SURFACE DIFFUSION AND INCORPORATION OF GROUP III ATOMS DURING III - V MBE. Tatau Nishinaga, Department of Electronic Engineering, The Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyoku, Tokyo 113, Japan

In MBE of III - V compounds, the group III atoms first arrive on the surface and migrate to the step where they are incorporated if the group V atoms come and fix them. If there is no group V atoms come, the group III atoms can easily detach and migrate to the next step. Hence, the diffusion length for incorporation of group III atoms depends strongly on the group V pressure. This has been clearly observed where inter-surface diffusion takes place. For instance, in MBE of GaAs, Ga diffuses from (111)A to (001) and the growth rate decreases on (001) surface exponentially as a function of the position from the corner where two faces meet. The diffusion length of incorporation takes the value of around 1 micron meter[1]. This means the group III atoms pass over many steps and the steps do not act as 100 percent sink. If all the group III atoms cannot enter the step, the rest should wait and this means the concentration increases resulting in the increase of the supersaturation at the step edge. When this happens on the vicinal surface, the critical temperature of mode transition between 2D nucleation and step flow should increase.

Basing on this model, the mode transition temperature was measured by changing group V to III flux ratio. It was found that the transition temperature decreases as the group V flux is increased[2]. This is explained in terms of the change of supersaturation at the step edge.

[1] S. Q. Shen, D.Kishimoto and T.Nishinaga : Jpn. J. Appl. Phys., 33(1994) L11.

[2] K. Miwa and T. Nishinaga : The 1st Topical Meeting on Structural Dynamics of Epitaxy and Quantum Mechanical Approach, Jan. 1996, Tokyo, p.p.25-30.