In initial experiments, H2 pulses of different lengths were added between the TMA and NH3 pulses. Without addition of H2 pulse, the C content in an AlN film deposited at 480 °C was measured to be 3.1 at. % from XPS analysis. Addition of an H2 pulse decreased the C content, Figure . A short H2 pulse of 3.3s decreases the C content to around 1 at. %. The carbon content is at this low level also for longer durations of the H2 pulse. The same trend is also observed for a deposition temperature of 400 C (Fig. ). For depositions made at lower temperature, 400 °C, the carbon content is slightly lower without the H2 pulse (2.6 at %) as compared to 480 °C and the amount of carbon decreases to about 1.5 at. % with the addition of a H2 pulse. The growth per cycle of the AlN films is stable upon increasing the length of the H2 pulse, Figure . A slight decrease in the growth per cycle with increasing length of the H2 pulse could be observed. The composition from XPS of the film deposited at 480 C with 19.5 s H2 pulse was 49.1 at.% Al, 46.0 at.% N, 4.3 at.% O and 0.6 at.% C which gives a Al/N ratio of 1.07. High resolution XPS spectra for Al 2p were fitted with two sub-peaks at 74.7 eV and 75.5 eV attributed to Al-N and Al-O bonds respectively (Fig. ). For N 1s, the two sub-peaks were positioned at 397.9 eV and 399.