Self-assembly of germanium islands under pulsed irradiation by a low-energy ion beam during heteroepitaxy of Ge/Si(100) structures

Abstract

The effect of pulsed irradiation by a low-energy (50-250 eV) ion beam with a pulse duration of 0.5 s on the nucleation and growth of three-dimensional germanium islands during molecular-beam heteroepitaxy of Ge/Si(100) structures is investigated experimentally. It is revealed that, at specific values of the integrated ion flux (less than 10 12 cm -2 ), pulsed ion irradiation leads to an increase in the density of islands and a decrease in their mean size and size dispersion as compared to those obtained in the case of heteroepitaxy without ion irra- diation. The observed phenomena are explained in the framework of the proposed model based on the concept of a change in the diffusion mobility of adatoms due to the instantaneous generation of interstitial atoms and vacancies under pulsed ion irradiation. It is assumed that the vacancies and interstitial atoms give rise to an addi- tional surface strain responsible for the change in the binding energy of the adatoms. Under certain conditions, these processes bring about the formation of centers of preferential nucleation of three-dimensional islands at the places where the ions impinge on the surface. The model accounts for the possibility of annihilating vacan- cies and interstitial atoms on the surface of the growing layer. It is demonstrated that the results obtained from the Monte Carlo calculations based on the proposed model are in good agreement with the experimental data.