For example, when providing an upper silicon layer 22 having a thickness of about 900 .ANG., buried amorphous region 28 can be formed toextend from a distance D.sub.1 of about 100 .ANG. from the upper surface of the upper silicon layer 22 down to a distance D.sub.2 of about 800 .ANG. from the upper surface of the upper silicon layer 22.Subsequently, a metal, such as Co, is deposited and heating is