Issues involving infrared detector material systems

Objectives and Status—The original objectives of this project are two folded. One objective is to develop textured template for growth of epitaxial thin film ferroelectric (TFFE) IR detectors on polyimide coated Si. The commercial TFFE has a polycrystalline structure since it is directly grown on non-textured polyimide coating. This results in degraded device performance. The same problem also occurs widely to many other device applications. To achieve epitaxial growth of the devices on non-textured surface, an ultra-thin textured template, with high transparency to infrared photons in the infrared detector applications, must be developed on non-textured surface. To resolve this issue, we have developed a unique approach in this project to generate ultra-thin textured MgO buffers on amorphous substrates using ITEX technique (stand for ion beam texturing). This topic has been the main focus of this project and many exciting results have been obtained. The other topic is to improve the performance of Hg-Cd-Te by engineering substrate surface at nano-scales aiming at reducing the defect densities such as dislocations in the device. The main approach is to prepare surfaces that have alternating areas of perfect lattice match—area 1 or no match (amorphous, for example)—area 2 to Hg-Cd-Te. Each area has a dimension on the order of few hens of nanometers. It is anticipated that Hg-Cd-Te will only nucleate in area 1, not area 2. If the Hg-Cd-Te domains grown in area 1 can overlay on the area 2, the strain induced from lattice mismatch between substrate and Hg-Cd-Te layer may be minimized. We have successfully achieved the surface nanoengineering using electron-beam lithography (EBL). The dimension of the engineered surface area is, however, small typically on the order of few hundred micrometers. This topic was not pursued after one year experiment, due to limitation of characterization capability on small sample spot on our ARL collaborator side.