Abstract: The invention provides a Hall effect magnetic field sensor (10, 50) including carrier excluding or extracting means (36, 66) for reducing an intrinsic contribution to carrier concentration in the active region (14e, 53c) to provide for the sensor to be operative in an extrinsic saturated regime. This provides an advantage that magnetic field measurement sensitivity of the sensor (10, 50) can be made substantially insensitive to sensor temperature thereby improving measurement accuracy.

Abstract: A field effect transistor (FET) is of the type which employs base biasing to depress the intrinsic contribution to conduction and reduce leakage current. It incorporates four successive layers (102 to 108): a p+ InSb base layer (102), a p+ InAlSb barrier layer (104), a &pgr; intrinsic layer (106) and an insulating SiO2 layer (108); p+ source and drain regions (110, 112) are implanted in the intrinsic layer (106). The FET is an enhancement mode MISFET (100) in which biasing establishes the FET channel in the intrinsic layer (106). The insulating layer (108) has a substantially flat surface supporting a gate contact (116). This avoids or reduces departures from channel straightness caused by intrusion of a gate groove, and enables a high value of current gain cut-off frequency to be obtained. In FETs with layers that are not flat, departures from channel straightness should not be more than 50 nm in extent, preferably less than 5 nm.

Abstract: The invention provides a Hall effect magnetic field sensor (10, 50) including carrier excluding or extracting means (36, 66) for reducing an intrinsic contribution to carrier concentration in the active region (14e, 53c) to provide for the sensor to be operative in an extrinsic saturated regime. This provides an advantage that magnetic field measurement sensitivity of the sensor (10, 50) can be made substantially insensitive to sensor temperature thereby improving measurement accuracy.

Abstract: An infra-red detector (10) comprises a detector region (38) and a collector region separated by a barrier region. Operation of these regions is controlled by potentials applied to respective gate electrodes (30, 34, 32), insulated from the detector, barrier and collector regions by an insulating oxide layer (36). The detector, barrier, and collector regions may be arranged on a silicon substrate (24). In operation, photo-excited electrons are generated in the detector region and these cross the barrier region for readout from the collector region.

Abstract: A noise reduced photon detector incorporates an array (10) of semiconductor diode detector elements (12). Each element (12) has an extrinsic active layer (20) sandwiched between two layers (18, 22) of wider bandgap and mutually opposite conductivity type. These layers are in turn sandwiched between two further layers (16, 24) of wider bandgap than the active layer (20) and of higher doping than the other layers (18, 22). A mirror (34) extends round much the array (10) and isolates each element (12) from photons emitted by other elements (12). In operation the elements (12) are reverse biased and exhibit negative luminescence which reduces their photon emission. These two effects reduce unwanted photon generation and absorption, and consequently photon noise is also reduced.

Abstract: A field effect transistor (FET) is of the type which employs base biasing to depress the intrinsic contribution to conduction and reduce leakage current. It incorporates four successive layers (102 to 108): a p+ InSb base layer (102), a p+ InAlSb barrier layer (104), a &pgr; intrinsic layer (106) and an insulating SiO2 layer (108); p+ source and drain regions (110, 112) are implanted in the intrinsic layer (106). The FET is an enhancement mode MISFET (100) in which biasing establishes the FET channel in the intrinsic layer (106). The insulating layer (108) has a substantially flat surface supporting a gate contact (116). This avoids or reduces departures from channel straightness caused by intrusion of a gate groove, and enables a high value of current gain cut-off frequency to be obtained. In FETs with layers that are not flat, departures from channel straightness should not be more than 50 nm in extent, preferably less than 5 nm.

Abstract: A thermal imaging system (10) which is accoupled and by scanning recreates a thermal image by superimposing measured variations in infrared emission from a scene (22) onto a reference level supplied by a light emitting diode (28). The diode (28) is both a positive and negative luminescent emitter. Emitted flux is current controlled to be equivalent to black body radiation at a range of temperatures which may be colder or hotter than ambient. A signal generated with the system (10) switches between scene and diode observation is a measure of the difference between the mean scene temperature and the diode effective temperature. In response to this digital, control means adjust the bias current through the diode (28) in order to reduce the temperature difference. The reference temperature converges towards the mean scene temperature as this process is repeated. Absolute temperature is thus restored and some image defects removed.

