Current-Confined Formation of a Buried Ge/Si Free Surface for Defect Filtering

Abstract

Lattice-mismatched heteroepitaxy is limited by misfit dislocations, threading defects, and residual strain generated at buried interfaces. Here, we show that current-confined electrochemistry transforms the Ge/Si heterointerface into a laterally continuous nanometric free surface while preserving the Ge epilayer. A low-doped Ge layer on a conductive p-type Si substrate redirects anodization current toward the misfit-dislocation-rich interface. Numerical modelling including charge-transfer kinetics shows that this confinement arises from hole-limited charge transfer and, together with electrochemical calibration, defines a process window that combines interfacial current confinement with controlled Si porosification. STEM reveals an approximately 15 Ang separation, while EDX shows localized interfacial oxygen enrichment. After soft annealing, geometric phase analysis and plan-view TEM show a modified strain-relaxation pathway and strongly suppressed threading-dislocation emergence. Raman spectroscopy indicates a reduction in residual tensile strain from approximately 0.10 % to 0.05 %, whereas spreading resistance profiling confirms preservation of the Ge carrier profile. Current-confined electrochemistry therefore provides a controllable post-epitaxial route for buried-interface decoupling, defect filtering, and strain control in lattice-mismatched semiconductor heterostructures.