High performance focal plane array technologies from short to long wavelength infrared bands

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2014
Arslan, Yetkin
This thesis work covers the development of three different state of the art infrared sensor technologies: quantum well infrared photodetectors (QWIPs), HgCdTe sensors and extended InGaAs photodetectors. QWIP is the leading member of the quantum structure infrared photodetector family providing excellent uniformity and stability with field proven performance. The utilization of the InP/In0.48Ga0.52As multi-quantum well structure (instead of the standard AlGaAs/GaAs material system) for the implementation of large format (640x512 format, 25 µm pitch) long wavelength infrared (LWIR) QWIP focal plane arrays (FPAs) and the careful design of the detector structure yielded a quantum efficiency as high as 31% in the diffraction grating coupled FPA pixels, which is almost an order of magnitude larger than the pixel quantum efficiency of a standard AlGaAs/GaAs QWIP FPA. The noise equivalent temperature difference of the FPA with f/2 optics is 30 mK with an integration time as low as 1 ms at 67 K. Above 20% conversion efficiency of the FPA allows desirable thermal imaging with integration times as low as several hundred µs. The results demonstrate that the main limitations of the standard QWIP technology can be overcome through the utilization of alternative material systems and proper FPA processing techniques. HgCdTe is the material of choice for high-end infrared imaging systems, offering high flexibility and still unmatched performance. In this work, complete production cycles for photovoltaic HgCdTe focal plane arrays are developed starting from the molecular beam epitaxy (MBE) growth of the material. The dynamic resistance-area product of the developed LWIR HgCdTe FPA (~ 10 µm cut-off wavelength) pixels is as high as ~2000 Ω-cm2 at 78 K. The peak detectivity of the pixels is as high as 1.28x1011 cm√Hz/W with f/1 optics which is comparable to that of the best LWIR HgCdTe detectors with similar cut-off wavelength. We have also developed the procedures to implement a solid source (MBE) grown large format (640x512) extended short wavelength infrared (SWIR) In0.83Ga0.17As sensor with desirable performance at both pixel and FPA levels. The FPA pixels in the mesa structure grown in our laboratory on a graded AlInAs buffer layer with 2.65 µm 300 K cut-off wavelength exhibited 300 and 200 K peak detectivities as high as ~2.5x1010 and ~1x1012 cm√Hz/W which are both equivalent to the theoretical limits set by the Johnson noise of the detector. Dark current analysis of the pixels displayed no considerable tunneling component with the dark current being dominated by generation-recombination and shunt leakage mechanisms above 200 K up to a reverse bias voltage of 3 V. Moreover, the noise measurements displayed no 1/f noise in the FPA pixels. In spite of the large lattice mismatch, the FPA yielded very good response linearity, as well as impressively good responsivity nonuniformity and pixel operability of 5.5 % and 99.8 %, which are among the best results reported for extended InGaAs FPAs with similar cut-off wavelengths. These results demonstrate the feasibility of the InGaAs SWIR FPA technology with extended cut-off wavelengths as high as ~2.7 µm as an alternative to SWIR HgCdTe FPAs with higher production cost. .

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Citation Formats
Y. Arslan, “High performance focal plane array technologies from short to long wavelength infrared bands,” Ph.D. - Doctoral Program, Middle East Technical University, 2014.