Characterization of the polysilicon thin film transistors elaborated in high and low temperature processes. Study of the density of traps

The states density of traps (DOS) in the gap has been determined by a study of the temperature influence on the field-effect conductance of polycrystalline silicon thin film transistors fabricated in high and low temperature technologies. The effect on the DOS value of the granular structure, film thickness (between 50 and 150 nm) and technological process has been investigated. On the one hand, for thin film transistors (TFTs) fabricated in a high temperature process, we observed that, when the film thickness is greater than 50 nm, the DOS distribution has a ‘band tailing’ with an exponential shape. The slope increases when the thickness decreases. This indicates the enhancement of the disorder due to an important density of defects localized in the grain and or in the grain boundaries. Moreover, for thin films (t_f = 50 nm), the DOS curve shows a characteristic hump which proves the presence of dangling bonds. They are localized at 0.35 eV above the top of the valence band. On the other hand, the effect of the low temperature process produces particularities on the TFT DOS. The classical doped drain (CDD) exhibits a high density of states with a classical distribution (band tailing with an exponential shape). However, the lightly doped drain (LDD) TFT DOS shows a hump localized at 0.4 eV below the bottom of the conduction band. The difference observed on the DOS distributions is related to the in situ doping level of the polysilicon-deposited thin films.     

Relaxation of InGaN thin layers observed by X-ray and transmission electron microscopy studies

Double-crystal and triple-axis x-ray diffractometry and transmission electron microscopy are used to characterize the microstructure, strain, and composition of InGaN layers grown on GaN by metalorganic chemical vapor deposition (MOCVD). Three different samples with increasing In concentration have been studied, all grown on GaN deposited on sapphire either with GaN or AlN buffer layers. It was found that InGaN layers with nominal 28% and 40% InN content consist of two sub-layers; the first sub-layer is pseudomorphic with the underlying GaN with lower In content than nominal. The top sub-layer is fully relaxed with a high density of planar defects and In content close to the nominal value. This is in contrast to a common assumption applied to InGaN quantum wells that ‘quantum-dot like areas’ are formed with different In content. The sample with the nominal indium concentration of 45% does not exhibit any intermediate strained layer, is fully relaxed and the In concentration (43.8%) agrees well with the nominal value.     

CAD model simplification using a removing details and merging faces technique for a FEM simulation

The simulation process is currently used in the design and dimensioning of mechanical parts. With the progress of computer materials, the finite elements method (FEM) becomes the most used approach in the simulation of mechanical behaviour. The simulation process needs multiple Design-FEM loops. In order to accelerate those analysis loops, an adaptation of computer aided design (CAD) model is necessary. The adaptation step consists in the simplification of the CAD model geometry by eliminating details (holes, chamfers, fillet, etc.) and faces. In this paper, a novel technique of simplification of the CAD geometry is developed. This technique is a hybrid method based on a combination of the elimination details and merging faces. The merging of faces is based on the energetic method. With this approach, the computing time is reduced by the elimination of geometric details which do not boundary conditions. An implementation of the proposed algorithm on the Open Cascade platform is also presented. The results of the developed method are compared with a previous publication. The reduction of the computing time and the amelioration of the result precision highlight the efficiency of the presented method.     

Electrical characterization of alumina layers deposited by evaporation cell on Si and restructured InP substrates

In the fast electronic area, studies on InP metal—insulator—semiconductor (MIS) devices have wide interest. Effectively, InP presents a considerable interest due to its high mobility and large bandgap for high speed MIS devices. However, the InP surface must be treated and well passivated before the deposition of insulator. We show that the InSb buffer layer can reduce the phosphorus atom migration and the defects at the interface. After the elaboration of Al₂O₃/Si, Al₂O₃/InP and Al₂O₃:InSb/InP structures, we have studied and characterized electrically the alumina—semiconductor systems. Thus, a mercury probe was used as a temporary gate contact. In the Al₂O₃:InSb/InP structure, the electrical C–V characteristics plotted at 1 MHz give, in the depletion region, a more important slope of the curves. The obtained results show clearly the reduction of the defects, dangling bonds and consequently the state density has been decreased by 50% compared to the InP protected by an InSb buffer layer and no treated surfaces. Then, the interfacial state density N_SS is evaluated as 4 × 10¹¹ eV⁻¹ cm⁻².     

