Point defect-dislocation interactions in BEOL-compatible Ge-on-Si epitaxy

Reduced thermal budget is required for back-end-of-line (BEOL) integration of application specific functionality into the multilevel metal stack of a processor "substrate." We report 400 degrees C BEOL-compatible Ge-on-Si growth (LT Ge) that is epitaxial and single crystalline with a defect density similar to high temperature growth and a small 0.05% tensile strain. Room temperature methanol-iodine passivation is employed pre-growth in lieu of the typical 800 degrees C oxide removal step. Undoped LT Ge exhibits p-type conductivity initially and n-type conductivity conversion upon annealing. Hall effect measurements following post growth heat treatment between 400 and 600 degrees C reveal an acceptor removal reaction that follows first-order kinetics with an activation energy of 1.7 +/- 0.5 eV and a pre-exponential factor of 2.3 x 10(7) s(-1) consistent with a point defect, diffusion limited process. We also observe that 90 degrees sessile dislocations identified via transmission electron microscopy are annihilated in the same temperature regime, which is evidence for point defect-mediated climb. Ensuring highquality epitaxy by characterizing defect reactions in a BEOL-compatible Ge-on-Si process flow is key to enabling vertical integration of optical interconnects.