Diffusion of ion-implanted group 4 n-type dopants in gallium arsenide and gallium/arsenide-based superlattices

As semiconductor device dimensions shrink, understanding and controlling dopant diffusion becomes increasingly important. For submicron FET's made in GaAs, dopant diffusion during post-implant anneal is undesirable. In addition, impurity induced intermixing of III-V heterostructures for optoelectronic devices requires a series of carefully controlled diffusion steps. A more complete understanding of the diffusion mechanisms of dopants and point defects in both GaAs and Al(x)Ga(1-x)As is thus required for several advanced technologies. Most of the published parameters for diffusion of dopants in III-V compound semiconductors are from thin film or vapor source diffusions. The effect of implant damage and extended defects on diffusion of implanted dopants in GaAs and Al(x)Ga(1-x)As has not been extensively studied. In this work we measure the carrier concentrations and diffusivities of the ion-implanted Group IV dopants Sn, Ge and Si in GaAs and Al(x)Ga(1-x)As, using SIMS, polaron and SUPREM 3.5 simulations. In the substrate, diffusion is modeled by an effective diffusivity which depends on the square of the electron concentration (n), due to enhancement of the negatively charged Ga vacancy concentration by the n-type doping. In the near-surface implanted region diffusion is suppressed for doses greater than 1 x 10(exp 14)/sq cm. The carrier concentrations for Sn implants are anomalously high in this region, and anomalously low for Ge and Si. Transmission electron microscopy shows that precipitates and dislocations form in the implanted region during annealing for doses greater than 1 x 10(exp 14)/sq cm. These extended defects may influence dopant diffusion by controlling the generation and recombination of point defects. The carrier concentration-dependent diffusion model is applied to interdiffusion of Al and Ga in AlAs/Al(x)Ga(1-x)As superlattice structures. We show that interdiffusion is enhanced more under an oxide film than under a nitride film, while a tungsten nitride film suppresses disordering. These effects are due to Fermi level enhancement of the vacancy concentration and vacancy injection from the encapsulant.