DIFFERENT INTERDIFFUSION CHARACTERISTICS BETWEEN AG/YBA2CU3O7-X AND AL/YBA2CU3O7-X CONTACT INTERFACES

The differences between the interdiffusion characteristics of Ag/YBa2Cu3O7-x and Al/YBa2Cu3O7-x contact interfaces have been revealed by secondary ion mass spectrometry (SIMS). The different electrical properties of Ag/YBa2Cu3O7-x and YBa2Cu3O7-x films after high temperature treatment are well understood by the SIMS results.

分子束外延生长的n型Al掺杂ZnS_(1-x)Te_x深中心研究

应用电容-电压、光致荧光和深能级瞬态谱技术研究了分子束外延生长的n型Al掺杂ZnS_(1-x)Te_x外延层深中心。Al掺杂ZnS_(0.977)Te_(0.023)的光致荧光强度明显低于不掺杂的ZnS_(0.977)Te_(0.023),这表明一部分Al原子形成非辐射深中心。Al掺杂ZnS_(1-x)Te_x(x=0,0.017,0.04和0.046)的深能级瞬态傅里叶谱表明，Al引进导带下的0.21和0.39eV电子陷阱，Te除了作为材料合金的成分和等电子中心外，还涉及到一个电子陷阱的形成，其相对导带的能级位置随Te组分增加而减小。实验结果还表明仅有少量掺杂的Al原子形成非辐射中心，这说明Al对于Te组分范围内(x≤0.046)的ZnS_(1-x)Te_x外延层的确是一种非常好的施主杂质。

Growth of crack-free GaN films on Si(111) substrate by using Al-rich AlN buffer layer

GaN epilayers were grown on Si(111) substrate by metalorganic chemical vapor deposition. By using the Al-rich AlN buffer which contains Al beyond stoichiometry, crack-free GaN epilayers with 1 mum thickness were obtained. Through x-ray diffraction (XRD) and secondary ion mass spectroscopy analyses, it was found that a lot of Al atoms have diffused into the under part of the GaN epilayer from the Al-rich AlN buffer, which results in the formation of an AlxGa1-xN layer at least with 300 nm thickness in the 1 mum thick GaN epilayer. The Al fraction x was estimated by XRD to be about 2.5%. X-ray photoelectron spectroscopy depth analysis was also applied to investigate the stoichiometry in the Al-rich buffer before GaN growth. It is suggested that the underlayer AlxGa1-xN originated from Al diffusion probably provides a compressive stress to the upper part of the GaN epilayer, which counterbalances a part of tensile stress in the GaN epilayer during cooling down and consequently reduces the cracks of the film effectively. The method using the Al diffusion effect to form a thick AlGaN layer is really feasible to achieve the crack-free GaN films and obtain a high crystal quality simultaneously. (C) 2004 American Institute of Physics.

RF-MBE Grown AlGaN/GaN HEMT Structure with High Al Content

A Si doped AlGaN/GaN HEMT structure with high Al content (x= 44%) in the barrier layer is grown on sapphire substrate by RF-MBE. The structural and electrical properties of the heterostructure are investigated by the triple axis X-ray diffraction and Van der Pauw-Hall measurement, respectively. The observed prominent Bragg peaks of the GaN and AlGaN and the Hall results show that the structure is of high quality with smooth interface.fabricated and characterized. Better DC characteristics, maximum drain current of 1.0A/mm and extrinsic transconductance of 218mS/mm are obtained when compared with HEMTs fabricated using structures with lower Al mole fraction in the AlGaN barrier layer. The results suggest that the high Al content in the AlGaN barrier layer is promising in improving material electrical properties and device performance.

Polaron effects on the optical absorptions in asymmetrical semi-parabolic quantum wells

The linear and nonlinear optical absorptions considering the weak-coupling electron-LO-phonon interaction in asymmetrical semiparabolic quantum wells are theoretically investigated. The numerical results for the typical GaAs/AlxGa1-xAs material show that the factors of Al content x, the relaxation time and the photon energy have great influence on the optical absorption coefficients. Moreover, the theoretical values of the optical absorptions are more than a factor of 2-3 higher than the one in the structure without considering the electron-LO-phonon interaction by calculating. (C) 2007 Elsevier B.V. All rights reserved.

