Lithium induced vacancy formation and its effect on the diffusivity of lithium in gallium arsenide

Diffusivity studies on Li in GaAs, where high concentrations of lithium have been introduced into undoped n-type starting material, reveal that diffusion of Li is trap-limited due to formation of complexes containing Li and native defects. The same defect complexes are found in Li-doped semi-insulating starting material and in p-type GaAs:Zn as well after passivation of the Zn acceptors. In partially Li-passivated Zn-doped starting material the Li is found predominantly in Li-Zn complexes which have a relatively low binding energy. In this case, the trapping effect is weak and the lithium exhibits high diffusivity. Using infrared absorption and positron lifetime measurements we investigate complexes of Li atoms and native defects which are formed in the Li-diffusion process. We observe significant V_Ga and Ga_As concentrations in the samples and demonstrate enhanced concentration of these native defects upon heat treatment. We show that Li also forms complexes with these native defects at low diffusion temperatures.