Unveiling Transition Dipole Moment Anisotropy and Symmetry Breaking Mechanism in Wurtzite Nitride Toward Polarization‐Sensitive Ultraviolet Detection

Polarization detection in shortwave spectrum using wurtzite wide-bandgap semiconductors remains challenging due to the isotropic limitations of conventional polar crystal planes. Nonpolar planes offer a promising route, yet the underlying physical mechanism is unclear. Here, we establish a direct correlation between crystallographic polarity and anisotropic photoresponse on nonpolar a-plane GaN, demonstrating an intrinsic polarization-sensitive photodetection scheme. Crystal-field-induced valence band splitting yields distinct transition dipole moments from heavy-hole and crystal field split-off bands to the conduction band minimum, enabling selective absorption for light polarized perpendicular or parallel to the c-axis. Using the nonpolar plane of GaN, electron transition probability between the heavy-hole band and conduction band minimum for polarization perpendicular to the c-axis is selectively enhanced, governing polarization-angle-dependent absorption. Our device achieves a high dichroic ratio of 3.79 (318% higher than c-plane) and an ultrafast response speed of 1.7 µs at 10 V, surpassing conventional polar-plane architectures and prior polarization-sensitive detectors. Furthermore, by introducing an oxygen injection layer to strategically break lattice symmetry, anisotropic charge density distribution around oxygen atoms further enhances the dichroic ratio. Exceptional polarization discrimination is validated in single-pixel polarized imaging and intensity/polarization binary-channel optical communication encryption. This work establishes a material-intrinsic paradigm for high-sensitivity polarization detection, offering new perspectives for multidimensional optoelectronics.