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.

Luminescence spectroscopy of ion implanted AlN bulk single crystal

High concentrations of Si and Zn were implanted into (0001) AlN bulk crystal grown by the self-seeded physical vapor transport (PVT) method. Cathode luminescence (CL) and photoluminescence (PL) spectroscopy were used to investigate the defects and properties of the implanted AlN. PL spectra of the implanted AlN are dominated by a broad near-band luminescence peak between 200 and 254 nm. After high temperature annealing, implantation induced lattice damages are recovered and the PL intensity increases significantly, suggesting that the implanted impurity Si and Zn occupy lattice site of Al. CL results imply that a 457 nm peak is Al vacancy related. Resistance of the AlN samples is still very high after annealing, indicating a low electrical activation efficiency of the impurity in AlN single crystal.

Wet etching and infrared absorption of AlN bulk single crystals

The defects and the lattice perfection of an AlN (0001) single crystal grown by the physical vapor transport (PVT) method were investigated by wet etching, X-ray diffraction (XRD), and infrared absorption, respectively. A regular hexagonal etch pit density (EPD) of about 4000 cm~(-2) is observed on the (0001) A1 surface of an AlN single crystal. The EPD exhibits a line array along the slip direction of the wurtzite structure, indicating a quite large thermal stress born by the crystal in the growth process. The XRD full width at half maximum (FWHM) of the single crystal is 35 arcsec, suggesting a good lattice perfection. Pronounced infrared absorption peaks are observed at wave numbers of 1790, 1850, 2000, and 3000 cm~(-1), respectively. These absorptions might relate to impurities O, C, Si and their complexes in AlN single crystals.

多晶AlN光学性质研究

运用X射线衍射仪和拉曼光谱仪，测量了物理气相输运（PVT）方法生长的AlN多晶材料的X射线衍射和常温拉曼光谱。常温拉曼光谱研究了晶界、晶面方向与拉曼频率的关系，观察到了E和E峰位基本不随测量位置变化，与晶界无关，但是E1（TO），A1（LO）和Quasi—LO声子峰位却明显与晶界有关，为研究晶粒间、晶粒内应力提供了有效手段。

用纳米棒ZnO作模板生长无支撑的AlN纳米晶

用金属有机物气相外延在纳米棒ZnO模板上沉积AlN薄膜.SEM测试表明该薄膜形成了一种倾倒纳米棒的表面.而GIXRD测试进一步证实它是纤锌矿结构的AlN,晶粒尺度约为12nm,接近于ZnO纳米棒的直径(30nm).这意味着纳米棒结构的ZnO能限制AlN的横向生长.此外,高温下用H_2刻蚀ZnO直接在生长中实现了外延层的剥离.最终得到了无支撑的AlN纳米晶,完整无破损的区域约为1cm×1cm.定义这个生长机制为"生长-刻蚀-合并"过程.

物理气相传输法生长大尺寸AlN晶体及其性质表征

利用物理气相传输法生长了直径40～50mm、厚约8～10mm的AlN多晶锭，最大晶粒尺寸为5mm,用喇曼散射和阴极荧光谱研究了AlN晶体的结晶质量、缺陷和结构特性．分析了不同温度下AlN晶体的导电特性，并确定在AlN晶体中存在一个激活能约为0．98eV的深能级缺陷．结合这些结果分析了PVT法生长条件对AlN体单晶生长和晶体质量的影响．

升华法生长AlN体单晶初探

研究了高温升华法（PVT）生长AlN体单晶的技术和材料的性质.使用陶瓷BN坩埚,加热温度约在1900℃左右,生长结果为AlN晶须或致密多晶,难以生长出较大的AlN晶粒.用钨坩埚加热生长温度达到2200℃左右时,在AlN陶瓷片和6H-SiC片上生长了直径22mm的AlN晶体,最大的晶粒尺寸长10mm、直径5mm.利用X射线粉末衍射分析了几种不同AlN样品的结构和组成.讨论了PVT法生长AlN晶体所涉及的化学热力学过程和现象.

