Ex-situ n-type heavy doping of Ge_1-xSn_x epilayers by surface Sb deposition and pulsed laser melting

Ge_1-xSn_x alloys have attracted considerable attention for their promising electrical and optical properties. One of the main challenges for their successful implementation in devices concerns the fabrication of n-type heavily doped surface layers. In this work, a new methodology for ex-situ doping of Ge_1-xSn_x layers is investigated. It consists of the deposition of Sb atoms on the surface of Ge_1-xSn_x layers followed by pulsed laser melting (PLM) that ensures the diffusion of Sb into the alloy. We demonstrate that Sb is incorporated very efficiently within a relaxed Ge_0.91Sn_0.09 epilayer, with supersaturated 4 × 10²⁰ cm⁻³ active concentrations, in line with literature records obtained in Ge_1-xSn_x with in-situ approaches. At the same time, we observe that the concentration of substitutional Sn close to the surface decreases from 9 to about 6 at. % after PLM, inducing a contraction of the lattice parameter perpendicular to the underlying Ge_1-xSn_x. These results demonstrate a possible route for ex-situ n-type heavy doping of Ge_1-xSn_x alloys, but indicate also that Sn redistribution and precipitation phenomena need to be carefully considered for a successful process development.