Strain and Defect Evolution of Si1-xGex/Si Heterostructures Grown by Pulsed Laser Induced Epitaxy

The relaxation mechanism of Si1-xGex/Si heterostructures subjected to pulsed laser melting was investigated by probing the pulsed laser induced epitaxy (PLIE) regime of undoped 20 nm Si0.5Ge0.5/Si thin films. The pseudomorphic “critical thickness” and evolution of bi-layer formation was determined as a function of average Ge concentration of the films via quantitative analysis of (004) HRXRD rocking curves. Comparison of pseudomorphic thicknesses alongside SIMS analysis reveals a “dynamic critical Ge concentration” of 27-30% Ge as the PLIE limit for pseudomorphic growth that is independent of average Ge concentration of the films. Plan-view weak-beam dark-field imaging revealed that surface dislocation half-loops are the primary strain relieving defects that reach concentrations on the order of 1010 cm−2. It is theorized that quasi-cellular solidification leads to lateral Ge segregation, creating nm scale localized regions of Ge pile-up and stress concentration. The morphology of the liquid/solid interface along with stress localization is what allows for the dislocation half-loop to be the primary strain relieving defect, with edge defects acting as secondary. These results are important for understanding the conditions and strategies necessary to utilize pulsed laser melting to its fullest potential in applications towards pMOS source/drain contact engineering.