is, graphene, transition metal dichalcogenides (TMDs), [ 2,3 ] topological insulators, [ 4 ] h-BN [ 5 ] and h-AlN, [ 6 ] as well the recent phosphorene, [ 7 ] silicene, [ 8 ] and germanene [ 9 ] provide the ability to control the channel thickness at atomic level. This characteristic translates into improved gate control over the channel barrier and into reduced short-channel effects, thus paving the way toward ultimate miniaturization and new device concepts. Recently, 2D transition metal dichalcogenides, have proven to be promising candidates for electronics and optoelectronic applications. [10][11][12][13][14][15][16] From a pioneering perspective, the availability of TMDs with different work functions and band structures guarantees a great potential for band gap engineering of heterostructures. These systems are fundamentally different and more fl exible than traditional heterostructures composed of conventional semiconductors. In particular, due to the weak interlayer interaction, a TMD molecular layer grows from the beginning with its own lattice constant forming an interface with reduced amount of defects. The relaxed lattice matching condition permits to combine almost any layered material and create artifi cial heterojunctions with designed band alignment. 2D heterostructures

Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) are of great interest for applications in nano-electronic devices. Their incorporation requires the deposition of nm-thin and continuous high-k dielectric layers on the 2D TMDs. Atomic layer deposition (ALD) of high-k dielectric layers is well established on Si surfaces: the importance of a high nucleation density for rapid layer closure is well known and the nucleation mechanisms have been thoroughly investigated. In contrast, the nucleation of ALD on 2D TMD surfaces is less well understood and a quantitative analysis of the deposition process is lacking. Therefore, in this work, we investigate the growth of AlO (using Al(CH)/HO ALD) on MoS whereby we attempt to provide a complete insight into the use of several complementary characterization techniques, including X-ray photo-electron spectroscopy, elastic recoil detection analysis, scanning electron microscopy, and time-of-flight secondary ion mass spectrometry. To reveal the inherent reactivity of MoS, we exclude the impact of surface contamination from a transfer process by direct AlO deposition on synthetic MoS layers obtained by a high temperature sulfurization process. It is shown that AlO ALD on the MoS surface is strongly inhibited at temperatures between 125°C and 300°C, with no growth occurring on MoS crystal basal planes and selective nucleation only at line defects or grain boundaries at MoS top surface. During further deposition, the as-formed AlO nano-ribbons grow in both vertical and lateral directions. Eventually, a continuous AlO film is obtained by lateral growth over the MoS crystal basal plane, with the point of layer closure determined by the grain size at the MoS top surface and the lateral growth rate. The created AlO/MoS interface consists mainly of van der Waals interactions. The nucleation is improved by contributions of reversible adsorption on the MoS basal planes by using low deposition temperature in combination with short purge times. While this results in a more two-dimensional growth, additional H and C impurities are incorporated in the AlO layers. To conclude, our growth study reveals that the inherent reactivity of the MoS basal plane for ALD is extremely low, and this confirms the need for functionalization methods of the TMD surface to enable ALD nucleation.

In this work, we report on wet-chemical defect revealing in InP fin structures relevant for device manufacturing. Both HCl and HBr solutions were explored using bulk InP as a reference. A distinct difference in pit morphology was observed between the two acids, attributed to an anisotropy in step edge reactivity. The morphology of the etch pits in bulk InP suggests that the dislocations are oriented mainly perpendicular to the surface. By studying the influence of the acid concentration on the InP fin recess in nanoscale trenches, it was found that aqueous HCl solution was most suitable for revealing defects. Planar defects in InP fin structures grown by the aspect ratio trapping technique could be visualized as characteristic shallow grooves approximately one nanometer deep. It is challenging to reveal defects in wide-field InP fins. In these structures, dislocations also reach the surface next to stack faults or twinning planes. Due to the inclined nature, dislocation-related pits are only a few atomic layers deep. Extending the pits is limited by the high reactivity of the fin sides and the strong surface roughening during etching. The process window for revealing wet-chemical defects in InP fins is limited.