Control of nano- and micro-scale inhomogenities
using surfactants in III/V alloys

G.B. Stringfellow

Department of Materials Science and Engineering
University of Utah
Salt Lake City, UT 84112

Thin films of semiconductor alloys are subject to spinodal decomposition due to the atomic-level-strain-energy induced deviations from thermodynamic ideality. This gives rise to micro-scale inhomogeneities that are controlled by kinetic factors during epitaxial growth. For (001) films, anisotropic surface diffusion coefficients give rise to a one-dimensional compositional modulation (CM) that is reflected in the surface morphology of the epitaxial layer. The nature of the inhomogeneities and the magnitude of the compositional fluctuations in GaInP grown by organometallic vapor phase epitaxy can be determined by controlling the surface diffusion kinetics during growth. This CM has profound effects on the optical properties of the material. In particular the effects on the low temperature photoluminescence energy, anisotropy, and decay lifetime are dramatic. Surface thermodynamic effects can produce an entirely different form of inhomogeneity, namely ordering. This phenomenon, occurring on the sub nanometer scale, also has a large effect on the bandgap energy as well as the polarization and lifetime. This paper describes how both of these phenomena, ordering and compositional modulation, can be controlled in GaInP via the addition of surfactants isoelectronic with P, most notably Sb and Bi, during the epitaxial growth process. This leads to a new level of control of the materials properties of an alloy without affecting the average solid composition or the Fermi level. It also allows the possibility of deliberately and controllably introducing bandgap inhomogeneities in grown structures to produce, e.g., heterostructures and quantum wells.