Active solid-state devices (e.g. – transistors – solid-state diode – Thin active physical layer which is – Heterojunction
Reexamination Certificate
1999-02-18
2001-05-08
Mintel, William (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Thin active physical layer which is
Heterojunction
C257S018000, C257S021000, C257S184000, C257S185000, C438S093000, C438S094000
Reexamination Certificate
active
06229152
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a method for extending the cutoff wavelength of Indium Galium Arsenide (InGaAs) primarily for spectroscopy and night vision applications by increasing the In content by the use of highly strained InGaAs. Highly strained InGaAs quantum wells are created by balancing compressive strain with tensile strain. A lattice matched intermediate layer can be used to transition from a compressive strained layer to a tensile strained layer. The present invention also relates to a semiconductor device having a strain compensated banier region.
2. Related Art
The paper by Dries, et al., STRAIN COMPENSATED In
1−x
Ga
x
As (x<0.47) ARSENIDE QUANTUM WELL PHOTODIODES FOR EXTENDED WAVELENGTH OPERATION, published in Applied Physics Letters, Volume 73, p. 2263, the entire disclosure of which is incorporated herein by reference, discusses experiments forming p-i-n PHOTODIODES using a strain compensated multiple quantum well absorption region. These detectors exhibit high quantum efficiencies (QE), low dark currents, and are potentially useful in night vision and spectroscopic applications as well as any other suitable applications.
Present technologies for the extension of InGaAs into the &lgr;=2 &mgr;m wavelength band utilize buffer layers of lattice-mismatched InAsP which produce laterally threading misfit dislocations. This threading mechanism reduces the effect of lattice-mismatch on subsequent epitaxial layers. The InGaAs detectors fabricated using this technique can have responses to a wavelength of 2.5 &mgr;m, but suffer from large dark currents due to residual defects in the epitaxial layers.
Applications for night vision, remote sensing and spectroscopy have increased interest in the 1.65 &mgr;m to 2 &mgr;m wavelength band. New detectors and detector materials with access to this range of wavelengths are particularly desirable due to the limited utility of HgCdTe, InAs, InSb, and strain-relaxed InGaAs based devices. HgCdTe is plagued by material growth issues and the narrow bandgaps of InAs and InSb result in detectors with large dark currents at room temperature. Furthermore, GaInAsSb devices grown on GaSb substrates have dark currents in the microamp range for detectors as small as 100 &mgr;m in diameter. Lattice-mismatched InGaAs, when grown on buffer layers of relaxed InAsP, results in detectors with acceptable dark currents and high bandwidth. However, residual defects in the epitaxial layers, as well as the lack of integration capability with InP electronics, highlight the need for novel materials and detectors for use at wavelengths &lgr;>1.65 &mgr;m.
In order to increase the cuttoff wavelength, it is necessary to increase the In content. The thickness of the absorption region is limited by critical thickness considerations, and thus quantum wells are formed. This is deleterious to the prospect of extending the absorption region to longer wavelengths, for the quantum confinement produces a blue shift from the bulk band edge. The cutoff wavelength is reduced to a lesser extent by strain in the InGaAs, for compressively strained InGaAs has a larger bandgap than relaxed InGaAs. Previously, the use of strained InGaAs for detection at &lgr;≦2 &mgr;m has been demonstrated in separate absorption, multiplication layer avalanche photodiodes (D. Gershoni, H. Temkin, and M. B. Panish, Appl. Phys. Lett. 53, 1294-1296, (1988)), but critical layer thickness considerations limited these devices to 10 quantum wells (QW), resulting in low quantum efficiencies. The present invention offsets the compressive strain in the QW by an equal and opposite strain in the barrier region surrounding the QW. Such strain-compensation techniques, in principle, permit the growth of an unlimited number of strained quantum wells, thus dramatically improving device quantum efficiency.
The additional degree of freedom for bandgap engineering afforded by strained layer materials has been used to advantage in achieving high performance lasers, detectors, and modulators. The present invention uses strain-compensated InGaAs grown on InP substrates in very low dark current multiple quantum well (MQW) p-i-n diodes for efficient detection of light to wavelengths as long as &lgr;=2.1 &mgr;m.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the invention is to provide a method which enables the use of highly strained InGaAs by balancing compressive strain with tensile strain.
It is another object of the present invention to provide a strain compensated multiple quantum well absorption region having a high In content.
Still another object of the invention is to increase the ability to detect optical radiation using InP based materials for wavelengths beyond the traditional cutoff wavelength of 1.65 &mgr;m.
A further object of the invention is the provision of a strain compensated broadband photodetector with responsivity to approximately 2.1 &mgr;m.
Even another object of the invention is to provide a method that balances the strain of compressive InGaAs on InP by subsequently depositing an equally strained tensile layer of InGaAs, InGaP, or InGaAsP.
A still further object and advantage of the invention is the provision of an optical detector such as a photoconductor or photodiode, a superlattice avalanche photodiode (APD), a bulk InP APD or a bulk InAlAs APD incorporating a strain-compensated multiple quantum well absorbing region.
An additional object of the present invention is to provide a strain compensated device having lattice matched transition layers between compressively strained layers and tensile strained layers.
An additional object of the present invention is the provision of a photodiode that increases the efficiency and ultimately the gain of avalanche photodiodes.
Even an additional object of the invention is to provide a photodiode that at proper wavelengths avoids saturation over a wide dynamic range.
Still even an additional object of the present invention is the ability to use highly strained InGaAs in various applications, including, but not limited to amplifiers, detectors, optical switches, imagers, etc.
Yet an additional object of the present invention is to provide an amplifier device with a “self-correcting” feature which avoids saturation over a wide dynamic range.
The use of highly compressively strained In
1−x
Ga
x
As quantum wells having a high In content for the detection of light to a wavelength of &lgr;≈2.1 &mgr;m is disclosed. Crystal quality is maintained through strain compensation using tensile strained barriers of InGaAs, InGaP, or InGaAsP. High efficiencies have been achieved in detectors fabricated using this technique. The theoretical cutoff wavelength limit for diodes fabricated using this technique is calculated to be &lgr;~2.1 &mgr;m. Lattice-matched layers may be used to transition between compressively strained layers and tensile strained layers to prevent the crystal from breaking up. Multiple quantum wells are formed with multiple periods of strained InGaAs, transition layers and tensile stained layers. These detectors have application in amplifiers, detectors, optical switches, images, etc.
REFERENCES:
patent: 5471068 (1995-11-01), Tsusi et al.
patent: 5521935 (1996-05-01), Irikawa
patent: 5825796 (1998-10-01), Jewell et al.
patent: 5880491 (1999-03-01), Soref et al.
patent: 5929462 (1999-07-01), Kasukawa et al.
patent: 363098158 (1988-04-01), None
Gershoni, et al., “Strained-layer Ga1-xInxAs/InP Avalanche Photodetectors”, Appl. Phys. Lett. 53, 1294-1296, (1988).
Dries John C.
Forrest Stephen R.
Gokhale Milind
Mintel William
The Trustees of Princeton University
Wolff & Samson
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