An apparatus includes a semiconductor layer, a dielectric layer, and a light prevention structure. The semiconductor layer has a front surface and a backside surface. The semiconductor layer includes a light sensing element and a periphery circuit region containing a light emitting element and not containing the light sensing element. The dielectric layer contacts at least a portion of the backside surface of the semiconductor layer. At least a portion of the light prevention structure is disposed between the light sensing element and the light emitting element. The light prevention structure is positioned to prevent light emitted by the light emitting element from reaching the light sensing element.