Reflectance difference spectroscopy microscope for circular defects on InN films.

Reflectance difference spectroscopy microscope (μ-RDS) is presented to characterize microstructural defects on the surface of materials. We use this microscope to study the circular defects on InN films and obtain the real normal reflectivity image and reflectance difference (RD) image by averaging the results before and after a 90° rotation of the sample. We analyze the experimental data along with other methods and formally ensure the reliability of this microscope. Comparing with the results of AFM, we prove that the reflectivity image of our μ-RDS can characterize the surface topography, size and location of the defects. We find the RD image generated by uniform height fluctuation is a standard four polar distribution in an established ideal circular defect model. However, a non-four polar distribution of RD image can be caused by the strain field as well as nonstandard height fluctuations, which is verified by simulation and Raman mapping technique. So the μ-RDS is an ideal tool for optical anisotropy distribution induced by small changes in the height and strain field around the defect boundary in plane.