非掺杂型Si/SiGe异质结外延与表征

Epitaxy and characterization of undoped Si/SiGe heterojunctions

以自旋为编码单元的硅基半导体量子计算与传统微电子工艺兼容,易拓展且可以同位素纯化提高退相干时间,因而备受关注.本研究工作通过分子束外延生长了高质量非掺杂型Si/SiGe异质结并测试了二维电子气迁移率.球差电镜观察到原子级尖锐界面,原子力显微镜表征显示其表面均方根粗糙度仅为0.44 nm,低温下迁移率达到20.21×10^(4)cm^(2)·V^(–1)·s^(–1).不同栅压下载流子浓度和迁移率的幂指数为1.026,材料丁格比值在7—12之间,表明载流子主要受到背景杂质散射和半导体/氧化物的界面散射.

Silicon-based semiconductor quantum computing with spin as the encoding unit is compatible with traditional microelectronic processes,easy to expand,and can improve isotope purification and decoherence time,thus attracting much attention.There are fewer reports on the work related to undoped Si/SiGe heterostructures grown by molecular beam epitaxy than those on chemical vapor deposition.An undoped Si/SiGe heterostructure is grown by molecular beam epitaxy(see the attached figure below).The results from scanning transmission electron microscopy and energy-dispersive spectroscopy mapping show an atomic-scale interface with a characteristic length of 0.53 nm.The surface root-mean-square roughness measured by atomic force microscope is 0.44 nm.The X-ray diffraction data show that the Si quantum well is fully strained and the in-plane strain is 1.03%.In addition,the performance of the two-dimensional electron gas is evaluated by low-temperature Hall measurements,which are conducted in the Hall-bar shaped field-effect transistor.The peak mobility is 20.21×104 cm2·V-1·s-1 when the carrier density is about 6.265×1011 cm-2 at 250 mK.The percolation density is 1.465×1011 cm-2.The effective mass of the two-dimensional electron gas is approximately 0.19m0.The power exponential between carrier density and mobility at different gate voltages is 1.026,and the Dingle ratio of the two-dimensional electron gas is in a range of 7-12,indicating that the electrons are scattered by background impurities and semiconductor/oxide interfaces charges.The atomically sharp interface of Si/SiGe heterostructures created by molecular beam epitaxy is beneficial for studying the valley physics properties in silicon.The structural and transport characterizations in this paper lay the foundation for the optimization of Si-based semiconductor quantum dot quantum computing materials.