【作者】 王如；

【导师】 杨瑞霞；

【作者基本信息】 河北工业大学 ， 微电子学与固体电子学， 2010， 博士

【摘要】 GaN的带隙宽,化学性质稳定、耐高温、耐腐蚀,GaN基器件具有抗辐射、高频和大功率的特点,在光显示、光存储、光照明、光探测等光电领域、航空航天和民用移动通信系统领域有着巨大的应用前景。由于熔点超过2500℃,不能使用熔体生长法获得GaN的体材料。氢化物气相外延法(HVPE)能获得每小时几十微米的快速生长率,设备简单,适合生长GaN厚膜,把得到的厚膜和衬底进行剥离,就可以得到自支撑衬底或是GaN体材料。本文主要研究高质量GaN厚膜的制备工艺。利用缓冲层技术和横向外延技术的原理,在Al2O3(0001)和Si(111)衬底上,通过优化射频磁控溅射系统的衬底温度、工作气体压强和溅射功率等参数,得到了c轴单一取向、晶粒尺寸均匀、三维岛状结构的ZnO缓冲层。三维岛状的ZnO缓冲层,既有效地降低了晶格失配度,同时,三维小岛之间形成的微孔中心又起到了横向外延掩膜的作用,这种微孔结构降低了GaN厚膜的位错密度,还有助于减小后续的剥离难度。通过优化HVPE系统的生长温度、V/III比值和载气种类等参数,制备了晶体质量良好的GaN厚膜,并对GaN厚膜穿透位错密度进行了估测,对厚膜的光学、电学性能进行了测试。采用先通H2气再通N2作载气的HVPE工艺有效地降低了晶体结构缺陷,消除了黄光发射带。GaN/RF-ZnO/Al2O3(0001)试样的(0002)面DCXRD半高宽(FWHM)为265arcsec、(1012)面为414arcsec,晶体结构缺陷少,杂质含量低,载流子受到的散射作用较小,霍尔迁移率为436 cm2/V·s,方块电阻为3.17×106?/□。对于Si(111)衬底生长GaN采用LT-GaN/RF-ZnO复合结构,ZnO缓冲层防止了无定形SiNx膜和Ga滴回溶的产生,消除GaN膜多晶化问题。低温GaN(LT-GaN)插入层进一步降低了衬底和GaN厚膜之间的晶格失配度,同时减小了ZnO层的高温分解和反应问题。对预氮化处理的Al2O3(0001)衬底采用低温GaN层插入层工艺,以及在Al2O3(0001)衬底上生长TiN作掩膜的工艺进行了初步探索,发现衬底氮化工艺容易造成N极性面生长,而TiN掩膜工艺的纳米级Ti膜的容易氧化,二者不易获得高质量GaN厚膜。对以ZnO为缓冲层的GaN厚膜进行了激光剥离和化学浸蚀分离的尝试。更多还原

【Abstract】 There are many outstanding characters for GaN material such as wide band gap, stable chemical property, high temperature resistance and corrosion resistance. GaN devices have radiation-resistance, high-frequency and high-power performances, so it is widely used in lightshow, photomemory, illumination, optical detection, aerospace and civil mobile communication fields. GaN bulk crystal can not be grown by the method of melt growth for its melting point is over 2500℃. Hydride vapor phase epitaxy (HVPE) suits to grow thick GaN films because it has faster growth ratio, which can reach about scores of microns per hour, and the required equipment is simple. Freestanding GaN substrate or GaN bulk crystal can be obtained by peeling away thick GaN film from the substrate.Preparation of thick GaN film is the main target of the dissertation.Based on the theories of epitaxial lateral overgrowth (ELOG) and buffer technology, adopting optimized growth parameters such as substrate temperature, the pressure of Ar gas and the power of radio frequency sputtering, three-dimensional-island and uniform-sized ZnO buffer layers with single <0002> orientation were grown on Al2O3(0001) substrates and Si(111) substrates by radio frequency magnetron sputtering (RFMS). The three-dimensional-island structure can reduce the lattice mismatch, decrease the threading dislocation density (TDD) of GaN film and is benefit for the film to peel away from the substrate. The surface voids of ZnO buffer layers can play a key role that is similar to the mask of ELOG.The high-quality thick GaN films grown on Al2O3(0001) and Si(111) substrate with high-property RF-ZnO buffers layers were fabricated through optimizing the HVPE system process parameters such as growth temperature, V/III ratio and the kind of carrier gas. The TDD of thick GaN films was estimated and the performance of optics and electricity were measured. At room temperature, it was found that H2 and N2 adopted as carrier gas in sequence was effective and yellow luminescence disappeared in PL spectrum, which indicated that the density of crystal defects reduced. The full width at half maximum (FWHM) of double crystal X-ray diffraction (DCXRD) (0002) peak of GaN films on RF-ZnO/Al2O3(0001) substrate got 265 arcsec and (1012) peak got 414 acrsec. Hall test of GaN/RF-ZnO/Al2O3(0001) indicated the GaN films had high quality, lower impurity content and less scatter of the carrier. Hall mobility got 436cm2/V·s and sheet resistance got 3.17×106?/□. Composite structure of LT-GaN/RF-ZnO was adopted on Si(111) substrates to grow thick GaN films. The RF-ZnO buffers avoid the poly-crystallization of GaN films which is from the formation amorphous state SiNx films or the autolysis of Ga drop in Si(111) substrate. Low temperature GaN (LT-GaN) interlayer reduced the lattice mismatch, and prevented the RF-ZnO layer from pyrolysing and reaction at high temperature.Preliminary studies of other kinds of thick GaN films had been done as the following : One was preparation through adopting LT-GaN interlayer between GaN layer and nitrided Al2O3(0001) substrate, another was preparation by using TiN as a mask layer on Al2O3(0001) substrate. The problem that N polar face of GaN films on nitrided Al2O3(0001) substrates and oxidation of nano-grade Ti films on Al2O3(0001) substrates led to bad crystal quality.Initial research about laser lift-off (LLO) and chemical corrosion of thick GaN films had been also done.更多还原