By: S.E. Babcock, T.F. Kuech, L. J. Mawst
| The presence of chemical species on a surface can radically change the surface chemical kinetics associated with atom placement and crystal growth. Recently, IRG1 researchers at the Wisconsin MRSEC completed a comparative study of the effect on epilayer composition and structural properties of reactant sequencing during the metalorganic vapor phase epitaxy of GaAs1−yBiy. The effect of growth temperature (370-430°C) and precursor flow rate on the film properties and Bi incorporation was also determined. Whereas the growth rate of GaAs decreased with decreasing growth temperature (due to slow surface chemical kinetics, as is well-established for this chemistry), in stark contrast, the GaAs1−yBiy growth rate was almost temperature insensitive over this broad temperature range. This unprecedented observation within a large literature dealing this growth technique indicates a change in growth mechanism. The catalytic effect of Bi metal or the trimethyl bismuth reactant (or its fragments) on the decomposition and incorporation of Ga serves as a mediator of the decomposition and growth of these materials. Our observations hint at the possibility of growing GaAs1-yBiy hetero-structures at temperatures below what was assumed to be the lowest possible temperature for the growth of GaAs, opening new growth regimes for multinary synthesis of this technologically important class of materials. |  |
| The Bi content, and GaAs and GaAs1-yBiy growth rates (as indicated by the layer thickness) change substantially with growth temperature. The GaAs growth, indicated by the blue squares, follows the expected trends with temperature. However, the presence of Bi or the Bi precursor alters that behavior dramatically leading to previously unseen temperature-independence to the growth rate. | |
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