Quantum dot heterostructures: Fabrication, properties, lasers (Review)

In the present review we summarize original results where 1) we have experimentally discovered a novel class of spontaneously ordered nanostructures, namely equilibrium arrays of threedimensional, coherently strained islands on crystal surfaces; 2) we have developed a theory of spontaneous formation of semiconductor nanostructures in heteroepitaxial systems; 3) we have experimentally demonstrated the existence of a novel class of semiconductor heterostructures, namely perfect quantum dots having an atom-like energy spectrum; we have performed a detailed investigation of the optical properties of quantum dots; 4) we have fabricated quantum dot-based injection lasers demonstrating unique charactristics, namely high-temperature stability of the threshold current and ultra-high material gain. Fiz. Tekh. Poluprovodn. 32, 385–410 (April 1998)     

量子点及量子点器件

量子点是纳米科学与技术研究重要的组成部分,量子点器件又是纳米器件的发展方向之一.详细介绍了量子点的分类、量子点的主要制备方式、量子点特性的传统研究和微波类比仿真研究方法,系统论述了量子点器件的分类应用及噪声抑制.     

Quantum dot based nanophotonics and nanoelectronics

Invention of non-disruptive fabrication technologies for semiconductor quantum dots presented a dream for generations of semiconductor device engineers. Today such technologies exist. A wealth of completely novel devices and such with dramatically improved properties based either on a single/few or a large density of quantum dots appears. Among them are single q-bit emitters, nano-flash memories, ultrafast lasers and amplifiers enabling a wealth of advanced systems.     

Quantum dot lasers: The birth and future trends

Despite its early age, laser based on arrays of self-organized quantum dots modified all the basic commandments of the heterostructure laser. Excitonic gain mechanism and discrete energy spectrum in a quantum dot provide principally new ways to control optical properties of the media. Extension of the spectral range using the same substrate will probably soon lead to the appearance of quantum dot lasers on the market. Fiz. Tekh. Poluprovodn. 33, 1039–1043 (September 1999) This article was published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

基于聚焦离子束注入的微纳加工技术研究

提出了聚焦离子束注入（focused ion beam implantation,FIBI）和聚焦离子束XeF2气体辅助刻蚀（gas assisted etching,GAE）相结合的微纳加工技术。通过扫描电镜观察FIBI横截面研究了聚焦离子束加工参数与离子注入深度的关系。当镓离子剂量大于1.4×1017ion/cm2时,聚焦离子束注入层中观察到均匀分布、直径10～15nm的纳米颗粒层。以此作为XeF2气体反应的掩膜,利用聚焦离子束XeF2气体辅助刻蚀（FIB-GAE）技术实现了多种微纳米级结构和器件加工,如纳米光栅、纳米电极和微正弦结构等。结果表明该方法灵活高效,很有发展前途。     

量子点发光器件的制备与仿真分析

为研究量子点发光器件结构与性能的关系,制备了以CdSe/ZnS量子点作为发光层、poly-TPD作为空穴传输层,Alq3作为电子传输层的量子点发光二极管,对器件结构及性能参数进行了表征,结果显示器件具有开启电压低、色纯度高等特点.结合测试数据,对量子点发光二极管进行了器件结构建模,利用隧穿模型及空间电荷限制电流模型对实验结果进行了分析,研究了器件中载流子的注入与传输机理.器件测试与仿真结果表明:各功能层厚度会影响载流子在量子点层的注入平衡,同时器件中载流子的注入与传输存在一转变电压,当外加电压低于转变电压时,器件中载流子的注入主要符合隧穿模型;当外加电压高于转变电压时,器件中载流子的注入主要符合空间电荷限制电流模型.研究结果验证了器件结构建模的合理性,可以利用仿真的方法进行器件结构优化并确定相关参数,这对器件性能的提高具有指导意义.     

量子点制备方法的研究进展

量子点以其类似于原子的性质近年来受到很大关注,通过Stranski-Krastanow(SK)生长模式外延自组织生长的量子点具有诸多有利于红外应用的性质,例如工作温度较高、信噪比较大、暗电流较低、波段较宽以及垂直入射光响应等.对于新型红外探测器的研发而言,它们是一类很有潜力的候选者.本文主要对近期国外文献报道的量子点制备方法的部分研究进展做了总结和评述.     

半导体量子阱材料及其制备技术

综述了半导体量子阱材料的最新发展动态及其制备技术。     

Exciton characteristics and exciton luminescence of silicon quantum dot structures

The exciton binding energy, the energies of the basic radiative exciton transition, and the zerophonon radiative lifetime of excitons in silicon quantum dots embedded in the SiO_x matrix are calculated in effective mass approximation with quadratic dispersion relation. In addition, the spectra of steady-state photoluminescence and of time-resolved photoluminescence of excitons in the silicon quantum dots are calculated, and the kinetics of the photoluminescence relaxation is considered. The theory is compared with the experiment. It is shown that, for nanostructures involving silicon quantum dots with diameters smaller than 4 nm, the governing factor in the broadening of the spectral photoluminescence bands is the effect of mesoscopic quantum fluctuations. In this case, either an even one dangling bond at the interface, or one intrinsic point defect, or one foreign atom located inside the small-sized nanocrystallite or in its close surroundings produces a pronounced effect on the energy of the exciton transition.     

