Surface reconstruction induced by a pulsed low-energy ion beam during Si(111) molecular beam epitaxy

Abstract

The morphology and reconstruction of a vicinal Si(111) surface during Si molecular beam epitaxy (MBE) by reflection high-energy electron diffraction (RHEED) was investigated in conjunction with pulsed actions (0.25–1s) by low-energy (80–150eV) Kr+ ions in the dose range of 1011–1012cm−2. Ion pulsed action was found to increase RHEED specular beam intensity corresponding to the improvement of surface smoothness during MBE growth. The maximum intensity enhancement was found if the pulsed ion beam is turned on at a fractional surface coverage of θ≈0.8 and the substrate temperature ca 400°C. It was revealed that ion beam pulsed action induces (5×5) to (7×7) superstructure phase transition. As the substrate temperature increases, the area of (7×7) reconstruction induced by ion beam action was found to expand, and reached a maximum at 400°C. Above this temperature the (7×7) reconstruction area tends to the value of common Si MBE without ion beam action. We present a simulation model of MBE growth, which includes surface reconstruction under low-energy pulsed ion beam action. It is suggested that the ion beam induced (5×5)⇒(7×7) superstructure phase transition allows a decrease in the activation energy of adatom diffusion and improves the surface smoothness at Si MBE. The modeling results are in good agreement with the main experimental data at a different surface coverage, with the temperature of the substrate being the same for both single- and multi-pulsed ion beam actions.