Abstract: A thermal sensing system (10) including an array of photon detectors (14) produces a detector-dependent response to irradiation. Variations in individual detector characteristics produce a fixed pattern noise which degrades an image or other response. A switchable mirror (M1) may at one position (P.sub.cal) direct infrared radiation from a light emitting diode (20) onto the detector array (14). The diode (20) is both a negative and positive luminescent emitter, the flux emitted is current controlled to be equivalent to black body radiation at a range of temperatures both colder and hotter than ambient. Calibration relationships comprising transfer functions relating incident intensity to signal response are derived for each detector. Alternatively the mirror (M1) may be at an observation position (P.sub.obs) and infrared radiation from a remote scene reaches the detector array (14).

Abstract: A dynamic infrared scene projector for use infrared detections systems which has particular, although not exclusive, use in thermal imaging or seeker systems. In such systems, a dynamic infrared scene projector is used to simulate the thermal scene for testing and calibration purposes. The device comprises an array of electroluminescent semiconductor diode structures, capable of emitting both positiveand negative luminescence, and electronic circuitry for supplying currents of both polarity to each diode independently so that the emission of positive and negative luminescence can be controlled. The diode structures in the array are based on narrow bandgap semiconductor materials, for example, the Hg.sub.1-x Cd.sub.x Te, In.sub.1-x Al.sub.x Sb, Hg.sub.1-x Zn.sub.x Te or In.sub.1-x Tl.sub.x Sb materials systems (where x is the composition). In a preferred embodiment, the diodes are capable of emitting infrared radiation in the wavelength regions between 3-5 .mu.m or 8-13 .mu.m.

Abstract: A semiconductor device in the form of a metal insulator field effect transistor (MISFET) (200) is constructed as a heterostructure of narrow bandgap In.sub.1-x Al.sub.x Sb semiconductor materials. The MISFET (200) is formed from four semiconducting layers (112 to 118) arranged in series as follows: a heavily doped p-type first layer (112), a heavily doped relatively wider bandgap p-type second layer (114), a lightly doped p-type third layer (116) and a heavily doped n-type fourth layer (118). A source (202) and a drain (204) are formed in the fourth layer (118) and a gate (116/205) in the third layer. An n.sup.+ p.sup.- junction (124) is formed between the third and fourth layers and a p.sup.+ p.sup.- junction (122) between the second and third layers. The second layer (114) provides a conduction band potential energy barrier to minority carrier (electron) flow to the gate (116/205), and is sufficiently wide to prevent tunnelling of minority carriers therebetween.

Abstract: A thermal imaging device having both serial and parallel content is provided by a number of infra-red radiation detector strips supported side by side on an insulating substrate, each strip having a number of read-out regions. To allow connection from the side of the device to the innermost detector strips, conductors err end across outer strips. These conductors may extend over the strips and over insulating material therebetween. Alternatively the conductors may be in the form of conductive tracks embodied in a substrate of semiconductor material. The strips may be indented at the read-out regions to provide, with very close spacing, sufficient room for contact between the read-out regions and the conductive tracks. Preformed aluminium contact pads may be used between bridging links to the read-out regions and the conductive tracks the contact pads and preformed tracks being centered during preformation to ensure a good ohmic contact.

Abstract: An infrared detector comprises a thin film of photo-responsive material on transparent dielectric material with an array of planar antennae adjacent to the film surface. The antennae are separate from ohmic contacts arranged to connect the film to an external circuit. The antennae concentrate radiation in fringe fields at antenna edges and extremities interacting with the photo-responsive material. The detectors may be photovoltaic or photoconductive. The antennae may be rectangular, bow-tie, cruciform, elliptic, circular or square, and are dimensioned for resonance (preferably half-wavelength resonance) at frequencies within the photo-responsive material absorption band. Half-wavelength resonant antennae are best matched by F/0.7 optics. The detector may be a reticulated array. The dielectric material may be formed as a lens.

Abstract: A photodetector (10) of the non-equilibrium kind incorporates three successively disposed sections (14, 16, 18) of like layer construction. Each of the sections (e.g. 14) contains three layers (14A, 14B, 14C) of semiconductor materials of the Cd.sub.x Hg.sub.1-x Te alloy system (CMT). The central layer (14B) of each section (14) is of narrow bandgap CMT, i.e. x=0.19 or 0.265 for absorption at 3-5 .mu.m or 8-12 .mu.m, and has very low doping (10.sup.15 cm.sup.-3) providing intrinsic conductivity. It is 1.5 .mu.m thick, less than one third of an optical absorption length. The outer layers of each section (14A, 14B) are 10 .mu.m thick and are of wide bandgap CMT, i.e. x=0.4. They have respective n and p type dopant concentrations of 3.times.10.sup.16 cm.sup.-3 providing extrinsic conductivity. Each central layer (14B) is therefore bounded by an excluding contact (14AB) and an extracting contact (14BC), which depress its carrier concentration to an extrinsic level under the action of electrical bias.

