共查询到20条相似文献,搜索用时 0 毫秒
1.
Under nitrogen-rich growth conditions, the present ab initio study predicts that hydrogen passivation is more effective on the acceptor Be instead of Mg in a co-doped p-type GaN. The formation energy is 0.24 eV for (H-BeGa) complex, and 0.46 eV for (H-MgGa) complex. Congruently, the binding energy is 1.40 eV for (H-BeGa), and 0.60 eV for (H-MgGa). Owing to the lower binding energy, (H-MgGa) is not thermally stable. As Be is incorporated in Mg-doped GaN, a (H-MgGa) may release a H+ cation at relatively elevated temperatures. Consequently, the H+ diffuses swiftly away from a Mg−Ga, across a barrier of 1.17 eV, towards a Be−Ga and forms a stable (H-BeGa) with it. The activation of Mg acceptors can be thus facilitated. In this view, the process of hydrogen depassivation of the Mg acceptor by Be can convert the as-grown high-resistivity Mg-doped GaN into a p-conducting material, as observed in the experiments. 相似文献
2.
N vacancy,substitutional O,and AI defects in the bandgap of composition-tunable nonstoichiometric AIN powder
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
AlN powders are prepared by direct nitridation via Al liquid and vapor phases in mixed atmospheres of N2 and NH3 with different NH3/N2 ratios. The reaction analysis reveals that NH3 acts as catalyst for N2 dissociation and the transportations of N, O, and Al in the liquid phase are different from those in the vapor phase. Accordingly, the products are Al-rich and composition-tunable nonstoichiometric AlN in which N, O, and Al content values change with nitridation atmosphere and temperature, leading to the variation of the relevant defect concentration. Therefore, the AlN powders exhibit prominent absorption bands around 5.30, 3.40, and 1.50 eV, which are tentatively assigned to VN, ON donors, and AlN acceptor respectively. Furthermore, a new donor named [VN-ON] complex is predicted at 4.40 eV within the 5.90 eV bandgap. It is demonstrated that the optical spectra of nonstoichiometric AlN are preferable to the nominal stoichimometric one for the identification of the defects energy level. 相似文献
3.
C. M.J. Wijers J.-H. Chu O. Voskoboynikov 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(2):225-241
The influence of the surrounding semiconducting matrix upon the
optical response of embedded nano-objects (quantum dots) has been
investigated. This system can be described by means of a hybrid model, where the full response is a combination of a macroscopic
electrostatic response term and a dynamic response term, obtained quantum mechanically. The result is a modified discrete
dipole model, where excess discrete dipoles having an excess polarizability with respect to a uniform background identical
to the dielectric host material represent the response. In this model all electrodynamic interactions are screened by the
host material. The electrostatic response is obtained by approximating the quantum dots by embedded dielectric oblate ellipsoids.
Closed expressions for the electrostatic response of these ellipsoids have been derived. The electrodynamic nature of the
dynamic quantum mechanical polarizability term however is unclear. It is not certain whether this polarizability is dressed
or bare. Therefore we have investigated in detail the consequences of both options. Although there is no real qualitative
difference between them, the difference is so large that experiment can easily discriminate between both. Results should be
easily measurable anyhow. 相似文献
4.
Byeong-Yun Oh Jeong-Hwan KimJin-Woo Han Dae-Shik Seo Hwan Soo JangHo-Jin Choi Seong-Ho BaekJae Hyun Kim Gi-Seok HeoTae-Won Kim Kwang-Young Kim 《Current Applied Physics》2012,12(1):273-279
Structural, electrical, and optical properties of atomic layer-controlled Al-doped ZnO (ZnO:Al) films grown by atomic layer deposition (ALD) on glass substrates were characterized at various growth temperatures for use as transparent electrodes. The Al atomic content in ZnO:Al films increased due to the reduced ZnO film growth rate with increasing temperature. The preferred orientation of ZnO:Al films was changed, and the optimum condition for best crystallinity was identified by varying the growth temperature. Furthermore, the carrier concentration of free electron was increased by substituting the Zn sites with Al atoms in the crystal, resulting from monolayer growth based on alternate self-limiting surface chemical reactions. The electrical resistivity of ZnO:Al film grown by ALD at 225 °C reached the lowest value of 8.45 × 10−4 Ω cm, with a carrier mobility of 9.00 cm2 V−1 s−1 and optical transmittance of ∼93%. This result demonstrates that ZnO:Al films grown by ALD possess excellent potential for applications in electronic devices and displays as transparent electrodes and surface passivation layers. 相似文献
5.
