The slow positron beam was used to study the defects in the MBE(molecular beam epitaxial) Si. The relations between the quality of the MBE Si and the growth temperature as well as the thickness were discussed. It is concluded that the optimum growth temperature for several-hundred-nanometer MBE Si is about 500℃; and if the temperature is too high (about 700℃ )
the enhanced diffusion of antimony will greatly effect the property of the Si material.