Imaging the Evolution of Lateral Composition Modulation in Strained Alloy Superlattices

Abstract

Scanning tunneling microscopy is used to investigate the morphological evolution of GaAs/InAs short period superlattice structures. The layers of the superlattice, either grown in compression or tension, exhibit an island or trench morphology. With increasing film thickness, the islands or trenches grow in size and develop a characteristic spacing along [110] of approximately 150 A. This is the first experimental evidence to suggest that lateral composition modulation arises from both thickness variations of the layers and compositional nonuniformities within the atomic plane.

Phase-field-crystal dynamics for binary systems: Derivation from dynamical density functional theory, amplitude equation formalism, and applications to alloy heterostructures

“…Recent intensive studies on thin film epitaxy and atomic deposition have shown the important effects of intermixing on nanostructure self-assembly. Typical examples include InAs(InGaAs)/GaAs(001) [66][67][68] or Ge(SiGe)/Si(001) [69,70] heteroepitaxy that has been investigated extensively (particularly the intermixing-caused alloying of wetting layers and quantum dots), and the interlayer diffusion in semiconductor multilayers or superlattices such as InP/InGaAs [71], GaAs/GaSb [72], and GaAs/InAs [73]. An important phenomenon in these epitaxial layers is the occurrence of surface segregation, in which an enrichment of one of the film components at a surface or interface region occurs.…”

“…An important phenomenon in these epitaxial layers is the occurrence of surface segregation, in which an enrichment of one of the film components at a surface or interface region occurs. This has been observed in a variety of material systems including III-V and II-VI semiconductor heterostructures [66][67][68][69][70][71][72][73]. To address these complicated phenomena and effects, the basic processes and mechanisms of intra-and inter-layer diffusion at nearly-planar interfaces as well as their coupling with material processing and growth parameters needs to be clarified.…”

“…V. The results are compared to experimental findings of vertical composition segregation or surface enrichment as widely encountered during the growth of various alloy heterostructure systems such as InAs/GaAs, Ge/Si, GaAs/GaSb, InP/InGaAs, etc. [66][67][68][69][70][71][72][73].…”

Engineering lateral composition modulation in GaAsSb multilayers

“…Imaging parameters were 73.1 V sample bias and 100 pA of tunneling current for all samples. While it is possible that the STM images do not show the precise atomic structure during growth, the gross morphology of the layers visible in these images are likely present during growth, as post growth annealing does not significantly alter the step and island structure [7].…”

“…This suggests that in the SPS structure, the GaSb layers evolve towards an intermixed GaSbAs alloy composition, which reduces the interlayer strain even though the GaAs layers remain relatively pure. This reduction in interlayer strain will prevent strain-induced roughening, in turn suppressing the formation of lateral composition modulation [7,14].…”