The GaAs(111)B surface has recently received much attention because of its advantage in fabricating various nanostructures, such as nano-dots and nano-wires, by using molecular-beam epitaxy (MBE) and metal-organic vapor-phase epitaxy. This also demands the detailed understanding of the crystal growth processes on GaAs(111)B surface. Although many experimental and theoretical studies have shown that 2×2 reconstruction with As trimer appears around usual growth temperature of the MBE (300-450 °C), [1] the growth processes has remained far less examined. Here, we investigate the initial growth processes on GaAs(111)B-2×2 surface by using the total-energy electronic-structure calculation based on density-functional theory. In particular, the desorption behavior of As trimer, which is necessary to maintain the layer-by-layer growth, are discussed based on the surface phase diagram obtained by comparing the calculated desorption energy and As2 chemical potential estimated by quantum statistical approach. [2] The calculations demonstrate that Ga atoms are absorbed near the As-trimer with the energy gain of ~2.0 eV, indicating the plausibility of Ga absorbed GaAs(111)B-2×2 surface. Furthermore, the calculated surface phase diagram as functions of temperature and As pressure shows that the desorption of As trimer occurs beyond ~350 °C in the Ga absorbed surface whereas the desorption without Ga adatom does beyond ~530 °C. This result implies that the growth promoted by Ga absorption becomes prominent around ~350 °C, qualitatively consistent with the growth temperature in the MBE. [1] The analysis of calculated energy reveals that the enhancement of As-trimer desorption by Ga atoms is due to the decrease in the desorption energy of As trimer with increasing Ga coverage, exhibiting self-surfactant effect as seen in GaAs(001) surface. [3] These results thus suggest that Ga atoms crucially affects the growth processes on GaAs(111)B surface.
References: [1] A. Ohtake et al., Phys. Rev. B 64, 45318 (2001).[2] Y. Kangawa et al., Surf. Sci. 493, 178 (2001).[3] K. Shiraishi and T. Ito, Phys Rev. B 57, 6301 (1998). |