Thermoelectric materials and devices
Inventors
Park, Yeonjoon • Choi, Sang H. • King, Glen C. • Elliott, James R. • Talcott, Noel A.
Assignees
National Aeronautics and Space Administration NASA
Publication Number
US-8044294-B2
Publication Date
2011-10-25
Expiration Date
2028-10-20
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Abstract
New thermoelectric materials comprise highly [111]-oriented twinned group IV alloys on the basal plane of trigonal substrates, which exhibit a high thermoelectric figure of merit and good material performance, and devices made with these materials.
Core Innovation
The invention provides new thermoelectric materials comprising highly [111]-oriented twinned group IV alloys, specifically alloys of two or more of carbon (C), silicon (Si), germanium (Ge), and tin (Sn), grown on the basal plane of trigonal substrates such as sapphire. These materials exhibit a high thermoelectric figure of merit and good material performance, as well as devices made from these materials.
The problem being solved arises from the difficulty in developing thermoelectric materials that combine high electrical conductivity with low thermal conductivity. Past materials, such as SiGe alloys, could operate at high temperatures but exhibited relatively low figures of merit due to their high thermal conductivity. Conversely, materials like Skutterudite CoSb have good thermoelectric figures but operate only at intermediate temperatures. The invention addresses the challenge of providing SiGe and other group IV thermoelectric materials with improved thermoelectric properties capable of high-temperature operation.
To achieve these objectives, the invention involves fabricating group IV alloys as highly [111]-oriented twinned crystal structures on trigonal substrates. These twinned crystals, created through stacking faults and twin defects, provide poly-type crystalline structures that scatter phonons (reducing thermal conductivity) while maintaining good electrical conductivity and Seebeck coefficient. Devices can be fabricated using vertically bonded n-type and p-type doped wafers of these materials, with electrical circuits formed on the wafers to generate thermoelectric power efficiently.
Claims Coverage
The patent includes two independent claims covering thermoelectric materials and thermoelectric devices with specified crystal orientations and twin crystal content. The main inventive features focus on material composition, crystal orientation, twin crystal concentration, and device structure configurations.
Thermoelectric cubic crystalline material with high [111] orientation and twin crystal content
A cubic crystalline material composed of an alloy of two or more of silicon, germanium, carbon, and tin, fabricated on the basal plane of a trigonal or hexagonal crystalline substrate. The material is highly oriented in the [111] direction relative to the substrate and contains greater than about 40% twin crystals.
Thermoelectric device comprising highly [111]-oriented twinned cubic crystalline material
A thermoelectric device made from a cubic crystalline material alloy of two or more of silicon, germanium, carbon, and tin fabricated on the basal plane of a trigonal or hexagonal substrate with high [111] orientation and twin crystal content exceeding about 40%. The device includes two vertically bonded wafers doped respectively with n-type and p-type materials, and one or more electrical circuit elements connecting the thermoelectric materials in series or parallel. The circuitry may be formed from heavily doped semiconductors or conducting materials such as metals, semi-metals, silicides, germanicides, zinc oxide, or indium tin oxide (ITO).
The independent claims cover a novel thermoelectric material formed by highly [111]-oriented twinned group IV alloys on trigonal or hexagonal substrates and thermoelectric devices composed of vertically bonded n-type and p-type wafers of such materials integrated with various electrical circuit elements to optimize performance.
Stated Advantages
The materials exhibit a high thermoelectric figure of merit by reducing thermal conductivity through phonon scattering from twin crystals and stacking faults while maintaining high electrical conductivity and Seebeck coefficients.
The device structures maximize the temperature difference across thermoelectric materials, improving electric power output.
Materials and devices operate effectively at higher temperatures, combining advantages of prior materials such as SiGe and Skutterudite CoSb.
Documented Applications
Thermoelectric power generators, including radio-isotope thermoelectric generators.
Thermoelectric cooling devices and integrated thermoelectric cooling devices.
Thermal semiconductors, thermal sensors, and thermal barriers.
Electric power generation from automobile engine heat where maintaining a constant engine temperature is important.
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