金属有机物化学气相沉积生长GaN薄膜的室温热电特性研究

采用金属有机物化学气相沉积技术生长了不同掺杂浓度的GaN薄膜, 并且通过霍尔效应测试和塞贝克效应测试, 表征了室温下GaN薄膜的载流子浓度、迁移率和塞贝克系数. 在实验测试的基础上, 计算了GaN薄膜的热电功率因子, 并且结合理论热导率确定了室温条件下GaN薄膜的热电优值(ZT). 研究结果表明: GaN薄膜的迁移率随着载流子浓度的增加而减小, 电导率随着载流子浓度的增加而增加; GaN 薄膜材料的塞贝克系数随载流子浓度的增加而降低, 其数量级在100–500 μV/K范围内; GaN薄膜材料在载流子浓度为1.60×10¹⁸ cm^-3时, 热电功率因子出现极大值4.72×10^-4 W/mK²; 由于Si杂质浓度的增加, 增强了GaN薄膜中的声子散射, 使得GaN薄膜的热导率随着载流子浓度的增加而降低. GaN薄膜的载流子浓度为1.60×10¹⁸ cm^-3时, 室温ZT达到极大值0.0025.     

金属有机物化学气相沉积生长的$lt;i$gt;a$lt;/i$gt;(1120)面GaN三角坑缺陷的消除研究

用金属有机物化学气相沉积方法在r面蓝宝石上生长了非极性a面GaN薄膜,通过采用AlGaN多量子阱插入层,得到了高质量的非极性GaN材料. 用原子力显微镜和高分辨X射线衍射仪研究了a面GaN的表面形貌和结晶质量,发现非极性材料上典型的三角坑缺陷被消除,（1120）面X射线双晶摇摆曲线的半峰宽为680″. 关键词： GaN 原子力显微镜 高分辨X射线衍射仪 非极性     

金属有机物化学气相沉积同质外延GaN薄膜表面形貌的改善

为了获得高质量的GaN薄膜材料,研究了金属有机物气相沉积系统中GaN插入层对GaN衬底同质外延层表面宏观缺陷和晶体质量的影响.研究发现,插入层生长温度是影响GaN同质外延膜表面形貌和晶体质量的关键因素.由于生长模式与插入层生长温度相关,随着插入层生长温度的降低,外延膜生长模式由准台阶流模式转变为层状模式,GaN同质外延膜表面丘壑状宏观缺陷逐渐减少,但微观位错密度逐渐增大.通过对插入层温度和厚度的优化,进一步调控外延层的生长模式,最终有效降低了外延层表面的宏观缺陷,获得了表面原子级光滑平整、位错密度极低的GaN同质外延膜,其X射线衍射摇摆曲线(002),(102)晶面半峰宽分别为125arcsec和85arcsec,表面粗糙度均方根大小为0.23nm.     

金属有机物化学气相沉积生长的a(11-20)面GaN三角坑缺陷的消除研究

用金属有机物化学气相沉积方法在r面蓝宝石上生长了非极性a面GaN薄膜,通过采用AlGaN多量子阱插入层,得到了高质量的非极性GaN材料.用原子力显微镜和高分辨X射线衍射仪研究了a面GaN的表面形貌和结晶质量,发现非极性材料上典型的三角坑缺陷被消除,(11-20)面X射线双晶摇摆曲线的半峰宽为680″.     

蓝宝石衬底上RF-MBE生长的GaN中的极性控制和螺旋位错的降低

近年来人们报道了用MBE方法生长GaN的飞速进展,利用RF-MBE方法可以获得高的GAN生长速率和高的电子迁移率.本文讨论了用RF-MBE方法在蓝宝石衬底上生长GaN过程中的极性控制和螺旋位错的降低.在充分氮化的蓝宝石衬底上直接生长GaN,使GaN的极性控制为N-极性,并用高温生长的AlN核化层实现GaN的Ga-极性.对于N-和Ga-极性的GaN这两种情况,高温生长的AlN中间迭层的引入,可以有效地抑制螺旋位错的扩散.位错的降低使GaN的室温电子迁移率得到提高,对于Ga-极性的GaN,其值为332cm²/V·s;而对于N-极性的GaN,其值为688cm²/V·s.     

