This paper reports preliminary results obtained on 1.7µm InGaAs, Vis-InGaAs, extended-wavelength InGaAs, InSb, and HgCdTe 320x256 FPAs fabricated at Judson. Test structures designed to characterize fundamental detector parameters are presented. FPA performance and imaging analysis are reported. Possible performance improvements by means of architectural design and fabrication process refinement are described. Future development plan and preliminary experimental results on FPAs with larger format and smaller pitch are also discussed. Relatively low dark current and NEI values, as well as high operability, are achieved for 1.7µm InGaAs FPAs at room temperature. High quantum efficiency in the visible wavelength range is achieved for Vis-InGaAs FPAs. Low NETD values are achieved for InSb FPAs at LN2 and MWIR HgCdTe FPAs at -70°C (203°K).
A novel InGaAs structure has been developed specifically for use in high-speed applications that require large active
area diodes with greater than 3mm diameter size. The device design is based on a thick and fully depleted PIN structure.
The intrinsic layer thickness is 2 to 4 times thicker than that of the conventional PIN detectors. Greater than 3-fold
reduction in detector capacitance per unit area and the corresponding RC time constant has been demonstrated. Even
with such significant speed enhancement, other diode performance characteristics such as dark current and breakdown
voltage of these novel InGaAs PIN detectors remain comparable to those of the conventional structure. Front- and
backside-illuminated InGaAs detectors are fabricated. Both show equally high-quality spectral response and spatial
uniformity. Comprehensive electro-optical tests are performed and the data and analysis are presented. Temperature
dependent performance characteristics are also reported. Well-behaved performance characteristics are observed from
TE-cooled temperatures to elevated temperatures above ambient.
Advanced detector fabrication technology and high reliability packaging processes have been developed for the manufacturing of high performance HgCdTe photoconductors. These infrared array assemblies for use in GOES and other weather satellites operate at radiative cooler temperatures ranging from 95 to 115 K. A large quality of flight detectors sensitive to spectral wavelengths ranging from 7 to 16 micrometers have been fully characterized. Detector performance data as a function of bias, temperature, frequency and cutoff wavelength are presented. A computerized model has been developed and reasonable agreements between computer projections and measured performance are obtained. This model has been used successfully to identify an optimum set of materials and device parameters for a given set of system requirements. In addition, advanced assembly and packaging techniques have been developed to ensure tight alignment tolerances, long- life hermeticity, low-outgassing and low internal reflection. Detector array assemblies have been demonstrated to withstand extensive qualification and environmental tests and the results are summarized.
The low frequency noise characteristics of HgCdTe photoconductors are very important to the weather satellite user community because of the extremely long integration time used in these sensor applications. There are several detector technologies critical to the reduction of 1/f noise including surface passivation, bulk material selection, defect-free wafer thinning, contact metallurgy, off-HgCdTe bonding,and planar/low pressure substrate mounting. Each of these technical building blocks is discussed. When integrated to form a combined process, these critical technologies lead to a significant improvement in 1/f noise. Tow widely accepted empirical models of 1/f noise are reviewed. Experimental results validate Kruse's model but repudiate Broudy's model, namely, 1/f noise is inversely proportional to the square root of the detector volume but does not depend on the gr noise of the detector. Furthermore, we find no correlations between 1/f noise and total detector surface area or the detector contact effects. A novel test structure is presented which suggests that by using innovative detector geometries, the detector designers may be able to increase D* at low frequencies compared to the conventional square or rectangular detector structures.
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