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电子信息材料南昌大学研制成功硅衬底GaN蓝色发光二极管日前,南昌大学材料科学研究所在Si衬底上获得了高质量的GaN基多量子阱LED外延材料,并研制成功硅衬底GaN蓝色发光二极管。据专家评价,南昌大学的硅衬底蓝色发光二极管材料及器件工艺路线为我国发展自主知识产权的发光材料开辟了崭新的空间。蓝色发光二极管用途十分广泛,主要包括手机背光源、手机来电闪发光电池、仪器及汽车音响显示面板背光等。目前国外商品化GaN材料是在Si衬底或蓝宝石上生长的。由于GaN 与Si衬底间存在巨大的晶格失配和热失配的难题,在Si衬底上很难得到器件质量的GaN材     

氮化时间对扩镓硅基GaN晶体膜质量的影响

采用射频磁控溅射在扩镓硅基上溅射Ga2O3薄膜,然后氮化反应组装GaN晶体膜,并研究氮化时间对薄膜晶体质量的影响。测试结果表明：采用两步法生长得到六方纤锌矿结构的GaN多晶膜,扩镓硅层有效的抑制了硅衬底的氮化和弛豫了GaN与Si衬底的热失配。同时显示：在相同的氮化温度下,晶粒尺寸随氮化时间的增加而增大,薄膜的晶化程度相应的得到提高。     

基于薄膜SOI材料的GaN外延生长应力释放机制

本文研究了SOI衬底上采用MOCVD方法生长GaN材料的应力释放机制.采用SIMOX工艺制备的具有薄膜顶层硅的SOI材料作为外延生长的衬底材料,采用MOSS在位检测系统以及拉曼测试作为GaN内部应力的表征手段.结果表明,SOI材料对硅基GaN异质外延中的晶格失配应力和热应力的释放都有显著作用.薄膜SOI材料通过顶层硅与外延层的界面滑移,将一部分晶格失配应力通过界面的滑移释放,并且通过柔性薄膜顶层硅自身的应力吸收作用,将一部分热失配应力转移到衬底,从而有效地降低了GaN外延层的张应力.     

SiC缓冲层用于改善硅基氮化镓薄膜的质量研究

用脉冲激光沉积法在硅衬底上沉积GaN薄膜,为了减小Si衬底与GaN薄膜之间的热失配和晶格失配引入SiC缓冲层.脉冲激光沉积后的GaN薄膜是非晶结构,将样品在氨气氛围中在950℃下退火15min.得到结晶的GaN薄膜.并用X 射线衍射、原子力显微镜、傅立叶红外吸收谱、光致发光谱研究了SiC缓冲层对GaN薄膜的结晶、形貌和光学性质的影响.     

Si衬底GaN基LED理想因子的研究

首次报道Si衬底GaN LED的理想因子.通过GaN LEDI-V曲线与其外延膜结晶性能相比较,发现理想因子的大小与X射线双晶衍射摇摆曲线(102)面半峰宽有着对应关系:室温时Si衬底GaN LED的理想因子为6.6,对应着半峰宽707arcsec;理想因子为4.5时,对应半峰宽530arcsec.蓝宝石衬底GaN LED理想因子为3.0,其对应半峰宽401arcsec.硅衬底GaN LED理想因子大的原因可以归结为高缺陷密度所致,高缺陷密度使电流隧穿更容易进行.     

激光剥离技术制备GaN/metal/Si的结构和光学特性研究

采用激光剥离技术结合金属熔融键合技术将生长在蓝宝石衬底上的GaN外延层转移到Si衬底上.GaN和Si表面分别用电子束蒸发Al/Ti/Au和Ti/Au/In后,在氮气环境下200℃加压实现GaN和Si的键合.采用脉冲宽度30 ns、波长248 nm的准分子脉冲激光透过蓝宝石衬底辐照GaN薄膜,在脉冲激光能量密度为380 mJ/cm2的条件下将蓝宝石衬底剥离下来,实现GaN薄膜向Si衬底的转移.样品截面显微镜和扫描电镜(SEM)照片说明经过键合工艺形成了致密的GaN/Al/Ti/Au/In/Au/Ti/Si结构.对转移衬底后的GaN薄膜进行原子力显微镜(AFM)和光致发光谱(PL)测试,结果表明金属熔融键合和激光剥离工艺没有对GaN薄膜的结构和光学特性带来明显的不利影响.     

