Studies of Conduction Electron Tunneling across the Ohmic Metal-Silicon Interface Utilizing Cesr

The transport of Phosphorus conduction electrons, in heavily doped (>10^{19 } cm^{-3}) Si, from the Si, into metal layers evaporated on the Si surface has been studied. We utilize Conduction Electron Spin Resonance (CESR) as a method of spin labeling the phosphorus electrons. Electrons which tunnel from the Si into the metal overlayer, are subject to an increased relaxation rate, resulting in a change in the resonance width. This technique requires no leads or biasing, hence even submonolayer metal coverage can be studied. The electron transport, across the Si-metal interface, into bulk (>50A) metal layers, was studied as a function of Phosphorus concentration at the Si surface. Metals studied were Al, Ag, Au, and Cu. The metal films were prepared in a UHV system, however CESR measurements were made in air. These results are compared to a simple Schottky barrier theory. The change in CESR line width was studied as a function of metal layer thickness (submonolayer to 200A). These studies were performed in a dedicated UHV apparatus, which is capable of in situ metal evaporation, CESR measurement, and Auger analysis. (The design of this system is discussed in detail.) The metals studied are Al, Ag, and Cu. Results show little coupling to layers ~3A thick, with a rapid increase to the maximum coupling by 60A of metal. The CESR line width was also studied with metal bilayers on the Si surface. In these experiments metal A is deposited on the Si surface, then metal B is deposited on metal A. Systems studied are Cu-Ag, Al-Ag, Al-Cu, and Cu-Al. These results can give insight to the metal layer thickness required to define the properties of the Schottky barrier.