Systematic studies of the semiconductor/liquid junction: n-gallium arsenide phosphide anodes in aqueous selenide (Se²⁻/Se₂²⁻) solutions

Abstract

Epitaxial layers of n-GaAs₁₋ₓPₓ (0 < x < 1) have been studied as photoelectrodes and as Au Schottky junctions. We observe increases in open-circuit voltage, V_(OC), with increases in P content for n-GaAs₁₋ₓPₓ, (x < 0.4) and decreases in V_(OC) for x > 0.6. Under 88 mW/cm² of ELH-type (3350 K color temperature with a dichroic rear reflector) tungsten-halogen irradiation, we observe that n-GaAs_(0.72)P_(0.28) anodes exhibit a V_(OC) of 0.95-0.99 V, short-circuit currents of 15-17 mA/cm², and energy conversion efficiencies of 13.0 ± 1.0%. Irradiation at 632.8-nm yields monochromatic conversion efficiencies of greater than 30%, and solar irradiation (85-100 mW/cm²) yields efficiencies of 11.0 ± 1.0% in 1.0 M KOH/l.0 M Se²⁻/0.01 M Se₂²⁻ solutions. The n-GaAs_(0.72)P_(0.28) anodes exhibit stable photocurrent for passage of over 3000 C/cm² at AM1 photocurrent densities. Ru(H₂O)₆³⁺ ions are effective in improving photocurrent-voltage characteristics for n-GaAs₁₋ₓPₓ (0 < x < 1) anodes but have no effect for n-GaP,. indicating chemical interactions of the Ru ion with As or As oxide sites at the semiconductor/liquid junction. Direct comparison of V_(OC) for n-GaAs₁₋ₓPₓ/Au junctions with n-GaAs₁₋ₓPₓ/Se²⁻ barriers indicates that liquid junctions have higher V_(OC) values than some Schottky barriers and that pinning of the Fermi level by intrinsic surface states may not play a dominant role in determining interface parameters for these junctions.

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