IHP Ltd.

We investigate the distribution of Sn in GeSn nano-heteroepitaxial clusters deposited at temperatures well exceeding the eutectic temperature of the GeSn system. The 600 °C molecular beam epitaxy on Si-patterned substrates results in the selective growth of GeSn nano-clusters having a 1.4 ± 0.5 at% Sn content. These nano-clusters feature Sn droplets on their faceted surfaces. The subsequent deposition of a thin Ge cap layer induced the incorporation of the Sn atoms segregated on the surface in a thin layer wetting the nano-dots surface with 8 ± 0.5 at% Sn. The presence of this wetting layer is associated with a relatively strong photoluminescence emission that we attribute to the direct recombination occurring in the GeSn nano-dots outer region.

We report on the direct observation of lattice relaxation and Sn segregation of GeSn/Ge/Si heterostructures under annealing. We investigated strained and partially relaxed epi-layers with Sn content in the 5 at. %-12 at. % range. In relaxed samples, we observe a further strain relaxation followed by a sudden Sn segregation, resulting in the separation of a β-Sn phase. In pseudomorphic samples, a slower segregation process progressively leads to the accumulation of Sn at the surface only. The different behaviors are explained by the role of dislocations in the Sn diffusion process. The pos. impact of annealing on optical emission is also discussed. (c) 2018 American Institute of Physics.

The authors demonstrate a novel method for the stable and selective surface functionalization of germanium (Ge) embedded in silicon dioxide. The Ge(001) surface is functionalized using α-lipoic acid (ALA), which can potentially be used for the immobilization of a wide range of biomols. The authors present a detailed pH-dependence study to establish the effect of the incubation pH value on the adsorption layer of the ALA mols. A threshold pH value for functionalization is identified, dividing the examined pH range into two regions. Below a pH value of 7, the formation of a disordered ALA multilayer is observed, whereas a stable well-ordered ALA mono- to bi-layer on Ge(001) is achieved at higher pH values. Furthermore, the authors analyze the stability of the ALA layer under ambient conditions, revealing the most stable functionalized Ge(001) surface to effectively resist oxidation for up to one week. The authors' established functionalization method paves the way towards the successful immobilization of biomols. in future Ge-based biosensors. (c) 2018 American Institute of Physics.