AVS 50th International Symposium
    Thin Films Thursday Sessions
       Session TF-ThM

Paper TF-ThM2
Effect of Crosshatch Formation on the Kinetics of Si@sub 1-x@Ge@sub x@ Growth on Si(001) from Hydride Precursors

Thursday, November 6, 2003, 8:40 am, Room 329

Session: Modeling & Fundamentals in Thin Film Deposition
Presenter: T. Spila, University of Illinois
Authors: T. Spila, University of Illinois
P. Desjardins, École Polytechnique de Montréal, Canada
J. D'Arcy-Gall, University of Illinois
R.D. Twesten, University of Illinois
J.E. Greene, University of Illinois
Correspondent: Click to Email
Compressively-strained Si@sub 0.7@Ge@sub 0.3@ layers were grown on Si(001) by gas-source molecular beam epitaxy from Ge@sub 2@H@sub 6@/Si@sub 2@H@sub 6@ mixtures at 450 °C. The combination of the relatively low growth temperature and high steady-state hydrogen surface coverage, @theta@@sub H@ = 0.52 ML, suppresses strain-induced roughening and provides extremely flat surfaces with root mean square widths w < 1.5 Å for fully-coherent layers. These samples were used to probe mechanisms controlling misfit-dislocation-induced surface roughening (i.e., crosshatch) along 90°-rotated <110> directions. For film thicknesses t just larger than the critical value for misfit dislocation formation, t@sub c@ = 1000 Å, the surface roughness (w = 3.1 Å at t = 1350 Å) is dominated by single- and multiple-atomic-height steps generated by the motion of threading dislocations associated with the interfacial misfits. The surface steps are preferential H desorption sites and the increased total step length results in a decrease in @theta@@sub H@ on terraces as well as at step edges. The latter effect allows higher adatom crossing probabilities at ascending steps leading to the formation of periodic ridges (w = 27 Å at t = 4400 Å) in response to local strain fields associated with the misfit dislocation clusters. Simultaneously, the decrease in @theta@@sub H@ on terraces strongly affects film growth kinetics as deposition rates increase from 10 Å min@super -1@ with t < t@sub c@ to 60 Å min@super -1@ with t = 1400-4400 Å. Overall, for films with strain relaxation R < 5%, crosshatch is due to surface steps that result from multiple misfit dislocations on single glide planes, but for R = 22-78%, crosshatch becomes dominated by local strain-induced roughening and leads to periodic ridge formation.