Molecular dynamics study of dimer formation on GaAs (001) surface at low temperatures

The simulation of dimers formation during the low-temperature reconstruction of GaAs (001) surface terminated with Ga or As atoms was performed by the molecular dynamics method using the analytical Bond-Order Potential based on quantum mechanical theory incorporating both $\sigma$- and $\pi$- bonds between atoms. A decrease in values of potential energy of the atoms during formation of isolated surface dimer have been determined. It has been found that potential energy of an atom in As-dimer is several tenths of an eV lower than in Ga-dimer. Kinetics of the initial stages of Ga-dimers formation in the temperature range of 25–40 K was studied. It was found that the characteristic thermal activation energy of single isolated Ga-dimers formation is $\sim$29 meV, which is lower than the same value for As-dimers ($\sim$ 38 meV). Time constants characterizing the average rate of transformation of one dimer into a chain of two dimers at temperature range of 28–37 K were estimated. Inverse values of these parameters for paired Ga- and As-dimers are in the ranges of 10$^{11}$–10$^{12}$ s$^{-1}$ and 10$^9$–10$^{10}$ s$^{-1}$, respectively, while corresponding parameters for the formation of single dimers are in the ranges of 4$\times$10$^6$–10$^8$ s$^{-1}$ and 1.4$\times$10$^6$–7.4$\times$10$^7$ s$^{-1}$.