Vacancy-Impurity Complexes in Highly Sb-Doped Si Grown by Molecular Beam Epitaxy

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. DOI: 10.1103/PhysRevLett.94.165501 PACS numbers: 61.72.-y, 61.82.Fk, 78.70.Bj The interest in highly doped Si is fundamentally related to the miniaturization of field-effect transistors, where increased doping is needed to maintain a sufficient conductance of the source and drain regions The molecular beam epitaxy (MBE) growth at low temperature ( < 600 K) can be applied to achieve metastable doping and free electron concentrations, which become compensated only at 10 21 cm ÿ3 In this work we apply positron annihilation spectroscopy to study vacancies formed in the low-temperature MBE growth of highly Sb-doped Si. Positrons get trapped at open-volume defects. The measured annihilation photons carry information on the electron momentum density, which can be utilized to identify the size of the open volume of the defect and the neighboring dopant atoms. Our results show that the MBE growth creates vacancies and vacancy clusters, which are neighbored by 1-2 Sb atoms. The vacancy concentrations are relevant for the compensation of the Sb doping. We also show that the low-temperature MBE Si is atomically metastable, and annealings at low temperatures of 400 -500 K lead to clustering of vacancies and dopant impurities. We studied Si(100) layers grown by MBE on the Si substrate at 550 K We used a low-energy positron beam to measure the Doppler broadened energy spectrum of the annihilation radiation. The shape of the spectrum was described with conventional S and W parameter