Electronic transport properties of hydrogenated amorphous silicon-germanium thin films
2022-01
Loading...
View/Download File
Persistent link to this item
Statistics
View StatisticsJournal Title
Journal ISSN
Volume Title
Title
Electronic transport properties of hydrogenated amorphous silicon-germanium thin films
Authors
Published Date
2022-01
Publisher
Type
Thesis or Dissertation
Abstract
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-Si_{1-x}Ge_{x}: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.
Description
University of Minnesota Ph.D. dissertation. 2022. Major: Physics. Advisor: James Kakalios. 1 computer file (PDF); 95 pages.
Related to
Replaces
License
Collections
Series/Report Number
Funding information
Isbn identifier
Doi identifier
Previously Published Citation
Suggested citation
Stolik Valor, Lis. (2022). Electronic transport properties of hydrogenated amorphous silicon-germanium thin films. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/226638.
Content distributed via the University Digital Conservancy may be subject to additional license and use restrictions applied by the depositor. By using these files, users agree to the Terms of Use. Materials in the UDC may contain content that is disturbing and/or harmful. For more information, please see our statement on harmful content in digital repositories.