Characterization of p-n junctions and surface-states on silicon devices by photoemission electron microscopy

We have investigated p-n junctions on a silicon device fabricated on a (100) surface using photoemission electron microscopy (PEEM). We show that different doping levels for the p-and n-doped regions in the surface give rise to a contrast in the PEEM images. The contrast is due to the change in the photoemission threshold for different bulk doping levels when the Fermi level is pinned between the valence and the conduction-band edge at the surface. The intensity profiles change when the Fermi level is pinned at different positions within the band gap. We present a detailed analysis of intensity profiles of p-n junctions in a PEEM image. We show that PEEM is capable of characterizing p-n junctions and surface-states on silicon devices. The images are significantly affected by electron optical deflections of the photoemitted electrons caused by the high lateral electrical field of a biased p-n junction. We are able to identify this as an electron optical effect on the profile shape by simulations of the electron trajectories between the sample and the first aperture of the PEEM.