Titova, Lyubov V. and Cocker, Tyler L. and Xu, Sijia and Baribeau, Jean-Marc and Wu, Xiaohua and Lockwood, David J. and Hegmann, Frank A. (2016) Ultrafast carrier dynamics and the role of grain boundaries in polycrystalline silicon thin films grown by molecular beam epitaxy. SEMICONDUCTOR SCIENCE AND TECHNOLOGY, 31 (10): 105017. ISSN 0268-1242, 1361-6641
Full text not available from this repository. (Request a copy)Abstract
We have used time-resolved terahertz spectroscopy to study microscopic photoconductivity and ultrafast photoexcited carrier dynamics in thin, pure, non-hydrogenated silicon films grown by molecular beam epitaxy on quartz substrates at temperatures ranging from 335 degrees C to 572 degrees C. By controlling the growth temperature, thin silicon films ranging from completely amorphous to polycrystalline with minimal amorphous phase can be achieved. Film morphology, in turn, determines its photoconductive properties: in the amorphous phase, carriers are trapped in bandtail states on sub-picosecond time scales, while the carriers excited in crystalline grains remain free for tens of picoseconds. We also find that in polycrystalline silicon the photoexcited carrier mobility is carrier-density-dependent, with higher carrier densities mitigating the effects of grain boundaries on inter-grain transport. In a film grown at the highest temperature of 572 degrees C, the morphology changes along the growth direction from polycrystalline with needles of single crystals in the bulk of the film to small crystallites interspersed with amorphous silicon at the top of the film. Depth profiling using different excitation wavelengths shows corresponding differences in the photoconductivity: the photoexcited carrier lifetime and mobility are higher in the first 100-150 nm from the substrate, suggesting that thinner, low-temperature grown polycrystalline silicon films are preferable for photovoltaic applications.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | RESOLVED TERAHERTZ SPECTROSCOPY; CHEMICAL-VAPOR-DEPOSITION; TEMPERATURE SI GROWTH; AMORPHOUS-SILICON; LIMITING THICKNESS; NANOCRYSTAL FILMS; ON-SAPPHIRE; CONDUCTIVITY; SI(100); RECOMBINATION; silicon thin films; terahertz spectroscopy; grain boundaries; low-temperature MBE; carrier dynamics |
| Subjects: | 500 Science > 530 Physics |
| Divisions: | Physics > Institute of Experimental and Applied Physics > Chair Professor Huber > Group Rupert Huber |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 24 Apr 2019 13:28 |
| Last Modified: | 24 Apr 2019 13:28 |
| URI: | https://pred.uni-regensburg.de/id/eprint/4214 |
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