Influence of growth parameters on the properties of InGaN/GaN multiple quantum well grown by metalorganic chemical vapor deposition

The effects of growth parameters such as barrier growth time, growth pressure and indium flow rate on the properties of InGaN/GaN multiple quantum wells (MQWs) were investigated by using photoluminescence (PL), high resolution X-ray diffraction (HRXRD), and atomic force microscope (AFM). The InGaN/GaN MQW structures were grown on c-plane sapphire substrate by using metalorganic chemical vapor deposition. With increasing barrier growth time, the PL peak energy is blue-shifted by 18 nm. For InGaN/GaN MQW structures grown at different growth pressures, the PL intensity is maximized in the 300 Torr – grown structure, which could be attributed to the improved structural quality confirmed by HRXRD and AFM results. Also, the optical properties of InGaN/GaN MQW are strongly affected by the indium flow rate.     

GaN外延层的拉曼散射研究

ＧａＮ外延层的拉曼散射研究１李国华１韩和相１汪兆平２段树琨３王晓亮（１半导体超晶格国家重点实验室２集成光电子学国家重点联合实验室３半导体材料科学实验室中国科学院半导体研究所北京１０００８３）ＲａｍａｎＳｃａｔｅｒｉｎｇｏｆＧａＮＥｐｉｌａｙｅｒ１Ｌ...     

一种外延生长高质量GaN薄膜的新方法

采用化学方法腐蚀c-面蓝宝石衬底，以形成一定的图案；利用LP-MOCVD在经过表面处理的蓝宝石衬底上以及常规c-面蓝宝石衬底上外延生长GaN薄膜.采用高分辨率双晶X射线衍射(DCXRD)、三维视频光学显微镜(OM)、扫描电子显微镜(SEM)和原子力显微镜(AFM)进行分析，结果表明，在经过表面处理形成一定图案的蓝宝石衬底上外延生长的GaN薄膜明显优于在常规蓝宝石衬底上外延生长的GaN薄膜，其(0002)面上的XRD FWHM为208.80弧秒，(1012)面上的为320.76弧秒.同时，此方法也克服了传统 关键词： 表面处理 MOCVD 横向外延生长 GaN薄膜     

用MOVPE和RF-MBE方法极性控制生长GaN

本文报道了用低压MOVPE和RF-分子束外延法在蓝宝石衬底上作极性控制的GaN生长.以“双Al单层”模型讨论了用MOVPE和MBE法在蓝宝石衬底上生长GaN的极性选择的机理,并对AlN在极性转换过程中的作用给出了适当的解释.通过极性控制的生长,使MBE法生长的GaN的表面形貌和电学特性都得到了改善;并对LP-MOVPE生长开发出了一种“三步生长法”,这样就可以用更多的外延方式在蓝宝石衬底上生长出高质量的GaN膜.     

AlGaN/GaN heterostructure grown on 1 -tilt sapphire substrate by MOCVD

AlGaN/GaN epitaxial layers were grown on 0^°-tilt and 1^°-tilt sapphire substrates by metalorganic chemical vapor deposition (MOCVD). With exactly the same growth conditions, it was found that dislocation density was smaller and crystal quality was better for the AlGaN/GaN epitaxial layers prepared on 1^°-tilt sapphire substrate. We also found that AlGaN/GaN epitaxial layers on 1^°-tilt sapphire substrate were grown with step growth mode while those on 0^°-tilt substrate were grown with two-dimensional island growth. From the temperature-dependent mobility, it was found that crystal quality of the AlGaN/GaN epitaxial layer prepared on 1^°-tilt sapphire substrate is better.     

