In-plane optical polarization and dynamic properties of the near-band-edge emission of an m-plane freestanding AlN substrate and a homoepitaxial film

摘要

For accelerating the development of deep-ultraviolet light-emitting diodes based on high AlN mole fraction (x) AlxGa1-xN for sterilization, disinfection, and skin therapy applications, in-plane optical polarization and dynamic properties of the near-band edge (NBE) cathodoluminescence (CL) peak of a low threading dislocation density (10(3) cm(-2)) m-plane freestanding AlN substrate and a homoepitaxial film are assessed. Consistent with the polarization selection rules, the electric field (E) component of the NBE emission was essentially polarized parallel to the c-axis (E parallel to c). Low-temperature CL spectra of the homoepitaxial film exhibited exciton fine structures: CL peaks at 6.041(0) and 6.027(9) eV, which were polarized E parallel to c and E perpendicular to the c-axis (E perpendicular to c), respectively, are assigned as being due to the recombination of free A-excitons of irreducible representations Gamma(1) and Gamma(5). The hydrogenic binding energy of the Gamma(1) A-exciton being 51 meV is verified. Detectable CL peaks under E parallel to c polarization at 6.031(5) and 6.021(2) eV are tentatively assigned as Gamma(1)-mixed Gamma(5)-exciton-polaritons. The concentration of multiple vacancies consisting of an Al-vacancy (V-Al) and N-vacancies (V(N)s), namely, V-Al(V-N)(2-3), in the substrate was estimated by the positron annihilation measurement to be 2-3 x 10(16) cm(-3), while that in the epilayer was lower than the detection limit (10(16) cm(-3)). The NBE CL lifetime of 28 ps of the epilayer subsurface at 300 K is likely limited by the recombination at carbon deep-acceptors on nitrogen sites (3 x 10(17) cm(-3)) and/or V-Al(V-N)(2-3) Shockley-Read-Hall nonradiative recombination centers (similar to 1 x 10(16) cm(-3)) with hole capture coefficients of approximately 1x10-7 and 3x10-6 cm(3) s(-1), respectively.