Investigation of reactively sputtered amorphous silicon-hydrogen alloy thin films for photovoltaic application
Thin film amorphous silicon-hydrogen alloys (a-Si:H) have received ever increasing attention since the first cognizance of their superior semiconducting properties a decade ago. Questions concerning the fundamental nature of their formation, structure, and properties as well as the promise of technological application continue to motivate intensive investigation of this class of materials. This thesis is concerned with the understanding and control of growth mechanisms important in determining the composition, structure, and semiconducting properties of a-Si:H produced by sputtering of Si in an inert gas/H/sub 2/ plasma. These growth processes have been investigated by systematically varying critical external deposition parameters and by observing resultant changes in the plasma-film environment and in film microstructure and properties. Film microstructure, which is associated with electronically-active defects and post-depositional oxidative degradation, is reduced or eliminated when growth occurs under conditions of negative substrate bias and induced gas ion bombardment. Energetic bombardment, probably by backreflected H neutrals, is also important in the formation of the favorable monohydride configuration for H bonded to Si. However, these beneficial consequences of depositional bombardment are offset by bombardment-produced, atomic-scale defects. An elevated substrate temperature has only effect on microstructure and hydrogen bonding configuration, but is crucial in reducing the density of intrinsic and bombardment-related gap states. The hydrogen partial pressure in the plasma directly controls the amount of hydrogen in the film. A minimum of 10 to 15 atomic percent H is essential for defect minimization.
- OSTI ID:
- 6631451
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
36 MATERIALS SCIENCE
SILICON
MICROSTRUCTURE
SPUTTERING
AMORPHOUS STATE
CRYSTAL DEFECTS
ENERGY-LEVEL DENSITY
HYDROGEN
PARTIAL PRESSURE
PLASMA
SUBSTRATES
TEMPERATURE EFFECTS
THIN FILMS
CRYSTAL STRUCTURE
ELEMENTS
FILMS
NONMETALS
SEMIMETALS
140501* - Solar Energy Conversion- Photovoltaic Conversion
360601 - Other Materials- Preparation & Manufacture