An apparatus comprises a layer of channel material, source and drain electrodes configured to enable a flow of electrical current through the channel material, and a layer of quantum dot material configured to generate electron-hole pairs on exposure to electromagnetic radiation to produce a detectable change in the electrical current indicative of one or more of the presence and magnitude of the electromagnetic radiation. The layer of quantum dot material is positioned between the channel material and a layer of conductive material. The layers of channel and conductive material have work functions such that respective built-in electric fields are created at the interfaces between the layer of quantum dot material and the channel and conductive material. The electric field at each interface acts in the same direction to promote separation of the electrons and holes of the electron-hole pairs to facilitate production of the detectable change in electrical current.