The Role of Carrier Diffusion and Indirect Optical Transitions in the Photoelectrochemical Behavior of Layer Type d-Band Semiconductors

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Abstract
Photocurrents at n‐type single crystals of , , and , with the van der Waals surfaces exposed to the electrolyte, have been studied by varying the voltage applied and the wavelength of the light. The experiments have been performed under conditions where a depletion layer is formed beneath the semiconductor surface and in the presence of I−‐ions in the electrolyte which act as scavengers for the photogenerated holes and prevent corrosion of the electrodes. An evaluation of the quantum yield in relation to the absorption coefficient and the extension of the space charge layer shows that generation of minority carriers outside the space charge layer contributes to a large extent to the photocurrents. A mean diffusion length for holes of and is derived from the experiments. The wavelength dependence of the photocurrent yield is analyzed in terms of light absorption for indirect transitions. This gives a measure of the bandgaps in these materials which turn out as 1.17 eV , 1.06 eV , and 1.16 eV in good accordance with optical measurements.

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