磁控反应溅射AlN缓冲层对GaN基LED器件性能的影响

以直流磁控反应溅射法(RMS)在图形化蓝宝石衬底上制备的AlN薄膜作为缓冲层,采用金属有机化学气相沉积法(MOCVD)外延生长了GaN基LED。与MOCVD生长的低温GaN缓冲层相比,RMS制备的AlN缓冲层具有表面更平整、颗粒更小的形核岛,有利于促进GaN外延的横向生长,减少了形核岛合并时的界面数量和高度差异,降低了缺陷和位错产生的几率。研究结果表明,溅射AlN缓冲层取代传统低温GaN缓冲层后,外延生长的GaN材料具有更高的晶体质量,LED器件在亮度、漏电和抗静电能力等光电特性上均有明显提升。     

The effects of vicinal sapphire substrates on the properties of AlGaN/GaN heterostructures

AlGaN/GaN heterostructures on vicinal sapphire substrates and just-oriented sapphire substrates (0001) are grown by the metalorganic chemical vapor deposition method. Samples are studied by high-resolution x-ray diffraction, atomic force microscopy, capacitance--voltage measurement and the Van der Pauw Hall-effect technique. The investigation reveals that better crystal quality and surface morphology of the sample are obtained on the vicinal substrate. Furthermore, the electrical properties are also improved when the sample is grown on the vicinal substrate. This is due to the fact that the use of vicinal substrate can promote the step-flow mode of crystal growth, so many macro-steps are formed during crystal growth, which causes a reduction of threading dislocations in the crystal and an improvement in the electrical properties of the AlGaN/GaN heterostructure.     

N极性GaN薄膜的MOCVD外延生长

采用MOCVD技术在c面蓝宝石衬底上外延制备了N极性GaN薄膜。通过KOH腐蚀的方法判定了GaN外延薄膜的极性。通过X射线双晶衍射(XRD)摇摆曲线和光致荧光(PL)谱测试研究了成核层生长时间对N极性GaN薄膜晶体质量和发光性能的影响。研究结果表明,成核层生长时间为300 s时,N极性GaN薄膜样品的位错密度最低,发光性能最好。采用拉曼(Raman)光谱对样品的应变状态进行了分析。     

Investigation of GaN layer grown on different low misoriented sapphire by MOCVD

GaN layer on c-plane misoriented sapphire, grown by metal organic chemical vapor deposition, has been studied. It was observed that the random and non-uniform distribution of the step was caused by the step reconstruction for GaN grown on 0° sapphire by atomic force microscopy. The image quality parameter analysis of electron back-scatter diffraction indicated that the strains were reduced for GaN grown on 0.2° and 0.3° sapphire, and optical and electrical properties were improved. The electroluminescence intensity of LED grown on 0.2° and 0.3° sapphire was 2 times as that of 0° sapphire.     

GaN-based light-emitting diodes directly grown on sapphire substrate with holographically generated two-dimensional photonic crystal patterns

As an approach to enhance light extraction from GaN-based light-emitting diodes (LEDs), we inserted a submicron period photonic crystal (PC) pattern at the interface between GaN epilayer and sapphire substrate. A two-dimensional square-lattice pillar array of 600-nm period was produced directly onto the sapphire substrate by a combination of laser holography and inductively-coupled-plasma etching. A standard GaN LED heterostructure was grown on top of the nano-patterned substrate, which was then processed to conventional bottom-emitting LED chips. At the drive current of 20 mA, the PC-LED produced surface-normal output power about 40% higher than that of the reference LED (with no PC integrated). Temperature-dependent photoluminescence measurement indicated that the emission enhancement was solely a structural effect by the integrated PC pattern.     

蓝宝石邻晶面衬底MBE生长GaN薄膜的瞬态光电导弛豫特性研究

在实验优化MBE工艺条件的基础上，采用蓝宝石(0001)邻晶面衬底制备出了具有较高质量的GaN薄膜.XRD分析表明邻晶面衬底生长的GaN薄膜晶体结构质量明显提高，AFM表征结果显示邻晶面生长的样品表面形貌显著改善.蓝宝石衬底GaN薄膜的瞬态光电导弛豫特性对比实验研究发现，常规衬底生长的GaN薄膜光电导弛豫特性出现双分子复合、单分子复合和弛豫振荡三个过程，持续时间分别为0.91，7.7和35.5ms；蓝宝石邻晶面衬底生长的GaN薄膜光电导弛豫过程主要是双分子复合和单分子复合过程，持续时间分别为0.78和14ms.理论分析表明MBE生长GaN薄膜的持续光电导效应主要起源于本生位错缺陷引发的深能级. 关键词： 邻晶面蓝宝石衬底 GaN薄膜 瞬态光电导 弛豫特性     

