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Computer simulations of crystal growth by molecular‐beam epitaxy (MBE) are used to study the nature of surface (interface) roughness as the crystal is being grown. The simulations were done on a Cray X‐MP computer using a 100×100 atom substrate. The results presented use parameters for gallium arsenide but can be generalized to other systems. The nature of the surface is presented in terms of three quantities: (1) reflection high‐energy electron diffraction (RHEED) intensity; (2) step density, and (3) island size distribution; all of which are calculated directly from the simulated crystal and expressed as a function of growth time. The RHEED intensity is evaluated, within the kinematical approximation, for the ‘‘off‐Bragg’’ specular condition using the surface atoms only. The step density is the number of monolayer steps (up or down) that a tiny man would take as he walked along the surface in either the (110) or (11¯0) direction. This quantity is normalized and evaluated along both directions on the surface as a function of time. It is in the step density that asymmetry of the order of 30% can be seen. The cause of the aforementioned asymmetry is shown to be due to anion incorporation mechanisms. Detailed analysis of anion incorporation along different configurations is presented, as well as important effects arising from anion to cation flux ratio.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures (Volume:5 , Issue: 3 )
Date of Publication: May 1987