Reflection high-energy electron diffraction/scanning tunneling microscopy study of InAs growth on the three low index orientations of GaAs: Two-dimensional versus three-dimensional growth and strain relaxation

It is generally believed that strain relaxation in semiconductor heterostructures having a significant misfit (>2%) occurs by the formation of coherent three-dimensional islands, following the growth of one or two continuous two-dimensional monolayers in a manifestation of the Stranski–Krastanov (SK) growth mode. For the InAs–GaAs system, for which the misfit is ≈7.2%, we have shown that this is a very special case, at least during growth by molecular beam epitaxy, as it occurs on only one of the low index orientations, the (001), and then only under As-rich growth conditions. On (110) and (111) surfaces, growth is always two-dimensional layer by layer and strain is relieved by the formation of misfit dislocations. Even when three-dimensional islands are formed on (001) substrates, the process is much more complex than the conventional SK mechanism would imply. We have used a combination of in situ reflection high-energy electron diffraction (RHEED) and scanning tunneling microscopy (STM) and ex situ tran...