Active solid-state devices (e.g. – transistors – solid-state diode – Thin active physical layer which is – Heterojunction
Reexamination Certificate
1999-11-19
2001-08-07
Lee, Eddie (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Thin active physical layer which is
Heterojunction
C257S184000, C257S189000, C257S436000, C257S446000, C257S447000, C257S448000, C438S071000, C438S073000, C250S338400, C250S339020
Reexamination Certificate
active
06271537
ABSTRACT:
BACKGROUND
This specification relates to quantum-well radiation sensors and techniques of constructing quantum-well radiation sensors with reduced noise.
An infrared quantum-well semiconductor sensor includes a quantum-well structure formed of alternating active and barrier semiconductor layers. Such a quantum-well structure can have different energy bands which each can have multiple quantum states. An intraband transition between a ground state and an excited state in the same band (i.e., a conduction band or a valance band) can be used to detect infrared (“IR”) radiation by absorbing IR radiation at or near a selected resonance IR wavelength. Only incident radiation with a polarization that is perpendicular to the quantum well layers can be absorbed, because this polarization can induce an intraband transition. The absorption of the radiation generates electric charge indicative of the amount of received radiation. The radiation-induced charge can then be converted into an electrical signal (e.g., a voltage or current) to be processed by signal processing circuitry.
The total charge produced by an IR quantum-well sensor generally includes two major contributions. One is radiation-induced charge which indicates the amount of radiation being absorbed by the quantum-well layers. Another contribution is the charge that is not produced by absorption of radiation. Rather, such non-radiation-induced charge is caused by thermal effects, quantum tunneling effect, shot noise, and other fluctuation processes. The motion of certain non-radiation-induced charge under a bias electrical field generates an electrical current called the dark current. This dark current is undesirable since it does not reflect the amount of radiation to be detected. In addition, it can saturate the detection circuitry and hence adversely affect the detection of the radiation-induced signal.
SUMMARY
The present devices and techniques use an array of quantum-well columns of either one dimension or two dimensions formed on a substrate to couple incident radiation to have a polarization perpendicular to the quantum-well layers for intraband absorption and to reduce the dark current.
In one embodiment, a quantum-well semiconductor device includes a plurality of quantum-well columns spatially separated from one another by a gap which is electrically insulating and formed over a substrate to form a periodic array. Each quantum-well column includes, a first conductive contact layer formed over the substrate, a quantum-well stack having a plurality of alternating quantum-well layers parallel formed over the first conductive contact layer and operating to absorb radiation polarized perpendicularly to the quantum-well layers, and a second conductive contact layer formed over the quantum-well stack.
These and other features and associated advantages of the devices and techniques are described in detail in the following.
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Gunapala, Sarath D. et al., “9-micrometer 256x256 GaAs/A1xGa1-As Quantum Well Infrared Photodetector Hand-Held Camera,” IEEE Transactions on Electron Devices, vol. 44, No. 1, Jan. 1997 (01.97), pp. 51-57.
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Bandara Sumith V.
Gunapala Sarath D.
Liu John K.
Wilson Daniel W.
Baumeister Bradley W.
California Institute of Technology
Fish & Richardson P.C.
Lee Eddie
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