AlN/GaN heterostructures are very attractive because their theoretical two-dimensional electron gas (2DEG) density may exceed 5 x 10(13)/cm(2) [1]. However, there are very few reports on AlN/GaN heterostructures grown by MOVPE. In this work, we show that good quality AlN layers can be grown on GaN at a relatively low growth temperature when TMIn is added to the carrier gas flow as a surfactant. Analysis by RBS revealed that at a growth temperature of 900 degrees C or higher no Indium is actually incorporated. Various thicknesses of AlN are grown, from 2 to 8 nm. Finally, 2-3 nm in situ Si3N4 is deposited in order to protect the AlN surface and thus prevent stress relaxation. AFM revealed that the root-mean-square (RMS) roughness in a 1 x 1 mu m(2) area is 0.25 nm. When the AlN thickness reaches 8 nm, the sheet resistance can be as low as 186 +/- 3 Omega/square. Van der Pauw-Hall measurements show that the electron density is about 2.5 x 10(13)/cm(2) with electron mobility exceeding 1140 cm(2)/V s when extra 50 nm PECVD SiN is deposited. (C) 2010 Elsevier B.V. All rights reserved.