Point defects in proton-irradiated highly Ga- and B-doped Ge

In this study, point defects in highly Ga- and B-doped Ge bulk crystalline samples were investigated using Positron Annihilation Lifetime Spectroscopy. The samples were irradiated with 6 MeV protons at room temperature up to a fluence of 3×1014cm−2 in order to produce vacancy-type defects along the ion track. Initially after irradiation, vacancy-dopant complexes are observed in all samples. However, measurements performed a year after irradiation suggest evolution of the defects, indicating a low binding energy between the vacancy and the dopants. An increase in the size of the vacancy-type defects is observed with increasing dopant concentration in the 5×1017-, 1×1018-, and 1×1019cm−3-doped samples. Interestingly, the defect lifetime component for the 1×1020cm−3 Ga-doped sample is significantly lower than in the less-doped samples, which is concluded to be a result of a high concentration of negative ions complicating decomposition of the spectra. Temperature-dependent measurements show evidence in support of this conclusion, while also observing an abnormal positron annihilation state characterized by a lifetime below that in defect-free bulk.