Hole and positron interaction with vacancies and p-type dopants in epitaxially grown silicon

The concentration of vacancies and impurities in semiconductors plays a crucial role in determining their electrical, optical, and thermal properties. This study aims to clarify the nature of the interaction between positrons and ionized p-type impurities, emphasizing the similarities they share with the interaction between holes and this type of impurity. An overall strategy for investigating defects in semiconductor crystals that exhibit a combination of vacancies and p-type impurities is presented. By using positron annihilation spectroscopy, in particular, Doppler broadening of the annihilation radiation, we quantify the concentration of vacancies in epitaxial Si crystals grown by low-energy plasma-enhanced chemical vapor deposition. The vacancy number densities that we find are (1.2 ± 1.0) × 1017 cm−3 and (3.2 ± 1.5) × 1020 cm−3 for growth rates of 0.27 and 4.9 nm/s, respectively. Subsequent extended annealing of the Si samples effectively reduces the vacancy density below the sensitivity threshold of the positron technique. Secondary ion mass spectrometry indicates that the boron doping remains unaffected during the annealing treatment intended for vacancy removal. This study provides valuable insights into the intricate interplay between vacancies and ionized impurities with positrons in semiconductor crystals. The obtained results contribute to advance the control and understanding of material properties in heterostructures by emphasizing the significance of managing vacancy and dopant concentrations.