Rami Khazaka

Silicon growth on 3C-SiC(001)/Si(001): pressure influence and thermal effect

We evaluate the influence of the growth parameters on the crystal quality of Si films grown by chemical vapor deposition on 3C-SiC(001)/Si (001) epilayers. It is shown that the pressure plays a major role on the final quality of the films, with two distinct growth regimes. The defects in the films were found to be antiphase boundaries and μ-twins. The influence of the growth parameters as well as the 3CSiC structural properties on these defects are discussed. The impact of a subsequent thermal annealing, under different gas environments, is also investigated and reveals some noticeable differences according to the gas environment used in the annealing process.

Realization of minimum number of rotational domains in heteroepitaxied Si(110) on 3C-SiC(001)

Structural and morphological characterization of a Si(110) film heteroepitaxied on 3C-SiC(001)/Si(001) on-axis template by chemical vapor deposition has been performed. An antiphase domain (APD) free 3C-SiC layer was used showing a roughness limited to 1 nm. This leads to a smooth Si film with a roughness of only 3 nm for a film thickness of 400 nm. The number of rotation domains in the Si(110) epilayer was found to be two on this APD-free 3C-SiC surface. This is attributed to the in-plane azimuthal misalignment of the mirror planes between the two involved materials. We prove that fundamentally no further reduction of the number of domains can be expected for the given substrate. We suggest the necessity to use off-axis substrates to eventually favor a single domain growth.

Turning the undesired voids in silicon into a tool: In-situ fabrication of free-standing 3C-SiC membranes

In this contribution, we present a method to form free-standing cubic silicon carbide (3C-SiC) membranes in-situ during the growth stage. To do so, we exploit the presence of voids in the silicon (Si) epilayer underneath the 3C-SiC membrane, in stark contrast to the conventional view of voids as defects. The shape and the size of the 3C-SiC membranes can be controlled by a preceding patterning step of the Si epilayer. Afterwards, by controlling the expansion of voids in Si, the structured sacrificial layer is consumed during the 3C-SiC growth step. Consequently, the membranes are grown and released simultaneously in a single step process. This straightforward technique is expected to markedly simplify the fabrication process of membranes by reducing the fabrication duration and cost. Furthermore, it helps to overcome several technical issues and presents the cornerstone for micro and nano-electromechanical systems applications, profiting from the outstanding properties of cubic silicon carbide.

Novel 3C-SiC Microstructure for MEMS Applications

The aim of this paper is to review the recent developments conducted for the achievement of 3C-SiC‑based heterostructures compatible with MEMS applications. Indeed, the research activities engaged since years permitted to demonstrate that the defect density has an impact towards the Young’s modulus of sub-micron 3C‑SiC epilayers. We also gained knowledge about the stress relaxation mechanisms, targeting to master the stress gradient, as stress is a key parameter to consider MEMS applications.Based on these results, we investigated the elaboration of microstructures using 3C‑SiC/Si/3C‑SiC stacks on silicon substrates. Our first noticeable result was the elaboration of a (110)-oriented 3C‑SiC membrane on a 3C‑SiC pseudo-substrate, using the silicon epilayer as a sacrificial one. But the surface of the 3C‑SiC membrane was facetted and rough, which could hamper its use for the development of new MEMS devices. Then, with further improvements, we succeeded to master the growth of a (111)‑oriented 3C‑SiC epilayer. This feature led to a drastic reduction of the roughness in comparison with the (110) orientation. Actually, using the same experimental protocol than previously, we succeeded to complete a (111)‑oriented 3C‑SiC membrane with a RMS roughness limited to 9nm. Such an optimized structure could be the starting point for the achievement of new MEMS devices operating in harsh environment or for medical applications benefiting of the 3C‑SiC biocompatibility

Structural Study of the Innovative 3C-SiC/Si/3C-SiC/Si Heterostructure for Electro-Mechanical Applications

