Atomic structure of the (4 × 3) reconstructed InGaAs monolayer on GaAs(0 0 1)

We investigated the atomic structure of a surface layer forming at about 2/3 of a monolayer of InAs deposited on the GaAs(0 0 1)-c(4 × 4) surface using in situ scanning tunneling microscopy. The samples were grown by molecular beam epitaxy under arsenic-rich growth conditions at a temperature of about 450 °C. We found a surface layer terminated by three arsenic top dimers oriented along the [1 1 0] direction-similar to the arsenic dimers of the GaAs(0 0 1)-c(4 × 4) reconstruction-with additional two arsenic dimers oriented in a trench along the [1¯10] direction, all together forming a (4 × 3) surface unit cell. The (4 × 3) surface unit cells are arranged in-line as well as in a brick-lined alignment, then forming a c(4 × 6) reconstruction. The periodicity offset between both reconstructions along the [1¯10] direction is locally interrupted by an η(6 × 3) surface unit cell, composed of two pseudo-(3 × 3) unit cells beneath each other, each exhibiting only two top dimers and both together sharing three trench dimers. Rarely, also single η(2 × 3) surface unit cells were observed, characterized by only one top dimer and one trench dimer. The (4 × 3) surface unit cell consists of eight indium atoms, located at the end of the backbonds of the two arsenic trench dimers, and of four gallium atoms underneath the top dimer rows. Thus, for this layer an In2/3Ga1/3 stoichiometry results. Occasionally, also single hetero-dimers are found, containing one arsenic and one group-III atom. The observed structural arrangement is further supported by previous density functional theory calculations of this surface. The occasional breaking of the periodicity along the [1¯10] direction also explains the often reported (1 × 3) patterns observed in reflection high-energy electron diffraction.