In various embodiments, semiconductor structures and methods to manufacture these structures are disclosed. In one embodiment, a method to manufacture a semiconductor structure includes forming a cavity in a substrate. A portion of the substrate is doped, or a doped material is deposited over a portion of the substrate. At least a portion of the doped substrate or at least a portion of the doped material is converted to a dielectric material to enclose the cavity. The forming of the cavity may occur before or after the doping of the substrate or the depositing of the doped material. Other embodiments are described and claimed.