A single-stack broadband quantum well infrared photodetector (QWIP) has been developed that consists of stacked layers of GaAs/AlGaAs quantum wells with absorption peaks centered at various wavelengths spanning across the 9-to-11-μm spectral regions. The correct design of broadband QWIPs was a critical step in this task because the earlier implementation of broadband QWIPs suffered from a tuning of spectral response curve with an applied bias. Here, a new QWIP design has been developed to overcome the spectral tuning with voltage that results from nonuniformity and bias variation of the electrical field across the detector stacks with different absorption wavelengths.
In this design, a special effort has been made to avoid non-uniformity and bias tuning by changing the doping levels in detector stacks to compensate for variation of dark current generation rate across the stacks with different absorption wavelengths. Single-pixel photodetectors were grown, fabricated, and tested using this new design.
The measured dark current is comparable with the dark measured current for single-color QWIP detectors with similar cutoff wavelength, thus indicating high material quality as well as absence of performance degradation resulting from broadband design. The measured spectra clearly demonstrate that the developed detectors cover the desired special range of 8 to 12 μm. Moreover, the shape of the spectral curves does not change with applied biases, thus overcoming the problem plaguing previous designs of broadband QWIPs.
This work was done by Alexander Soibel, David Z. Ting, Arezou Khoshakhlagh, and Sarath D. Gunapala of Caltech for NASA’s Jet Propulsion Laboratory. NPO-48398
This Brief includes a Technical Support Package (TSP).
Mid- and Long-IR Broadband Quantum Well Photodetector
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Overview
The document presents a Technical Support Package from NASA's Jet Propulsion Laboratory (JPL) detailing advancements in Mid- and Long-IR Broadband Quantum Well Photodetectors (QWIPs). These detectors are crucial for infrared focal plane arrays (FPAs) used in spectroscopic and imaging instruments for various Earth and planetary science missions, including HyspIRI, HyTES, and QWEST.
Traditional QWIPs have limited spectral coverage, which poses challenges for applications requiring broader wavelength detection. The document outlines the development of a novel single stack broadband QWIP designed to overcome these limitations. This new design features stacked layers of GaAs/AlGaAs quantum wells with absorption peaks spanning the 9-11 mm spectral range, enabling a wider operational spectrum while maintaining high performance.
A significant challenge addressed in this work is the bias sensitivity of previous broadband QWIPs, which affected their spectral response. The new design mitigates this issue by adjusting doping levels in the detector stacks to compensate for variations in dark current generation rates across different absorption wavelengths. This results in a spectral response that remains stable regardless of the applied operational bias, enhancing the reliability and performance of the detectors.
The document highlights the fabrication process, which involves molecular beam epitaxy on a semi-insulating GaAs substrate, followed by characterization using techniques like X-ray diffraction (XRD) and atomic force microscopy (AFM). The resulting detectors exhibit high crystalline quality and low dark current, comparable to single-color QWIPs, indicating that the broadband design does not compromise performance.
The potential applications of these broadband QWIPs are significant, as they can be integrated into large-format FPAs that are uniform, reproducible, low-cost, and resistant to radiation. This technology is poised to enable a new generation of infrared instruments that can enhance scientific understanding in various fields, including Earth and planetary sciences.
In summary, the document outlines the successful development of bias-insensitive broadband QWIPs, addressing previous limitations and paving the way for advanced infrared detection technologies that can be utilized in future space missions. The work represents a significant step forward in the capabilities of infrared photodetectors, with broad implications for scientific research and exploration.
