Rapid ion-implantation-induced amorphization ofInxGa1−xAsrelative to InAs and GaAs

Abstract

We report on the rapid implantation-induced amorphization of the ternary ${\text{In}}_{x}{\text{Ga}}_{1\ensuremath{-}x}\text{As}$ alloys. Unlike ${\text{Al}}_{x}{\text{Ga}}_{1\ensuremath{-}x}\text{As}$, ${\text{In}}_{x}{\text{Ga}}_{1\ensuremath{-}x}\text{As}$ did not exhibit amorphization kinetics intermediate between the two binary-alloy extremes. Instead, our investigation of the crystalline-to-amorphous phase transformation over the entire stoichiometry $(x)$ range demonstrated that ${\text{In}}_{x}{\text{Ga}}_{1\ensuremath{-}x}\text{As}$ alloys with $x=\ensuremath{\sim}0.06--0.53$ were rendered amorphous at fluences less than that required for both InAs and GaAs. Implantation-induced disorder was quantified with Rutherford backscattering spectroscopy in the channeling configuration and fit to the Hecking model to yield the probabilities of direct-impact and stimulated amorphizations. The phase transformation was dominated by stimulated amorphization, which was a maximum at the stoichiometry $(x=\ensuremath{\sim}0.34)$ most easily amorphized, while the probability of direct-impact amorphization was effectively stoichiometry independent. From extended x-ray-absorption fine-structure spectroscopy measurements of unimplanted ${\text{In}}_{x}{\text{Ga}}_{1\ensuremath{-}x}\text{As}$ alloys, separate stoichiometry-dependent In-As and Ga-As bond lengths were measured. Distortion in both the bond-length and bond-angle distributions was apparent though structural perturbation was primarily accommodated in the latter as consistent with measured deviations from the tetrahedral bond angle. We attribute the relative ease with which the ${\text{In}}_{x}{\text{Ga}}_{1\ensuremath{-}x}\text{As}$ alloys were amorphized to the presence of localized regions of strain due to structural distortion. Equivalently, atomistic configurations comprised of strained bond lengths and bond angles represent pre-existing and preferential sites for stimulated amorphization. To demonstrate the general applicability of our model, we report on preliminary measurements with the ${\text{In}}_{x}{\text{Ga}}_{1\ensuremath{-}x}\text{P}$ alloys which also exhibit a bimodal bond-length distribution and distortion in the bond-angle distribution. Comparable amorphization behavior to that of the ${\text{In}}_{x}{\text{Ga}}_{1\ensuremath{-}x}\text{As}$ alloys has been observed.