共查询到20条相似文献,搜索用时 15 毫秒
1.
A. Alsaad A. Ahmad 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(2):151-156
First-principles calculations are performed to compute the e33
piezoelectric coefficients of GaN, ScN and (ScxGa1-xN) alloys
exhibiting an alternation of hexagonal GaN, with hexagonal ScN along the c-axis. For Sc compositions larger than 50%, each atom has nearly five nearest
neighbors (i.e., the ground state exhibits a phase that is five-fold
coordinated). On the other hand, Sc-deficient (Sc, Ga) N alloys adopt a
ground-state that is four-fold coordinated). The magnitude of e33 in
the Sc-deficient ideally ordered (Sc0.25Ga0.75N) is found to be larger
than the magnitude of the corresponding e33 coefficients resulting from
the compositional weighted average over the hexagonal (h-ScN) and the wurtzite (w-GaN) parent compounds. On the other hand, the e33 coefficients of the Sc-rich
ordered (Sc0.75Ga0.25N) is found to be negligibly small. In addition, e33
piezoelectric coefficients in ordered (Sc0.5Ga0.5N) exhibit quite
large magnitudes, due to the nonpolar to polar transition occurs at Sc composition x = 0.5, and thus can bridge the corresponding coefficients of (Ga, In) N and
ferroelectric alloys. The microscopic origins for this huge enhancement in
the piezoelectric behavior in Sc-low and Sc-intermediate alloys and the role
of each atom are revealed and discussed. 相似文献
2.
0.38Bi(Gax Sc1–x )O3–0.62PbTiO3 (BGSPTx) ceramics have been prepared by using the conventional mixed oxide method. X‐ray diffraction analysis revealed that BGSPTx has a pure perovskite structure, and the crystal symmetry of BGSPTx changed from rhombohedral to tetragonal with increasing Ga content (x). The Curie temperature (TC) of BGSPTx ceramics is in the range of 448–467 °C for different x. The ferroelectric phase transition of BGSPTx was found to be of the first order type according to the Curie–Weiss law. For x = 0.125, BGSPTx ceramics show enhanced piezoelectric properties: piezoelectric constant d33 = 420 pC/N and d31 = –142 pC/N, planar and thickness electromechanical coupling factors kp = 56.27% and kt = 56.00%, respectively. The high‐TC of BGSPTx coupled with its excellent piezoelectric properties suggests those future high‐temperature applications. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
3.
S. Saib N. Bouarissa P. Rodríguez-Hernández A. Muñoz 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(4):435-438
We present a theoretical study of the structural properties, namely
lattice constant, bulk modulus and its pressure derivative of zinc-blende
GaxIn1-xN. The calculations are performed using first-principles
calculations in the framework of the density-functional-theory
within the local density approximation under the virtual
crystal approximation. The computed values are in good
agreement with the available experimental data. The composition dependence
of the studied quantities is examined. Besides, the deviation of the alloy
lattice constant from Vegard's law is evaluated. 相似文献
4.
Y. Yuan K. Deng Y. Liu C. Tang G. Lu J. Yang X. Wang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,40(2):243-246
The ground state structures of MC3 (M = Sc, V, and Cr) and their
anions have been investigated, employing the first-principles DFT
at the B3LYP level. The calculations predict that the equilibrium
geometries of both neutral MC3 and their anions are cyclic
structures with C2v symmetry. The Mulliken charge and spin
populations of MC3 and their anions have also been calculated,
and it is found the electron charge changes mainly take place on
the M atoms from anions to neutral molecules. The low-lying
excited states for the clusters are calculated with time-dependent
DFT to assign the features of the photoelectron spectra. Our
results agree well with the available experimental and theoretical
data. 相似文献
5.
6.
采用基于密度泛函理论的BP86/CEP-121G (O原子采用6-311G**基组)方法,对ScnO (n=1—9)团簇的几何结构、能量与稳定性、电子结构性质及其随团簇尺寸的变化趋势进行了研究.随着团簇原子个数的增加,O原子从位于Scn团簇结构的边缘转变为占据团簇的内部位置.O原子的掺入增加了Scn团簇的稳定性,使其能隙升高,并改变了其稳定性及电子结构性质随团簇尺寸变化的规律;含有偶数个Sc原子的氧化物团簇比其周围邻近的含有奇数个Sc原子的氧化物团簇具有相对较高的稳定性.ScnO团簇电离势的理论计算值与实验值符合得较好,而其电子亲和势呈现振荡交替上升的变化趋势;用最大化学硬度规律等方法表征了ScnO氧化物团簇的稳定性和电子结构性质.
关键词:
nO团簇')" href="#">ScnO团簇
几何结构
电子性质
密度泛函理论 相似文献
7.
