Various embodiments of the present disclosure are directed towards a semiconductor structure including a buffer layer disposed between an active layer and a substrate. The active layer overlies the substrate. The substrate and the buffer layer include a plurality of pillar structures that extend vertically from a bottom surface of the active layer in a direction away from the active layer. A top electrode overlies an upper surface of the active layer. A bottom electrode underlies the substrate. The bottom electrode includes a conductive body and a plurality of conductive structures that respectively extend continuously from the conductive body, along sidewalls of the pillar structures, to a lower surface of the active layer.