Growth temperature dependence for the formation of vacancy clusters in Si/Si0.64Ge0.36/Si structures

The incorporation of vacancy clusters and vacancy point defects during the growth of Si/Si0.64Ge0.36/Si structures has been observed for growth temperatures between 250 °C and 550 °C using positron annihilation spectroscopy. A strong correlation between the electrical characteristics of the structures and the size and concentration of the clusters is observed. For the onset of two-dimensional hole gas behavior, a defect concentration less than 5×1016 cm−3 is required. A further reduction in concentration below 1×1016 cm−3 results in optimum electrical performance. The depth at which defects are observed increases with decreasing growth temperature indicating defect mobility during growth or subsequent annealing.