化学法高效载体钛催化剂的乙烯/α-烯烃共聚合

研究了化学反应催化剂制备及其乙烯/α-烯烃共聚反应规律与机理，探讨了共聚活性增大的原因，提出了α烯烃存在下活性中心浓度增大这一基本论点，并对所得共聚物进行了表征。用WAXD、IR等方法研究了化学反应催化剂制备过程，结果表明原料MgCl_2、n-BuOH、i-Bu_3 Al、TiCl_4之间通过①醇解②解醇③载钛，三步反应最后得到了活性组分高度分散在X射线衍射无定形的MgCl_2微晶上而形成的高效载体催化剂。讨论其乙烯/α-烯烃共聚合的基本规律。提出了α-烯烃促进共聚速率较乙烯均聚速率增大这一实验结果。动力学研究结果表明，催化剂系的非均匀性和多活性中心的存在及α-烯烃分子使活性中心浓度增大是共聚速率增大的根本原因。催化体系及其聚合过程的ESCA与ESR研究 证明了α-烯烃存在下催化活性中心浓度的增大，并得出了ESR信号所反应的Ti~3离子中，也有没有活性的Ti~3离子。同时ESR还从乙烯与乙烯/丙烯共聚合不同的共振吸收峰提出了多活性中心存在的初步证据。从不同侧面探讨了多活性中心存在的证据。指出酯不仅可影响共聚反应的催化效率，而且可以影响共聚物的组成及序列分布。共聚物的形态随α-烯烃加入逐渐变为非晶性无定形。不同α-烯烃对共聚物结晶性能有显著影响。不同α-烯烃共聚物具有不同的临界结晶序列长度。乙烯/丙烯/辛烯三无共聚合催化效率比乙烯/丙烯及乙烯/辛烯二元共聚全催化效率进一步增大，反映了α-烯烃促活作用具有迭加性。从取代基效应理论求得了乙烯/丙烯和乙烯/辛烯共聚物取代基效应参数，以很好地对其~(13)C NMR谱图进行归属。成功地对乙烯/丙烯/辛烯三元共聚物~(13)C NMR结果进行了处理，并指出了文献中的两处错误。

Electronic properties of zinc-blende GaN, AlN, and their alloys Ga1-xAlxN

The electronic properties of wide-energy gap zinc-blende structure GaN, A1N, and their alloys Ga(1-x)A1(x)N are investigated using the empirical pseudopotential method. Electron and hole effective mass parameters, hydrostatic and shear deformation potential constants of the valence band at Gamma and those of the conduction band at Gamma and X are obtained for GaN and AIN, respectively. The energies of Gamma, X, L conduction valleys of Ga(1-x)A1(x)N alloy versus Al fraction x are also calculated. The information will be useful for the design of lattice mismatched heterostructure optoelectronic devices based on these materials in the blue light range application. (C) 1995 American Institute of Physics.

Band structure parameters of zinc-blende GaN, AlN and their alloys Ga1-xAlxN

The electronic properties of wide energy gap zinc-blende structure GaN, AlN and their alloys Ga1-xAlxN are investigated using the empirical pseudopotential method. Electron and hole Effective mass parameters, hydrostatic and shear deformation potential constants of the valence band at Gamma and those of the conduction band at Gamma and X are obtained. The energies of Gamma, X, L conduction valleys of Ga1-xAlxN alloy versus Al fraction x are also calculated. The information will be useful for the design of lattice mismatched heterostructure optoelectronic devices in the blue light range.

~(40)Ar~(16+)入射金属表面的近红外光谱线发射

速度小于Bohr速度(vBhor=2.9×106m/s)的高电荷态离子40Ar16+(动能EK=150keV,速度v=8.5×105m/s)入射金属(Ni,Mo,Au和Al)表面,同时测量产生的Ar原子近红外光谱线和X射线谱.实验结果表明,低速高电荷态离子在金属表面俘获电子中性化,形成多激发态的Ar空心原子,空心原子退激辐射从近红外光谱线到X射线波段谱线,近红外光谱线辐射强度说明,低速高电荷态离子在金属表面中性化过程中,金属的功函数起着重要作用,进而验证了经典过垒模型.

