Photoluminescence properties of Al-rich AlXGa1-XN grown on AlN/sapphire template by MOCVD

Optical properties of the un-doped and the Si-doped Al-GaN epilayers have been studied by using the deep ultraviolet photoluminescence (PL) spectrum. The samples were grown under the same conditions on a HT-AlN template by low pressure metal-organic chemical vapour deposition (LP-MOCVD). The Al composition and the relaxation status were detected to be 0.654 and 42% for the un-doped AlGaN, 0.657 and 63% for the Si-doped AlGaN by use the high resolution XRD. The temperature dependent PL spectra of both AlGaN epilayers reveal a typical energy broadband around 2.85 eV involving the deep level impurity transitions and the different peak shift behaviour of localized excitons around 4.97 eV with temperature increasing from 13 K to 120 K. The luminescence intensity of the excitons in both samples indicated a thermal quenching process with two activation energies. The two activation energies E-act1 and E-act2 were assigned to the thermal barrier resulting from the strong composition fluctuation in AlGaN and the binding energy of the excitons, respectively. The different PL oscillation properties of two samples at the 2.85 eV emission band indicate the Si-doped AlGaN epilayer has significant interference of interface and surface. The significant oscillations were attributed to less centres of nucleation in the Si-doped AlGaN, as has been supported by atomic force microscopy. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim