ESTIMATION OF PHOTOEMISSION INTENSITIES AND THE SURFACE PHOTOELECTRICEFFECT

Going beyond a simple Fresnel like correction, surface-state peaks in normal emission spectra offer a sensitive probe to detect the screenin g of the light wave by the surface of the solid below the plasma frequ ency. The background resulting from distant bulk peaks should vary rat her slowly with photon energy as compared with the intensity of the su rface state. Above the plasma frequency the surface sensitivity of scr eening vanishes and bulk-plasmon excitation dominates the dependence o n photon energy. The photocurrent is estimated here by approximations to the matrix elements between the initial and final photoemission sta tes. In the case of surface states the two-density-step hydrodynamic m odel is applied for the electrodynamic response. It has proven to yiel d similar results as the selfconsistent calculation on one hand and it is well suited by geometrical aspects on the other. The electronic de nsity distribution of a surface state may be regarded as an overlayer sheet representing the lower density step of that model. The behavior of the emission from dangling bond states of semiconductors dependent on photon frequency is discussed for frequencies below and above the p lasma frequency.