A. K. Ivanov-Shits 《Physics of the Solid State》1997,39(1):72-74
The results of measurements of the ionic conductivity σ in Li3M2(PO4)3 (M=Fe, Sc) single crystals along various crystallographic directions are analyzed. Possible causes of the different behavior
of σ in the isostructural crystals are discussed: a jump of the conductivity in the transition to the superionic phase in Li3Sc2(PO4)3 and its absence in Li3Fe2(PO4)3; the existence of a conductivity maximum in different crystallographic directions (along the c axis in Li3Sc2(PO4)3 and along the a axis in Li3Fe2(PO4)3).
Fiz. Tverd. Tela (St. Petersburg) 39, 83–86 (January 1997) 相似文献
8.
Bernard Piechal Jens W. Tomm Artem Bercha Witold Trzeciakowski Martin Reufer Alvaro Gomez-Iglesias 《Applied Physics A: Materials Science & Processing》2009,97(1):179-184
The hydrostatic pressure behavior of red-emitting diode lasers packaged on Si, AlN, and diamond submounts is studied in the
0–2 GPa range by emission and photocurrent spectroscopy. Photocurrent spectroscopy allows for simultaneous measurement of
the InGaP quantum well and (Al0.5Ga0.5)0.5In0.5P waveguide. A broadening of the absorption edge of the waveguide is observed for all devices and explained by the pressure-induced
direct-to-indirect transition in this material. For the QW resonance, distinct differences are observed for differently packaged
devices. Thus, very low pressure tuning rates are demonstrated for devices packaged on diamond and AlN submounts and explained
by the presence of shear strain components. Consistently we find the device packaged on Si to be least affected by the strain
caused by the pressure cycling. 相似文献
9.
T. J. Kim S. W. Lee B. K. Kang D. S. Kim A. S. Kim K. H. Shin M. K. Park Y. K. Sin 《Optical and Quantum Electronics》1995,27(5):465-471
High-quality and uniform bulk layers of (Al
x
Ga1–x
)0.5In0.5P (x=0–0.7) and AlGalnP/GainP quantum wells (QWs) are grown on 2°-off (100) GaAs substrates by low-pressure metal organic vapour phase epitaxy at a low growth rate of 0.3 nm s-1. The amount of lattice mismatch and the variation of PL peak energy of (Al0.5Ga0.5)0.5In0.5P on the 50-mm substrate are less than 6×10-4 and 2 meV, respectively. (Al0.5Ga0.5)0.5In0.5P/Ga0.5In0.5P SQWs show narrow PL spectra even from a 0.6 nm well measured at 20 K. The variation of PL peak energy from (Al0.5Ga0.5)0.5In0.5P/Ga0.5In0.5P MQWs is less than 10 meV. Also, as-cleaved AlGalnP/GalnP lasers fabricated by a three-step MOVPE show a pulsed threshold current of 82 mA at room temperature, output power of 12 mW, and the lasing wavelength at 668.2 nm. 相似文献
10.
The specific heat of the cryolites (NH4)3Ga1−x
ScxF6 with x=1.0, 0.1, and 0 was measured. The thermodynamic parameters of the phase transitions were determined. A previously unknown
phase transition was found in the scandium compound at T=243 K.
Fiz. Tverd. Tela (St. Petersburg) 41, 523–528 (March 1998) 相似文献
11.
X. Wu Z. Wu 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(4):521-526
First-principles calculations based on density functional
theory were used to study the high-pressure phases of both ZnF2 and
CdF2. We found that the sequence of the pressure-induced phase
transitions is: Rutile (P42/mnm) ↦ CaCl2 (Pnnm) ↦ PdF2
(Pa-3) and CaF2 (Fm3m) ↦ PbCl2 (Pnma) ↦ Ni2In
(P63/mmc) for ZnF2 and CdF2 respectively. In ZnF2 the
behavior of the ground-state total energy, of the Gibbs free energy and of
the lattice constant vs. pressure shown that the phase transition at 4 GPa
from the rutile-type phase to the CaCl2-type phase is a second-order
phase transition. The mechanism of the structural change was also revealed
by the transition from the PbCl2-type phase to the Ni2In-type
phase in CdF2. Moreover, the high-pressure behavior of divalent metal
fluorides was compared and discussed. 相似文献
12.
In0.3Ga0.7N metal-insulator-semiconductor (MIS) and metal-semiconductor (MS) surface barrier photodetectors have been fabricated. The In0.3Ga0.7N epilayers were grown on sapphire by metalorganic chemical vapour deposition (MOCVD). The photoresponse and reverse current-voltage characteristics of the In0.3Ga0.7N MIS and MS photodetectors were measured. A best zero bias responsivity of 0.18 A/W at 450 nm is obtained for the In0.3Ga0.7N MIS photodetector with 10 nm Si3N4 insulator layer, which is more than ten times higher than the In0.3Ga0.7N MS photodetector. The reason is attributed to the decrease of the interface states and increase of surface barrier height by the inserted insulator. The influence of the thickness of the Si3N4 insulator layer on the photoresponsivity of the MIS photodetector is also discussed. 相似文献
13.
