High-sensitive MIS structures with silicon nanocrystals grown via solid-state dewetting of silicon-on-insulator for solar cell and photodetector applications

This work reports an original method for the fabrication of Metal-Isulator-Semiconductor (MIS) structures with silicon nanocrystals (Si NCs) based active layers embedded in the insulating SiO 2 oxide, for high performance solar cell and photodetector applications. The Si NCs are produced via the in situ solid-state dewetting of ultra-pure amorphous silicon-oninsulator (a-SOI) grown by solid source molecular beam epitaxy (SSMBE). The size and density of Si NCs are precisely tuned by varying the deposited thickness of silicon. The morphological characterization carried out by using atomic force microscopy (AFM) and scanning electron microscopy (SEM) shows that the Si NCs have homogeneous size with welldefined spherical shape and densities up to ~10 12 /cm 2 (inversely proportional to the square of nominal a-Si thickness). The structural investigations by high resolution transmission electron microscopy (HR-TEM) show that the ultra-small Si NCs (with mean diameter ~7 nm) are monocrystalline and free of structural defects. The electrical measurements performed by current versus voltage (I-V) and photocurrent spectroscopies on the Si-NCs based MIS structures prove the efficiency of Si NCs to enhance the electrical conduction in MIS structures and to increase (x10 times) the photocurrent (i.e. at bias voltage V =-1 V) via the photogeneration of additional electron-hole pairs in the MIS structures. These results evidence that the Si NCs obtained by the combination of MBE growth and solid-state dewetting are perfectly suitable for the development of novel high performance optoelectronic devices compatible with the CMOS technology

Shape relaxation of epitaxial mesa for finite-size strain-engineering

Silicon-Germanium (Si$_{1-x}$Ge$_x$) layers are commonly used as stressors in the gate of MOSFET devices. They are expected to introduce a beneficial stress in the drift and channel regions to enhance the electron mobility. When reducing the gate lateral size, one of the major issues is the stress relaxation which results in a significant decrease in the electron mobility. We report a new morphological evolution of a strained epitaxial SiGe nanolayer on a silicon gate (mesa) driven by strain inhomogeneity due to finite-size effects. Unlike the self-induced instability of strained films, this evolution arises here due to the elastic inhomogeneity originating from the free frontiers. We analyze the growth dynamics within the thermodynamic surface diffusion framework accounting for elasticity and capillarity, the former being solved in two dimensions thanks to the Airy formalism. The resulting dynamical equation is solved with a decomposition on eigenmodes, and reveals different developments depending upon the mesa geometric parameters. Mass transfer occurs towards the relaxed areas and creates a beading at the nanolayers free surface with either a W or V shape as a function of time and geometry. The evolution is then controlled by the proportions of the structure as well as its scale.Comment: 10 pages, 5 figure

Strain-Driven Dewetting and Interdiffusion in SiGe Thin Films on SOI for CMOS-Compatible Nanostructures

This study provides new insight into the mechanisms governing solid state dewetting (SSD) in SiGe alloys and underscores the potential of this bottom-up technique for fabricating self-organized defect-free nanostructures for CMOS-compatible photonic and nanoimprint applications. In particular, we investigate the SSD of Si1-xGex thin films grown by molecular beam epitaxy on silicon-on-insulator (SOI) substrates, focusing on and clarifying the interplay of dewetting dynamics, strain elastic relaxation, and SiGe/SOI interdiffusion. Samples were annealed at 820 degrees C, and their morphological and compositional evolution was tracked using atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and Raman spectroscopy, considering different annealing time steps. A sequential process typical of the SiGe alloy has been identified, involving void nucleation, short finger formation, and ruptures of the fingers to form nanoislands. XRD and Raman data reveal strain relaxation and significant Si-Ge interdiffusion over time, with the Ge content decreasing from 29% to 20% due to mixing with the underlying SOI layer. EDX mapping confirms a Ge concentration gradient within the islands, with higher Ge content near the top

Population Dynamics of the Critically Endangered\ud Golden Lancehead Pitviper, Bothrops insularis: Stability\ud or Decline?

