Construction of Basic Physics Laboratory for the Next Century

根据物理基础实验室的现状和任务，本文介绍了在体制、制度、人员、课程、设备、环境等方面，为建立面向新世纪实验室所进行的一系列整顿和改革，收到较好的效果On the basis of present conditions and missions, we have straightened out and reconstructed the organization system, institutions, staves, courses, instruments, environment, and so on of our basic physics laboratory for the next century.The reform results turned out to be well

Microscopic origin of light emission in Al_yGa_{1-y}N/GaN superlattice: Band profile and active site

We present first-principles calculations of AlGaN/GaN superlattice, clarifying the microscopic origin of the light emission and revealing the effect of local polarization within the quantum well. Profile of energy band and distributions of electrons and holes demonstrate the existence of a main active site in the well responsible for the main band-edge light emission. This site appears at the position where the local polarization becomes zero. With charge injection, the calculated optical spectra show that the broadening of the band gap at the active site leads to the blueshift of emission wavelength

Polarization effect on p-type doping efficiency in Mg-Si codoped wurtzite GaN from first-principles calculations

The electronic structures of two Mg-Si codoped configurations in wurtzite GaN were calculated by an ab initio "mixed-basis + norm conserving nonlocal pseudopotential" method. The results show that the charge densities redistribute and concentrate in the N-Mg bonds for the configuration with a local polarized field component that strengthens the polarizability. The tops of the valence bands are thus split widely and shifted up towards the conduction band. The N atoms bonding to the Mg atom are found to be as important as the Mg atom for the formation of the tops of the valence band. These electronic structure shifts can enhance the hole concentration about 10(3) times higher than that of Mg-doped GaN

The structural properties of wurtzite and rocksalt MgxZn1-xO

A first principles calculation is used to simulate the variation of the lattice constant, structure, induced charge-density difference, total energy, and band gap of the hexagonal and cubic MgZnO semiconductor alloys with different MgO mole fractions. The calculated results show that the lattice constant and the ratio c/a of the hexagonal Mg(x)Zn(1-x)O diminish as the MgO mole fraction is increased, which results in the structure gradually deviating from the wurtzite structure. The angle between the nearest neighbor Zn-O bonds is larger than that between the nearest neighbor Mg-O bonds. The total energy of the hexagonal alloys is lower than, equal to, and larger than that of the cubic one in the lower MgO mole fraction, the MgO mole fraction with 0.69, and the higher MgO mole fraction, respectively. The phase transition is likely to occur as the MgO mole fraction is increased. The crystal structure will become unstable as temperature is raised to a critical value for the different MgO mole fractions no matter what kind the structure is. The band gaps of the hexagonal and cubic Mg(x)Zn(1-x)O alloys are the direct type and widen as the MgO mole fraction is increased, which demonstrates that both the structures of the Mg(x)Zn(1-x)O alloys are suitable for fabricating the short wavelength devices

Modulation of band structure in wurtzite ZnO via site-selective Ga-N codoping

We investigated the electronic structures of two Ga-N codoping isoelectronic configurations in wurtzite ZnO by means of first-principles calculations. The calculated total energies show that both the isoelectronic configurations are stable in ZnO. This result is attributable to the strong hybridization between the Ga 3d and N 2p states. The polarization is significantly changed and the top of the valence band is substantially split up towards the conduction band in a site-selective isoelectronic configuration, which causes a reduction of the activation energy of the N related acceptor and thus enhances the hole concentration by more than three orders of magnitude

INFLUENCE of DEFECTS ON THE OPTICAL PROPERTIES of GaN EPILAYERS

用金属有机化合物气相外延（MOVEP）方法生长具有不同表面形貌的非掺杂gAn，并对部分样品的外延层表面进行镜面加工.用阴极射线发光、光散射和拉曼散射方法观察gAn中深能级发光、缺陷散射光分布和拉曼散射光频移.结果表明，缺陷不但影响gAn的发光和光散射，而且影响拉曼频移Undoped GaN epilayers with different surface morphologies were grown by MOVPE, and surfaces of part of epilayers were polished.Luminescence distribution of deep levels, scattering light of defects, and Raman shift were measured by cathodoluminescence, light scattering, and Raman scattering, respectively.The results show that the defects in GaN epilayers influence not only on the luminescence and light scattering properties but also on the Raman shifts.国家自然科学基金;福建省自然科学基

