each of said pair of {TAIL ~ SiGe mixed crystal regions} including a main part formed right underneath {HEAD ~ an uppermost part} of said SiGe mixed crystal region, said main part having a sidewall surface, 
each of said pair of { TAIL ~ SiGe mixed crystal regions } including a main part formed right underneath { HEAD ~ an uppermost part } of said SiGe mixed crystal region , said main part having a sidewall surface ,
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH