Amethyst Resonant-Cavity Detector Photodiode (RCE-PD)

Amethyst Research’s Resonant-Cavity Detectors are an exciting, new, disruptive  technology which promises improved spectroscopic  detection of gases and other  narrow-band optical signals in the eSWIR, MWIR, and LWIR wavelength ranges.

Advantage of Resonant-Cavity Technology Vs. Broadband Detectors

The spectral response of a resonant-cavity detector is naturally narrow owing to the presence of the optical cavity. This allows for high-performance spectroscopic detection of a single wavelength. The optical response linewidth is controllable down to several nanometers FWHM via resonant-cavity detector design within the known detector performance trade-off space.

As stated above, the resonant-cavity detector architecture allows for a significantly thinner optical absorbing region when compared to conventional, broadband infrared detectors (>10 reduction in absorber thickness). This reduction in absorber thickness naturally reduces the magnitude of the dark current generated within the optical absorber which causes detector noise and is the fundamental limit for the SNR of the detector. As dark current is naturally suppressed in a resonant-cavity detector, detector noise is consequentially reduced and SNR improved.

The narrow spectral response prohibits detection of background radiation away from the resonant wavelength naturally reducing the background photocurrent inherent to conventional broadband detectors. This will inherently result in a decrease in the BLIP temperature and background detector noise compared to conventional infrared detectors.

Solid-state optical physics fundamental to the detector materials allows for limited resonant-wavelength tunability via two mechanisms:
• Resonance tuning via the angle of incident light
• Resonance tuning via the operating temperature of the detector
When the resonant-cavity detector is cooled, a small reduction in the resonant wavelength results. The opposite is true when the detector  temperature is increased with the tradeoff of higher detector noise at higher detector temperatures. When the resonant-cavity detector is tilted away from normal optical incidence, the resonant wavelength shifts to a slightly shorter wavelength as the angle of incidence increases. The  magnitude of these shifts is fundamental to the material and optical properties of the detector.

The responsivity of the resonant-cavity detector at resonance is comparable to the responsivity of a broadband infrared detector at that same wavelength. As a result, there is no decrease in responsivity at the desired wavelength of detection. An additional inherent  advantage to the resonant-cavity detector architecture is the suppression of optical response of consequence away from resonance which is desirable when a narrowband optical signal is of interest.

The resonant-cavity detector design space offers extensive freedom. Amethyst Research can develop resonant-cavity detectors with resonant  wavelengths within the SWIR, eSWIR, MWIR, and LWIR bands within the known performance trade-off space. The linewidth of the optical response  can be adjusted to the given application and exhibit a relatively wide spectral range (10s of nm) or a spectral linewidth <10nm (allowing for isotope discrimination for some gases). Amethyst Research has detector designs available for several wavelengths of interest within the MWIR and LWIR  bands although development has focused primarily on resonant-cavity detectors in the 3.1-3.4 and 4.0-4.2 micron ranges. Given the availability of additional development funding, other wavelengths can be explored relatively easily or performance within the aforementioned wavelength ranges can be improved.

Amethyst Resonant-Cavity Detector Photodiode Technical Paper

Amethyst Barrier Technology (ABaT™)

Amethyst Research’s new ABaT™ unipolar barrier detector offers low noise and high responsivity with excellent linearity over a broad spectral range in the mid-wave IR. The advanced unipolar barrier architecture reduces dark current while the use of III-V materials leverages mature and stable fab processes for superior manufacturability. The result is a low cost, high performance single element detector, suitable for Gas & Chemical sensors and other applications.

Detectors are available in T0-39 and T0-8 packages with active areas from ¼ to 1 mm2. The operating temperature is optionally controllable by thermoelectric cooling.

eSWIR ABaT Detector Datasheet ~2.8µm Cut Off

MWIR ABaT Detector Datasheet ~3.5µm Cut Off

MWIR ABaT Detector Datasheet ~4.7µm Cut Off

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