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 <110> 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.