9. Surface Mediated Growth of Dilute Bismides

It has been well established that growing semiconductor films in the presence of a surfactant significantly influences the surface morphology and the compositional homogeneity in the bulk [1]. There is a great deal of evidence in the literature that suggests that this is particularly true in Bi-containing films. Kawano and co-workers [2] first showed that pre-depositing Bi on Si(001) did not result in its incorporation into the subsequent Ge film. Furthermore, Bi suppressed the formation of 3D islanding despite the lattice mismatch. The classic model for surface segregation in III-V compound semiconductor films is thermodynamic in nature, where there is an energetic driving force for the segregating species to reside at the surface as a surfactant [3]. Since that initial report of the smoothing effect of Bi on surface morphology, similar results have been reported for other materials systems including GaAs [4] and GaAsN [5] thin films, InGaAs/GaAs heterostructures, [6] and InAs/InGaAs(001) nanocomposites. [7] Pre-deposition of Bi was also observed to impact ordering in GaAsSb [8] and InGaP [9] and the incorporation of Sb in InAsSb [10]. Furthermore, the presence of Bi has been shown to change the crystal phase of GaAs nanowires, [11] and the sizes of InAs/GaAs quantum dots increase when a Bi surfactant is used [12]. All of these phenomena point to the fact that Bi strongly alters the growing surface of a semiconductor film. This chapter describes the atomic-scale surface reconstructions present during the growth of Bi-containing films, and the factors that contribute to the incorporation of Bi. A major part of this work also considers the mechanisms that compete with Bi incorporation, including the formation of droplets, and their ramifications on the uniformity of the films.