Influence of optical phonons on the electronic mobility in a strained wurtzite AlN/GaN heterojunction under hydrostatic pressure

also indicate that scattering from half space phonon modes in the channel side plays a dominant role in mobility.     

金属有机化学气相沉积法生长条件对AlN薄膜面内晶粒尺寸的影响

研究了金属有机化学气相沉积设备生长条件对AlN 薄膜质量的影响. 应用Williamson-Hall方法测试并分析了不同氮化时间、AlN缓冲层生长时间、 载气流量生长参数对AlN薄膜的面内晶粒尺寸的影响. 实验结果表明, 随着氮化时间减小, 缓冲层生长时间增加, 载气流量减少, AlN薄膜的侧向生长和岛的合并能力增强, 面内晶粒尺寸增大, 从而晶体质量也变好. 关键词： AlN Williamson-Hall 面内晶粒尺寸     

Unusual nucleation and growth of γ′ iron nitride upon nitriding Fe–4.75 at.% Al alloy

The influence of substitutionally dissolved Al in ferritic Fe–4.75 at.% Al alloy on the nucleation and growth of γ′ iron nitride (Fe₄N_{1? x} ) was investigated upon nitriding in NH₃/H₂ gas mixtures. The nitrided specimens were characterised employing optical microscopy, scanning electron microscopy, transmission electron microscopy, electron probe microanalysis and X-ray diffraction. As compared to the nitriding of pure ferrite (α-Fe), where a layer of γ′ develops at the surface, upon nitriding ferritic Fe–4.75 at.% Al an unusual morphology of γ′ plates develops at the surface, which plates deeply penetrate the substrate. In the diffusion zone, nano-sized precipitates of γ′ and of metastable, cubic (NaCl-type) AlN occur, having, with the ferrite matrix, a Nishiyama–Wassermann orientation relationship and a Bain orientation relationship, respectively. The γ′ plates contain a high density of stacking faults and fine ε iron nitride (Fe₂N_{1? z} ) precipitates, although the formation of ε iron nitride is not expected for the employed nitriding parameters. On the basis of dedicated nitriding experiments it is shown that the unusual microstructural development is a consequence of the negligible solubility of Al in γ′ and the obstructed precipitation of the thermodynamically stable, hexagonal (wurtzite-type) AlN in ferrite.     

高温AlN为模板的AlGaN基p-i-n背照式日光盲探测器

第一次报道了以高温AlN为模板层的AlGaN基p-i-n背照式日光盲探测器的制作和器件特性.利用MOCVD方法在(0001)面的蓝宝石衬底上生长了探测器的AlxGa1-xN多层外延材料.在无需核化层的高温AlN模板上生长了p-i-n背照式日光盲探测器的无裂纹高Al组分(0.7)AlGaN多层外延结构.利用在线反射监测仪、三轴X射线衍射及原子力显微镜表征了外延材料的晶体质量.在1.8V的反向偏压下,制作的探测器表现出了日光盲响应特性,在270nm处最大响应度为0.0864A/W.具有约3.5V的正向开启电压,大于20V的反向击穿电压,在2V的反向偏压下暗电流小于20pA.     

The profile of temperature and voltage dependent series resistance and the interface states in (Ni/Au)/Al0.3Ga0.7N/AlN/GaN heterostructures

The temperature dependence of capacitance-voltage (C-V) and the conductance-voltage (G/w-V) characteristics of (Ni/Au)/Al_0.3Ga_0.7N/AlN/GaN heterostructures were investigated by considering the effect of series resistance (R_s) and interface states N_ss in a wide temperature range (79-395 K). Our experimental results show that both R_s and N_ss were found to be strongly functional with temperature and bias voltage. Therefore, they affect the (C-V) and (G/w-V) characteristics. The values of capacitance give two peaks at high temperatures, and a crossing at a certain bias voltage point (∼3.5 V). The first capacitance peaks are located in the forward bias region (∼0.1 V) at a low temperature. However, from 295 K the second capacitance peaks appear and then shift towards the reverse bias region that is located at ∼−4.5 V with increasing temperature. Such behavior, as demonstrated by these anomalous peaks, can be attributed to the thermal restructuring and reordering of the interface states. The capacitance (C_m) and conductance (G/w-V) values that were measured under both reverse and forward bias were corrected for the effect of series resistance in order to obtain the real diode capacitance and conductance. The density of N_ss, depending on the temperature, was determined from the (C-V) and (G/w-V) data using the Hill-Coleman Method.     

AlN/Si3N4纳米多层膜的外延生长与力学性能

采用射频磁控溅射方法制备单层AlN, Si₃N₄薄膜和不同调制周期的AlN/Si₃N₄纳米多层膜.采用X射线衍射仪、高分辨透射电子显微镜和纳米压痕仪对薄膜进行表征.结果发现,多层膜中Si₃N₄层的晶体结构和多层膜的硬度依赖于Si₃N₄层的厚度.当AlN层厚度为4.0nm、 Si₃N₄层厚度 关键词： 3N₄纳米多层膜')" href="#">AlN/Si₃N₄纳米多层膜 外延生长 应力场 超硬效应     

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。     

双靶磁控溅射聚焦共沉积AlN薄膜生长速率研究

采用直流双靶磁控溅射聚焦共沉积技术在Fe衬底上高速率生长A lN薄膜,结果表明,双靶共沉积技术有效地提高了A lN薄膜生长速率,相同工作气压或低N2浓度时双靶磁控溅射沉积速率约为单靶沉积速率的2倍;随着溅射系统内工作气压或N2浓度的升高,薄膜生长速率不断减小;薄膜择优取向与薄膜生长速率相互影响,随着工作气压的升高,(100)晶面的择优生长减缓了薄膜生长速率的降低,随着N2浓度的升高,(002)晶面的择优生长加剧了薄膜生长速率的降低,而相对较低的溅射沉积速率有利于(002)晶面择优取向生长。     

Structural Stabilization and Piezoelectric Enhancement in Epitaxial (Ti1−xMgx)0.25Al0.75N(0001) Layers

Epitaxial (Ti_1?xMg_x)_0.25Al_0.75N(0001)/Al₂O₃(0001) layers are used as a model system to explore how Fermi‐level engineering facilitates structural stabilization of a host matrix despite the intentional introduction of local bonding instabilities that enhance the piezoelectric response. The destabilizing octahedral bonding preference of Ti dopants and the preferred 0.67 nitrogen‐to‐Mg ratio for Mg dopants deteriorate the wurtzite AlN matrix for both Ti‐rich (x < 0.2) and Mg‐rich (x ≥ 0.9) alloys. Conversely, x = 0.5 leads to a stability peak with a minimum in the lattice constant ratio c/a, which is caused by a Fermi‐level shift into the bandgap and a trend toward nondirectional ionic bonding, leading to a maximum in the expected piezoelectric stress constant e₃₃. The refractive index and the subgap absorption decrease with x, the optical bandgap increases, and the elastic constant along the hexagonal axis C₃₃ = 270 ± 14 GPa remains composition independent, leading to an expected piezoelectric constant d₃₃ = 6.4 pC N^?1 at x = 0.5, which is 50% larger than for the pure AlN matrix. Thus, contrary to the typical anticorrelation between stability and electromechanical coupling, the (Ti_1?xMg_x)_0.25Al_0.75N system exhibits simultaneous maxima in the structural stability and the piezoelectric response at x = 0.5.