Recent Advances in Seeded and Seed-Layer-Free Atomic Layer Deposition of High-K Dielectrics on Graphene for Electronics

Graphene (Gr) with its distinctive features is the most studied two-dimensional (2D) material for the new generation of high frequency and optoelectronic devices. In this context, the Atomic Layer Deposition (ALD) of ultra-thin high-k insulators on Gr is essential for the implementation of many electronic devices. However, the lack of out-of-plane bonds in the sp2 lattice of Gr typically hinders the direct ALD growth on its surface. To date, several pre-functionalization and/or seed-layer deposition processes have been explored, to promote the ALD nucleation on Gr. The main challenge of these approaches is achieving ultra-thin insulators with nearly ideal dielectric properties (permittivity, breakdown field), while preserving the structural and electronic properties of Gr. This paper will review recent developments of ALD of high k-dielectrics, in particular Al2O3, on Gr with "in-situ" seed-layer approaches. Furthermore, recent reports on seed-layer-free ALD onto epitaxial Gr on SiC and onto Gr grown by chemical vapor deposition (CVD) on metals will be presented, discussing the role played by Gr interaction with the underlying substrates

Near-surface processing on AlGaN/GaN heterostructures: a nanoscale electrical and structural characterization

The effects of near-surface processing on the properties of AlGaN/GaN heterostructures were studied, combining conventional electrical characterization on high-electron mobility transistors (HEMTs), with advanced characterization techniques with nanometer scale resolution, i.e., transmission electron microscopy, atomic force microscopy (AFM) and conductive atomic force microscopy (C-AFM). In particular, a CHF3-based plasma process in the gate region resulted in a shift of the threshold voltage in HEMT devices towards less negative values. Two-dimensional current maps acquired by C-AFM on the sample surface allowed us to monitor the local electrical modifications induced by the plasma fluorine incorporated in the material

Advanced materials nanocharacterization

This special issue of Nanoscale Research Letters contains scientific contributions presented at the Symposium D "Multidimensional Electrical and Chemical Characterization at the Nanometer-scale of Organic and Inorganic Semiconductors" of the E-MRS Fall Meeting 2010, which was held in Warsaw, Poland from 13th to 17th September, 2010

Electrical Properties of Self-Assembled Nano-Schottky Diodes

A bottom-up methodology to fabricate a nanostructured material by Au nanoclusters on 6H-SiC surface is illustrated. Furthermore, a methodology to control its structural properties by thermal-induced self-organization of the Au nanoclusters is demonstrated. To this aim, the self-organization kinetic mechanisms of Au nanoclusters on SiC surface were experimentally studied by scanning electron microscopy, atomic force microscopy, Rutherford backscattering spectrometry and theoretically modelled by a ripening process. The fabricated nanostructured materials were used to probe, by local conductive atomic force microscopy analyses, the electrical properties of nano-Schottky contact Au nanocluster/SiC. Strong efforts were dedicated to correlate the structural and electrical characteristics: the main observation was the Schottky barrier height dependence of the nano-Schottky contact on the cluster size. Such behavior was interpreted considering the physics of few electron quantum dots merged with the concepts of ballistic transport and thermoionic emission finding a satisfying agreement between the theoretical prediction and the experimental data. The fabricated Au nanocluster/SiC nanocontact is suggested as a prototype of nano-Schottky diode integrable in complex nanoelectronic circuits

Pulmonary Hypertension

Pulmonary hypertension (PH) is a complex and multifactorial syndrome, partly unknown, characterized by a profound alteration of pulmonary vasculature and, consequentially, a rise in the pulmonary vascular load, leading to hypertrophy and remodeling of the right heart chambers. The World Health Organization assembles the several forms of PH into five clinical groups: group 1 includes pulmonary arterial hypertension, previously defined as idiopathic forms, group 2 is PH due to left-sided heart diseases, group 3 PH due to lung diseases, hypoxia, or both, group 4 due to pulmonary-artery obstruction, and group 5 PH, which includes forms with multifactorial or unclear mechanisms. In this chapter, we would like to delineate the clinical and hemodynamic definitions of PH and, for each group, we will describe the pathophysiological mechanisms, the diagnostic pathway, and the pharmacological approach and treatment. Finally, we would also like to focus on the latest trials and future therapeutic perspectives for this disease

Active dopant profiling and Ohmic contacts behavior in degenerate n-type implanted silicon carbide

This Letter reports on the active dopant profiling and Ohmic contact behavior in degenerate P-implanted silicon carbide (4H-SiC) layers. Hall measurements showed a nearly temperature-independent electron density, corresponding to an electrical activation of about 80% of the total implanted dose. Using the Hall result as calibration, the depth resolved active P-profile was extracted by scanning capacitance microscopy (SCM). Such information on the active P-profile permitted to elucidate the current injection mechanism at the interface of annealed Ni Ohmic contacts with the degenerate n-type 4H-SiC layer. Modeling the temperature dependence of the specific contact resistance with the thermionic field emission mechanism allowed extracting a doping concentration of 8.5 × 1019 cm−3 below the metal/4H-SiC interface, in excellent agreement with the value independently obtained by the SCM depth profiling. The demonstrated active dopant profiling methodology can have important implications in the 4H-SiC device technology