DIFFUSIVITY AND DEFECT REACTIONS OF LITHIUM IN GAAS

The diffusion of lithium in GaAs is shown to be trap limited at high d oping levels. As in the case of other reactive impurity species in sem iconductors, the intrinsic diffusivity of Li in GaAs can only be measu red in lightly Li-doped material that has high purity or exhibits weak pairing interactions. From charge-density profiles in Zn-doped GaAs m easured by the capacitance-voltage technique we determine the intrinsi c diffusivity of Li to be D-i = D(0)exp(-E-m/k(B)T) with E-m = 0.67 +/ - 0.02 eV and D-0 = (0.5 - 2) x 10(-2) cm(2)/s. In Li-rich, nominally undoped starting material, however, the diffusion is limited by the fo rmation of complexes involving several Li atoms and native defects. Th e most weakly bound Li atoms are released from the complexes above 100 degrees C and a dissociation energy of E-d = 1.20 +/- 0.03 eV can be used to characterize the effective diffusion behavior. A previously re ported 1.0-eV migration energy for lithium in Li-saturated GaAs at hig h temperatures is consistent with our observations under the model of trap-limited diffusion.