Abstract High pressure and high temperature synthesis experiments were carried out on In-Sb and B-Sb systems with a laser heated diamond-anvil cell. InSb was synthesized starting from In and Sb at various pressures ranging from 0.2 to 10 GPa. The cubic as well as the high pressure phases were successfully synthesized. Experiments above 8 GPa, wherein antimony exists in the tetragonal phase, have revealed no new phases of InSb. Trials of synthesizing a compound from B and Sb gave negative result to at least 30 GPa. 相似文献
6.
Theoretical calculations of structural,electronic, and elastic properties of CdSe_(1-x)Te_x:A first principles study
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
M Shakil Muhammad Zafar Shabbir Ahmed Muhammad Raza-ur-rehman Hashmi M A Choudhary T Iqbal 《中国物理 B》2016,25(7):76104-076104
The plane wave pseudo-potential method was used to investigate the structural, electronic, and elastic properties of Cd Se_(1-x)Te_x in the zinc blende phase. It is observed that the electronic properties are improved considerably by using LDA + U as compared to the LDA approach. The calculated lattice constants and bulk moduli are also comparable to the experimental results. The cohesive energies for pure Cd Se and Cd Te binary and their mixed alloys are calculated. The second-order elastic constants are also calculated by the Lagrangian theory of elasticity. The elastic properties show that the studied material has a ductile nature. 相似文献
7.
Studies on CdS nanoparticles dispersed in silica matrix prepared by sol-gel technique 总被引:2,自引:0,他引:2
B. Bhattacharjee S.K. Bera D. Ganguli S. Chaudhuri A.K. Pal 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(1):3-9
SiO2/CdS-nanoparticle composite films (SiO2:CdS=85:15, 80:20, 75:25 and 70:30) were prepared by the sol-gel route. The films were characterized by studying microstructural
(XRD and TEM) and optical (transmittance and photoluminescence) properties. Band gaps of these films annealed at different
temperatures (373-473 K) for different times (10-120 min) indicated that the signature of nanocrystallinity is retained throughout
the range of our experimental conditions. A thermal diffusion process controlled growth in the crystallite size with increasing
annealing time and temperature. The average radii of the nanoparticles varied as the cube root of the annealing time but showed
exponential dependence on the inverse of annealing temperature. Photoluminescence (PL) studies of the composite films indicated
excitonic transitions. Theoretical analysis of the line shapes of the PL peaks recorded at 300 K and 80 K could be accounted
for by the combined effects of size distribution and phonon broadening. It was observed that the deformation potential (E
d) effectively controlled the line shapes of the PL measurements.
Received 24 May 2002 Published online 27 January 2003
RID="a"
ID="a"e-mail: msakp@mahendra.iacs.res.in 相似文献
8.
Siddheshwar Chopra 《Molecular physics》2013,111(13):2074-2080
Density functional theory (DFT)/time dependent density functional theory (TDDFT) based calculations were performed for basis sets 6-31G for DFT and 6-31G (d), 6-31G (d,p) and 6-31+G (d,p) for TDDFT calculations on pure boron nitride nanoribbon (BNNR) B15N15H14 and metal decorated B15N14H14-X BNNRs, where X = Ni+, Fe+, Co, Cr+, Cu and Al. The metal doping ratio = 3.45% and the doping site (nitrogen atom), were fixed for all the BNNRs. Electronic properties dipole moment, binding energy and bandgap were determined. Absorption properties in the wavelength range (100–600 nm) were studied, and optical gaps, absorption wavelengths, oscillator strengths and dominant transitions were calculated. The effect of metal doping on the electronic and optical properties was investigated. Single metal doping shifts the electronic gap of pure BNNR from insulating to semiconducting nature. Red shift in the absorption wavelengths from ultraviolet to visible in all the BNNRs was noticed. 相似文献
9.
