Thermal Donors in Silicon: A Study with ENDOR

ENDOR experiments on paramagnetic thermal donors are presented for the first time. They show that the ESR spectra of all thermal donors identified by ir bands are superimposed in one narrow line ("$\mathrm{NL}8\mathrm{}$"). Only ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}$ superhyperfine interactions were found and determined for up to seven neighbor shells of four thermal donors. From the analysis of the data with effective-mass theory it is concluded that the thermal-donor defect most probably does not contain a central Si atom assumed in most current models. It is tentatively suggested that it is an ${\mathrm{O}}_2$ molecule.