Quantum-well infrared photodetectors (QWIPs) that include two-dimensional surface grating light couplers would be modified, according to a proposal to incorporate crossed slots. It should be possible to increase signal-to-noise ratios by suitable positioning and dimensioning of the slots, as explained below.
The figure depicts part of a typical GaAs/AlGaAs QWIP with a two-dimensional surface grating light coupler. The need for, and function of, a light coupler on a QWIP is described in the preceding article. In the case of a two-dimensional surface grating light coupler, there is an important effect incidental to the basic light-coupler function; the absorption of light inside the QWIP becomes concentrated into columns under the surface grating.
Because little or no light is absorbed in regions between the columns, material could be removed from these regions without reducing photocurrent much, if at all. This leads to the concept of slots. The positions and dimensions of the slots would be chosen to correspond to the low-absorption regions.
While the incorporation of slots would exert little or no effect on photocurrent, it would significantly affect noise. The dark current of a QWIP is proportional to its effective area. In the presence of slots, the effective area would be the cross-sectional area of the columns between the slots. In a typical case, this remaining area would be only one-fourth the original area; consequently, the dark current of the slotted QWIP would be only one-fourth the dark current of the unslotted QWIP. Inasmuch as the noise current of a QWIP is proportional to the square root of its dark current, the noise current of the slotted QWIP would be reduced to half that of the unslotted QWIP, resulting in a signal-to-noise ratio twice that of the unslotted QWIP at any wavelength and temperature.
Another anticipated benefit of slotting would be an increase in the fraction of incident light converted to polarization perpendicular to the planes bounding the quantum wells and thus an increase in light-coupling efficiency. The estimated net effect of slotting would be an enhancement of detectivity by a factor of 3 to 4.
This work was done by Sarath Gunapala, Sumith Bandara, John K. Liu, and Daniel Wilson of Caltech for NASA's Jet Propulsion Laboratory.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to
Technology Reporting Office
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Refer to NPO-20518
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Noise-Reducing Slots in Quantum-Well Infrared Photodetectors
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Overview
The document appears to be a technical report related to advancements in quantum-well infrared photodetectors (QWIPs), specifically focusing on a novel approach to enhance their performance through the incorporation of slotted structures. The primary objective of the research is to improve the signal-to-noise ratio of QWIPs, which are critical components in infrared detection applications.
The report outlines the necessity for innovation in QWIP technology, addressing the inherent challenges associated with noise in photodetectors. It emphasizes the importance of achieving a balance between light absorption and noise reduction to enhance the overall efficiency and effectiveness of these devices. The proposed solution involves the integration of slotted designs within the QWIP structure, which is expected to optimize the interaction between incoming infrared light and the detector material.
Key sections of the report include:
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Novelty: The introduction of slotted structures in QWIPs represents a significant advancement in the field, potentially leading to improved performance metrics compared to traditional designs.
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Problem Statement: The document identifies the persistent issue of noise in infrared detection, which can severely limit the functionality of QWIPs in practical applications.
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Solution: The report details the implementation of slotted-QWIPs, explaining how these modifications can enhance light absorption while simultaneously mitigating noise. This dual benefit is crucial for applications requiring high sensitivity and precision.
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Technical Details: While specific technical data and experimental results are not provided in the excerpts, the report likely includes detailed methodologies, experimental setups, and performance evaluations to substantiate the claims made regarding the effectiveness of the slotted design.
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Implications: The advancements discussed in the report have potential implications for various fields, including remote sensing, environmental monitoring, and military applications, where infrared detection plays a vital role.
Overall, the document serves as a comprehensive overview of a promising innovation in QWIP technology, highlighting the importance of addressing noise issues to enhance the capabilities of infrared photodetectors. The research conducted at the Jet Propulsion Laboratory under NASA's auspices underscores the ongoing efforts to push the boundaries of photodetector technology for future applications.
