单晶硅是制造硅太阳能电池的主要材料之一,但其中的各类缺陷对其光电转换效率影响颇大。针对这些问题,采用空气耦合Lamb波检测方法对单晶硅产品的质量进行快速评价。理论计算Lamb波在各向异性的单晶硅中的频散曲线,得到Lamb波在不同方向上的理论速度分布;利用空气耦合超声传感器在(001)晶面的单晶硅中激励出A0模态的Lamb波,研究200 k Hz频率下Lamb波的入射角度与信号幅值的关系,确定最优入射角度为13°。采用相位谱的方法计算A0模态的相速度,试验结果与理论值吻合良好。利用波包幅值法和相关函数法分别计算A0模态的群速度,结果说明相关函数法测得的群速度与理论值误差更小;采用扫描方法对单晶硅进行缺陷检测,通过计算接收信号与参考信号的相关系数,确定出缺陷的位置和大小。
Monocrystalline silicon is one of the main materials that is used to make silicon solar cells. However, all kinds of defects existing in monocrystalline silicon have a great influence on the photoelectric conversion efficiency. In order to solve this problem, air-coupled Lamb waves testing method is proposed to achieve rapid quality evaluation of monocrystalline silicon products. The dispersion curves of Lamb waves in anisotropic monocrystalline silicon are calculated theoretically. The velocity distribution of Lamb waves at different directions is obtained. A0 mode of Lamb waves is excited in the monocrystalline silicon of(001) crystal plane by the air-coupled transducers. The relationship between the incident angle of Lamb waves and the amplitude of signal at 200 k Hz is investigated,by which 13° is chosen as the optimal incident angle. The phase velocity is calculated by phase spectrum method. Experiment results show a great agreement with those theoretical values. The group velocity is measured by amplitude of wave packet method and the correlation function method. The deviation by the latter method is smaller to acquire the group velocity. Scanning method is used to detect the defect in the monocrystalline silicon. The location and size of the defect is reconstructed by calculating the correlation coefficient of the received signals and reference signals.