耦合双量子点中基态电子的隧穿特性

介绍了以Si/SiO2系统构成的量子异或门的工作原理,研究了耦合不对称双量子点所构成的量子比特的电子隧穿特性.研究结果表明,通过栅压可很好地实现控制电子在两个量子点间共振隧穿,其隧穿时间随势垒厚度和量子点尺寸结构参数发生显著的变化.目前模拟的特征变化曲线表明,可获得实验上理想的隧穿时间(工作频率)和相应的栅压(工作电压).     

量子效应和小型化对隧穿晶体管特性的影响

基于二维器件仿真工具,研究了量子效应和小型化对双栅隧穿场效应晶体管的特性和可靠性的影响.隧穿晶体管中的量子效应除了带间隧穿,还包括量子统计效应和垂直沟道方向的量子限制效应.研究表明,量子统计效应和量子限制效应对隧穿晶体管的电流电压特性,特别是正偏压温度不稳定性(PBTI)是非常重要的.另外,随着沟道长度和体硅厚度的缩小,隧穿晶体管的电流电压特性和可靠性都得到了改善,但在保持相同等效氧化层厚度的情况下,使用高介电常数的栅介质不会改善器件的电流电压特性及可靠性.     

GaAs基单电子晶体管低温探测THz光子的研究

低温条件下具有肖特基围栅结构的GaAs基单电子晶体管可重复探测到THz光子的光电流响应.实验表明,2.54THz的CH3OH气体激光垂直入射到单电子晶体管的量子点上,在随栅压变化的源漏共振电流峰附近,产生附加电流峰.通过这两个峰位的栅压间距可以估算出THz光子的能量.这表明附加电流峰是由THz光子辅助电子隧穿产生的.实验和理论都表明,单电子晶体管量子点尺寸的减小有利于THz光电流信号的增强.     

GaAs基单电子晶体管低温探测THz光子的研究

低温条件下具有肖特基围栅结构的GaAs基单电子晶体管可重复探测到THz光子的光电流响应.实验表明,2.54THz的CH3OH气体激光垂直入射到单电子晶体管的量子点上,在随栅压变化的源漏共振电流峰附近,产生附加电流峰.通过这两个峰位的栅压间距可以估算出THz光子的能量.这表明附加电流峰是由THz光子辅助电子隧穿产生的.实验和理论都表明,单电子晶体管量子点尺寸的减小有利于THz光电流信号的增强.     

ZnCdSe量子阱/CdSe量子点耦合结构中的激子复合

采用MOCVD方法制备了ZnCdSe量子阱/CdSe量子点耦合结构,利用低温(5K)光致发光光谱和变密度发光光谱研究了该结构中的激子隧穿和复合.观察到在该结构中存在由量子阱到量子点的激子隧穿现象.改变垒层厚度会对量子阱和量子点的发光产生显著影响.在垒层较薄的阱/点耦合结构中,隧穿效应可以有效地抑制量子阱中的带填充和饱和效应.     

ZnCdSe量子阱/CdSe量子点耦合结构中的激子复合

采用MOCVD方法制备了ZnCdSe量子阱/CdSe量子点耦合结构,利用低温(5K)光致发光光谱和变密度发光光谱研究了该结构中的激子隧穿和复合. 观察到在该结构中存在由量子阱到量子点的激子隧穿现象. 改变垒层厚度会对量子阱和量子点的发光产生显著影响. 在垒层较薄的阱/点耦合结构中,隧穿效应可以有效地抑制量子阱中的带填充和饱和效应.     

多量子阱系统结构变化对电子共振隧穿的影响

文中通过求解薛定谔方程得到由Ｎ个矩形势垒构成的量子系统的变换矩阵和电子透射系数的精确解，研究了多量子阱系统结构变化对电子共振隧穿的影响。     

隧穿注入量子点激光器概述

介绍了一种新型的载流子隧穿注入量子点激光器,具体内容涉及量子点激光器研究现状、存在的问题、隧穿注入量子点激光器的工作原理和优势、研究现状等。采用隧穿注入这一新的载流子注入方式,可有效提高量子点激光器的温度特性和高频调制特性。     

电子在耦合的多量子点器件中的动力学特性

本文通过对三量子点的对称和不对称耦合的研究,揭示了电子在耦合的三量子点体系中的动力学特性,研究发现,当三个量子点耦合在一起时,电子在三个量子点之间隧穿,在大多数情况下,电子在第三个量子点的几率小于1。     

单电子器件中电子在耦合能级上的几率分布

两量子点耦合时,根据简并态微扰理论,单量子点的一个能级分裂为系统的两个能级,即对称态和反对称态,当单电子从外部隧穿进入一个量子点时,则电子在两耦合的量子点间振荡,本文讨论了电子在两能级上分布几率随时间的演化规律。     

Charging energy and spin polarization in artificial atoms and molecules

We investigate the electronic properties of single and coupled quantum dot systems by a self-consistent solution of Schrödinger and Poisson equations within the density functional theory. The single and coupled quantum dots show remarkable similarities to atoms and molecules. We observe that in the case of single quantum dots with cylindrical symmetry, the electrons in the dot form shells like in atoms. This sheel structure is slightly distorted due to the electron-electron interaction, as the number of electrons, N, increases. In the case of coupled quantum dots, we observe that the dots can be driven from a state wherein the individual dots are separate, akin to two isolated atoms, to one in which the dots couple forming an “artificial molecule.” By using the local spin density approximation, we observe spin polarization in the double dot for specific values of N.     

