应变Si1-xGex pMOSFET反型沟道空穴低场迁移率模型

在考虑应变对SiGe合金能带结构参数影响的基础上,提出了一个半经验的应变Sil-xGex/Si pMOSFET反型沟道空穴迁移率模型.在该模型中,给出了迁移率随应变的变化,并且考虑了界面陷阱电荷对载流子的库仑散射作用.利用该模型对室温下空穴迁移率随应变的变化及影响空穴迁移率的因素进行了分析讨论.     

应变Si1-x Gex pMOSFET反型沟道空穴低场迁移率模型

在考虑应变对SiGe合金能带结构参数影响的基础上,提出了一个半经验的应变Sil-xGex/Si pMOSFET反型沟道空穴迁移率模型.在该模型中,给出了迁移率随应变的变化,并且考虑了界面陷阱电荷对载流子的库仑散射作用.利用该模型对室温下空穴迁移率随应变的变化及影响空穴迁移率的因素进行了分析讨论.     

有限元法分析透镜形自组织生长量子点的弹性应变场分布

利用有限元法对应变自组织生长量子点的应力应变分布进行了系统分析.给出了抽象的孤立量子点系统模型,采用有限元分析方法,利用二维和三维模型对透镜形的量子点内部及周围材料的应力应变进行了计算,计算结果可以直接应用于量子点应变场对导带和价带限制势以及载流子有效质量的影响,从而用于精确计算量子点的电子结构.     

In_xCa_(1-x)As/GaAs应变量子阱结构中热载流子分布的皮秒光谱研究

用皮秒时间分辨荧光相关技术研究了In_xGa_(1-x)As/GaAS应变量子阱中的热载流手弛豫过程,结果表明,In组分x值(不同应变)对载流子弛豫寿命有明显的影响;与体材料相比,热载流子分布弛豫过程明显变慢,寿命明显增加.     

卷曲量子阱薄膜中的应变特性

嵌入非对称耦合量子阱(quantum wells)的纳米薄膜经过化学腐蚀后,在应变工程技术下卷曲成三维的管状结构,不同管径的微管其光学特性存在不同的模式,对应两种应变释放:单轴应变释放和双轴应变释放.为研究应变状态之间的内在联系以及影响应变状态的客观因素,实验上用不同浓度的HF酸腐蚀液对纳米薄膜牺牲层进行腐蚀并卷曲成三维管状结构.对微管荧光光谱的测试结果显示,微管的单轴应变释放和双轴应变释放不仅与衬底有关,还与微管卷曲的起始状态有关,在一定条件下两种应变可以相互转换.     

应变自组织量子点的几何形态对应变场分布的影响

采用自组织生长应变量子点的二维轴对称模型,系统分析了量子点内部及周围材料的应变分布.分别对透镜形、圆柱形、圆锥形和金字塔形量子点的应变分布进行了比较.结果表明主应变和切应变的分布受几何形状影响比较明显,静水应变几乎不受几何形状改变的影响,无论是在中心轴路径还是量子点周边路径静水应变基本一致,中心轴路径无切向应变分量,切向应变分量主要集中在量子点的边界,但在量子点几何边界的中心无切向应变,切向应变的极值分布在几何边界的拐点处.     

应变自组织量子点的几何形态对应变场分布的影响

采用自组织生长应变量子点的二维轴对称模型,系统分析了量子点内部及周围材料的应变分布.分别对透镜形、圆柱形、圆锥形和金字塔形量子点的应变分布进行了比较.结果表明主应变和切应变的分布受几何形状影响比较明显,静水应变几乎不受几何形状改变的影响,无论是在中心轴路径还是量子点周边路径静水应变基本一致,中心轴路径无切向应变分量,切向应变分量主要集中在量子点的边界,但在量子点几何边界的中心无切向应变,切向应变的极值分布在几何边界的拐点处.     

单轴应变Si NMOS电流模型研究

应变Si技术是目前延续摩尔定理,推动集成电路高速发展的重要技术,本文从单轴应变Si技术提升器件结构出发,基于基本的器件物理方程,建立单轴应变Si器件电流-电压模型,该模型充分考虑了应力等因素对阈值电压和电流的影响,仿真结果表明仿真结果与试验结果一致.     

