A comprehensive study of mid-wavelength infrared (MWIR) InAs/InAsSb type-II superlattice (T2SL) photodetectors was performed for full characterization of the E-O performance, reliability, and linearity as well as response speed. Teledyne Judson Technologies has recently developed high operating temperature (HOT) MWIR InAs/InAsSb T2SL large area discrete detectors of 0.25mm and 1mm for front-side illumination. The 50% cut-off wavelength of the detectors ranges from ~5.4 to ~5.7μm at room temperature. For the reliability tests, the T2SL detectors were thermally cycled and humidity tested. Initial testing data showed excellent stability to the temperature and humidity, indicating the T2SL detectors have long-term stability. Linearity, response speed and capacitance were measured at various temperatures and reverse biases. This work presents comprehensive test results, data analysis, and discussion, showing these large size, discrete T2SL detectors have the potential to replace conventional MWIR detector materials.
At present, InGaAs and HgCdTe are still the primary choices of materials for 1-3μm short wavelength infrared (SWIR) photodetectors (photodiodes). Besides lattice matched 1.7μm cutoff standard InGaAs photodetectors, demands for extended wavelength (EW) InGaAs photodetectors (1.9-2.6μm cutoff) continue to grow in a broad range of markets such as Internet-of-Things (IoT), gas sensing, food processing, etc. This paper reviews recent progress in EW InGaAs photodetectors at Teledyne Judson Technologies (TJT). For 1.7μm cutoff at room temperature, InGaAs detectors generally have higher performance (lower dark current and higher shunt resistance) than the conventional SWIR HgCdTe detectors as characterized by the famous Rule-07 formula. In contrast, up to just recent years, EW InGaAs detectors generally had performance below the corresponding SWIR HgCdTe per Rule-07 for the same cutoff wavelength and operating temperature. The performance gap between the two materials became larger as the cutoff wavelength increases. This performance difference is primarily due to the lattice mismatch or strain induced defects in EW InGaAs materials. However, the recent progress in both EW InGaAs material growth and detector fabrication has resulted in dramatic improvement of EW InGaAs detector performance. The performance gap between the two materials is becoming much smaller or negligible at some wavelengths, while at other wavelengths, EW InGaAs even exceeds SWIR HgCdTe per Rule-07. In this paper, we will present recent detector performance data taken from EW InGaAs, as well as SWIR HgCdTe photodetectors, manufactured at TJT through state-of-the-art technologies. These discrete frontside illuminated detectors have sizes ranging from <0.25mm up to 5mm dia. and operate at temperatures from thermoelectric cooled (TEC, -20°C to -85°C) to above room temperature. An in-depth analysis of dark current density at reverse biases, as well as shunt resistance-area product at zero bias (R0A), over a broad temperature range, is performed. The data is compared with Rule-07 over the wavelength and temperature ranges of interest. Other detector performance parameters, such as spectral responsivity (quantum efficiency) and capacitance, are also compared between the two materials.
A comprehensive study of photoresponse linearity characteristics, for high performance short wavelength infrared (SWIR) photodiodes of various materials, is performed. These photovoltaic (PV) detectors were manufactured at Teledyne Judson Technologies (TJT) as standard products, with the state-of-the-art technologies. A broad range of detectors made from several IR materials were selected for linearity tests, including InGaAs (cutoff wavelength from lattice matched 1.7μm to extended wavelength of 1.9-2.6μm), SWIR PV HgCdTe (2.5-2.8μm cutoff), Ge (1.8μm cutoff), and InAs (3.5μm cutoff). Comprehensive linearity test data are presented for each detector material. Characterization of linearity dependence on detector size, operating temperature, reverse bias, and light spot size is studied. Detector size ranges from <0.25mm dia. up to 10mm dia., detector operating temperature from room temperature to thermoelectric cooled (TEC) temperatures, detector bias from 0V up to 10V reverse bias for some materials, and light spot size from 10μm up to 1mm. This work focuses on photocurrent saturation in the high optical power (or photon flux) range. Two saturation mechanisms are investigated, including series resistance effect and Auger recombination effect.
High performance short-wavelength infrared (SWIR) HgCdTe focal plane arrays (FPAs) of 320x256/30μm have been well developed and are now in production at Teledyne Judson Technologies (TJT). These FPAs have two cutoff wavelengths, 2.5μm and 2.9μm in general, and can operate over a wide temperature range. The detector arrays were fabricated primarily with molecular beam epitaxy (MBE) HgCdTe materials, although liquid phase epitaxy (LPE) materials were also used, both materials on CdZnTe substrates. These FPAs use ISC 9809 Si readout integrated circuit (ROIC) and have excellent operability, low dark current, high quantum efficiency (QE), good uniformity and high yield. Comprehensive characterization of FPA performance was performed from room temperature to LN2, and the test results are presented and discussed in this paper. Typical operability is ~99.9%, and peak QE ~85%. FPA noise is background limited at -70°C with field-of-view (FOV) ~100° and becomes lab camera electronics limited when FOV ~0°. Pixel dark current either matches or is below the values from Rule-07 model over a wide temperature range. Noise equivalent irradiance (NEI) of 2-3E9 Ph/cm2-s is achieved at -70°C and could be further reduced under smaller FOV.
