Application of electron tomography for comprehensive determination of III-V interface properties

Control over epitaxy and the role of the InAs/Al interface in hybrid two-dimensional electron gas systems

“…We found that nanoscale surface roughening of the SE induced by GaAs deposition is anisotropic along the [110] and [1 10] directions, as shown in the STEM images in Fig. 4e and as investigated by STEM tomography [34] in the Supplemental Material [30]. This is likely related to highly anisotropic diffusion of Ga atoms during deposition at elevated temperatures [35] and a large mismatch between the In 0.75 Ga 0.25 As top barrier and GaAs cap [36].…”

Three-Dimensional Reconstruction of Interface Roughness and Alloy Disorder in Ge/GeSi Asymmetric Coupled Quantum Wells Using Electron Tomography

“…The specified error bars of ±6 pm for the individual values are based on statistical data noise. No significant difference can be seen between the interfaces at the direct GeSi-to-Ge transition compared to that in the reverse case (as it is known for the III–V compounds, e.g., the material system AlAs-GaAs), i.e., the interfaces are symmetric. Systematic errors in the Δ rms values could occur due to broadening of the electron beam in the needle sample.…”

“…For further quantification of the data, the measured composition profiles are simulated by sigmoidal functions, which contain as fit parameters the inflection point of the interface transition w i (ideally defining the interface position, cf. Figure (a)) and a parameter L i as a measure for the transition width for every interface i , c false( z false) = c GeSi 1 + exp true( z − w 1 L 1 true) + c Ge 1 + exp true( prefix− z − w 1 L 1 true) + prefix∑ i = 2 16 ( c GeSi 1 + exp true( prefix− z − w i L i true) − c Ge 1 + exp ( − z − w i L i ) true) The parameters c Ge and c GeSi correspond to the nominal Ge concentration of 100 and 80 atom % and were taken as fixed for the simulation for all of thin and thick wells and barriers, respectively.…”

“…For this purpose, the JEOL Multi Beam System JIB-4501 was used, which has a scanning electron microscope for observation and a focused ion beam (FIB) for milling. Continuously at a voltage of 30 kV, a cross-sectional lamella is first prepared from the sample using the standard lift-out technique, transferred to a support needle, and then successively thinned with straight cuts and additionally brought into a needle shape. , The needle geometry is adjusted so that the needle axis, which is also the tilt axis in the experiment, coincides with the [001] growth direction of the heterostructure, i.e., the interfaces are observed end-on to the electron beam. Figure (a) is a dark-field STEM image of the final prepared needle with a diameter of about 200 nm.…”

“…Herein, we report on a comprehensive electron tomography study performed to reconstruct the complete 3D structure of a stack of Ge/GeSi heterointerfaces. , To this aim, an MQW sample has been selected featuring 20 repetitions of two asymmetric Ge QWs coupled by a very thin tunneling Ge 0.8 Si 0.2 barrier. The electron tomography method is capable of quantitatively determining the interfacial parameters introduced above over a relatively large sample volume. , The 3D reconstruction is based on a series of 2D projections taken from different viewing angles with high-angle annular dark-field (HAADF) scanning transmission electron microscopy (S-TEM). We used HAADF-STEM images since their intensities are chemically sensitive and change monotonically with density, thus satisfying the so-called projection requirement for a 3D reconstruction.…”