Abstract

I‐V characteristics, voltage dependence of the quantum efficiency, and spectral response were compared for annealed single‐crystal photoanodes. Annealing in cadmium atmosphere improved the overall solar response considerably, while annealing under vacuum revealed a poor response for photon energies larger than 1.8 eV and a high quantum efficiency for near‐bandgap energies. This behavior may be attributed to electron‐hole pair generation from interbandgap states and a large density of minority carrier recombination centers near the crystal surface, owing to a high nonstoichiometry and a selenium layer at the surface. Annealing in selenium atmosphere resulted in very poor solar response caused by compensation. Simultaneous illumination of the electrodes with a He‐Ne laser strongly enhanced the quantum efficiency for vacuum‐annealed crystals for near‐bandgap photons. We attribute this to electron trapping in the selenium‐rich surface, with a resulting increase in depletion‐layer width in the cadmium selenide.

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