Incorporation of Bi atoms in InP studied at the atomic scale by cross-sectional scanning tunneling microscopy

Abstract

We show the potential of cross-sectional scanning tunneling microscopy to address structural properties of dilute III-V bismides by investigating Bi:InP. Bismuth atoms down to the second monolayer below the {110} InP surfaces, which give rise to three classes of distinct contrast, are identified with the help of density functional theory calculations. Based on this classification, the pair-correlation function is used to quantify the ordering of Bi atoms on the long range. In a complementary short-ranged study, we investigate the Bi ordering at the atomic level. An enhanced tendency for the formation of first-nearest-neighbor Bi pairs is found. In addition, the formation of small Bi clusters is observed whose geometries appear to be related to strong first-nearest-neighbor Bi pairing. We also identify growth related crystal defects, such as In vacancies, P antisites, and Bi antisites.

Influence of sample momentum space features on scanning tunnelling microscope measurements

“…Remarkably, it was also shown that the computed STM images were in excellent agreement with the measured images only when the tip orbital consisted of a dominant d z 2 −r 2 /3 orbital, consistent with the earlier prediction for a transition metal tip [24]. This behaviour was in stark contrast to the observed STM images of impurities in direct band-gap semiconductor materials such as GaAs [13,14] and InP [25], where the images of electrons bounded to subsurface Bismuth (Bi), Nitrogen (N), and Antimony (Sb) impurities at various depths were in good agreement with theory based on only s orbital in the tip state.…”

“…Therefore, we conclude that for the GaAs:N system, the precise tip orbital composition does not play an important role, and the s orbital Tersoff-Hamann approximation provides a qualitatively accurate understanding of the measurements. This has indeed been true in several recent studies where the computed s orbital images were quite accurate to understand direct band-gap STM experiments [13,14,25].…”

Structural and electronic properties of isovalent boron atoms in GaAs

“…In addition, we have recently demonstrated that the structural modifications of the {110} surfaces by Bi atoms down to the second layer can be detected in topographic X-STM measurements. 20 In filled state X-STM images, which are taken at a high negative sample voltage, the large Bi atoms in even or odd numbered layers lead to a displacement of either one or a rectangle of four atoms out of the surface. Similar observations have been made for small N atoms, which give rise to local depressions in the surface with the same symmetry as for Bi.…”

Structural Properties of Bi Containing InP Films Explored by Cross-Sectional Scanning

“…This is essential for a deeper understanding of the mechanism behind the unusually strong influence of Bi on the band structure of its host, which goes beyond the phenomenological band anticrossing (BAC) model [6]. We have used cross-sectional scanning tunneling microscopy (X-STM), which allows the direct imaging nanostructures and impurities below the growth surface without averaging, to address these questions [7].…”