Electronic, thermoelectric and vibrational properties of silicon nanowires and copper chalcogenides

Zhuo, Keenan

Title:

Electronic, thermoelectric and vibrational properties of silicon nanowires and copper chalcogenides

dc.contributor.advisor	Chou, Mei-Yin
dc.contributor.author	Zhuo, Keenan
dc.contributor.committeeMember	Zangwill, Andrew
dc.contributor.committeeMember	Landman, Uzi
dc.contributor.committeeMember	Jiang, Zhigang
dc.contributor.committeeMember	Wang, Xiao-Qian
dc.contributor.department	Physics
dc.date.accessioned	2016-05-27T13:10:12Z
dc.date.available	2016-05-27T13:10:12Z
dc.date.created	2015-05
dc.date.issued	2015-03-31
dc.date.submitted	May 2015
dc.date.updated	2016-05-27T13:10:12Z
dc.description.abstract	Silicon nanowires (SiNWs) and the copper chalcogenides, namely copper sulfide (Cu2S) and selenide Cu2Se, have diverse applications in renewable energy technology. For example, SiNWs which have direct band gaps unlike bulk Si, have the potential to radically reduce the cost of Si based photovoltaic cells. However, they degrade quickly under ambient conditions. Various surface passivations have therefore been investigated for enhancing their stability but it is not yet well understood how they affect the electronic structure of SiNWs at a fundamental level. Here, we will explore, from first-principles simulation, how fluorine, methyl and hydrogen surface passivations alter the electronic structures of [111] and [110] SiNWs via strain and quantum confinement. We also show how electronic charge states in [111] and [110] SiNWs can be effectively modelled by simple quantum wells. In addition, we address the issue of why [111] SiNWs are less influenced by their surface passivation than [110] SiNWs. Like SiNWs, Cu2S and Cu2Se also make excellent photovoltaic cells. However, they are most well known for their exceptional thermoelectric performance. This is by virtue of their even more unique solid-liquid hybrid nature which combines the low thermal conductivity and good electrical characteristics required for a high thermoelectric efficiency. We use first-principles molecular dynamics simulations to show that Cu diffusion rates in Cu2S and Cu2Se can be as high as 10-5cm2s-1. We also relate their phonon power spectra to their low thermal conductivities. Furthermore, we evaluate the thermoelectric properties of Cu2S and Cu2Se using a combination of Boltzmann transport theory and first-principles electronic structure calculations. Our results show that both Cu2S and Cu2Se are capable of maintaining high Seebeck coefficients in excess of 200μVK-1 for hole concentrations as high as 3x1020cm-3.
dc.description.degree	Ph.D.
dc.format.mimetype	application/pdf
dc.identifier.uri	http://hdl.handle.net/1853/54878
dc.language.iso	en_US
dc.publisher	Georgia Institute of Technology
dc.subject	Thermoelectric
dc.subject	Silicon nanowire
dc.subject	Copper chalcogenide
dc.subject	Cu2s
dc.subject	Cu2se
dc.subject	Molecular dynamics
dc.subject	First-principles
dc.subject	Ab-initio
dc.subject	Density functional theory
dc.subject	Electronic structure
dc.subject	Diffusion
dc.subject	Superionic
dc.subject	Solid-liquid hybrid
dc.subject	Quantum confinement
dc.title	Electronic, thermoelectric and vibrational properties of silicon nanowires and copper chalcogenides
dc.type	Text
dc.type.genre	Dissertation
dspace.entity.type	Publication
local.contributor.corporatename	College of Sciences
local.contributor.corporatename	School of Physics
relation.isOrgUnitOfPublication	85042be6-2d68-4e07-b384-e1f908fae48a
relation.isOrgUnitOfPublication	2ba39017-11f1-40f4-9bc5-66f17b8f1539
thesis.degree.level	Doctoral