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1.
A. Alsaad A. Ahmad 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,65(1):65-77
Theoretical results are presented regarding the incorporation of Scandium into wurtzite GaN and InN binaries. The electric,
optical and piezoelectric properties of the resulting ScGaN and ScInN systems are reported by using first-principles Local-density
approximation (LDA) within density functional theory (DFT), Berry phase approach within modern theory of polarization and
phonon calculations within the density functional perturbation theory. Our results predict the existence of breaking-symmetry
structural phase transition in ordered Sc0.5Ga0.5N and Sc0.5In0.5N alloys when subjected to a compressive or tensile strain. Moreover, our results demonstrate the existence of symmetry preserving pressure-induced isostructural phase transitions
in ordered ScGaN and ScInN systems for different Sc concentrations. It has been shown that the existence of isostructural
phase transitions leads to dramatic changes in optical, acoustic, and piezoelectric properties of ordered ScGaN and ScInN
systems under high pressure. In particular, this study demonstrates that the existence of first-order isostructural phase
transitions in Sc1Ga1N2 at a critical hydrostatic pressure of 12.3 GPa leads to a huge enhancement of piezoelectricity (i.e., the e
33 piezoelectric coefficient adopts a huge value as large as 13 C/m2). In addition, It has been shown that ordered Sc0.5Ga0.5N and Sc0.5In0.5N alloys exhibit tremendous piezoelectric response, associated with a breaking-symmetry phase transition from nonpolar P63/mcc(D6h) space group to a polar P63
mc(C6v) structure, at fixed Ga, In and Sc compositions, as a function of the in-plane compressive and tensile strains. We also reveal
the reason behind, and consequences of, these unusual properties associated with the strain-induced and pressure-induced structural
phase transitions in the novel ScGaN and ScInN ordered structures. 相似文献
2.
Different temperature dependence of carrier transport properties between AlxGa1-xN/InyGa1-yN/GaN and AlxGa1-xN/GaN heterostructures
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The temperature dependence of carrier transport properties of AlxGa1-xN/InyGa1-yN/GaN and AlxGa1-xN/GaN heterostructures has been investigated.It is shown that the Hall mobility in Al0.25Ga0.75N/In0.03Ga0.97N/GaN heterostructures is higher than that in Al0.25Ga0.75N/GaN heterostructures at temperatures above 500 K,even the mobility in the former is much lower than that in the latter at 300 K.More importantly,the electron sheet density in Al0.25Ga0.75N/In0.03Ga0.97N/GaN heterostructures decreases slightly,whereas the electron sheet density in Al0.25Ga0.75N/GaN heterostructures gradually increases with increasing temperature above 500 K.It is believed that an electron depletion layer is formed due to the negative polarization charges at the InyGa1-yN/GaN heterointerface induced by the compressive strain in the InyGa1-yN channel,which e-ectively suppresses the parallel conductivity originating from the thermal excitation in the underlying GaN layer at high temperatures. 相似文献
3.
4.
Performance comparison of Pt/Au and Ni/Au Schottky contacts on AlxGa1-x N/GaN heterostructures at high temperatures
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In contrast with Au/Ni/Al 0.25 Ga 0.75 N/GaN Schottky contacts,this paper systematically investigates the effect of thermal annealing of Au/Pt/Al 0.25 Ga 0.75 N/GaN structures on electrical properties of the two-dimensional electron gas in Al 0.25 Ga 0.75 N/GaN heterostructures by means of temperature-dependent Hall and temperature-dependent current-voltage measurements.The two-dimensional electron gas density of the samples with Pt cap layer increases after annealing in N 2 ambience at 600℃ while the annealing treatment has little effect on the two-dimensional electron gas mobility in comparison with the samples with Ni cap layer.The experimental results indicate that the Au/Pt/Al 0.25 Ga 0.75 N/GaN Schottky contacts reduce the reverse leakage current density at high annealing temperatures of 400-600℃.As a conclusion,the better thermal stability of the Au/Pt/Al 0.25 Ga 0.75 N/GaN Schottky contacts than the Au/Ni/Al 0.25 Ga 0.75 N/GaN Schottky contacts at high temperatures can be attributed to the inertness of the interface between Pt and AlxGa1-xN. 相似文献
5.
