We present cross-sectional scanning-tunneling microscopy results of threefold stacked InAs quantum dots prepared by metal-organic chemical-vapor deposition at 485 °C and a growth rate of 0.18 nm/s. The dots consist of stoichiometrically pure InAs and show a layer-dependent size. The images indicate a prismatic dot shape with {101} and additional {111} side faces as well as a (001) top face.

Cross-sectional scanning-tunneling microscopy of stacked InAs quantum dots

We quantify the rates and total amounts of the arsenic for antimony exchange on both the Sb-terminated and Ga (or In)-terminated GaSb (001) surfaces using in situ real time line-of-sight mass spectrometry (LOS-MS) during molecular beam epitaxy. On the Sb-terminated GaSb (001) surface, an As for Sb exchange is observed to occur at all values of incident As2 flux considered. At high substrate temperature, three-dimensional (3D) nanometer-sized clusters from as a consequence of As/Sb exchange and lattice mismatch strain between GaAs and GaSb. The 3D clusters are found to have lateral dimensions of ∼10–30 nm and heights of 1–3 nm by atomic force microscopy (AFM). By contrast, at lower substrate temperatures a two-dimensional surface morphology is maintained, and AFM reveals an array of atomically flat terraces. On the surface terminated by one monolayer (ML) of Ga or In, there exists a critical As2 flux below which the As/Sb exchange is greatly diminished. The net amounts of Sb leaving the surface during one ...

Arsenic for antimony exchange on GaSb, its impacts on surface morphology, and interface structure

This review attempts to recount, from my perspective, some of the science and technology highlights (and pitfalls) that fueled the nanoscience and nanotechnology revolution—an odyssey of sort on nanoscale measurements and manipulation. Seminal papers by several pioneering groups are given special attention as well as the role played by the AVS who hosted many of the earlier conferences and published proceedings that recorded the field’s early progress. This review is organized around the introduction and evolution of the various scanning probe microscopes that have revolutionized the way we study the structure and properties of surfaces. The use of these enabling tools in pursuit of more ambitious goals in nanotechnology, such as creating unique structures by manipulating individual atoms or molecules, and developing concepts in electronics, information storage, sensor technology, nanotribology, and nanomechanics, is also discussed.

Nanoscale measurements and manipulation

We present a detailed cross-sectional scanning-tunneling microscopy investigation of threefold stacked InAs quantum dots in a GaAs matrix grown by metal-organic chemical vapor deposition. The dots are vertically aligned and show a layer-dependent size. Detailed images with atomic resolution indicate that the dots consist of pure InAs with a shape well described by prisms with {110} and additional {111} side faces as well as a (001) top face. The wetting layer is found to be inhomogeneous, while no In diffusion into the overgrowing GaAs layer is observed. These findings demonstrate that growth in the present sample is more related to kinetics than to equilibrium conditions. Furthermore it is demonstrated that the image contrast is strongly influenced by a cleavage-induced outward relaxation of the strained quantum dots.

Atomic structure of stacked InAs quantum dots grown by metal-organic chemical vapor deposition

InAs/GaSb superlattices are leading candidates for next generation long-wave infrared and very-long-wave infrared photodetectors. These heterostructures are expected to hold important advantages over existing materials systems, primarily bulk HgCdTe alloys. To realize their inherent potential, however, superlattice materials with low defect density and improved device characteristics must be demonstrated. Here, we report on the molecular beam epitaxy growth and characterization of an 11 μm cutoff wavelength InAs/GaSb superlattice detector with a state-of-the-art single-pass, internal quantum efficiency of 36%. The shutter sequencing used to form the GaSb-on-InAs and InAs-on-GaSb superlattice heterojunctions is described in detail, and the latter specifically identified as a source of morphological defects in these devices.

Molecular beam epitaxy growth of high quantum efficiency InAs/GaSb superlattice detectors

We have used cross-sectional scanning tunneling microscopy (STM) to examine two important aspects of material and interface quality in the mixed-anion InAs/GaSb/AlSb system under growth conditions similar to those presently employed for type-II quantum well and interband cascade lasers: (1) anion cross incorporation in the bulk (specifically, unintended substitution of As for Sb within the GaSb layers); and (2) the roughness spectrum at the common-anion AlSb-on-GaSb heterojunction. Two apparently different anion defects are noted in the GaSb layers, but the demonstration of a linear correlation between the bulk defect density observed with STM and the arsenic valve setting during antimonide layer growth clearly establishes background arsenic incorporation as the common origin for both of these defects. The roughness spectrum at the AlSb-on-GaSb interface displays a surprisingly short correlation length that is dominated by heterogeneity in the cation rather than anion sublattice. The relationship of these...

Cross-sectional scanning tunneling microscopy characterization of molecular beam epitaxy grown InAs/GaSb/AlSb heterostructures for mid-infrared interband cascade lasers

M. Weimer

Papers

Cross-sectional scanning tunneling microscopy characterization of molecular beam epitaxy grown InAs/GaSb/AlSb heterostructures for mid-infrared interband cascade lasers