Tuning Light Absorption in Core/Shell Silicon Nanowire Photovoltaic Devices through Morphological Design
- Authors
- Kim, Sun-Kyung; Day, Robert W.; Cahoon, James F.; Kempa, Thomas J.; Song, Kyung-Deok; Park, Hong-Gyu; Lieber, Charles M.
- Issue Date
- 9월-2012
- Publisher
- AMER CHEMICAL SOC
- Keywords
- Facet-selective growth; solar energy; nanoelectronic device; coaxial p/i/n nanostructure; FDTD simulations; optical resonances
- Citation
- NANO LETTERS, v.12, no.9, pp.4971 - 4976
- Indexed
- SCIE
SCOPUS
- Journal Title
- NANO LETTERS
- Volume
- 12
- Number
- 9
- Start Page
- 4971
- End Page
- 4976
- URI
- https://scholar.korea.ac.kr/handle/2021.sw.korea/107522
- DOI
- 10.1021/nl302578z
- ISSN
- 1530-6984
- Abstract
- Subwavelength diameter semiconductor nanowires can support optical resonances with anomalously large absorption cross sections, and thus tailoring these resonances to specific frequencies could enable a number of nanophotonic applications. Here, we report the design and synthesis of core/shell p-type/intrinsic/n-type (p/i/n) Si nanowires (NWs) with different sizes and cross-sectional morphologies as well as measurement and simulation of photocurrent spectra from single-NW devices fabricated from these NW building blocks. Approximately hexagonal cross-section p/i/n coaxial NWs of various diameters (170-380 nm) were controllably synthesized by changing the Au catalyst diameter, which determines core diameter, as well as shell deposition time, which determines shell thickness. Measured polarization-resolved photocurrent spectra exhibit well-defined diameter-dependent peaks. The corresponding external quantum efficiency (EQE) spectra calculated from these data show good quantitative agreement with finite-difference time-domain (FDTD) simulations and allow assignment of the observed peaks to Fabry-Perot, whispering-gallery, and complex high-order resonant absorption modes. This comparison revealed a systematic red-shift of equivalent modes as a function of increasing NW diameter and a progressive increase in the number of resonances. In addition, tuning shell synthetic conditions to enable enhanced growth on select facets yielded NWs with approximately rectangular cross sections; analysis of transmission electron microscopy and scanning electron microscopy images demonstrate that growth of the n-type shell at 860 degrees C in the presence of phosphine leads to enhanced relative Si growth rates on the four {113} facets. Notably, polarization-resolved photocurrent spectra demonstrate that at longer wavelengths the rectangular cross-section NWs have narrow and significantly larger amplitude peaks with respect to similar size hexagonal NWs. A rectangular NW with a diameter of 260 nm yields a dominant mode centered at 570 nm with near-unity EQE in the transverse-electric polarized spectrum. Quantitative comparisons with FDTD simulations demonstrate that these new peaks arise from cavity modes with high symmetry that conform to the cross-sectional morphology of the rectangular NW, resulting in low optical loss of the mode. The ability to modulate absorption with changes in nanoscale morphology by controlled synthesis represents a promising route for developing new photovoltaic and optoelectronic devices.
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