Infrared absorption study of Li-diffused Mg-doped GaAs

The infrared absorption of Mg-doped GaAs compensated by Li diffusion is measured and the results are compared with those of similar material compensated by electron irradiation and for double-doped material. The absorption bands observed in the GaAs : Mg–Li are consistent with a model in which there is only one type of (Mg–Li) pair defect and one Li paired with each Mg. The (Mg–Li) pair has orthorhombic or lower symmetry with the pair axis probably in a 〈001〉 direction. The Li is in an interstitial position. In GaAs : Mg–Li there is no measurable concentration of Mg which is not paired with Li. Unpaired MgGa absorption is observed in electron-irradiated and in double-doped samples. The ωL values are 331, 326, and 321.5 cm−1 for 24MgGa, 25MgGa, and 26MgGa, respectively. At liquid-nitrogen temperature, the unpaired MgGa has an absorption cross section of σ(24MgGa)≈1.0×10−17 cm2. There is no evidence for pairing between MgGa and any defect centers produced by electron irradiation. The existence of Mg–Te and Mg–Se pairs, probably with C3v symmetry, has been established for impurity concentrations ∼ 1019 cm−3.