Atomic-Resolution EDX, HAADF, and EELS Study of GaAs1-xBix Alloys

Abstract

The distribution of alloyed atoms in semiconductors often deviates from a random distribution which can have significant effects on the properties of the materials. In this study, scanning transmission electron microscopy techniques are employed to analyze the distribution of Bi in several distinctly MBE grown GaAs 1−x Bi x alloys. Statistical quantification of atomic-resolution HAADF images, as well as numerical simulations, are employed to interpret the contrast from Bi-containing columns at atomically abrupt (001) GaAs-GaAsBi interface and the onset of CuPt-type ordering. Using monochromated EELS mapping, bulk plasmon energy red-shifts are examined in a sample exhibiting phase-separated domains. This suggests a simple method to investigate local GaAsBi unit-cell volume expansions and to complement standard X-ray-based lattice-strain measurements. Also, a single-variant CuPt-ordered GaAsBi sample grown on an offcut substrate is characterized with atomic scale compositional EDX mappings, and the order parameter is estimated. Finally, a GaAsBi alloy with a vertical Bi composition modulation is synthesized using a low substrate rotation rate. Atomically, resolved EDX and HAADF imaging shows that the usual CuPt-type ordering is further modulated along the [001] growth axis with a period of three lattice constants. These distinct GaAsBi samples exemplify the variety of Bi distributions that can be achieved in this alloy, shedding light on the incorporation mechanisms of Bi atoms and ways to further develop Bi-containing III-V semiconductors.

Polarization dependent photoluminescence and optical anisotropy in CuPtB-ordered dilute GaAs1–xBix alloys

“…Our previous atomically-resolved STEM-EDX ordering parameter evaluation yielded a η = 0.07 value for a sample with 5.5 % Bi. 13,14 Although the ordering parameters for the present S1-S6 samples were not examined by EDX, one can expect them to be of the order of η ~ 0.1. Next, sample S6 is examined, which together with S1-S5, was used in the optical anisotropy analysis.…”

“…This typically leads to larger ordered domains, and a single subvariant ordering has also been confirmed in GaAsBi. 13,14 The ordering is never perfect and is quantified by the ordering parameter η. A partially ordered alloy AB1−xCx can be described as AB1−(x−η/2)Cx−η/2 and AB1−(x+η/2)Cx+η/2 monolayers on (1 ̅ 11) or (11 ̅ 1) planes, with a maximal value of ordering parameter ηmax= min[2x, 2(1−x)].…”

“…Previous studies of the atomic ordering of bismides focused primarily on their atomic and microstructure analysis. [13][14][15][16][17] The present article examines the influence of the ordering on GaAsBi optoelectronic properties. This is the first study that reports the optical anisotropy in GaAsBi alloys.…”

Techniques for the characterization of single atom catalysts

“…Besides, the superficial area and the focused shape of electronic beam must be contemplated, which also affects the detection resolution. 65 In addition to these factors, higher peak to background ratio indicated that SACs could be identified by EDX.…”

Atomic-scale 3D imaging of individual dopant atoms in an oxide semiconductor

“…Despite their high sensitivity, these measurements cannot be applied to probe small volumes, let alone the lattice position of individual dopants and their interactions at the local scale, as they lack the necessary spatial resolution. To image single dopant atoms within the lattice and quantify their concentration, scanning transmission electron microscopy (STEM) has been applied in combination with energy-dispersive X-ray spectroscopy (EDX) 13,14 . This correlated approach represents a breakthrough in the atomic-scale characterization of doped oxides, but it is limited to doping levels higher than a few at.%.…”