A multi-layer film 10 is formed by stacking a Si.sub.1-x1-y1 Ge.sub.x1
C.sub.y1 layer (0.ltoreq.x1<1 and 0y2) having a high Ge mole
fraction, e.g., a Si.sub.0.2 Ge.sub.0.8 layer 12. In this manner, the
range in which the multi-layer film serves as a SiGeC layer with C atoms
incorporated into lattice sites extends to high degrees in which a Ge mole
fraction is high.
