Impact of growth conditions on vacancy-type defects in silicon–germanium structures grown by molecular-beam epitaxy

Silicon–germanium layers of either 200nm or 250nm have been grown via molecular-beam epitaxy (MBE) on p-type (001) silicon substrates. Each sample was prepared using a unique combination of buffer-layer type, buffer-layer growth temperature, and layer Ge content. Vacancy-type defects have been identified using beam-based positron annihilation. These results, combined with those from previous work, indicate the size and concentration of defects in MBE grown SiGe layers depend strongly upon the buffer-layer growth temperature (T). For T>500°C vacancy point defect concentrations are below the detectable limit of the measurement. As T is decreased to 300°C, vacancy clusters form in the buffer layer and point defects appear in the SiGe film, even for a SiGe growth temperature of 500°C.