The rapid cadence of MOSFET scaling is stimulating the development of new technologies and accelerating the introduction of new semiconducting materials as silicon alternative. In this context, 2D materials with a unique layered structure have attracted tremendous interest in recent years, mainly motivated by their ultra-thin body nature and unique optoelectronic and mechanical properties. The development of scalable synthesis techniques is obviously a fundamental step towards the development of a manufacturable technology. Metal-organic chemical vapor deposition has recently been used for the synthesis of large area TMDs, however, an important milestone still needs to be achieved: the ability to precisely control the number of layers and surface uniformity at the nano-to micro-length scale to obtain an atomically flat, self-passivated surface. In this work, we explore various fundamental aspects involved in the chemical vapor deposition process and we provide important insights on the layer-dependence of epitaxial MoS ₂ film’s structural properties. Based on these observations, we propose an original method to achieve a layer-controlled epitaxy of wafer-scale TMDs.

We present in this paper the use of Gas Source Molecular Beam Epitaxy for the large-scale growth of transition metal dichalcogenides. Fiber-textured MoS₂ co-deposited thin films (down to 1 MLs) are grown on commercially 200 mm wafer size templates where MX₂ crystalline layers are achieved at temperatures ranging from RT to 550 °C. Raman Spectroscopy and photoluminescence measurements along with X-Ray Photoelectron Spectroscopy show that a low growth rate is essential for complete Mo sulfurization during MoS₂ co-deposition. Finally, cross-section Transmission Electron Microscopy investigations are discussed to highlight the influence of SiO₂ and Al₂O₃ used surfaces on MoS₂ deposition.

The effective bandgap for heterojunction band-to-band tunneling (E _g,eff ) is a crucial design parameter for a heterojunction tunneling FET (TFET). However, there is significant uncertainty on E _g,eff , especially for In _0.53 Ga _0.47 As/GaAs _0.5 Sb _0.5 . This makes the prediction of TFET performance difficult. We calibrate E _g,eff by fabricating heterojunction p+/i/n+ diodes, comparing the simulated and the measured current-voltage and capacitance-voltage curves, while taking E _g,eff as a fitting parameter. Our calibration significantly reduces the uncertainty on E _g,eff compared with the range found in the literature. The comparison with the previous work on highly doped heterojunction diodes suggests that dopant-dependent bandgap narrowing reduces E _g,eff and therefore significantly impacts the performance of highly doped TFET.

Using transmission electron microscopy we investigate the influence of AlSb monolayers and substrate surface preparation on the microstructure of GaSb grown on GaAs (001) by molecular beam epitaxy. The geometric phase analysis method is used to analyze the interface dislocation type and the residual strain, as well as the dislocation core behavior versus the thickness of the AlSb interface layer. A quantitative measurement of the local Burgers vectors shows that the misfit dislocations at the GaSb/GaAs interface are always 60° dislocations. They are arranged in pairs which are more or less distant. For the samples with the lower threading dislocation density, the average distance between the 60° pairs is smaller, the interface is flatter and the local strain is more relieved. These results show that understanding the atomic structure of interfaces may be of great help in improving the quality of GaSb grown on GaAs substrates.

Two-dimensional transition metal dichalcogenide (TMD) semiconductors have risen as an important material class for novel nanoelectronic applications. Molybdenum disulfide (MoS₂) is the most representative TMD compound due to its superior stability and attractive properties for (opto-) electronic devices. However, the synthesis of single-crystalline and functional MoS₂ across large-area substrates remains crucial for its successful integration in semiconductor industry platforms. Therefore, this work focuses on the study of MoS₂ epitaxy via two well-established industry-compatible synthesis methods, promising for the large-area and single-crystalline integration of van der Waals (vdW) materials. These methods are molecular beam epitaxy (MBE) and metalorganic vapor phase epitaxy (MOVPE) and have studied MoS₂ quasi-vdW heteroepitaxy on reconstructed sapphire substrates and MoS₂ vdW homoepitaxy on exfoliated MoS₂ flakes. By examining the MoS₂ structural properties using diffraction and spectroscopy techniques, the epitaxial relation and crystal quality are assessed, which reveals insights into the prevalence of inter- and intragrain defects such as grain boundaries and sulfur vacancies. The MBE method yields superior epitaxial MoS₂ registry on both sapphire and MoS₂ surfaces as compared to MOVPE, although inferior defectivity arises from the typical lower MBE growth temperature and chalcogen partial pressure. Moreover, both synthesis methods generate high densities of twinned MoS₂ grain boundaries, which hamper defect-free integration. As a result, this challenging integration might become an important bottleneck for industrial TMD-based applications with a low tolerance for material defects.