在双热舟化学气相沉积系统中通过掺In技术生长GaN纳米线和纳米锥

在现有的一台蒸发镀膜机基础上，设计加工了一个双热舟化学气相沉积系统.该系统具有真空度高、升温速度快、源和衬底温度可分别控制等优点，有利于化合物半导体纳米材料的生长.利用该生长系统，通过在生长过程中掺入等电子杂质In作为表面活性剂，分别在Si衬底和3C-SiC/Si衬底上生长出高质量的具有纤锌矿结构的单晶GaN纳米线和纳米尖三棱锥.所得产物通过场发射扫描电子显微镜、高分辨透射电子显微镜、能量色散x射线谱仪、x射线衍射仪，和荧光谱仪进行表征.这里所用的生长方法新颖，生长出的GaN纳米尖三棱锥在场发射和激光方面有潜在的应用价值. 关键词： GaN 纳米结构 透射电子显微镜 光致荧光谱     

金属有机化学气相沉积外延技术生长GaN基半导体发光二极管和激光二极管(Ⅰ)

文章评论性地介绍了金属有机化学气相外延技术（MOCVD）生长氮化物半导体 GaN和InGaN以及激子局域化效应、量子束缚斯塔克效应对它们的光学性能的影响,详细比较了这两种效应对GaN基半导体发光二极管和激光二极管特性的影响,特别是量子束缚斯塔克效应以显著不同的方式影响着发光二极管和激光二极管的性能;文章还讨论了在A面蓝宝石衬底上生长GaN的情况.     

金属有机化学气相沉积外延技术生长GaN基半导体发光二极管和激光二极管(Ⅱ)

如今，InGaN／GaN基量子阱发光二极管已经商业化，而且InGaN／GaN基量子阱激光二极管已实现连续波室温运转，使用寿命超过10000小时，虽然如此，但还没有完全搞清楚这些器件的发光机理．试验中通常使用连续输出He-Cd激光器（325nm）作光源，或者使用20—50mA注入电流来研究In—GaN量子阱样品或发光二极管光学性质，本文上篇研究了量子阱厚度与发光二极管发光功率的关系，lnGaN和GaN之间的晶格失配产生压电场，从而导致量子束缚斯塔克效应，而量子束缚斯塔克效应强     

金属有机化合物气相外延生长GaN薄膜的电子微结构研究

研究了金属有机化合物气相外延(MOVPE)方法在(0001)氧化铝基底上生长的GaN薄膜的微结构,目的在于解释GaN缓冲层在二步法生长过程中的作用及其对外延层晶体质量的影响.在缓冲层中观察到了高密度的结构缺陷,并发现了两种晶体结构(立方和六角)的GaN.进而对两种结构GaN的成因进行讨论,并对缓冲层和外延层中结构缺陷的关系进行了研究.     

AlGaN插入层对6H-SiC上金属有机物气相外延生长的GaN薄膜残余应力及表面形貌的影响

研究了具有不同台阶数目的AlGaN插入层对在6H-SiC衬底上利用金属有机物气相外延（MOVPE）生长的GaN体材料残余应力和表面形貌的影响.高分辨率X射线衍射测试表明样品的c轴晶格常数随台阶数目的增多而增大;低温光荧光谱中GaN发光峰也随着台阶数目增多而发生蓝移,这些变化都反映出GaN中残余张应力的减小.此外,原子力显微镜测试表明样品表面起伏和粗糙度也都随着插入层的引入和台阶数目的增多得到了明显的改善. 关键词： 残余应力 表面形貌 SiC衬底 AlGaN插入层     

High-performance InAlGaN/GaN enhancement-mode MOS-HEMTs grown by pulsed metal organic chemical vapor deposition

Pulsed metal organic chemical vapor deposition was employed to grow nearly polarization matched InAlGaN/GaN heterostructures. A relatively low sheet carrier density of 1.8×10~(12)cm~(-2), together with a high electron mobility of1229.5 cm~2/V·s, was obtained for the prepared heterostructures. The surface morphology of the heterostructures was also significantly improved, i.e., with a root mean square roughness of 0.29 nm in a 2 μm×2 μm scan area. In addition to the improved properties, the enhancement-mode metal–oxide–semiconductor high electron mobility transistors(MOSHEMTs) processed on the heterostructures not only exhibited a high threshold voltage(VTH) of 3.1 V, but also demonstrated a significantly enhanced drain output current density of 669 m A/mm. These values probably represent the largest values obtained from the InAlGaN based enhancement-mode devices to the best of our knowledge. This study strongly indicates that the InAlGaN/GaN heterostructures grown by pulsed metal organic chemical vapor deposition could be promising for the applications of novel nitride-based electronic devices.     

Structure of diamond nanoparticles grown by chemical vapor deposition

We studied the structure of diamond nanoparticles grown by chemical vapor deposition. SEM images show that the material contains cubic, hexagonal, and possibly icosahedral structures ranging in size from 10 to 200 nm. Raman spectroscopy shows bands, which are characteristic of crystalline diamond, E_2g mode of hexagonal diamond, a-C, and graphite.     

