Epitaxy of Group-IV Semiconductors for Quantum Electronics

Abstract

We are growing at CEA (i) high purity 28Si layers and (ii) c-Ge/SiGe heterostructures for electron and hole spin quantum bits. We describe here strategies usable for the fabrication of 28SOI substrates, with a focus on 28SiH4 consumption minimization, as such a gas is very expensive and hard to come by. We also focus on the properties of Si0.26Ge0.74 and Si0.21Ge0.79 Virtual Substrates (VS) grown at 850°C, 20 Torr and a forward Ge ramping-up on Si(001) substrates. After some chemical polishing (to remove the surface cross-hatch), those VS are used as templates for the 500°C, 100 Torr growth of SiGe/c-Ge/SiGe 2D Hole Gas Gas (2DHG) stacks. Those c-Ge layers are, in X-Ray Diffraction, fully compressively strained on the relaxed SiGe VS underneath and of high crystalline quality. Some slight undulations are evidenced at c-Ge / SiGe cap interfaces, hinting at elastic strain relaxation, however. Magnetotransport measurements in Hall-bar devices were performed at 4.2 K to assess the electrical properties of the 2DHG in those SiGe/c-Ge heterostructures. At low magnetic field, a hole mobility of 1.2 x 105 cm2 V-1 s-1 was obtained for a hole density of n2DHG = 3.7x1011 cm-2 in a 16 nm thick c-Ge/55 nm thick Si0.21Ge0.79 cap sample.

Compressively Strained Epitaxial Ge Layers for Quantum Computing Applications

“…x Ge x growth for Ge gate all around (GAA) field effect transistors [20,21]. The use of higher order precursor gases, disilane (Si 2 H 6 ) and digermane (Ge 2 H 6 ) for Si and Ge, respectively, allows to cover a wide range of Ge concentrations with a relatively high growth rate at a temperature which can be as low as 350 • C. The Ge growth at low temperatures also allows the deposition of strained Ge without the risk for 3-dimensional island growth (Stranski-Krastanov growth), which has been reported to be challenging when using conventional GeH 4 as Ge precursor [22]. However, spin qubit devices require the elimination of the nuclear spin.…”