Epitaxial growth of Ge nanoislands on Si/Ge heterostructure by ion-assisted MBE method

The ion-assisted molecular beam epitaxy (MBE) method allows for construction of self-assembling quantum dot structures in a controllable manner. In the present work we have clearly observed the dependence of the formation behaviour of Ge nanoislands on the ion energy during ion-assisted MBE deposition of Ge on a silicon substrate. In our experiment, we have employed the partial ionization of the Ge atom flow, with the following acceleration of the ions to the desired energy. The best quantum dot structure (the smallest size and the densest population of the nanoislands) has been achieved at the ion energy of 1 keV. We suggest a theoretical model, which describes the process of ion-assisted formation of Ge nanoislands on the surface. In order to estimate the effect of radiation damage on the process of nanoisland formation we performed computer simulation of the cascades in the binary collision approximation and by means of molecular dynamics technique.