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SPARKS RESEARCH GROUP

NEWS

Aug

2015 Prof Sparks awarded

collaborative Utah Principle Energy

Initiative Program along with Prof.

Roberts from USU and Jones from

BYU

Aug

2015 Prof Sparks and Kyu

present at the DOE C/CBTL

Workshop in Morgantown WV

July

2015 Profs Shetty and Sparks

awarded research contract from

Honeywell International

July

2015 Sparks group summer

BBQ

Jun

2015 Prof Sparks participates in

the NSF Future of Graduate

Education in Materials Workshop

May

2015 Congrats to Dr. Kyu Han

for graduating and welcome to the

summer interns!

May

2015 "Datamining our way to

the next generation of

thermoelectrics" published as

invited Viewpoint Set article in

Scripta Materialia

OUTSIDE LINKS

MSE Department

HOW DO THERMOELECTRICS WORK?

The basic diagrams for power generation and thermoelectric cooling are shown below.

A thermoelectric device fundamentally consists of metal­semiconductor junctions. The above devices can be split into

five regions and the one­dimensional band diagram is shown below before they are placed into contact.

Once the materials are brought into contact the fermi level must be equal through the device so band bending occurs.

How will a temperature gradient affect this diagram? Consider first how metals behave under a temperature gradient.

The hot side of the metal has a higher concentration of electrons above the fermi level than the cold side. Diffusion of

electrons from the hot side to the cold side occurs because electrons move to where energy is lower; thus removing

the concentration gradient. Alternately, the electrons on the hot end have a larger momentum than those on the cold

end. Therefore, the hot electrons diffuse faster towards the cold side than the cold electrons diffuse away. (figure

adapted from Dr. Foll, at University of Keil, here)

8/31/2015 Sparks : research

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Materials Characterization Lab

University of Utah

Likewise, the presence of a thermal gradient across the p and n type materials leads to unequal carrier concentration

since carriers are thermally activated. The fermi level is tied to the carrier concentration distorting the bands further.

The gradient in concentration drives diffusion of electrons and holes from hot to cold. Charges build up when electrons

and holes migrate towards the cold side leaving behind charged donors/acceptors. This charge build up leads to an

electric field causing backflow of current that will eventually cause the system to reach steady­state equilibrium.

In the case of thermoelectric cooling devices (Peltier coolers) a potential is applied across the device directing a

current through the materials. As an electron moves from the metal to the p­type semiconductor it must release energy

in the form of heat to enter the valence band (technically electrons do not transport through the p­type material­ only

holes, so a temporary electron­hole pair is assumed). This released energy heats the metal. Conversely the electron

must absorb energy as it passes back to the central metal region and again as it is promoted into the conduction band

of the n­type semiconductor. The heat absorption results in active cooling in this metal region. Finally, the electron

leaves the conduction band of the n­type material releasing heat into the last metal region.

learn more about my oxide thermoelectric research

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Copyright © 2013 Taylor Sparks

Why thermoelectrics?