Annealing effects on crystallized aluminum doped hydrogenated amorphous germanium (a-Ge:H) thin films have been studied by Raman spectroscopy, as a function of Al concentration ([Al/Ge] ∼10–6–10–2 range). All the as-deposited Al-doped a-Ge:H samples with [Al/Ge] < 1.3 at% possess a Raman spectra that includes the signal given by the amorphous phase and a shoulder at around 300 cm–1, that evolves with increasing impurity content, to a well defined peak, corresponding to the contribution of the TO vibration of crystallized Ge. The scattering intensity of samples having 1.4 ≤ [Al/Ge] ≤ ∼1.8 at% is dominated by the c-Ge TO vibration. Aluminum concentrations above [Al/Ge] > ∼1.8 at% do not indicate crystallization of a-Ge:H films to levels detectable by Raman spectroscopy. An abrupt crystallization was observed to occur after annealing at Ta ∼ 500 °C for all the range of the Al-doped samples, including the intrinsic one. These results and the comparison with data of the local order and coordination of Ga atoms into the a-Ge:H network, suggest that Al-induced crystallization originates from fourfold coordinated aluminum atoms that act as crystallization seeds. These seeds have only small influence on the abrupt crystallization of Al doped a-Ge:H films due to annealing treatments. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)