The lack of scalable-methods for the growth of 2D MoS crystals, an identified emerging material with applications ranging from electronics to energy storage, is a current bottleneck against its large-scale deployment. We report here a two-step ALD route with new organometallic precursors, Mo(NMe) and 1,2-ethanedithiol (HS(CH)SH) which consists in the layer-by-layer deposition of an amorphous surface Mo(iv) thiolate at 50 °C, followed by a subsequent annealing at higher temperature leading to ultra-thin MoS nanocrystals (∼20 nm-large) in the 1-2 monolayer range. In contrast to the usual high-temperature growth of 2D dichalcogenides, where nucleation is the key parameter to control both thickness and uniformity, our novel two-step ALD approach enables chemical control over these two parameters, the growth of 2D MoS crystals upon annealing being ensured by spatial confinement and facilitated by the formation of a buffer oxysulfide interlayer.

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Nanolayer stacks are technologically very relevant for current and future applications in many fields of research. A non-destructive characterization of such systems is often performed using X-ray reflectometry (XRR). For complex stacks of multiple layers, low electron density contrast materials or very thin layers without any pronounced angular minima, this requires a full modeling of the XRR data. As such modeling is using the thicknesses, the densities and the roughnesses of each layer as parameters, this approach quickly results in a large number of free parameters. In consquence, cross-correlation effects or interparameter dependencies can falsify the modeling results. Here, we present a route for validation of such modeling results which is based on the reference-free grazing incidence X-ray fluorescence (GIXRF) methodology. In conjunction with the radiometrically calibrated instrumentation of the Physikalisch-Technische Bundesanstalt the method allows for reference-free quantification of the elemental mass depositions. In addition, a modeling approach of reference-free GIXRF-XRR data is presented, which takes advantage of the quantifiable elemental mass depositions by distributing them depth dependently. This approach allows for a reduction of the free model parameters. Both the validation capabilities and the combined reference-free GIXRF-XRR modeling are demonstrated using several nanoscale layer stacks consisting of HfO 2 and Al 2 O 3 layers.

Ge-rich GeSbTe alloys allowed overcoming temperature limitations of Phase-Change Memory technology. In this paper, we present a thorough investigation of the structural evolution and crystallization process of these alloys as a function of increasing temperature of annealing. We highlight the progressive rearrangement of the structure towards the demixing of Ge and GeSbTe phases. In particular, we show the stability of Sb-Te units and the development of Ge-Te bonds around these features. We observe the formation of a transient GeSbTe phase, which is driven by crystallization phenomena, leading to a gradual diffusion and expulsion of Ge. Therefore, the system moves towards the complete separation of Ge and Ge2Sb2Te5 stable phases. Furthermore, we investigate the effect of N doping in Ge-rich GeSbTe, which induces the formation of Ge-N bonds. Such features are demonstrated to be responsible for a delayed structural reorganization to higher temperatures, thus affecting the entire process of crystallization and phase separation in the alloy.

We have quantified the impact of various process parameters on the growth of thin, pseudomorphic SiyGe1-x-ySnx layers on 2.5 µm Ge buffers (themselves on Si(001) substrates). For GeSn layers, we found that 100 Torr was appropriate for the growth of high crystalline quality layers. The impact of the HCl mass-flow on the growth kinetics of thin Ge1-xSnx layers was also evaluated. Adding HCl retained Ge in the gaseous phase, resulting at 325°C in a growth rate decrease and a Sn content increase. Moreover, the growth of Ge1-xSnx was shown to be selective against SiO2 and SiN-covered Si substrates, even without HCl. Finally, various Si2H6 flows were added to the gas mixture to grow pseudomorphic SiGeSn layers. The quality of these layers was assessed by X-ray diffraction (XRD), wavelength dispersive X-ray fluorescence (WDXRF) and atomic force microscopy (AFM).

In this contribution, we report on the growth of pseudomorphic SiGeSn layers on 2.5 μm thick Ge virtual substrates on Si(001). A single wafer reduced pressure chemical vapor deposition reactor was used for the 100 Torr epitaxy of those layers, with digermane (Ge 2 H 6 ), tintetrachloride (SnCl 4 ) and disilane (Si 2 H 6 ) as precursors. Detailed analyses regarding the growth kinetics, layer composition and surface morphology as function of the growth temperature and Si 2 H 6 flow are presented. As the temperature increases we have, for the same precursor flows, a Si content increase and a Sn content decrease. The activation energy associated with the exponential increase of the SiGeSn growth rate with the temperature, 9.5 kCal.mol −1 , is close to that of GeSn (10.6 kCal.mol −1 ). Furthermore, we show that the addition of Si 2 H 6 to the gaseous mixture results (besides the expected Si content increase) in a Sn content increase and a Ge content decrease. This study yields a better understanding of the growth of SiGeSn compound semiconductors.

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We report on the electrical, optical and photoluminescence properties of industry-ready Al doped ZnO thin films grown by physical vapor deposition, and their evolution after annealing under vacuum. Doping ZnO with Al atoms increases the carrier density but also favors the formation of Zn vacancies, thereby inducing a saturation of the conductivity mechanism at high aluminum content. The electrical and optical properties of these thin layered materials are both improved by annealing process which creates oxygen vacancies that releases charge carriers thus improving the conductivity. This study underlines the effect of the formation of extrinsic and intrinsic defects in Al doped ZnO compound during the fabrication process. The quality and the optoelectronic response of the produced films are increased (up to 1.52 and 3.73 eV) and consistent with the industrial device requirements.