Properties of hydrogenated amorphous silicon prepared by chemical vapor deposition
Hydrogenated amorphous silicon (a-Si:H) films were prepared by chemical vapor deposition (CVD) from mixtures of silane, disilane, trisilane, and higher polysilanes in hydrogen carrier gas at 1 atm total pressure, at substrate temperatures from 420--530 /sup 0/C. Experimental parameters are explained and properties as a function of these parameters are shown. The measurements include hydrogen content (by IR), optical, electrical, and photovoltaic properties of the material. In most respects, the CVD material closely resembles the a-Si:H usually prepared by glow discharge. The following differences have been noted: (1) the CVD a-Si:H shows no IR absorption at 840--850 cm/sup -1/, which is consistent with the expected better thermal stability of the CVD material because of the much higher substrate temperatures in the CVD process than in the glow discharge process. (2) The band gap of CVD a-Si:H is lower by about 0.1 eV than glow discharge a-Si:H of the same hydrogen content. Thus, the band gap of CVD a-Si:H is better matched to the solar spectrum than is glow discharge a-Si:H. (3) All three IR absorption bands due to hydrogen are about 20% narrower in the CVD a-Si:H, suggesting a simpler structure. (4) The temperature dependence of the dark conductivity of CVD a-Si:H fits a curve for a single activation energy, in contrast to the more complicated temperature dependence often found in glow discharge a-Si:H, in which two different activation energies are seen at high and low temperatures. This suggests that the conduction mechanism is also simpler in the CVD a-Si:H.
- Research Organization:
- Department of Chemistry and Division of Applied Sciences, Harvard University, Cambridge, Massachusetts 02138
- DOE Contract Number:
- AC02-77CH00178
- OSTI ID:
- 7025634
- Journal Information:
- J. Appl. Phys.; (United States), Vol. 55:12
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SILANES
ABSORPTION SPECTRA
CHEMICAL COMPOSITION
CHEMICAL VAPOR DEPOSITION
ELECTRICAL PROPERTIES
OPTICAL PROPERTIES
PHOTOVOLTAIC EFFECT
ABSORPTIVITY
ACTIVATION ENERGY
AMORPHOUS STATE
ELECTRIC CONDUCTIVITY
ENERGY GAP
GLOW DISCHARGES
HIGH TEMPERATURE
HYDROGENATION
INFRARED RADIATION
SILICON
TEMPERATURE DEPENDENCE
THIN FILMS
CHEMICAL COATING
CHEMICAL REACTIONS
DEPOSITION
ELECTRIC DISCHARGES
ELECTROMAGNETIC RADIATION
ELEMENTS
ENERGY
FILMS
HYDRIDES
HYDROGEN COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC SILICON COMPOUNDS
PHOTOELECTROMAGNETIC EFFECTS
PHYSICAL PROPERTIES
RADIATIONS
SEMIMETALS
SILICON COMPOUNDS
SPECTRA
SURFACE COATING
360603* - Materials- Properties