Teledyne Judson Technologies (TJT) has developed high operating temperature (HOT) mid-wavelength infrared (MWIR) photodetectors based on InAs/InAsSb type-II superlattice (T2SL) with an electron barrier. Large area discrete detectors of 0.25mm and 1mm diameters were designed and fabricated for front-side illumination. Comprehensive E-O characterization was performed at room temperature and thermo-electric cooled (TEC) temperatures. The unique fabrication process was developed for a quasi-planar structure, enabling simplified fabrication for low-cost large volume production. The detector shows a 50% cut-off wavelength of ~5.5μm at room temperature. Peak responsivity of 2.47 A/W was achieved on 1mm detectors at peak wavelength ~ 4.24μm, -0.3V bias and 295K. Peak quantum efficiency (QE) was 72% with an antireflection coating. The 1mm detectors showed peak detectivity (D*) of 1.9x109 cm-√Hz/W at -0.3V bias, 295K and 10 kHz. Dark current density as low as 1.17 A/cm2 was achieved at -0.3V bias and 295K on 1mm detectors. The dark current was diffusion-limited at higher temperatures above ~120K while it was dominated by either tunneling or surface leakage currents at lower temperatures. Similar results were obtained on 0.25mm detectors.
In this paper, we present the test results of a flight-grade 13μm pixel pitch 6000-element 1.7μm InGaAs linear array in a hermetic package, designed and developed for space remote sensing and imaging applications. The array consists of a single 13μm pixel pitch 6000-element InGaAs linear array and a custom single digital 2.0 Mecapacitance trans-impedance amplifier (CTIA) readout integrated circuit (ROIC) with four gains. We have achieved greater than 80% peak quantum efficiency and higher than 1100 signal-to-noise ratio (SNR) at 90% well fill. The focal plane array is in a vacuum hermatically sealed package with an anti-reflective (AR)-coated Sapphire window and 29 pins, including four for low voltage differential signaling (LVDS) outputs.
Teledyne Judson Technologies (TJT) has been developing technology for small pixel, large format, low dark current, and
low capacitance NIR/SWIR InGaAs detector arrays, aiming to produce <10μm pixels and >2Kx2K format arrays that
can be operated at or near room temperature. Furthermore, TJT is now developing technology for sub-10μm pixel arrays
in response to requirements for a variety of low light level (LLL) imaging applications. In this paper, we will review test
data that demonstrates lower dark current density for 10-20μm pixel arrays. We will present preliminary results on the
successful fabrication of test arrays with pixels as small as 5μm. In addition, a lot of effort has been made to control and
reduce the detector pixel capacitance which can become another source of detector noise. TJT is also developing 4"
InGaAs wafer process and now offers four different types of InGaAs 2D arrays/FPAs that are tailored to different
customer requirements for dark current, capacitance, spectral response, and bias range.
The new NASA Enhanced MODIS Airborne Simulator (eMAS) is based on the legacy MAS system,
which has been used extensively in support of the NASA Earth Observing System program since
1995. eMAS consists of two separate instruments designed to fly together on the NASA ER-2 and
Global Hawk high altitude aircraft.
The eMAS-IR instrument is an upgraded version of the legacy MAS line-scanning spectrometer,
with 38 spectral bands in the wavelength range from 0.47 to 14.1 μm. The original LN2-cooled
MAS MWIR and LWIR spectrometers are replaced with a single vacuum-sealed, Stirling-cooled
assembly, having a single MWIR and twelve LWIR bands. This spectrometer module contains a
cold optical bench where both dispersive optics and detector arrays are maintained at cryogenic
temperatures to reduce infrared background noise, and ensure spectral stability during high altitude
The EMAS-HS instrument is a stand-alone push-broom imaging spectrometer, with 202 contiguous
spectral bands in the wavelength range from 0.38 to 2.40 μm. It consists of two Offner
spectrometers, mated to a 4-mirror anastigmatic telescope. The system has a single slit, and uses a
dichroic beam-splitter to divide the incoming energy between VNIR and SWIR focal plane arrays.
It will be synchronized and bore-sighted with the IR line-scanner, and includes an active source for
monitoring calibration stability.
eMAS is intended to support future satellite missions including the Hyperspectral Infrared Imager (
HyspIRI,) the National Polar-orbiting Operational Environmental Satellite System (NPOESS)
Preparatory Project (NPP,) and the follow-on Joint Polar Satellite System (JPSS.)
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.
An engineering design of an imager upgrade is under consideration for the GOES-N/Q series. The upgrade consist of adding up to three new IR channels at 4 km resolution and doubling the earth coverage rate. The design approach introduces advanced technology as needed to minimize impacts to the sensor optical and mechanical configuration, electronics box layout, data communication links and ground systems. By operating presently redundant portions of detector arrays and developing double rate signal processors, the scanning servo system and electronics modules are largely retained. Bicolor detectors and optical coatings are used to add channels while retaining the present relay optics and radiant cooler layouts. Lossy data compression of visible imagery and lossless data compression of IR imagery are used to preserve the sensor data and precessed data relay communications links. System NEDT and SNR performance and implementation issues for new technologies are addressed.