Papers by Keyword: Spontaneous Polarization

Abstract: 3C-SiC with a moderate band gap and a large electron affinity is expected to have superior long-term stability against performance degradation. We have fabricated Al-gate MOS diodes in 3C-on-4H-SiC and 4H-SiC regions on a simultaneous lateral epitaxy (SLE) wafer. Here, evaluation results of their high-frequency differential capacitance-voltage (C-V) characteristics are reported and, from suggested band diagrams, carrier transport involved in the phenomena are considered. In the case of n^--type 3C-on-4H-SiC MOS diode, increase in capacitance due to fast modulation in the inversion layer charge (hole) concentration can be confirmed in the negative bias below-5 V. 2-dimensional hole gas (2DHG) is considered at the Si-face 3C/4H heterointerface negatively charged by spontaneous polarization and is expected to be an effective supply source of holes. Especially in the case of p-type 3C-on-4H-SiC MOS diode, it is considered that injection of holes from neutral p-type region into the heterointerface induces compensation of the fixed charges and lowering of the electron barrier at conduction band, and then, electron injection through the barrier causes the fast response of inversion-layer modulation. Appearance of the larger frequency dependence can be understood by inclusion of the larger-activation-energy phenomena, such as “a deep acceptor level” and “2DHG confined by fixed charges”. These findings are believed to contribute to building new production platforms of high-performance power semiconductor devices utilizing the polytype heterostructure of SiC.

Abstract: The bonds structure, atomic coordination situation and local cluster structure in SrBi₂Ta₂O₉ were analyzed by means of the Atomic Environment Calculation (AEC), and then the SrBi₂Ta₂O₉ crystal was decomposed into 20 pseudo-binary crystals with the crystal decomposition method. The chemical bonds properties, such as effective valence electron density and iconicity of the individual bond were calculated by the dielectric chemical bonds theory. And the correlation between chemical bonds properties and spontaneous polarization of the bismuth layered ferroelectrics was established. Finally, the spontaneous polarization in ferroelectric SrBi₂Ta₂O₉ and other relevant ferroelectrics were calculated, which are in good agreement with the experimental values and other theoretical calculated values.

Abstract: Ferroelectric niobates with tetragonal tungsten bronze TTB-type structure have shown great technology interest for application in pyroelectric detectors and piezoelectric transducers, sensor/filter in composite. The synthesis and structural characterization of the solid solution of iron doped potassium strontium niobate with stoichiometry KSr₂(Fe_0.25Nb_4.75)O_15-δ prepared by modified polyol method were carried out. The highest crystallinity was obtained for the precursor powder calcined at 1150oC for 10 hours in oxygen atmosphere. The structural characterization was performed by X-Ray diffraction. The average crystallite size obtained was equal to 25 nm. The structural parameters were determined by Rietveld method giving a tetragonal system with space group P4bm. The spontaneous polarization of the solid solution was calculated, being equal to 39.46 μC.cm^-2. Polihedra distortion and its correlation with niobium off-center are discussed.

Abstract: In this paper, we propose a physics-based analytical model of novel InAlN/GaN High Electron Mobility Transistor (HEMT) by considering the quasi-triangular quantum well with minimal empirical parameters. The derived model is compared for different short and long gate length devices. The results are calibrated and verified with experimental data over a full range for gate and drain applied voltages. Significant improvement in n_s, drain Current, and transconductance are observed for InAlN HEMT making it suitable for nanoscale and microwave analysis in circuit design. Therefore, the proposed model can deal directly with device/physical parameters, and it can be expressed by a very small number of model parameters.

Abstract: Barium Zirconium Titanate (BZT) films doped by Indium and Lanthanum were prepared using Chemical Solution Deposition followed by spin coating method. After deposition, the spesimen was annealed at 800 °C for 3 hours, using 3000 rpm angular spin coating speed. From crystallographic examination we found that the system is perovskite tetragonal with lattice parameters of a = 3.967 Ǻ, c = 3.988 Ǻ. On adding Indium and Lanthanum dopants, their lattice parameters have slightly increased. The spontaneous polarization of BZT is 23.13 µC/cm², and their spontaneous polarizations increase on adding La dopant. The best spontaneous polarization is at 1 mol % dopant of Lanthanum.

Abstract: We studied the crystallographic of Barium Zirconium Titanate thin films with Aluminum doped (BZAT). These films were prepared by sol-gel process and followed by spin coating. The sintering temperature is taken at 800°C and 900°C. We found that the crystallographic system of BZAT thin films have tetragonal structure with the lattice parameter slightly changed by various Aluminum partial substitution. When 0.01 Al moles added, the grain size of the films is 29.42 nm at 800°C. The sintering temperature 900°C increased the grain size into 50.95 nm. We also calculated the spontaneous polarization theoretically and we found the optimum value of BZT thin film with 0.01 mole Al heated at 800°C, is 0.143 C/m². This way, we could predict that the film has ferroelectric phase.

Abstract: The spontaneous polarization property of mineral tourmaline was evaluated by the conductivity method of alkaline solution. The conductivity changing rate of the alkaline solution (k) was adopted as the evaluation index. In this paper, the deionized water and alkaline solution were treated by mineral tourmaline powders, respectively. Their conductivity values were tested by a Digital Conductivity Meter. On this basis, the conductivity difference was achieved. The results showed that, the changing rate k increased as the spontaneous polarization property. When 0<k2, the spontaneous polarization was weak; when 2<k10, the spontaneous polarization was stronger; when k >10, the spontaneous polarization was strongest.Key words: Tourmaline, Spontaneous polarization, Alkaline solution, Conductivity, Evaluation

Abstract: High power InGaN-based blue LEDs have been commercialized despite the presence of a high dislocation density in the heteroepitaxial structures. Traditional trial-and-error techniques are very inefficient for improving the process of MOVCD. We analyze the effects of spontaneous and piezoelectric polarization on spontaneous emission rate of blue LEDs on SiC substrate by adjusting screening values and barrier doped concentration. The simulation results indicate to improve characteristics of blue LEDs on SiC substrate, interfacial charges for piezoelectric and polarization should get equilibrium with crystal defects and barrier doped concentration. There is an optimization point.

Abstract: Within the scope of the Harrison’s bond orbital model the spontaneous polarization, high- and low frequency dielectric constants are obtained in an analytical form. Theoretical results are in a reasonable agreement with the experimental data available and the numerical calculations based on the ab initio methods.

Abstract: By triangular wave method, we studied the effects of ultraviolet irradiation on the polarization of a binary liquid crystal mixture. The mixture was comprised of 94 wt% of banana-shaped liquid crystal 4-chloro-1,3-phenylene bis [4-(4-n-tetradecyl) phenylimino methyl] benzoate and 6 wt% of an azo-containing rod-shaped liquid crystal hexanoic acid 4-(4-ethoxy-phenylazo)-phenyl ester. Under the 365 nm irradiation for 40 minutes, the polarization of the mixture was observed to decrease 10% although the component of the banana-shaped liquid crystal was photostable. Our results demonstrated that photolysis took place in the component of azo-containing rod-shaped liquid crystal.