THE DIFFERENCE BETWEEN THE SURFACE RECONSTRUCTIONS OF AlAs(001) AND GaAs(001)

Abstract

AlAs(001) is compared with GaAs(001) by ab initio pseudopotential total energy calculation. The results show that either similarities or differences in the stability of the surface reconstructions are obvious. On the Al-rich AlAs surface the reconstruction (2×1)/c (2×2) has an obvious energetic advantage. In this reconstruction the topmost Al atoms abnormally locate below the As atomic layer. Besides, on the As-rich GaAs surface a metastable reconstruction phase of γ(2×4) appears if the surface coverage of As atoms is less than 1, while on the AlAs surface it is fully dimerized (2×1) phase more stable. In addition the thermodynamical analysis also indicates that in the mid-temperature range of MBE growth (e.g. 600°C with As 2 pressure of 2 × 10-6 τ) this (2×1) phase is stable. Further calculations show that 0.2–1 monolayer of Ga atoms deposited on AlAs surface will result in γ(2×4) phase rather than (2×1) phase, while the deposited Ga atoms on the AlAs surface do not go below the topmost As atomic layer. The plausible conclusion is that formation of (2×1) phase on As-rich AlAs surface and the inner location of Al atoms on Al-rich (2×1)/c(2×2) reconstruction surface could be closely related to the obviously different modes of MBE growth on AlAs and GaAs surface, in the mid-temperature range.