Molecular beam epitaxy and defect structure of Ge (111)/epi-Gd2O3 (111) /Si (111) heterostructures

TL;DR

This study reports on the epitaxial growth, defect analysis, and potential applications of Ge (111) films on Gd2O3/Si(111) substrates, highlighting defect formation, structural characteristics, and improved photodiode performance.

Contribution

It provides a systematic investigation of Ge growth modes, defect structures, and the impact of Gd2O3 layers on device performance in Ge-on-insulator heterostructures.

Findings

Ge growth begins in Volmer-Weber mode and coalesces within 10 nm

Formation of microtwins constitutes less than 1% volume fraction

Significant dark current suppression in GeOI photodiodes due to Gd2O3 layer

Abstract

Molecular beam epitaxy of Ge (111) thin films on epitaxial-Gd2O3/Si(111) substrates is reported, along with a systematic investigation of the evolution of Ge growth, and structural defects in the grown epilayer. While Ge growth begins in the Volmer-Weber growth mode, the resultant islands coalesce within the first 10 nm of growth, beyond which a smooth two-dimensional surface evolves. Coalescence of the initially formed islands results in formation of rotation and reflection microtwins, which constitute a volume fraction of less than 1 %. It is also observed that while the stacking sequence of the (111) planes in the Ge epilayer is similar to that of the Si substrate, the (111) planes of the Gd2O3 epilayer are rotated by 180 degree about the [111] direction. In metal-semiconductor-metal schottky photodiodes fabricated with these all-epitaxial Ge-on-insulator (GeOI) samples, significant suppression of dark current is observed due to the presence of the Gd2O3 epilayer. These results are promising for application of these GeOI structures as virtual substrates, or for realization of high-speed group-IV photonic components.