The Energy Band Gap of AlxGa1-xN Thin Films as a Function of Al-Mole Fraction

In this work, the effects of Al mole fraction on energy band gap (Eg) of Al_xGa_1-xN epilayers grown on sapphire substrate are investigated. Attention is focused on the Ga- rich composition samples (0 les x < 0.10). The Al-mole fraction is determined by high- resolution X-ray diffraction (HR-XRD) spectroscopy. Ultraviolet-visible (UV-VIS) transmission and micro-photoluminescence (mu-PL) spectroscopy are employed to determine the energy band gap of the samples. The XRD results revealed that the Bragg angle of the rocking curve (RC) peak gradually increases as the Al-mole fraction increases, indicating the reductions in the lattice constant c of the alloys. By the application of Vegard´s law, the Al-mole fractions of Al_xGa_1-xN samples have been calculated. Overall, the UV-VIS transmission and mu-PL results showed that as the Al-mole fraction increases, blue shifts of the absorption edge and band edge emission are observed in all samples. These indicate the strong dependence of the band gap energy of Al_xGa_1-xN on the Al-mole fraction. Finally, the band gap energy of the Al_xGa_1-xN as a function of Al-mole fraction have been plotted and the energy band gap bowing parameter of 14.62 eV is obtained from the best fit of the non-linear interpolation of the UV-VIS transmission and the PL data.