Computational and experimental study of surfactant effects on compound semiconductors.

摘要

Organometallic vapor phase epitaxy (OMVPE) is used for fundamental research and commercial production of III-V electronic and optical devices. An understanding of the surface processes leads to improved control of epitaxial thin film properties and enables development of next-generation optoelectronic devices. Surfactants are also proving to be an essential tool for engineering novel materials. The effects of surfactants such as Sb, Bi, and Te on GaP, InP, GaInP, and GaAs were studied by experiment and simulation. These surfactants were found to induce changes in surface structure, control ordering, and modify fundamental surface kinetics.; Due to the nature of the OMVPE environment, detailed in-situ study of atomic scale growth processes is not possible. Ab-initio calculations, making use of Kohn-Sham Density Functional Theory (DFT), were performed to identify Sb induced surface reconstructions on GaP and InP (001) surfaces. A method for calculating the surface energies of these reconstructions was developed and used to create surface phase diagrams for the surfactant covered alloys. Reconstructions predicted by these phase diagrams, with (4 x 3) and (2 x 3) periodicity, explain the triple-period ordering in GaInP grown with Sb surfactant.; Surfactant modified surface mass transport is certain to have interesting consequences. To investigate this, the surfactant effects of Sb, Bi, and Te on the surface kinetics of GaAs were studied. Homoepitaxy of patterned GaAs (001) substrates was performed with increasing concentrations of surfactant. The morphological evolution of the surface and lateral growth rates were studied by optical and atomic force microscopy.; Both Sb and Bi enhanced the [110] lateral growth rate as much as 300 percent, while having little effect on the orthogonal direction. Results from kinetic simulations indicate that the enhanced lateral growth rate is due to an increased adatom hop frequency.; The surfactant Te did not modify lateral growth rates, but the morphology of the singular surface and the profiles of the patterned features were significantly altered. These changes in GaAs (001) morphology were interpreted as due to an increase in step velocity (sticking coefficient) and an increase in the Ehrlich-Schwoebel barrier. Kinetic simulations support this interpretation.