ZnO薄膜的晶体性能的分析

在硅基上制备出了c轴取向高度一致的ZnO薄膜 ,这将有可能成为新型GaN单晶薄膜的过渡层。对ZnO薄膜的晶体性能进行了分析 ,研究不同衬底和不同衬底温度对ZnO薄膜的结晶状况的影响 ,并着重用TEM研究了硅基ZnO薄膜的晶体性能。     

离子束溅射Si薄膜的低温晶化生长

采用离子束溅射技术,在低生长束流(4～10 mA)范围内,对低温(25～300 ℃)Si薄膜的晶化进行了研究.由Raman和XRD表征分析得出:在300℃采用6mA的生长束流,可在硅衬底上得到结晶性和完整性较好的Si外延薄膜;25℃时,在硅衬底上得到Si薄膜的多晶结构,实现了Si薄膜的低温晶化生长.     

高质量GaN薄膜生长工艺的研究进展

概述了GaN异质外延生长中衬底的选择以及缺陷的形成机理,从缓冲层技术、横向外延技术、柔性衬底技术等生长工艺方面综述了国内外GaN基半导体薄膜生长的最新研究和进展,并对其优缺点进行了分析比较,认为发展同质外延将有希望解决现在异质外延生长中存在的问题,最后展望了GaN基薄膜同质外延生长的前景.     

图形化SOI衬底上侧向外延生长GaN研究

采用MOCVD系统,在图形化的绝缘体上硅(SOI:silicon-on-insulator)衬底上侧向外延生长了GaN薄膜。利用SEM、TEM和Raman光谱对生长的GaN薄膜的质量进行了分析研究。研究发现,在GaN的侧向外延生长区域,侧向生长的GaN能够完全合并,GaN薄膜内的残余应力减小,穿透位错密度大幅度降低。     

Silicon—a new substrate for GaN growth

Generally, GaN-based devices are grown on silicon carbide or sapphire substrates. But these substrates are costly and insulating in nature and also are not available in large diameter. Silicon can meet the requirements for a low cost and conducting substrate and will enable integration of optoelectronic or high power electronic devices with Si based electronics. But the main problem that hinders the rapid development of GaN devices based on silicon is the thermal mismatch of GaN and Si, which generates cracks. In 1998, the first MBE grown GaN based LED on Si was made and now the quality of material grown on silicon is comparable to that on sapphire substrate. It is only a question of time before Si based GaN devices appear on the market. This article is a review of the latest developments in GaN based devices on silicon.     

硅基沉积氮化镓,碳化硅,III –V 族及其合金材料研究进展

硅基沉积氮化镓, 碳化硅, III-V 族及其合金材料是近年来的研究热点. 氮化镓, 碳化硅及其III-V 材料在光电子和电子元件领域有着广泛的应用.例如大功率, 高速器件, 大型激光器, 紫外探测器等等. 尽管硅基片具有低成本, 大的尺寸,和极好的电热导性能等优点, 硅基片仍没有成为氮化镓, 碳化硅及III – V 的主要沉积基片, 其原因在于硅基片与氮化镓, 碳化硅及III-V 材料之间的热膨胀系数和晶格常数之间的失配. 自从1998年, IBM 的课题组用分子外延方法在硅基片上沉积氮化镓, 并且成功地制备了氮化镓激光器之后, 硅基氮化镓的研究开始备受关注. 近年来的研究发现, 使用氧化铝和氮化铝镓作为过渡层. 硅基氮化镓的热应力及与硅基片之间的晶格失配可以明显降低.在 6英寸的(111) 取向的硅基片上用化学气相方法可以成功地沉积超过一个微米厚的无裂纹的单晶氮化镓. 德国的AZZURRO 公司成功地制备硅基片氮化镓的大功率的蓝色激光器. 美国的NITRINEX公司也生产了硅基氮化镓大功率电子元件. 超大功率的硅基氮化镓电子元件仍在研究中. 在2007年, 英国政府设立了一个固体照明器件的研究项目. 主要着手研究6英寸的硅基氮化镓激光器. 另一方面, 在过去的40年, 超大规模硅基CMOS 技术已有了长足的发展, 下一代低功耗高速逻辑电路要求低的驱动电流, 小的活门尺寸低于 30 nm 和快速反应性能. 这就要求器件通道材料具有很高的电子(或空穴)迁移率. III-V 材料, 例如InSb, InAs, 和InGaAs 具有电子迁移率高达 80000 cm2/VS. 它们将是下一代低于 30 nm 硅基CMOS 器件最好的候选材料. 在 2007 年美国DARPA/MTO 设立了一个研究项目来发展硅基 III-V材料器件, 着重于发展高速硅基III-V材料CMOS 器件. 第一届”硅基氮化镓,碳化硅,III-V及其合金材料研究进展 ”国际会议也将于3月 24日-28日在旧金山MRS 2008年初春季会议上召开.     

