Role of critical thickness in SiGe/Si/SiGe heterostructure design for qubits
Yujia Liu, Kevin‐P. Gradwohl, Chen-Hsun Lu, T. Remmele, Y. Yamamoto, Marvin Hartwig Zoellner, Thomas Schroeder, Torsten Boeck, Houari Amari, Carsten Richter, M. Albrecht
Abstract
We study the critical thickness for the plastic relaxation of the Si quantum well layer embedded in a SiGe/Si/SiGe heterostructure for qubits by plan-view transmission electron microscopy and electron channeling contrast imaging. Misfit dislocation segments form due to the glide of pre-existing threading dislocations at the interface of the Si quantum well layer beyond a critical thickness given by the Matthews–Blakeslee criterion. Misfit dislocations are mostly 60° dislocations (b=a/2 <110>) that are split into Shockely partials (b=a/6 <112>) due to the tensile strain field of the Si quantum well layer. By reducing the quantum well thickness below critical thickness, misfit dislocations can be suppressed. A simple model is applied to simulate the misfit dislocation formation and the blocking process. We discuss consequences of our findings for the layer stack design of SiGe/Si/SiGe heterostructures for usage in quantum computing hardware.