Microstructure and strain films using in-plane grazing analysis of GaN epitaxial incidence x-ray diffraction

This paper investigates the major structural parameters, such as crystal quality and strain state of （001）-oriented GaN thin films grown on sapphire substrates by metalorganic chemical vapour deposition, using an in-plane grazing incidence x-ray diffraction technique. The results are analysed and compared with a complementary out-of-plane x- ray diffraction technique. The twist of the GaN mosaic structure is determined through the direct grazing incidence t of （100） reflection which agrees well with the result obtained by extrapolation method. The method for directly determining the in-plane lattice parameters of the GaN layers is also presented. Combined with the biaxial strain model, it derives the lattice parameters corresponding to fully relaxed GaN films. The GaN epilayers show an increasing residual compressive stress with increasing layer thickness when the two dimensional growth stage is established, reaching to a maximum level of-0.89 GPa.     

氮化镓籽晶的表面损伤处理及氨热生长研究

籽晶的表面损伤会导致后续生长的晶体位错增多.为了降低籽晶表面的损伤,通常采用粗磨-精磨-抛光的多步过程处理的晶片作为籽晶,工艺步骤多、复杂,成本高.本文采用磷酸去除表面损伤层的粗磨GaN与化学机械抛光的GaN分别作为籽晶,对比了两种籽晶氨热生长后晶体表面、生长速率、结晶质量、应力状况.光学显微镜表明两种籽晶生长后晶体的表面具有相似的丘状表面.氨热法生长速率较慢,化学机械抛光籽晶生长速率略高于粗磨籽晶.X射线单晶衍射(XRD) (002)和(102)的摇摆曲线半高宽显示抛光籽晶与粗磨籽晶生长得到GaN结晶质量基本一致.Raman E2(high)频移表明抛光籽晶生长的GaN晶体接近无应力状态,粗磨籽晶生长的晶体存在较小的压应力.     

Microstructure and strain analysis of GaN epitaxial films using in-plane grazing incidence x-ray diffraction

This paper investigates the major structural parameters,such as crystal quality and strain state of (001)-oriented GaN thin films grown on sapphire substrates by metalorganic chemical vapour deposition,using an in-plane grazing incidence x-ray diffraction technique.The results are analysed and compared with a complementary out-of-plane xray diffraction technique.The twist of the GaN mosaic structure is determined through the direct grazing incidence measurement of (100) reflection which agrees well with the result obtained by extrapolation method.The method for directly determining the in-plane lattice parameters of the GaN layers is also presented.Combined with the biaxial strain model,it derives the lattice parameters corresponding to fully relaxed GaN films.The GaN epilayers show an increasing residual compressive stress with increasing layer thickness when the two dimensional growth stage is established,reaching to a maximum level of-0.89 GPa.     

高温X射线衍射法鉴别珍珠粉及贝壳粉

用高温X射线衍射法(XRD)研究了珍珠粉及贝壳粉中碳酸钙的相变过程。结果表明:随着试验温度的升高,上述2种样品均发生文石型向方解石型的相变,但相变程序不同;当温度从室温升至330℃,贝壳粉中方解石的质量分数由0.5%增至25.5%,而珍珠粉中方解石的质量分数则由5.0%增至8.1%。根据测定温度条件试验并综合考虑其它因素选择测定温度为330℃。试验了珍珠粉和贝壳粉混合样品中碳酸钙的上述2种晶体的相变情况,结果发现:样品中方解石的含量与其混入的贝壳粉含量呈线性关系,表明两者的混合并不影响其相变机制。在相同试验温度条件下,珍珠粉的相变程度明显低于贝壳粉。利用这一现象,可以用高温XRD快速而准确地对珍珠粉和贝壳粉进行鉴别。