Engin Tiras Ozlem Celik Selman Mutlu Sukru Ardali Sefer Bora Lisesivdin Ekmel Ozbay 《Superlattices and Microstructures》2012
The two-dimensional (2D) electron energy relaxation in Al0.25Ga0.75N/AlN/GaN heterostructures was investigated experimentally by using two experimental techniques; Shubnikov-de Haas (SdH) effect and classical Hall Effect. The electron temperature (Te) of hot electrons was obtained from the lattice temperature (TL) and the applied electric field dependencies of the amplitude of SdH oscillations and Hall mobility. The experimental results for the electron temperature dependence of power loss are also compared with the current theoretical models for power loss in 2D semiconductors. The power loss that was determined from the SdH measurements indicates that the energy relaxation of electrons is due to acoustic phonon emission via unscreened piezoelectric interaction. In addition, the power loss from the electrons obtained from Hall mobility for electron temperatures in the range Te > 100 K is associated with optical phonon emission. The temperature dependent energy relaxation time in Al0.25Ga0.75N/AlN/GaN heterostructures that was determined from the power loss data indicates that hot electrons relax spontaneously with MHz to THz emission with increasing temperatures. 相似文献
6.
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
7.
S. Munawar Basha S. Ramasubramanian R. Thangavel M. Rajagopalan J. Kumar 《Journal of magnetism and magnetic materials》2010,322(2):238-241
Investigations have been carried out to study the ferromagnetic properties of transition metal (TM) doped wurtzite GaN from first principle calculations using tight binding linear muffin-tin orbital (TBLMTO) method within the density functional theory. The present calculation reveals ferromagnetism in nickel doped GaN with a magnetic moment of 1.13 μB for 6.25% of Ni doping and 1.32 μB for 12.5% of nickel doping, there is a decrease of magnetic moment when two Ni atoms are bonded via nitrogen atom. The Ga vacancy (VGa) induced defect shows ferromagnetic state. Here the magnetic moment arises due to the tetrahedral bonding of three N atoms with the vacancy which is at a distance of 3.689 Å and the other N atom which is at a distance of 3.678 Å .On the other hand the defect induced by N vacancy (VN) has no effect on magnetic moment and the system shows metallic character. When Ni is introduced into a Ga vacancy (VGa) site, charge transfer occur from the Ni ‘d’ like band to acceptor level of VGa and formed a strong Ni–N bond. In this Ni–VGa complex with an Ni ion and a Ga defect, the magnetic moment due to N atom is 0.299 μB .In case of Ni substitution in Ga site with N vacancy, the system is ferromagnetic with a magnetic moment of 1 μB. 相似文献
8.
L. Boudaoud W. Adli R. Mecheref Nadir Sekkal F. Tair B. Amrani S. Louhibi A. Tebboune 《Superlattices and Microstructures》2010
The electronic properties of both ScxGa1−xAs and ScxGa1−xN ternary alloy and superlattice systems are investigated within the first-principles full-potential linear muffin-tin orbitals method (FPLMTO) in its atomic sphere approximation (ASA) using the technique of empty spheres, which allows an accurate treatment of the interstitial regions. The phase transition from the rocksalt (B1) to the zinc blende (B3) structure is investigated and the possibility of zinc blende/zinc blende GaN/ScxGa1−xN and GaAs/ScxGa1−xAs superlattices is expected. Wide and direct gaps are found to be possible in these systems, predicting them as good candidates for optoelectronic applications. 相似文献
9.
The Shubnikov-de Haas (S-dH) results at 1.5 K for AlxGa1−xN/AlN/GaN heterostructures and the fast Fourier transformation data for the S-dH data indicated the occupation by a two-dimensional electron gas (2DEG) of one subband in the GaN active layer. Photoluminescence (PL) spectra showed a broad PL emission about 30 meV below the GaN exciton emission peak at 3.474 eV that could be attributed to recombination between the 2DEG occupying in the AlN/GaN heterointerface and photoexcited holes. A possible subband structure was calculated by a self-consistent method taking into account the spontaneous and piezoelectric polarizations, and one subband was occupied by 2DEG below the Fermi level, which was in reasonable agreement with the S-dH results. These results can help improve understanding of magnetotransport, optical, and electronic subband properties in AlxGa1−xAs/AlN/GaN heterostructures. 相似文献
10.
Quantum dots-templated growth of strain-relaxed GaN on a c-plane sapphire by radio-frequency molecular beam epitaxy
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We investigated the quantum dots-templated growth of a(0001) GaN film on a c-plane sapphire substrate.The growth was carried out in a radio-frequency molecular beam epitaxy system.The enlargement and coalescence of grains on the GaN quantum dots template was observed in the atom force microscopy images,as well as the more ideal surface morphology of the GaN epitaxial film on the quantum dots template compared with the one on the AlN buffer.The Ga polarity was confirmed by the reflected high energy electron diffraction patterns and the Raman spectra.The significant strain relaxation in the quantum dots-templated GaN film was calculated based on the Raman spectra and the X-ray rocking curves.Meanwhile,the threading dislocation density in the quantum dots-templated film was estimated to be 7.1×107cm-2,which was significantly suppressed compared with that of the AlN-buffered GaN film.The roomtemperature Hall measurement showed an electron mobility of up to 1860cm2 /V·s in the two-dimensional electron gas at the interface of the Al 0.25Ga0.75 N/GaN heterojunction. 相似文献
11.