非完全深部非弹的简单模型分析 多参数大面积电离室

根据~(16)O+~(27)AL反应α粒子和类弹碎片符合实验中的一些特殊现象，提出了一个弹核先碎裂，然后碎裂余核与靶核进一步发生深部非弹的非完全深部非弹模型，计算的结果和实验的能谱，角分布和维率斯基图进行了对比和分析。 多参数大面积电离室结合放在电离室前的PPAC，能对重离子反应产物进行全运动学参数测量（x,y,A,Z,E），本工作进行了这种探测器的制做和测试，用PLO气体在气压的290mbar下，对Thc-α粒子，电离室ΔE_1,ΔE_2,ΔE_3,ΔE_4及E_k得到的分辩为6.1%、5.7%、4.8%、4.6%及1.5%。对252cf源，y位置分辩为3.65mm，另外还设计，制做和测试了螺旋阴极位置灵敏正比室探测量，其位置分辩为0.94mm、ΔE分辩为16%，并对这种探测器进行电离室x位置测量的可能性进行了探讨

Change of the dominant luminescent mechanism with increasing current density in molecularly doped organic light-emitting devices

We have fabricated and measured a series of electroluminescent devices with the structure of ITO/TPD/Eu(TTA)(3)phen (x):CBP/BCP/ ALQ/LiF/Al, where x is the weight percentage of Eu(TTA)3phen (from 0% to 6%). At very low current density, carrier trapping is the dominant luminescent mechanism and the 4% doped device shows the highest electroluminescence (EL) efficiency among all these devices. With increasing current density, Forster energy transfer participates in EL process. At the current density of 10.0 and 80.0mA/ cm(2), 2% and 3% doped devices show the highest EL efficiency, respectively. From analysis of the EL spectra and the EL efficiency-current density characteristics, we found that the EL efficiency is manipulated by Forster energy transfer efficiency at high current density. So we suggest that the dominant luminescent mechanism changes gradually from carrier trapping to Forster energy transfer with increasing current density. Moreover, the conversion of dominant EL mechanism was suspected to be partly responsible for the EL efficiency roll-off because of the lower EL quantum efficiency of Forster energy transfer compared with carrier trapping.

First-principles study of p-type transparent conductive oxides CuXO2 (X=Y, Sc, and Al)

Using first-principles methods we have calculated electronic structures, optical properties, and hole conductivities of CuXO2 (X=Y, Sc, and Al). We show that the direct optical band gaps of CuYO2 and CuScO2 are approximately equal to their fundamental band gaps and the conduction bands of them are localized. The direct optical band gaps of CuXO2 (X=Y, Sc, and Al) are 3.3, 3.6, and 3.2 eV, respectively, which are consistent with experimental values of 3.5, 3.7, and 3.5 eV. We find that the hole mobility along long lattice c is higher than that along other directions through calculating effective masses of the three oxides. By analyzing band offset we find that CuScO2 has the highest valence band maximum (VBM) among CuXO2 (X=Y, Sc, and Al). In addition, the approximate transitivity of band offset suggests that CuScO2 has a higher VBM than CuGaO2 and CuInO2 [Phys. Rev. Lett. 88, 066405 (2002)]. We conclude that CuScO2 has a higher p-type doping ability in terms of the doping limit rule. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2991157]

Comparison of valence band x-ray photoelectron spectrum between Al-N-codoped and N-doped ZnO films

The valence band structures of Al-N-codoped [ZnO:(Al, N)] and N-doped (ZnO:N) ZnO films were studied by normal and soft x-ray photoelectron spectroscopy. The valence-band maximum of ZnO:(Al, N) shifts up to Fermi energy level by about 300 meV compared with that of ZnO:N. Such a shift can be attributed to the existence of a kind of Al-N in ZnO:(Al, N), as supported by core level XPS spectra and comparison of modified Auger parameters. Al-N increased the relative quantity of Zn-N in ZnO:(Al, N), while N-N decreased that of Zn-N in ZnO:N. (c) 2006 American Institute of Physics.