Capacitors are ubiquitous in signal processing circuits. Dielectric capacitors based on metal-oxide-semiconductor (MOS) and metal-insulator-metal (MIM) designs are currently the industry standard for on-chip charge storage. By comparison, electric double-layer capacitors (EDLC), or supercapacitors, offer capacitances that are orders of magnitude higher than dielectric capacitors. In this paper we present some early work in fabricating solid-state, on-chip EDLC.

Advanced LADAR receivers enable high accuracy identification of targets at ranges beyond standard EOIR sensors. Increased sensitivity of these receivers will enable reductions in laser power, hence more affordable, smaller sensors as well as much longer range of detection. Raytheon has made a recent breakthrough in LADAR architecture by combining very low noise similar to 30 electron front end amplifiers with moderate gain >60 Avalanche Photodiodes. The combination of these enables detection of laser pulse returns containing as few as one photon up to 1000s of photons. Because a lower APD gain is utilized the sensor operation differs dramatically from traditional "Geiger mode APD" LADARs. Linear mode photon counting LADAR offers advantages including: determination of intensity as well as time of arrival, nanosecond recovery times and discrimination between radiation events and signals. In our talk we will present an update of this development work: the basic amplifier and APD component performance, the front end architecture, the demonstration of single photon detection using a simple 4 x 4 SCA and the design and evaluation of critical components of a fully integrated 8x8 linear mode photon counting camera under development in support of the Ultra-Sensitive Detector (USD) program sponsored by AFRL-Kirtland.

An initial investigation of the use of atomic nitrogen for controlled p-type doping of wide-bandgap Hg0.3Cd0.7Te (x = 0.7) is reported. Mixtures of argon and nitrogen, ranging in nitrogen concentration from 0.1% to 100%, have been utilized to demonstrate well-controlled nitrogen incorporation in the 1016 cm−3 to 1020 cm−3 range using total gas flow rates of 0.3 sccm to 4.0 sccm and radiofrequency (RF) powers of 100 W to 400 W. Nitrogen doping exhibits several desirable attributes including abrupt turn-on and turn-off and minimal sensitivity to variations in growth temperature and HgCdTe composition, with no negative effects on HgCdTe dislocation density and morphology. Preliminary electrical measurements indicate primarily n-type behavior in the 1014 cm−3 to 1015 cm−3 range in as-grown x = 0.7 HgCdTe and CdTe films doped with nitrogen at 1018 cm−3 to 1020 cm−3 concentrations, while ZnTe films have exhibited p-type electrical activity with hole concentrations approaching 1020 cm−3.

The application of spectroscopic ellipsometry (SE) for real-time composition determination during molecular beam epitaxy (MBE) growth of Hg1−xCdxTe alloys with x>0.5 is reported. Techniques previously developed for SE determination of composition in long-wavelength infrared (LWIR) HgCdTe have been successfully extended to near-infrared HgCdTe avalanche photodiode (APD) device structures with x values in the range of 0.6–0.8. Ellipsometric data collected over a spectral range of 1.7–5 eV were used to measure depth profiles of HgCdTe alloy composition through the use of an optical model of the growth surface. The optical model used a dielectric-function database collected through the growth of a set of HgCdTe calibration samples with x ranging from 0.6 to 0.8. The sensitivity of this SE method of composition determination is estimated to be Δx ∼0.0002 at x=0.6, which is sufficiently low to sense composition changes arising from flux variations of less than 0.1%. Errors in composition determination because of Hg-flux variations appear to be inconsequential, while substrate-temperature fluctuations have been observed to alter the derived composition at a rate of −0.0004/°C. By comparing the composition inferred from SE and postgrowth 300 K IR transmission measurements on a set of APD device structures, the run-to-run precision of the Se-derived composition (at x=0.6) is estimated to be ±0.0012, which is equivalent to the precision achieved with the same instrumentation during the growth of mid-wavelength infrared (MWIR) HgCdTe alloys in the same MBE system.

