ADVANCED COMPOSITE SUBSTRATE DEVELOPMENT OF CD-BASED-II-VI MATERIALS FOR IR APPLICATIONS G. N. Brill, Y. Chen, P. M. Amirtharaj, W. L. Sarney, P. S. Wijewarnasuriya, and N. K. Dhar U.S. Army Research Laboratory, Sensors and Electron Devices Directorate AMSRD-ARL-SE-EI, 2800 Powder Mill Rd., Adelphi, MD 20783 ABSTRACT Through its mature materials development and ability to detect any wavelength of interest within the infrared (IR) spectrum, HgCdTe is currently, and is positioned to remain, the leading choice among IR sensing material for high performance applications. However, a major roadblock lies ahead for HgCdTe IR systems. With array sizes increasing through the need for higher resolution systems, current substrate technology based on bulk CdZnTe material will not be suitable for future systems. The lack of CdZnTe bulk wafer size available (currently limited to less than 7 x 7 cm 2 ) and high cost in the market place (~$250/cm 2 ) will stop the progression of HgCdTe based IR systems. To mitigate these and other issues, the Army Research Laboratory (ARL) has played a key role in the development of Si-based composite substrate technology for HgCdTe material applications. By transitioning current molecular beam epitaxial (MBE) HgCdTe materials technology to a novel Si-based composite substrate, physical size limitations of HgCdTe material is no longer an issue. Furthermore, besides material cost, manufacturing cost will also be reduced as more dies per wafer will be processed. Specifically, CdTe material technology grown on Si substrates has already been successfully developed for short-wave and mid-wave detector arrays. However, it is recognized that ternary and quarternary Cd-based II-VI materials with lattice matching to that of HgCdTe may be even better suited for HgCdTe growth and IR device processing, particularly for long-wavelength HgCdTe detector arrays. ARL has taken the lead in this research area for the Army. 1. INTRODUCTION Today, modern war fighters tasked with battlefield management have a critical need to rapidly detect, identify, and constantly survey events in the battlefield. To be effective in this contingency, sensors must continuously view the entire field of regard with ultra high resolution that provides increased probability of detection and identification. It is hoped that the Third Generation Infrared Imaging technology will offer a new suite of products to meet such challenges. The Third Generation family of IR sensors will include very high resolution and high quantum efficiency cooled IR arrays as well as large-format uncooled arrays. It is envisioned that such an enabling technology will facilitate advanced protocols for battlefield management with a suite of sensors that offer high, medium and low performance deployed strategically and activated as needed. Coupled with large-format, multi-color and other sensor products, the Third Generation IR Imaging system will equip the war fighter with the tools needed to maintain dominance in the night. To achieve ultra high resolution and wide area surveillance capability, very large-format and possibly HDTV (16:9 aspect ratio) format arrays will be necessary. For high performance cooled applications, Mercury Cadmium Telluride (Hg 1-x Cd x Te) is the material of choice used for state-of-the-art infrared focal plane array (IRFPA) systems. Through careful control of the alloy composition, the semiconductor can be tuned, within the entire IR spectrum, to detect any wavelength of light, giving a HgCdTe detector array both complex and sensitive detecting abilities. The current material growth process using Molecular Beam Epitaxy (MBE) is to nucleate the HgCdTe layer on a thick, bulk-grown, CdZnTe substrate that is itself lattice-matched to HgCdTe. However, production of very large-format HgCdTe IRFPAs using bulk CdZnTe substrates presents several technology barriers. Bulk CdZnTe substrates are very brittle, costly, relatively small, and have physical limitations when combined with the Si read out integrated circuitry (ROIC) necessary for IRFPA fabrication. These issues make the fabrication of HgCdTe devices extremely costly with a low production yield. Instead of utilizing bulk grown CdZnTe substrates, a thin film of Cd 1-y Zn y Te can be epitaxially deposited directly on a Si substrate using Molecular Beam Epitaxy (MBE). By doing this, the lattice matching property and crystal structure of CdZnTe can be retained. Additionally, the strength, size, and technological maturity of the Si substrate becomes incorporated into the properties of the CdZnTe layer and hence into the HgCdTe material. Therefore using a Si- based substrate template (composite substrate) is very attractive and provides an avenue for a scalable, more reliable, and more affordable alternative towards realizing large-format arrays beyond the limitation posed by the current bulk CdZnTe substrates. The research effort made during the past few years have already led to a relatively mature MBE growth process for high quality CdTe/Si substrates (Dhar et al,