Thermal desorption spectra from cavities in helium-implanted silicon

Abstract

Thermal desorption spectra at constant ramp rate have been determined after helium implantation into bare silicon prepared for a large set of experimental conditions. The spectra can phenomenologically be classified as composed by two peaks: the $\ensuremath{\alpha}$ peak, centered on a temperature of $750--800\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ with a shoulder extending to lower temperature (down to $550\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}),$ and the $\ensuremath{\beta}$ peak, centered on a lower temperature depending on the implantation-annealing conditions. The $\ensuremath{\alpha}$ peak is attributed to the emission from cavities, while the $\ensuremath{\beta}$ peak is attributed to the emission from vacancylike defects. A detailed theory describing helium effusion from stable cavities as controlled by the interatomic helium-helium potential is proposed and found to reproduce accurately most of the $\ensuremath{\alpha}$ peaks. The postimplantation of hydrogen into samples displaying a pure $\ensuremath{\beta}$ emission results in an $\ensuremath{\alpha}$ peak which can be described by the same model as above provided that the cavities are unstable and shrink during desorption in such a way as to maintain constant the concentration of contained helium.