Qinetiq Limited

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

Timothy Jonathan Phillips

Charles Thomas Elliott

Timothy Ashley

John Henry Jefferson

George W Gray

John Clifford Jones

Damien Gerard McDonnell

John William Goodby

Michael Hird

Kevin Michael Brunson

Neil Thomson Gordon

Anthony B Dean

David Richard Beattie

Carl J Anthony

Michael J Uren

Paul Hindmarsh

Anthony Brian Dean

In a transistor in which the majority carriers are holes, at least one narrow bandgap region or layer is doped p-type or contains an excess of holes and is subject to compressive mechanical strain, whereby hole mobility may be significantly increased. In a p-channel quantum well FET, the quantum well InSb well p-type layer(modulation or directly doped) lies between InAlSb layerswhere x is of a value sufficient to induce strain in layerto an extent that light and heavy holes are separated by much more than kT. Transistors falling within the invention, including bipolar pnp devices, may be used with their more conventional electron majority carriers counterparts in complementary logic circuitry.

Strained quantum-well semiconductor devices

In a field effect transistor having a quantum well is provided by a primary conduction channel, at least one secondary conduction channel immediately adjacent and in contact with the primary channel has an effect bandgap greater than the effective bandgap of the primary channel, and the modulus of the difference between the impact ionisation threshold IIT of the primary channel and the effective conduction band offset (the height of the step) between the primary and secondary channels being no more than 0.5 Eg (effective), or (alternatively) no more than 0.4 eV. Higher energy carriers which might otherwise cause impact ionization leading to runaway are thus diverted into the secondary channel allowing the device to run faster at increased voltages and/or to exhibit much greater resistance to runaway. The primary channel is prefereably of low bandgap material, for example InSb, InAs, InAs, InGaAs.

Field effect transistor

A bipolar transistor with vertical geometry comprises a base region () provided with a base contact (), emitter and collector regions () arranged to extract minority carriers from the base region, and an excluding structure for counteracting entry of minority carriers into the base region via the base contact, wherein the base region has a bandgap of greater than 0.5 eV and a doping level greater than 10cm. As shown the base includes an excluding heterojunction () preventing entry of carriers from the base contact (), but alternatively the base region could comprise a 'high-low' doping homojunction. The construction shows improved resistance to thermal runaway even in multi-finger transistors. It is particularly useful for high power, high frequency transistors, e.g. base on gallium indium arsenide. The collector region preferably has a heterostructure.

Wide band gap bipolar transistor with reduced thermal runaway

The invention provides a Hall effect magnetic field sensor ( ) including carrier excluding or extracting means ( ) for reducing an intrinsic contribution to carrier concentration in the active region ( ) 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 ( ) can be made substantially insensitive to sensor temperature thereby improving measurement accuracy.

Magnetic field sensor including carrier excluding for reducing an instrinsic contribution to carrier concentration in the active region

An extracting transistor ( )&mdash;an FET&mdash;includes a conducting channel extending via a p-type InSb quantum well ( ) between p-type InAlSb layers ( ) of wider band-gap. One of the InAlSb layers ( ) incorporates an ultra-thin n-type &dgr;-doping layer ( ) of Si, which provides a dominant source of charge carriers for the quantum well ( ). It bears n source and drain electrodes ( ) and an insulated gate ( ). The other InAlSb layer ( ) adjoins a barrier layer ( ) of still wider band-gap upon a substrate layer ( ) and substrate ( ) with electrode ( ). Biasing one or both of the source and drain electrodes ( ) positive relative to the substrate electrode ( ) produces minority carrier extraction in the quantum well ( ) reducing its intrinsic contribution to conductivity, taking it into an extrinsic saturated regime and reducing leakage current.

Charge carrier extracting transistor

A quantum wire field-effect transistor having at least one, one-dimensional, elongate conducting means ( ) provided by at least a first semiconductor layer surrounded by a wider bandgap, second semiconductor layer ( ) and extending between source ( ) and drain ( ) electrodes, and in which there is provided a backgate structure ( ) to control conduction in the elongate conducting means. The transistor can be a Single Electron Transistor (SET) wherein two adjacent gate electrode ( ) are disposed over the elongate conducting means to induce a quantum dot ( ) therein, and it can be made with the first semiconductor layer material as GaAs and the second semiconductor layer material as AlGaAs. A method of making the transistor involves preferentially growing the elongate conducting means at the bottom of a groove ( ) lined with second semiconductor layer ( ).

Quantum wire field-effect transistor and method of making the same

A bipolar transistor having base and collector regions of narrow bandgap semiconductor material and a minority-carrier excluding base contact has a base doping level greater than 10 cm . The transistor has a greater dynamic range, greater AC voltage and power gain-bandwidth products and a lower base access resistance than prior art narrow band-gap bipolar transistors.

Bipolar transistor

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 ( to ): a p InSb base layer ( ), a InAlSb barrier layer ( ), a &pgr; intrinsic layer ( ) and an insulating SiO layer ( ); p source and drain regions ( ) are implanted in the intrinsic layer ( ). The FET is an enhancement mode MISFET ( ) in which biasing establishes the FET channel in the intrinsic layer ( ). The insulating layer ( ) has a substantially flat surface supporting a gate contact ( ). 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.

High frequency field effect transistor with carrier extraction to reduce intrinsic conduction

A single electron on hole field effect transistor fabricated from a narrow band gap semiconductor. The transistor is such that the valence and conduction bands have sufficiently similar energy levels such that a top region of the valence band at one point ( ), e.g. under a gate electrode ( ), within the current path of the transistor can be forced to be higher than the bottom region of the conduction band at another point within the transistor, allowing Zener tunelling to occur. The transistor is fabricated from semiconductors with band gaps narrow enough to allow this to occur, for instance InSb and InAISb, CdTe and CD Hg Te.

Single charge carrier transistor, method of holding a charge carrier within a quantum dot, and method of detection

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

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Malvern, United Kingdom

Timothy Jonathan Phillips