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Published September 2012 | public
Journal Article

Photoelectrochemical Behavior of Planar and Microwire-Array Si|GaP Electrodes


Gallium phosphide exhibits a short diffusion length relative to its optical absorption length, and is thus a candidate for use in wire array geometries that allow light absorption to be decoupled from minority carrier collection. Herein is reported the photoanodic performance of heteroepitaxially grown gallium phosphide on planar and microwire-array Si substrates. The n-GaP|n-Si heterojunction results in a favorable conduction band alignment for electron collection in the silicon. A conformal electrochemical contact to the outer GaP layer is produced using the ferrocenium/ferrocene (Fc^+/Fc) redox couple in acetonitrile. Photovoltages of ∼750 mV under 1 sun illumination are observed and are attributed to the barrier formed at the (Fc^+/Fc)|n-GaP junction. The short-circuit current densities of the composite microwire-arrays are similar to those observed using single-crystal n-GaP photoelectrodes. Spectral response measurements along with a finite-difference-time-domain optical model indicate that the minority carrier diffusion length in the GaP is ∼80 nm. Solid-state current–voltage measurements show that shunting occurs through thin GaP layers that are present near the base of the microwire-arrays. The results provide guidance for further studies of 3D multi-junction photoelectrochemical cells.

Additional Information

© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. Received: November 29, 2011. Published online: June 15, 2012. We acknowledge the National Science Foundation (NSF) Center for Chemical Innovation (CHE-0802907) and DARPA for support. NCS acknowledges the NSF for an American Competitiveness in Chemistry postdoctoral fellowship (CHE-1042006). DBTE acknowledges the NSF for a Graduate Research Fellowship. The authors acknowledge helpful discussions from Dr. Chengxiang Xiang and Prof. Shannon W. Boettcher.

Additional details

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October 20, 2023