Interface structure and growth mode of quantum wire and quantum dot GaAs-AlAs structures on corrugated (311)A surfaces

GaAs-AlAs corrugated superlattices (CSL) are formed on spontaneously nanofa ceted (311)A surfaces. Using high-resolution transmission electron microsco py (HRTEM) along the [(2) over bar 33] zone axis with an appropriate image evaluation technique to enhance the contrast between GaAs and AlAs we found two distinct lateral periodicities along the [0(1) over bar1] directions f or two different CSL layer thickness regimes. For multilayer deposition wit h GaAs layer thickness exceeding 1 nm the lateral periodicity of 3.2 nm is clearly revealed. The contrast originates from the thickness modulation of both AlAs and GaAs layers with a period of 3.2 nM in the [0(1) over bar1] d irection. The corrugation height is about 1 nm and it is symmetric for both upper and lower GaAs-AlAs interfaces. Thicker sections of the thickness-mo dulated AlAs and GaAs layers of the CSL are shifted by a half period with r espect to each other. In the regime when the GaAs deposited average thickne ss is below 1 nm, which is necessary for complete coverage of the AlAs surf ace, a lateral periodicity of similar to1.5-2 nm is additionally revealed. We attribute this effect to the formation of local GaAs clusters dispersed on a corrugated (311)A AlAs surface resulting in a local phase reversal of the AlAs surface in their vicinity upon subsequent overgrowth. This reversa l can be explained by the same effect as the phase shift, of the surface co rrugation upon heteroepitaxy on (311)A. In our model AlAs does not wet the GaAs cluster surface, unless different more energetically favorable scenari o is possible. This causes accumulation of AlAs in the vicinity of the GaAs cluster and, as a result, the local phase reversal of the AlAs surface. Th e AlAs corrugated surface domains with different phases coexist on the surf ace resulting in an additional periodicity revealed in the HREM contrast mo dulation. Additionally HRTEM studies indicate that the AlAs-GaAs interface inclination angles in both regimes are 40 degrees and 140 degrees with resp ect to the flat(311) surface in an agreement with the {331} facet geometry model proposed by R. Notzel, N.N. Ledentsov, L. Daweritz, M. Hohenstein, an d K. Ploog [Phys. Rev. Lett. 67, 1812 (1991)].