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

For accelerating the development of deep-ultraviolet light-emitting diodes based on high AlN mole fraction (x) Al_xGa_1-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 (<10³ 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 (⁠$E∥c$⁠). Low-temperature CL spectra of the homoepitaxial film exhibited exciton fine structures: CL peaks at 6.041₀ and 6.027₉ eV, which were polarized $E∥c$ and E perpendicular to the c-axis (⁠$E⊥c$⁠), respectively, are assigned as being due to the recombination of free A-excitons of irreducible representations $Γ1$ and $Γ5$⁠. The hydrogenic binding energy of the Γ₁ A-exciton being 51 meV is verified. Detectable CL peaks under $E∥c$ polarization at 6.031₅ and 6.021₂ eV are tentatively assigned as $Γ1$-mixed $Γ5$-exciton-polaritons. The concentration of multiple vacancies consisting of an Al-vacancy (V_Al) and N-vacancies (V_Ns), namely, $VAlVN2−3$⁠, in the substrate was estimated by the positron annihilation measurement to be 2–3 × 10¹⁶ cm⁻³, while that in the epilayer was lower than the detection limit (<10¹⁶ 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 × 10¹⁷ cm⁻³) and/or $VAlVN2−3$ Shockley-Read-Hall nonradiative recombination centers (∼1 × 10¹⁶ cm⁻³) with hole capture coefficients of approximately $1×10−7$ and $3×10−6$ cm³s⁻¹, respectively.