According to one embodiment, a radiation detector includes a first layer, a first conductive layer, a second conductive layer, and an organic semiconductor layer. The first layer includes a first organic substance. The first layer emits light based on beta rays incident on the first layer. A period from a time of a maximum value of an intensity of the light until the intensity of the light drops to 1/2.72 of the maximum value is not less than 10 ns. The second conductive layer is located between the first layer and the first conductive layer. The organic semiconductor layer is located between the first conductive layer and the second conductive layer.

A display device including: a display layer including a light emitting device, a photo-detector, and a dummy device; and a circuit layer including a pixel driving part, which is connected to the light emitting device, and a sensor driving part which is connected to the photo-detector, wherein the light emitting device and the dummy device are overlapped with the pixel driving part, and wherein the photo-detector is overlapped with the sensor driving part.

A display device including: a display layer including a light emitting device, a photo-detector, and a dummy device; and a circuit layer including a pixel driving part, which is connected to the light emitting device, and a sensor driving part which is connected to the photo-detector, wherein the light emitting device and the dummy device are overlapped with the pixel driving part, and wherein the photo-detector is overlapped with the sensor driving part.

An organic/inorganic composite structure includes a silicon substrate and a conductive polymer layer. The silicon substrate includes a plurality of microstructures disposed on a surface of the silicon substrate. The conductive polymer layer is disposed on the plurality of microstructures. A spaced distance is between the conductive polymer layer and the surface of the silicon substrate.