InAlN/GaN异质结二维电子气波函数的变分法研究

使用变分法推导了InAlN/GaN异质结二维电子气波函数和基态能级的解析表达式,并讨论了InAlN/GaN异质结结构参数对二维电子气电学特性的影响.在假设二维电子气来源于表面态的前提下,使用了一个包含两个变分参数的尝试波函数推导电子总能量期望值,并通过寻找能量期望极小值确定变分参数.计算结果显示,二维电子气面密度随InAlN厚度的增大而增大,且理论结果与实验结果一致.二维电子气面密度增大抬高了基态能级与费米能级,并保持二者之差增大以容纳更多电子.InAlN/GaN界面处的极化强度失配随着In组分增大而减弱,二维电子气面密度随之减小,并导致基态能级与费米能级减小.所建立的模型能够解释InAlN/GaN异质结二维电子气的部分电学行为,并为电子输运与光学跃迁的研究提供了解析表达式.     

分数量子Hall体系的电荷分布

对1/3 Landau填充因子的二维电子气体系,用迭代自洽的计算方法得到了局域电中性背景下的电荷密度分布。我们发现电荷密度分布与基态能量的尖角有密切的联系。 关键词：     

电中性背景中二维电子气基态能的迭代计算

本文讨论了强磁场中局域电中性二维电子气的基态能的数值迭代计算方法。计算结果表明基态能随总角动量的变化曲线只在某些角动量处出现尖角。 关键词：     

双轴应变调控二维单层C2X2TM（X = O, H; TM=Fe, Cr） 的多铁性研究

基于密度泛函理论的第一性原理计算,系统地研究了过渡金属原子插层的单层氧化/氢化石墨烯的磁学性质和铁电性质.在考虑了电子在位库仑作用和自旋轨道耦合作用下,得到了过渡金属Fe、Cr插层形成的C₂X₂TM二维单层膜的稳定结构以及基态磁性结构,研究了不同应变作用下C₂X₂TM的磁性、能带、铁电极化以及电子结构的变化.结果发现,对于任何应变下的C₂X₂TM其基态磁性都为手性逆时针反铁磁结构.在无应变时体系存在一个较大的离子翻转势垒,通过外加双轴应变,可有效调控体系的势垒高度和能隙,发现25%应变下C₂O₂Cr和30%应变时C₂O₂Fe单层薄膜具有与GeS等二维铁电材料相近的铁电极化和翻转势垒,这些研究结果表明C₂O₂Fe(Cr)单层薄膜是一种新型二维多铁性材料.     

半导体束缚激子基态能的变尺度法

提出了计算体系基态能的变尺度法，用该算法计算了电子和空穴有效质 量比值不同时，离子化施主束缚激子（D+，X）的基态能. 在求解体系基态能上与传统的变分法相比有很大的优势，尤其适合复杂体系基态能的计算. 关键词： 束缚激子 氦原子 基态能 变尺度方法     

半导体反型层中的电子关联和多体波函数

本文运用CBF(correlation basis function)理论,由电子间的有效势V_eff(R)和电子气的集体振荡行为,给出准二维电子体系——半导体反型层中的电子的关联因子U(R),得到该体系的对关联函数、关联能和多体波函数。 关键词：     

半导体反型层中的电子关联和多体波函数

本文运用CBF(correlation basis function) 理论, 由电子间的有效势V_eff_(R) 和电子气的集体振荡行为, 给出准二维电子体系— 半导体反型层中的电子的关联因予U (R), 得到该体系的对关联函数、关联能和多体波函数. 关键词：     

InP基HEMT器件中二维电子气浓度及分布与沟道层厚度关系的理论分析

利用数值计算的方法研究了InP基高电子迁移率晶体管(HEMT)中沟道厚度对沟道中二维电子气(2DEG)性质的影响，并对产生这种影响的原因进行了深入探讨.计算结果表明，当沟道层厚度从10nm增加到40nm时，沟道中2DEG的密度几乎没有变化，但激发态和基态上的电子密度之比(R)先增加后减小.当沟道层厚度在20—25nm之间时，R达到最大.此结果可作为优化器件结构设计的依据. 关键词： HEMT 异质结 二维电子气 自洽计算     

In0.53Ga0.47As/In0.52Al0.48As量子阱中的正磁电阻效应

在低温强磁场条件下,对In_0.53Ga_0.47As/In_0.52Al_0.48As量子阱中的二维电子气进行了磁输运测试.在低磁场范围内观察到正磁电阻效应,在高磁场下这一正磁电阻趋于饱和,分析表明这一现象与二维电子气中的电子占据两个子带有关.在考虑了两个子带之间的散射效应后,通过分析低磁场下的正磁电阻,得到了每个子带电子的迁移率,结果表明第二子带电子的迁移率高于第一子带电子的迁移率.进一步分析表明,这主要是由两个子带之间的 关键词： 二维电子气 正磁电阻 子带散射     

GaAs基InAs量子点中类氢杂质的束缚能

在有效质量近似下,采用微扰法研究了InAs/GaAs量子点内类氢杂质基态及低激发态的束缚能.受限势采用抛物形势,在二维平面极坐标下,精确地求解了电子的薛定谔方程.数值计算结果表明,类氢杂质基态及低激发态的束缚能敏感地依赖于抛物形势的角频率,受类氢杂质的影响,谱线发生蓝移.这一结果对设计和制备量子点器件是有价值的.     

On the ground state energy of a two-dimensional electron fluid

A new theory of the ground state energy of a two-dimensional electron fluid is presented. It is shown that the ring diagram contribution changes its analytical behavior atr _s =2^1/2, wherer _s is the usual density parameter defined by r_S = 1/a ₀(π n)^1/2,a ₀ being the Bohr radius andn is the electron density. For smallr _s , a high density series is obtained in agreement with the previous calculation. For larger _s , a hitherto unknown low density series is obtained. In the low density region, the first order exchange energy is completely cancelled out by a term from the ring contribution so that the ground state energy decreases in proportion tor _s ^?2/3 , followed byr _s ^/?4/3 and higher order terms. The energy is found to be minimum atr _s=1.4757, the minimum value being ?0.481915 Rydbergs.     

On the ground state energy of a two-dimensional electron fluid

A new theory of the ground state energy of a two-dimensional electron fluid is presented. It is shown that the ring diagram contribution changes its analytical behavior atr _s =2^1/2, wherer _s is the usual density parameter defined by r_S = 1/a ₀( n)^1/2,a ₀ being the Bohr radius andn is the electron density. For smallr _s , a high density series is obtained in agreement with the previous calculation. For larger _s , a hitherto unknown low density series is obtained. In the low density region, the first order exchange energy is completely cancelled out by a term from the ring contribution so that the ground state energy decreases in proportion tor _s ^–2/3 , followed byr _s ^/–4/3 and higher order terms. The energy is found to be minimum atr _s=1.4757, the minimum value being –0.481915 Rydbergs.     

Ground-state properties of jellium metals with low electron densities

The ground state of a three-dimensional electron gas is theoretically investigated within the framework of the local spin density approximation with the Perdew–Zunger exchange-correlation energy. The system has been found to be in a one- or two-dimensional crystal state, when the Wigner sphere radius r_s has an intermediate value. At r_s=60, a triangular lattice with the lattice spacing 96.10 is the lowest energy state among fluids, 1D, 2D, and 3D crystals.     

Correlation energy of 2-D electrons

The correlation energy and the Fermi momentum of an electron gas in 2-D are evaluated explicitly as functions of density. The ring diagram and first- and second-order exchange contributions are treated. In comparison with the 3-D case, the kinetic energy for the same r_s is approximately one-half and the exchange and correlation energies are somewhat larger. The ground state energy plotted against r_s shows a minimum at around r_s = 1.65 with a minimum value of ?0.9858 Ryd. If the third-order ring contribution is added, the curve is shifted upward. The correlation energy is ?0.6258 to order e⁴. The third-order ringw contribution increases this value almost linearly with r_s. The Fermi momentum decreases with r_s due to the contribution. Different from the 3-D case, no ln r_s term appears in the correlation energy within the approximation.     

Rigorous evaluation of the ring diagram contribution to the ground state energy of an electron gas

The ground state energy and the correlation energy of an electron gas are evaluated rigorously without using the smallr _s expansion and the small momentum-transfer approximation in the ring diagram contribution and taking into consideration the first order and second order exchange graphs. The Fermi momentum is determined by solving the number density equation without using iteration and is compared with that obtained by iteration. The ground state energy is found to stay positive in contrast to the iterative solution which becomes negative beyond a certain value ofr _s .     

