The theory of the crystal-photoeffect

H. Dember has observed that the illumination of semi-conductors (cuprite, proustite pyargyrite) produces a new photoelectric effect. If both sides of the crystal are connected by a circuit containing a galvanometer, fig. 1, a photoelectric current arises in such a direction that electrons in the semi-conductor move always in the direction of the incident lig h t; the current can be measured without application of any accelerating potential. He has found a negative charge on the back of the single-crystal when the potential was measured by a compensation-method, or directly with an electrometer, even if the electrodes had been prevented from touching the semi-conductor, fig. 2. H. Dember has given to this phenomenon the name Crystal-Photoeffect in order to distinguish it from the other photoelectric effects, especially from the “Sperrschicht’’-Photoeffect. The latter is caused by photo-electrons excited near the boundary between a semi-conductor and a metal and can be explained by the unipolar conduction of the contact.