| AVS 54th International Symposium | |
| Surface Science | Thursday Sessions |
| Session SS2-ThM |
| Session: | Surface Structure of Compound Semiconductors |
| Presenter: | M.B. Whitwick, University of British Columbia, Canada |
| Authors: | M.B. Whitwick, University of British Columbia, Canada T. Tiedje, University of British Columbia, Canada T. Li, University of British Columbia, Canada |
| Correspondent: | Click to Email |
By a combination of theoretical and experimental work, using GaAs as a model system, we show that time evolution of surface morphology during epitaxial growth can be used to obtain rather detailed information on step densities and adatom dynamics. From in-situ light scattering we find that homoepitaxial growth on randomly rough GaAs (100) substrates causes the surface to smooth towards a characteristic surface roughness determined by kinetic roughening. A recent theoretical model for the surface morphology as a function of growth time,1 based on a Burton-Cabrera-Frank picture of crystal growth2 in which adatoms incorporate at step edges, suggests that the smoothing of GaAs can be described by a conservative Kardar-Parisi-Zhang type equation in which the dominant linear term in the growth equation is due to a negative Ehrlich-Schwoebel potential barrier for adatom migration at step edges. The surface smoothing rate is found experimentally to depend on the deposition rate and temperature during growth. In the model the coefficient of the linear term in the growth equation is inversely proportional to the step density (~F/S), where F is the flux of deposited adatoms and S is the step length density. Although the full growth equation is nonlinear, for low amplitude roughness the linear term dominates. We have used this fact to determine the linear smoothing coefficient as a function of substrate temperature (400-610 C) and growth rate (0.01-10 ML/s) by in-situ UV (244 nm) diffuse light scattering along the [011] and [01-1] directions. The coefficient of the linear smoothing term was found to have a power law dependence on flux with exponent of 0.7 and an exponential temperature dependence on temperature with activation energy 0.50 eV. The surface step density was measured ex-situ by AFM. The step density was found to be ~0.10±0.05 1/nm with a tendency towards higher density at high growth rates. This step density is in good agreement with the step density inferred from theoretical expression for the linear smoothing coefficient. The coefficient of the nonlinear smoothing term is also found to be in good agreement with theory.
1 A. Ballestad and T. Tiedje, Phys. Rev. B 74, 153405 (2006).
2 W.K. Burton, N. Carrera, F. Frank. Phil. Trans. Roy. Soc. 243(866):299-358. (1951).