Nanovoids in MBE-grown SiGe alloys implanted in situ with Ge⁺ ions

Spherically shaped voids, of nanometer size, are observed in molecular-beam epitaxially grown SiGe alloy layers implanted in-situ at elevated temperature with low-energy Ge ions, followed by thermal treatments. The voids are exclusively assembled in the narrow, implanted band. The voids only appear in the layers after a heat treatment at a temperature higher than 700 °C, and they are stable up to 900 °C. Arsenic ion implantation at similar conditions does not give rise to void formation but to regular interstitial dislocation loops. The nucleation stage of the voids is accompanied by a strong photoluminescence-yield enhancement in the range of 1.4–1.55 μm, originating from the strained SiGe alloy layer which contain vacancy clusters or small voids.