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.     

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。     

用于GaN基发光二极管的蓝宝石图形衬底制备进展

近几年, 图形化蓝宝石衬底因其作为GaN基发光二极管外延衬底, 不仅能降低GaN外延薄膜的线位错密度, 还能提高LED的光提取效率而引起国内外许多科研机构的广泛研究兴趣. 本文综述了图形化蓝宝石衬底提高GaN基发光二极管性能的作用机理, 重点评述了目前图形化蓝宝石衬底的制备方法(湿法刻蚀、干法刻蚀、固相反应)和图形尺寸(微米图形化、纳米图形化), 分析比较了不同制备方法和图形尺寸制备蓝宝石图形衬底对GaN基发光二极管性能改善, 最后针对蓝宝石图形衬底制备存在的问题对其今后的发展方向做出展望.     

用MOCVD法在LiGaO2(001)上生长GaN的研究

LiGaO2单晶是目前所知的GaN最为理想的衬底材料，本研究用金属有机物气相沉积法（MOCVD）在LiGaO2(001)衬底上进行了外延生长GaN膜的试验，生长出了表面较为平整的GaN外延膜。应用原子力显微镜（AFM）、X射线粉末衍射（XRD）和高分辨X射线双晶衍射分别对衬底对外延膜和衬底材料进行了分析测试。结果表明，用MOCVD法可以在LiGaO2(001)衬底上生长出较高质量的无掺杂GaN(0001)外延膜。但由于MOCVD法是在高温还原气氛中生长GaN外延膜的，LiGaO2在这种气氛中不够稳定，实验发现衬底材料在生长过程中部分样品发生开裂，但没有发生相变。     

立式高真空MOCVD装置CaN外延生长与器件制备

自行设计了一套具有创新性的研究型立式高真空MOCVD装置,能够较好的调节反应气体的流动状态,从而在衬底上生长大面积均匀的外延层.利用该装置在蓝宝石和硅单晶衬底上成功地生长出高质量的GaN晶体薄膜.在蓝宝石衬底上生长出n、p型GaN以及多量子阱多层结构材料,并成功制备了GaN基多层量子阱结构的蓝光发光二极管,性能良好,具有实用价值.     

衬底温度对Si(111)衬底上MBE异质外延3C-SiC薄膜的影响

利用固源分子束外延(SSMBE)技术, 在Si(111)衬底上异质外延生长3C-SiC单晶薄膜, 通过RHEED、XRD、AFM、XPS等实验方法研究了衬底温度对薄膜结构、形貌和化学组分的影响. 研究结果表明, 1000℃生长的样品具有好的结晶质量和单晶性. 在更高的衬底温度下生长, 会导致大的孔洞形成, 衬底和薄膜间大的热失配使降温过程中薄膜内形成更多位错, 从而使晶体质量变差. 在低衬底温度下生长, 由于偏离理想的化学配比也会导致薄膜的晶体质量降低.     

蓝宝石衬底的斜切角对GaN薄膜特性的影响

利用金属有机物化学气相沉积技术在具有斜切角度的蓝宝石衬底(0～0.3°)上生长了非故意掺杂GaN薄膜,并采用显微镜、X射线双晶衍射、光荧光及霍尔技术对外延薄膜的表面形貌、晶体质量、光学及电学特性进行了分析.结果表明,采用具有斜切角度的衬底,可以有效改善GaN外延薄膜的表面形貌、降低位错密度、提高GaN的晶体质量及其光电特性,并且存在一个衬底最优斜切角度0.2°,此时外延生长出的GaN薄膜的表面形貌和晶体质量最好.     

纳米晶粒受控生长抑制PZNT铁电薄膜中异相形成

在LaAlO3（001）、MgO（001）、SrTiO3（001）衬底以及SrTiO3（001）／PZT（001）种膜上用液相外延方法生长了PZNT薄膜。生长结果表明：在LaAlO3（001）基片PZNT晶粒以三维岛状自发生长。薄膜中有大量的焦绿石异相；在MgO（001）和SrlriO3（001）衬底上，为三维岛状异质外延生长。薄膜中焦绿石异相几乎消失；引入[001]取向的PZT种膜后，岛状三维生长变为二维生长，显著改善了外延膜的质量，获得了完整的PZNT膜。分析了衬底取向对紧邻层纳米尺寸范围的晶粒形成、薄膜晶粒的发育、克服薄膜中异相形成等的影响，总结了获得完整PZNT薄膜的生长条件。     

新型硅基双异质外延SOI材料Si/γ-Al2O3/Si制备

异质外延法是目前制备新型SOI材料的技术途径之一。采用低压化学气相沉积技术(LPCVD)在硅衬底上先外延γ-Al2O3绝缘单晶薄膜，制备出硅衬底上外延氧化物外延结构γ-Al2O3/Si(EOS)，然后采用类似SOS薄膜生长的常压CVD(APCVD)方法在EOS上外延硅单晶薄膜，形成新型硅基双异质SOI材料Si／γ-Al2O3／Si。利用反射高能电子衍射(RHEED)、X射线衍射(XRD)、俄歇电子能谱(AES)及MOS电学测量等技术表征分析了Si(100)／γ-Al2O3(100)／Si(100)SOI异质结构的晶体结构、组分和电学性能。测试结果表明，已成功实现了高质量的新型双异质外延SOI结构材料Si(100)／γ-Al2O3(100)／Si(100)，γ-Al2O3与Si外延薄膜均为单晶，γ-Al2O3薄膜具有良好绝缘性能，SOI结构界面清晰陡峭，该SOI材料可应用于CMOS电路的研制。     