J.A. Gupta M.W.C. Dharma-wardana E.D. Crozier M. Prange 《Solid State Communications》2005,136(6):351-355
X-ray absorption near-edge spectroscopy (XANES) is used to study the N environment in bulk GaN and in GaNyAs1−y epilayers on GaAs (0 0 1), for y∼5%. Density-functional optimized structures were used to predict XANES via multiple-scattering theory. We obtain striking agreement for pure GaN. An alloy model with nitrogen pairs on Ga accurately predicts the threshold energy, the width of the XANES ‘white line’, and features above threshold, for the given X-ray polarization. The presence of large quantitities of N-pairs may point to a role for molecular N2 in epitaxial growth kinetics. 相似文献
12.
(Ga1−xMnx)N/GaN digital ferromagnetic heterostructures (DFHs) and (Ga1−xMnx)N/GaN grown on GaN buffer layers by using molecular beam epitaxy have been investigated. The photoluminescence (PL) spectra showed band-edge exciton transitions. They also showed peaks corresponding to the neutral donor-bound exciton and the exciton transitions between the conduction band and the Mn acceptor, indicative of the Mn atoms acting as substitution. The magnetization curves as functions of the magnetic field at 5 K indicated that the saturation magnetic moment in the (Ga1−xMnx)N/GaN DFHs decreased with increasing Mn mole fraction and that the saturation magnetic moment and the coercive field in the (Ga1−xMnx)N/GaN DFHs were much larger than those in (Ga1−xMnx)N thin films. These results indicate that the (Ga1−xMnx)N/GaN DFHs hold promise for potential applications in spintronic devices. 相似文献
13.
Influence of Ga(Al)As substrates on surface morphology and critical thickness of InGaAs quantum dots
《Current Applied Physics》2019,19(5):557-562
Influence of Ga(Al)As substrates on surface morphology of InGaAs quantum dots and critical thickness of In0.5Ga0.5As film grown by molecular beam epitaxy is investigated. The In0.5Ga0.5As quantum dots are grown on (001) surfaces of GaAs and Al0.25Ga0.75 A at 450 °C, scanning tunneling microscope images show that the size of quantum dots varied slightly for 10 ML of In0.5Ga0.5As grown on GaAs and Al0.25Ga0.75As surfaces. Reflection high energy electron diffraction (RHEED) is used to monitor the growth of 4 monolayers (ML) In0.5Ga0.5As on Al0.25Ga0.75As and GaAs surfaces during deposition. The critical thickness is theoretically calculated by adding energy caused by surface roughness and heat from substrate. The calculations show that the critical thickness of In0.5Ga0.5As grown on GaAs and Al0.25Ga0.75As are 3.2 ML and 3.8 ML, respectively. The theoretical calculation agrees with the experimental results. 相似文献
14.
Ning Tang Bo Shen Kui Han Xiao-Wei He Chun-Ming Yin Zhi-Jian Yang Zhi-Xin Qin Guo-Yi Zhang Tie Lin Wen-Zheng Zhou Li-Yan Shang Jun-Hao Chu 《Applied Physics A: Materials Science & Processing》2009,96(4):953-957
The subband structure and occupation in the triangular quantum well at Al
x
Ga1−x
N/GaN heterointerfaces have been investigated by means of temperature dependent Shubnikov–de Haas (SdH) measurements at low
temperatures and high magnetic fields under illumination. After the illumination of the heterostructures, the total two-dimensional
electron gas concentration increases, and the SdH oscillation amplitudes are enhanced when there is no additional subband
occupation. It is also found that the energy separation between the subbands decreases after the illumination. We suggest
that the illumination decreases the electric field and thus weakens the quantum confinement of the triangular quantum well
at Al
x
Ga1−x
N/GaN heterointerfaces. The GaN layer is thought to be the primary contributor of the excited electrons by the illumination. 相似文献
15.
Woo-Sik Jung Hyeong Uk Joo Bong-Ki Min 《Physica E: Low-dimensional Systems and Nanostructures》2007,36(2):226-230
Various β-gallium oxide (β-Ga2O3) nanostructures such as nanowire, nanobelt, nanosheet, and nanocolumn were synthesized by the thermal annealing of compacted gallium nitride (GaN) powder in flowing nitrogen. We suggest that Ga2O3 vapor might be formed by the reaction of oxygen with the gaseous Ga formed by GaN decomposition. The Ga2O3 vapor diffuses into voids derived by compacting GaN powder and is supersaturated there, resulting in the growth of Ga2O3 nanostructures via the vapor–solid (VS) mechanism. Ga2O3 plate-like hillocks and nanostructures were also grown on the surface of a c-plane sapphire placed on the GaN pellet. 相似文献
16.
