Nondestructive inspection of crystal defects in LiNbO3 wafers by using an optical technique

In order to develop a nondestructive technique for inspection of optical-grade LN wafers used as substrate to fabricate optoelectronic devices such as electro-optic modulator, a scanning IR polariscope (SIRP), which was developed to measure a small amount of residual strain in optically isotropic GaAs wafers, has been employed. It is demonstrated that the sensitivity of SIRP adopted for LN wafers is high enough to detect the change in refractive index caused by crystal defects, down to the order of 10-7. X-ray topography measurement is also carried out to confirm the usefulness of SIRP as an inspection tool of crystal defects in optical-grade LN wafers.