Defects in ⅢNitrides Epilayers

【中文摘要】 采用光荧光和阴极荧光方法 ,对 Ga N外延层中的黄色和蓝色发光进行测量分析 ;同时 ,采用原子力显微镜、扫描电镜及其能谱测量外延层中的缺陷。结果表明 ,黄色和蓝色发光与残留杂质有关。采用第一原理计算结果显示 ,残留 C、O杂质、本征缺陷等是黄色和蓝色的可能物理起源。采用原子力显微镜、扫描电镜、透射电镜及其能谱对 Ga N/Al Ga N异质结中的纳米管进行观测 ,了解了纳米管的形貌。结果表明 ,构成纳米管的小面可能是外延过程中表面吸附引起的 ;计算结果显示 ,纳米管形貌变化与 Ga N/Al Ga N界面处晶格失配应力有关。采用透射电镜观察外延层中沉积物及其周围位错的结构表明 ,沉积物附近应力的存在是位错产生的主要原因 【英文摘要】 Blue and yellow luminescence bands in undoped GaN epilayers were investigated and related to main residual C and O impurities by photoluminescence, which are suggested to be attributable to the electron transitions from O N states to V Ga states and between the inner levels of the C N O N complex, respectively, according to ab initio local density functional calculations. Larger nanopipes in undoped GaN/AlGaN hetero epilayers were imaged as dodecagonal pyramidal indentations, using atomic fo...国家重点基础研究发展规划项目 (批准号 :001CB610505 );国家自然科学基金 (批准号 :69976023、90206030、10134030 );福建省自然 科学基金 (批准号 :A0020001);教育部部分资助项

Adsorption/desorption and electrically controlled flipping of ammonia molecules on graphene

In this paper, we evaluate of the adsorption/ desorption of ammonia molecules on a graphene surface by studying the Fermi level shift. Based on a physically plausible model, the adsorption and desorption rates of ammonia molecules on graphene have been extracted from the measured Fermi level shift as a function of exposure time. An electric field-induced flipping behavior of ammonia molecules on graphene is suggested, based on field effect transistor (FET) measurements

Structural design of communication filters using two-dimensional photonic crystals with defect modes

采用平面波展开法分别模拟设计了理想和带有点缺陷与线缺陷的二维光子晶体能带结构;进一步构建具有点缺陷和线缺陷联合结构滤波器,通过改变介质折射率、介质柱半径和背景材料折射率,使点缺陷的滤波中心波长处于光子晶体禁带中的1.31和1.55μm两个主要通迅波长.同时,采用时域有限差分算法模拟滤波器的传播和滤波频谱特性,结果显示,该结构滤波器的滤波频谱中心波长刚好分别位于1.31和1.55μm,透射峰尖锐,显现出优良的滤波特性.The band structures of 2D photonic crystals without and with point and line defects were simulated using plane wave expansion method.By calculating different index and radius of lattices,the 2D photonic crystal structures combining a point and a line defects were successfully designed to have modes in 1.31 and 1.55μm.The optical transmission and leaching characteristics of the designed structures were simulated by finite-difference time-domain(FDTD) method.The results show that the leaching spectra are shape and centered at 1.31 and 1.55μm,respectively,which suggests the designed structures are good to apply to the communication filters.“863”计划资助项目(2006AA03A110);; 基础科研资助项目(A1420060155);; 国家自然科学基金资助项目(60336020);; 厦门市科技计划资助项目(3502Z20063001

Core structures of the decorate edge dislocations in GaN epilayers

Threading dislocations with edge components were investigated by a high-resolution transmission electron microscope in undoped GaN epilayers grown on Al2O3 substrates. Two types of core images were observed. One is a fully filled core with regular contraction and expansion of diffraction bright dots and the other is incompletely filled with one bright dot less and irregular contraction and expansion of bright dots. The impurities around the cores were detected to contain oxygen and carbon elements by energy-dispersive x-ray spectrometer. This suggests that both types of dislocations be decorated with impurities