Nucleation of Ge clusters at high temperatures on Ge/Si(001) wetting layer

TL;DR

This study investigates how Ge clusters nucleate at high temperatures on Ge/Si(001) surfaces, revealing two distinct processes: pyramid formation via structured precursors and faceting of Ge heaps, unique to high-temperature conditions.

Contribution

It uncovers two nucleation mechanisms of Ge clusters at high temperatures, including a process not observed at low temperatures, enhancing understanding of temperature-dependent nucleation behaviors.

Findings

Pyramids nucleate via structured precursors on wetting layers.

Faceting of Ge heaps occurs only at high temperatures.

Two distinct nucleation pathways are identified.

Abstract

Difference in nucleation of Ge quantum dots during Ge deposition at low (< 600C) and high (> 600C) temperatures on the Si(001) surface is studied by high resolution scanning tunneling microscopy. Two process resulting in appearance of {105}-faceted clusters on the Ge wetting layer have been observed at high temperatures: Pyramids have been observed to nucleate via the previously described formation of strictly determined structures, resembling blossoms, composed by 16 dimers grouped in pairs and chains of 4 dimes on tops of the wetting layer M x N patches, each on top of a separate single patch, just like it goes on at low temperatures; an alternative process consists in faceting of shapeless heaps of excess Ge atoms which arise in the vicinity of strong sinks of adatoms, such as pits or steps. The latter process has never been observed at low temperatures; it is typical only for the high-temperature deposition mode.