杂质对方形量子点基态能和束缚能的影响

用有限差分法求解了二维方形量子点中有 杂质时的量子体系,得到了离散薛定谔方程。对体系中电子处于基态时的能量和杂质的束缚能进行了数值计算,讨论了不同间距的杂质离子对不同尺寸量子点中电子的基态能量和束缚能的影响。计算结果表明：量子点中电子基态能量是杂质位置和量子点尺度的函数;基态能量随着量子点尺度的增加先急剧减小后缓慢增大,最后趋于定值;杂质对电子的束缚能随着量子点尺度的增加而减小;杂质间距越小对量子点基态能影响越大。     

Photoluminescence of strain-induced coupled InGaAs/GaAs quantum-dot pairs

Coupled quantum dot-pairs were fabricated by growing InP self-assembled islands as stressors on InGaAs/GaAs double quantum wells. State filling in the photoluminescence spectra was used to resolve the quantum states in the coupled dots. The total strain field below the stressor decays exponentially with a penetration depth of about 25 nm, within which a dot-pair can be fabricated. Strong coupling is observed at a barrier width less than 4 nm separating the dot-pair. By increasing the indium composition in the lower well in order to match its dot level with one in the upper dot with identical quantum numbers, resonant coupling between the electron states with identical quantum numbers in the two dots can be achieved. Decoupling of the hole states and exchange of the electron bonding states from dominating the upper dot to the lower one are clearly resolved from the state energies and their spacings.     

Self-assembled semiconductor structures: electronic andoptoelectronic properties

Strained epitaxy has been shown to produce pyramidal-shaped semiconductor dot structures by single-step epitaxy. The very high density of these dots (approaching per wafer) and their ever improving uniformity suggest that these features could have important applications in future microelectronics. Understanding the structural and electronic properties of these quantum dots is therefore of great importance. In this paper, we examine some of the physics controlling the performance of devices that could be made from such structures. The self-assembled quantum dots are highly strained and we will examine the strain tensor in these quantum dots using a valence force-field model. In this paper we will address the following issues: (1) What is the general nature of the strain tensor in self assembled quantum dots? (2) What are the electron and hole spectra for InAs-GaAs quantum dots? (a) What are the important intersubband radiative and nonradiative scattering processes in the self assembled quantum dots? In particular, we will discuss how the electron-phonon interactions are modified in the quantum dot structures. Consequences for uncooled intersubband devices such as lasers, detectors, and quantum transistors will be briefly discussed     

A quantum dot image processor

A two-dimensional (2-D) periodic array of quantum dots, where each dot is coupled with its nearest neighbors and interfaced with an underlying material exhibiting a negative differential resistance, is theoretically investigated as a dynamical system for image processing. A circuit level study of such a system is performed and the circuit parameters for this paper are extracted by experimentally measuring them in an electrochemically self-assembled quasi-periodic quantum dot array. Large 2-D dot arrays with 4-neighborhood rectangular lattice structure are then simulated and it is shown that if image data are introduced as initial conditions to these arrays, the steady-state response of the system realizes an image processing task similar to edge detection-enhancement. In addition, the quantum dot architecture is capable of horizontal-vertical line detection with a simple arrangement of the coupling resistances between the dots. These applications are demonstrated via numerical experiments.     

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.     

Three-State Quantum Dot Gate FETs Using ZnS-ZnMgS Lattice-Matched Gate Insulator on Silicon

This paper presents the three-state behavior of quantum dot gate field-effect transistors (FETs). GeO _x -cladded Ge quantum dots (QDs) are site-specifically self-assembled over lattice-matched ZnS-ZnMgS high-κ gate insulator layers grown by metalorganic chemical vapor deposition (MOCVD) on silicon substrates. A model of three-state behavior manifested in the transfer characteristics due to the quantum dot gate is also presented. The model is based on the transfer of carriers from the inversion channel to two layers of cladded GeO _x -Ge quantum dots.     

Energy band diagram of a Si metal-oxide-semiconductor field-effect transistor

We have calculated the energy band diagram of a Si metal-oxide-semiconductor field-effect transistor (FET) with two-storied gates most recently experimentally investigated by Matsuoka et al. (see Appl. Phys. Lett., vol. 64, p. 586, 1994). From out numerical calculations of the three-dimensional Hartree-Fock equation, it is found that the increase of the upper gate negative bias does not transform the simple quantum wire (conducting channel created by the lower gate) into coupled quantum dots, it only makes the conducting channel narrower. Without the lower gate, the system can be well approximated by a two-dimensional Laplace equation. By the corresponding analytical solution it is shown that only in the spatial region very close to the upper gate where can we observe very weak quantum barriers induced by individual metal lines in the upper gate. For the FET structure of Matsuoka et al., coupled quantum dots and thus Coulomb blockade effect are not very likely. The experimental results of transconductance and conductance as functions of upper gate and lower gate can be well explained by the carrier transport through the part of the conducting channel compressed by the upper gate. Precaution should therefore be exercised when analysing experimental results concerning small-size and quantum structure systems,.<>