One embodiment provides a semiconductor device comprising: a substrate; a first semiconductor layer disposed on the substrate; a second semiconductor layer disposed on the first semiconductor layer; a third semiconductor layer disposed on the second semiconductor layer; and a reflective layer disposed on the third semiconductor layer, wherein the part between the first and second semiconductor layers, the part between the third and second semiconductor layers, and the second semiconductor layer comprise a depletion region, and the conductivity of the first semiconductor layer and the conductivity of the third semiconductor layer are different from each other, and the second semiconductor layer comprises an intrinsic semiconductor layer.