Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Patent
1998-05-07
2000-01-04
Ngo, Ngan V.
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
257 77, 257459, H01L 310312
Patent
active
060112964
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
TECHNICAL FIELD
The present invention relates to a solid state microstructure, and particularly to a microstructure having an optoelectronically triggered onboard gating arrangement.
BACKGROUND OF THE INVENTION
Many imaging and probing applications in the infrared and visible light regions (lidar, mammography), in the UV and x-ray regions (medical imaging), and applications using ionising particles, suffer from scattering problem. Typically, scattered photons or particles which do not pass directly from the source to the object and to the detection system result in noise. This noise may greatly degrade the desired signal or image, particularly in the case of soft tissue probing by use of visible or infra-red laser light. In many applications, the image can greatly be improved by the use of a time-resolved or a time-gated detection system.
Such systems are currently complex and expensive, and currently are conceived as separate add-on units which are normally used in conjunction with conventional detectors. Gating using light, for example, is conventionally carried out using the relatively expensive device known as a pockels cell.
Similar problems apply to particle detection techniques such as slow neutron imaging. Time gating in the sub-nanosecond range, particularly with silicon detectors, can be difficult. In the x-ray range the time gate of, of example, microchannel plate devices can approach the loops range, and the best spatial resolution which can be obtained in the dimension along the line of the light without some sophisticated deconvolution technique, for example, is thus of order a few-cm. This is inadequate for most useful medical imaging techniques.
The time resolution of these gated structures is accordingly not entirely satisfactory, and generally depends upon a combination of the rise time of the gating pulse, and the response of the detector.
SUMMARY OF THE INVENTION
It is an object of the present invention at least to alleviate the problems of the prior art.
It is a further object to provide a solid state microstructure detector which can be gated very rapidly and which does not require a separate gating element such as a pockels cell.
According to the present invention there is provided a solid state (switch) microstructure comprising a substrate, a detector element extending outwardly from a surface of the substrate and having first and second electrodes on opposing sides thereof, the detector element incorporating an onboard optoelectronic gating structure.
For the ultra-violet region of light below about 224 nm, the substrate is preferably made of UV sensitised silicon, or more simply, chemical vapour deposition (CVD diamond. For the visible region, and the infra-red region, silicon, gallium, arsenide and indium phosphide are suitable detector materials, among other solid state materials.
Such an arrangement can give exceptionally high electrically controlled gating speeds for photon and particle detection across the visible, UV and x-ray range, and also for neutrons. X-ray detectors will normally--but not exclusively--incorporate high z materials in front of the detector medium. In exceptional cases, it may be necessary for the detector to have low efficiency to avoid electronic pile-up. For neutron detection, low z materials may be incorporated in front of the plane of, between the individual elements of, or actually within, the detector material.
The advantages of using diamond are many fold. Diamond can be made extremely transparent in the wavelengths greater than 224 nm, and it is also the best heat conductor and diffuser known, at room temperature. Due to the small voltage required efficiently to extract electron-hole pairs, the gate voltage can be relatively small, and therefore easily generated with a fast rising and falling edge. This contrasts with the kV range required to gate channel plate devices.
The gating structure may be optically driven, for example from an onboard or off-board laser diode. In a typical arrangement, a radiation-sensitive region o
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Applied Physics Letters, vol. 41, No. 7, Oct. 1982, pp. 599-601, Auston D.H. and Smith P.R. entitled "Picosecond Optical Electronic Sampling: Characterization of High-Speed Photodectors."
Applied Physics Letters, vol. 54, No. 6, Feb. 6, 1989, pp. 543-545, Taylor G.W. et al. entitled "Optoelectronic Dynamic Random Access Memory Cell Utilizing a Three-Terminal N-Channel Self-Aligned Double-Heterostructure Optoelectronic Switch."
Hassard John Francis
Smith Roland
Imperial College of Science Technology & Medicine
Ngo Ngan V.
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