Novel Materials for Transverse Peltier Refrigeration

Novel Materials for Transverse Peltier Refrigeration Statement of Objectives This effort will explore materials that function as p n transverse thermoelectrics, a newly discovered paradigm for Peltier cooling discovered theoretically by the PI, whereby an electrical current in a narrow-gap semiconductor drives a transverse heat flow. These new materials promise to deliver thermoelectric cooling at arbitrarily low temperatures. As single-leg devices, they can provide micro-device platforms for thermoelectric refrigeration that are easily fabricated, efficient, portable, light-weight, and compact. Thermoelectric Peltier refrigerators made of such materials are advantageous for remote environments such as space and for portable platforms in-the-field that require light-weight, low vibration sensor cooling. Because of the novelty of this field, the first step is to identify the best materials having the necessary properties, and a prior literature search by the author has identified half a dozen prime candidates. The research objectives in exploring these new materials are: a) calculate and optimize band structures for materials that exhibit p n behavior; b) realize growth of such superlattice structures in the InAs/GaSb and InAs/InAsSb superlattice systems, as well as crystals of bulk low-symmetry compounds; and c) measure the thermoelectric transport properties of these materials and compare to theory to flesh out a universal transverse thermoelectric figure of merit plot ZT. Because the p n transverse thermoelectric paradigm uses intrinsic semiconductors, it is possible for active cooling to be driven at any temperature – there is no “extrinsic freeze out”. Thus one objective is to characterize materials at cryogenic temperatures to identify the maximum cooling that one can achieve at arbitrarily low temperatures, and optimize structural parameters to realize such a low-temperature thermoelectric material. Because p n devices function as single-leg Peltier coolers, they can be scaled to small sizes, integrated monolithically with other active III-V circuit elements such as infrared detectors, and the p n devices can be shaped to enhance performance. These unique geometric abilities of p n type II devices will be pursued in this work, with an emphasis on micron-scale dimensions, since device dimensions are limited by the epitaxial layer thickness. Because of the flexibility of the design parameters of superlattices and compounds, these materials have tunable band properties, such as bandgap, effective mass, and mobility. Thus another objective is to investigate improved Seebeck and electron mobility, and reduced phonon mobility and map this phase space as a function of temperature for high-promise materials. In summary, the overall research objectives lead to the design of superlattices and identification of new transverse thermoelectric compounds, and their complete thermoelectric transport characterization as a function of temperature down to cryogenic temperatures, for use as Peltier cryocoolers.