Abstract: A particle detector for detecting ionizing particles incident on the detector which form electron-hole pairs upon penetrating the detector, the detector comprising a substrate, a first electrode formed on the substrate, a body portion supported by the first electrode, a second electrode formed over the body portion, and a voltage source for applying a forward bias voltage across the first and the second electrodes. The body portion includes two monolithic, contiguous amorphous silicon regions. A first region is doped to be of a first conductivity type, and a second region is an intrinsic region. The applied forward bias voltage must be greater than the flat band voltage of the detector and sufficient to bias the detector into the space charge limited regime so that charge carriers, injected at the first electrode, are blocked by a potential barrier formed near the interface between the first and the second regions.