Damage accumulation during ion implantation of unstrained Si1−xGex alloy layers

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Abstract
The growth of damage induced by ion implantation in unstrained Si1−xGex epilayers is examined as a function of epilayer composition and of implant temperature and dose rate. Relaxed, epitaxial layers having compositions x=0.15, 0.50, and 0.80 were implanted with 30Si+ ions at energies of 80–90 keV, doses of 1 and 6×1014/cm2, and temperatures between −100 and +140 °C. Damage in the implanted layers was measured by ion channeling at room temperature (RT). For RT implantation, the amount of ion‐induced damage increased with Ge fraction x at a rate much greater than expected from calculations of the displacement rate. In addition, the damage growth was suppressed in each of these alloys as the implantation temperature was increased such that over a range of ion doses, the damage yield approached zero at a temperature, T0, which increased with the Ge fraction, x. Furthermore, the damage was found to become strongly dependent on the dose rate at elevated implantation temperatures near T0. Based upon comparisons to a simple model, these observations suggest that increasing the Ge fraction progressively reduces the mobilities of primary defects within the collision cascades.