Diffusion and trapping of positrons in Si-doped GaAs

The diffusion trapping model has been applied to understand the mechanism of slow positron annihilation in Si-doped compound semiconductors. The positron diffusion at the surface has been treated in terms of one dimensional diffusion equation. The trapping of positron has been considered in Ga monovacancies and negative ion vacancies. The Doppler broadening line shape parameter (S-parameter) and positron mean lifetime in Si-doped GaAs is calculated as a function of temperature for the temperature range 20–290 K. The calculated results have been compared with the available experimental data (T. Laine, K. Saarinen, J. Makinen, P. Hautojarvi, Phys. Rev. B 62, (2000) 8058). The theoretical results show a good agreement with the experimental curve. The S-parameter vs temperature curve shows that the S-parameter is nearly constant up to 100 K and then starts increasing and gets saturated at 200 K. This has been found to be due to the increase in the monovacancy concentration.