研究发展了用肖特基电容电压特性数值模拟确定调制掺杂AlxGa1-xN/GaN异质结中极化电荷的方法.在调制掺杂的Al0.22Ga0.78N/GaN异质结上制备了Pt肖特基接触,并对其进行了C-V测量.采用三维费米模型对调制掺杂的Al0.22Ga0.78N/GaN异质结上肖特基接触的C-V特性进行了数值模拟,分析了改变样品参数对C-V特性的影响.利用改变极化电荷、n-AlGaN
关键词:
xGa1-xN/GaN异质结')" href="#">AlxGa1-xN/GaN异质结
极化电荷
电容电压特性
数值模拟 相似文献
17.
Daqing Xu Yimen Zhang Yuming Zhang Peixian Li Chao Wang 《Journal of magnetism and magnetic materials》2009,321(16):2442-2445
Manganese ions were implanted into unintentionally doped GaN epilayers grown by metal organic chemical vapor deposition (MOCVD). The (Ga,Mn)N and GaxMny phases were formed after Mn-implanted undoped GaN epilayers annealed at 700 and 800 °C. The samples showed ferromagnetic behavior at room temperature with the highest magnetization obtained in the sample annealed at 800 °C. Ferromagnetic signal reduces as annealing temperature increased above 900 °C. It is believed that the room-temperature ferromagnetic property of Mn-implanted undoped GaN epilayers are mainly from (Ga,Mn)N. The GaxMny phases play a critical role in providing holes and also contribute to increasing the ferromagnetic property. 相似文献
18.
S.-g. Zhu J.-j. Shi S. Zhang M. Yang Z.-q. Bao M. Zhang 《Applied physics. B, Lasers and optics》2011,104(1):105-111
In order to give an atomic level understanding of the light emission mechanism and seek In distribution patterns closely related
to the elusive electron localization centers, we optimize the crystal structure of zinc blende In
x
Ga1−x
N (0≤x≤1) alloys with different In distributions and investigate their electronic structures using first-principles calculations.
Our results show that In
x
Ga1−x
N forms a random alloy, in which several-atom In–N clusters and In–N chains can exist stably with a high concentration due
to their small formation energy. These In–N clusters and chains form more easily in zinc blende structure than in wurtzite
structure. The band gap of zinc blende In
x
Ga1−x
N alloys insensitively depends on the In distribution. Moreover, we find that both small In–N clusters and straight In–N chains
with three or more In atoms, acting as radiative recombination centers, highly localize the electrons of the valence band
maximum state and dominate the light emission of Ga-rich In
x
Ga1−x
N alloys. The strains of In
x
Ga1−x
N layers can enhance the electron localization in In
x
Ga1−x
N/GaN strained quantum wells. Our results are in good agreement with experiments and other calculations. 相似文献
19.
利用卢瑟福背散射/沟道技术和高分辨率X射线衍射技术对在Si(111)衬底上利用金属有机化合物气相外延技术(MOVPE)生长有多缓冲层的六方GaN外延膜进行结晶品质计算、晶格常数计算和应变分析. 实验结果表明:GaN外延膜的结晶品质为χmin=1.54%,已达到完美晶体的结晶品质(χmin=1%—2%);GaN外延膜的水平方向和垂直方向晶格常数分别为:aepi=0.31903nm,cepi=0.51837nm,基本达到G
关键词:
GaN
高分辨X射线衍射
卢瑟福背散射/沟道
弹性应变 相似文献
20.
Second harmonic generation coefficients of GaN and AlxGa1–xN (x=0.08) thin films deposited by MOCVD on a sapphire 0001 substrate were deduced through the standard Maker fringes method. Measurements were performed at =1064 nm using a Nd:YAG Q-Switched laser. The measured ratio between the d33 and d31 coefficients allowed one to retrieve information on the degree of crystallinity of the thin film samples that was found to be higher in thicker films. The presence of tiny oscillations in the SHG detected signal as a function of the incidence angle of the fundamental beam on the samples is discussed and related to the reflectance at the sample-air interfaces. Finally, nonlinear coefficients for three AlxGa1–xN/GaN multiple quantum well (MQW) samples (x=0.08 and x=0.15) were determined and compared to the values obtained for GaN crystalline thin films. PACS 42.65.Ky, 78.66.Fd, 78.67.De, 78.67.Pt 相似文献