Low Temperature Thermoelectric Refrigeration with HgCdTe-based Superlattices

ABSTRACT: A major limitation to the wide deployment of high sensitivity infrared detector arrays in space environment is the cooling system. Major developments of active cooling capabilities in terms of performance, capacity, reliability and cost remains a primary need. Current conventional cooling systems are bulky and introduce additional vibration, heat, and power consumption. The goal of this project is to develop the technology required for the fabrication of thermoelectric devices capable of cooling infrared arrays from 300 to 123 K. We propose the development of tall barriers nanoscale superlattices as the active elements of multi-stage thermoelectric coolers. The top stage element in contact with the infrared array will be able to remove at least 0.5 W of heat at 123 K. Recent models predict that metallic and HgCdTe-based superlattices have thermoelectric figures of merit ZT compatible with these operational needs. We will perform calculations to optimize material parameters to maximize ZT for each cooling stage. We will use our extensive experience in molecular beam epitaxy to grow the designed structures. Finally, we will develop device structures and metallization methods appropriate to perform ZT measurements, measure the ZTs of fabricated devices and compare results with theory. BENEFIT: High efficiency thermoelectric coolers possess a myriad of applications including portable cooling and precise temperature control for electronics, optics and medical systems. The temperature differences required in air conditioning are usually within the capacity of thermoelectric heat pumps, but their relatively poor coefficient of performance prohibits wide deployment. An increase of the thermoelectric figure of merit ZT above 3 is needed before thermoelectric technology can replace current refrigeration and air conditioning technologies. Thermoelectric coolers have long contributed to space missions. For example, thermoelectric devices cool HgCdTe-based infrared imaging cameras such as those on the Hubble Space Telescope. They are employed as refrigerators in various space science experiments. The same materials also hold great potential in thermionic energy conversion. The proposed project will also enable the commercialization of molecular beam epitaxy-grown HgCdTe-based materials and devices for various DOD, DOE and NASA applications. Advanced heterostructures, will significantly improve the performance of HgCdTe-based infrared detectors and therefore improve infrared imaging capabilities.