Abstract: A photodetector of semiconductor material includes a photosensitive region adjacent to a minority carrier extraction region arranged when biased to depress the photosensitive region minority carrier concentraction, and means for inhibiting injection of minority carriers to the photosensitive region. Depression of the minority carrier concentration produces low noise and high responsivity properties as obtained by cooling, but without the need for cooling equipment. The minority carrier extraction region may be a pn homo- or heterojunction. Minority carrier injection may be inhibited by a homo- or hetero-structure excluding contact to the photosensitive region, or alternatively by providing the photosensitive region with at least one subsidiary pn junction biasable to inhibit minority carrier flow. The photosensitive region may have an array of extraction regions spaed by less than a minority carrier diffusion length. The extraction regions may have separate outputs to provide respective pixels in a display.

Abstract: Between the spaced biasing electrodes of a thermal radiation imaging device A D.C. bias source is connected to cause the flow of a bias current in the device body which is preferably of n-type cadmium mercury telluride. The bias current supports an ambipolar drift of radiation-generated minority carriers (holes) in the opposite direction. The device is operated in a system in which the radiation pattern is scanned across the device body in the same direction and at the same rate as the ambipolar velocity. Instead of having a single read-out electrode, a more sophisticated system with better performance is obtained by distributing between the spaced biasing electrodes a plurality of read-out electrodes each of which forms a Schottky barrier or p-n junction with the body material.

Abstract: A detector, of photosensitive semiconductor material with input and output bias contacts. To improve both frequency response and spatial resolution, minority carriers having tendency to accumulate in the vicinity of the output bias contact are instead rapidly swept out, being driven towards this contact by a concentrated electric field. To produce a local field concentration, the output bias contact may be extended towards the input bias contact, or the detector material near this contact may be configured by slotting or tapering.

Abstract: A thermal imaging system including a biassed elongate detector element of photoconductive material, over which an image of a thermal scene is scanned at a velocity that is matched to the drift velocity of photocarriers generated in the element. In order to improve responsivity and detectivity the length of the detector element or the magnitudes of bias and scan velocity are selected so that the time taken to scan the detector element from one end to a read-out region of the detector element is greater than the lifetime of the photocarriers generated in the element. In order to avoid loss of resolution by photocarrier diffusion the photocarrier lifetime of the detector material is of relatively low value. The system may include one detector element only, or it may include several detector elements arranged in parallel.

Abstract: An infra red photo detector system comprises a piece of detector material, such as Cd.sub.x Hg.sub.1-x Te, InSb, InAs, etc, carrying at least a pair of spaced electrodes. An optical arrangement directs a small spot of radiation onto the detector. The position of the small spot on the much larger detector is found by applying an electrical bias between the electrodes causing a drift of photo carriers. The bias may be of alternating polarity and the detector output measured at each polarity. Alteratively a high frequency bias may be applied and the A.C. offset from the detector used to indicate spot position. Alternatively the spot position may be modulated or swept along the detector by a mirror moving in a sawtooth scanning action.

Abstract: A thermal imager includes an infrared sensitive light valve and a light source arranged to illuminate the full responsive area of the valve. The imager also includes an optical stage having focussing optics for forming an infrared image upon the surface of the valve and a chopper for modulating infrared radiation from a scene. Modulated light from the valve is read out in parallel by a detector array, and frame signals corresponding to alternate positions of the chopper are subtracted to provide uniformity correction. The light valve may comprise an infrared sensitive optically active liquid crystal cell and an analyzer adjusted to near extinction. An optical processor comprising a lens and an apodized stop filter lies in the light path between the valve and the detector array. The light source may comprise an array of light emitting diode elements and the filter a number of corresponding off-axis stop regions.

Abstract: An infra red photo detector system comprises a piece of detector material, such as Cd.sub.x Hg.sub.1-x Te, InSb, InAs, etc, carrying at least a pair of spaced electrodes. An optical arrangement directs a small spot of radiation onto the detector. The position of the small spot on the much larger detector is found by applying an electrical bias between the electrodes causing a drift of photo carriers. The bias may be of alternating polarity and the detector output measured at each polarity. Alternatively a high frequency bias may be applied and the A.C. offset from the detector used to indicate spot position. Alternatively the spot position may be modulated or swept along the detector by a mirror moving in a sawtooth scanning action.