Composition and bandgap control of AlxGa1−xN films synthesized by plasma-assisted pulsed laser deposition

Abstract

Ternary Al_xGa_1−xN films with different Al compositions were synthesized on sapphire and Si substrates by pulsed laser co-ablation of a polycrystalline GaAs target and a metallic Al target in nitrogen plasma generated by electron cyclotron resonance discharge of N₂ gas. Spectroscopy was used to characterize the synthesis process for the mechanisms responsible for Al_xGa_1−xN synthesis and film deposition. The synthesized Al_xGa_1−xN films were evaluated using field emission scanning electron microscopy, atomic force microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, Raman scattering spectroscopy, transmission electron microscopy and optical transmission measurements. The Al_xGa_1−xN films have hexagonal wurtzite structure, which degenerates as the Al composition increases, and show high optical transparency with the absorption edge blue shifted and the bandgap widened with the increasing Al composition. A comparison of the synthesized Al_xGa_1−xN films with the binary GaN and AlN films synthesized by a similar method reveals their similarity in the structure and the optical properties.