An apparatus (400, 600, 700, 800, 900), comprising a layer of channel material (403, 603, 703, 803, 903, 1003), source and drain electrodes (401, 402, 601, 602, 701, 702, 801, 802, 901, 902) configured to enable a flow of electrical current through the layer of channel material (403, 603, 703, 803, 903), and a layer of quantum dot material (406, 606, 706, 806, 906) configured to generate electron-hole pairs on exposure to incident electromagnetic radiation to produce a detectable change in the electrical current which is indicative of one or more of the presence and magnitude of the electromagnetic radiation, wherein the layer of quantum dot material (406, 606, 706, 806, 906) is positioned between the layer of channel material (403, 603, 703, 803, 903) and a layer of conductive material (413, 613, 713, 813a, 813b, 913a, 913b), and characterized in that either: the Fermi energy of the layer of quantum dot material (406, 606, 706, 806, 906) is lower than the work function of the layer of channel material (403, 603, 703, 803, 903), and the work function of the layer of conductive material (413, 613, 713, 813a, 813b, 913a, 913b), is lower than the work function of the channel material (403, 603, 703, 803, 903), or; the Fermi energy of the layer of quantum dot material (406, 606, 706, 806, 906) is higher than the work function of the layer of channel material (403, 603, 703, 803, 903), and the work function of the layer of conductive material (413, 613, 713, 813a, 813b, 913a, 913b) is higher than the work function of the channel material (403, 603, 703, 803, 903); so that respective built-in electric fields are created at the interfaces between the layer of quantum dot material (406, 606, 706, 806, 906) and the layers of channel (403, 603, 703, 803, 903) and conductive material (413, 613, 713, 813a, 813b, 913a, 913b), the built-in electric field at each interface acting in the same direction to promote separation of the electrons and holes of the generated electron-hole pairs to facilitate production of the detectable change in electrical current. the Fermi energy of the layer of quantum dot material (406, 606, 706, 806, 906) is lower than the work function of the layer of channel material (403, 603, 703, 803, 903), and the work function of the layer of conductive material (413, 613, 713, 813a, 813b, 913a, 913b), is lower than the work function of the channel material (403, 603, 703, 803, 903), or; the Fermi energy of the layer of quantum dot material (406, 606, 706, 806, 906) is higher than the work function of the layer of channel material (403, 603, 703, 803, 903), and the work function of the layer of conductive material (413, 613, 713, 813a, 813b, 913a, 913b) is higher than the work function of the channel material (403, 603, 703, 803, 903); so that respective built-in electric fields are created at the interfaces between the layer of quantum dot material (406, 606, 706, 806, 906) and the layers of channel (403, 603, 703, 803, 903) and conductive material (413, 613, 713, 813a, 813b, 913a, 913b), the built-in electric field at each interface acting in the same direction to promote separation of the electrons and holes of the generated electron-hole pairs to facilitate production of the detectable change in electrical current.