Viewing SiGe Heterostructure for Qubits with Dislocation Theory

Strained isotopically enriched 28Si strained layers in SiGe/Si/SiGe heterostrustructures is an excellent material platform for electron spin qubits. In this work, we report the fabrication of 28SiGe/28Si/28SiGe heterostructures for qubit devices by a hybrid MBE/CVD growth, where the thick relaxed SiGe buffer is realized by a reduced-pressure CVD and the 28SiGe/28Si/28SiGe stack is grown by an MBE. Here, we achieve a fully strained 28Si layer in such heterostructure with a 29Si concentration as low as 200 ppm within the MBE grown layers. It was possible to conclude that 29Si primarily originates from the residual natural Si vapour in the MBE chamber. Furthermore, we also present our studies about the growth temperature effect on the misfit dislocation formation in this heterostructure. It was possible to show that at a low MBE growth temperature, such as 350°C, the misfit dislocation formation is significantly suppressed.