Surface-excited photoconduction is compared with volume-excited photoconduction in cadmium sulfide crystals with a wide range of sensitivities. Measurements are presented as a function of exciting wavelength for (1) spectral response, (2) photocurrent as a function of light intensity, (3) photocurrent decay time, (4) infrared quenching, and (5) thermally stimulated current. The results supply additional evidence that the free electron lifetime for surface excitation is smaller than the lifetime for volume excitation because of a higher rate of recombination at the surface, associated with the adsorption of moist air on the crystal surface.

Correlations are found between the distribution of traps, as indicated by thermally stimulated current measurements, and both (1) the low-temperature spectrum for photoconduction-photostimulation published by Lambe for CdS: Ag, and (2) the variation of photocurrent with light intensity.

• Received 17 November 1955

DOI:https://doi.org/10.1103/PhysRev.101.1668