Hexagonal germanium grown by molecular beam epitaxy on self-assisted GaAs nanowires

TL;DR

This paper reports the first successful growth of hexagonal germanium on self-assisted GaAs nanowires via molecular beam epitaxy, highlighting a defect-free, phase-controlled synthesis with arsenic incorporation.

Contribution

It introduces an Au-free method for synthesizing hexagonal germanium on GaAs nanowires, enabling phase control and high-quality crystal growth.

Findings

Achieved 500 nm hexagonal Ge segment with high structural quality

Demonstrated phase control of GaAs nanowires during growth

Observed strong arsenic incorporation in germanium

Abstract

Hexagonal group IV materials like silicon and germanium are expected to display remarkable optoelectronic properties for future development of photonic technologies. However, the fabrication of hexagonal group IV semiconductors within the vapour-liquid-solid method has been obtained using gold as a catalyst thus far. In this letter, we show the synthesis of hexagonal Ge on self-assisted GaAs nanowires using molecular beam epitaxy. With an accurate tuning of the Ga and As molecular beam flux we selected the crystal phase, cubic or hexagonal, of the GaAs NWs during the growth. A 500 nm-long hexagonal segment of Ge with high structural quality and without any visible defects is obtained, and we show that germanium keeps the crystal phase of the core using scanning transmission electron microscopy. Finally X-ray Photoelectron Spectroscopy reveals a strong incorporation of As in the Ge. This study demonstrates the first growth of hexagonal Ge in the Au-free approach, integrated on silicon substrate.