We report simple room temperature synthesis of Mg doped ZnO nanostructures through the sol–gel method. X-ray diffraction shows the prepared ZnO particles are in wurtzite structure and replacement of Zn2+ by Mg2+ alters the position of the X-ray diffraction peak slightly towards higher angle. Measured optical absorption spectra show the exciton peaks of ZnO present around 366, 296 and 235 nm. Room temperature photoluminescence measurements show strong peaks around 385, 394 nm are attributed to band edge exciton emission; other peaks found at 469 and 558 are attributed to oxygen ion vacancy and formation of Vo+ and Vo++ centers in nanostructures. 相似文献
10.
Y. Duan G. Tang L. Qin L. Shi 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(2):211-215
Elasticity and polarization of GaxAl1-xN alloys subjected
to uniaxial and homogeneous biaxial compression are calculated using
first-principles methods. The uniaxial compression along the c-axis
reduces Young’s modulus along the c-axis, and enhances bulk
modulus and total polarization, whereas the biaxial compression in
the plane perpendicular to the c-axis enhances bulk and Young’s
moduli. It is also found that when the in-plane biaxial compression
is applied by constraining the a-axis lattice constant to that of
AlN, the bulk and Young’s moduli dramatically increase with
increasing Ga concentration, and the total polarization could be
suppressed, even annihilated, and finally enhanced by controlling Ga
concentration. 相似文献
11.
H.-L. Shi Y. Duan 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(4):439-444
Using a first-principles band-structure method and a
special quasirandom structure (SQS) approach, we systematically
calculate the band gap bowing parameters and p-type doping
properties of (Zn, Mg, Be)O related random ternary and quaternary
alloys. We show that the bowing parameters for ZnBeO and MgBeO
alloys are large and dependent on composition. This is due to the
size difference and chemical mismatch between Be and Zn(Mg) atoms.
We also demonstrate that adding a small amount of Be into MgO
reduces the band gap indicating that the bowing parameter is
larger than the band-gap difference. We select an ideal N atom
with lower p atomic energy level as dopant to perform
p-type doping of ZnBeO and ZnMgBeO alloys. For N doped in
ZnBeO alloy, we show that the acceptor transition energies become
shallower as the number of the nearest neighbor Be atoms
increases. This is thought to be because of the reduction of
p-d repulsion. The NO acceptor transition
energies are deep in the ZnMgBeO quaternary alloy lattice-matched
to GaN substrate due to the lower valence band maximum. These
decrease slightly as there are more nearest neighbor Mg atoms
surrounding the N dopant. The important natural valence band
alignment between ZnO, MgO, BeO, ZnBeO, and ZnMgBeO quaternary
alloy is also investigated. 相似文献
12.
First-principles study on electronic and optical properties of S,N single-doped and S-N co-doped ZnO
《Physics letters. A》2020,384(8):126172
The electronic and optical properties of undoped, N single-doped, S single-doped, and S-N co-doped ZnO were systematically investigated by first-principles calculations. The lattice parameters of S single-doped and S-N co-doped ZnO clearly increased. After N-doping, a strongly localized impurity energy level of N was formed near the Fermi level at the top of valence band (VB). In S-N co-doped ZnO, the localization of N weakened, and the Fermi level went deeper into the VB, indicating that the acceptor energy level of N formed in S-N co-doped system became shallower due to the effect of 3p state of S. Therefore, S-N co-doping is beneficial to obtain p-type ZnO with a higher hole concentration than N single-doping. Compared with undoped ZnO, the static dielectric constant, absorption coefficient, refractive index, energy loss function, and reflectivity of N single-doped, S single-doped, and S-N co-doped ZnO exhibited an increase in low-energy area. 相似文献
13.
