Strain relaxation from annealing of SiGe heterostructures for qubits

Abstract

The misfit dislocation formation related to plastic strain relaxation in Si or Ge quantum well layers in SiGe heterostructures for spin qubits tends to negatively affect the qubit behaviors. Therefore, it is essential to understand and then suppress the misfit dislocation formation in the quantum well layers in order to achieve high-performance qubits. In this work, we studied the misfit dislocation propagation kinetics and interactions by annealing the strained Si or Ge layers grown by molecular beam epitaxy. The annealing temperatures are from 500 to 600 °C for Si layers and from 300 to 400 °C for Ge layers. The misfit dislocations were investigated by electron channeling contrast imaging. Our results show that the misfit dislocation propagation is a thermally activated process. Alongside, the blocking and unblocking interactions during misfit dislocations were also observed. The blocking interactions will reduce the strain relaxation according to theoretical calculation. These observations imply that it is possible to suppress the misfit dislocation formation kinetically by reducing the temperatures during the SiGe heterostructure epitaxy and post-epitaxy processes for developing well-functional SiGe-based spin qubits.