Depletion layer photo current

A great effect on the rate of ion transfer reactions can only be expected if the minorities are moved to the surface. An additional photo-generation of majorities has little Influence on their concentration if this is already relatively high. Large photocurrents are therefore found when a depletion layer is formed, namely for n-type specimen at anodic reactions and p-type specimen at cathodic ones. Some typical photo-current spectra for anodic bias of n-type specimen and cathodic bias of p-type specimen are shown in Fig. 18. One sees that the photocurrent spectrum reveals the light absorption properties of the semiconductor and indicates clearly the energy of the band gap by a steep increase of the photocurrent. 

---