Using first-principles calculations based on density functional theory, we investigated systematically the electronic structures and magnetic properties of ZnO:Cu. The results indicate that Cu-doped ZnO prefers a ferromagnetic ground state and behaves like a half-metallic ferromagnet. The magnetic moment mainly localizes at Cu atom and the rest mainly comes from the spin polarized O atoms. It has been found that the ferromagnetic stability can be enhanced slightly by substituting an oxygen atom with one N atom; while the ferromagnetic stability can be weakened by replacing one O atom with a C atom. Due to absence of magnetic ion and the 100% spin polarization of the carriers in ZnO:Cu, one can expect that Cu-doped ZnO would be a useful half-metallic ferromagnet both in practical application and in theoretical studies. 相似文献
14.
Effect of pressure on electronic and thermoelectric properties of magnesium silicide: A density functional theory study
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We study the effect of pressure on electronic and thermoelectric properties of Mg_2Si using the density functional theory and Boltzmann transport equations. The variation of lattice constant, band gap, bulk modulus with pressure is also analyzed. Further, the thermoelectric properties(Seebeck coefficient, electrical conductivity, electronic thermal conductivity) have been studied as a function of temperature and pressure up to 1200 K. The results show that Mg_2Si is an n-type semiconductor with a band gap of 0.21 eV. The negative value of the Seebeck coefficient at all pressures indicates that the conduction is due to electrons. With the increase in pressure, the Seebeck coefficient decreases and electrical conductivity increases. It is also seen that, there is practically no effect of pressure on the electronic contribution of thermal conductivity.The paper describes the calculation of the lattice thermal conductivity and figure of merit of Mg_2Si at zero pressure. The maximum value of figure of merit is attained 1.83 × 10~(-3) at 1000 K. The obtained results are in good agreement with the available experimental and theoretical results. 相似文献
15.
16.
目前,虽然Zn1-xT Mx O1-y Ny(TM=Al,Ga,In)p型掺杂的理论计算研究已有报道,但是,掺杂均是随机的,没有考虑ZnO的非对称性进行择优位向掺杂.因此,本研究采用基于密度泛函理论框架下的第一性原理平面波超软赝势方法,构建TM:N=1:2比例择优位向共掺,共设六种不同的Zn1-xT Mx O1-y Ny(TM=Al,Ga,In.x=0.03125,y=0.0625)超胞模型,并分别进行几何结构优化、态密度分布和能带结构分布的计算.结果表明,重掺杂条件下,择优位向共掺后,同类择优位向共掺的体系中,TM-N沿c轴方向成键体系的电导率大于垂直于c轴方向成键体系的电导率.不同类TM-N沿c轴方向成键共掺的体系中,In-N沿c轴方向成键共掺时ZnO的电导率最强,电离能最小,Bohr半径最大,In-N沿c轴方向成键共掺对ZnO p型导电更有利.因此,TM:N=1:2比例择优位向共掺,对设计和制备导电性能更强的ZnO功能材料具有一定的理论指导作用. 相似文献
17.
Yunhua Zhou Yingfang Fan Zhongchao Wang Weiwei Mao Yakui Weng Jian Zhang Yong Pu Jianping Yang Xingao Li 《Physics letters. A》2019,383(4):383-388
In this study, the structural, magnetic, electric and optical properties in X (X=F, N, S) and Cr co-doped BiFeO3 (BFO) are calculated using the density functional theory. For Cr–X co-doping case, the structure of BFO undergo a phase transition from monoclinic to triclinic structure accompanying net magnetic moments of 5.92 μB, 6.04 μB and 7.80 μB, for Cr–F co-doping, Cr–N co-doping and Cr–S co-doping, respectively. The underlying physical mechanisms are the lattice distortions tunned by doping. The decreased Fe–O–Fe bond angles and Fe–O bond lengths will bring weak antiferromagnetism superexchange interaction. In addition, the band gaps of Cr–X co-doping cases are decreased from 2.20 eV (BFO bulk) to 1.31 eV and 1.80 eV for Cr–F co-doping and Cr–S co-doping, respectively, which are well for photovoltaic applications according to the well-known Shockley-Queisser criterion, suggesting a possible great improvement optical properties in Cr–X co-doped samples. 相似文献
18.
