TARGET CURRENT SPECTROSCOPY OF THE ALKALI-HALIDES KCL, CSCL AND KBR

Thin films of KCl, CsCl and KBr deposited on Si(111) were investigated by means of target current spectroscopy (TCS). From the TCS initial p eak position the surface potential changes during deposition were obta ined. From the surface potential dependence on the alkali halide film thickness the critical island size in the initial stage of the film gr owth was estimated: for CsCl, 10 Angstrom; for KCl, 18 Angstrom; for K Br, 25 Angstrom. In the target current spectra of the alkali halides a n intensive structure in the energy region corresponding with the band gap was discovered. One group of peaks was induced by electron irradia tion and vanished at high temperatures. This fine structure was consid ered to be due to an electronic transition related to the defect state s in the bandgap. From the evolution of the TCS maximum intensities th e defect concentration changes caused by electron irradiation were est imated.