Diffusion length of minority carrier in n-type semiconductors: A photoelectrochemical determination in aqueous solvents

Photoelectrochemical measurements with aqueous electrolyte-semiconductor junctions under monochromatic illumination for five n-type semiconductor compounds are presented: ZnSe, CdSe, CdTe (II-VI) and GaP, InP (III-V). The Schottky behavior of these junctions is demonstrated in the dark and under illumination. Only if conditions such as surface preparation, proper band bending, and doping level as well as energy of incident photons are achieved, the photocurrent versus potential characteristics are described using Gärtner’s equation. Values of the diffusion length L of holes are determined by an extrapolation and a fitting method. They depend on the particular properties of the samples, particularly the concentration of free electrons. Results obtained are: ZnSe (7×1017 cm−3) L=0.025 μm; CdSe (2.5×1018 cm−3) L=0.124 μm; CdTe (8.5×1017 cm−3) L=0.14 μm; GaP (4×1016 cm−3) L=0.24 μm; InP (3×1017 cm−3) L=0.15 μm.