14.
Within the framework of the effective-mass approximation, the exciton states and interband optical transitions in InxGa1−xN/GaN strained quantum dot (QD) nanowire heterostructures are investigated using a variational method, in which the important built-in electric field (BEF) effects, dielectric-constant mismatch and three-dimensional confinement of the electron and hole in InxGa1−xN QDs are considered. We find that the strong BEF gives rise to an obvious reduction of the effective band gap of QDs and leads to a remarkable electron-hole spatial separation. The BEF, QD height and radius, and dielectric mismatch effects have a significant influence on exciton binding energy, electron interband optical transitions, and the exciton oscillator strength. 相似文献
15.
16.
Miao-Chan Tsai Sheng-Horng Yen Yen-Kuang Kuo 《Applied Physics A: Materials Science & Processing》2011,104(2):621-626
The concept of a step-like quantum well is proposed with the purpose to reduce the influence of electrostatic field resulting
from the piezoelectric effect on the optical performance of blue InGaN light-emitting diodes. Particularly, the optical properties
of the LED structures with the In0.23Ga0.77N single quantum well, In0.20Ga0.80N/In0.26Ga0.74N step-like quantum well, and In0.26Ga0.74N/In0.20Ga0.80N step-like quantum well are numerically investigated in detail. Simulation results show that the In0.20Ga0.80N/In0.26Ga0.74N step-like-quantum-well LED structure has the best optical performance in virtue of the improvement in spatial overlap of
electrons and holes in the quantum well. 相似文献
17.
本文基于第一性原理中的Heyd-Scuseria-Ernzerh方法研究了单层In1-xGaxN的电子结构和光学性质.计算得到单层In1-xGaxN的能带结构和态密度(DOS),发现随着掺杂比例的变化,体系带隙的变化范围是1.8~3.8 eV,表明通过Ga的掺杂可以实现体系带隙值的调节.并且还研究了单层In1-xGaxN的介电函数,折射率和吸收系数等光学性质,结果表明随着Ga掺杂浓度的增加,介电函数谱的主峰和吸收谱发生了显著的蓝移.此外,基于能带结构和态密度图谱,对单层In1-xGaxN的光学性质进行分析,预测这种材料独特的光学性质在纳米电子学和光学器件中会有广泛的应用. 相似文献
18.
R. Schwedler F. Brüggemann A. Kohl K. Wolter K. Leo H. Kurz 《Applied Physics A: Materials Science & Processing》1993,57(2):199-201
The formation of minibands is demonstrated in photocurrent experiments on shallow In0.53Ga0.47As/In0.40Ga0.60 As superlattices grown by low-pressure metal-organic vapor-phase epitaxy. Field-dependent variations of the spectral shape are attributed to Wanner-Stark localization. Both type-I transitions between electrons and heavy holes and type-II transitions involving light holes confined in the In0.40Ga0.60 As layers are observed and distinguished by their characteristic field dependence. 相似文献
19.
The effect of built-in-polarization (BIP) field on thermal properties of InxGa1−xN/GaN heterostructure has been investigated. The thermal conductivity k of InxGa1−xN alloy has been estimated using Callaway's formula including the BIP field for In content x = 0, 0.1, 0.3, 0.5 and 0.9. This study reports that irrespective of In content, the room temperature k of InxGa1−xN/GaN heterostructure is enhanced by BIP field. The result predicts the existence of a characteristic temperature Tp at which both thermal conductivities (including and excluding BIP field) show a crossover. This gives signature of pyroelectric nature of InxGa1−xN alloy which arises due to variation of polarization with temperature indicating that thermal conductivity measurement can reveal pyroelectric nature. The pyroelectric transition temperature of InxGa1−xN alloy has been predicted for various x. The composition dependent nature of room temperature k for x = 0.1 and 0.5 are in line with prior experimental studies. The result can be used to minimize the self heating effect in InxGa1−xN/GaN heterostructures. 相似文献
20.
M. Geddo R. Pezzuto M. Capizzi A. Polimeni D. Gollub M. Fischer A. Forchel 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):39-43
The optical response of as grown and hydrogenated In0.32Ga0.68As1-yNy/GaAs single quantum wells (y = 0, 0.027) has been investigated from T = 80 K to room temperature by photoreflectance. Three excitonic spectral features detected in the N free sample shift to
lower energy in the N containing sample and back to higher energy upon H irradiation of the N containing sample. In the hydrogenated
sample, a progressive change with increasing temperature of the nature of the lowest energy transition from an excitonic to
a band-to-band character has been explained in terms of an increasing release of carriers from traps formed by H and N clusters.
A reduction in the oscillator strength of the lowest energy transition and an increase in the binding energy of the heavy-hole
exciton have been explained in terms of an increase in the electron effective mass upon N introduction into the InxGa1-xAs lattice.
Received 23 June 2002 Published online 19 November 2002 相似文献