【作者】 秦福文；

【导师】 杨大智； 顾彪；

【作者基本信息】 大连理工大学 ， 材料学， 2004， 博士

【摘要】 氮化镓（GaN）基Ⅲ族氮化物宽禁带半导体材料是制备蓝光到紫外光波段的半导体发光二极管（LED）、半导体激光二极管（LD）等光电器件的首选材料。同时由于GaN基材料具有电子漂移饱和速度高、介电常数小、导热性能好、化学和热稳定性好等特点，也非常适合于制作高温、高频及大功率电子器件。在常规的以氨气为氮源生长GaN的金属有机物化学气相沉积（MOCVD）方法中，为了使氨气有效热解，不得不采用1000℃以上的高温生长。由于在GaN基薄膜材料的生长过程中，氮的分解压很高，所以高温生长更容易加剧氮的挥发，使薄膜中留下大量的氮空位，从而使GaN薄膜有很高的背景电子浓度，造成p型掺杂困难。而且高温不利于亚稳态立方相GaN的生长。 为了降低生长温度，必须首先解决活性氮源问题。本论文采用电子回旋共振微波等离子体增强MOCVD（ECR-PEMOCVD）方法，以氮等离子体为氮源，在GaAs（001）、Si（001）以及蓝宝石（α—Al₂O₃）等衬底上实现了GaN基Ⅲ族氮化物薄膜的低温异质外延生长。并对GaN基Ⅲ族氮化物薄膜的初始层生长、生长工艺、材料生长机理以及反射高能电子衍射（RHEED）原位监测结果进行了研究，主要工作和结论如下： 1．在综合分析了第一代ECR-PEMOCVD装置（ESPD）优缺点的基础上，作为主要参与者研制成功配有RHEED原位监测设备的第二代ECR—PEMOCVD装置（ESPD—U），并已成功申请到国家发明专利《电子回旋共振微波等离子体增强金属有机化学气相沉积外延系统与方法》。ESPD—U可以制备各种单质和多元素化合物半导体薄膜，特别是能对复杂层状结构，超薄层微结构半导体材料实现原子尺度控制生长的原位监测；由于能对外延膜表面原位监测，提供生长表面微结构信息，对薄膜生长工艺的优化，尤其对在大晶格失配对底上薄膜生长至关重要的初始生长工艺的优化十分有利，将大大缩短用MOCVD生长新型半导体薄膜材料的研发周期。此外，还能满足等离子体与生长表面相互作用等相关基础研究的要求。 2．实验结果表明，腔祸合—磁多极ECR等离子体源（MEP源）能以很高的微波—等离子体耦合效率（＞94％）产生高密度、高电离度、低离子温度（＜2eV）、低空间电位（＜30V）、大面积均匀、稳定的ECR放电。由于离子温度和空间电位都比较低，有利于控制和减少基片损伤，这使得MEP源更适合于半导体薄膜生长及无损伤刻蚀等。而且等离子体发射光谱的研究表明该ECR源具有很强的活化功能。 3．由不同入射方向的RHEED条纹间距，可以测出蓝宝石衬底在经过清洗、氮化、生长GaN和氮化铝（AlN）外延层的不同工艺过程中，其外延表面晶格常数的大小，并由此分析其表面的应变状态。实验中以α—Al₂O₃（0001）衬底表面晶格常数a_S的公认标准值4.758来标定RHEED条纹间距与a_S的比例系数，间接测出氮化、缓冲层、AlN外延层等情况下的外延表面的点阵排列间距。 摘要数据分析表明，氮化所形成的AIN层明显处于压应变状态;GaN缓冲层的情况也与此类似。在误差范围内，可以认为AIN外延层的应力得到充分的释放。根据由RHEED分析推断出的外延薄膜表面的晶格匹配方式，对外延膜中产生的压应变状态进行了合理解释。 4.本文讨论了ESPD装置中的氢等离子体清洗、氮化及缓冲层生长等预处理条件对立方GaN/GaAs（001）外延层质量的影响。发现决定氮化过程的主要因素是活性氮粒子的化学活性和氮化时间，适当时间的氮化可以提高外延立方GaN薄膜的结晶质量和相纯度，氮化过程中适量氢等离子体的加入可以有效消除As聚集和AsNx化合物形成，促进氮化过程的进行，获得在衬底上的高密度均匀成核:对缓冲层在GaAs（001）衬底上外延生长立方GaN过程中的作用进行了分析，发现其主要作用与在Q一Ab03（0001）衬底上外延生长六方GaN过程中缓冲层的作用是相一致的。 5.在GaA，;（001）衬底上成功地生长出高质量的外延立方GaN单晶薄膜，并用X射线衍射（XRD）、透射电镜（TEM）和光致发光（PL）测量进行了表征。结合霍尔（Hall）测量结果，表明我们的外延薄膜达到了较高的光电特性。 6.51（001）衬底表面的原位氢等离子体清洗对于GaN/Si（001）薄膜的生长是非常必要的;具有平坦表面和高晶体质量的缓冲层对于高质量GaN薄膜的外延生长是非常有必要的:HRTEM图像显示出外延生长，但没有立方相出现，而是外延出高度c轴取向的六方GaN薄膜，并且观察到在GaN/Si（001）界面处自然形成了一层非晶层，其两个表面平坦而陡峭，厚度均匀（约Znm）。分析认为，在初始成核阶段N与si之间反应所产生的这层SixNy非晶层使立方相GaN没有形成:， 7.在ESPD一U装置上，对蓝宝石衬底的清洗与氮化进行了RHEED研究。结果表明，氢氮混合等离子体清洗效果明显优于纯氢等离子体清洗，可以获得非常光滑平整的蓝宝石衬底表面;而采用氮等离子体可实现衬底的氮化，从而获得平整的AIN成核层;通过比较氮化与不氮化所生长的GaN缓冲层的RHEED图像，证明在蓝宝石衬底上还必须通过氮化才能生长出取向好的GaN晶体薄膜。 8.在ESPD一U装置上，采用ECR一PEMOCVD技术，在550’C的低温下生长出表面粗糙度在两个原子层左右的GaN缓冲更多还原

【Abstract】 GaN-based III group nitrides are the best candidates for manufacturing LED and LD in the range from blue to ultraviolet and other opto-electronic devices, they also suit for manufacturing high-temperature?high-frequency and high power electronic or microwave devices, because of their excellent properties such as wide band gap, high electron saturation drift velocity, low dielectric constant, high thermal conductivity, good chemical and thermal stability, and so on. In usual MOCVD for growing GaN with ammonia as nitrogen source, people have to grow GaN under high temperature (over 1000@) in order to effectively pyrolyse ammonia. However, during the high temperature growth of GaN-based film materials, a mass of nitrogen hollow space will be resulted in the films due to the high decomposition pressure of nitrogen and quick volatilization of nitrogen, then the GaN film has very high background electron concentration, and the p-type doping is very difficult to achieve. So, the high temperature is a main impediment to grow good quality of metastable cubic GaN.Fristly. an active nitrogen source at low temperature must be obtained in order to reduce growth temperature. Nitrogen plasma as nitrogen source for heteroepitaxy growth of GaN-based III group nitride films at low temperature on GaAs(OOl), Si(OOl) and a -A12O3(0001) substrates by ECR-PEMOCVD is presented in this thesis. Additionally, the initial nucleation, the processing and mechanism of material growth, and the results detected in situ by RHEED during the growth of GaN-based III group nitride films are investigated. The major work and conclusions are as follows:1. Based on synthetical analysis of the advantages and defects of ESPD equipment. as a major participator , we successfully developed a super-high vacuum equipment ESPD-U with RHEED in situ monitoring equipment, and our national invention patent -#Electron cyclotron resonance microwave plasma enhance MOCVD epitaxy system and method$ has been publicized. The growth of various mono-element and multi-element compound semiconductor films can be realized on ESPD-U, especially the control growth for complex sandwich and super-thin film microstructure semiconductor materials with in situ detection of mono-atom layer level can be realized. The surface appearance of epitaxy layer and microstructure information of growth surface can be detected in situ by RHEED. It benefits to optimize the growth processing of thin film, especially to optimize the initial growth processing which is very important for heteroepitaxy on substrates with big misfit of crystal lattice. So the investigation and developing periods for growing new type semiconductor thin film materials by MOCVD can be greatly shortened. Furthermore, the correlative basic research, such as the interaction between plasma and growing surface, can be carried out on ESPD-U also.2. Experiment results demonstrated that the cavity coupling-magnetic multipole ECR plasma source (MEP source) can produce large area uniform and steady ECR plasma with higher microwave-plasma coupling efficiency (94%), high density, high ionization, low ion energy (<2eV) and low space potential (30V). It has an advantage to control and reduce werfer damage, owing to the ion energy and space voltage are very low, so MEP source is very adequate for growing semiconductor thin film and etching without damage, etc. And the investigation of plasma emission spectra indicated that ECR source has very strong activation function.3. The crystal lattice constant of growing surface in different processes, such as cleaning and nitridation of substrate, growth of GaN and A1N epilayer, could be measured through RHEED from different incidence direction. So the strain state of surface could be analyzed. According to the crystal lattice constant of growing surface is inversely proportioned to the space of RHEED stripes and using standard value 4.758 A of lattice constant of a -Al2O3(000l) surface (as) as a scale of demarcation, the lattice spacing of epilayer surface was measured indir更多还原