A novel approach for the complete removal of threading dislocations from ZnSe on GaAs (001)
Here we demonstrate a novel approach to the complete removal of threading dislocations in ZnSe on GaAs (001). This approach, which we call patterned heteroepitaxial processing (PHP), involves post-growth patterning and thermal annealing. Eyitaxial layers of ZnSe on GaAs (001) were grown to thicknesses of 2000–6000 A by photoassisted metalorganic vapor phase epitaxy (MOVPE). Following growth, layers were patterned by photolithography and then annealed at elevated temperatures under flowing hydrogen. Threading dislocation densities were determined using a bromine/methanol etch followed by microscopic evaluation of the resulting etch pit densities. We found that as-grown layers contained more than 107 CM-2 threading dislocations. The complete removal of threading dislocations was accomplished by patterning to 70 gm by 70∼tm square regions followed by thermal annealing for 30 minutes at temperatures greater than 5000C. Neither post-growth annealing alone nor post-growth patterning alone had a significant effect. The effectiveness of this approach dminishes significantly below 500 C so that annealing at 400 C produces no measurable effect. We propose that the underlying mechanism for dislocation removal is the thermally activated glide of dislocations to the sidewalls of patterned regions, as promoted by sidewall image forces.