Growth of high-quality thick GaN using a tungsten interlayer

A high-quality GaN film was (W-GaN) grown by hydride vapor phase epitaxy (HVPE) on metalorganic chemical vapor deposition (MOCVD) GaN templates with a tungsten (W) interlayer.A sample without interlayer was also grown at the same time for comparison.Significant reductions of dislocation density in W-GaN film is confirmed by the result of high-resolution X-ray diffraction and transmission electron microscope (TEM) observation.The improvement of optical properties of the W-GaN is confirmed by photoluminescence (PL) result.A shift of PL peak suggests that the strain is lower in the W-GaN than the film without W interlayer.This technique offers a potential path to obtain high-quality GaN film as free-standing substrate.     

Effect of AlN intermediate layer on growing GaN film by hydride vapor phase epitaxy

Thick GaN layer deposited by hydride vapor phase epitaxy (HVPE) on a metalorganic chemical vapor deposition (MOCVD) GaN template with a thin low temperature (LT) AlN intermediate layer was investigated.High resolution X-ray resolution diffraction (HRXRD) shows that the crystalline quality of thick GaN layer was improved compared with the template.As confirmed by atomic force microscopy (AFM) observations, the surface morphology of AlN intermediate layer helps to improve the nucleation of GaN epilayer.Photoluminescence (PL) spectra measurement shows its high optical quality and low compressive stress, and micro Raman measurement confirms the latter result.Thus, the deposition of the LT-AlN interlayer has promoted the growth of an HVPE-GaN layer with an excellent crystalline quality.     

自支撑GaN厚膜制备及其光学性能研究

采用镀Ti插入层在氢化物外延设备中制备了高质量自支撑GaN厚膜。X射线衍射测试发现(0002)峰摇摆曲线的半高宽为260 arcsec;5 K下样品带边发光峰的半高宽为3 meV,室温下样品的带边发光峰也只有20 meV,并且在室温的PL谱中观察不到黄光带;扫描电子显微镜观察显示,腐蚀后的自支撑GaN厚膜表面有位错延伸形成的六角坑,并估算出样品位错密度约为2.1×l07 cm-2。这些结果说明镀Ti插入层有助于提高GaN外延层的晶体质量。通过Raman和低温荧光分析,可以看出自支撑GaN厚膜表面应力已经完全释放。研究了不同温度下样品的荧光特性,证明得到的无应力自支撑GaN厚膜具有很好的晶体质量和光学质量     

Effect of ammoniating temperature on microstructure and optical properties of one-dimensional GaN nanowires doped with magnesium

One-dimensional GaN nanowires doped with Mg element have been successfully prepared on Si (1 1 1) substrates by magnetron sputtering through ammoniating Ga₂O₃/Mg thin films, and the effect of the ammoniating temperatures on the microstructure and optical properties of the GaN nanowires was investigated in detail. X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS), FT-IR spectrophotometer, Scanning electron microscope (SEM), high-resolution transmission electron microscope (TEM), and photoluminescence (PL) spectrum were carried out to characterize the microstructure, morphology, and optical properties of GaN nanowires. The results demonstrate that ammoniating temperature has a significant effect on microstructure, morphology and optical properties of GaN nanowires. GaN nanowires after ammoniation at 900 °C for 15 min are straight, smooth and of uniform thickness along spindle direction with the highest crystalline quality. The growth direction of these nanowires is parallel to [1 0 0] orientation.     

钽催化磁控溅射法制备GaN纳米线

利用磁控溅射技术通过氮化Ga2O3/Ta薄膜,合成大量的一维单晶纤锌矿型氮化镓纳米线.用X射线衍射、扫描电子显微镜、高分辨透射电子显微镜,选区电子衍射和光致发光谱对制备的氮化镓进行了表征.结果表明;制备的GaN纳米线是六方纤锌矿结构,其直径大约20～60 nm,其最大长度可达10 μm左右.室温下光致发光谱测试发现363 nm处的较强紫外发光峰.另外,简单讨论了氮化镓纳米线的生长机制.     

Effect of temperature on GaN nanowires fabricated via thermal heating of GaN powders

GaN nanowires have been successfully synthesized by heating GaN powders under flowing ammonia gas in a temperature range of 950–1050 °C. The nanowire morphology was changed with varying temperature, and higher temperature favored thinner nanowires. The growth mechanisms of GaN nanowires at 950 °C included a vapor-liquid-solid process. The photoluminescence (PL) spectra of the samples commonly exhibited violet to yellow emission, whereas red emission occurred preferentially in samples synthesized at lower temperature. We have discussed the possible mechanisms by which growth temperature affected the nanowire morphology and PL spectrum.     

High-density arrays of low-defect-concentration zinc oxide nanowire grown on transparent conducting oxide glass substrate by chemical vapor deposition

High-density ZnO nanowire arrays with low defect concentrations were directly grown on transparent conducting oxide glass substrates under catalyst-free and low temperature conditions by chemical vapor deposition (CVD). A possible growth mechanism of the nanowires is studied. The experiments indicate that correct levels of supersaturation and evaporation temperature are beneficial to the growth of ZnO nanowires. Photoluminescence exhibits a weak ultraviolet emission at 380 nm and a strong green emission at 495 nm. While using a double-tube growth system, the visible light emission diminishes and the 380 nm emission is the only emission, suggesting that ZnO nanowires with few defects can be prepared using the present CVD technique at low temperature.     

