We have successfully been able to deposit GaN on Si (100) and 4H-SiC (0001) using tris(dimethylamido)gallium(III) together with NH3 by both thermal and plasma ALD. The NH3 plasma process showed surface saturation could be obtained with a GPC of 1.4 Å/cycle after 4 s of 1 and 6 s of NH3 plasma. The growth per cycle was independent of temperature between 130-250  C and the growth rate was 3-5 times higher than previously reported ALD of GaN.