采用ECR-PEMOCVD方法进行立方和六方GaN单晶薄膜生长的准热力学模型和相图

基于热力学平衡理论,对在电子回旋共振等离子体增强金属有机化学气相沉积系统中的Ga N薄膜生长给出了一个化学平衡模型.计算表明,Ga N生长的驱动力Δp是以下生长条件的函数: 族输入分压,输入 / 比,生长温度.计算了六方和立方Ga N的生长相图,计算结果和我们的实验结果显示出一定的一致性.通过分析,解释了高温和高 / 比生长条件适合六方Ga N的原因.上述模型可以延伸到用于Ga N单晶薄膜生长的类似系统中.     

NH3流量调控Ⅴ/Ⅲ比对HVPE生长GaN薄膜的影响

氢化物气相外延(HVPE)法具有生长成本低、生长条件温和、生长速率快等优点,被认为是生长高质量GaN单晶衬底的最有潜力的方法。为了优化HVPE生长GaN的条件,通过改变NH3流量调控Ⅴ/Ⅲ比(NH3流量与HCl流量之比)。通过建立简单的生长模型,对不同Ⅴ/Ⅲ比下GaN薄膜形态变化的机理进行了分析,研究了HVPE生长过程中氮源(Ⅴ族)和镓源(Ⅲ族)不同流量比对结晶质量和表面形貌的影响。实验结果表明,低Ⅴ/Ⅲ比会导致成核密度低,岛状晶胞难以合并;高Ⅴ/Ⅲ比会降低表面Ga原子的迁移率,导致表面高度差异大,结晶质量差。与Ⅴ/Ⅲ比为15.000和28.125相比,Ⅴ/Ⅲ比为21.250时更适合GaN薄膜生长,得到的晶体质量最高。     

MOCVD生长GaN材料的模拟

基于计算流体力学在三维空间中模拟了水平行星式金属有机物化学气相沉积(MOCVD)反应器生长GaN材料的流场、热场、反应物与生成物的分布以及材料生长速率等重要物理参数.计算结果与同样条件下的实验结果吻合程度相当高,表明化学反应机理和计算方法是非常可靠的,能够以此来模拟和指导GaN基材料的MOCVD生长工艺.研究并讨论了GaN的MOCVD生长中输入Ⅴ/Ⅲ比、进气口双束流上下比、总流量、反应室压力等工艺条件对局域Ⅴ/Ⅲ比的影响.     

MOCVD生长GaN材料的模拟

基于计算流体力学在三维空间中模拟了水平行星式金属有机物化学气相沉积（MOCVD）反应器生长GaN材料的流场、热场、反应物与生成物的分布以及材料生长速率等重要物理参数．计算结果与同样条件下的实验结果吻合程度相当高，表明化学反应机理和计算方法是非常可靠的，能够以此来模拟和指导GaN基材料的MOCVD生长工艺．研究并讨论了GaN的MOCVD生长中输入Ⅴ/Ⅲ比、进气口双束流上下比、总流量、反应室压力等工艺条件对局域Ⅴ/Ⅲ比的影响．     

利用低温插入层改善GaN外延层晶体质量研究

采用MOCVD系统在蓝宝石衬底上生长了GaN外延薄膜,在高温GaN生长中插入了低温GaN.通过改变低温GaN的生长温度和Ⅴ/Ⅲ比得到不同样品.对样品薄膜进行了高分辨X射线衍射(HRXRD)和光致发光谱(PL)测试,PL半峰宽变化不大,XRD半峰宽有明显变化.实验结果表明,低温GaN缓冲层可以使后续生长更好,达到二维生长...     

MOCVD生长源流量对p型GaN薄膜特性影响的研究

利用金属有机物化学气相淀积(MOCVD)技术在蓝宝石衬底上生长p型GaN:Mg薄膜,对不同二茂镁(CP2Mg)流量和Ⅴ族和Ⅲ族摩尔(Ⅴ/Ⅲ)比生长的p型GaN:Mg薄膜特性进行研究。研究表明,增加Ⅴ/Ⅲ比,可以降低螺旋位错密度,提高p型GaN晶体质量。当Ⅴ/Ⅲ比为3 800时,Cp2Mg流量最高为170sccm,获得p型GaN(002)面峰值半高宽(FWHM)最窄为232"。同时研究发现,单纯提高Ⅴ/Ⅲ比对降低刃型位错影响较不明显。     

利用高频Plasma CVD在蓝宝石衬底上生长 立方GaN缓冲层及其光学性质

研究了采用高频PlasmaCVD技术在较低温度下(300—400℃)生长以GaN为基的Ⅲ-Ⅴ族氮化物的可行性,在蓝宝石衬底上生长了GaN缓冲层.热处理后的光致发光谱和X光衍射表明,生长的GaN缓冲层为立方相,带边峰位于3.15eV.在作者实验的范围内,最优化的TMGa流量为0.08sccm(TMAm=10sccm时),XPS分析结果表明此时的Ga/N比为1.03.这是第一次在高Ⅴ/Ⅲ比下得到立方GaN.相同条件下石英玻璃衬底上得到的立方GaN薄膜,黄光峰很弱,晶体质量较好.     

