Search for thermally generated monovacancies in silicon using monoenergetic positrons

Using a monoenergetic, variable-energy positron beam, measurements of Doppler broadening and positronium fraction for positron-annihilation radiation from high-resistivity silicon have been made up to the melting point. The measurements show no clear evidence of positron trapping into thermally generated monovacancies which Dannefaer, Mascher, and Kerr observed by measuring the lifetimes of positrons emitted by an in situ source. A lower limit of about 3.6 eV is placed on the formation enthalpy of a neutral monovacancy, subject to assumptions about positron-trapping rate, binding energy, and monovacancy formation entropy.