等离子体增强化学气相沉积法实现硅纳米线掺硼

用等离子体增强化学气相沉积(PECVD)方法成功实现硅纳米线的掺B.选用Si片作衬底，硅烷 （SiH4）作硅源，硼烷（B2H6）作掺杂气体， Au作催化剂，生长温度440℃.基于气-液-固(VLS)机制，探讨了掺B硅纳米线可能的生长机制.PECVD法化学成分配比更灵活，更容易实现纳米线掺杂，进一步有望生长硅纳米线pn结，为研制纳米量级器件提供技术基础. 关键词： 硅纳米线 化学气相沉积 纳米器件     

Morphology transition during low-pressure chemical vapor deposition

Assuming a reemission model, we have studied, in detail, the effect of sticking coefficient on the morphology evolution in low-pressure chemical vapor deposition processes. We have shown that the surface morphology changes from a self-affine fractal to a columnarlike morphology with increasing sticking coefficient, which agrees qualitatively with experimental observations.     

Thin strain-relaxed SiGe grown by ultrahigh vacuum chemical vapor deposition

Large-scale preparation of thin strain-relaxed SiGe is achieved by combining ion implantation and ultrahigh vacuum chemical vapor deposition. The resulting materials were analyzed by double crystal X-ray diffraction, micro-Raman spectroscopy, and tapping mode atomic force microscope. Results revealed that 100-nm-thick Si_0.7Ge_0.3 layers with the diameter of 125 mm and full strain relaxation are successfully prepared by pre-modifying the Si substrates using 50 keV Ar⁺ ions. The strain relaxation is also disclosed to change with both ion species and energy. However, post-modification of SiGe by ion implantation will cause serious damage to the crystal structures, and result in the formation of poly-crystal SiGe.     

Self-organized InGaN nanodots grown by metal-organic chemical vapor deposition system

It has been demonstrated that self-organized InGaN nanodots can be vertically grown by utilizing metal-organic chemical vapor deposition epitaxy (MOCVD). We report the investigation of the characteristics of InGaN with various indium contents and the fabrication of self-organized InGaN nanodots will also be discussed. Using a temperature ramping growth method, self-organized InGaN nanodots were formed vertically protruding above the sample. It was found that typical height of these nanodots is around 45 nm with an average width of 5 nm. It was also found that the local density of the vertically grown self-organized InGaN nanodots could reach 8.2 × 10¹² cm⁻². These self-organized InGaN nanodots will result in a red shift in PL spectrum indicating that In droplets act as an indium source to form an InGaN intermediate layer near the heterointerface.     

Phase-separation suppression in GaN-rich side of GaNP alloys grown by metal–organic chemical vapor deposition

The GaN-rich side of GaNP ternary alloys has been successfully synthesized by light-radiation heating and low-pressure metal–organic chemical vapor deposition. X-ray diffraction (XRD) rocking curves show that the (0002) peak of GaNP shifts to a smaller angle with increasing P content. From the GaNP photoluminescence (PL) spectra, the red shifts from the band-edge emission of GaN are determined to be 73, 78 and 100 meV, respectively, in the GaNP alloys with the P contents of 1.5%, 5.5% and 7.5%. No PL peak or XRD peak related to GaP is observed, indicating that phase separation induced by the short-range distribution of GaP-rich regions in the GaNP layer has been effectively suppressed. The phase-separation suppression in the GaNP layer is associated with the high growth rate and the quick cooling rate under the given growth conditions, which can efficiently restrain the accumulation of P atoms in the GaNP layer. PACS 68.55.Nq; 78.55.Cr; 81.15.Gh; 82.80.Pv; 78.66.Fd     

金属有机化学气相淀积技术制备GaMnN薄膜材料光学性质研究

研究由MOCVD 技术制备的 GaMnN 外延薄膜光吸收谱.实验发现Mn掺杂后较未掺杂GaN吸收系数在近紫外区增加,在吸收谱低能区144 eV附近观察到吸收峰,吸收系数随Mn浓度的增加而增大.实验结果与基于密度泛函理论的第一性原理计算结果一致,结合理论计算分析认为144 eV附近的吸收峰源于Mn³⁺离子e态与t₂态间的带内跃迁⁵T₂→⁵E. 关键词： GaMnN MOCVD 密度泛函理论 光学性质     

同质与异质外延掺杂CVD金刚石薄膜的结构与性能

采用化学气相沉积(CVD)技术,以高温高压(HTHP)合成的(100)金刚石和p型(100)Si为衬底制备了硫掺杂和硼-硫共掺杂金刚石薄膜,利用原子力显微镜(AFM)、扫描隧道显微镜(STM)及隧道电流谱(CITS)等手段分析同质和异质外延CVD掺杂金刚石薄膜的结构和性能.结果表明:异Si衬底上CVD金刚石的形核密度低,薄膜表面比较粗糙,粗糙度达到18.5nm;同质HTHP金刚石衬底上CVD金刚石薄膜晶粒尺寸约为10—50nm,表面平整,表面粗糙度为1.8nm.拉曼测试和电阻测量的结果显示,在HTHP金刚 关键词： 金刚石 掺杂 外延