GaN生长速率的研究

采用在位监控方法研究了MOCVD系统中GaN材料的外延生长速率与NH3流量、TMGa流量、Ⅴ/Ⅲ比等生长参数的关系.GaN生长速率随NH3流量的提高先增加后减小,而随TMGa流量的增加线性的增加.在不同NH3流量的情况下,GaN生长速率随TMGa流量增加的速率不同.GaN的生长速率与Ⅴ/Ⅲ比没有直接的关系,而与NH3,TMGa等条件有关.实验结果表明,MOCVD系统中存在着较强的预反应.预反应的程度与TMGa的流量成正比.     

不同Ⅴ/Ⅲ族元素比对m面GaN薄膜性能的影响?

采用分子束外延( MBE)方法在蓝宝石衬底上外延生长m面GaN薄膜。利用原子力显微镜( AFM)、扫描电子显微镜( SEM)分析薄膜表面形貌,发现Ⅴ/Ⅲ族元素比从1∶80降低到1∶90时,外延膜表面均方根粗糙度从13.08 nm降低到9.07 nm。利用光谱型椭偏仪研究m面GaN薄膜,得到了m面GaN薄膜的厚度、折射率和消光系数。拟合结果显示,GaN样品厚度和理论值一致,且Ⅴ/Ⅲ族元素比为1∶90时,所得外延膜折射率较低,透射率大。两种测试方法表明,Ⅴ/Ⅲ族元素比较小的样品晶体质量高。     

GaN生长速率的研究

采用在位监控方法研究了MOCVD系统中GaN材料的外延生长速率与NH3流量、TMGa流量、Ⅴ/Ⅲ比等生长参数的关系．GaN生长速率随NH3流量的提高先增加后减小,而随TMGa流量的增加线性的增加．在不同NH3流量的情况下,GaN生长速率随TMGa流量增加的速率不同．GaN的生长速率与Ⅴ/Ⅲ比没有直接的关系,而与NH3,TMGa等条件有关．实验结果表明,MOCVD系统中存在着较强的预反应．预反应的程度与TMGa的流量成正比．     

Quasi-Thermodynamic Model of MOVPE of InAIN

A quasi-thermodynamic model of MOVPE growth of InxAl1-xN alloy with TMAl,TMIn and ammonia as sources has been proposed. In this improved model,the effect of low decomposition rate of ammonia has been considered and the number of moles is used to express the mass conservation constraints of element N,H,Al and In. It is assumed that the alloy is synthesized by the reactions between ammonia and group Ⅲ elements. The results show that it is more difficult to grow the InxAl1-xN alloy,especially for the InxAl1-xN lattice matched the GaN. In order to enhance the incorporation of indium into InA1N,we should use the lower growth temperature,optimized input Ⅴ/Ⅲ ratio and high nitrogen fraction in the carrier gas. In addition,the decomposed fraction of ammonia should be reduced. Indium droplets would be deposited if the growth conditions have not been selected properly.     

MOCVD growth of cubic GaN on 3C-SiC deposited on Si (100) substrates

The growth of cubic GaN on 3C-SiC/Si(100) by metal-organic chemical vapor deposition (MOCVD) under various growth temperatures, thicknesses of 3C-SiC, and V/III ratios was studied. The fractions of cubic and hexagonal phases in the films were estimated from the integrated x-ray diffraction intensities of the cubic (002) and hexagonal (1011) planes. A smooth SiC layer, a high growth temperature, and a moderate V/III ratio are three key factors for the nucleation of the cubic phase and its subsequent growth. Hexagonal GaN with its c-axis perpendicular to the substrate preferentially grows at the low temperature of 750°C. The inclusion of the cubic phase increases with increasing growth temperature. The optimum growth conditions for dominant cubic GaN formation were a growth temperature of 950°C, a 1.5 μm thick SiC layer, and a V/III ratio of 1500. With these growth conditions, a cubic GaN layer with the cubic component of 91% was obtained.     

