Photoelectromagnetic and Photoconductive Effects in Lead Sulphide Single Crystals

For the first time bulk photo-effects have been observed in single crystals of lead sulphide. Both photoelectromagnetic and photoconductive measurements have been made, and carrier lifetimes and quantum efficiencies estimated therefrom. Quantum efficiencies are near unity for all samples, while lifetimes are found to range from 6 × 10 -10 to 9 × 10 -6 second. Measurements on lifetimes by two other methods give values in reasonable accord with the photoelectromagnetic values. Study of the spectral distribution of sensitivity establishes that there is no appreciable change in quantum efficiency with wavelength except for the rapid fall at 3μ, thus establishing that photoelectrically there is no difference between the main absorption band and the `tail' band. The optical activation energy (i.e. quantum energy at which sensitivity is halved) is 0.41 eV, and it is concluded that the thermal activation energy is very close to this value.