Mechanisms of Implantation Damage Formation in Al_<i>x</i>Ga_1–<i>x</i>N Compounds

Abstract

AlxGa1–xN alloys, covering the entire compositional range (0 ≤ x ≤ 1), were implanted at room temperature with 200 keV argon (Ar) ions to fluences ranging from 1 × 1013 to 2 × 1016 Ar/cm2. The damage formation mechanisms and radiation resistance of AlxGa1–xN alloys were investigated combining in situ Rutherford backscattering spectrometry/channeling (RBS/C) and ex situ X-ray diffraction (XRD) in order to assess the damage profiles and the elastic response of the material to radiation. For all compounds, damage buildup proceeds in four stages revealing a saturation of the defect level for high fluences without any sign of amorphization. Surprisingly, in this high fluence regime, RBS/C reveals higher defect levels in samples with high AlN concentrations in contrast to the common believe that AlN is more radiation resistant than GaN. A model is proposed ascribing this behavior to a lower defect recombination cross section at room temperature combined with the formation of stable extended defects. The processes are probably dependent on the collision cascade density, that is, the mass of the implanted ions. XRD shows that implantation leads to the incorporation of large lattice strain in the implanted layer which increases with increasing fluence. Above a threshold fluence, an abrupt change of the elastic properties of the crystals is observed and strain saturates in the entire implanted region. This threshold fluence is reached earlier for GaN than for AlxGa1–xN alloys with x > 0.