Very wide-gap and device-quality a-Si:H from highly H{sub 2} diluted SiH{sub 4} plasma decomposed by high rf power
The H{sub 2} dilution technique at a high deposition rate (R{sub D}) was investigated by depositing hydrogenated amorphous silicon (a-Si:H) under a high rf power density of 750 mW/cm{sup 2}, which is 20 times as large as that of conventional conditions. It was found that the H{sub 2} dilution ratio {gamma}(=[H{sub 2} gas flow rate]/[SiH{sub 4} gas flow rate]) tendency of the film properties, such as the H content (C{sub H}), optical gap (E{sub opt}), SiH{sub 2}/SiH and photoconductivity ({sigma}{sub ph}) of a-Si:H is different for the high rf power (750 mW/cm{sup 2}) and the medium rf power (75 mW/cm{sup 2}) conditions. Under medium rf power, the C{sub H}, E{sub opt} and SiH{sub 2}/SiH decrease as {gamma} increases. Under the high rf power, on the contrary, the C{sub H} and E{sub opt} monotonously increase while maintaining a low SiH{sub 2}/SiH and a high {sigma}{sub ph} of 10{sup {minus}6} S/cm as {gamma} increases. These results suggest that increasing the rf power enhances the H incorporation reactions due to H{sub 2} dilution. It is thought that a high rf power causes the depletion of SiH{sub 4} and hence the extinction of H radicals, expressed by SiH{sub 4} + H* {yields} SiH{sub 3}* + H{sub 2}, is suppressed. A high H radical density enhances the incorporation of H into a-Si:H, resulting in very wide-gap a-Si:H with a high C{sub H}. Consequently, very wide-gap a-Si:H with device-quality (E{sub opt} of 1.82 eV with an ({alpha}h{nu}){sup 1/3} plot, corresponding to > 2.1 eV with Tauc's plot, and {sigma}{sub ph} of 10{sup {minus}6} S/cm) can be obtained at a high R{sub D} of 12 {angstrom}/s without carbon alloying.
- Research Organization:
- Sanyo Electric Co., Ltd., Osaka (JP)
- Sponsoring Organization:
- New Energy and Industrial Technology Development Organization
- OSTI ID:
- 20107898
- Country of Publication:
- United States
- Language:
- English
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