Electrical properties of extended defects in strain relaxed GeSn

Abstract

We report the electrical properties of 60° dislocations originating from the +1.2% lattice mismatch between an unintentionally doped, 315 nm thick Ge0.922Sn0.078 layer (58% relaxed) and the underlying Ge substrate, using deep level transient spectroscopy. The 60° dislocations are found to be split into Shockley partials, binding a stacking fault. The dislocations exhibit a band-like distribution of electronic states in the bandgap, with the highest occupied defect state at ∼EV + 0.15 eV, indicating no interaction with point defects in the dislocation's strain field. A small capture cross-section of 1.5 × 10−19 cm2 with a capture barrier of 60 meV is observed, indicating a donor-like nature of the defect-states. Thus, these dislocation-states are not the source of unintentional p-type doping in the Ge0.922Sn0.078 layer. Importantly, we show that the resolved 60° dislocation-states act as a source of leakage current by thermally generating minority electrons via the Shockley-Read-Hall mechanism.