MOCVD-Grown AlGaN/AlN/GaN HEMT Structure with High Mobility GaN Thin Layer as Channel on SiC

AlGaN/AlN/GaN high electron mobility transistor (HEMT) structures with a high-mobility GaN thin layer as a channel are grown on high resistive 6H-SiC substrates by metalorganic chemical vapor deposition. The HEMT structure exhibits a typical two-dimensional electron gas (2DEG) mobility of 1944cm2/(V · s) at room temperature and 11588cm2/(V· s) at 80K with almost equal 2DEG concentrations of about 1.03 × 1013 cm-2 High crystal quality of the HEMT structures is confirmed by triple-crystal X-ray diffraction analysis. Atomic force microscopy measurements reveal a smooth AlGaN surface with a root-mean-square roughness of 0. 27nm for a scan area of 10μm × 10μm. HEMT devices with 0.8μm gate length and 1.2mm gate width are fabricated using the structures. A maximum drain current density of 957mA/mm and an extrinsic transconductance of 267mS/mm are obtained.

GaN／AlN组织平顶金字塔量子点的应变场分布

利用有限元法，研究了GaN／AlN自组织量子点材料的应变场分布。量子点模型采用了实验观察到的六角平顶金字塔形状，材料的弹性常数考虑了晶体材料的Wurtzite结构特性。在晶格失配处理上，采用了三维各项异性伪热膨胀模型。将基于有限元法的计算结果与简化的基于格林函数理论的解析计算结果进行了比较，验证了模型和计算结论的正确性。最后，讨论了各向异性效应对层间量子点垂直对准的影响，指出量子点材料的各向异性效应可以忽略。本文采用的模型没有采用类似解析计算的假设条件，因此在计算精度和可靠性上，要优于格林函数法。

RF-MBE生长AlN/GaN超晶格结构二维电子气材料

用射频等离子体辅助分子束外延技术（RF-MBE）在c面蓝宝石衬底上外延了高质量的GaN膜以及AlN/GaN超晶格结构极化感应二维电子气材料。所获得的掺Si的GaN膜室温电子浓度为2.2 * 10~(18)cm~(-3)，相应的电子迁移率为221cm~2/(V·s);1μm厚的GaN外延膜的（0002）X射线衍射摇摆曲线半高宽（FWHM）为7’；极化感应产生的二维电子气室温电子迁移率达到1086cm~2/(V·s)，相应的二维电子气面密度为7.5 * 10~(12)cm~(-2)。

原位合成AlN及添加钇的复合AlN粉体

以Al-Mg和Al-Mg-Y合金为原料，通入高纯度的氮气，利用原位合成法制备了AlN粉体及含烧结助剂的复合AIN粉体。合金氮化产物的组织排列疏松，有利于粉化。粉化后的AlN粉体纯度较高，含氧量为1.23%，平均粒径为6.78μm, 物相为单相AIN；复合AIN粉体物相组成为AIN主相与稀土钇的氧化物烧结助剂Y2O3相。粒径分布曲线呈双峰现象，从提高粉体的充填系数角度考虑，具有这种粒径分布的粉体有利于烧结致密化。

Ti-AlN快速退火的界面

国家自然科学基金

Ti薄膜与AlN陶瓷的界面反应

用X射线衍射分析、二次离子质谱、卢瑟福背散射谱、俄歇电子能谱等表面分析技术，研究了Ti膜与AlN陶瓷衬底的界面固相反应。在高真空中用电子束蒸发的方法在抛光的200℃AlN陶瓷衬底上淀积200nm的Ti膜，并在真空恒温炉中退火。实验表明，退火中Ti膜与AlN界面发生了扩散与反应。650℃，1h退火已观测到明显的界面反应。界面反应产物主要是钛铝化物及Ti-N化合物。铝化物是Ti-Al二元化合物和Ti-Al-N三元化合物，850℃,4h退火后则主要由Ti_2AlN组成。

AlN陶瓷基板在空气中的热氧化行为探讨

利用二次离子质谱(SIMS)并结合X-射线衍射分析(XRD)研究了AlN陶瓷基板在850-1100℃空气中退火时的初始氧化行为。结果表明, 未退火AlN陶瓷基板表面区存在很薄的富氧层。在退火10min的条件下, 随着退火温度的增加, 富氧层迅速增厚。在1100℃退火20min的条件下, AlN陶瓷基板表面区有连续的氧化层生成。最后, 结合化学热力学, 探讨了AlN陶瓷基板表面的初始氧化机理。