A method for producing an insulating or barrier layer, useful for semiconductor devices, comprises depositing a layer of silicon and at least one additional element on said silicon substrate whereby said deposited layer is substantially free of defects such that epitaxial silicon substantially free of defects can be deposited on said deposited layer. Alternatively, a monolayer of one or more elements, preferably comprising oxygen, is absorbed on a silicon substrate. A plurality of insulating layers sandwiched between epitaxial silicon forms a barrier composite. Semiconductor devices are disclosed which comprise said barrier composite.