MBE CdTe on Compliant Substrates for High Performance IRFPAs

Current state-of-the-art infrared focal plane arrays are based on HgCdTe grown on bulk CdZnTe substrates. The use of Si-based substrates would eliminate a number of drawbacks related to the HgCdTe/CdZnTe system and permit larger formats. We have developed growth protocols that produce material with good crystal quality for such a highly mismatched heteroepitaxial system. Double crystal rocking curves (DCRC), a typical benchmark for crystal quality, are measured with full widths as low as 50 arc seconds. We believe that by transferring this growth process to appropriate compliant substrates, material quality can be significantly improved. The enhanced compliance can significantly alter the forces acting on threading dislocations, facilitating the reduction of dislocations in HgCdTe device layers. Our recent data on molecular beam epitaxy (MBE) growth of thin CdTe layers on compliant substrates shows drastically improved DCRC values are achieved at early stages of growth. We plan to grow optimized material below the 50 arc second DCRC value, while reducing the concentration of macroscopic defects by reduction in the total layer thickness. Other material characteristics such as carrier mobility, lifetime, and etch pit density are typically poorer in HgCdTe/CdTe/Si compared to HgCdTe/CdZnTe, and will be used as diagnostics for optimization.