The National Polar-orbiting Operational Environmental Satellite System (NPOESS), is overseen by the Integrated Program Office (IPO), a joint effort of the Department of Defense, Department of Commerce and NASA. One of the instruments on the NPOESS satellite is the Cross-track Infrared Sounder (CrIS) instrument. CrIS is a Fourier Transform interferometric infrared (FTIR) sensor used to measure earth radiance at high spectral resolution to derive pressure, temperature, and moisture profiles of the atmosphere from the ground on up. Each CrIS instrument contains three different cutoff wavelength (lambda(c))focal plane modules (FPMs): an SWIR FPM [lambda(c)(98 K) similar to 5 mu m], MWIR FPM [lambda(c)(98 K) similar to 9 mu m] and a LWIR FPM [lambda(c)(81 K) similar to 15.5 mu m]. There are nine large (850 mu m diameter) photodiodes per FPM, the nine detectors being arranged in a 3 x 3 array. The nine detectors are placed under tight tolerances in the X, Y, and Z dimensions. The steps involved in the transfer of photodiodes as part of a newly fabricated wafer to the mounting of the photodiodes on the FPM involves many processing steps including a significant amount of dicing, cleaning, wire bonding and baking at elevated temperatures.Quantum efficiency and I/f noise in Hg1-xCdxTe photodiodes are critical parameters that limit the sensitivity of infrared sounders. The ratio alpha, defined as the noise current in unit bandwidth i(n)(f = 1 Hz, V-d, Delta f = 1 Hz) to the dark current I-d(V-d) that is, alpha = i(n)/I-d is one of the parameters used to select photodiodes for placement in FPMs. alpha is equivalent to root alpha(H)/N that appears in the well-known Hooge expression. For the sixty-one, lambda(c) similar to 9 mu m photodiodes measured at 60 mV reverse bias and at 98 K, the average value of alpha(dark) = 1.3 x 10(-4) in the dark and alpha(PHOTO) = i(n)/i(PHOTO) is 2 x 10(-6) under illuminated conditions. These values of (x are a factor of two lower than that reported previously. The lambda(c) similar to 15.5 mu m photodiodes have average alpha(dark) = 1.3 x 10(-5) with the highest performance, diffusion current limited photodiodes having values of alpha(dark) in the mid 10(-6) range. All of the 850 mu m diameter, lambda(c) similar to 15.5 mu m photodiodes measured have excess low frequency noise, with the best performers having i(n)(f = 100 Hz, V-d =-60 mV, Delta f = 1 Hz) similar to 2 x 10(-11) A/Hz(1/2) and the best photodiode alpha(dark) = 3.92 x 10(-6).I-V measurements, noise, and visual inspections are performed at several steps in the photodiodes manufacturing process. It was observed, following FPM fabrication, photodiode dark current and noise had increased from the initial pre-mounting leadless chip carrier (LCC) measurements for some of the nine photodiodes. The performance degradation observed led to an investigation into the cause (baking at elevated temperatures, mechanical handling, electrical stress etc.) of photodiode degradation that occurred between LCC and FPM testing. Correlations between I-V, noise and surface visual defects have been performed on some lambda(c) similar to 15.5 mu m photodiodes. This paper outlines the results of the study, correlating the electrical performance observed to visual defects on the surface and to defects seen following cross sectioning of degraded photodiodes. In addition, other lessons-learned and the corrective actions implemented that led to the successful manufacture of SWIR, MWIR and LWIR large photodiodes from the material growth to insertion into and successful demonstration of flight FPMs for the CrIS program are described.

The National Polar-orbiting Operational Environmental Satellite System (NPOESS) Cross-track Infrared Sounder (CrIS) is a Fourier Transform interferometric sensor that measures earth radiances at high spectral resolution. Algorithms use the data to provide pressure, temperature, and moisture profiles of the atmosphere. The CrIS instrument contains photovoltaic detectors with spectral cut-offs denoted by SWIR, MWIR and LWIR. The CrIS instrument requires large-area, photovoltaic detectors with state-of-art detector performance at temperatures attainable with passive cooling. For example, detectors as large as 1 mm in diameter are required. To address these needs, Molecular Beam Epitaxy (MBE) is used to grow the appropriate bandgap n-type Hg1-xCdxTe on lattice matched CdZnTe. The p-side is obtained via arsenic implantation followed by appropriate annealing steps.