First-Principle Calculations of Magnetic Properties of Hexagonal BaTi<Subscript>0.95</Subscript>TM<Subscript>0.05</Subscript>O<Subscript>3−<Emphasis Type="Italic">δ</Emphasis></Subscript>; TM = [Fe,Cr, Co]

We have studied the magnetism in the hexagonal polymorph of BaTiO₃ doped with one of the transition metals (TM = Co, Fe, Cr) and in the presence of oxygen vacancies. The formation energies for BaTi_0.95TM_0.05O_3?δ ; (TM = Co, Fe, Cr) are 8.10, 8.80, and 12.36 eV, respectively. The antiferromagnetic (AFM) phase of BaTiO₃ has changed to a ferromagnetic phase because of doping. For each case of doping, the transition metal induced a non-negligible magnetic moment in the structure BaTi_0.95TM_0.05O₃. Furthermore, the amount of oxygen defects influences directly the total magnetic moment and also the electronic conduction properties. For BaTi_0.95Co_0.05O_2.95, we have found that the system is half metallic ferromagnet and the magnetic moment is reversed with respect to oxygen vacancy free system. The half metallic character is also present in BaTi_0.95Cr_0.05O_2.95 but with no flipping of the total magnetic moment. For BaTi_0.95TM_0.05O_2.5 systems, the magnetic structure is ferromagnetic and the influence of oxygen vacancy concentration is shown in the enhancement of the ferromagnetic state.     

Self‐Assembly of Multiple Stacked Nanorings by Vertically Correlated Droplet Epitaxy

Fabrication of advanced artificial nanomaterials is a long‐term pursuit to fulfill the promises of nanomaterials. In the last ten years, Droplet Epitaxy has been emerging as a versatile fabrication method for various complex nanomaterials, but there is a lack of growth protocol to control the growth vertically. Here we report a vertically correlated Droplet Epitaxy growth method. We find that the nanodroplets form preferable on the preexisting nanorings, which enables fabrication of vertically aligned nanostructures by Droplet Epitaxy. Nucleation thermodynamics and growth kinetics have been proposed to explain the vertically correlated Droplet Epitaxy. Heterojunctions can be realized at nanoscale by the presented method. In addition, the nucleation thermodynamics of nanodroplets observed in this article will allow site‐controlled fabrication of nanostructures.     

Multi-fidelity POD surrogate-assisted optimization: Concept and aero-design study

We combine multiple sets of variable-precision full-field simulations within a single surrogate model. The approach is based on an original formulation of the “Constrained Proper Orthogonal Decomposition” (C-POD), interpolating precise, albeit costly, high-fidelity data and approximating abondant, yet less accurate, lower-fidelity data. We compute the optimal high-dimensional subspace spanning the sparse high-fidelity full-field solutions and refine the output subspace definition thanks to the orthogonal information contained in abondant low-fidelity full-field solutions. We then build “hierarchised” multi-fidelity surrogate models based on the previously refined subspace and giving a fast estimation of the high-fidelity full-field solution of any new location in the design space. The proposed model is illustrated by exploring the prediction of an analytical 2D functional space on the one hand, and demonstrated by studying the efficiency of a 1.5-stage low-pressure compressor on the other.     

Vacuum Drying of Common Date Pulp Cubes

Drying ability of date (Phoenix dactylifera L.) pulp cubes from three Algerian common varieties (Mech-Degla, Degla-Beida, and Frezza) were investigated. Drying process was carried out under partial vacuum (200 mbar) at 60, 80, and 100°C. Compared to the Newton model, the Henderson and Pabis model better described drying kinetic of Mech-Degla and Frezza pulps at 60 and 80°C with a mean relative error (MRE) not higher than 6.07%. The same model fits experimental data at 60°C for Degla-Beida (R² = 0.988; MRE = 6.07) as well as at 100°C for only Mech-Degla (R² > 0.98, MRE = 8.61%).