We present the growth of ZnO nanostructures on indium-doped ZnO film on a non-conductive glass substrate. The indium-doped ZnO film was used as the transparent conductive layer replaces the ITO layer. Various indium doping concentrations can change the electrical properties of ZnO film. The reduced electrical resistivity was investigated from 16.60 × 10−2 to 10 × 10−2 Ω cm. after doping with the optimal concentration of 2 wt% indium. It is found that the characteristic of ZnO nanostructures was strongly affected with indium doping concentration in ZnO films. The overall structural characteristics of ZnO ranged from 100–500 nm in size and 7–10 μm in length and the branch-like structures can be revealed from the 2 wt% indium-doped ZnO film. The room-temperature photoluminescence spectra show a sharp ultraviolet band of 353 nm, indicated to the ZnO nanorods structure. The branch-like structures on the 2 wt% indium-doped film can be yielded the photovoltaic properties with a short-circuit current density of 3.96 mA/cm2, an open-circuit voltage of 0.72 V, a fill factor of 20% and an overall power conversion efficiency of 0.56% under irradiance of 100 mW/cm2 (AM 1.5 G). 相似文献
19.
E. Wongrat 《Applied Surface Science》2009,256(4):968-971
Gold colloid:ZnO nanostructures were prepared from Zn powder by using thermal oxidation technique on alumina substrates, then it was impregnated by gold colloid for comparative study. The gold colloid is the solution prepared by chemical reduction technique; it appeared red color for gold nanoparticle solution and yellow color for gold solution. The heating temperature and sintering time of thermal oxidation were 700 °C and 24 h, respectively under oxygen atmosphere. The structural characteristics of gold colloid:ZnO nanostructures and pure ZnO nanostructures were studied using filed emission scanning electron microscope (FE-SEM). From FE-SEM images, the diameter and length of gold colloid:ZnO nanostructures and ZnO nanostructures were in the ranges of 100-500 nm and 2.0-7.0 μm, respectively. The ethanol sensing characteristics of gold colloid:ZnO nanostructures and ZnO nanostructures were observed from the resistance alteration under ethanol vapor atmosphere at concentrations of 50, 100, 200, 500, and 1000 ppm with the operating temperature of 260-360 °C. It was found that the sensitivity of sensor depends on the operating temperature and ethanol vapor concentrations. The sensitivity of gold colloid:ZnO nanostructures were improved with comparative pure ZnO nanostructures, while the optimum operating temperature was 300 °C. The mechanism analysis of sensor revealed that the oxygen species on the surface was O2−. 相似文献
20.
V. Ganesh Ch. Snehalatha ReddyMohd. Shakir M.A. WahabG. Bhagavannarayana K. Kishan Rao 《Physica B: Condensed Matter》2011,406(2):259-264
〈1 1 1〉 oriented bis thiourea cadmium acetate (BTCA) crystal of diameter 15 mm and length 45 mm was grown for the first time by the unidirectional Sankaranarayanan-Ramasamy (SR) method. The conventional and SR method grown BTCA crystals were characterized by using high-resolution X-ray diffraction (HRXRD), chemical etching, Vickers microhardness, UV-vis, dielectric studies and differential scanning calorimetry. The HRXRD analysis indicates that the crystalline perfection of SR method grown crystal is good without having any low angle internal structural grain boundaries. The transmittance of SR method grown BTCA is 14% higher than that of conventional grown crystal. The dielectric constant was higher and the dielectric loss was less in SR method grown crystal. The crystals grown by SR method possess less dislocation density and higher microhardness. 相似文献