Influence of spatial and temporal coherences on atomic resolution high angle annular dark field imaging

Volz

2019

Adv Materials Inter

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The combination of III/V semiconductors with Si is very attractive, since it allows the fabrication of high efficient optoelectronic devices like solar cells, lasers or the integration of III/V transistors on Si substrates. However, the growth of polar III/V materials on nonpolar Si holds several challenges. The different valences of group III and group V atoms as well as Si possibly give rise to the formation of charged defects, i.e., antiphase boundaries, as well as to charge accumulation at the interface between the different materials. Accordingly, the interfaces present, i.e., the ones between antiphase and main phase and the one between III/V and Si, eventually limit any device's performance. Electron microscopy, in particular transmission electron microscopy, has proven to be a valuable tool to acquire quantitative information from III/V–Si heterostructures. Among this information are defect densities as well as the structure of the involved interfaces at spatial resolutions down to the atomic level. Moreover, information on charge distribution can be retrieved. In this review, the authors collocate the results gained for the model system GaP on Si utilizing various electron microscopy related techniques.

Section: Structure and Formation Of The Gap–si Interfacementioning

confidence: 96%

Section: Introductionmentioning

confidence: 98%

Advanced Electron Microscopy for III/V on Silicon Integration

Volz

2019

Adv Materials Inter

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“…8a is the central unit cell of the image, whereas for the lower right part the ∼ 50 individual unit cells present in the whole image are averaged to achieve a higher signalto-noise ratio according to Ref. 30 . Figure 8b,c depict the images derived from the simulations neglecting and taking into account plasmon excitation, respectively.…”

Section: Angular Dependencies Of Elastic and Inelastic Scatteringmentioning

confidence: 99%

“…However, potential factors other than inelastic scattering, which may contribute to the low-angle intensities, should be mentioned here as well, e.g. if phonons in the simulations are described by a correlated or uncorrelated movement 18,20,25 , the correct choice of atomic scattering potentials 13,[26][27][28] or the presence of amorphous layers from sample preparation [29][30][31] .…”

mentioning

confidence: 99%

Influence of plasmon excitations on atomic-resolution quantitative 4D scanning transmission electron microscopy

Krause

Robert

et al. 2020

Sci Rep

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Scanning transmission electron microscopy (STEM) allows to gain quantitative information on the atomic-scale structure and composition of materials, satisfying one of todays major needs in the development of novel nanoscale devices. The aim of this study is to quantify the impact of inelastic, i.e. plasmon excitations (PE), on the angular dependence of STEM intensities and answer the question whether these excitations are responsible for a drastic mismatch between experiments and contemporary image simulations observed at scattering angles below $$\sim $$ ∼ 40 mrad. For the two materials silicon and platinum, the angular dependencies of elastic and inelastic scattering are investigated. We utilize energy filtering in two complementary microscopes, which are representative for the systems used for quantitative STEM, to form position-averaged diffraction patterns as well as atomically resolved 4D STEM data sets for different energy ranges. The resulting five-dimensional data are used to elucidate the distinct features in real and momentum space for different energy losses. We find different angular distributions for the elastic and inelastic scattering, resulting in an increased low-angle intensity ($$\sim $$ ∼ 10–40 mrad). The ratio of inelastic/elastic scattering increases with rising sample thickness, while the general shape of the angular dependency is maintained. Moreover, the ratio increases with the distance to an atomic column in the low-angle regime. Since PE are usually neglected in image simulations, consequently the experimental intensity is underestimated at these angles, which especially affects bright field or low-angle annular dark field imaging. The high-angle regime, however, is unaffected. In addition, we find negligible impact of inelastic scattering on first-moment imaging in momentum-resolved STEM, which is important for STEM techniques to measure internal electric fields in functional nanostructures. To resolve the discrepancies between experiment and simulation, we present an adopted simulation scheme including PE. This study highlights the necessity to take into account PE to achieve quantitative agreement between simulation and experiment. Besides solving the fundamental question of missing physics in established simulations, this finally allows for the quantitative evaluation of low-angle scattering, which contains valuable information about the material investigated.

“…The simulated images were convoluted by a Lorentzian source distribution with a width of 45 pm. Performing this simulation procedure, a nearly perfect agreement between simulation and experiment could be achieved for GaP (Beyer et al ., ). Theoretical PACBED patterns were derived by averaging 400 simulated CBED patterns from one unit cell of the respective super cell.…”

Section: Introductionmentioning

confidence: 97%

Surface relaxation of strained Ga(P,As)/GaP heterostructures investigated by HAADF STEM

Duschek

Belz

et al. 2017

Journal of Microscopy

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SummaryThe surfaces of thin transmission electron microscopy (TEM) specimens of strained heterostructures can relax. The resulting bending of the lattice planes significantly influences high-angle annular dark field (HAADF) measurements. We investigate the impact by evaluating the intensities measured at the atomic columns as well as their positions in high-resolution HAADF images. In addition, the consequences in the diffraction plane will be addressed by simulated position averaged convergent beam electron diffraction (PACBED) patterns. The experimental column intensities and positions acquired from a strained Ga(P,As) quantum well (QW) embedded in a in a GaP matrix agree very well with frozen phonon contrast simulations, if the surface relaxation is taken into account by finite element relaxation. Neglecting the surface relaxation the As content of the QW can be significantly underestimated. Taking the effects into account correctly, we find that the lower interface of the investigated Ga(P,As) QW is atomically abrupt whereas the upper one is smeared out.