Growth of SiGe bulk single crystals with low defect density and creation of functional heterostructures

本研究的目的是在衬底上实现组成均匀、缺陷密度低、晶格常数和禁带宽度灵活选择的SiGe大块晶体，这为探索新材料的研究提供了机会，与先进的异质外延方法相结合，可以制备出成分可控的应变和/或带隙不连续的异质结构。通过界面温度在线监测系统、拉拔速率的动态控制、晶种取向的优化等一系列改进，建立了获得高质量SiGe大块晶体的晶体生长技术。以InGaAs体晶体的实现为例，说明该方法同样适用于其他具有完全溶解度的多元半导体材料。此外，浮区生长有助于实现低缺陷密度的SiGe大块晶体。在自制的SiGe大块衬底上，与在SiGe虚拟衬底上相比，我们获得了结构完好性更好的应变硅薄膜。此外，还获得了各种功能异质结构，如应变硅薄膜中具有高电子迁移率的二维电子，具有高峰谷电流比的共振隧穿二极管，来自应变量子阱的强烈的光致发光等。在块状InGaAs衬底上，利用晶格锁存效应，成功地生长出了具有立方对称性和理想In、N含量的InGaAsN。生长的0.2-μm厚InGaAsN薄膜的光致发光范围为1.33-1.55μm。这些结果表明，由于我们的晶体生长技术可以应用于各种成分的多组分晶体的任意成分的生长，并且在液体和固体状态下都具有完全的溶解性，因此多组分半导体块材衬底可以用于各种材料的研究。

The purpose of this research is to realize SiGe bulk crystals with uniform composition and low defect density for substrates with a flexible choice in lattice constants and bandgaps since those offer opportunities to explore novel materials research when combined with an advanced heteroepitaxy method to prepare heterostructures with controlled stain and/or band discontinuity in constituent materials. By integration of a series of improvements such as the in-situ monitoring system of the interface temperature, the dynamical control of the pulling rate, the optimization of the seed orientation, we established a crystal growth technique to obtain high-quality SiGe bulk crystals. The method was revealed to be applicable other multicomponent semiconductors with complete solubility as demonstrated by realization of InGaAs bulk crystal. In addition, floating zone growth was shown to be useful to realize SiGe bulk crystal with low defect density.On homemade SiGe bulk substrates, we realized strained Si thin film with improved structural perfection compared with that on SiGe virtual substrate. Furthermore, various functional heterostructures have been achieved such as two-dimensional electron with high electron mobility in strained Si thin film, resonant tunneling diodes with high peak-to-valley current ratio, intense photoluminescence from strained quantum wells and so on. On bulk InGaAs substrates, InGaAsN with cubic symmetry and desirable In and N contents were grown successfully owing to the lattice-latching effect. As-grown 0.2-μm-thick InGaAsN films exhibited photoluminescence in the range of 1.3-1.55 μm.These results demonstrate that multicomponent semiconductor bulk substrates are available for various materials research since our crystal growth technique can be applied to arbitrary compositions of various multicomponent crystals with complete solubility in both the liquid and solid states.