AVS 53rd International Symposium
    Electronic Materials and Processing Friday Sessions
       Session EM+TF-FrM

Paper EM+TF-FrM10
Comparison of the Calculated Electronic Structure of Oxygen and Nitrogen Adsorption onto Ge(100)

Friday, November 17, 2006, 11:00 am, Room 2003

Session: High-k Dielectric & Multi-Functional Oxide Growth & Processing
Presenter: S.R. Bishop, University of California, San Diego
Authors: S.R. Bishop, University of California, San Diego
T.J. Grassman, University of California, San Diego
A.C. Kummel, University of California, San Diego
Correspondent: Click to Email
For high-k dielectrics on Ge(100), a germanium oxynitride (GeON) interface leads to superior C-V characteristics compared to GeO@sub 2@ passivation layers. Experimental studies show GeON is both a better diffusion barrier and surface passivant than GeO@sub 2@. To understand why GeON is an effective passivating layer, it is necessary to first determine the oxygen and nitrogen binding sites independently. STM studies have shown that the initial stage of O and N adsorption is insertion into the backbonds and into the 2x1 surface dimers, while the final stage is Ge displacement by O and N. The clean Ge(100) surface, oxygen adsorption sites, and nitrogen adsorption sites were modeled using density functional theory (DFT). The DFT calculations show that all oxygen insertion and displacement sites leave the near-Fermi level density of states essentially unchanged compared to the clean surface. This is consistent with O atom insertion and displacement creating no new unfilled dangling bonds. In contrast, the insertion and adsorption sites for nitrogen all create new electronic states in the near-Fermi level region, consistent with nitrogen atoms making two bonds to the surface, but retaining a half-filled dangling bond. However, the Ge-N bonds were found to be stronger than the Ge-O bonds, consistent with GeON being more effective than GeO@sub 2@ as a diffusion barrier. Since the efficiency of GeON as an electronically passivating layer is not intrinsic to its chemisorption states on Ge(100), it may be related to the nitrogens' ability to be electronically passivated by hydrogen. The DFT calculations show that even though N atom displacement of Ge creates states near the Fermi level, hydrogen passivation greatly reduces or eliminates the density of those states.