An ab initio-based approach was made to understand the influences of temperature and beam equivalent pressure (BEP) on the structural stability of GaAs surfaces. The theoretical approach incorporates free energy of vapor phase; therefore we can calculate how structural stability of GaAs surfaces depends on the temperature and beam equivalent pressure. By the theoretical investigations, temperature and BEP dependences of the stability of GaAs(001)-(4×2) β 2 were predicted. The results agree with experimental results, and feasibility of the theoretical approach was confirmed. Furthermore, the relative stability of Ga adatom among the case of that on GaAs(001)-(2×4) β 2 and (11n)A (n = 2, 3 and 4) surfaces were studied. The results imply that Ga on (113)A is the most stable amongst (001) and all (11n)A surfaces. This is because the strain around the Ga adatom on (113)A is the smallest in the systems.
