Thermoelectric Characteristics in MBE-Grown HgCdTe-Based Superlattices |
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Authors: | S Velicu CH Grein J Zhao Y Chang S-Y An A Yadav K Pipe W Clark |
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Affiliation: | (1) EPIR Technologies, Inc., 590 Territorial Dr., Unit B, Bolingbrook, IL 60440, USA;(2) Microphysics Laboratory, University of Illinois at Chicago, Chicago, IL 60607, USA;(3) Mechanical Engineering Department, University of Michigan, Ann Arbor, MI 48109-2125, USA |
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Abstract: | We present a study on the thermoelectric properties of n-type Hg0.75Cd0.25 Te/Hg0.7Cd0.3Te superlattices (SLs). This material system was chosen because HgCdTe is the primary material used in high-performance infrared
imaging applications. HgCdTe-based devices can be directly grown on Hg1−x
Cd
x
Te/Hg1−y
Cd
y
Te SL coolers using advanced growth methods such as molecular-beam epitaxy (MBE), making the monolithic integration of infrared
sensors and thermoelectric elements possible. Also, the thermoelectric figure of merit ZT for Hg0.75Cd0.25Te/Hg0.7Cd0.3Te SLs is predicted to reach values of 2.09, more than two times greater than that achieved in the best thermoelectric devices
based on bulk Bi2Te3. This large ZT is due to the unique and superior electrical and thermal properties of the HgCdTe system, which has not yet been experimentally
explored in any great depth as a thermoelectric material. We used a Riber 32P MBE system equipped with a Hg valved cell, reflection
high-energy electron diffraction, infrared pyrometer and in situ spectroscopic ellipsometry to grow the thermoelectric structures. MBE was chosen as a growth technique since it allows for
the lowest growth temperature compared with other methods, which limits interdiffusion at the interfaces, thereby allowing
for a precise control over electrical and thermal properties. Thermal devices were fabricated using standard photolithography
and etching techniques. Thermal properties were evaluated using a differential technique. A thermal conductivity of 0.82 ± 0.07 W/m K
and a Seebeck coefficient of 811 ± 150 μV/K were measured. Using a measured value of 0.017 Ω cm for the resistivity, an upper bound ZT of 1.4 is estimated.
An erratum to this article can be found at |
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Keywords: | Thermoelectric HgCdTe superlattice ZT molecular-beam epitaxy Seebeck coefficient thermal conductivity |
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