GaInAs/AlGaAs应变量子阱结构的荧光特性

本文报道了4—300K温度范围内量子阱宽度分别为20、40、90和130A的GaInAs/AlGaAs应变量子阱结构的光荧光特性。我们考虑量子尺寸对载流子子能带的影响和弹性应变引起带隙的移动,计算了量子阱中本征激子发光的能量位置,计算值与实验结果基本吻合。还研究了荧光峰强度随阱宽的变化以及不同温度下荧光峰的半高宽度。     

应变异质结构中超薄中间层的应变协调作用

用一个简单模型讨论了应变异质结构中嵌入中间层对界面失配位错产生和应变释放的影响.根据能量最小原理得到了弹性能最小状态下界面失配位错密度,发现当中间层材料的晶格常数比衬底和外延层的都大或者都小并且厚度足够薄时,超薄中间层可以完全吸收支撑衬底和外延层之间的应变而不产生任何界面失配位错,具有所谓无支撑衬底的应变协调作用.     

Photoluminescence study of single-side doped n-AlGaAs/GaAs structures with quantum wells

Photoluminescence spectra of single-side doped n-AlGaAs/GaAs structures have been studied at different quantum well widths and temperatures. The sharp growth of the photoluminescence intensity due to the resonant capture of photoexcited holes by a quantum well has been observed for the first time in such structures. A theoretical model for calculating the quantum states in single-side doped structures is proposed. The self-consistent solution of the system of Schrödinger and Poisson equations is obtained by the perturbation method.     

In-situ monitoring, structural, and optical properties of ultrathin GaSb/GaAs quantum wells grown by OMVPE

We present a study of the growth of strained ultrathin GaSb quantum well (QW) layers in a GaAs host crystal by organometallic vapor phase epitaxy (OMVPE). We report surface anisotropy features observed by reflectance difference spectroscopy (RDS) during exposure of the GaAs (001) surface to trimethylantimony (TMSb) and during subsequent growth interruption. We demonstrate the formation of a floating layer of Sb during growth of GaAs over GaSb quantum well layers. The periodic nature of the RDS signal during growth of multiple quantum well (MQW) structures allows us to construct time-resolved RDS spectra, detailing the evolution of the surface anisotropy. We show how x-ray diffraction (XRD) data may be used to determine the graded compositional profile resulting from Sb segregation at the GaAs/GaSb interface. Photoluminescence (PL) spectra at 2 K from MQW structures exhibit two peaks below the GaAs bandgap. The lower-energy peak, which we attribute to a type-II transition at the GaSb/GaAs interface, shifts logarithmically with excitation power density. The higher energy peak shows no shift with excitation power, and is attributed to a transition occurring within the graded barrier layers.     

Optical properties of germanium monolayers on silicon

Photoluminescence and Raman spectra of thin germanium layers grown on silicon at a low temperature (250°C) have been studied. In structures of this kind, in contrast to those grown at high temperatures, luminescence from quantum wells is observed at germanium layer thicknesses exceeding ～9 monolayers (ML). With the development of misfit dislocations, the luminescence lines of quantum wells are shifted to higher energies and transverse optical (TO) phonons involved in the luminescence are confined to a quasi-2D germanium layer. Introduction of an additional relaxed Si_0.95Ge_0.05 layer into the multilayer Ge/Si structure leads to a substantial rise in the intensity and narrowing of the luminescence line associated with quantum dots (to 24 meV), which points to their significant ordering.     

InGaN nanoinclusions in an AlGaN matrix

GaN-based structures with InGaN quantum dots in the active region emitting in the near-ultraviolet region are studied. In this study, two types of structures, namely, with InGaN quantum dots in a GaN or AlGaN matrix, are compared. Photoluminescence spectra are obtained for both types of structures in a temperature range of 80–300 K and at various pumping densities, and electroluminescence spectra are obtained for light-emitting (LED) structures with various types of active region. It is shown that the structures with quantum dots in the AlGaN matrix are more stable thermally due to the larger localization energy compared with quantum dots in the GaN matrix. Due to this, the LED structures with quantum dots in an AlGaN matrix are more effective.     

Improvement in heat dissipation by transfer of IV-VI epilayers from silicon to copper

A successful metallization (Au-InSn alloy) bonding and substrate removal procedure is described for improving epilayer heat dissipation. Two IV-VI semiconductor multiple quantum well (MQW) structures grown on silicon host substrates by molecular beam epitaxy with a CaF/sub 2/ (or CaF/sub 2/-BaF/sub 2/) buffer layer were bonded epilayer down to the tips of a copper bar assembly and then the Si substrates were removed by dissolving the CaF/sub 2/ (or CaF/sub 2/-BaF/sub 2/) buffer layer in water. The bonded IV-VI epilayers were cleaved by separation of the copper bars. Photoluminescence (PL) data before and after transfer showed that an increase in diode laser pumping caused a smaller blue shift in the PL energies for the structures bonded to copper when compared to the as-grown samples. Calculations revealed that epilayers transferred to copper were at least 20/spl deg/C cooler than the same epilayers on silicon when illuminated with a continuous wave (/spl lambda/=911 nm) laser at a power density of about 25 W/cm/sup 2/.     

