Low energy electron excited nanoscale luminescence spectroscopy of erbium doped AIN

We have investigated the optical activity of Er³⁺ ions in AlN via depth-resolved, (5 nm to 250 nm), low energy electron-excited nanoscale (LEEN) luminescence spectroscopy and compared it with the luminescence of an Er-free AlN film. For the Er-free film, there was no emission in the IR from the AlN at any depth, and at higher energies we measured only a broad, weak feature between 1.7–3.25 eV along with an O defect related feature at 3.8 eV, which is significantly enhanced toward the surface. We found strong emission in the AlN:Er films from the first excited → ground state transition of Er³⁺ at 0.80 eV along with many other excited state transitions, although the features are broad compared to those of GaN:Er. The AlN:Er luminescence saturates near a concentration of 10²¹ cm⁻³, at which point we also observe enhanced O defect related luminescence uniformly distributed throughout the film. This finding suggests a role for O in activating the Er at low Er concentrations, while inhibiting the Er activity at high O concentrations.     

The properties of annealed AlN films deposited by pulsed laser deposition

AlN films deposited on SiC or sapphire substrates by pulsed laser deposition were annealed at 1200°C, 1400°C, and 1600°C for 30 min in an inert atmosphere to examine how their structure, surface morphology, and substrate-film interface are altered during high temperature thermal processing. Shifts in the x-ray rocking curve peaks suggest that annealing increases the film density or relaxes the films and reduces the c-axis Poisson compression. Scanning electron micrographs show that the AlN begins to noticeably evaporate at 1600°C, and the evaporation rate is higher for the films grown on sapphire because the as-deposited film contained more pinholes. Rutherford backscattering spectroscopy shows that the interface between the film and substrate improves with annealing temperature for SiC substrates, but the interface quality for the 1600°C anneal is poorer than it is for the 1400°C anneal when the substrate is sapphire. Transmission electron micrographs show that the as-deposited films on SiC contain many stacking faults, while those annealed at 1600°C have a columnar structure with slightly misoriented grains. The as-deposited films on sapphire have an incoherent interface, and voids are formed at the interface when the samples are annealed at 1600°C. Auger electron spectroscopy shows that virtually no intermixing occurs across the interface, and that the annealed films contain less oxygen than the as-grown films.     

氮化铝薄膜的低温沉积

介绍了一种 ECR微波放电和脉冲激光沉积相结合低温沉积 Al N薄膜的新方法 .在 ECR氮等离子体环境中用脉冲激光烧蚀 Al靶 ,以低于 80℃的衬底温度在 Si衬底上沉积了 Al N薄膜 .结合样品表征和等离子体光谱分析 ,探讨了膜层沉积的机理 ,等离子体中活性氮物质的存在是 Al- N化合的重要因素 ,等离子体对衬底的辐照促进膜层的形成     

Controlled growth and field emission of vertically aligned AlN nanostructures with different morphologies

The controllable growth of three different morphologies of AlN nanostructures (nanorod, nanotip and nanocrater) arrays are successfully realized by using chemical vapour deposition (CVD) technology. All three nanostructures are of single crystal h-AlN with a growth orientation of [001]. Their growth is attributed to the vapour-liquid-solid (VLS) mechanism. To investigate the factors affecting field emission (FE) properties of AlN nanostructures, we compare their FE behaviours in several aspects. Experimental results show that AlN nanocrater arrays possess the best FE properties, such as a threshold field of 7.2~V/μm and an emission current fluctuation lower than 4%. Moreover, the three AlN nanostructures all have good field emission properties compared with a number of other excellent cathode nanomaterials, which suggests that they are future promising FE nanomaterials.     

Thick GaN layers on sapphire with various buffer layers

Thick GaN layers deposited in HVPE system on composite substrates made on sapphire substrates in Metalorganic Vapour Phase Epitaxy (MOVPE) system have been investigated. The following substrates were used: (00.1) sapphire substrates with AlN, AlN/GaN and GaN thin layers. The crystallographic structure and the quality of the epitaxial thick GaN layers were determined. Comparison of the three types of thick layers was performed. Significant differences were observed. It was found that thick GaN deposited on the simplest MOVPE‐GaN/sapphire composite substrate has comparable structure's properties as the other, more complicated. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

5d过渡金属原子掺杂氮化铝纳米管电子结构、磁性性质的第一性原理计算

采用基于密度泛函理论(DFT)的第一性原理计算方法, 研究了5d过渡金属原子(Lu、Hf、Ta、W、Re、Os、Ir、Pt、Au、Hg)取代AlN纳米管(AlNNTs)中的铝原子或氮原子时体系的几何结构、电子结构和磁性性质; 并且以理想AlN纳米管(AlNNTs)、Al缺陷体系(VAl)和N缺陷体系(VN)的结果作为对比. 研究发现: 5d 原子取代Al(Al5d)时体系的局域对称性接近于C3v, 但是取代N(N5d)时体系的局域对称性偏离C3v对称性较大; 当掺杂的5d元素相同时, Al5d的成键能比N5d的成键能大; 当掺杂体系相同时(Al5d或N5d), 其成键能基本上随着5d原子的原子序数的增大而降低; 掺杂体系中出现了明显的杂质能级, 给出了态密度等结果; 不同掺杂情况的磁矩不同, 总磁矩呈现出较强的规律性. 利用C3v对称性和分子轨道理论解释了过渡金属原子取代Al时杂质能级的产生和体系磁性的变化规律.     

相变及空位缺陷对AlN在高压下光学性质的影响

采用基于密度泛函理论(DFT)的第一性原理方法, 计算了AlN理想晶体和含铝、氮空位点缺陷晶体在100 GPa压力范围内的光学性质. 波长在532 nm处的折射率计算结果表明：AlN从纤锌矿结构相转变为岩盐矿结构相将导致其折射率增加; 铝空位缺陷将引起AlN岩盐矿结构相的折射率增大, 而氮空位缺陷却导致其折射率降低. 能量损失谱计算数据指明：结构相变使得AlN能量损失谱蓝移、主峰峰值强度增强;铝和氮空位缺陷将导致AlN岩盐矿结构相的能量损失谱主峰进一步蓝移、峰值强度再次增强. 计算预测的结果将为进一步的实验探究提供理论参考.     

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。     

Influence of AlN buffer layer thickness on structural properties of GaN epilayer grown on Si (111) substrate with AlGaN interlayer

We present the growth of GaN epilayer on Si (111) substrate with a single AlGaN interlayer sandwiched between the GaN epilayer and AlN buffer layer by using the metalorganic chemical vapour deposition. The influence of the AlN buffer layer thickness on structural properties of the GaN epilayer has been investigated by scanning electron microscopy, atomic force microscopy, optical microscopy and high-resolution x-ray diffraction. It is found that an AlN buffer layer with the appropriate thickness plays an important role in increasing compressive strain and improving crystal quality during the growth of AlGaN interlayer, which can introduce a more compressive strain into the subsequent grown GaN layer, and reduce the crack density and threading dislocation density in GaN film.     

The physical process analysis of the capacitance-voltage characteristics of AlGaN/AlN/GaN high electron mobility transistors

This paper deduces the expression of the Schottky contact capacitance of AlGaN/AlN/GaN high electron mobility transistors (HEMTs), which will help to understand the electron depleting process. Some material parameters related with capacitance-voltage profiling are given in the expression. Detailed analysis of the forward-biased capacitance has been carried on. The gate capacitance of undoped AlGaN/AlN/GaN HEMT will fall under forward bias. If a rising profile is obviously observed, the donor-like impurity or trap is possibly introduced in the barrier.