There is a class of devices known as solid state detectors which work on the principle that they collect the charge generated by ionising radiation in a solid. These detectors are made of semi-conducting material and are operated much like a solid state diode with a reverse bias. The applied high voltage generates a thick `depletion layer' and any charge created by the radiation in this layer is collected at an electrode . The charge collected is proportional to the energy deposited in the detector and therefore these devices can also yield information about the energy of individual particles or photons of radiation. The detectors are made mostly from silicon or germanium. Most are research or analytical grade instruments although some small PIN diodes are used in electronic dosimeters .