Date of Award

Spring 2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Electrical & Computer Engineering

Program/Concentration

Electrical and Computer Engineering

Committee Director

Helmut Baumgart

Committee Member

Gon Namkoong

Committee Member

Hani Elsayed-Ali

Call Number for Print

Special Collections LD4331.E55 R35585 2014

Abstract

Alloys composed of lead, telluride and selenide compounds exhibit very high figure of merit ZT values at intermediate temperatures, making them exceptional thermoelectric materials in a particular temperature range. Advancement in thermoelectric devices and applications hinges on increasing ZT, which is a ratio of the thermoelectric power factor to the thermal conductivity. One of the proposed avenues to achieving this goal is the use of low dimensional structures such as quantum wells, quantum dots, superlattices (SL) and nanolaminates to affect heat transport. SL structures can effectively confine charge carriers as well as scatter phonons which contribute significantly to thermal conductivity. In this thesis the Angstrom precision of the novel technique of Atomic Layer Deposition (ALD) has been employed to synthesize new nanostructures such as superlattices and nanolaminates of PbTe and PbSe layers for innovative thermoelectric device applications. ALD thin film growth takes advantage of self limiting surface reactions between the chemical precursor and surface species of the substrate. This feature enables precise control of thin film layer thickness, stoichiometry, uniformity and conformity. Recently, the development of suitable chemical ALD precursors for metal tellurides has triggered increasing research activity in SL structures of PbTe and PbSe.

In this thesis work, systematic ALD thin film experiments were performed to investigate PbTe and PbSe thin film growth to obtain the optimum growth conditions. The ALD experiments were performed using a Cambridge NanoTech Savannah 100 cross-flow reactor with Bis (trimethylsilyl) telluride ((Me3Si)2Te), bis-(triethyl silyl) selane ((Et3Si)2Se), and (Il)bis(2,2,6,6-tetramethyl-3,5-heptanedionato) (Pb(C11H19O2)2) as chemical ALD precursors for telluride, selenide and lead respectively. Once the individual thin film growth conditions were optimized, the basic unit cell for a superlattice (SL) structure was synthesized by ALD. Various physical characterization techniques to study the physical and electrical properties have been performed in order to optimize and study the individual layers and the nanolaminate structures grown by ALD. Structural characterization of the obtained ALD thin films were carried out by transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and other techniques. This successful ALD synthesis of a basic double layer nanolaminate of alternating PbTe and PbSe layers opens up new experimental avenues for improved thermoelectric device structures based on films grown by ALD.

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DOI

10.25777/4c5j-st20

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