A study of porous silicon prepared under different HF concentrations by positron annihilation

Abstract

Two-dimensional angular correlation of positron-electron annihilation radiation and positron-lifetime experiments have been performed on lightly doped porous silicons prepared under different HF concentrations. Positronium formation in the etched pores and positron trapped in voids are observed in both experiments. A surprising result is found that both positron lifetime and momentum spectra show a reduction in the size of the etched pores with decreasing HF concentration in the etching solution. This trend is different from the intuitive expectation that the pore size increases with increasing porosity. Our result can be explained in terms of the formation mechanism of porous film in lightly doped silicon.