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Positron annihilation spectroscopy in the Doppler and coincidence Doppler mode was applied on Ge 1 − x Sn x epitaxial layers, grown by chemical vapor deposition with different total As concentrations (∼ 10 19 – 10 21 cm − 3 ), high active As concentrations (∼ 10 19 cm − 3 ), and similar Sn concentrations (5.9%–6.4%). Positron traps are identified as mono-vacancy complexes. Vacancy-As complexes, V-As i , formed during the growth were studied to deepen the understanding of the electrical passivation of the Ge 1 − x Sn x :As epilayers. Larger mono-vacancy complexes, V-As i (i ≥ 2), are formed as the As doping increases. The total As concentration shows a significant impact on the saturation of the number of As atoms (i = 4) around the vacancies in the sample epilayers. The presence of V-As i complexes decreases the dopant activation in the Ge 1 − x Sn x :As epilayers. Furthermore, the presence of Sn failed to hinder the formation of larger V-As i complexes and thus failed to reduce the donor-deactivation. [ABSTRACT FROM AUTHOR]

We examined the vacancy trapping proficiency of Sn and P atoms in germanium using positron annihilation spectroscopy measurements, sensitive to the open-volume defects. Epitaxial Ge 1 − x Sn x films were grown by chemical vapor deposition with different P concentrations in the ∼ 3.0 × 10 19 – 1.5 × 10 20 cm − 3 range. We corroborate our findings with first principles simulations. Codoping of Ge with a Sn concentration of up to 9% is not an efficient method to suppress the free vacancy concentration and the formation of larger phosphorus–vacancy complexes. Experimental results confirm an increase in the number of P atoms around the monovacancy with P-doping, leading to dopant deactivation in epitaxial germanium–tin layers with similar Sn content. Vice versa, no impact on the improvement of maximum achieved P activation in Ge with increasing Sn-doping has been observed. Theoretical calculations also confirm that P n -V (vacancy) complexes are energetically more stable than the corresponding Sn m P n -V and Sn m -V defect structures with the same number of alien atoms (Sn or P) around the monovacancy. The strong attraction of vacancies to the phosphorus atoms remains the dominant dopant deactivation mechanism in Ge as well as in Ge 1 − x Sn x. [ABSTRACT FROM AUTHOR]