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.

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.

Over the past decade, liquid-phase epitaxy (LPE) has become an established technique for the growth of HgCdTe. This article reviews one of the successful LPE technologies developed for HgCdTe, specifically, ''infinite-melt'' vertical LPE (VLPE) from Hg-rich' solutions.In spite of the relatively low solubility of Cd in Hg-rich solutions and the relatively high Hg vapor pressure at the usual growth temperatures, this approach has been found to offer superior results for growth of HgCdTe suitable for various compositions and layer structures.An historical perspective and the current status of VLPE technology are presented. Particular emphasis is placed on the important role of the thermodynamic parameters (phase diagram), on control of stoichiometry (defect chemistry) and on impurity doping (distribution coefficient) for growth of HgCdTe layers from Hg solutions. Critical material characteristics, such as transport properties, minority-carrier lifetime, morphology and crystal structure, are also discussed.

Liquid-phase epitaxy (LPE) has emerged as the predominant materials growth technology for the fabrication of HgCdTe infrared (IR) detectors in the IR community over the past decade. This paper reviews one of the most successful LPE technologies developed for HgCdTe, specifically, 'infinite-melt' vertical LPE (VLPE) from Hg-rich solutions. A historical perspective and the current status of VLPE technology are reported. Extensive statistics of performance and producibility of the VLPE technology are elaborated to show its maturity and manufacturing readiness. Particular emphasis is placed on the key role of the double-layer heterojunction (DLHJ) detectors realized by the VLPE technology for high-performance second-generation focal plane arrays. Recent developments in the successful use of the VLPE technology for epitaxial growth on Si-based alternative substrates and for growth of triple- layer heterostructures for two-color applications, which further demonstrate the versatility of the technology, are also reported. The review concludes with a discussion of the prospects for use of the VLPE technology for fabricating advanced device structures of high performance as well as investigating fundamental material properties of HgCdTe.