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Scanning tunneling microscopy has been used to study the transition in surface structure between the As-terminated 2ϫ4 and c͑4ϫ4͒ reconstructions on both GaAs͑001͒ and InAs͑001͒, as a function of surface temperature under an As 2 flux. For both materials, two-phase surface reconstructions exist through the transition regime. On GaAs, the two-phase surface consists of disordered ͑2ϫ4͒-like structures plus a c͑4ϫ4͒-like phase terminating one monolayer below the 2ϫ4 surface. On InAs, a disordered asymmetric 1ϫ3 phase occurs ͕a͑1ϫ3͖͒ in addition to the main phases, one monolayer below each main phase. In both cases, simple addition of As via As-on-As chemisorption cannot account for the formation of the c͑4ϫ4͒ reconstruction from the 2ϫ4 surface. The c͑4ϫ4͒ phase is inherently multilayered, which explains how the structure can form without the addition or removal of the group III component and still maintain its layering registry with the residual 2ϫ4 or a͑1ϫ3͒ phase. One result of this formation process is the necessary intermixing of group III and group V species in the second layer of the c͑4ϫ4͒ reconstruction. Direct evidence of species intermixing on the top layer of the InAs͑001͒-a͑1ϫ3͒ structure is also shown and models for all of these reconstructions are proposed.

The effects of GaAs overgrowth on the structural properties of large low-growth-rate InAs quantum dots (LGR-QDs) grown on GaAs(001) are examined using in situ scanning tunneling microscopy. Strongly anisotropic surface diffusion produces a characteristic valley-ridge structure above the LGR-QDs and the surface is not planarized even after a cap thickness >400 Å. The evolution of surface morphology proceeds very differently to the case of smaller conventional growth rate QDs capped under the same conditions, due to the different initial strain states of the QDs.

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