Ultrafast excitonic radiative recombination in Al-rich semipolar AlGaN quantum wells for far-UVC emitters

Abstract

Ultrafast excitonic radiative recombination in Al-rich semipolar AlGaN quantum wells was characterized by photoluminescence and analyzed with a non-equilibrium Green's function (NEGF) model. The heterostructures consisted of Al0.69Ga0.31N/Al0.9Ga0.1N multiple quantum wells grown on (202¯1) bulk AlN substrates by MOVPE. The quantum wells were 3 nm thick, separated by 10-nm thick barrier layers, and possessed a low (<100 kV/cm) polarization field. Radiative lifetimes as low as ∼60 ps were recorded at 75 K. Experimental results validated the NEGF model, which incorporated excitons and free carriers and enabled calculation of the radiative lifetimes for different growth planes, temperatures, and carrier densities. Including intersubband scattering in the NEGF model significantly reduced the calculated radiative lifetimes for QW widths larger than the Bohr radius of the excitons in semipolar and nonpolar orientations, for which the polarization field is reduced or eliminated. These wide wells with low polarization fields and high radiative recombination are less susceptible to the deleterious effects of alloy and interface fluctuations, making them an attractive possibility for future devices.