Visualizing interfacial structure at non-common-atom heterojunctions with cross-sectional scanning tunneling microscopy

Atomic-scale mapper for superlattice photodetectors analysis

In this work, a new Python-based tool for atomic-scale mapping of high-angle annular dark-field (HAADF) and annular bright-field (ABF) scanning transmission electron microscopy (STEM) images using the Z-contrast method is introduced, aimed to help in the analysis of superlattice layers' composition, and in the determination of material of interfaces. The operation principle of the program, as well as specific examples of use, are explained in many details. Good customization flexibility using the user-friendly graphical user interface (GUI), allows the processing of a wide range of images, demonstrating a decent accuracy of coordinates extraction and performance.

Multi-heterojunction InAs/GaSb nano-ridges directly grown on (001) Si

We report on multi-stacked InAs/GaSb nano-ridges directly grown on (001) patterned Si substrates by metal-organic chemical vapor deposition (MOCVD). Uniform GaSb and InAs nano-ridges were demonstrated with optimized growth parameters. By adjusting the switching sequences, we also obtained defect-free InAs/GaSb and GaSb/InAs interfaces. Based on these fine-tuned growth conditions, multi-stacked InAs/GaSb nano-ridges were developed and characterized. The nano-ridges showed uniform morphology from scanning electron microscopy (SEM), and no observable crystalline defects were detected at the hetero-interfaces by transmission electron microscopy (TEM). These InAs/GaSb nano-ridges show great potential for applications in nano-scale tunneling devices and long wavelength light emitters and detectors. The demonstrated growth techniques provide helpful insights for the growth process control of 6.1 Å family compound semiconductors directly on Si by MOCVD.

Atomic scale interface engineering for strain compensated epitaxially grown InAs/AlSb superlattices

This paper presents a systematic investigation of strain compensation schemes for InAs/AlSb superlattices (SLs) on GaSb substrates. Short growth interruptions (soak times) under varying arsenic and/or antimony beam equivalent pressures in InAs/AlSb SLs with exemplary dimensions of about ((2.4/2.4) ± 0.2) nm were investigated to achieve strain compensation. When using uncracked As(4), strain compensation was found to be unaccomplishable unless sub-monolayer AlAs spikes were inserted at the InAs → AlSb interface. In contrast, the supply of cracked As(2) dimers leads directly to the formation of strain compensating AlAs-like interfaces. This mechanism allows various growth sequences for strain compensated superlattices, including soak-time-free and Sb-soak-only SL growth. Each of the two latter approaches yields layers with excellent crystal quality and minimal intermixing at the heterointerfaces as verified by high resolution x-ray diffraction analysis and transmission electron microscopy.

Origin of antimony segregation in GaInSb/InAs strained-layer superlattices

We show how cross-sectional scanning tunneling microscopy may be used to reconstruct the Sb segregation profiles in GaInSb /InAs strained-layer superlattices. These profiles are accurately described by a one-dimensional model parametrizing the spatial evolution of an Sb seed at the InAs-on-GaInSb interface in terms of two-anion-layer exchange. We argue that the segregation seed, which decreases from 2 / 3 to 1 / 2 monolayer when growth conditions are made less anion rich, has its origin in the Sb-bilayer reconstruction maintained during GaInSb epitaxy.