Electron Holographic Study of Semiconductor Light‐Emitting Diodes

Semiconductor light‐emitting diodes (LEDs), especially GaN‐based heterostructures, are widely used in light illumination. The lack of inversion symmetry of wurtzite crystal structures and the lattice mismatch at heterointerfaces cause large polarization fields with contributions from both spontaneous polarization and piezoelectric polarization, which in turn results in obvious quantum confined stark effect. It is possible to alleviate this effect if the local electrostatic fields and band alignment induced charge redistribution can be quantitatively determined across the heterostructures. In this Concept, the applications of electron holography to investigate semiconductor LEDs are summarized. Following the off‐axis electron holography scheme, the GaN‐based LED heterostructures including InGaN/GaN‐based quantum wells, other GaN‐based quantum wells, and other forms of GaN‐based LED materials are discussed, focusing on the local potential drops, polarization fields, and charge distributions. Moreover, GaAs‐based LED heterostructures are briefly discussed. The in‐line electron holography scheme emphasizes the capability of large area strain mapping across LED heterostructures with high spatial resolution and accuracy, which is combined with quantitative electrostatic measurements and other advanced transmission electron microscopy characterizations to provide an overall nanometer scale perspective of LED devices for further improvement in their electric and optical properties.     

Processing of nanocrystalline diamond thin films for thermal management of wide-bandgap semiconductor power electronics

High current densities in wide-bandgap semiconductor electronics operating at high power levels results in significant self-heating of devices, which necessitates the development thermal management technologies to effectively dissipate the generated heat. This paper lays the foundation for the development of such technology by ascertaining process conditions for depositing nanocrystalline diamond (NCD) on AlGaN/GaN High Electron Mobility Transistors (HEMTs) with no visible damage to device metallization. NCD deposition is carried out on Si and GaN HEMTs with Au/Ni metallization. Raman spectroscopy, optical and scanning electron microscopy are used to evaluate the quality of the deposited NCD films. Si device metallization is used as a test bed for developing process conditions for NCD deposition on AlGaN/GaN HEMTs. Results indicate that no visible damage occurs to the device metallization for deposition conditions below 290 °C for Si devices and below 320 °C for the AlGaN/GaN HEMTs. Possible mechanisms for metallization damage above the deposition temperature are enumerated. Electrical testing of the AlGaN/GaN HEMTs indicates that it is indeed possible to deposit NCD on GaN-based devices with no significant degradation in device performance.     

New perspective on nano-porous gallium nitride formation on p-type silicon with plasma focus device

For the first time, the formation of nano-porous (NP) gallium nitride (GaN) on p-type silicon (Si) (100) substrate with the plasma focus device was observed. Four and six main plasma focus shots with GaN as the target on the Si substrate were applied. Subsequently, two shots of nitrogen plasma without the GaN target were applied to both of the Si surfaces. Then the substrates were gone through a 1050°C nitrogen treatment by a thermal chemical vapor deposition (TCVD) device. Field emission scanning electron microscopy and atomic force microscopy indicated NP structures on the surface of the substrates. With the increase in the amount of shots, thicker and rougher NP structures were formed. Additionally, X-ray diffraction shows GaN polycrystalline formation on the surface with the energy-dispersive X-ray spectroscopy, indicating that there was nitrogen deficiency on the Si substrates.     