In this work, we report the growth of a 3C-SiC layer oriented along the [111] direction on Si (110)/3C-SiC(001)/Si (001) heterostructure. The growth of the complete layer stack occurs in one deposition run in a Chemical Vapor Deposition (CVD) reactor on on-axis Si (001) substrate. The structural properties of the 3CSiC(111) layer are discussed and the impact of the first 3C-SiC layer on the subsequent growth is highlighted. The 3C-SiC(111) top layer shows two domains rotated by 90o around the growth direction directly linked to the domains rotation in the Si epilayer underneath it. Furthermore, μtwins and stacking faults are present on the inclined (111) planes in the 3C-SiC epilayer.

On the interplay between Si(110) epilayer atomic roughness and subsequent 3C-SiC growth direction

In this contribution, we performed the growth of a 3C-SiC/Si/3C-SiC layer stack on a Si(001) substrate by means of chemical vapor deposition. We show that, by tuning the growth conditions, the 3C-SiC epilayer can be grown along either the [111] direction or the [110] direction. The key parameter for the growth of the desired 3C-SiC orientation on the Si(110)/3C-SiC(001)/Si(001) heterostructure is highlighted and is linked to the Si epilayer surface morphology. The epitaxial relation between the layers has been identified using X-ray diffraction and transmission electron microscopy (TEM). We showed that, regardless of the top 3C-SiC epilayer orientation, domains rotated by 90° around the growth direction are present in the epilayer. Furthermore, the difference between the two 3C-SiC orientations was investigated by means of high magnification TEM. The results indicate that the faceted Si(110) epilayer surface morphology results in a (110)-oriented 3C-SiC epilayer, whereas a flat hetero-interface has been o...

Local lateral integration of 16-nm thick Ge nanowires on silicon on insulator substrates

In this contribution, we report on the growth of horizontal Ge nanowires inside extremely thin tunnels surrounded by oxide. This is achieved through selective lateral growth of Ge on silicon-on-insulator (001) substrates. The 16 nm high tunnels are formed by HCl vapor etching of Si followed by Ge growth in the same epitaxy chamber. First, the benefit of growing the Ge nanowires at high temperature was highlighted to homogenize the length of the nanowires and achieve a high growth rate. Afterwards, we showed that increasing the tunnel depth led to a significant reduction in the growth rate. Finally, transmission electron microscopy showed that no defects were present in the Ge nanowires. These results are encouraging for the planar co-integration of heterogeneous materials on Si.In this contribution, we report on the growth of horizontal Ge nanowires inside extremely thin tunnels surrounded by oxide. This is achieved through selective lateral growth of Ge on silicon-on-insulator (001) substrates. The 16 nm high tunnels are formed by HCl vapor etching of Si followed by Ge growth in the same epitaxy chamber. First, the benefit of growing the Ge nanowires at high temperature was highlighted to homogenize the length of the nanowires and achieve a high growth rate. Afterwards, we showed that increasing the tunnel depth led to a significant reduction in the growth rate. Finally, transmission electron microscopy showed that no defects were present in the Ge nanowires. These results are encouraging for the planar co-integration of heterogeneous materials on Si.

Structural Investigation of Si Quantum Dots Grown by CVD on AlN/Si(111) and 3C-SiC/Si(100) Epilayers

Structural investigations of Si quantum dots (QDs) grown by CVD on two different heterostructures: AlN/Si (111) and 3C-SiC/Si (100) are conducted. The Si QDs have been grown using silane as precursor, diluted in hydrogen, at fixed temperature and pressure (830°C - 800mbar). High densities of dots can be obtained (up to 1011 cm-2) with typical heights below 10nm. The kinetic of deposition lets suppose the presence of an initial wetting layer before the dots formation. Different durations are required for nucleating dots on AlN and 3C-SiC. Si QDs on AlN present a luminescence band which can be attributed to quantum confinement.