主讲人: |
Maxime Vallet |
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主 题: |
Experimental and theoretical study of interfaces in the InAs/AlSb multilayer heterostructures |
时 间: |
2018-09-04 14:00 |
地 点: |
机械工程楼八层大会议室 |
[主讲人简介] |
Dr Maxime Vallet is a materials scientist specialized in the structural and chemical characterization of materials. He obtained his PhD in 2014 at the PPrime Institute, Poitiers (France). He is currently working in CEMES-CNRS, Toulouse (France) as a research scientist.
His research activities aim to understand macroscopic properties of semiconductor-based materials induced during an engineering process through the study at the nanometre scale of strain, defects and their chemical organization. To this end, he mainly uses transmission electron microscopy techniques such as bright/dark fields, HRTEM, HAADF-HRSTEM, EELS as well as in situ experiments. His research activities also include the use of the focused ion beam, the use of X-ray diffraction and the writing of numerical calculations based on the theory of linear elasticity.
Maxime Vallet博士,工作于图卢兹的法国科学院CEMES研究所,研究领域为材料结构和化学特性的,于2014在法国普瓦捷大学-法国科学院Pprimes研究所获得博士学位。
他致力于研究加工半导体基材料引起的宏观性能变化与纳米尺度的应变、缺陷及化学组织关系。为此,他主要使用透射电子显微镜技术,如明/暗场、高倍透射、高倍扫描透射、能量损失吸收谱及原位实验观察等手段。还包括聚焦离子束的使用、X射线衍射的使用以及基于线性弹性理论的数值计算的编写。 |
[内容简介] |
In multilayers based devices such as quantum cascade lasers (QCLs), the electronic and optical properties are very dependent of structural and chemical properties of interfaces because of nanometer thicknesses of layers. The InAs/AlSbsystem coherently grown on InAs substrateis particularly sensitive to interfacial structures: the chemical bonds at interfaces (Al-As or In-Sb) are different from those existing in the InAs and AlSb layers. In bulk materials, given the lattice parameters(aAlAs=0.566 nm,aInSb=0.6479 nm, aInAs=0.6058 nm) AlAs or InSb bonds are 6.6% smaller or 6.9% higher than InAs bonds, respectively. The stress states at interfaces are therefore highly dependent on their dominant bond type, being tensile for AlAs-like interfaces or compressive for InSb-like interfaces. In a previous study [1],we qualitatively showed that the formation of the tensile AlAs-type interface is spontaneously favored compared to InSb-type, which is attributed to its higher thermal stability.
In this work we aim to investigate the elastic properties of interfaces in the InAs/AlSb system both from experimental and theoretical points of view. In this perspective, the variations of lattice parameter through interfaces were studied by using the geometrical phase analysis (GPA) on atomic resolved images obtained from high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Negative strains ofabout 6% was measured at interfaces which are of the sameorder of magnitude as measured in an image generated froma model structure with perfect AlAs interfaces. We also discuss the relevance of strain measurement at the scale of an interface [2]. The elastic properties of the InAs/AlSb heterostructure were also investigated by using the density functional theory (DFT). Firstly, asignificant deviation to the theory of linear elasticity was achieved in the stress-strain curves of bulk InAs, AlAs, InSb, and AlSb forstrain above 2.5% (in absolute value). This deviation was similar for these four binary compounds.Then we focused on the interfacial strains generated by perfect AlAs-likeand InSb-like interfaces in [InAs/AlSb]heterostructures with various InAs and AlSb layer thicknesses.The structuresof perfect Al-As (In-Sb) interfaces calculated by DFT and those predicted by applyingthe linear elasticity as in bulk AlAs (InSb) were in asurprisingly good agreement [3].
This work was supported by the French national project ANR NAIADE (ANR-11-BS10-017) and by ESTEEM2
在基于多层的器件,如量子级联激光器(QCLSs)中,由于纳米层的厚度,电子和光学性质非常依赖于界面的结构和化学性质。在InAs衬底上相干生长的InAs/AlSb系统对界面结构特别敏感:界面上的化学键(Al-As或In-Sb)与InAs和AlSb层中存在的化学键不同。在块状材料中,给定晶格参数(aAlAs=0.566 nm,aInSb=0.6479 nm,aInAs=0.6058 nm),Al-As或In-Sb键分别比In-As键低6.6%或高6.9%。因此,界面处的应力状态高度依赖于它们的主导键类型,对于Al-As界面是拉伸的,对于In-Sb界面是压缩的。在先前的研究(1)中,我们定性地发现,与In-Sb界面压缩相比,拉伸型Al-As界面更容易自发形成,这归因于其较高的热稳定性。
在这项工作中,我们从实验和理论角度研究InAs/AlSb界面的弹性性质。在此基础上,利用几何相位分析(GPA)研究了高角度环形暗场扫描透射电子显微镜(HADAD-STEM)获得的原子分辨图像的界面参数变化。在具有完美Al-As界面的模型结构产生的图像中测量的界面处测量的负应变约为6%。我们还讨论了应变测量在界面尺度上的相关性〔2〕。利用密度泛函理论(DFT)研究了InAs/AlSb异质结构的弹性性质。首先,在体积InAs、AlAs、InSb和AlSb应变2.5%以上(绝对值)的应力-应变曲线上,获得了与线性弹性理论的显著偏差。这四种二元化合物的这种偏差是相似的,然后我们着重研究了具有不同的InAs和AlSb层厚度的[InAs/AlSb]异质结构中由完美的AlAs和InSb类似的界面所产生的界面应变。t和用线性弹性体预测的散装AlAs(InSb)的预测值吻合得很好[3]。
这项工作得到了法国国家计划ANR NIADE(ANR 11-BS10-017)的支持,并受到了ESTEEM2的支持
[1] J. Nicolaiet al., J. Appl. Phys. 118, 035305 (2015)
[2] M. Valletet al.,Appl. Phys. Lett. 108, 211908 (2016)
[3] Claveauet al.,Appl. Phys. Lett. 109, 041903 (2016) |
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