1,721,077 research outputs found
2D scaling behavior of nanotextured GaN surfaces: A case study of hillocked and terraced surfaces
No full textThe 2D scaling properties of GaN surfaces have been studied by means of the 2D height–height correlation function (HHCF). The GaN layers under investigation presented exemplar morphologies, generated by distinct growth methods: a molecular beam epitaxy (MBE) grown surface decorated by hillocks and a metal organic vapor phase epitaxy (MOVPE) grown surface with terraced structure. The 2D statistical analysis of these surfaces has allowed assessing quantitatively the degree of morphological variability along all the different directions across each surface, their corresponding roughness exponents and correlation lengths. A scaling anisotropy as well as correlation length anisotropy has been detected for both hillocked and terraced surfaces. Especially, a marked dependence of correlation length from the direction across the terraced surface has been observed. Additionally, the terraced surfaces showed the lower root mean square (RMS) roughness value and at the same time, the lower roughness exponent value. This could appear as a contradiction, given that a low RMS value is associated to a smooth surface, and usually the roughness exponent is interpreted as a “measure” of the smoothness of the surface, the smoother the surface, the higher (approaching the unity) is the roughness exponent. Our case study is an experimental demonstration in which the roughness exponent should be, more appropriately, interpreted as a quantification of how the roughness changes with length scale
Nanostructured surfaces investigated by quantitative morphological studies
No full textThe morphology of different surfaces has been investigated by atomic force microscopy and quantitatively analyzed in this paper. Two different tools have been employed to this scope: The analysis of the height-height correlation function and the determination of the mean grain size, which have been combined to obtain a complete characterization of the surfaces. Different materials have been analyzed: SiOxNy, InGaN/GaN quantum wells and Si nanowires, grown with different techniques. Notwithstanding the presence of grain-like structures on all the samples analyzed, they present very diverse surface design, underlying that this procedure can be of general use. Our results show that the quantitative analysis of nanostructured surfaces allows us to obtain interesting information, such as grain clustering, from the comparison of the lateral correlation length and the grain size
TCAD low-field mobility model for InGaAs UTB MOSFETs including quasi-ballistic corrections
No full textA new approach for including quasi-ballistic effects into TCAD drift diffusion simulations of short-channel III-V MOSFETs at low longitudinal fields is presented. The model is based on the concept of ballistic mobility through a modified Matthiessen rule. It has been applied to double-gate thin-body InGaAs MOSFETs and benchmarked against multi-subband Monte Carlo simulations. Our results indicate that the model provides I-V characteristics in good agreement with Monte Carlo for channel lengths as short as 15 nm
Cold field electron emission of large-area arrays of SiC nanowires: photo-enhancement and saturation effects
No full textThis paper explores the cold field emission (CFE) properties of SiC nanowire (NW) arrays. The CFE currents were studied in the dark and under ultra-violet (UV) irradiation conditions. An increase in CFE current was observed when the SiC NW arrays were illuminated, with a consequent decrease in the values of the turn-on field and the threshold field. Furthermore, while dark CFE currents were well described by the standard Fowler-Nordheim (FN) theory for metals, the photo-enhanced CFE currents showed nonlinearity in FN plots. Specifically, a voltage range of current saturation appeared, which is appealing for nanotechnological applications, and it is indeed an essential prerequisite for realizing devices such as FE photocathodes
Processing-Induced Electrically Active Defects in Black Silicon Nanowire Devices
No full textSilicon
nanowires (Si NWs) are widely investigated nowadays for
implementation in advanced energy conversion and storage devices,
as well as many other possible applications. Black silicon (BSi)-NWs
are dry etched NWs that merge the advantages related to low-dimensionality
with the special industrial appeal connected to deep reactive ion
etching (RIE). In fact, RIE is a well established technique in microelectronics
manufacturing. However, RIE processing could affect the electrical
properties of BSi-NWs by introducing deep states into their forbidden
gap. This work applies deep level transient spectroscopy (DLTS) to
identify electrically active deep levels and the associated defects
in dry etched Si NW arrays. Besides, the successful fitting of DLTS
spectra of BSi-NWs-based Schottky barrier diodes is an experimental
confirmation that the same theoretical framework of dynamic electronic
behavior of deep levels applies in bulk as well as in low dimensional
structures like NWs, when quantum confinement conditions do not occur.
This has been validated for deep levels associated with simple pointlike
defects as well as for deep levels associated with defects with richer
structures, whose dynamic electronic behavior implies a more complex
picture
TCAD Mobility Model of III-V Short-Channel Double-Gate FETs Including Ballistic Corrections
No full textA TCAD-oriented mobility model, whose main features are: 1) inclusion of ballistic effects in the linear region and 2) smooth transition between the linear and saturation regions, is presented. It is applied to short-channel double-gate thin-body InGaAs MOSFETs. The bases of the model are the concept of ballistic mobility and Matthiessen's rule in the linear regime, and the saturation velocity within a modified Canali model at high-longitudinal fields. Comparisons with accurate semiclassical multivalley multisubband Monte Carlo transport simulations indicate that TCAD simulations making use of the proposed model are able to correctly predict the terminal currents and the internal device quantities in the linear regime in a 15-nm device with no need of fitting parameters. In the saturation region, an empirical adjustment of the saturation velocity is needed, after which currents are accurately predicted for a wide range of gate lengths and bias conditions
Quantification of roughness and spatial distribution of dislocations in MBE and MOVPE grown LED heterostructures
No full textA combination of nanoscale imaging techniques such as atomic force microscopy and scanning electron microscopy are used to investigate the relationship between surface morphology and height statistics of GaN cap layers in InGaN/GaN light emitting diode heterostructures. The investigated samples were grown in two very different growth regimes which lead to distinct characteristic superficial landscapes. We also report here on the introduction of a new methodological approach that adapt the concept of height-height correlation function, a well known statistical tool in the field of studies on rough surfaces. We evaluate to which extent the geometrical properties of the constitutive 'bricks' (hillocks for ammonia assisted molecular beam epitaxial film) and structural defects (dislocation pits for metal organic vapor phase epitaxial film) affects the statistical properties of heights of these GaN surfaces. Finally, we have studied the spatial distribution of dislocation pits in both the samples to assess the quantitative differences between these heterostructures of very distinct surface morphology. (C) 2016 Elsevier Ltd. All rights reserved.LASP
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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