Micro-polarimetry of anisotropic materials using infrared microscopy.

Infrared spectroscopic techniques can uncover extensive information about structural and electronic properties of semiconductor and dielectric materials. However, determining the properties of arbitrarily anisotropic, and small-scale samples pose challenges. In this talk, we will detail instrumental improvements to infrared microscopy which allow precise measurements of the optical properties of materials. We will show that through the correct experimental techniques and physical models, we are able to extract anisotropy, birefringence and polarization asymmetries from artificial and natural materials. We will also discuss the limitations of these techniques, as it pertains to the accuracy of fitted parameters and experimental design. As case studies, we will discuss Gallium Nitride, Boron Nitride, and gallium oxide as exemplar cases. For Gallium Nitride and Boron Nitride, we will show we are able to extract the in and out of plane optical constants of these materials and can extract temperature dependent carrier densities using micro-polarimetry. For gallium oxide, we will show how the lattice symmetry can be tracked through orientation specific polarized reflectance, revealing the low lattice symmetry.  Our approach offers a generalizable framework for materials studies, which could be further optimized for full infrared micro-ellipsometry.