斜切蓝宝石衬底MOCVD生长GaN薄膜的透射电镜研究

利用MOCVD技术在斜切角度为0.3°的c面蓝宝石衬底上生长了非故意掺杂 GaN 薄膜, 并采用透射电子显微镜对材料的质量和材料内部缺陷进行了分析. 研究发现斜切蓝宝石衬底上外延的GaN材料中,位错在距离衬底0.8 μm附近大量湮灭, 同时位错扎堆出现.基于上述现象, 提出了斜切衬底上GaN材料中位错的湮灭机制, 解释了斜切衬底能够提高GaN晶体质量的原因.     

Properties comparison of GaN epilayers deposited under different growth temperatures

Undoped GaN epilayers were grown on c-plane sapphire substrates under different growth temperatures by metalorganic chemical vapour deposition (MOCVD). The optical and structural characteristics of these grown samples were studied and compared. It was found that the crystalline quality of GaN film deposited at 1050°C was better that of other samples. Photoluminescence spectra showed that the intensities of yellow luminescence band of the samples decreased as the growth temperature increased. All above test results demonstrate that high temperature deposition can serve as a good method for high-quality GaN epilayer growth and there exists an optimal growth temperature.     

外延在蓝宝石衬底上的非掺杂GaN研究

采用改变生长条件的方法制备GaN薄膜,在(0001)面蓝宝石衬底上利用金属有机物化学气相沉积技术制备了不同样品,并借助X射线双晶衍射仪(XRD)、PL谱测试仪和光学显微镜对材料进行了分析。XRD(0002)面和(1012)面测试均表明TMGa流量为70 cm3/min时样品位错密度最低。利用该TMGa流量进一步制备了改变生长温度的样品。XRD和PL谱测试结果表明,提高生长温度有利于提高GaN样品的晶体质量和光学性能。最后,利用光学显微镜对样品的表面形貌进行了分析。     

蓝宝石表面处理对氮化镓薄膜的影响

采用化学方法腐蚀c-面蓝宝石衬底,以形成一定的图案;利用LP-MOCVD在经过不同腐蚀时间的蓝宝石衬底上外延生长GaN薄膜。采用高分辨率双晶X射线衍射（DCXRD）、三维视频光学显微镜（OM）、扫描电子显微镜（SEM）和原子力显微镜（AFM）进行分析。结果表明,对蓝宝石衬底腐蚀50min情况下,外延生长的GaN薄膜晶体质量最优,其（0002）面上的XRD 半峰全宽为202.68arcsec,（10-12）面上的XRD 半峰全宽为300.24arcsec;其均方根粗糙度（RMS）为0.184nm。     

New design of nozzle structures and its effect on the surface and crystal qualities of thick GaN using a horizontal HVPE reactor

High-quality thick GaN films without cracks were achieved by using a new nozzle structure in the reactor grown by the hydride vapor phase epitaxy on sapphire substrates. Optical contrast microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray double diffraction (XRD) and cathodoluminescence (CL) were carried out to reveal the surface, crystal and optical properties of the GaN epilayer. It was found that the nozzle structure in the reactor has a large effect on the growth rate, surface flat, crystal quality, and the uniformity of the growth. Compared with the old one, the new nozzle structure (denoted as multi-layers nozzle) can improve dramatically the properties of thick GaN. Mirror, colorless and flat GaN thick film was obtained and its (0 0 0 2) FWHM results were reduced from 1000 to 300 arcsec when the new nozzle was used. AFM result revealed a step flow growth mode for GaN layer with the new nozzle. Room-temperature CL spectra on the GaN films showed a strong near-band-edge peak for the new nozzle, but there is only weak emitting peak for the old nozzle. New nozzle structure can improve the uniform of flow field near the surface of substrates compared with the old one, which leads to the improvement of properties of GaN thick film by hydride vapor phase epitaxy (HVPE).     

