# The formation of intermediate layers in covered Ge/Si heterostructures with low-temperature quantum dots: a study using high-resolution transmission electron microscopy and Raman spectroscopy

## TL;DR

This study combines high-resolution TEM and Raman spectroscopy to analyze lattice deformations and intermixing in Ge/Si heterostructures with low-temperature quantum dots, revealing stress relaxation mechanisms and critical thickness for diffusion.

## Contribution

It introduces a combined TEM and Raman spectroscopy method to investigate stress and intermixing in Ge/Si quantum dot structures at low temperatures, identifying the critical Si coverage for diffusion.

## Key findings

- Stress does not spread in thick Si layers above quantum dots.
- Intermixing of Ge and Si is absent beneath the Ge layer at low coverage.
- Critical Si thickness for diffusion is between 5 and 8 nm.

## Abstract

The method of software analysis of high-resolution TEM images using the peak pairs algorithm in combination with Raman spectroscopy was employed to study lattice deformations in Ge/Si(001) structures with low-temperature Ge quantum dots. It was found that the stresses do not spread in a thick Si layer above quantum dots, but completely relax via the formation of a thin boundary layer of mixed composition. However, intermixing of Ge and Si is absent beneath the Ge layer in samples with a Ge coverage of 10 \r{A}. Besides intermixing was not observed at all, both beneath and above the Ge layer, in samples with a Ge coverage of 6 \r{A} or less. This may be due to the predominance of Ge diffusion into the Si matrix from the {105} facets of Ge huts, not from the Ge wetting layer, at low temperatures of the Ge/Si structure deposition. The critical thickness of Si coverage at which the intense stress-induced diffusion takes place is determined to lie in the range from 5 to 8 nm.