Search

Positron annihilation measurements, supported by first-principles electron-structure calculations, identify vacancies and vacancy clusters decorated by 1-2 dopant impurities in highly Sb-doped Si. The concentration of vacancy defects increases with Sb doping and contributes significantly to the electrical compensation. Annealings at low temperatures of 400-500 K convert the defects to larger complexes where the open volume is neighbored by 2-3 Sb atoms. This behavior is attributed to the migration of vacancy-Sb pairs and demonstrates at atomic level the metastability of the material grown by epitaxy at low temperature.

Using positron annihilation measurements we observed the formation of thermal vacancies in highly As and P doped Si. The vacancies start to form at temperatures as low as 650 K and are mainly undecorated at high temperatures. Upon cooling the vacancies form stable vacancy-impurity complexes such as V-As3. We determine the vacancy formation energy of E(f)=1.1(2) eV and the migration energy of E(m)=1.2(1) eV in highly doped Si. By associating these values with the vacancy-impurity pair, we get an estimate of 2.8(3) eV for the formation energy of an isolated neutral monovacancy in intrinsic Si.

We have used positron annihilation spectroscopy to determine the nature and the concentrations of the open volume defects in as-grown and electron irradiated (E(el)=2 MeV, fluence 6 x 10(17) cm(-2)) ZnO samples. The Zn vacancies are identified at concentrations of [V(Zn)] approximately 2 x 10(15) cm(-3) in the as-grown material and [V(Zn)] approximately 2 x 10(16) cm(-3) in the irradiated ZnO. These concentrations are in very good agreement with the total acceptor density determined by temperature dependent Hall experiments. Thus, the Zn vacancies are dominant acceptors in both as-grown and irradiated ZnO.

Positron annihilation experiments have been applied to verify the formation mechanism of electrically inactive vacancy-impurity clusters in highly n-type Si. We show that the migration of V-As pairs at 450 K leads to the formation of V-As2 complexes, which in turn convert to stable V-As3 defects at 700 K. These processes manifest the formation of V-As3 as the dominant vacancy-impurity cluster in highly n-type Si. They further explain the electrical deactivation and clustering of As in epitaxial or ion-implanted Si during postgrowth heat treatment at 700 K.