Contrast of small SiX particles in silicon by computed HREM images

Abstract

The contrast in HREM images of small spherical coherent precipitates in silicon, having a hypothetical sphalerite structure and an S i x composition, is computed by the multislice method; X represents a dopant (or impurity) atom, ranging from boron u p t o platinum. The particles are assumed to have a diameter of 2 nm and t o exert different amounts of in situ strain E on the silicon matrix. The ideal case of no misfit ( E = 0) is also considered. For in situ strains 0 < 6 < 2y0, the maximum contrast, corresponding to the optimum defocus, depends mainly on the atomic number of the element X. For larger strains, which can occur in some cases if the Si-X bond length in the Six particle is determined by the covalent radius of the impurity atom X, the strain contrast dominates over the structure factor contrast.Der Kontrast in hochauflosenden, elektronenmikroskopischen Abbildungen kleiner, kugelformiger, koharenter Ausscheidungen in Silizium, die eine hypothetische Sphaleritstruktur und die Zusammensetzung S i x haben, wird mittels der Vielschichtmethode berechnet; X stellt hier ein Dotierungs-bzw. Verunreinigungsatom von Bor bis Platin dar. Es wird angenommen, daS die Ausscheidungen einen Durchmesser von 2 nm haben und verschiedene in-situ-Dehnunsen E auf die Siliziummatrix ausiiben. Der Idealfall, wo keine Fehlanpassung ( E = 0) vorhanden ist, wird auch betrachtet. Fur 0 < E < 2y0 ist der maximale Kontrast, der der optimalen Defokussierung entspricht, hauptsiichlich yon der Atomzahl des X-Elementes abhangig. F u r groCere Dehnungen, die in einigen Fallen vorkommen konnen, wenn die Si-X-Bindungslange im Six-Teilchen vom kovalenten Radius des X-Verunreinigungsatoms bestimmt wird, iiberwiegt der Dehnungekontrast den Strukturfaktorkontrast.

High‐Temperature Equilibrium Carrier Density of Arsenic‐Doped Silicon

“…A negligible configurational entropy, as it is usually assumed for the intermediate compounds, seems justified also in our case. A high degree of order of these precipitated is in fact keeping with the results of lattice imaging simulations of their high-resolution micrographs (7) as well as with extended x-ray absorption fine structure (EXAFS) determinations (15). By combining the above relations the saturated atomic fraction of arsenic results…”

“…It is known that under usual experimental conditions the precipitation of monoclinic SiAs, the conjugate equilibrium phase, is not observed. TEM experiments, both in weak beam and highresolution imaging of annealed slices implanted with excess As, showed high density of particles 1.5-2.0 nm diam, coherent with the silicon lattice (5)(6)(7)(8). A sphalerite structure with Si and As on alternate lattice sites is proposed for this metastable phase.…”

Electrical activity and structural evolution correlations in laser and thermally annealed As-implanted Si specimens

“…43 (2) Clusters and precipitates coexist in equilibrium with the active As fraction. In this case at least a part of the observed discrepancy between precipitated and inactive As fractions can be explained by the limited visibility of the very small precipitates in HREM observations.…”