(Fig. ). Also, the composition of the AlN film changes when different gases were used were higher O impurities was detected for N2 and Ar compared to when H2 was used. When N2 and Ar was used 5.2 and 5.5 at.% O was detected compared to 4.3 at.% when H2 was used. The Al/N ratio was 1.07 when H2 was used while the ratio was 1.13 and 1.16 when N2 and Ar was used respectively. We speculate that the hydrogen pulse act to scavenge oxygen from the film surface and that this, together with the higher thermal conductivity of H2 (0.182 Wm -1 deg -1 )