| AVS 57th International Symposium & Exhibition | |
| Surface Science | Monday Sessions |
| Session SS2-MoA |
| Session: | Stress and Bonding Energetics in Nucleation and Growth |
| Presenter: | J.-F. Veyan, University of Texas at Dallas |
| Authors: | J.-F. Veyan, University of Texas at Dallas M.P. Nadesalingam, University of Texas at Dallas M. Huang, University of Texas at Dallas H. Dong, University of Texas at Dallas J.N. Randall, Zyvex Labs W.P. Kirk, University of Texas at Dallas J. Cho, University of Texas at Dallas R.M. Wallace, University of Texas at Dallas Y.J. Chabal, University of Texas at Dallas |
| Correspondent: | Click to Email |
Atomic Layer Epitaxy (ALE) is a critical step for constructing 3-D structures at the atomic scale, necessary for Atomically Precise Manufacturing (APM) of new devices such as quantum dots. We present here a comprehensive study of Ge ALE on Si(100)×(2x1) surface using digermane (Ge2H6) as a precursor. Si(100) samples are clean at passivated by SiO2 by standard wet chemical procedures. The oxide is then removed in ultra high vacuum (1.5 10^-10 Torr) by resistive annealing (1173 K). The clean and Ge2H6 exposed Si(100)-(2x1) surfaces are characterized using Infrared absorption spectroscopy (IRAS) and X-ray Photoelectron Spectroscopy (XPS). IRAS measurements are performed in transmission at the Brewster angle, and XPS measurements at a takeoff angle of 45 degrees. The Ge2H6 is introduced through either capillaries for the IR measurements or a directed doser for the XPS studies. In both cases, the fluxes on the samples are calculated to be ~10^-6 Torr.sec.
At room temperatures, a saturation coverage was achieved on a clean Si(100) surface after ~10 L, corresponding to an estimated sticking coefficient of ~0.5. IR absorption bands in the ~1950-2000 cm^-1 range indicate that mono- (GeH), di- (GeH2) and tri- (GeH3) -hydrides species are chemisorbed on the surface, consistent with the shifts of the Ge 2p3/2 core level observed by XPS. In addition, a feature observed at 2098 cm^-1, associated with silicon monohydride (Si-H), indicates that Ge2H6 dissociates via beta-hydride elimination, involving the intermediate states Si-H and Si-GeH2-GeH3. Measurements of Ge-H and Si-H stretch intensities at saturation coverage as a function of substrate temperature from 173 K up to 700 K suggest that the mechanism involved in the chemisorption of Ge2H6 on Si(100) proceeds via dissociation of Ge2H5 into GeH3, GeH2, and GeH. At a temperature of 600 K, all the vibrational modes associated with Ge hydrides species vanish, which is consistent with the thermal desorption temperature of H on pure Ge(100) surface. However, the intensity of the Si-H vibrational mode increases with the temperature, reaching a maximum intensity around 600 K, and then decreases and vanishes at 713 K, which is 100 K lower that the normal desorption temperature of H on pure Si(100). A quantitative understanding of both the chemisorption pathway and desorption mechanisms is achieved using Density Functional Theory (DFT) calculations.
This work is supported by the Defense Advanced Research Project Agency (DARPA), Space, Naval Warfare Center, San Diego (# N66001-08-C-2040), and the Emerging Technology Fund of the State of Texas to the A.P.M. Consortium.