Optical polarization anisotropy of nonpolar InN epilayers

Photoluminescence (PL) intensity of both a‐plane and m‐plane InN epilayers has been observed to strongly depend on polarization angle. The PL intensity for polarization perpendicular to c‐axis (E⟂c) is up to four times as that of polarization parallel to c‐axis (E//c) for a‐plane InN, and this ratio is up to seven times for m‐plane InN. The absorption edges of a‐plane samples for the two polarizations are separated by 19 meV, with (E//c) at higher energy side. The PL detected from sample edge also shows such anisotropy. X‐ray diffraction experiments for a series of a‐plane samples, taking orthorhombic distortion of lattice into account, have shown some samples are compressively strained along growth direction and others have negligible strain. With measured strain, the polarization anisotropy has been analyzed by comparing the experimental results with calculated transition energies and relative oscillator strengths including anisotropic in‐plane strain.