横向过生长 (LEO)外延 GaN材料及其生长机理

由于没有合适的衬底材料与之匹配，使外延生长的GaN材料缺陷密度很大，从而限制了它的应用。采用LEO（横向过生长外延）技术能使缺陷密度降低3－4个数量级,可生长出高质量的GaN材料。本文简要介绍了应用LEO技术生长GaN材料的现状及对生长机理研究的进展。     

硅衬底GaN基LED研究进展

由于硅具有价格低、热导率高、大直径单晶生长技术成熟等优势以及在光电集成方面的应用潜力,GaN/Si基器件成为一个研究热点.然而,GaN与Si之间的热失配容易引起薄膜开裂,这是限制LED及其它电子器件结构生长的一个关键问题.近年来,随着工艺的发展,GaN晶体质量得到大幅度的提高.同时不少研究小组成功地在Si衬底上制造出LED.介绍了GaN薄膜开裂问题及近期硅衬底GaN基LED的研究进展.     

Room-temperature red emission from light-emitting diodes with Eu-doped GaN grown by organometallic vapor phase epitaxy

We obtained room-temperature red emission from GaN-based light-emitting diodes (LEDs) using a Eu-doped GaN (GaN:Eu) as an active layer. The bright emission was observed under normal lighting condition, which is associated with the intra-4f shell transition of Eu³⁺ ions. The LED properties depends on the growth condition of GaN:Eu layer. Since the high-quality GaN can be grown at higher growth pressure, the intense electroluminescence (EL) was observed in the LED with a GaN:Eu active layer grown at atmospheric pressure, which is due to the enhancement of the energy transfer efficiency from the GaN host material to the Eu ions. At a d.c. current of 20 mA, the light output power and external quantum efficiency were 17 μW and 0.04%, respectively. These results indicate the feasibility of GaN:Eu to realize a GaN-based red emitter for fabrication of nitride-based monolithic optical devices.     

GaN基稀磁半导体的离子注入研究动态

离子注入掺Mn的GaN基稀磁半导体,由于具有高于室温的居里温度及一系列独特性质而受到广泛重视.综述了GaN基稀磁半导体离子注入的近期研究成果,讨论了能量、剂量、温度、束流、退火条件等因素对GaMnN结构和性能的影响,并对GaMnN中铁磁性的起源,就理论和实验两方面的结果作了讨论.     

Enhanced performance of GaN-based light-emitting diodes by using a p-InAlGaN/GaN superlattice as electron blocking layer

The electrical and optical characteristics of GaN-based light-emitting diodes (LEDs) with various kinds of electron blocking layers (EBLs) are analyzed numerically. The results indicate that an enhanced hole injection efficiency and a reduced electron leakage could be achieved with the GaN-based LED where a p-InAlGaN/GaN superlattice (SL) was employed as EBL as compared with the conventional GaN-based LEDs using rectangular p-AlGaN EBL or p-AlGaN/GaN SL EBL. Moreover, it was found that the efficiency droop could be significantly improved at high injection current density for GaN-based LEDs with p-InAlGaN/GaN SL EBL.     

GaN-based semiconductor saturable absorber mirror operating around 415 nm

We report a broadband GaN-based semiconductor saturable absorber mirror (SESAM) operating around 415 nm. The GaInN quantum wells (QWs) acting as saturable absorbers were grown by metal-organic chemical vapor deposition (MOCVD). A broadband dielectric high-reflective distributed Bragg reflector (DBR) was deposited onto the QW sample using plasma-enhanced chemical vapor deposition (PECVD) to build the SESAM. The SESAM has a stopband of over 100 nm. The linear and nonlinear transmission/absorption from QWs and the reflectance from DBR and SESAM were studied. This SESAM can be applied in passively mode-locking blue lasers such as GaN-based semiconductor lasers for producing ultra-short optical pulses.     

GaN基材料及其在短波光电器件领域的应用

GaN具有禁带宽度大，热导纺高，电子饱和漂移速度大，临界击穿电压高和介电常数小等特点，在高亮度发光二极管，短波长激光二极管，高性能紫外探测器和高温、高频、大功率半导体器件等领域有着广泛的应用前景，本文介绍了GaN基半导体材料的各种特性，材料生长以及在光电器件领域的应用，并对存在的问题和今后的发展趋势提出了自己的看法。     

GaN-based PIN alpha particle detectors

GaN-based PIN alpha particle detectors are studied in this article. The electrical properties of detectors have been investigated, such as current-voltage (I-V) and capacitance-voltage (C-V). The reverse current of all detectors is in nA range applied at 30 V, which is suitable for detector operation. The charge collection efficiency (CCE) is measured to be approximately 80% but the energy resolution is calculated to be about 40% mostly because the intrinsic layer is not sufficiently thick enough.     

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.     

Synthesis of GaPO4-GaN Coaxial Nanowires

GaPO₄-GaN coaxial nanowires were synthesized by two-step chemical vapor deposition method using H₂ and NH₃ as reactant gas in turn at 950°C. The morphology and microstructures of the GaPO4-GaN coaxial nanowires were studied by scanning elctron microscopy (SEM), X-ray diffraction (XRD) and transmission lectron microscopy (TEM). The nanowires have an average diameter of ~15 nm and length of hundreds of anometers. The core is GaPO₄ crystal and the outer shell is GaN crystal. The formation mechanism was iscussed and the key factors controlling the growth are temperature and the concentration of reactant gases. hese coaxial nanowires may have potential application for piezoluminescence nano-devices, and the two-step ynthetic technique could be used to grow rationally other 1D GaN-based nanowire heterostructures.