Der photodielektrische Effekt in CdS-Einkristallen

Measurements of the photodielectric effect in CdS-crystals at frequencies between 50 Hz and 300 kHz, temperatures between 300°K and 78°K and excitation with 577 nm resulted in a sixfold increased permittivity if the excitation density reached a value of 66 μW/cm². This increase of capacity can be understood as due to an increase in conductivity if an equivalent circuit of the crystal with four elements — two capacities and two photoresistors — is supposed. The observed variations of the time constant in the frequency response of the permittivity can be explained by variations of the data in the many-layer-system of the crystal. Measurements of the temperature dependence and decay of the photodielectric effect are further arguments for our model and against a true dielectric change.     

Untersuchungen zum photokapazitiven Effekt von Phosphoren

Capacitance and loss angle of several phosphors are measured as a function of exciting irradiation intensity at different temperatures and different frequencies. Furthermore, the decay of the photocapacitive effect after shutting off the radiation is observed. Criteria are developed for deciding whether the photocapacitive effect is due to conduction band electrons (photoconductive effect of first kind), to impurity band electrons (photoconductive effect of second kind), or to polarization of filled traps (photodielectric effect). These are based on the decay behavior at low temperature (fast, slow, slow, respectively) and the dispersion at low frequencies (strong, strong, weak, respectively). It is shown that even for the photoconductive effect of first kind the interplay of conduction band and shallow traps is essential but that, nevertheless, conductivity data can be obtained from capacitance measurements.