
scattering mechanism for electrons in the conduction channel of
actual ZnO/Zn 1-x Mg x O heterostructures of the both O- and Zn-polar
faces in ZnO layer. In combination with the normal surface
roughness (SR) scattering from roughness-induced fluctuations in
the potential barrier position, the carriers must be extra scattered
from the polarization charges bound on a rough interface of the
heterostructure. This ad hoc scattering mechanism tends to reduce
carrier mobility down to a half of value in comparison with the one
Hội nghị Vật lý lý thuyết toàn quốc lần thứ 35
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Tp. Hồ Chí Minh, 02-06/8/2010