Composition modulations in tensile strained In 1− xGa xAs yP 1− y films grown on (1 0 0) InP substrates

Abstract

The correlation between compositional modulations and surface morphology has been studied by transmission electron microscopy (TEM) and atomic force microscopy (AFM) for a series of tensile strained In 1− x Ga x As y P 1− y films grown by molecular beam epitaxy (MBE) on (1 0 0) InP substrates. At low values of strain (0.6%), both a quaternary In 0.65Ga 0.35As 0.6P 0.4 film and ternary In 0.45Ga 0.55As film show anisotropic behavior (both with regards to composition modulation and surface morphology) between [0 1 1] and [0 1 ̄ 1] cross-sections. The composition modulation and surface undulation are prominent only in the [0 1 ̄ 1] cross-section. The In 0.45Ga 0.55As films develop a coarse faceted structure on (4 1 1) and 4 1 ̄ 1 ̄ planes after ∼100 nm of film growth. Composition modulations (scaling with the size of the facets) are observed in films 0.1–1 μm thick, but in thicker films (>1 μm) the faceted structure disappears while the scale of the compositional modulations decays to that found in unstrained films. On the other hand 2% tensile strained In 0.25Ga 0.75As and In 0.72Ga 0.28P films show pronounced faceting with no evidence for compositional modulations, and 2% tensile strained In 0.5Ga 0.5As 0.5P 0.5 films show composition modulation without scaling and no faceted surface. The results are discussed in terms of the interplay between thermodynamic driving force, leading to segregation and faceting, and kinetic factors.