Little is known about vital rates of snakes generally because of the difficulty in collecting data. Here we used a robust design\ud mark-recapture model to estimate survival, behavioral effects on capture probability, temporary emigration, abundance and\ud test the hypothesis of population decline in the golden lancehead pitviper, Bothrops insularis, an endemic and critically\ud endangered species from southeastern Brazil. We collected data at irregular intervals over ten occasions from 2002 to 2010.\ud Survival was slightly higher in the wet season than in the dry season. Temporal emigration was high, indicating the\ud importance of accounting for this parameter both in the sampling design and modeling. No behavioral effects were\ud detected on capture probability. We detected an average annual population decrease (l= 0.93, CI = 0.47–1.38) during the\ud study period, but estimates included high uncertainty, and caution in interpretation is needed. We discuss the potential\ud effects of the illegal removal of individuals and the implications of the vital rates obtained for the future persistence and\ud conservation of this endemic, endangered species

Unilateral giant renal angiomyolipoma and pulmonary lymphangioleiomyomatosis

Angiomyolipomas (AMLs) are mesenchymal neoplasms, named so because\ud of the complex tissue composition represented by variable proportions of\ud mature adipose tissue, smooth muscle cells, and dysmorphic blood vessels.\ud Although AMLs may rise in different sites of the body, they are mostly observed\ud in the kidney and liver. In the case of renal AMLs, they are described in two\ud types: isolated AMLs and AMLs associated with tuberous sclerosis (TS). While\ud most cases of AMLs are found incidentally during imaging examinations and\ud are asymptomatic, others may reach huge proportions causing symptoms.\ud Pulmonary lymphangioleiomyomatosis (LAM) is a rare benign disease\ud characterized by cystic changes in the pulmonary parenchyma and smooth\ud muscle proliferation, leading to a mixed picture of interstitial and obstructive\ud disease. AML and LAM constitute major features of tuberous sclerosis\ud complex (TSC), a multisystem autosomal dominant tumor-suppressor gene\ud complex diagnosis. The authors report the case of a young female patient\ud who presented a huge abdominal tumor, which at computed tomography (CT)\ud show a fat predominance. The tumor displaced the right kidney and remaining\ud abdominal viscera to the left. Chest CT also disclosed pulmonary lesions\ud compatible with lymphangioleiomyomatosis. Because of sudden abdominal\ud pain accompanied by a fall in the hemoglobin level, the patient underwent an\ud urgent laparotomy. The excised tumor was shown to be a giant renal AML with\ud signs of bleeding in its interior. The authors call attention to the diagnosis of\ud AML and the huge proportions that the tumor can reach, as well as for ruling\ud out the TSC diagnosis, once it may impose genetic counseling implications

Influence of Patterning on the Nucleation of Ge Islands on Si and SiO2 Surfaces

Surface patterning is expected to influence the nucleation site of deposited nanostructures. In the present study, clean Si and SiO2 surfaces were patterned by a nanolithographic process using a Focused Ion Beam (FIB). Ge was evaporated in ultra high vacuum at 873 K on these substrates, resulting in the formation of island arrays. Based on scanning tunneling microscopy and atomic force microscopy images, a statistical analysis was performed in order to highlight the effect of patterning on the size distribution of islands compared to a non-patterned surface. We find that the self-organization mechanism on patterned substrates results in a very good arrangement and positioning of Ge nanostructures, depending on growth conditions and holes distance, both on Si and SiO2 surfaces

Auto-organisation de boites quantiques de Ge sur des substrats nanostructurés

Le but de ce travail est l auto-organisation des boites quantiques (BQ) de Ge sur des substrats de Si(001) nanostructurés afin de réaliser des mémoires à nanocristaux de Ge. La croissance du Ge est effectuée par épitaxie par jets moléculaires et la nanostructuration des substrats par faisceau d ions focalisés. Nous avons développé deux procédés d auto-organisation l un sur Si l autre sur SiO2/Si qui permettent d obtenir des réseaux parfaitement ordonnés et très denses (>1011cm-2) de BQ nanométrique (15nm). Les procédés s appuient sur des mécanismes de germination préférentielle. Sur Si(001) les BQ germent dans les trous à basse température de par l inhomogénéité de la barrière de diffusion et aux bords des trous à haute température de par la relaxation de l énergie élastique. Sur SiO2/Si(001) les BQ se forment dans les trous pour minimiser l énergie de surface du système. Un procédé de fabrication des mémoires à nanocristaux a été proposé et des mémoires ont été fabriquées avec succès.AIX-MARSEILLE3-BU Sc.St Jérô (130552102) / SudocSudocFranceF