IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Semiconductors Monday Sessions
       Session SC-MoA

Paper SC-MoA5
STM Study of Dislocation-Mediated Surface Morphology of GaN Grown by ECR-Plasma Assisted MBE

Monday, October 29, 2001, 3:20 pm, Room 124

Session: GaN Surfaces, Interfaces, and Devices
Presenter: Y. Cui, University of Wisconsin
Authors: Y. Cui, University of Wisconsin
L. Li, University of Wisconsin
Correspondent: Click to Email
The surface morphology of GaN films grown on the 6H-SiC substrates by ECR-plasma assisted molecular beam epitaxy was studied by reflection high-energy electron diffraction (RHEED) and in situ scanning tunneling microscopy (STM). Clean SiC substrates were prepared by a two-step method of etching in hydrogen atmosphere at 1600 °C and annealing under Si beam in ultrahigh vacuum at 950 °C. These processes remove the polishing damages of the SiC substrates. The resulting surfaces are composed of atomically flat terraces that are separated by triple-layer steps. At temperature between 550 and 600 °C and plasma power of 30 W, two-dimensional growth was observed. The surface morphology of the films can be characterized by two dislocation-mediated structures: pinned steps and spiral hillocks. Straight-pinned steps along the {1120} directions were found for film thickness of 500 Å, created due to the emergence of screw and mixed dislocations at the crystal surface from the bulk of the film. By counting the number of the steps, the dislocation density is estimated to be in the order of 10@super10@ cm@super-2@. At film thickness greater than 1000 Å, these pinned steps grow outward and around the dislocation, forming spiral hillocks with a density in the order of 10@super8@ cm@super-2@. The reduction of the density is explained by annihilation of the dislocations during the formation of the spirals. These results and their implications for GaN epitaxy will be presented at the meeting. This research is supported by NSF DMR-0094105.