The Secretary of State for Defence in Her Britannic Majesty's Government

The Secretary of State for Defence

Qinetiq Limited

Anthony M White

Charles Thomas Elliott

Neil Thomson Gordon

Timothy Ashley

Huw D Rees

Anthony B Dean

Robin F Farrow

Howard J Field

Piero Migliorato

Gerald M Williams

Raymond Brewitt-Taylor

A multi-layer semiconductor diode having a layer of wide bandgap material located between the active layer and a first contact zone, where the active layer and additional wide bandgap layer are of one dopant type, and the first contact zone is of the opposite dopant type. A specific embodiment of the invention comprises a stack formed from a first contact zone () of p-type material, a lightly doped p-type active layer (), an additionallayer () and a second contact zone () of n-type material. The diode may be used as an infrared detector or a negative luminescent source.

Semiconductor diode device

A multi-layer Auger suppressed diode having at least two exclusion interfaces and at least two extraction interfaces. A specific embodiment has two composite contacts, each consisting of a heavily doped layer ( ) and a buffer layer ( ) of lower doped, high bandgap material sandwiched between the heavily doped layer and the active region ( ) of the device.

Semiconductor diode with suppression of auger generation processes

A noise reduced photon detector incorporates an array ( ) of semiconductor diode detector elements ( ). Each element ( ) has an extrinsic active layer ( ) sandwiched between two layers ( ) of wider bandgap and mutually opposite conductivity type. These layers are in turn sandwiched between two further layers ( ) of wider bandgap than the active layer ( ) and of higher doping than the other layers ( ). A mirror ( ) extends round much the array ( ) and isolates each element ( ) from photons emitted by other elements ( ). In operation the elements ( ) 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.

Noise reduced photon detector

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.

Infrared detectors

Multiple heterostructure photodetector

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.

Photoconductive detector arranged for bias field concentration at the

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.

Infra red photo detector systems

A detector in which a barrier region is interposed in the current path between the emitter and collector of the detector. This region is of a material having a valance band edge approximately level to that of the emitter material and an appreciably wider band gap. It thus serves to impede majority carrier current flow and as a consequence device resistance is high. When the detector is biased, the pedestal contribution to detector signal is low. The collector may be of semiconductor material of the same majority carried type as the emitter material; or may be of opposite type but dopant enriched; or it may be a Schottky metal contact. In one variant of the detector, the emitter and collector are located on opposite sides of the barrier and are of different bandgap materials. The infra red band response of this detector can be changed by reversing bias polarity. In another variant of the detector the emitter is in strip form and has a pair of bias contacts. The barrier and collector are located on the strip at a position between these contacts and provide a high resistance read-out structure. In one further variant of the detector the emitter, the collector, together with additional emitter-collector regions, are formed from a single layer of photosensitive material on one side of the barrier and provide a high resistance, series connected, multi-element structure.

Infra red detectors

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.

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.

Photoconductive detector with an A/C bias and responsivity dependent

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.

Method of biasing a photoconductive detector and detector apparatus

A photo diode formed by a substrate of Cd.sub.x Hg.sub.1-x Te covered with a layer of CdTe forming a p-n junction. The substrate may be p-type in which case the layer is n-type or vice versa. An array of photo diodes may be formed by covering the substrate with semi-insulating CdTe and forming islets of In on the CdTe. Heating causes In to diffuse into the CdTe doping it n-type. This results in regions of n-type CdTe surrounded by semi-insulating CdTe each region forming, with the substrate, a photo diode. The heating also causes diffusion between the Cd.sub.x Hg.sub.1-x Te and CdTe to give a graded heterostructure. Electrical connections are made to the substrate, and each n-type region. The n-type CdTe region may alternatively be formed by molecular beam epitaxial growth techniques using a beam of In dopant.

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Malvern, United Kingdom

Anthony M White