热壁化学气相沉积Si基GaN晶体膜的研究

采用热壁化学气相沉积工艺在Si(111)衬底上生长GaN晶体膜，并对其生长条件进行研究。用X射线衍射(XRD)、扫描电镜(SEM)、荧光光谱(PL)对样品进行结构、形貌和发光特性的分析。测试结果表明：用此方法得到了六方纤锌矿结构的GaN晶体膜。实验结果显示：采用该工艺制备GaN晶体膜时，选择H2作反应气体兼载体，对GaN膜的形成起着非常有利的作用。     

氨化Ga2O3 /Nb膜制备的GaN纳米线的光学和微观结构特性的研究

采用射频磁控溅射技术在硅衬底上制备Ga2O3/Nb薄膜,然后在900℃下于流动的氨气中进行氨化制备GaN纳米线.用X射线衍射(XRD)、透射电子显微镜(TEM)和高分辨透射电子显微镜详细分析了GaN纳米线的结构和形貌.结果表明:采用此方法得到的GaN纳米线有直的形态和光滑的表面,其纳米线的直径大约50nm,纳米线的长约几个微米.室温下以325nm波长的光激发样品表面,只显示出一个位于367 nm的很强的紫外发光峰.最后,简单讨论了GaN纳米线的生长机制.     

Vapor growth of SiC bulk crystals and its challenge of doping

The paper reviews the so-called Modified-PVT (M-PVT) technique which combines the state of the art PVT technique for SiC crystal growth with physical and chemical vapor deposition (PVD and CVD) for fine tuning of growth parameters and improved doping. Using this technique, currently the highest aluminum doping levels and lowest resistivity values in p-type bulk SiC were achieved that for the first time meet device fabrication needs. The paper will address fundamentals of the Modified-PVT technique including a comparison of experimental results with numerical modeling of the gas flow. As additional gas feeding helium, helium-aluminum vapor for p-type doping, phosphine for n-type doping and propane for fine tuning of the C/Si gas phase composition will be discussed. So far, the M-PVT concept, i.e. mixture of conventional PVT and fine tuning by PVD/CVD, enables the most flexible doping of SiC single crystals.     

Mg-doped ZnO radial spherical structures via chemical vapor deposition

Mg-doped ZnO radial spherical structures with nanorods grown on both sides of the spherical shell were successfully prepared via chemical vapor deposition (CVD) of Zn and Mg powders in the absence of a catalyst. The structures associated with different growth temperatures (700, 800, and 850°C) were monitored by scanning electron microscopy (SEM), and the result shows that the length of the nanorods increase progressively with the growth temperature increasing. X-ray diffraction (XRD) shows that the as-obtained samples can be indexed to high crystallinity with wurtzite structure. The growth of the nanostructures mainly depends on the formation of sphere-like Mg-doped Zn droplets before adding oxygen. Photoluminescence (PL) spectra that show a 39 meV blue shift indicates that the band gap becomes large, because Mg substitutes Zn in the lattice.     

Si（111）衬底上生长GaN晶环的研究

利用热壁化学气相沉积在Si(111)衬底上获得GaN晶环，采用扫描电镜(SEM)、选择区电子衍射(SAED)、X射线衍射(XRD)，光致发光(PL)谱和傅里叶红外吸收谱(FTIR)对晶环的组成、结构、形貌和光学特性进行分析。初步结果证明：在Si(111)衬底上获得择优生长的六方纤锌矿结构的GaN晶环。SEM显示在均匀的薄膜上出现直径约为10μm的5品环，由XRD和SAED的分析证实晶环呈六方纤矿多晶结构，FTIR显示GaN薄膜的主要成分为GaN，同时含有少量的C污染，PL测试表明晶环呈现不同于GaN薄膜的发光特性。     

Etching Effect on CMP of Different GaN Layers

Chemical mechanical polishing (CMP) was used to etch various GaN materials, such as GaN layers on sapphire and silicon carbide substrates grown by metal-organic chemical vapor deposition and thick GaN layers grown by physical vapor transport. It was found that CMP could reveal the dislocations in GaN surfaces due to a selective etching component. After the optimization of CMP condition, the surface finish improved and the subsurface damage was almost completely removed, demonstrated by atomic force microsco...     

Growth and applications of HVPE-GaN nanorods

We demonstrate the properties of gallium nitride nanorods by hydride vapor phase epitaxy (HVPE). Single crystalline gallium nitride nanorods are formed on a sapphire substrate by HVPE. Single crystalline p-type and n-type gallium nitride nanorods have been grown and characterized by electrical transport measurements. HVPE was used to controllably introduce either magnesium or silicon dopants during the growth of the gallium nitride nanorods. The electron emission properties of gallium nitride nanorod array electron emitters were comparable with (or displayed even lower turn-on voltage than) those of carbon nanotubes. Wide-bandgap current rectifiers with high breakdown voltage (over −10 V) and near-ultraviolet p-n junction LEDs with emission wavelength of 390 nm, based on the single-rod gallium nitride p-n junction array, were obtained.     