The 1/f noise in photovoltaic (PV) molecular-beam epitaxy (MBE)-grown Hg1-xCdxTe double-layer planar heterostructure (DLPH) large-area detectors is a critical noise component with the potential to limit sensitivity of the cross-track infrared sounder (CrIS) instrument. Therefore, an understanding of the origins and mechanisms of noise currents in these PV detectors is of great importance. Excess low-frequency noise has been measured on a number of 1000-mum-diameter active-area detectors of varying "quality" (i.e., having a wide range of I-V characteristics at 78 K). The 1/f noise was measured as a function of cut-off wavelength under illuminated conditions. For short-wave infrared (SWIR) detectors at 98 K, minimal 1/f noise was measured when the total current was dominated by diffusion with white noise spectral density in the mid-10(-15) A/Hz(1/2) range. For SWIR detectors dominated by other than diffusion current, the ratio, alpha, of the noise current in unit bandwidth i(n)(f = I Hz, V-d = -60 mV, and Deltaf = I Hz) to dark current I-d(V-d = -60 mV) was alpha(SW-d) = i(n)/I-d similar to 1 X 10(-3). The SWIR detectors measured at 0 mV under illuminated conditions had median alpha(SW-P) = i(n)/I-ph similar to 7 x 10(-6) For mid-wave infrared (MWIR) detectors, alpha(MW-d) = i(n)/I-d similar to 2 x 10(-4) due to tunneling current contributions to the 1/f noise. Measurements on forty-nine 1000-mum-diameter MWIR detectors under illuminated conditions at 98 K and -60 mV bias resulted in alpha(MW-P) = i(n)/I-ph = 4.16 +/- 1.69 x 10(-6). A significant point to note is that the photo-induced noise spectra are nearly identical at 0 mV and 100 mV reverse bias, with a noise-current-to-photocurrent ratio, alpha(MW-P), in the mid 10(-6) range. For long-wave infrared (LWIR) detectors measured at 78 K, the ratio, alpha(LW-d) = i(n)/I-d similar to 6 x 10(-6), for the best performers. The majority of the LWIR detectors exhibited alpha(LW-d) on the order of 2 x 10(-5). The photo-induced 1/f noise had alpha(LW-p) = i(n)/I-ph similar to 5 x 10(-6). The value of the noise-current-to-dark-current ratio, a appears to increase with increasing bandgap. It is not clear if this is due to different current mechanisms impacting 1/f noise performance. Measurements on detectors of different bandgaps are needed at temperatures where diffusion current is the dominant current. Excess low-frequency noise measurements made as a function of detector reverse bias indicate 1/f noise may result primarily from the dominant current mechanism at each particular bias. The 1/f noise was not a direct function of the applied bias.

The 1/f noise in photovoltaic (PV) molecular-beam epitaxy (MBE)-grown Hg1−xCdxTe double-layer planar heterostructure (DLPH) large-area detectors is a critical noise component with the potential to limit sensitivity of the cross-track infrared sounder (CrIS) instrument. Therefore, an understanding of the origins and mechanisms of noise currents in these PV detectors is of great importance. Excess low-frequency noise has been measured on a number of 1000-µm-diameter active-area detectors of varying “quality” (i.e., having a wide range of I-V characteristics at 78 K). The 1/f noise was measured as a function of cut-off wavelength under illuminated conditions. For short-wave infrared (SWIR) detectors at 98 K, minimal 1/f noise was measured when the total current was dominated by diffusion with white noise spectral density in the mid-10−15A/Hz1/2 range. For SWIR detectors dominated by other than diffusion current, the ratio, α, of the noise current in unit bandwidth in(f = 1 Hz, Vd = −60 mV, and Δf = 1 Hz) to dark current Id(Vd = −60 mV) was αSW-d = in/Id ∼ 1 × 10−3. The SWIR detectors measured at 0 mV under illuminated conditions had median αSW-P = in/Iph ∼ 7 × 10−6. For mid-wave infrared (MWIR) detectors, αMW-d = in/Id ∼ 2 × 10−4, due to tunneling current contributions to the 1/f noise. Measurements on forty-nine 1000-µm-diameter MWIR detectors under illuminated conditions at 98 K and −60 mV bias resulted in αMW-P = in/Iph = 4.16 ± 1.69 × 10−6. A significant point to note is that the photo-induced noise spectra are nearly identical at 0 mV and 100 mV reverse bias, with a noise-current-to-photocurrent ratio, αMW-P, in the mid 10−6 range. For long-wave infrared (LWIR) detectors measured at 78 K, the ratio, αLW-d = in/Id ∼ 6 × 10−6, for the best performers. The majority of the LWIR detectors exhibited αLW-d on the order of 2 × 10−5. The photo-induced 1/f noise had αLW-P = in/Iph ∼ 5 × 10−6. The value of the noise-current-to-dark-current ratio, α appears to increase with increasing bandgap. It is not clear if this is due to different current mechanisms impacting 1/f noise performance. Measurements on detectors of different bandgaps are needed at temperatures where diffusion current is the dominant current. Excess low-frequency noise measurements made as a function of detector reverse bias indicate 1/f noise may result primarily from the dominant current mechanism at each particular bias. The 1/f noise was not a direct function of the applied bias.

