Thermal desorption spectra from cavities in helium-implanted silicon

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 alpha peak, centered on a temperature of 750-800 degrees C with a shoulder extending to lower temperature (down to 550 degrees C), and the beta peak, centered on a lower temperature depending on the implantation-annealing conditions. The alpha peak is attributed to the emission from cavities, while the 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 alpha peaks. The postimplantation of hydrogen into samples displaying a pure beta emission results in an 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.