SiC nanowire-toughened SiC-MoSi2-CrSi2 oxidation protective coating for carbon/carbon composites

To prevent carbon/carbon (C/C) composites from oxidation, a dense SiC nanowire-toughened SiC-MoSi₂-CrSi₂ multiphase coating was prepared by the two-step technique composed of chemical vapor deposition (CVD) and pack cementation. The coatings were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). SiC nanowires could decrease the dimension of cracks and improve the oxidation and thermal shock resistance of SiC-MoSi₂-CrSi₂ multiphase coating. Oxidation test shows that, after introducing SiC nanowires, the weight loss of the coated sample can be reduced from 1.06% to 0.64% after oxidation at 1773 K for 155 h and decreased from 6.92% to 3.42% after thermal cycling between 1773 K and room temperature for 30 times.     

Growth and Morphology Modulation of Needle-like Silicon Nanowires for SERS Application

半导体纳米线作为一种潜在的表面增强拉曼光谱（SERS）基底材料正受到广泛的关注。本文采用金作为催化剂,通过等离子体增强化学气相沉积系统,以气-液-固生长机制制备一种直径可控的针尖状硅纳米线。基于合金液滴控制硅纳米线形貌的事实,通过设计调节合金催化剂的尺寸,制备了针尖状硅纳米线。所制备硅纳米线形貌通过SEM清晰可见,为针尖状。TEM和XRD分析表明,硅纳米线为同轴结构,单晶硅核包覆非晶SiO2壳层。作为SERS活性基底,通过伽伐尼置换在纳米线表面沉积活性Ag颗粒,同等条件下对R6G的检测显示,针尖状硅纳米线基底其增强因子是柱状硅纳米线的十多倍。由此预测,这种针尖状的硅纳米线可应用于新型传感器、环境监测、生物医疗诊断等领域。此外,这种针尖硅纳米线的制备方法也可以用作制备其他的针尖状纳米线,例如同族的锗针尖纳米线等等。     

以CuSe纳米粒子为催化剂制备超长ZnSe纳米线

采用化学气相沉积的方法,以Zn粉末为原料,CuSe纳米粒子为催化剂,在Si衬底上成功制备了毫米级ZnSe纳米线。用X射线衍射、EDS和SEM对产物的结构、成分和形貌进行了测试与表征。结果表明：生长的ZnSe纳米线为立方闪锌矿结构,长度达0.35～0.7mm,Zn和Se的摩尔比为1？0.97,其室温光致发光谱显示在325nm波长激发下,ZnSe纳米线在439nm处呈现自由激子的强烈发射,表明生长的ZnSe纳米线具有高的结晶质量。纳米线生长符合氧化还原反应下的气液固生长机制,并证明Cu3Zn合金充当了实际的ZnSe纳米线生长催化剂。     

Catalytic Growth of Large-Scale GaN Nanowires

A novel lanthanon seed was employed as the catalyst for the growth of GaN nanowires. Large-scale GaN nanowires have been synthesized successfully through ammoniating Ga₂O₃/Tb films sputtered on Si(111) substrates. Scanning electron microscopy, x-ray diffraction, high-resolution transmission electron microscopy, and Fourier transform infrared spectroscopy were used to characterize the samples. The results demonstrate that the nanowires are single-crystal hexagonal wurtzite GaN. The growth mechanism of GaN nanowires is also discussed.     

CVD growth of InGaN nanowires

In this paper, the chemical vapor deposition (CVD) growth of InGaN nanowires was systematically studied. The catalyst was Au and the starting materials were Ga, In and NH₃. The samples were characterized with scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron spectroscopy (TEM), and X-ray diffraction (XRD), etc. The influence of the growth temperatures, Au thicknesses, gas flowrates and Ga and In amount on the morphology and properties of InGaN nanowires was investigated. It is found that 600 °C is a suitable growth temperature. On the substrate with Au thickness of 150 Å, helical InGaN nanowires are obtained. The change of NH₃ partial pressure and Au thickness will result in the morphology change of the samples. An increase of Ga results in shorter InGaN nanowires while an increase of In amount will lead to longer InGaN nanowires. The morphology will also change when both the amount of In and Ga were increased or reduced without changing the ratio of Ga to In.     

Synthesis of one-dimensional GaN nanorods by Tb intermediate layer with different thicknesses

GaN nanorods were synthesized by magnetron sputtering and ammonification system, and the thickness of Tb intermediate layer was changed to study the effect on GaN nanorods. The resultant was tested by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) spectra. The results show that the thickness of Tb layer has an evident effect on the modality, quality, and luminescence properties of GaN nanorods. PL spectra at room temperature show a very strong emission peak at 368 nm and a weak emission peak at 387 nm, and the intensities of the peak for the produced samples reach the maximum when Tb layer is 20 nm. Finally, the optimal thickness of 20 nm of Tb intermediate layer for synthesizing GaN nanostructures is achieved.