In-situ curvature measurements were employed to analyse stress generation and relaxation during epitaxial growth of undoped and Si-doped AlGaN layers on AlN/sapphire templates. While AlGaN films with a lower Al content exhibit a compressive strain during growth including a gradual relaxation, layers with a high Al content (x >= 0.8) grow under tension due to the AlN/sapphire effective substrate properties. Wafer curvature analysis and accompanying STEM measurements suggest that compressive stress relaxation involves misfit dislocations at or near the heterointerface as well as effective dislocation climb during growth. In addition, introduction of Si as n-type dopant in AlxGa1-xN adds a tensile stress component, most likely driven by a surface-mediated dislocation climb process. (C) 2013 Elsevier B.V. All rights reserved.