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The Low Temperature grown GaAs (LT GaAs) layers were studied by micro-Raman spectroscopy on ex situ annealed and as grown samples. For investigation of arsenic excess incorporation into LT GaAs the Raman spectroscopy have been employed by using two different excitation wavelengtlui. Raman measurements show that the La phonon of LT GaAs shifted down in frequency from the bulk GaAs for as grown and for annealed samples up to 550??C. Thi.s shift is related to the presence of ASGtJ antisile defects. After Ihe sample is annealed, the epilayer has Ihe same lattice constant as the substrate and the La phonon move closer to the bulk GaAs La phonon . The annealing behavior of LT GaAs layers can be evaluated from TO and La phonon. peaks ratio in Raman spectra and optimal annealing temperature 600"C for investigated samples was detennined from these measurements.