Alexandria Digital Research Library

The Thermoelectric Properties of Rare Earths as Dopants in InGaAs Films

Author:
Koltun, Rachel Ann
Degree Supervisor:
John E. Bowers and Christopher J. Palmstrom
Place of Publication:
[Santa Barbara, Calif.]
Publisher:
University of California, Santa Barbara
Creation Date:
2014
Issued Date:
2014
Topics:
Physics, High Temperature, Engineering, Materials Science, and Engineering, Electronics and Electrical
Keywords:
MBE
Thermoelectric
Dopant
Rare Earth
InGaAs
Genres:
Online resources and Dissertations, Academic
Degree Grantor:
University of California, Santa Barbara. Materials
Dissertation:
Ph.D.--University of California, Santa Barbara, 2014
Description:

Current energy technologies lose over half of the energy input to waste heat. Thermoelectric materials can recover some of this waste heat by converting it into electricity. Thermoelectric devices have no moving parts, so they are low noise and highly reliable, making them particularly suitable for extreme environments. A good thermoelectric has low thermal conductivity to maintain large temperature gradients and high electrical conductivity to effectively transport carriers across that temperature gradient. One of the major challenges in engineering such thermoelectrics is effectively decoupling these parameters. These relationships are quantified in the dimensionless thermoelectric figure of merit, ZT, where a ZT of 1 is considered commercially viable.

Doping MBE grown InGaAs films with rare earths forms embedded nanoparticles that have been shown to improve thermoelectric efficiency of InGaAs. Rare earth doping effectively overcomes the problematic relationship between electrical and thermal conductivities. These embedded particles effectively decouple thermal and electrical properties by contributing carriers to increase electrical conductivity as well as forming scattering centers for mid to long wavelength phonons to decrease thermal conductivity. However, the mechanism for carrier generation from rare earths is poorly understood. Comparing different rare earths as dopants in InGaAs, we find a positive correlation with the electrical activation efficiency as the rare earth arsenide nanoparticles are more closely lattice matched to the host matrix. This is in contrast to traditional Si doped InGaAs, which is fully ionized at room temperature. The high doping efficiency of Si leads it to be as good or better of a dopant for thermoelectrics compared to the best rare earths studied. We observe that rare earth doped InGaAs has thermal activation of carriers at high temperature, giving it the potential to be a more efficient thermoelectric in this regime than traditionally doped InGaAs.

A method was developed to determine the thermoelectric efficiency of a material system over a range of conductivities using only a few experimental data points. This allows for more efficient mapping of a material system for thermoelectrics. Using this analysis, high temperature measurements show that carrier scattering from rare earth impurities compensates the enhancement from thermally generated carriers, giving Si the potential to be a better thermoelectric dopant in InGaAs at high temperature. Extrapolating temperature dependent measurements to higher temperatures shows that a ZT greater than 3 should be theoretically possible for Gd or Si doped InGaAs at 700°C.

Physical Description:
1 online resource (225 pages)
Format:
Text
Collection(s):
UCSB electronic theses and dissertations
ARK:
ark:/48907/f3m32sz7
ISBN:
9781321568097
Catalog System Number:
990045118500203776
Rights:
Inc.icon only.dark In Copyright
Copyright Holder:
Rachel Koltun
File Description
Access: Public access
Koltun_ucsb_0035D_12360.pdf pdf (Portable Document Format)