Since its initial synthesis and investigation more than 40 years ago, the HgCdTe alloy semiconductor system has evolved into one of the primary infrared detector materials for high-performance infrared focal-plane arrays (FPA) designed to operate in the 3-5 mum and 8-12 mum spectral ranges of importance for thermal imaging systems. Over the course of the past decade, significant advances have been made in the development of thin-film epitaxial growth techniques, such as molecular-beam epitaxy (MBE), which have enabled the synthesis of IR detector device structures with complex doping and composition profiles. The central role played by in situ sensors for monitoring and control of the MBE growth process are reviewed. The development of MBE HgCdTe growth technology is discussed in three particular device applications: avalanche photodiodes for 1.55 mum photodetection, megapixel FPAs on Si substrates, and multispectral IR detectors.

Raytheon has recently been funded by DARPA to develop an FPA for single shot eyesafe ladar operation. The goal of the program is to develop new high speed imaging arrays to rapidly acquire high resolution, three dimensional images of tactical targets at ranges as long as 7 to 10 kilometers. This would provide precision strike, target identification from rapidly moving platforms, such as air-to-ground seekers, which would enhance counter-counter measure (CCM) performance and the ability to lock-on after launch. Also a goal is to demonstrate the acquisition of hidden, camouflaged and partially obscured targets. Raytheon's approach consists of using HgCdTe APD arrays which offer unique advantages for high performance eyesafe LADAR sensors. These include: eyesafe operation at room temperature, low excess noise, high gain to overcome thermal and preamp noise, GHz bandwidth and high packing density. The detector array will be coupled with a Readout Integrated Circuit, ROIC, that will capture all the information required for accurate range determination. The two components encompass a hybrid imaging array consisting of two IC circuit chips vertically integrated via an array of indium metal "bumps." The chip containing the APD detector array and the silicon signal processing readout chip are independently optimized to provide the highest possible performance for each function.

In the U.S. CELRAP laser radar hardware, 25mJ KTA OPO shifted Nd:YAG laser pulses at 1.54 microns are transmitted through beam fan optics. The return signal is imaged onto InGaAs PIN or HgCdTe APD linear multiple channel detector arrays.

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 (>80%), low crosstalk (<2%), excellent uniformity, low dark currents (<10nA), 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 I-cm wires, and range imaging. Work is presently underway under DARPA's 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.

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.

The InAs/Ga1−xInxSb strained-layer superlattice (SLS) holds promise as an alternative III–V semiconductor system for long wavelength infrared detectors. In this article, we present the first investigation, to the best of our knowledge, of heterojunction photodiodes using this new material. The devices were grown by molecular beam epitaxy on GaSb substrates, and are comprised of a 38 Å InAs/16 Å Ga0.64In0.36Sb SLS used in double heterojunctions with GaSb contact layers. The structures were designed to optimize the quantum efficiency while minimizing transport barriers at the heterointerfaces. The photodiodes are assessed through the correlation of their performance with the SLS material quality and the detector design. X-ray diffraction, absorption, and Hall measurements are used to determine the SLS material properties. The electrical and optical properties of the photodiodes are determined using current–voltage and spectral responsivity measurements. At 78 K, these devices exhibit rectifying electrical behavior and photoresponse out to a wavelength of 10.6 μm corresponding to the SLS energy gap. The responsivity and resistance in these thin-layered (0.75 μm), unpassivated photodiodes result in a detectivity of 1×1010 cm √Hz/W at 8.8 μm and 78 K. Based upon the performance of these devices, we conclude that high-sensitivity operation of long-wavelength photovoltaic detectors at temperatures well in excess of conventional III–V band gap-engineered systems, and potentially in excess of HgCdTe, is feasible using this material system.

Heterojunction Hg1.,CdxTe (HCT) diodes fabricated by liquid phase epitaxy (LPE) are a key to ultrahigh performance Infrared Focal Planes [ll. The authors present for the first time the results of measurements of both heterojunction FETs and bipolar transistors fabricated using LPE. These offer benefits for low noise amplification. Breakthroughs in 11-VI Molecular Beam Epitaxy (MBE) now enable excellent control of layer width and doping. Simulations utilizing a program developed for IIVI heterojunction devices show that MBE-based HCT he terojun c ti on bi p ol ar transistors (HBTs) can be competitive with state-of-the-art silicon and 111-V HBTs at low temperatures.