Methods of forming titanium-aluminum layers for gate electrodes and related semiconductor devices

Methods of forming a semiconductor device are provided in which a first titanium-aluminum layer is formed in a recess. A first titanium layer is formed in the recess on top of the first titanium-aluminum layer. A first aluminum layer is formed in the recess on top of the first titanium layer to form a first preliminary gate electrode structure in the recess. The first preliminary gate electrode structure is heated to a temperature sufficient to convert the first titanium-aluminum layer, the first titanium layer and at least some of the first aluminum layer into a second titanium-aluminum layer. A second titanium layer is formed on top of the second titanium-aluminum layer. A second aluminum layer that is thicker than the first aluminum layer is then formed on top of the second titanium layer. The structure is heated to a temperature sufficient to convert the second titanium-aluminum layer, the second titanium layer and the second aluminum layer to a final third titanium-aluminum layer and final gate structure.