Fabrication and Characterization of Nanostructured Thermoelectric Materials and Devices

Abstract

We present results of modeling and experimental characterization of thermoelectric (TE) materials built on new fabrication principles, involving the coating of three-dimensionally structured quantum well super-lattice substrates with PbTe/PbSe. A new system for wafer-scale electrochemical deposition of such structures was specifically developed and will be described in this paper. Scanning electron microscopy (SEM) was used to measure film thickness and electron diffraction spectroscopy (EDS) was used to determine film material concentration. By adjusting deposition parameters, we were able to build stoichiometric PbSe, PbTe and stacked PbSe/PbTe super-lattice films on planar and pre-structured surfaces. The films were thermoelectrically modelled using COMSOL and then characterized using an infrared Seebeck effect measurement system which measured surface heating of the film while measuring the voltage associated with the temperature gradient. We report advances in the design and fabrication of TE materials which improve cost-effectiveness and TE efficiency.

Seebeck Coefficient Enhancement of ALD PbTe/PbSe Nanolaminate Structures Deposited inside Porous Silicon Templates

“…21 For the Seebeck coefficient measurements in the direction vertical to the surface, our collaborator in MicroXact Inc. reported similar results that the PbTe/PbSe nanolaminate structure grown on micro-porous silicon membranes exhibits higher Seebeck coefficients (78670 ± 15540 μV/K) compared with the thermoelectric nanolaminate structure grown on a planar bulk silicon wafer (250 ± 27 μV/K). 22 This porous Si membrane is fabricated by removing the Si from the back side with KOH etching until the pores are reached from the back side. From the results of our Seebeck measurements in both the horizontal and vertical directions, the low dimensional ALD nanolaminate structures synthesized inside the pores of porous silicon membranes exhibit higher Seebeck coefficients than previously reported values.…”

Advances in Atomic Layer Deposition (ALD) Nanolaminate Synthesis of Thermoelectric Films in Porous Templates for Improved Seebeck Coefficient

“…However, our non-doped PbTe and PbSe films evidently have a lower carrier concentration than the doped films in the literature, which consequently results in the onset of intrinsic conduction at a lower temperature [75]. For the Seebeck coefficient measurements in the direction vertical to the surface, our collaborator at MicroXact, Inc. measured similar trends and found that the PbTe/PbSe nanolaminate structure grown on round-shaped porous silicon membranes exhibits even higher absolute Seebeck coefficients, with values of 78670 ± 15540 µ V/K in the vertical direction, compared with the thermoelectric nanolaminate structure grown on a planar bulk silicon wafer (250 ± 27 µ V/K), shown as Figure S2 in the supplementary materials [68].…”

“…Both bulk alloy compound and nanostructured PbTe/PbSe have been investigated over the decades. Nanostructured PbTe/PbSe film can be deposited by MBE [8,48] and E-ALD [68,69]. To the best of our knowledge, vacuum based thermal ALD technology was first applied for the synthesis of PbTe/PbSe nanolaminate structures in our work [1,70].…”

“…(b) cross-sectional images of PbTe/PbSe nanolaminates with period of 10 nm[73]. (c) and (d) SEM image of ALD deposited PbTe/PbSe on porous Si templates[68]. (e) and (f) are ALD deposited Sb 2 Te 3 film on porous Si templates with square shaped pore structures from the team at MicroXact Inc [71]…”