Michael D. Jack

Large format short-wave infrared (SWIR) focal plane array (FPA) with extremely low noise and high dynamic range

Raytheon Vision Systems (RVS) has obtained the initial performance data on a 1280x1024 format short wave infrared (SWIR) sensor with a dark current of 1 nA/cm2 and low noise input circuit of five noise electrons (5 e-), which is 2× lower electronic read-out noise and 2× lower dark current than previous designs. A remarkable feature of the sensor is that a novel high dynamic range circuit is also designed into the 15 × 15 μm pixel unit cell, in a large format, high density 1280×1024 SWIR FPA. The integration of the conflicting design requirements of extremely low noise with high dynamic range allows recognition of low contrast targets, without saturation from bright sources within the same frame of information. This enables operation in urban environments at low levels of ambient illumination, and simultaneously with bright sources that saturate conventional sensors.

Millimeter- and submillimeter-wave characterization of various fabrics

Transmission measurements of 14 fabrics are presented in the millimeter-wave and submillimeter-wave electromagnetic regions from 130 GHz to 1.2 THz. Three independent sources and experimental set-ups were used to obtain accurate results over a wide spectral range. Reflectivity, a useful parameter for imaging applications, was also measured for a subset of samples in the submillimeter-wave regime along with polarization sensitivity of the transmitted beam and transmission through doubled layers. All of the measurements were performed in free space. Details of these experimental set-ups along with their respective challenges are presented.

Advances in linear and area HgCdTe APD arrays for eyesafe LADAR sensors

HgCdTe APDs and APD arrays offer unique advantages for high-performance eyesafe LADAR sensors. These include: operation at room temperature, low-excess noise, high gain, high-quantum efficiency at eyesafe wavelengths, GHz bandwidth, and high-packing density. The utility of these benefits for systems are being demonstrated for both linear and area array sensors. Raytheon has fabricated 32 element linear APD arrays utilizing liquid phase epitaxy (LPE), and packaged and integrating these arrays with low-noise amplifiers. Typical better APDs configured as 50-micron square pixels and fabricated utilizing RIE, have demonstrated high fill factors, low crosstalk, excellent uniformity, low dark currents, and noise equivalent power (NEP) from 1-2 nW. Two units have been delivered to NVESD, assembled with range extraction electronics, and integrated into the CELRAP laser radar system. Tests on these sensors in July and October 2000 have demonstrated excellent functionality, detection of 1-cm wires, and range imaging. Work is presently underway under DARPAs 3-D imaging Sensor Program to extend this excellent performance to area arrays. High-density arrays have been fabricated using LPE and molecular beam epitaxy (MBE). HgCdTe APD arrays have been made in 5 X 5, 10 X 10 and larger formats. Initial data shows excellent typical better APD performance with unmultiplied dark current < 10 nA; and NEP < 2.0 nW at a gain of 10.

HgCdTe APD-based linear-mode photon counting components and ladar receivers

Linear mode photon counting (LMPC) provides significant advantages in comparison with Geiger Mode (GM) Photon Counting including absence of after-pulsing, nanosecond pulse to pulse temporal resolution and robust operation in the present of high density obscurants or variable reflectivity objects. For this reason Raytheon has developed and previously reported on unique linear mode photon counting components and modules based on combining advanced APDs and advanced high gain circuits. By using HgCdTe APDs we enable Poisson number preserving photon counting. A metric of photon counting technology is dark count rate and detection probability. In this paper we report on a performance breakthrough resulting from improvement in design, process and readout operation enabling >10x reduction in dark counts rate to ~10,000 cps and >104x reduction in surface dark current enabling long 10 ms integration times. Our analysis of key dark current contributors suggest that substantial further reduction in DCR to ~ 1/sec or less can be achieved by optimizing wavelength, operating voltage and temperature.

Epitaxial growth of HgCdTe 1.55-μm avalanche photodiodes by molecular beam epitaxy

