介观压阻效应

为了突破传统机电转换,如压电、压阻及压容等效应的宏观物理局限,着手研究介观压阻效应.本文提出,通过四个物理过程来实现介观压阻效应.原理上讲,在力学信号作用下,纳米结构中的应力分布会发生变化;应力变化可引起内建电场的产生;内建电场将导致纳米结构中量子能态发生改变;量子能态改变会引起共振隧穿电流的变化.简述了国内外在上述四个过程方面所做的工作.     

介观压阻效应

为了突破传统机电转换，如压电、压阻及压容等效应的宏观物理局限，着手研究介观压阻效应。本文提出，通过四个物理过程来实现介观压阻效应。原理上讲，在力学信号作用下，纳米结构中的应力分布会发生变化；应力变化可引起内建电场的产生；内建电场将导致纳米结构中量子能态发生改变；量子能态改变会引起共振隧穿电流的变化。简述了国内外在上述四个过程方面所做的工作。     

P型硅纳米板压阻特性的理论研究

考虑量子尺寸效应与自旋轨道耦合作用,从含有应变的6×6 Luttinger-Kohn哈密顿量出发,采用有限差分方法建立了p型硅纳米板的能带结构模型.基于硅纳米板压阻特性与其能带结构的相关性,采用改进的压阻理论定量分析了厚度、杂质浓度与温度对其压阻系数的影响.研究结果表明:量子尺寸效应强烈改变了硅纳米板的能带结构,是其压阻系数增大的主要因素,而自旋轨道耦合作用仅对含较高应变的硅纳米板的能带结构有较大影响;硅纳米板的压阻系数具有尺寸效应,随厚度减小而增大,随杂质浓度增加或温度升高而减小.在高简并条件下,硅纳米板的压阻系数与温度无关,完全由杂质浓度的大小控制;在非简并条件下,情况刚好相反.最后,利用施加应力前后空穴等能面形状的变化定性分析了硅纳米板压阻特性的起源.     

P型硅纳米板压阻特性的理论研究

考虑量子尺寸效应与自旋轨道耦合作用,从含有应变的6×6 Luttinger-Kohn哈密顿量出发,采用有限差分方法建立了p型硅纳米板的能带结构模型.基于硅纳米板压阻特性与其能带结构的相关性,采用改进的压阻理论定量分析了厚度、杂质浓度与温度对其压阻系数的影响.研究结果表明:量子尺寸效应强烈改变了硅纳米板的能带结构,是其压阻系数增大的主要因素,而自旋轨道耦合作用仅对含较高应变的硅纳米板的能带结构有较大影响;硅纳米板的压阻系数具有尺寸效应,随厚度减小而增大,随杂质浓度增加或温度升高而减小.在高简并条件下,硅纳米板的压阻系数与温度无关,完全由杂质浓度的大小控制;在非简并条件下,情况刚好相反.最后,利用施加应力前后空穴等能面形状的变化定性分析了硅纳米板压阻特性的起源.     

共振隧穿二极管的力电耦合特性

报道了微结构中共振隧穿二极管(RTD)的压阻效应.分析并加工了四梁结构,其中RTD置于应力敏感区.沿[110]晶向和[110]晶向的应力导致RTD电流-电压曲线的改变,即介观压阻变化,尤其是在微分负阻(NDR)区.采用不同测试方法,研究了RTD的力电耦合特性,并获得了较相近的压阻系数为10-9Pa-1.     

共振隧穿二极管的力电耦合特性

报道了微结构中共振隧穿二极管（RTD）的压阻效应. 分析并加工了四梁结构,其中RTD置于应力敏感区. 沿［110］晶向和［110］晶向的应力导致RTD电流-电压曲线的改变,即介观压阻变化,尤其是在微分负阻（NDR）区. 采用不同测试方法,研究了RTD的力电耦合特性,并获得了较相近的压阻系数为1E-9Pa-1.     

一维铝-环氧树脂声子晶体的介观压声效应

用传递矩阵法研究了由铝和环氧树脂两种材料构成了二组元一维声子晶体在应力作用下的透射谱特性。通过分析透射谱线的变化发现,在压变量的影响下,声波带隙能可控的出现和消失及平移,特别是会随着压变量的变化而出现带隙的反转,由通带变为禁带。为与体材料中的声弹性效应区别,参照介观压阻和介观压光效应的提法,称这种效应为介观压声效应。研究了在压变量存在下该结构透射谱线与声子晶体周期数的关系。结果表明,单轴应力对声子晶体带隙有明显的影响。这些特性可为新型声学器件的设计提供理论参考。     

内建电场对应变多量子阱带阶的影响

隧穿电流的大小依赖于带阶的大小.内建电场会改变多量子阱的结构,使其由方阱变为斜阱,导致其带阶发生改变.本文定量地给出了由内建电场导致的价带阶变化及其斜率.对沿任意方向生长的立方超晶格系统,当其特征厚度小于临界值(欠临界系统)时,给出了内建电场与应变的定量关系.针对不同的量子阱系统,当生长方向沿着[111]方向时,计算了三种类型、21种组分、由内建电场引起的价带阶变化量.所有结果在线性领域及没有相变的情况下都是适用的.     

