Polarity Assignment in ZnTe, GaAs, ZnO, and GaN-AlN Nanowires from Direct Dumbbell Analysis

Abstract

Aberration corrected scanning transmission electron microscopy (STEM) with high angle annular dark field (HAADF) imaging and the newly developed annular bright field (ABF) imaging are used to define a new guideline for the polarity determination of semiconductor nanowires (NWs) from binary compounds in two extreme cases: (i) when the dumbbell is formed with atoms of similar mass (GaAs) and (ii) in the case where one of the atoms is extremely light (N or O: ZnO and GaN/AlN). The theoretical fundaments of these procedures allow us to overcome the main challenge in the identification of dumbbell polarity. It resides in the separation and identification of the constituent atoms in the dumbbells. The proposed experimental via opens new routes for the fine characterization of nanostructures, e.g., in electronic and optoelectronic fields, where the polarity is crucial for the understanding of their physical properties (optical and electronic) as well as their growth mechanisms.

Surface-Guided Core–Shell ZnSe@ZnTe Nanowires as Radial p–n Heterojunctions with Photovoltaic Behavior

“…1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Further atomic-resolution aberration-corrected HAADF STEM analyses obtained on the lamellae cut along the guided nanowires growth direction on A-plane confirmed the ZB structure for both the core and the shell ( Figure S3). In addition, the crystal polarity of the nanowire could be extracted from the HAADF-STEM images 57 confirming that the NW is B-polar (Se/Te or anion polar) along the guided growth direction and A-polar (Zn or cation polar) in the vertical direction from the substrate. The B-polarity along the guided growth direction is in good agreement with the usual polarity observed in vertically grown ZnTe NWs.…”

“…The B-polarity along the guided growth direction is in good agreement with the usual polarity observed in vertically grown ZnTe NWs. 57,58 Once the crystallographic orientation and polarity of the core and shell are known, we can also gain insight into the morphology of the shell and its mechanism of formation. During our efforts to find the growth parameters for the desired morphology and thickness of the shell overgrowth, we observed some extreme cases ranging from a massively thick shell to an incomplete shell growth (figure S4a).…”

Long-lived excitons in GaN/AlN nanowire heterostructures

“…At this temperature and under N-rich growth conditions, PAMBE is known to produce N-polar catalyst-free GaN NWs with a radius in the range of a few tens of nanometers [29][30][31][32][33][34]. The structures under study consist of a nonintentionally doped (NID) GaN NW base with a length of 600 nm and a radius ranging from 25-40 nm, followed by 40 periods of GaN:Ge/AlN (nominally 4 nm/4 nm) nanodisks, and a 20-nm-thick NID GaN cap layer.…”

Transmission electron microscopy analysis of some transition metal compounds for energy storage and conversion

“…However, both ADF and HAADF STEM imaging exclude the electrons scattered by light elements [39]. Recently, the newly developed annular bright field (ABF) detector that positioned within the illumination cone of focused electron beam permits direct visualization of light elements such as oxygen and nitrogen atomic columns as well as heavy atoms at the same time [42,43].…”