Silicon-related local vibrational mode absorption in bulk AlGaAs

A new silicon-related local vibrational mode (LVM) absorption in bulk AlGaAs is reported. It consists of six peaks grouped around 450 cm(-1) which form a distinct pattern. The dependence of this LVM absorption pattern on the alloy composition, doping level and temperature was studied. We believe that the new LVM absorption is a fingerprint of a single defect. Among the discussed microscopic structures the most plausible is a Si-Ga-Si-As pair complex with Si-As acceptor interacting with different Ga, Al nearest neighbour local environments. The relation of the defect structure to the relaxed Si-Ga DX-centre configuration is also considered.