Abstract: A substrate structure is described, including a starting substrate, crystal piers on the starting substrate, and a mask layer. The mask layer covers an upper portion of the sidewall of each crystal pier, is connected between the crystal piers at its bottom, and is separated from the starting substrate by an empty space between the crystal piers. An epitaxial substrate structure is also described, which can be formed by growing an epitaxial layer over the above substrate structure form the crystal piers. The crystal piers may be broken after the epitaxial layer is grown.

Abstract: A substrate structure is described, including a starting substrate, crystal piers on the starting substrate, and a mask layer. The mask layer covers an upper portion of the sidewall of each crystal pier, is connected between the crystal piers at its bottom, and is separated from the starting substrate by an empty space between the crystal piers. An epitaxial substrate structure is also described, which can be formed by growing an epitaxial layer over the above substrate structure form the crystal piers. The crystal piers may be broken after the epitaxial layer is grown.