b) forming a composite layer comprising one or more non extractable insulation materials selected from the group consisting of {HEAD ~ an oxide} of {TAIL ~ 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 
of
b ) forming a composite layer comprising one or more non extractable insulation materials selected from the group consisting of { HEAD ~ an oxide } of { TAIL ~ 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 OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL 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