内建电场对应变多量子阱带阶的影响

隧穿电流的大小依赖于带阶的大小。内建电场会改变多量子阱的结构 ,使其由方阱变为斜阱 ,导致其带阶发生改变。本文定量地给出了由内建电场导致的价带阶变化及其斜率。对沿任意方向生长的立方超晶格系统 ,当其特征厚度小于临界值 (欠临界系统 )时 ,给出了内建电场与应变的定量关系。针对不同的量子阱系统 ,当生长方向沿着 [111]方向时 ,计算了三种类型、2 1种组分、由内建电场引起的价带阶变化量。所有结果在线性领域及没有相变的情况下都是适用的。     

介观压阻型微压力传感器设计

运用共振隧穿双势垒（DBRT）结构中的一种压阻效应原理-介观压阻效应,用GaAs／AlAs／InGaAs DBRT结构薄膜作为敏感元件,设计了一个周边固支平膜片结构的压力传感器。并对介观压阻和普通压阻灵敏度的量级作出了比较,验证了介观压阻效应原理,可以提高压力传感器的灵敏度,为制造基于介观压阻效应的新型超敏感型传感器提供了一定的理论依据。     

Influence of GaAs spacer-layer thickness on quantum coupling and optical polarization in a ten-layer system of vertically correlated InAs/GaAs quantum dots

The polarization anisotropy of electroluminescence and absorption in a ten-layer system of vertically correlated InAs quantum dots separated by 8.6-nm-thick GaAs spacer layers is investigated experimentally. The quantum-dot system is built into a two-section laser structure with sections of equal length. It is found that the polarization anisotropy in this system is smaller than the anisotropy in similar systems with a single layer of quantum dots or quantum-dot molecules, but larger than that in a quantum-dot superlattice. The spectra of differential absorption in the structure under study for different strengths of the applied electric field are also investigated. The rate of variation in the Stark shift as a function of the electric field is determined, the results giving evidence of controlled quantum coupling between adjacent quantum dots in tenlayer vertically correlated InAs/GaAs quantum-dot systems with 8.6- and 30-nm-thick GaAs spacer layers. The measured polarization dependences are explained by the participation of heavy-hole ground states in optical transitions. This effect is defined by the two dimensional nature of the system under study.     

Calculation of linear and nonlinear intersubband optical absorptions in a quantum well model with an applied electric field

Analytic forms of the linear and the third-order nonlinear optical intersubband absorption coefficients are obtained for general asymmetric quantum well systems using the density matrix formalism, taking into account the intrasubband relaxation. Based on this model, we calculate the electric field dependence of the linear and the third-order nonlinear intersubband optical absorption coefficients of a semiconductor quantum well. The energy of the peak optical intersubband absorption is around 100 meV (wavelength is 12.4 μm). Thus, electrooptical modulators and photodetectors in the infrared regime can be built based on the physical mechanisms discussed here. The contributors to the nonlinear absorption coefficient due to the electric field include 1) the matrix element variation and 2) the energy shifts. Numerical results are illustrated.     

电场驱动HgCdTe/CdTe量子阱拓扑相变引起的光吸收增强研究

HgTe/CdTe量子阱是研究拓扑绝缘体新奇物性的一个很好载体。采用Kane八带k·p模型,对电场驱动Hg1-xCdxTe/CdTe量子阱拓扑相变及其相变前后的光吸收性质进行了研究,并使用BHZ模型对吸收系数进行了解析计算和分析。结果表明:在电场能够驱动Hg1-xCdxTe/CdTe量子阱拓扑相变后继续增大电场,其能带可变为墨西哥帽形状,联合态密度将会增强,导致光吸收相比于无电场时显著增强,与解析计算结果相吻合。对于平行界面偏振光(TE)吸收曲线在带边还形成了双峰结构。文章结果可用于新型红外光电探测器、激光器以及频率选择器等量子阱器件的研究和设计。     

Compact LDD nMOSFET degradation model

In this paper, we present a compact degraded I-V model for submicron lightly-doped drain (LDD) MOSFET's. The analytical and physics-based model was developed using the drift equation and considering the nonuniform spatial hot-carrier-induced interface states and the detailed LDD structure. It can be used to calculate fresh channel electric field and drain current by turning off the effect of hot-carrier-induced interface states. Using the fresh electric field in conjunction with a simplified energy balance equation, the nonuniform spatial distribution of induced interface states ran be calculated. By incorporating this distribution into the degraded current model, we can describe the damaged I-V characteristics and channel electric fields as a function of stress time. The model includes the effects of series resistances and carrier velocity saturation. It can be used to calculate time-dependent degraded drain current, and is a time-saving CAD model     

Energy levels of a quantum ring in a lateral electric field

The electronic states of a semiconductor quantum ring (QR) under an applied lateral electric field are theoretically investigated and compared with those of a quantum disk of the same size. The eigenstates and eigenvalues of the Hamiltonian are obtained from a direct matrix diagonalization scheme. Numerical calculations are performed for a hard-wall confinement potential and the electronic states are obtained as a function of the electric field and the ratio r₂/r₁, where r₂ (r₁) is the outer (inner) radius of the ring. The effects of decreasing symmetry and mixing on the energy levels and wave functions due to the applied electric field are also studied. The direct optical absorption are reported as a function of the electric field.     

Room-temperature optical absorption in the InAs/GaAs quantum-dot superlattice under an electric field

Electroluminescence and absorption spectra of a ten-layer InAs/GaAs quantum dot (QD) superlattice built in a two-section laser with sections of equal length is experimentally studied at room temperature. The thickness of the GaAs spacer layer between InAs QD layers, determined by transmission electron microscopy, is ∼6 nm. In contrast to tunnel-coupled QDs, QD superlattices amplify the optical polarization intensity and waveguide absorption of the TM mode in comparison with the TE mode. It is found that variations in the multimodal periodic spectrum of differential absorption of the QD superlattice structure are strongly linearly dependent on the applied electric field. Differential absorption spectra exhibit the Wannier-Stark effect in the InAs/GaAs QD superlattice, in which, in the presence of an external electric field, coupling of wave functions of miniband electron states is suppressed and a series of discrete levels called the Wannier-Stark ladder states are formed.     

Physics of Hole Transport in Strained Silicon MOSFET Inversion Layers

A comprehensive quantum anisotropic transport model for holes was used to study silicon PMOS inversion layer transport under arbitrary stress. The anisotropic band structures of bulk silicon and silicon under field confinement as a twodimensional quantum gas are computed using the pseudopotential method and a six-band stress-dependent k.p Hamiltonian. Anisotropic scattering is included in the momentum-dependent scattering rate calculation. Mobility is obtained from the Kubo–Greenwood formula at low lateral field and from the fullband Monte Carlo simulation at high lateral field. Using these methods, a comprehensive study has been performed for both uniaxial and biaxial stresses. The results are compared with device bending data and piezoresistance data for uniaxial stress, and device data from strained Si channel on relaxed SiGe substrate devices for biaxial tensile stress. All comparisons show a very good agreement with simulation. It is found that the hole band structure is dominated by 12 “wings,” where mechanical stress, as well as the vertical field under certain stress conditions, can alter the energies of the few lowest hole subbands, changing the transport effective mass, density-of-states, and scattering rates, and thus affecting the mobility.     

QUANTUM MECHANICAL MODEL AND SIMULATION OF GaAs/AlGaAs QUANTUM WELL INFRARED PHOTO- DETECTOR-Ⅰ OPTICAL ASPECTS

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Stark effect in vertically coupled quantum dots in InAs-GaAs heterostructures

The results of studies of hole energy states in vertically coupled quantum dots in InAs-GaAs p-n heterostructures by deep-level transient spectroscopy are reported. Spectra were recorded at different reverse-bias voltages. Levels related to bonding and antibonding s and p states of vertically coupled quantum dots were revealed. The energies of these states significantly depend on an external electric field applied to a heterostructure. This dependence was attributed to the quantum-dimensional Stark effect for the hole states of vertically coupled quantum dots. In addition to this, it was found that the energy of thermal activation of carriers from vertically coupled quantum dots depends on the conditions of isochronous annealing that was carried out both with the reverse bias switched-on and switched-off and both in the presence and absence of illumination. These changes, as in the case of isolated quantum dots, are typical of a bistable electrostatic dipole formed by carriers, localized in a coupled quantum dot, and ionized lattice point defects. The built-in electric field of this dipole reduces the energy barrier for the carriers in the coupled quantum dot. The investigated structures with vertically coupled quantum dots were grown using molecular-beam epitaxy taking account of self-assembling effects.     

磁光效应对BB84协议的影响分析

BB84协议采用四种极化态来进行密钥分发,但在传输的过程中极化态受磁光效应的影响将会发生一定角度的偏转,这将对密钥分发产生非常不利的影响,因此为了顺利得进行量子密钥分发,必须要维持极化态.首先简要介绍了BB84模型以及模型中使用的四种极化态,然后分析了极化态偏转后对量子密钥分发的影响,同时用Matlab进行了仿真,结果表明严重情况下磁光效应将会使通信双方持有的原始密钥不一致.最后给出了一种可行的解决方案.