Current leakage mechanisms related to threading dislocations in Ge-rich SiGe heterostructures grown on Si(001)

This work investigates the role of threading dislocation densities (TDD) in the low density regime on the vertical transport in Si_0.06Ge_0.94 heterostructures integrated on Si(001). The use of unintentionally doped Si_0.06Ge_0.94 layers enables the study of the impact of grown-in threading dislocations (TD) without interaction with processing-induced defects originating, e.g., from dopant implantation. The studied heterolayers, while equal in composition, the degree of strain relaxation, and the thickness feature three different values for the TDD as 3 × 10⁶, 9 × 10⁶, and 2 × 10⁷ cm⁻². Current–voltage measurements reveal that leakage currents do not scale linearly with TDD. The temperature dependence of the leakage currents suggests a strong contribution of field-enhanced carrier generation to the current transport with the trap-assisted tunneling via TD-induced defect states identified as the dominant transport mechanism at room temperature. At lower temperatures and at high electric fields, direct band-to-band tunneling without direct interactions with defect levels becomes the dominating type of transport. Leakage currents related to emission from mid-gap traps by the Shockley–Read–Hall (SRH) generation are observed at higher temperatures (>100 °C). Here, we see a reduced contribution coming from SRH in our material, featuring the minimal TDD (3 × 10⁶ cm⁻²), which we attribute to a reduction in point defect clusters trapped in the TD strain fields.