Multilayer AlN/AlGaN/GaN/AlGaN heterostructures for high-power field-effect transistors grown by ammonia MBE on silicon substrates

We report preliminary results on the transfer of the ammonia MBE technology of AlN/AlGaN/GaN/AlGaN heterostructures to silicon substrates. Optimization of the growth conditions allowed the number of macroscopic cracks in the epilayers to be reduced and ensured the growth of heterostructures with two-dimensional electron gas, which are suitable for the creation of field-effect transistors. The saturation current of prototype devices based on the heterostructures grown on silicon substrates are comparable with the analogous parameter of devices grown on sapphire and exhibits no decrease related to thermal scattering at high bias voltages.     

Improved growth of GaN layers on ultra thin silicon nitride/Si (1 1 1) by RF-MBE

High-quality GaN epilayers were grown on Si (1 1 1) substrates by molecular beam epitaxy using a new growth process sequence which involved a substrate nitridation at low temperatures, annealing at high temperatures, followed by nitridation at high temperatures, deposition of a low-temperature buffer layer, and a high-temperature overgrowth. The material quality of the GaN films was also investigated as a function of nitridation time and temperature. Crystallinity and surface roughness of GaN was found to improve when the Si substrate was treated under the new growth process sequence. Micro-Raman and photoluminescence (PL) measurement results indicate that the GaN film grown by the new process sequence has less tensile stress and optically good. The surface and interface structures of an ultra thin silicon nitride film grown on the Si surface are investigated by core-level photoelectron spectroscopy and it clearly indicates that the quality of silicon nitride notably affects the properties of GaN growth.     

Optical properties of GaN epilayers grown on Si (111) and Si (001) substrates

We report the observation of bright photoluminescence (PL) emission from two types of GaN epilayers grown by molecular beam epitaxy (MBE). Wurtzite phase GaN/Si (111) epilayers are grown by gas source MBE process, whereas cubic phase GaN epilayers are grown on (001) Si covered by thin SiC film in the process of Si annealing in propane prior to the GaN growth. PL emissions are identified based on the results of detailed PL and time-resolved PL investigations. For the wurtzite phase GaN we observe an efficient up in the energy transfer from bound to free excitons. This process is explained by a large difference in the PL decay times for two types (free and bound (donor, acceptor)) of excitonic PL emissions. For cubic phase GaN we confirm recent suggestion that acceptors have smaller thermal ionization energies than those in the wurtzite phase GaN.     

Si Complies with GaN to Overcome Thermal Mismatches for the Heteroepitaxy of Thick GaN on Si

Heteroepitaxial growth of lattice mismatched materials has advanced through the epitaxy of thin coherently strained layers, the strain sharing in virtual and nanoscale substrates, and the growth of thick films with intermediate strain‐relaxed buffer layers. However, the thermal mismatch is not completely resolved in highly mismatched systems such as in GaN‐on‐Si. Here, geometrical effects and surface faceting to dilate thermal stresses at the surface of selectively grown epitaxial GaN layers on Si are exploited. The growth of thick (19 µm), crack‐free, and pure GaN layers on Si with the lowest threading dislocation density of 1.1 × 10⁷ cm^?2 achieved to date in GaN‐on‐Si is demonstrated. With these advances, the first vertical GaN metal–insulator–semiconductor field‐effect transistors on Si substrates with low leakage currents and high on/off ratios paving the way for a cost‐effective high power device paradigm on an Si CMOS platform are demonstrated     

Piezoelectric field in highly stressed GaN-based LED on Si (1 1 1) substrate

Stress states in GaN epilayers grown on Si (1 1 1) and c-plane sapphire, and their effects on built-in piezoelectric field induced by compressive stress in InGaN/GaN multi-quantum well (MQW) light-emitting diodes (LEDs) were investigated using the electroreflectance (ER) spectroscopic technique. Relatively large tensile stress is observed in GaN epilayers grown on Si (1 1 1), while a small compressive stress appears in the film grown on c-plane sapphire. The InGaN/GaN MQWs of LED on c-plane sapphire substrate has a higher piezoelectric field than the MQWs of LEDs on Si (1 1 1) substrate by about 1.04 MV/cm. The large tensile stress due to lattice mismatch with Si (1 1 1) substrate is regarded as external stress. The external tensile stress from the Si substrate effectively compensates for the compressive stress developed in the active region of the InGaN/GaN MQWs, thus reducing the quantum-confined Stark effect (QCSE) by attenuating the piezoelectric polarization from the InGaN layer.