The difference between the surface reconstructions of AlAs(001) and GaAs(001)

AlAs(001) is compared with GaAs(001) by ab initio pseudopotential total ene rgy calculation. The results show that either similarities or differences i n the stability of the surface reconstructions are obvious. On the Al-rich AlAs surface the reconstruction (2 x l)/c(2 x 2) has an obvious energetic a dvantage. In this reconstruction the topmost Al atoms abnormally locate bel ow the As atomic layer. Besides, on the As-rich GaAs surface a metastable r econstruction phase of gamma(2 x 4) appears if the surface coverage of As a toms is less than 1, while on the AlAs surface it is fully dimerized (2 x 1 ) phase more stable. In addition the thermodynamical analysis also indicate s that in the mid-temperature range of MBE growth (e.g. 600 degrees C with As-2 pressure of 2 x 10(-6) tau) this (2 x 1) phase is stable. Further calc ulations show that 0.2-1 monolayer of Ga atoms deposited on AlAs surface wi ll result in gamma(2 x 4) phase rather than (2 x 1) phase, while the deposi ted Ga atoms on the AlAs surface do not go below the topmost As atomic laye r. The plausible conclusion is that formation of (2 x 1) phase on As-rich A lAs surface and the inner location of Al atoms on Al-rich (2 x 1)/c(2 x 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.