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 deg. C, and they are stable up to 900 deg. 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