高Al组分AlGaN材料优化生长与组分研究

研究了金属有机化合物化学气相沉积(MOCVD)系统外延高Al组分较厚AlGaN薄膜材料的生长技术。实验发现,AlGaN/GaN结构中的AlGaN材料的相分离现象可能是由于过低的生长V/III以及材料所受的张应力状态所致,而V/III过高时则会出现Al源的并入效率饱和。采用AlN过渡层技术,外延生长了表面无裂纹的45%Al组分较厚(100～200nm)AlGaN薄膜材料。所得材料的Al组分与气相Al组分相同,(0002)面X射线衍射(XRD)双晶摇摆曲线半高宽(FWHM)为376arcsec,并发现AlN过渡层的质量影响着其上AlGaN材料的Al组分与晶体质量。实验观察到AlGaN材料的表面形貌随着样品中Al组分的增加从微坑主导模式逐步转变为微裂主导模式,采用AlN过渡层可延缓这一转变。     

Influence of growth conditions on the V-defects in InGaN/GaN MQWs

The influence of the growth temperature,TMIn/TEGa andⅤ/Ⅲratio on the V-defects of InGaN/GaN multi-quantum wells（MQWs） has been investigated and discussed.When the TMIn flow increases from 180 to 200 sccm,the density of V-defects increases from 2.72×10¹⁸ to 5.24×10¹⁸ cm^-2,and the V-defect width and depth increase too.The density also increases with the growth temperature.The densities are 2.05×10⁸,2.72×10¹⁸ and 4.23×10⁸ cm^-2,corresponding to a growth temperature of 748,753 and 758℃respectively.When the NH₃ flows are 5000,6600 and 8000 sccm,the densities of the V-defects of these samples are 6.34×10¹⁸,2.72×10¹⁸ and 4.13×10¹⁸ cm^-2,respectively.A properⅤ/Ⅲratio is needed to achieve step flow growth mode.We get the best quality of InGaN/GaN MQWs at a growth temperature of 753℃TMIn flow at 180 sccm,NH₃ flow at 6600 sccm,a flatter surface and less V-defects density.The depths of these V-defects are from 10 to 30 nm,and the widths are from 100 to 200 nm.In order to suppress the influence of V-defects on reverse current and electro-static discharge of LEDs,it is essential to grow thicker p-GaN to fill the V-defects.     

Growth of InGaN and double heterojunction structure with InGaN back barrier

We study the growth of an InGaN and AIGaN/GaN/InGaN/GaN double heterojunction structure by metalorganic chemical vapor deposition (MOCVD).It is found that the crystal quality of the InGaN back barrier layer significantly affects the electronic property of the AIGaN/GaN/InGaN/GaN double heterojunction.A high crystal quality InGaN layer is obtained by optimizing the growth pressure and temperature.Due to the InGaN layer polarization field opposite to that in the AIGaN layer,an additional potential barrier is formed between the GaN and the InGaN layer,which enhances carrier confinement of the 2DEG and reduces the buffer leakage current of devices.The double heterojunction high-electron-mobility transistors with an InGaN back barrier yield a drain induced barrier lowering of 1.5 mⅤ/Ⅴ and the off-sate source-drain leakage current is as low as 2.6μA/mm at VDs = 10 Ⅴ.     

The impact of nitridation and nucleation layer process conditions on morphology and electron transport in GaN epitaxial films

A systematic study has been performed to determine the characteristics of an optimized nucleation layer for GaN growth on sapphire. The films were grown during GaN process development in a vertical close-spaced showerhead metalorganic chemical vapor deposition reactor. The relationship between growth process parameters and the resultant properties of low temperature GaN nucleation layers and high temperature epitaxial GaN films is detailed. In particular, we discuss the combined influence of nitridation conditions, V/III ratio, temperature and pressure on optimized nucleation layer formation required to achieve reproducible high mobility GaN epitaxy in this reactor geometry. Atomic force microscopy and transmission electron microscopy have been used to study improvements in grain size and orientation of initial epitaxial film growth as a function of varied nitridation and nucleation layer process parameters. Improvements in film morphology and structure are directly related to Hall transport measurements of silicon-doped GaN films. Reproducible growth of silicon-doped GaN films having mobilities of 550 cm²/Vs with electron concentrations of 3 × 10¹⁷ cm⁻³, and defect densities less than 10⁸ cm⁻² is reported. These represent the best reported results to date for GaN growth using a standard two-step process in this reactor geometry.     

可用于Ⅲ族氮化物生长的50mm 3C-SiC/Si(111)衬底的制备

利用新研制出的垂直式低压CVD(LPCVD)SiC生长系统,获得了高质量的50mm 3C-SiC/Si(111)衬底材料.系统研究了3C-SiC的n型和p型原位掺杂技术,获得了生长速率和表面形貌对反应气体中SiH4流量和C/Si原子比率的依赖关系.利用Hall测试技术、非接触式方块电阻测试方法和SIMS,分别研究了3C-SiC的电学特性、均匀性和故意调制掺杂的N浓度纵向分布.利用MBE方法,在原生长的50mm 3C-SiC/Si(111)衬底上进行了GaN的外延生长,并研究了GaN材料的表面、结构和光学特性.结果表明3C-SiC是一种适合于高质量无裂纹GaN外延生长的衬底或缓冲材料.