Polycrystalline solar cell/substrate growth by integrated vacuum evaporation. Final report
GaAs epitaxy on a large-grained substrate would reduce grain-boundary shunting losses in polycrystalline solar cells. In pre-contract work, Fe was selected for its low cost and 1.4% lattice match, and was e-beam evaporated onto 850 to 1100/sup 0/C alumina and Kovar wafers, selected for reasonably good thermal expansion match to GaAs. Fe films developed 30 to 200 ..mu..m grains with a (211) texture and did not crack or peel upon cooldown. Under the contract, clean, single-crystal Fe surfaces for GaAs growth studies were generated by epitaxial growth of Fe onto 300/sup 0/C GaAs(211); but the reverse process, GaAs growth on Fe (by vacuum deposition from Ga and As/sub 4/) produced polycrystalline Ga-As-Fe mixed phases. The success of Fe epitaxy on GaAs is attributed to the availability of Ga and As at the interface only as the compound GaAs, which raises the activation energy for the formation of mixed phases. Fe passivation by NH/sub 3/ and H/sub 2/S exposure was tried unsuccessfully, although H/sub 2/S did passivate Fe against As/sub 4/. Various closely lattice-matching materials were vacuum-deposited on the Fe as buffer layers prior to GaAs growth. AlAs and Ge formed mixed phases with the Fe. Cr grew epitaxially because Cr and Fe are both bcc, but deposition of GaAs and of Ge on the Cr produced mixed phases. SrF/sub 2/ did grow epitaxially on Fe, and this was attributed to its existence as a molecule in the vapor. GaAs grew epitaxially on a 0.5 ..mu..m-thick buffer layer of SrF/sub 2/ on Fe, and electrical conductivity was observed between the GaAs and the Fe, apparently through microvoids in the facetted SrF/sub 2/ epilayer.
- Research Organization:
- Perkin-Elmer Corp., Norwalk, CT (USA)
- DOE Contract Number:
- AC02-77CH00178
- OSTI ID:
- 6777444
- Report Number(s):
- SERI/TR-8041-14-T1; ON: DE82017203
- Country of Publication:
- United States
- Language:
- English
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140501* -- Solar Energy Conversion-- Photovoltaic Conversion
ALKALINE EARTH METAL COMPOUNDS
AMMONIA
ARSENIC COMPOUNDS
ARSENIDES
CHALCOGENIDES
CRYSTAL GROWTH
CRYSTALS
CURRENTS
EFFICIENCY
ELECTRIC CONDUCTIVITY
ELECTRIC CURRENTS
ELECTRIC POTENTIAL
ELECTRICAL PROPERTIES
ELEMENTS
EPITAXY
EVAPORATION
FLUORIDES
FLUORINE COMPOUNDS
GALLIUM ARSENIDES
GALLIUM COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
HYDRIDES
HYDROGEN COMPOUNDS
HYDROGEN SULFIDES
IRON
METALS
MOLECULAR BEAM EPITAXY
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
PASSIVATION
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
PNICTIDES
POLYCRYSTALS
QUANTUM EFFICIENCY
SPECTRAL RESPONSE
STRONTIUM COMPOUNDS
STRONTIUM FLUORIDES
SUBSTRATES
SULFIDES
SULFUR COMPOUNDS
TRANSITION ELEMENTS
VACUUM EVAPORATION