(775c) Atomistic Origin of the Concentration Dependence of Si Dopant Mobility in III-V Semiconductor Alloys

Compound semiconductors made of elements from groups III and V in the periodic table have desirable properties such as high electron mobility and small band gaps. Such properties position them as excellent candidates for a wide range of electronic and photonic applications from high-performance transistors to lasers and optical detectors. Silicon is a typical dopant in III-V materials, but displays highly unusual diffusion behavior whether it is grown-in, implanted or deposited in those materials to make n-type devices. Interestingly, and somewhat counter-intuitively, silicon diffusivity in In(Ga)As alloys improves considerably at higher Si concentrations. Previous studies assume that this is related to a vacancy-mediated mechanism, but this is open to debate. Using InAs/GaAs alloys as a model system, we investigate preferred diffusional pathways of silicon dopants and intrinsic defects (vacancies and self-interstitials) using ab initio calculations. We show that Si-defect complexes, especially split interstitials, play an important role in the experimentally observed concentration-dependent diffusion of Si, as well as compensation effects at high dopant concentration. Vacancy-mediated mechanisms are less important as they are often kinetically inaccessible. We can also explain the differing roles of In versus Ga to affect dopant activation and modify trends of Si diffusion. These results significantly improve our understanding of diffusion and dopant activation in III-V semiconductors and could aid in the design of next-generation III-V based devices.