From anti‐Stokes photoluminescence to resonant Raman scattering in GaN single crystals and GaN‐based heterostructures

The progress on anti‐Stokes photoluminescence and Stokes and anti‐Stokes Raman scattering in GaN single crystals and GaN/AlN heterostructures is reviewed. Anti‐Stokes photoluminescence investigated in the past was primarily attributed to two‐photon absorption, three‐photon absorption, and phonon‐assisted absorption. On the other hand, anti‐Stokes Raman scattering was used to determine electron‐phonon scattering time and decay time constant for longitudinal‐optical phonons. In a typical high electron mobility transistor based on GaN/AlN heterostructures, strong resonances were reached for first‐order and second‐order Raman scattering processes. Therefore, both Stokes and anti‐Stokes Raman intensities were dramatically enhanced. The feasibility of laser cooling of a nitride structure has been demonstrated. Anti‐Stokes photoluminescence and Raman scattering have potential applications in upconversion lasers and laser cooling of nitride ultrafast electronic and optoelectronic devices.