To overcome the problem of the low decomposition rate of NH₃, we have developed the laser-assisted MOVPE (la-MOVPE) where an ArF excimer laser (λ=193 nm) dissociates NH₃ photolytically [1]. A film can be grown in a wide range of growth temperature, from RT to 700ºC. This growth technique provides a growth rate of more than 0.5 μm/h just by flowing a very little amount (100 sccm) of NH₃. Thus, the la-MOVPE is promising as a new growth technique for InN. In this paper, we report that, by employing ArF-laser assisted nitridation of sapphire substrate, an N-polarity InN film can be grown by the ArF-laser assisted MOVPE. Using a la-MOVPE system, an InN film is grown at 600ºC on (0001) sapphire substrates. An ArF excimer laser with an energy 50 mJ/pulse and a repetition rate 20 Hz is introduced parallel to the substrate surface. The surface morphology of a grown InN film is found to be markedly dependent on the nitridation conditions for sapphire substrate. When no nitridation is made, the surface of a grown InN film is very rough and many In droplets are seen on it. A film with a mixture of rough-surface regions with In droplets and smooth-surface regions is grown on the substrate nitrided thermally at 1000ºC for 30 min. By employing the ArF-laser irradiation to the NH₃ flow during the substrate nitridation at 1000ºC for 30 min, a smooth surface region is expanded to the entire surface of a film. The smooth surface is found to be stable at a growth temperature higher than 700ºC. The KOH etching of grown films reveals that the smooth surface has a 5-10 time higher etching rate than the rough one. These facts indicate that a film with the smooth surface has N-polarity. Thus, the ArF-laser assisted nitridation of sapphire substrate results in the successful growth of N-polarity InN by MOVPE. [1] A. G. Bhuiyan et al., Jpn. J. Appl. Phys. 42, 7284 (2003).

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