We report on electronic transport measurements of the magnetic semiconductor Ga_{1-x}Mn_{x}As, whereby the defect landscape in various metallic thin films (x=6%) was tuned by He-ion irradiation. Changes in the distribution of activation energies, which strongly determine the low-frequency 1/f-type resistance noise characteristics, were observed after irradiation and can be explained by deep-level traps residing in the As sublattice. Various other kinds of crystalline defects such as, for instance, Mn interstitials, which possibly form nanoscale magnetic clusters with a fluctuating spin orientation, also contribute to the 1/f noise and can give rise to random telegraph signals, which were observed in films with x=7%. In addition, we neither find evidence for a magnetic polaron percolation nor any features in the noise near the Curie temperature.
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