Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Reexamination Certificate
1995-06-16
2001-04-03
Crane, Sara (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
C257S454000, C257S455000
Reexamination Certificate
active
06211560
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to infrared detectors and more specifically the invention pertains to a Schottky diode infrared detector with a voltage tunable cutoff wavelength.
Infrared detectors are used to convert photons whose energy is in the IR portion of the electromagnetic spectrum to electrons. Once converted, these electrons are removed from the structure and external circuits are used to convert the information obtained into signals that may be viewed on a standard television monitor. This reconstruction allows for an invisible IR image to be presented in a manner that can be understood by an observer.
The infrared spectrum is considered to extend from just above the visible band (0.4 to 0.7 &mgr;m) out to more than 30 &mgr;m. Detectors can be fabricated from many materials that will respond to photons in the 1 to 30 &mgr;m spectrum. They are usually characterized by having a spectral response that is defined by the electronic band structure of the material. The structure allows for infrared detection to occur over a specific band of wavelengths. If a new wavelength band is desired, then a new material must be manufactured. There are no materials that are easily tunable by external means during operation after having been fabricated.
The task of providing a voltage tunable Schottky diode infrared detector is alleviated, to some extent, by the systems disclosed in the following U.S. Patents, the disclosures of which are incorporated herein by reference:
U.S. Pat. No. 4,533,933 issued to Pellegrini et al;
U.S. Pat. No. 6,319,204 issued to Wong, and
U.S. Pat. No. 5,107,317 issued to Takasaki.
The patent to Takasaki discloses the use of a Ge-containing crystalling layer as an intervening layer between an GaAs layer and a compound semiconductor layer. The Wong patent is of similar interest.
While the above-cited references are instructive, none of the cited patents disclose a Schottky diode infrared detector with a voltage tunable cutoff wavelength which is obtained by inserting a SiGe layer between the metal suicide and the Si substrate.
SUMMARY OF THE INVENTION
The invention includes a Schottky diode infrared detector with a voltage tunable cutoff wavelength. The tunability is due to modification of the Schottky diode band diagram by insertion of a SiGe layer, with the approplate parameters, between the suicide and the Si substrate, making the detector a silicide/SiGe/Si Schottky diode detector. The SiGe/Si interface has a valence band offset that can be used to engineer the shape, or depth profile, of the Schottky barrier. The energy offset can be gradual or abrupt, depending on the grading of the Ge concentration in the SiGe layer. When the offset is abrupt, it can be thought of as an additional, higher energy barrier to photoemitted carriers if the SiGe layer is thin enough. Because this offset, gradual or abrupt, is designed to be deeper in the semiconductor than the normal Schottky barrier maximum, it is easily modified by an external applied voltage. The sensitivity and the range of tunability are defined by the SiGe thickness and Ge concentration, respectively.
This invention will greatly expand the use of Schottky barrier and other photoemissive infrared detectors by allowing them to be fundamentally altered with an external applied potential. Present technology does not provide for this augmentation and current detectors are capable of responding to wavelengths over a well defined spectral band. The tunability of contemporary detector diodes is very small and defined by well known physical relationships. The new detectors have a novel internal structure that allows for modulation of spectral response with an externally applied potential and it is simple because it does not require additional external connections.
It is an object of the invention to provide a voltage tunable cutoff in Schottky infrared detectors.
It is another object of the invention to provide tunability in detector diodes without an addition of new external connections.
REFERENCES:
patent: 4533933 (1985-08-01), Pellegrini et al.
patent: 4939561 (1990-07-01), Yamaka et al.
patent: 5107317 (1992-04-01), Takasaki
patent: 5163179 (1992-11-01), Pellegrini
patent: 5319204 (1994-06-01), Wong
Sze, Physics of semiconductor devices, second edition, Wiley, pp. 249-254, 1981.*
Runyan and Bean, Semiconductor integrated circuit processing technology, Addison-Wesley, pp. 541-543, 1990.
Jimenez Jorge R.
Pellegrini Paul W.
Auton William G.
Crane Sara
The United States of America as represented by the Secretary of
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