基于蒙特卡罗方法的4H-SiC(0001)面聚并台阶形貌演化机理

针对SiC外延生长中微观原子动力学过程,建立了一个三维蒙特卡罗模型来研究偏向■或■方向4H-SiC(0001)邻晶面上台阶形貌演化过程,并且利用Burton-Cabera-Frank理论分析了其形成机理.在蒙特卡罗模型中,首先建立了一个计算4H-SiC晶体生长过程的晶格网格,用来确定Si原子和C原子晶格坐标以及联系它们之间的化学键;其次,考虑了原子在台阶面上的吸附、扩散,原子在台阶边上的附着、分离以及传输等过程;最后,为了更加详细地捕捉微观原子在晶体表面的动力学过程信息,该模型把Si原子和C原子分别对待,同时还考虑了能量势垒对吸附原子影响.模拟结果表明:在偏向■方向的4H-SiC(0001)邻晶面,有一个晶胞高度的聚并台阶形貌形成,而对于偏向■方向的邻晶面,出现了半个晶胞高度的聚并台阶形貌,该模拟结果与实验中观察到的结果相符合.最后,利用Burton-Cabera-Frank理论对聚并台阶形貌演化机理进行了讨论.     

The asymmetry of the tunneling time in type II semiconductor heterostructures

The tunneling time asymmetry in type II semiconductor heterostructures is related to the phase difference of the reflection coefficients for the two tunneling directions. Analytical expressions and numerical simulations are given for the difference between the left-to-right and right-to-left tunneling times in asymmetric, single and multiple barrier type II heterostructures.     

高温超导薄膜与超导机理研究

高温超导体的晶格结构通常呈现出层状特征,因此具有低维属性的外延薄膜与异质结构成为了探索高温超导机理的关键材料平台。近年来,原子级精准的外延生长技术更促进了新型超导体的发现。文章将按照超导体系维度下降的脉络,简要介绍高温超导薄膜和异质结构研究对深入理解超导机理的独特贡献。     

Quantum reflection pole method for determination of quasibound states in semiconductor heterostructures

The quantum reflection pole method (QRPM) is introduced for determining quasibound state eigenenergies and their lifetimes in symmetric, asymmetric, biased, and unbiased quantum heterostructures. In the QRPM the single-band effective-mass Schrödinger equation is solved without using complex arithmetic. Calculations are much simpler to perform than with previous methods. Further, results are found to be in excellent agreement with other rigorous techniques.     

扩展互作用谐振腔的模拟分析

分析了扩展互作用谐振腔的工作原理、特点以及工作过程,并利用PIC粒子模拟程序对其进行了数值模拟,分析了阴极电压、电子注半径、谐振腔个数以及谐振腔周期长度对输出功率、频率及转换效率的影响。结果表明：当阴极电压为28.5~30.0 kV时,谐振腔能正常工作;当电子注半径为1.4 mm,谐振腔个数为4,阴极电压为29 kV时输出功率和转换效率最大,输出功率为128 kW,频率12.9 GHz,转换效率达37.93%;输出频率随谐振腔周期长度的变小而增大。     

MOCVD外延生长AlGaAs组份的在线监测

利用反射各向异性谱(RAS)和反射谱在线监测了Al_xGa_1-xAs样品的金属有机化合物汽相淀积(MOCVD)外延生长过程。通过在线监测得到的RAS和反射谱可以敏感地反映出Al_xGa_1-xAs外延层组份发生的变化,从而优化外延生长工艺。实验表明,反射谱中的振荡周期可以在线计算组份和生长速率,利用反射谱中的振荡的第一个最小值与Al组份的线性关系,可以确定渐变组份初始值。通过在线计算得到的生长速率和组份与扫描电镜(SEM)和高分辨X射线衍射(HRXRD)测试得到的结果基本吻合。     

Interband tunneling depopulation in type-II InAs/GaSb cascade laser heterostructure

An exact analytical representation has been obtained for electron eigenstates in the full isotropic 8-band Kane model and applied to calculate the depopulation rate of the lower lasing state in the active region of a type-II intersubband cascade laser. We show that interband tunneling rate takes its maximum value when the depopulated states belong to the upper of the coupled electron- and hole-like subbands in the “leaky window” of the broken-gap InAs/GaSb heterostructure.     

The band gap and band offset in ultrathin oxide–semiconductor heterostructures

In ultrathin high-k$k$ oxide layers knowledge of the band line up and band gap is essential for modeling the transport properties and to learn about a device’s long term stability and reliability. However, such data are hard to determine in such ultrathin layers and usually are extrapolated from values for bulk samples or are taken from the literature. In our in situ approach we use electron energy loss spectroscopy, valence band photoelectron spectroscopy, X-ray absorption spectroscopy, and resonant inelastic X-ray scattering to obtain the loss function and the valence and conduction band densities of states. From such data we derive the values of the band offsets and of the band gap. We discuss the ability of this combination of different techniques for the analysis of such complex ultrathin dielectric systems and discuss in detail the properties of the native oxide in SiO₂/Si(001) and SiO₂/3C−SiC(001).     

Thermal redistribution of indium in amorphous silicon layers

A new impurity redistribution mechanism is reported for low temperature annealing (525°C) of (100) Si samples implanted with high indium doses. The redistribution is a strong function of implant dose and is believed to be stress related.     

Atomic hydrogen induced step bunching and fabrication of quantum wire arrays on GaAs（311） A Substrate by molecular eam epitaxy

Atomic hydrogen assisted molecular beam epitaxy (MBE) is a novel type of epitaxial growth of nanostructures. The GaAs (311)A surface naturally forms one-dimensional step arrays by step bunching along the direction of 〈-233〉 and the space period is around 40nm. The step arrays extend over several μm without displacement. The InGaAs quantum wire arrays are grown on the step arrays as the basis. Our results may prompt further development of more uniform quantum wire and quantum dot arrays.     

用激光分子束外延在Si衬底上外延生长高质量的TiN薄膜

采用激光分子束外延技术,利用两步法,在Si单晶衬底上成功地外延生长出TiN薄膜材料.原子力显微镜分析结果显示, TiN薄膜材料表面光滑,在10 μm×10 μm范围内,均方根粗糙度为0842nm.霍耳效应测量结果显示,TiN薄膜在室温条件下的电阻率为36×10^-5Ω·cm,迁移率达到5830 cm²/V·S,表明TiN薄膜材料是一种优良的电极材料.X射线θ—2θ扫描结果和很高的迁移率均表明,高质量的TiN薄膜材料被外延在Si衬底关键词：激光分子束外延TiN单晶薄膜外延生长