b) forming a composite layer comprising {HEAD ~ one or more non extractable insulation materials} selected from {TAIL ~ the group} consisting of an oxide of silicon, silicon nitride, aluminum oxide, an organic polymer, and mixtures of same and one or more extractable materials selected from the group consisting of germanium oxide, germanium sulfide, and silicon sulfide 
selected from
b ) forming a composite layer comprising { HEAD ~ one or more non extractable insulation materials } selected from { TAIL ~ the group } consisting of an oxide of silicon , silicon nitride , aluminum oxide , an organic polymer , and mixtures of same and one or more extractable materials selected from the group consisting of germanium oxide , germanium sulfide , and silicon sulfide
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH