| 题名 | III族氮化物半导体衬底材料的制备研究 |
| 作者 | 彭观良 |
| 学位类别 | 博士 |
| 答辩日期 | 2005 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 徐军 |
| 关键词 | III族氮化物 半导体 衬底 白宝石 铝酸锂 |
| 其他题名 | Fabrication of substrate material used for group III nitride semiconductors |
| 中文摘要 | III族氮化物半导体材料主要包括InN，GoN，AIN及其合金。近来，由于多方面的应用，III族氮化物（尤其是GaN）获得了极大的关注和广泛的研究。它们优异的物理性能，尤其是宽带隙、高物理强度和出色的化学稳定性，使之成为许多光电子器件（如太阳盲区紫外光电探测器，蓝、绿光发光二极管和激光二极管，等）的理想材料。III族氮化物的三元或四元合金（如AIGoN，InGoN，AlGalnN）覆盖的带隙宽度可从InN的1．9eV到GoN的3．4eV直到AIN的6．2eV。使用宽带隙川族氮化物材料制作的晶体管传送的微波功率密度得到空前的提高，这方面的潜在应用包括无线通信、卫星通信、军事和商业雷达系统等。此外，川族氮化物在全色显示、激光打印、高密度信息存储、水下通信、高温／高功率电子器件等众多领域也拥有巨大的应用前景。不幸的是，IH族氮化物体单晶迄今尚未能商用。所以它们的应用大名依靠沉积干剔的衬序卜的IJl桩氨朴物具活从杯膜。本论文探究三种可供洗择的衬底即白宝石、铝酸锂、γ－LiAlO2/α-Al2O3复合衬底，以用于GoN的外延生长详细地研究了上述三种衬底材料的结构，力学、热学及化学性能，以及制备技术、主要的创新性结论总结如下。（1)化学机械抛光技术可以提供平坦化而又不至于破坏材料的表面。采用化学机械抛光（CMP）及酸蚀工艺处理白宝石衬底，得到了平坦化的表面。平坦化的衬底表面是提高外延膜质量的关键。（2）采用温梯法生长出了透明γ－LiAIO2晶体。发现晶体上部为LIAl5O8和LiAlO2的多晶混合物，中部形成了透明的单相Y一LiA1O2晶体，底部检测到包含有1钥金属颗粒。这种现象是因为Li的挥发造成的。（3）采用提拉法生长了尺寸达中45x50mm3的Y一LIAloZ单晶。发现仅仅在晶体毛坯的底部生成了一种缺铿相（LIA15OS）。Y一LIAIOZ晶体化学稳定性差，在室温时轻微立解。当在空气中于1100℃退火70小时，Y一LIAlO2晶体挥发出钾组分，在表面产生缺铿相（LIA15O8）。值得注意的是，在Y一LiAlO2晶体的红外光谱区不存在氢氧根吸收带。（4）研究了Y一LIAlO2晶体的热稳定性。发现在1100℃空气或真空中退火使Y一LiAlO2晶片表层变成LIA15O8多晶，而富铿气氛退火可以有效地抑制晶体中铿组分的挥发，保持晶格完整性、提高晶体质量。（5）首次采用提拉法生长掺稼铝酸铿晶体。结果表明LIAI卜xGaxOZ（x＝0，0．1，0．2，0．3）晶体归属于Y一LiA1O2结晶结构，Ga3＋离子部分地取代A13＋离子。（6）首次采用提拉法生长Ti掺杂的铝酸铿晶体。发现掺Ti可以提高铝酸铿晶体的抗潮解能力。这是由于Ti的掺入改善了铝酸铿的晶格结构，使之更稳定。（7）根据柔性衬底的理论，利用气相传输平衡（VTE）技术，在白宝石衬底上制备出具有1100］择优取向的单相Y一LiAlO2层，从而形成Y一LiAlO2/α-A12O3复合衬底，在这种Y一LIAIOZ／a一A12O3复合衬底的结构中，a一A12O3既作为反应物参加固相反应，又起支撑其上的Y一LiAiO2薄层的作用，很好地解决了"柔性衬底"技术中衬底支撑的难题。同时，VTE实验发现当反应温度从750℃下降到730℃时补LIAIOZ晶核的尺寸一已在1μm以下，经稀盐酸（HCl）腐蚀后可形成多孔的表面，从而有望制备出用于外延GoN的新型多孔衬底。（8）研究了VTE处理温度及白宝石表面粗糙度对补LiA1O2层内的残余应力的影响，通过对这两个工艺参数的优化组合，制备出了残余应力较小的补LiAlO2层，进一步改善了Y一LIAlo2／a一A12O3复合衬底的性能。（9）研究了白宝石衬底表面形貌对Y一LIAlo2层质量的影响。发现白宝石衬11底的表面粗糙度和退火处理是两个影响Y一LiAlO2层质量的重要因素。要制备高质量的Y一LiAlO2层，适度的表面粗糙度是恰当的。退火使Y一LiAlO2层的择优取向变差。 |
| 英文摘要 | Group III nitride semiconductor materials mainly include indium nitride (InN), gallium nitride (GaN), aluminum nitride (A1N) and their alloys. They (especially GaN) have recently received considerable attention and been extensively studied for various applications. Their exceptional physical properties, notably their wide bandgap, high physical strength and outstanding chemical stability, make them ideal for many optoelectronic devices such as solar-blind ultraviolet (UV) photodetectors, blue and green light emitting diodes (LEDs) and laser diodes (LDs) , etc. Ternary or quaternary alloys of Ill-nitrides (such as AlGaN, InGaN, AlGalnN ) span a range of bandgaps from 1.9 eV for InN to 3.4 eV for GaN and to 6.2 eV for A1N at room temperature. Their wide bandgap allows transistors fabricated on them to deliver unprecedented levels of microwave power density. In this respect potential applications include wireless communications, satellite communications, military and commercial radar systems, etc. In addition, Ill-nitrides also have shown significant promise for a wide range of applications including full color displays, laser printers, high-density information storage, underwater communication, high temperature/high power electronic devices, and so on. Unfortunately, by far, bulk Ill-nitride single crystals are not commercially available. So most of their applications rely on Ill-nitride heteroepitaxial thin films deposited on foreign substrates. This dissertation explores three alternative substrates, namely sapphire, y-IJAlC^, and y-LiAlCVsapphire composite substrates, used for gallium nitride (GaN) epitaxial growth. The structure, mechanical, thermal, and chemical properties, and fabrication technique of above-mentioned three substrate material was studied in detail. The main original conclusions were summed up as follows. Chemo-mechanical polishing (CMP) technique can provide planarization without damaging the material surfaces. Sapphire substrates were treated by chemo-mechanical polishing (CMP) with subsequent chemical etching. Planarized surfaces of substrates have become a key to the advanced quality of epitaxial films. Transparent y-LiA102 crystal was grown by temperature gradient technique (TGT). It has been verified that polycrystalline mixture of LiAlsOg and LiAlC^ is formed in the upper part of crystal, and transparent single-phase y-LiAlC^ crystal is attained in the middle part, and molybdenum grains are detected in the bottom part. This kind of phenomenon is caused by the volatilization of Li. Large-size y-LiAlC>2 single crystal with dimension of O45X50 mm3 has been grown by Czochralski technique. It has been verified that only in the bottom of the crystal boule there produced a kind of lithium-poor phase (LiAUOg). The y-LiAlOi crystal exhibits poor chemical stability because it hydrolyzes slightly at room temperature. When the y-LiAlO? crystal was annealed for 70 h at 1100 °C in air-atmosphere, it volatilizes lithium component, and produces lithium-poor phase (LiAlsOg) layer on the surface. It is noteworthy that no hydroxyl absorption band presents in the infrared spectra region of y-LiA102 crystals. (4) The thermal stability of y-LiAlCb crystals has been investigated. It has been verified that the surface of y-LiA10? crystal annealed at 1100 °C in air or vacuum turns into a single-phase polycrystalline of LiAlsOg, and lithium-rich annealing ambient leads to elevated quality of y-LiA102 crystal with better crystallographic perfectness by restraining the volatilization of lithium component from crystal. Ga3+-participating y-LiA102 crystals were grown by Czochralski technique. The result shows that LiAli_xGaxO2 (x=0, 0.1, 0.2, 0.3) crystals should be assigned to y-LiA102 crystallography structure, and in which Al + ions were partly substituted by Ga ions. Ti-doped y-LiA10"2 crystals were grown by Czochralski technique. It has been verified that y-LiA10"2 crystals doped with Ti hold better deliquescence-resistant property, which attributes to that the participation of Ti results in an improvement of lattice structure and make y-LiAlO^ more stable. Based on the theory of compliant substrates, single-phase y-LiA102 layer with a preferred (100) orientation on sapphire substrate is fabricated by vapor transport equilibration (VTE) technique, thus form y-LiAlOVsapphire composite substrates. In the structure of this kind of y-LiAlOVsapphire composite substrates, sapphire not only as a reactant participates in solid-phase reaction, but also supports the upper y-LiA102 thin layer, so the difficult problem of substrate support in compliant substrates technique is validly resolved. At the same time, it has been verified by VTE experiments that when the VTE process temperature dropped from 750 °C to 730 °C the size of y-LiAlO? grains dropped up to under 1 um. Above-mentioned sapphire wafers with y-LiA102 grains were then subjected to dilute muriatic acid (HC1), so y-LiAlCh grains were etched and removed, thus brought froth porous surface, thereby it is promising to fabricate new porous substrates for GaN epitaxial growth. The effect of VTE process temperature and surface roughness of sapphire on residual stress in y-LiA102 layer has been investigated. Through the optimization and combination of this two technical parameters, y-LiA102 layer with little residual stress has been fabricated, thus further improved the properties of y-LiAlCVsapphire composite substrates. (9)The effect of surface morphology of c-plane sapphire substrate on quality of Y-L1AIO2 layer has been investigated. It has been verified that surface roughness and annealing treatment of sapphire are two essential factors to affecting y-LiA102 layer quality on the sapphire substrate. To grow high-quality Y-LiA102 layer, moderate surface roughness of sapphire substrate is suitable. Annealing of sapphire substrate deteriorates the oriented growth of the y-LiA102 layer on sapphire. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15543]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 彭观良. III族氮化物半导体衬底材料的制备研究[D]. 中国科学院上海光学精密机械研究所. 2005. |
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