Dislocations influence the background hole densities in Ge/Si virtual substrates

Abstract

In this study, the interaction between extended defects and the electrical activity of Ge/Si (001) plastically relaxed epitaxial layers is examined. We used depth-resolved electrochemical capacitance–voltage profiling to measure the background active carrier concentration in a set of epilayers featuring a threading dislocation density spanning more than four orders of magnitude (from 7 × 106 to 2.5 × 1010 cm−2). The depth profile of the carrier concentration shows a pronounced peak, which is attributed to the presence of misfit dislocations at the Ge/Si heterointerface; and a nearly constant p-type background extending throughout the Ge layer. This background level decreases with increased crystalline quality, and saturates at ∼1 × 1015 cm−3 when the dislocation density falls below ∼1 × 108 cm−2, indicating a lower limit governed by electrically active defect states and impurity-related point defect complexes formed during epitaxial growth and thermal processing. These findings suggest that extended and point defects critically influence the unintentional doping observed in Ge on Si epitaxy. Understanding their interplay provides valuable insights into defect engineering strategies that can suppress electrically active defects, enabling the fabrication of high-performance Ge-based electronic and photonic devices with improved doping control and more predictable electrical behavior.