We have studied strain-relaxation processes in InAs heteroepitaxy on $\mathrm{GaAs}\left(111\right)A$ using rocking-curve analysis of reflection high-energy electron diffraction. Strain relaxation in the direction parallel to the surface occurs at $\sim 1.5$ bilayers (BL) thickness. On the other hand, the lattice constant in the direction normal to the surface remains almost unchanged below $\sim 3$ BL thickness and is estimated to be $\sim 3.3Å$. This value, slightly larger than that of bulk GaAs (3.26 Å), does not quite reach the value predicted by classical elastic theory, 3.64 Å. The present result has been supported by the first-principles total-energy calculations.

• Received 22 October 1999

DOI:https://doi.org/10.1103/PhysRevLett.84.4665