Luminescence properties of heavily doped Al x Ga 1-x N/AlN films grown on sapphire substrate

Abstract Luminescent properties of the Al x Ga 1-x N films with Si dopant concentration more than 10 20 cm −3 grown by molecular beam epitaxy on sapphire substrates with AlN buffer film were investigate at room temperature. Time-resolved photoluminescence spectroscopy was employed to study the donor-acceptor pair transitions in the Al x Ga 1-x N/AlN/Al 2 O 3 structures with Al mole fraction x from 0.47 to 1 under action of Nd:YAG (λ = 266 nm) laser radiation. The radiation inside planar waveguide consists of spontaneous emission and amplified spontaneous emission. The spontaneous emission spectra demonstrated inhomogeneous broadening with FWHM of 0.58 eV covers full visible range and propagate randomly in all directions. The amplified spontaneous emission propagate at near the critical angle of incidence along zigzag path under total internal reflection conditions at the interfaces of the waveguide. Its spectrum consists of several TE m and TM m modes, which have mutually orthogonal polarizations. The optical measured gains are equals to g ≈ 58 cm −1 for Al 0.65 Ga 0.35 N at 510 nm and g ≈ 20 cm −1 for Al 0.74 Ga 0.26 N films at λ = 528 nm. The measured values of quantum yields of spontaneous emission for Al x Ga 1-x N films grow monotonically from 0.11 to 0.79 with increasing x from 0.47 to 0.74. Estimated emission cross-sections for the donor-acceptor pair transitions are more than 10 −18 cm 2 .