Diffusivity and defect reactions of lithium in GaAs

The diffusion of lithium in GaAs is shown to be trap limited at high doping levels. As in the case of other reactive impurity species in semiconductors, the intrinsic diffusivity of Li in GaAs can only be measured in lightly Li-doped material that has high purity or exhibits weak pairing interactions. From charge-density profiles in Zn-doped GaAs measured by the capacitance-voltage technique we determine the intrinsic 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 formation of complexes involving several Li atoms and native defects. The 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 reported 1.0-eV migration energy for lithium in Li-saturated GaAs at high temperatures is consistent with our observations under the model of trap-limited diffusion.