Preferred diffusional pathways of intrinsic defects and silicon dopants in an ordered phase of In_0.5Ga_0.5As: A first-principles study

Integrating III-V semiconductors into next-generation silicon-based transistors is a promising alternative being considered as a route to faster and more energy-efficient electronic devices. These III-V materials will be doped, typically with Si as a dopant. However, dopant activation remains an issue, compounded by the fact there is still insufficient knowledge of the ease and preferred mechanistic pathways by which dopants, like Si, become activated within the III-V matrix. Using Density Functional Theory calculations, we have determined many of these critically important properties, namely, the energy barriers associated with the diffusion of both intrinsic point defects and silicon impurities in a prototypical ternary III-V material, here a CuAuI-ordered In_0.5Ga_0.5As. Refuting assumptions in the current literature, vacancy-assisted diffusion was found to be an unfavorable mechanism for this ordered ternary alloy, unlike in GaAs. Hence, substitutional Si atoms are essentially immobile on experimental timescales. While vacancies are nearly immobile, interstitials, especially split interstitials, can move easily within the crystal lattice. These defects become significant at high Si concentration leading to the unexpected phenomenon of enhanced diffusion of Si at high concentrations, which explains experimental observations.