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Group III-nitride Materials for High Efficiency Photoelectrochemical Cells

  • J. W. Ager (a1), W. Walukiewicz (a1), K. M. Yu (a1), W. Shan (a1), J. Denlinger (a2) and J Wu (a3)...

Abstract

Two ternary alloys based on III-nitride semiconductor alloys are explored as potential components of photoelectrochemical cells (PECs) for the direct generation of hydrogen using solar energy. For In1-xGaxN, it will be shown using prior measurements of band offsets that spontaneous water splitting can occur for x up to 0.2 and potentially higher. Flat band potential and photocurrent measurements from an n-type epilayer with x = 0.37 will be presented. This initial data appears to indicate that the flat band potential lies just below the H+/H2 from pH 0 – 14. In the case of GaAsxN1-x we will demonstrate that the replacement of a few percent of As in N sublattice drives the bandgap down from the GaN value (3.4 eV) into a range that is attractive for PEC cells [1]. This band gap reduction is explained by the valence band anticrossing that pushes the valence band maximum up initially by 0.5 eV. From the point of view of a PEC cell, this reduces the gap (desirable for efficiency) without compromising the desired H+/H2 overpotential.

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