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Electronic Transport Properties of Hydrogenated Amorphous Silicon-Germanium Thin Films.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Electronic Transport Properties of Hydrogenated Amorphous Silicon-Germanium Thin Films.
Author:	Valor, Lis Stolik.
Published:	Ann Arbor : ProQuest Dissertations & Theses, 2022
Description:	96 p.
Notes:	Source: Dissertations Abstracts International, Volume: 83-09, Section: B.
Notes:	Advisor: Kakalios, James J.
Contained By:	Dissertations Abstracts International83-09B.
Subject:	Condensed matter physics.
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28966076
ISBN:	9798209878469

Electronic Transport Properties of Hydrogenated Amorphous Silicon-Germanium Thin Films.
Valor, Lis Stolik.

Electronic Transport Properties of Hydrogenated Amorphous Silicon-Germanium Thin Films. - Ann Arbor : ProQuest Dissertations & Theses, 2022 - 96 p.

Source: Dissertations Abstracts International, Volume: 83-09, Section: B.

Thesis (Ph.D.)--University of Minnesota, 2022.

This item must not be sold to any third party vendors.

Interest in amorphous semiconductors stems in part from their use in large-area thin-film applications, including photovoltaics, light-emitting diodes, thin film transistors, non-volatile memories and thermoelectrics. Furthermore, alloyed amorphous semiconductors have emerged as promising materials, as their optical bandgap can be easily engineered by controlling their chemical composition. Alloyed a-Si1-xGex:H thin film samples are fabricated in a dual-chamber plasma-enhanced chemical vapor deposition system, and a series of such films with Ge content raging from (0-100)% are obtained. The Ge content is determined through X-ray photoelectron spectroscopy and qualitatively corroborated through measurements of their Raman spectra. Measurements of their dark conductivity, photoconductivity, and thermopower reveal a dual-channel conduction through the dangling bond states. Alloys with concentrations of Ge below 20% exhibit anomalous hopping conduction, while the dark conductivity of alloys with higher Ge concentrations are best fit by a combination of anomalous hopping at high temperatures and power-law temperature dependence for the low to mid-ranges, characteristic of multi-phonon hopping transport. The samples' photoconductivies show evidence of high defect state densities in the mid-gap. Corresponding measurements of the thermopower find that conduction is n-type for the purely a-Si:H and a-Ge:H samples but that the Seebeck coefficient exhibits a transition from negative to positive values as a function of Ge content and temperature. A conduction model involving the parallel contributions of the two distinct conduction mechanisms is shown to describe both the conductivity and the thermopower data to a high degree of accuracy. The clear experimental evidence of hopping conduction reported here provides important information concerning the nature of electronic conduction in amorphous semiconductors, and suggests that the concept of a mobility edge, accepted for over four decades, may not be necessary to account for charge transport in certain amorphous semiconductors.

ISBN: 9798209878469Subjects--Topical Terms:

708726
Condensed matter physics.
Subjects--Index Terms:

Amorphous semiconductor

Electronic Transport Properties of Hydrogenated Amorphous Silicon-Germanium Thin Films.
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245 1 0 $a Electronic Transport Properties of Hydrogenated Amorphous Silicon-Germanium Thin Films.
260 1 $a Ann Arbor : $b ProQuest Dissertations & Theses, $c 2022
300 $a 96 p.
500 $a Source: Dissertations Abstracts International, Volume: 83-09, Section: B.
500 $a Advisor: Kakalios, James J.
502 $a Thesis (Ph.D.)--University of Minnesota, 2022.
506 $a This item must not be sold to any third party vendors.
520 $a Interest in amorphous semiconductors stems in part from their use in large-area thin-film applications, including photovoltaics, light-emitting diodes, thin film transistors, non-volatile memories and thermoelectrics. Furthermore, alloyed amorphous semiconductors have emerged as promising materials, as their optical bandgap can be easily engineered by controlling their chemical composition. Alloyed a-Si1-xGex:H thin film samples are fabricated in a dual-chamber plasma-enhanced chemical vapor deposition system, and a series of such films with Ge content raging from (0-100)% are obtained. The Ge content is determined through X-ray photoelectron spectroscopy and qualitatively corroborated through measurements of their Raman spectra. Measurements of their dark conductivity, photoconductivity, and thermopower reveal a dual-channel conduction through the dangling bond states. Alloys with concentrations of Ge below 20% exhibit anomalous hopping conduction, while the dark conductivity of alloys with higher Ge concentrations are best fit by a combination of anomalous hopping at high temperatures and power-law temperature dependence for the low to mid-ranges, characteristic of multi-phonon hopping transport. The samples' photoconductivies show evidence of high defect state densities in the mid-gap. Corresponding measurements of the thermopower find that conduction is n-type for the purely a-Si:H and a-Ge:H samples but that the Seebeck coefficient exhibits a transition from negative to positive values as a function of Ge content and temperature. A conduction model involving the parallel contributions of the two distinct conduction mechanisms is shown to describe both the conductivity and the thermopower data to a high degree of accuracy. The clear experimental evidence of hopping conduction reported here provides important information concerning the nature of electronic conduction in amorphous semiconductors, and suggests that the concept of a mobility edge, accepted for over four decades, may not be necessary to account for charge transport in certain amorphous semiconductors.
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653 $a Amorphous semiconductor
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653 $a Hopping
653 $a Thermopower
653 $a Thin films
653 $a Transport
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690 $a 0794
710 2 $a University of Minnesota. $b Physics. $3 942363
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