We have systematically studied the solubility limit and the activation temperature of As implanted in relaxed Si1-xGex (x = 0-0.3) alloys. The solubility limit of As in Si1-xGex alloys at an annealing temperature of 600 degrees C was found to decrease monotonically with increasing Ge content. The carrier activation temperature showed anomalous dependence on Ge content, and increased first and decreased with Ge content above x = 0.1. The presence of inter-atomic strain might explain this behavior, even though Si1-xGex alloys are macroscopically unstrained.