Stress influence on band-edge luminescence properties of 4H-AlN

The band-edge luminescence properties of 4H-AlN under biaxial and uniaxial stress are studied using the first-principle method. In equilibrium, excitons B and C have energies 92 and 14 meV lower than exciton A, respectively. When the uniaxial tensile strain exceeds ∼0.95%, the top valence band is the B exciton state. Its band-edge emission is no longer prohibited and changes to E⊥c. The shift in the A exciton energy is similar to that of 2H-AlN under stress of −5 to 5 GPa. When the compressive biaxial strain is larger than 5 GPa, the band structure of 4H-AlN becomes indirect.