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Issue 7, 2014
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Operation of lightly doped Si microwires under high-level injection conditions

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The operation of lightly doped Si microwire arrays under high-level injection conditions was investigated by measurement of the current-potential behavior and carrier-collection efficiency of the wires in contact with non-aqueous electrolytes, and through complementary device physics simulations. The current-potential behavior of the lightly doped Si wire array photoelectrodes was dictated by both the radial contact and the carrier-selective back contact. For example, the Si microwire arrays exhibited n-type behavior when grown on a n+-doped substrate and placed in contact with the 1,1′-dimethylferrocene+/0–CH3OH redox system. The microwire arrays exhibited p-type behavior when grown on a p+-doped substrate and measured in contact with a redox system with a sufficiently negative Nernstian potential. The wire array photoelectrodes exhibited internal quantum yields of ∼0.8, deviating from unity for these radial devices. Device physics simulations of lightly doped n-Si wires in radial contact with the 1,1′-dimethylferrocene+/0–CH3OH redox system showed that the carrier-collection efficiency should be a strong function of the wire diameter and the carrier lifetime within the wire. Small diameter (d < 200 nm) wires exhibited low quantum yields for carrier collection, due to the strong inversion of the wires throughout the wire volume. In contrast, larger diameter wires (d > 400 nm) exhibited higher carrier collection efficiencies that were strongly dependent on the carrier lifetime in the wire, and wires with carrier lifetimes exceeding 5 μs were predicted to have near-unity quantum yields. The simulations and experimental measurements collectively indicated that the Si microwires possessed carrier lifetimes greater than 1 μs, and showed that radial structures with micron dimensions and high material quality can result in excellent device performance with lightly doped, structured semiconductors.

Graphical abstract: Operation of lightly doped Si microwires under high-level injection conditions

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The article was received on 18 Jan 2014, accepted on 18 Mar 2014 and first published on 20 Mar 2014

Article type: Paper
DOI: 10.1039/C4EE00202D
Citation: Energy Environ. Sci., 2014,7, 2329-2338
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    Operation of lightly doped Si microwires under high-level injection conditions

    E. A. Santori, N. C. Strandwitz, R. L. Grimm, B. S. Brunschwig, H. A. Atwater and N. S. Lewis, Energy Environ. Sci., 2014, 7, 2329
    DOI: 10.1039/C4EE00202D

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