Growth of ZrB_2 Single Crystals for Substrates for GaN

GaN衬底ZrB_2单晶的生长

基本信息

批准号：
15550177
负责人：
OTANI Shigeki
金额：
$ 2.3万
依托单位：
National Institute for Materials Science
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-15550177/
关键词：
Gallium nitride substrate Zirconium diboride single crystal ニホウ化ジルコニウム

项目摘要

ZrB_2 has almost the same lattice constant and thermal expansion coefficient as those of gallium nitride, GaN, and further high thermal and electric conductivity. High quality GaN films with dislocation density of less than 10^7 /cm^2 were grown on the substrates of ZrB_2 crystals, which were prepared by the floating zone method because of high melting point, 3220℃. Therefore, in this research, improvement in the purity and quality of ZrB_2 crystals was tried for the practical use.The crystals prepared from the commercial powders, often cause some troubles because of the low purity, <99%. The main impurities are iron, carbon and so on. For example, carbon impurity in the crystal precipitates on the surface due to heating in vacuum. Therefore, in order to improve the purity, the starting material was synthesized by reaction of zirconia and boron, ZrO_2 + 4B. The contents of iron and carbon decreased to 30 ppm, respectively. They further decreased to 4 ppm and less than 20 ppm, respectively, due to the floating zone growth. The total purity of the crystal increased to >99.99%, high enough to suppress the above problems.Factors which determine the crystal quality were examined by comparison with the other diboride crystals, TiB_2, HfB_2, VB_2, NbB_2, TaB_2 and CrB_2. The etch pit densities decreased with decreasing the growth temperature. In the case of ZrB_2, the etch pit density was 5 x 10^6 /cm^2, which would decrease to half, decreasing the growth temperature by 200℃. The formation of the sub grain boundaries and cracks were influenced by the anisotropy of the thermal expansion. ZrB_2 crystals with the highest quality among the diborides had the small thermal expansion coefficients and the small anisothoropy. Therefore, to improve the crystal quality further, it was found to be important to find a flux which decreases the growth temperature.

ZRB_2的晶格常数和热膨胀核心几乎与硝酸盐，GAN和进一步的高热电导率的晶格膨胀核心。高质量的GAN膜的位错密度小于10^7 /cm^2在Zrb_2晶体的底物上生长，由于高熔点为3220℃，该晶体是通过浮动区方法制备的。因此，在这项研究中，尝试了Zrb_2晶体的纯度和质量的改善。主要杂质是铁，碳等。例如，由于真空加热，晶体中的碳杂质在表面沉淀。因此，为了提高纯度，起始材料是通过锆石和硼的反应（ZRO_2 + 4B的反应）合成的。由于浮动区的生长，铁和碳的含量分别降至4 ppm和小于20 ppm。晶体的总纯度增加到> 99.99％，足够高以抑制上述问题。通过与其他Diboride晶体，TIB_2，HFB_2，VB_2，VB_2，NBB_2，NBB_2，TAB_2，TAB_2，TAB_2和CRB_2进行比较，可以检查确定晶体质量的因子。随着生长温度的降低，蚀刻坑密度降低。在ZRB_2的情况下，蚀刻坑密度为5 x 10^6 /cm^2，将降至一半，将生长温度降低200℃。亚晶界和裂纹的形成受热膨胀的各向异性的影响。 Diborides中具有最高质量的ZRB_2晶体具有较小的热膨胀系数和小的各种矛盾。因此，为了进一步提高晶体质量，发现找到降低生长温度的通量很重要。