Fabrication of single-crystalline ZnSe multipod-based structures

ZnSe multipod-based structures,including tetrapod-like microrods,long microwires,and short nanorods,are selectively prepared by atmospheric pressure thermal evaporation of ZnSe nanoparticles without using any catalyst.The morphologies could be well controlled by simply adjusting the deposition position.The phase structures,morphologies,and optical properties of the products are investigated by X-ray diffraction(XRD),scanning electron microscopy(SEM),high-resolution transmission electron microscopy(TEM),and photoluminescence(PL) spectroscopy.A vapor-liquid mechanism is proposed for the formation of ZnSe multipod-based structures.The presented route is expected to be applied to the synthesis of other Ⅱ-Ⅵ groups or other group’s semiconductor materials with controllable morphologies.     

Annealing behavior of InAs/GaAs quantum dot structures

We investigate the annealing behavior of InAs layers with different thicknesses in a GaAs matrix. The diffusion enhancement by strain, which is well established in strained quantum wells, occurs in InAs/GaAs quantum dots (QDs). A shift of the QD luminescence peak toward higher energies results from this enhanced diffusion. In the case of structures where a significant portion of the strain is relaxed by dislocations, the interdiffusion becomes negligible, and there is a propensity to generate additional dislocations. This results in a decrease of the QD luminescence intensity, and the QD peak energy is weakly affected.     

Fabrication of CdSe sensitized SnO2 nanofiber quantum dot solar cells

In the present study, we report a cost-effective quantum dot solar cells based on a combination of electrospinning and successive-ionic-layer-adsorption and reaction (SILAR) methods. CdSe nanocrystals are deposited on electrospun SnO₂ nanofibers by SILAR method using CdCl₂ as the cadmium source and Na₂Se as selenium source. The as-prepared materials are characterized by spectroscopy and microscopy. CdSe deposited SnO₂ electrodes are also characterized by spectroscopy and microscopy. Cells are fabricated with platinum (Pt)-sputtered FTO glasses used as the counter electrodes and polysulfide solution used as the electrolyte. The efficiency of the cells is studied for different number of SILAR cycles. Current density–voltage (J–V) measurements on a cell having CdSe deposition of 7 SILAR cycles and SnO₂ coating area 0.25 cm² showed an overall power conversion efficiency of 0.29 % with a photocurrent density (J_SC) of 5.32 mA cm⁻² and open circuit voltage (V_OC) of 0.23 V under standard 1 Sun illumination of 100 mWcm⁻² (AM 1.5 G conditions). This is improved by carefully coating SnO₂ film without losing the structures. Also ZnS passivation layer is coated to obtain an improved efficiency of 0.48% with J_SC of 4.68 mAcm⁻², and V_OC of 0.43 V.     

采用锗硅异质外延方法制备硅量子线

报道了一种采用锗硅异质外延制备硅量子线的新方法。在超低压化学气相淀积外延生长Ｓｉ／ＳｉＧｅ／Ｓｉ异质结构基础上，采用光刻和反应离子刻蚀技术形成槽状图形，用选择腐蚀液进行选择化学腐蚀，获得Ｓｉ线阵列，最后通过湿氧、干氧氧化过程，成功实现了高质量Ｓｉ／ＳｉＯ２异质界面结构硅量子线。采用扫描电子显微镜对量子线形成特征进行了研究，并讨论了硅线的热氧化性质。     

量子器件与量子信息技术

从信息社会的发展分析提出了量子器件及量子信息技术产生和发展的必然性,介绍了谐振隧穿器件、单电子器件、电子波导晶体管等纳米电子器件及其特点,对量子激光器和量子信息技术及其性能作了简要介绍,并给出了应用前景.     

Fabrication of fully self-aligned joint-gate CMOS structures

A six-mask process that yields stacked CMOS structures with the source and drain of both transistors self-aligned to a joint-gate electrode has been developed. The features that permit full self-alignment are an edge-defined silicon nitride "filament," used as an oxidation mask, and overlapping polysilicon "handles," used to form the top transistor source and drain regions. The individual NMOS and PMOS transistors have been characterized and together are functional in joint-gate CMOS inverters.     

Fabrication of curved structures by electron-beam lithography

The suitability of electron-beam lithography for the fabrication of curved structures, of interest for integrated optical devices, can be limited by the available pattern data formats. Extensions to the input format of a Cambridge Instruments electron-beam microfabricator are reported, which have allowed complex patterns to be easily specified for both mask making and direct writing.     

晶格畸变分析及其在半导体量子点结构中的应用

在适当的成像条件下可以直接从高分辨透射电子像（HRTEM）以接近原子级的分辨率进行晶格畸变分析。本综述介绍晶格畸变分析（LADIA）程序包及其在半导体自组装量子点（QD）系统中的应用。对多层InP小QD系统中畸变分布的分析表明：光致发光（PL）能量峰位的红移和QD中的应变弛豫直接相关。在慢速生长的InAs大QD系统中应变引起的元素互溶是PL峰位蓝移的主要因素。多层系统中QD的垂直叠合可解释为间隔层厚度低于临界值时生长前沿的横向张应变的作用。研究了生长以后不同条件快速退火对QD稳定性的影响,观测到垂直叠合的InPQD中出现各向异性的退火不稳定性。     

Fabrication and photoelectric properties of oxide/CdTe structures

A new technological process is proposed for forming an energy barrier in cadmium telluride crystals, and rectifying photosensitive anisotype and isotype structures are obtained. The photoelectric properties of the obtained structures and their dependence on the geometry of illumination with natural or linearly polarized light were investigated and are discussed. The new technology can be applied to the fabrication of different kinds of photoconversion structures based on cadmium telluride.