Separate absorption and multiplication avalanche photodiode (SAM-APD) device structures, operating in the 1.1 - 1.6 micrometer spectral range, have been fabricated in the HgCdTe material system by molecular-beam epitaxy. These HgCdTe device structures, which offer an alternative technology to existing III-V APD detectors, were grown on CdZnTe(211)B substrates using CdTe, Te, and Hg sources with in situ In and As doping. The alloy composition of the HgCdTe layers was adjusted to achieve both efficient absorption of IR radiation in the 1.1 - 1.6 micrometer spectral range and low excess-noise avalanche multiplication. To achieve resonant enhancement of hole impact ionization from the split-off valence band, the Hg1-xCdxTe alloy composition in the gain region of the device, x equals 0.73, was chosen to achieve equality between the bandgap energy and spin-orbit splitting. The appropriate value of this alloy composition was determined from analysis of the 300 K bandgap and spin-orbit splitting energies of a set of calibration layers, using a combination of IR transmission and spectroscopic ellipsometry measurements. MBE-grown APD epitaxial wafers were processed into passivated mesa-type discrete device structures and diode mini-arrays using conventional HgCdTe process technology. Device spectral response, dark current density, and avalanche gain measurements were performed on discrete diodes and diode mini- arrays on the processed wafers. Avalanche gains in the range of 30 - 40 at reverse bias of 85 - 90 V and array-median dark current density below 2 X 10-4 A/cm2 at 40 V reverse bias have been demonstrated.

New developments in HgCdTe APDs and LADAR receivers

Raytheon is developing NIR sensor chip assemblies (SCAs) for scanning and staring 3D LADAR systems. High sensitivity is obtained by integrating high performance detectors with gain, i.e., APDs with very low noise Readout Integrated Circuits (ROICs). Unique aspects of these designs include: independent acquisition (non-gated) of pulse returns, multiple pulse returns with both time and intensity reported to enable full 3D reconstruction of the image. Recent breakthrough in device design has resulted in HgCdTe APDs operating at 300K with essentially no excess noise to gains in excess of 100, low NEP <1nW and GHz bandwidths and have demonstrated linear mode photon counting. SCAs utilizing these high performance APDs have been integrated and demonstrated excellent spatial and range resolution enabling detailed 3D imagery both at short range and long ranges. In the following we will review progress in real-time 3D LADAR imaging receiver products in two areas: (1) scanning 256 × 4 configuration for the Multi-Mode Sensor Seeker (MMSS) program and (2) staring 256 × 256 configuration for the Autonomous Landing and Hazard Avoidance Technology (ALHAT) lunar landing mission.

Advances in HgCdTe APDs and LADAR receivers

Raytheon is developing NIR sensor chip assemblies (SCAs) for scanning and staring 3D LADAR systems. High sensitivity is obtained by integrating high performance detectors with gain i.e. APDs with very low noise Readout Integrated Circuits. Unique aspects of these designs include: independent acquisition (non-gated) of pulse returns, multiple pulse returns with both time and intensity reported to enable full 3D reconstruction of the image. Recent breakthrough in device design has resulted in HgCdTe APDs operating at 300K with essentially no excess noise to gains in excess of 100, low NEP <1nW and GHz bandwidths and have demonstrated linear mode photon counting. SCAs utilizing these high performance APDs have been integrated and demonstrated excellent spatial and range resolution enabling detailed 3D imagery both at short range and long ranges. In this presentation we will review progress in high resolution scanning, staring and ultra-high sensitivity photon counting LADAR sensors.

Multifunction laser radar II

Laser radar systems are required for various military applications including obstacle detection, target recognition, and terrain mapping. Each application requires different system parameters such as pulse energy, repetition rate, and field of view. This paper is the second in a series of papers describing the progress toward a multifunction laser radar system under construction for the Cooperative Eyesafe Laser Radar Program (CELRAP) of the U.S. Army CECOM Night Vision and Electronic Sensors Directorate.

Multifunction laser radar

Laser radar systems are required for various military applications including obstacle detection, target recognition, and terrain mapping. Each application requires different system parameters such as pulse energy, repetition rate, and field of view. This paper presents a review of a multifunction laser radar system under construction for the Cooperative Eyesafe Laser Radar Program (CELRAP) of the U.S. Army CECOM Night Vision and Electronic Sensors Directorate.

Dual-band ultraviolet-short-wavelength infrared imaging via luminescent downshifting with colloidal quantum dots

Abstract. The performance of short-wavelength infrared (SWIR) cameras in the visible and ultraviolet (UV) regions is limited by the absorption of high-energy photons in inactive regions of the imaging array. Dual-band UV-SWIR imaging can be achieved by using PbS colloidal quantum dots (CQD) to downshift incident UV light to the SWIR band. The CQD downshifting layer has minimal impact on the SWIR imaging performance and greatly increases the UV sensitivity of an InGaAs camera. A dual-lens design in which the QDs are incorporated on a removable substrate is demonstrated, which provides UV sensitivity without modification of the InGaAs camera focal plane array. A single-lens design in which the QDs are deposited directly on the focal plane array is demonstrated using both a standard InGaAs focal plane and a substrate-thinned focal plane. Higher UV resolution for the substrate-thinned focal plane is observed.