Defect reduction in large lattice mismatch epitaxial growth through block copolymer full wafer patterning

The introduction of defects during the growth of large lattice mismatched III-V materials typically occurs through the injection of 60deg dislocations from the surface of the film or islands once a critical thickness or size has been reached. The threading segments from these dislocations lead to electrically active states which deteriorate device performance. Strain relaxation at the earliest stages of growth allows for the development of misfit arrays without the addition of threading segment. Forming and strain relieving small islands can be achieved by intentional patterning as long as the lateral length scale is on the order of the solid state diffusion length. Self-assembly method can be used to produce dense arrays of quantum dots. However, these arrays often develop a multi-modal size distribution as growth proceeds, and the initially pseudomorphic quantum dots evolve into relaxed islands, resulting in a loss of control of the island size and spatial distributions. Large islands form complex defect structures containing a high density of threading dislocations. External patterning on a nanoscale can provide control over island size and placement. Selective epitaxy can constrain the growing epitaxial material to within the patterned mask openings. Once relaxation occurs, the film growth process continues through island coalescence. Patterning at the required length scale and densities (mask openings of ~20 nm on a 40 nm pitch) would need e-beam lithography, a slow and time-demanding process.