Abstract: An alternating bias is applied to a modified photoconductive detector and photosignal extracted from each detector element. This extraction may be performed using an integrator to produce a dc signal output, or alternatively by using a high-pass filter or phase-sensitive detector to extract a photosignal at an harmonic of the bias frequency. The detector used is provided with elements that have a responsivity that is a different function of bias amplitude for each polarity. The detector element may be shaped with variation in width or depth, to produce this differential responsivity. Alternatively element bias contacts may be of different width to produce field gradient and differential responsivity. It is advantageous to obscure a part of each element area by including an opaque mask.

Abstract: It is a problem extracting the photosignal component from detector output, to the exclusion of pedestal bias response. To overcome this, a time varying bias signal is applied to each element of the detector. The duration of the time varying bias signal, or if a periodic signal, the signal period, is chosen as long compared to photocarrier lifetime and the signal amplitude is large enough to range over a non-linear portion of the responsivity characteristic of each element. The bias signal contains a d.c. component so that the bias signal ranges about a point of operation--a point of asymmetry lying on the responsivity characteristic. The photosignal component of the output signal may be removed by time averaging or by harmonic separation. Alternatively the bias signal may be modulated, and the photosignal component extracted by detection of demodulated signal.

Abstract: In a radiation detector including a substrate of photoconductive material having input and output contacts, the photocarrier flow-path between the two contacts includes regions of conductive material. These regions may be formed as strips overlying the substrate, or may be formed in grooves in the substrate. Alternatively, the substrate may comprise a number of separate regions of photoconductive material interconnected by regions of conductive material. The substrate is preferably of cadmium mercury telluride photoconductive material and the conductive regions of gold. Chromium may be used to provide a bond between the gold and cadmium mercury telluride. The substrate may be slotted to increase flow-path length between the two contacts.

Abstract: In order to improve the resolution and performance of an imaging device comprising an elongate strip of photconductive semiconductor material having first and second current electrodes and an associated read-out electrode the strip is modified so that generated photocarriers are caused to drift in a flow path in which their diffusive spread in the longitudinal direction, from the first electrode to the second electrode, is limited to a spread substantially less than the diffusion length characteristic of the material. In particular the strip may be modified by a plurality of fine interdigital slots extending alternately from opposite sides of the strip and which, in at least a terminal region adjacent the second electrode, are spaced apart by a distance less than the diffusion length.The device may be used in either a scanned, or a stationary, image system.