b) forming a composite layer comprising one or more non extractable insulation materials selected from 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 {HEAD ~ the group} consisting of germanium oxide, {TAIL ~ germanium sulfide}, and silicon sulfide 
b ) forming a composite layer comprising one or more non extractable insulation materials selected from 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 { HEAD ~ the group } consisting of germanium oxide , { TAIL ~ germanium sulfide } , and silicon sulfide
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