Surface nucleated half-loops in strained epilayers

Abstract

Mismatched epilayers, grown beyond some critical thickness, have commonly been observed to have arrays of misfit-relieving dislocations at the heterointerface. In diamond or sphalerite structures, these arrays are orthogonal <110> networks of long 60° type dislocations, which are glissile and have inclined Burgers vectors. Up to the point at which growth becomes three-dimensional (about 2% mismatch in the (In,Ga)As/GaAs system), internal defects act as the sources for the misfit dislocations. Examples of such sources include pre-existing threading dislocations, internal loops, precipitates, and mechanical damage.In higher mismatch two-dimensional growth, such as can be produced in the GeSi/Si(001) system, the density of epithreading dislocations suddenly increases as the length of interfacial misfit dislocations falls. Almost simultaneously, the misfit dislocation type changes from 60° to edge. While in-situ hot stage experiments have shown that 60° type dislocations become mobile at about the growth temperature of the epilayer, and have observable velocities from this temperature on up, our observations of edge dislocations in the same system have shown that velocities for edge dislocations are essentially nil (measurable limit <lnm/s) even at 750°C, some 200°C above the growth temperature.