Ex-situ doping and Ohmic contact formation with low contact resistance on MBE grown GeSn on Si


Ex-situ doping and Ohmic contact formation with low contact resistance on MBE grown GeSn on Si

Prucnal, S.; Augel, L.; Schulze, J.; Fischer, I. A.; Berencén, Y.; Hübner, R.; Böttger, R.; Rebohle, L.; Skorupa, W.; Wang, M.; Voelskow, M.; Helm, M.; Zhou, S.

GeSn with quasi-direct band gap is one of the most promising semiconductor materials for light emitters integrated with CMOS technology. The equilibrium solid solubility limit (SSL) of Sn in Ge is in the range of 0.5 % and the predicted theoretical Sn concentration needed for the direct band gap formation is above 5 %. This means that GeSn with direct band gap is metastable and any related material process cannot be thermal equilibrium. Here we propose to utilize strongly non-equilibrium processing i.e. ion implantation followed by millisecond range flash lamp annealing (FLA), for doping and the formation of Ohmic contacts with low contact resistance on Ge0.95Sn0.05. The effective carrier concentration in P+ implanted Ge0.95Sn0.05 layer followed by FLA for 3 ms is above 5×10^19cm-3 with a specific contact resistance rc=4×10^-6Ωcm2. NiGe for Ohmic contact is made by Ni diffusion into GeSn during a single 3 ms long flash pulse. TEM images reveal that NiGe is polycrystalline but with an atomically sharp interface between the metal contact and GeSn. The influence of non-equilibrium processing (ion implantation and FLA) on the optical, electrical and microstructural properties of the GeSn layer grown by MBE on Si will be discussed in details.

Keywords: GeSn; MBE; doping; flash lamp annealing

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Publ.-Id: 26113