1994 Fiscal Year Final Research Report Summary
Characterization of Sturctural Disorder by means of Polarized Photoreflectance in Amorphous Semiconductors
| Project/Area Number |
05650305
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Electronic materials/Electric materials
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| Research Institution | Osaka University |
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Principal Investigator |
OKAMOTO Hiroaki Osaka University, Faculty of Engineering Science, Associate Professor, 基礎工学部, 助教授 (90144443)
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| Co-Investigator(Kenkyū-buntansha) |
HATTORI Kiminori Osaka University, Faculty of Engineering Science, Research Associate, 基礎工学部, 助手 (80228486)
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| Project Period (FY) |
1993 – 1994
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| Keywords | Amorphous semiconductor / Structural disorder / Photoreflectance / Polarized electroabsorption / Band edge states / Carrier mobility |
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| Research Abstract |
Polarized Electroabsorption technique (PEA) has been developed for the determination of carrier mean free path as well as mobility near the band edge in amorphous semiconductors. The method is based upon the result of microscopic theory of optical spectrum in the presence of external electric fields, which indicates that an "extrinsic" polarization dependence of the EA signal appears due to the fieldinduced change in the matrix element for transitions involving localized states, so that it serves as a measure of the degree of disorder in amorphous semiconductors. Measured EA signal intensity ratio between field-light polarization parallel and perpendicular conditions is transrated into carrier mean free path and band edge mobility. We have applied this new technique to amorphous silicon alloys. The conclusions reached from the present work are as follows ;
1) The electron (hole) mean free path is about 12* (5*) for device quality undoped a-Si : H,which yields estimate of the electron (hole) mobility of 10 cm2/Vs (3cm2/Vs).
2) The mobilities attain maxima at a particular deposition temperature which would depend on details of deposition conditions.
3) Annealing treatment on a-Si : H deposited at a low temperature improves carrier mobilities through the relaxation of structural disorder.
4) Alloying with carbon leads to a continuous reduction of mobility, with the largest drop (15%) for a carbon concentration of about 10 at%, this being in sharp contrast to a less-pronounced effect by germanium alloying.
5) Phosphorus doping ramarkably detoriorates the electron mobility, while the hole mobility remains almost unchanged from that in undoped material.
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