Structures of the Ga-Rich4×2and4×6Reconstructions of the GaAs(001) Surface

Utilizing the advantages of migration enhanced epitaxy, a systematic molecular beam epitaxy–scanning tunneling microscopy investigation was carried out for the first time on the GaAs(001) Ga-rich $4\times 2$ and $4\times 6$ phases and a unified structural model has been proposed based on a first-principles total-energy calculation. The $4\times 2$ phase consists of two Ga dimers on the top layer and another Ga dimer at the third layer, a mirror image of the As-rich $2\times 4$ phase, and the $4\times 6$ phase accommodates the periodic array of Ga clusters at the $4\times 6$ unit corner on top of the $4\times 2$ phase.