Optical anisotropy studies of sapphire by raman scattering and spectroscopic transmission ellipsometry

摘要

Optical anisotropy of sapphire have been studied by both polarized Raman scattering and transmission variable angle spectroscopic ellipsometry (TVASE). The polarized Raman effect was measured on both c-plane (0001) and a-plane (21-bar 1-bar 0) sapphire substrates. Two TO phonons (379 and 431 cm~(-1) and four LO phonons (418, 450, 577, and 750 cm~(-1)) were observed when the opticla axis is perpendicular to the polarization of the incident laser beam (for both c-plane and a-plane). While only two TO phonons (379 and 431 cm~(-1)) and two LO phonons (418 and 645 cm~(-1)) can be seen when the optical axis is parallel to the polarization for an a-plane sapphire. The optical axis of the a-plane sapphire can then be quickly determined by either maximizing or minimizing the 645 LO peak intensity with about +- 10 deg error. TVASE measrurements were carried out in the energy rangy of 0.75eV to 5.8 eV at room temperature. Sizable off-diagonal Jones matrix elements A_(pst) and A_(spt) can be detected even with the optical axis 1 deg off the X-axis. THis indicates that TVASE has a high sensitivity to optical anisotropy. By minimizing these off-diagonal elements and combining the Raman analysis, the optical axis orientation of an a-plane or m-plane (011-bar0) sapphire can therefore be fully determined with an error of less than 1 deg.