Epitaxy and characterization of undoped Si/SiGe heterojunctions

Abstract

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 0.19<i>m</i>₀. 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.