Misfit dislocation dynamics in Si1−xGex/(100) Si: Uncapped alloy layers, buried strained layers, and multiple quantum wells

Abstract

Misfit dislocation glide velocities have been measured in Si/Si1−xGex/Si heterostructures. Si capped single Si1−xGex alloy layers and multiple quantum well geometries were investigated and no difference was found between dislocation kinetics in these structures and the equivalent alloy layer of the same average composition. Velocities in the range 25 nm s−1 to 2 nm s−1 were determined from the length of a/2〈110〉 60° type misfit dislocation segments after annealing in the temperature range 450–950 °C, for times between 5 and 2000 s. Two dislocation mechanisms were observed; a single misfit array at the first Si1−xGex/Si interface was found in multiple quantum wells and alloy layers while paired misfit segments were observed at both strained interfaces in Si capped Si1−xGex alloy layers. An expression for the effective stress, τeff, for single and paired misfit dislocation propagation is presented which accommodates variation in the unstrained Si cap thickness. The mean activation energy for misfit disclocation glide Qv for Si1−xGex/Si heterostructures with 0.035<x<0.25 was found to be 2.25±0.05 eV and Qv was independent of τeff. For all geometries and for τeff in the range 100–750 MPa the misfit dislocation glide velocity can be defined by V(mm s−1)= (4±2)×1014(τeff/μ)2 exp−(2.25/kT).