Material characterization of an ion-implantation process for p-type (InGa)As/GaAs quantum-well structures

We have performed a detailed study of the formation of Be⁺-implanted contacts to modulation-doped, p-channel, (InGa)As/GaAs, single-strained quantum wells. Photoluminescence at 4 K from these structures is shown to be an excellent monitor of implant and annealing effects, as corroborated by Hall-effect measurements. Rapid thermal annealing produced higher electrical activation of the Be implants than did arsine-over-pressure annealing at comparable temperatures, similar to the trend in bulk GaAs. In contrast to conventional, alloyed-contact technologies, the rapid-annealed, implanted structures provided ohmic contact to the quantum well even at 4 K.     

Optical phenomena in InAs/GaAs heterostructures with doped quantum dots and artificial molecules

Spectra of intraband absorption of polarized mid-IR light were investigated in undoped, p-, and n-doped InAs/GaAs quantum dots (QDs) covered with an InGaAs layer. Optical matrix elements for intraband electron and hole transitions in QDs have been calculated for different polarizations of light, and a good agreement with the experimental data is obtained. It is shown that the intraband absorption of light by electrons strongly exceeds the absorption by holes. Photoluminescence spectra and TEM images of structures with artificial molecules formed by pairs of QDs were studied.     

Resonances related to an array of InAs quantum dots and controlled by an external electric field

Photoluminescence of multilayer structures with InAs quantum dots grown in the p-n junction in GaAs by molecular-beam epitaxy is studied. Formation of vertical columns of quantum dots is verified by the data of transmission electron microscopy. It is shown that a natural increase in the size of quantum dots from layer to layer brings about their vertical coalescence at the upper part of a column. An unbalance of electronic levels caused by the enlargement of quantum dots was compensated by an external electric field, so that the resonance of ground electronic states in the column was attained. The onset of resonances was checked by the methods of steady-state and time-resolved photoluminescence. It is shown that, in the case of a resonance, the photoluminescence intensity and the radiative lifetime of excitons increase (up to 0.6–2 ns), while the time of tunneling of charge carriers becomes shorter (shorter than 150 ps). Outside the resonances, tunneling of electrons is appreciably enhanced owing to the involvement of longitudinal optical phonons. If only these phonons are involved, the time of nonresonance tunneling between quantum dots becomes shorter than the time of relaxation of charge carriers from the barrier (100 and 140 ps, respectively).     

Visible light emitting Si/SiO2 superlattices

Six-period superlattices of Si/SiO₂ have been grown at room temperature using molecular beam epitaxy. With this mature technology, the ultra-thin (1–3 nm) Si layers were grown to atomic layer precision. These layers were separated by 1 nm thick SiO₂ layers whose thickness was also well controlled by using a rate-limited oxidation process. The chemical and physical structures of the multilayers were characterized by cross-sectional TEM, X-ray diffraction, Raman spectroscopy, Auger sputter-profile, and X-ray photoelectron spectroscopy. The analysis showed that the Si layer is free of impurities and is amorphous, and that the SiO₂/Si interface is sharp (0.5 nm). Photoluminescence (PL) measurements were made at room temperature using 457.9 nm excitation. The PL peak occurred at wavelengths across the visible range for these multilayers. The peak energy position E was found to be related to the Si layer thickness d by E (eV) = 1.60+0.72d⁻² in accordance with a quantum confinement mechanism and the bulk amorphous-Si band gap.     

Optoelectronic properties of heteronanostructures with combined layers of In(Ga)As/GaAs quantum wells and dots

The effect of the incorporation of an InGaAs quantum well into structures with InAs/GaAs quantum dots grown by gas-phase epitaxy on their optoelectronic properties is analyzed in the mode with increased growth-interruption time. It is established that the quantum-dot energy spectrum is weakly sensitive to variations in the thickness and composition of the double InGaAs/GaAs coating layer. The deposition of a quantum well onto a layer of quantum dots decreases the emission-barrier effective height in them. The conditions under which the quantum well can be used for protecting the quantum-dot active layer against penetration by defects generated during structure-surface anodic oxidation are determined.