We report on a multi-year development effort demonstrating resonant cavity enhanced photodiodes (RCE-PDs) with an all-epitaxial architecture, exploiting the GaSb matched material system and its increasingly popular family of IR absorbers. RCE-PDs redefine the relationship between signal and noise generation within IR detectors, breaking some of the performance limits constraining conventional IR detectors. High performance RCE-PDs are achieved with resonance wavelengths from the SWIR to the LWIR, using GaSb/AlAsSb DBR mirrors and InGaAsSb, InAs, InAsSb and T2SL absorbers. Finally, we introduce a graded thickness RCE-PD which can perform the function of a spectrometer on a chip.
Absorption fingerprints of substances such as glucose, acetone and CO2 fall within the short-wave infrared range (SWIR), in the wavelength range 1.7 μm – 2.4 μm; improved detection of these substances will be impactful to health, wellbeing and the environment. A design of detector based on the emerging material system InGaAsSb with cut-off wavelengths in this range, 2.25 μm, is presented. By controlling the composition of the InGaAsSb, the cut-off wavelength can be extended beyond GaSb (1.7 μm) to a particular target with minimal leakage increase. Unbiased operation has been obtained using a p-B-n structure design and a quasi-planar device design with good optical power resolution (40 pW). At the current state of optimisation, D* is 9.4×1010 Jones at 0 V bias and 2.0 μm which is approaching the much more mature extended InGaAs technology, grown mismatched on InP, with the same cut-off wavelength. InGaAsSb is grown on GaSb substrates which are increasingly popular for IR optoelectronics and being lattice matched will offer a higher yield in production compared to mismatched growth. With InGaAsSb, the GaSb-matched material system can support lattice matched epilayers exhibiting cut-off wavelengths from the near to the longwave infrared. This work looks towards future applications through evaluations and measurements of low concentration glucose solutions. These detectors show great promise for future commercial applications.
We investigate the characteristics of the quaternary alloy InxGa1−xAsySb1−y as a viable alternative to extended InGaAs for sensing in short wavelength infrared. InxGa1−xAsySb1−yp-i-n photodetectors with 0 < x < 0.3 have been grown on GaSb substrates in the wavelength region between 1 - 3 µm. Absorption coefficient up to ∼ 104 cm−1 compares well with that of InGaAs, increasing for samples with narrower bandgaps. Capacitance measurements shed light on the intrinsic unintentional doping levels, which are up to an order of magnitude lower than in typical bulk GaSb, due to a reduction in native defects of the material. Current density initially decreases with addition of small fractions of In/As to GaSb, then proceeds to increase once again towards higher alloy fractions as the bandgap narrows.
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