Effects of Ⅴ/Ⅲ ratio on species diffusion anisotropy inthe MOCVD growth of non-polar a-plane GaN films

Non-polar a-plane (110) GaN films have been grown on r-plane (102) sapphire substrates by metal organic chemical vapour deposition. The influences of Ⅴ/Ⅲ ratio on the species diffusion anisotropy of a-plane GaN films were investigated by scanning electron microscopy, cathodoluminescence and high-resolution x-ray diffraction measurements. The anisotropy of a-plane GaN films may result from the different migration length of adatoms along two in-plane directions. Ⅴ/Ⅲ ratio has an effect on the growth rates of different facets and crystal quality. The stripe feature morphology was obviously observed in the film with a high V/III ratio because of the slow growth rate along the [100] direction. When the Ⅴ/Ⅲ ratio increased from 1000 to 6000, the in-plane crystal quality anisotropy was decreased due to the weakened predominance in migration length of gallium adatoms.     

柱状与孔状图形衬底对MOVPE生长GaN体材料及LED器件的影响

在柱状图形蓝宝石衬底（PSS-p）和孔状图形蓝宝石衬底（PSS-h）上外延了GaN体材料和LED结构并进行了详细对比和分析.X射线衍射仪（XRD）和原子力显微镜（AFM）测试结果表明,PSS-h上体材料的晶体质量和表面形貌都优于PSS-p上体材料的特性,通过断面扫面电子显微镜（SEM）照片看出PSS-h上GaN的侧向生长是导致这种差异的原因.另外,基于PSS-p和PSS-h上外延的LED材料制作而成的器件结果表明,其20?mA下光功率水平相比普通蓝宝石衬底（CSS）分别提高了46%和33%.通过变温光荧光 关键词： 蓝宝石图形衬底 氮化镓 发光二极管 侧向生长     

Structural and optical properties of an InxGa1−xN/GaN nanostructure

The structural and optical properties of an In_xGa_1−xN/GaN multi-quantum well (MQW) were investigated by using X-ray diffraction (XRD), atomic force microscopy (AFM), spectroscopic ellipsometry (SE) and photoluminescence (PL). The MQW structure was grown on c-plane (0 0 0 1)-faced sapphire substrates in a low pressure metalorganic chemical vapor deposition (MOCVD) reactor. The room temperature photoluminescence spectrum exhibited a blue emission at 2.84 eV and a much weaker and broader yellow emission band with a maximum at about 2.30 eV. In addition, the optical gaps and the In concentration of the structure were estimated by direct interpretation of the pseudo-dielectric function spectrum. It was found that the crystal quality of the InGaN epilayer is strongly related with the Si doped GaN layer grown at a high temperature of 1090 °C. The experimental results show that the growth MQW on the high-temperature (HT) GaN buffer layer on the GaN nucleation layer (NL) can be designated as a method that provides a high performance InGaN blue light-emitting diode (LED) structure.     

蓝宝石表面处理对氮化镓光学性质的影响

采用化学方法腐蚀部分c面蓝宝石衬底,在腐蚀区域形成一定的图案,利用LP-MOCVD在经过表面处理的蓝宝石衬底上外延生长GaN薄膜.利用GaN薄膜光学透射谱,结合椭偏测量得到的折射率色散公式,计算得到GaN薄膜厚度,与椭偏光谱结果几乎一致;在经过表面处理的蓝宝石衬底上外延生长的GaN薄膜表现出更优异的光学质量和结晶质量,其透射谱具有更高的透射率和更大的调制深度,而且其光致发光谱中的黄光带几乎可以忽略.