杂质和缺陷对SiC单晶导热性能的影响

Effect of Impurities and Defects on the Thermal Conductivity of Single Crystal SiC

目前关于SiC单晶室温的导热性能,以及导热特性随温度的变化方面的研究报道还存在较大的差异,有关SiC单晶热导率的研究主要是沿c轴<0001>晶向或者垂直于c轴的某一晶向进行的,无法有效地解释热导率的各向异性。本文研究了4H-SiC和6H-SiC单晶<1100>,<1120>,<0001>三个不同晶向上热导率以及其随温度的变化。对SiC单晶切割分别得到沿<1100>,<1120>,<0001>晶向的样品,尺寸为∅12.7 mm×3 mm,利用闪光法对样品测试得到热扩散系数,通过计算获得了SiC单晶不同晶向的热导率数值,采用辉光放电质谱仪(GDMS)和扫描电子显微镜(SEM)进行了杂质和缺陷表征。实验结果表明,SiC晶体<1100>,<1120>,<0001>三个晶向的热导率随温度升高而下降,沿<0001>晶向的SiC样品热导率最小;含有较高杂质离子浓度的6H-SiC样品热导率高于4H-SiC样品;缺陷相比杂质对SiC晶体导热性能影响更大,缺陷是SiC热导率具有各向异性的主要原因。

Currently the investigations on room-temperature thermal conductivity of single crystal SiC and the dependence of thermal conductivity on temperature show some differences.What’s more,most researches relating to the thermal conductivity of single crystal SiC concentrate on the crystalline orientation along c-axis<0001>or vertical to c-axis randomly,which can’t account for the anisotropy of thermal conductivity for SiC rigorously.In this paper,the effect of impurities and defects on thermal conductivity of single crystal 4H-SiC and 6H-SiC in three accurately different directions were studied.These samples(sized∅12.7 mm×3 mm)along<1100>,<1120>,<0001>,respectively cut from a 4H-SiC and 6H-SiC single crystal were characterized by flash method in order to get their thermal diffusion.The thermal conductivity was derived from the product of thermal diffusion and specific heat.Impurities and defects of these samples were characterized by glow discharge mass spectroscope(GDMS)and scanning electron microscope(SEM),respectively.The experimental results indicate that the thermal conductivity of single crystal SiC along<1100>,<1120>,<0001>decreases with increasing the temperature,while the thermal conductivity along<0001>is the smallest among all samples.And the thermal conductivity of 6H-SiC is abnormally larger than that of 4H-SiC as a result of many of impurities within 6H-SiC.Therefore,defect has more obvious effect on the thermal conductivity of single crystal than impurity,which is the reason for the anisotropy of thermal conductivity.