The Ground State Energy of Dilute Bose Gas in Potentials with Positive Scattering Length

The leading term of the ground state energy/particle of a dilute gas of bosons with mass m in the thermodynamic limit is 2p(^h/_2p)² a r/m{2\pi \hbar^2 a \varrho/m} when the density of the gas is r{\varrho}, the interaction potential is non-negative and the scattering length a is positive. In this paper, we generalize the upper bound part of this result to any interaction potential with positive scattering length, i.e, a > 0 and the lower bound part to some interaction potentials with shallow and/or narrow negative parts.     

Ferromagnetism of the electron gas

The ground-state energy of the ferromagnetic electron gas is calculated for the relative polarizationζ=0−1 and the interelectron separationr _s =5−12. The method consists in describing the electron gas approximately by a quadratic boson Hamiltonian, and contains the random-phase approximation as a special case. Numerical studies show that in both the random-phase and the present approximations the paramagnetic state has the lowest energy: the energy increases withζ for all values ofr _s considered. In the present approximation instabilities are found to occur forr _s above a critical value, due to exchange processes of finite momentum transfers. Forζ=0 this critical value ofr _s is 9.4; it decreases with increasingζ. However, the fully-polarized state (ζ=1), which lies above the rest, is always stable. The conclusions are as follows: (1) Forr _s <9.4 the electron gas is paramagnetic. (2) Atr _s =9.4 it goes over to the fully-polarized ferromagnetic state. (3) This phase transition requires an energy absorption of 0.03 rydberg per electron. (4) The fully-polarized state is not obtainable as the limitζ→1.     

Electronic properties of metals at low temperatures

A many body theory of an electron gas is developed to find the internal and correlation energies at low but finite temperatures. The contribution from the first order exchange, second order (regular and anomalous) exchange, and ring diagrams are treated. The Fermi momentum and the correlation energy are determined as functions of the density by two different methods, one being based on iteration and the other a direct solution of the number density relation. It was found that the iterative solutions which are correct to ordere ² ore ⁴ become negative forr _s of order 5 while the direct solutions do not, indicating the invalidity of the former. Hence, the correlation energy evaluated to the same orders by iteration will not be satisfactory in the same range. The highest order iterative solution which includes terms of ordere ⁶ does not show such a breakdown. These terms which give the contribution of orderr _s to the correlation energy are therefore important and tend to reduce the magnitude of the correlation energy. The corresponding curve is indeed close to that determined by the direct method for smallr _s but a significant deviation takes place at largerr _s . The Coulomb interaction seems less effective at higher temperatures. The internal energy is also determined as a function of density and temperature.     

Photothermal ionization via excited states of sulfur donor in silicon

Structures in the photoionization cross-section spectra below the extrinsic edge of the doubly charged sulfur donor (613 meV) are attributed to the two-step photothermal excitation process in which the bound electron at the ground state first makes an optical transition to an excited state and it is then thermally released from the excited state to the conduction band. A weak peak (cross-section 7 × 10⁻¹⁹ cm²)at 425 meV is attributed to the intervalley optical transition 1s(A₁)→1s(T₂). Peak observed at 570 meV (10⁻¹⁷ cm²) is attributed to the 1s(A₁→2p₀ intervalley optical transition and the peak at 591 meV (3 × 10⁻¹⁷ cm²) to the 1s(A₁)→2p± intravalley optical transition. Data for electron bound at the neutral gold center has no structures which is consistent with the lack of excited states of a neutral impurity potential.     

Metal-insulator transition in hydrogen and in expanded alkali metals

Two methods are considered for testing the stability of an electron gas to formation of bound states round a pair of protons. In the first, the screened potential for the two protons is set up as a superposition, which is appropriate in a very high density electron gas. The condition for bound state formation is then examined in the two-centre problem. The density thus obtained is in the right density range to accord with the experiment of Hawke et al. for producing cold metallic hydrogen.This has encouraged us to attempt a more ambitious calculation, namely the investigation of the Heitler-London energy of a model H₂ molecule with screened electron-nuclear and electron-electron interactions, the screening being again through appropriate introduction of the Thomas-Fermi screening radius. The merit of this second model is that the theory contains the Heitler-London value of the dissociation energy of the free H₂ molecule in the limit when the density of the electron gas tends to zero. This feature, the binding energy of the diatomic and its importance in distinguishing the metal-insulator transition in hydrogen from those expected to occur in expanded alkali metals is stressed. The second point we stress is that, in both the models discussed above, there is a close connection with the one-centre criterion for bound state formation. Though we have not carried out detailed two-centre calculations for expanded alkali metals, nevertheless some discussion is given of the one-centre bound state criterion in these metals.Some remarks are also made on the dielectric function of molecular crystals, in relation to the insulator-metal transition.