photogalvanic

Photogalvanic effects are phenomena in which a material generates an electric current under illumination without an external electrical bias. They arise from the bulk photovoltaic effect seen in homogeneous, non-centrosymmetric materials or at interfaces, where broken inversion symmetry allows photoexcited carriers to acquire a net momentum, producing a dc current that flows in response to light. The effect is of interest in fundamental studies of light–matter interactions as well as in polarization-sensitive photodetection.

Two main variants are recognized: the linear photogalvanic effect (LPGE) and the circular photogalvanic effect (CPGE). In LPGE, the current depends on the linear polarization state of the incident light and scales with light intensity, reflecting anisotropic carrier excitation and relaxation in the crystal. In CPGE, the current is sensitive to the helicity of circularly polarized light and often requires spin-orbit coupling and spin-split bands; it can be related to Berry-curvature effects and selective optical transitions. The direction and magnitude of the current are constrained by crystal symmetry and material structure.

Materials that exhibit photogalvanic effects include non-centrosymmetric semiconductors and materials with strong spin–orbit coupling, such as GaAs, tellurium, certain quantum wells, and the surfaces of topological insulators like Bi2Se3. The effects have been explored for polarization-sensitive photodetectors, terahertz sensors, and studies of spin and valley physics. While not a general replacement for p–n junction photovoltaics, photogalvanic effects provide insight into light–matter interactions and offer routes to detector technologies that directly convert light polarization into electrical signals.