The National Polar-orbiting Operational Environmental Satellite System (NPOESS) Cross-track Infrared Sounder (CrIS) is a Fourier Transform interferometric sensor that measures earth radiances at high spectral resolution. Algorithms use the data to provide pressure, temperature, and moisture profiles of the atmosphere. The CrIS instrument contains photovoltaic detectors with spectral cut-offs denoted by SWIR [lambda(c)(98 K) similar to 5 mum], MWIR [lambda(c)(98 K) similar to 9 mum] and LWIR [lambda(c)(81 K) similar to 15 mum]. The CrIS instrument requires large-area, photovoltaic detectors with state-of-art detector performance at temperatures attainable with passive cooling. For example, detectors as large as 1 mm in diameter are required. To address these needs, Molecular Beam Epitaxy (MBE) is used to grow the appropriate bandgap n-type Hg1-xCdxTe on lattice matched CdZnTe. The p-side is obtained via arsenic implantation followed by appropriate annealing steps.1/f noise in photovoltaic Hg1-xCdTe detectors is a critical parameter that limits the sensitivity of the CrIS instrument. Therefore, an understanding of the mechanisms that impact noise currents in a photovoltaic detector is of great importance. MBE grown Hg1-xCdxTe Double Layer Planar Heterostructure (DLPH) photovoltaic detectors have been characterized, to determine the dominant mechanisms impacting detector I-V performance. Excess low frequency noise has been measured on a number of 1000 gm diameter active area detectors of varying "quality" (i.e. having a wide range of I-V performance at 78 K). The 1/f noise was measured as a function of bias, cutoff wavelength, and under illuminated conditions. For SWIR [lambdac(98 K) similar to 5 mum] detectors at 98 K, minimal 1/f noise was measured. The noise was white and in the mid 10-(15) A/Hz(1/2) range. For MWIR [lambda(c)(98 K) similar to 9 mum] detectors, the most important point to note is that the photo-induced noise spectra are nearly identical at 0 mV and 100 mV reverse bias, with a noise current to photocurrent ratio of alpha(P) in the mid x 10(-6) range. For the LWIR [lambda(c)(81 K) similar to 15 mum] detectors measured at 78 K, the ratio, alpha, of the noise current in unit bandwidth i,(f = 1 Hz, V-d = -0.1 V, Deltaf = 1 Hz) to the dark current I-d(V-d = -0.1 V) is alpha(DLW) = i(n)/I-d similar to 6 x 10(-6) for the best performers. The majority of the detectors had alpha(DLW) similar to 2 x 10(-5) (Our alpha(DLW) is equivalent to rootalpha(H)/N which appears in the well-known Hooge expression.). The photo-induced 1/f noise had alpha(PLW) = i(n)/I-photo similar to 5 x 10(-6). For the MWIR detectors measured at 98 K, alpha(DMW) = i(n)/I-d = 1.59 +/- 0.69 x 10(-4). The value of alpha increases as the bandgap, increases. Excess low frequency noise measurements made as a ftinction of detector reverse bias indicate 1/f noise appears to result from the dominant current at each particular bias. 1/f noise was not a direct function of the applied bias.

The National Polar-orbiting Operational Environmental Satellite System (NPOESS) Cross-track Infrared Sounder (CrIS) is a Fourier Transform interferometer-based sensor used to measure earth radiance at high spectral resolution and low spatial resolution. Measured radiance data are analyzed by end users to provide pressure, temperature and moisture profiles of the atmosphere. The CrIS instrument contains Mercury-Cadmium-Telluride (MCT) photovoltaic (PV) detectors with spectral response in the SWIR (lambda(c) similar to 5 mum at 98K), MWIR (lambda(c) similar to 9 mum at 98K) and LWIR (lambda(c) similar to 15 mum at 81K) ranges. The CrIS instrument requires large area detectors (1mm diameter) with state-of-the-art detector performance at temperatures attainable with passive cooling.In the case of the LWIR bands noise associated with the detectors limit the instrument performance. In this paper we describe a study of the noise characteristics of a sample of CrIS MCT PV detectors, emphasizing acquisition and validation of Lfnoise measurements for these devices. Interesting aspects of the 1/f noise dependence on bias-voltage and bias-current are noted. The results are analyzed further in a companion paper(1) that emphasizes the relationship between leakage current mechanisms in the diodes and 1/f noise observed.