Various embodiments of the present disclosure are directed towards an image sensor. The image sensor includes and image sensor element disposed within a substrate. The substrate comprises a first material. The image sensor element includes an active layer comprising a second material different from the first material. A buffer layer is disposed between the active layer and the substrate. The buffer layer extends along outer sidewalls and a bottom surface of the active layer. A capping structure overlies the active layer. Outer sidewalls of the active layer are spaced laterally between outer sidewalls of the capping structure such that the capping structure continuously extends over outer edges of the active layer.