Nucleation of Ge quantum dots on the Si(001) surface

TL;DR

This study provides the first direct observation of Ge quantum dot nucleation on Si(001), revealing different growth mechanisms for pyramidal and wedge-like clusters and suggesting the role of epinucleation in hut formation.

Contribution

It presents the first direct imaging of Ge hut cluster nucleation and details distinct growth scenarios for different cluster types on Si(001).

Findings

Different structures of nuclei for pyramidal and wedge-like clusters.

Wedge-like clusters have point defects and grow along ridges.

The {105} facet structure aligns with the PD model.

Abstract

A direct observation of nucleation of Ge hut clusters formed by ultrahigh vacuum molecular beam epitaxy is reported for the first time. The nuclei of the pyramidal and wedge-like clusters have been observed on the wetting layer blocks and found to have different structures. The growth of the clusters of both species goes on following different scenarios: Formation of the second atomic layer of the wedge-like cluster results in rearrangement of its first layer. Its ridge structure does not replicate the structure of the nucleus. The pyramidal cluster grows without phase transitions. The structure of its vertex copies the structure of the nucleus. The wedge-like clusters contain point defects on the triangular faces and have preferential directions of growth along the ridges. The derived structure of the {105} facet corresponds to the PD model. The critical epinucleation phenomenon may be responsible for hut formation.