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We have investigated influence of substrate polarity on the growth of InN films by RF-MBE. It was found that the temperature required for successful growth of InN strongly depended on the substrate polarity. InN could be grown on C-face SiC at 550 °C, whereas no InN growth occurred on Si-face SiC at 550 °C. InN growth on Si-face SiC was realized at lower temperature of 450 °C. In the case of the growth on freestanding GaN substrates, InN could be grown on N-face GaN at 550 °C, whereas InN growth on Ga-face GaN was realized at 450 °C. It was found that InN with N polarity can be grown at higher temperature than that with In polarity. These results indicate that control of polarity is essential for successful growth of InN.1 Introduction InN is a very attractive material for future optical and electronic devices due to its excellent physical properties. However, the growth of high-quality InN is very difficult, because of the low dissociation temperature of InN and the extremely high equilibrium vapour pressure of nitrogen. Therefore, physical properties of InN and its growth mechanism are still not fully understood. In the case of GaN growth, the polarity of GaN is a key characteristic because the film with Ga polarity has better surface morphology and crystal quality than the film with N polarity [1]. It is also reported that the decomposition rate of GaN is dependent on the polarity [2]. Furthermore, for GaN-based electronic devices using piezoelectric effect, the strain and the polar direction of the film influence device performances [3]. Thus, to understand and control the effect of the polarity is essential and many efforts have been made on these issues for GaN-related materials [4][5][6]. However, the number of reports on polarity of InN is only a few [7,8] and it is not understood how the polarity of substrate influences the growth of InN. In this paper, we investigate the influence of substrate polarity on growth of InN films.

The direct growth of a GaN epitaxial layer on a Si(111) substrate by metalorganic vapor phase epitaxy (MOVPE) was performed using a low-temperature (LT)-GaN buffer layer with no Al-containing intermediate layer (e.g., AlN or AlGaN). No deterioration in the Si surface caused by the reaction between Si and Ga vapor was observed. However, when there were Ga droplets on the surface, Ga and Si formed a Ga–Si alloy, which caused the generation of numerous holes on the surface by melt-back etching at high temperatures. In addition, it was revealed that the coverage of the LT-GaN buffer layer on Si was strongly affected by the hydrogen (H2) partial pressure in the carrier gas. Using nitrogen (N2) carrier gas, a complete coverage of the LT-GaN buffer layer could be achieved directly over the Si surface. These features can be explained by the facts that the Si surface is partially terminated by hydrogen atoms and the coverage of hydrogen on Si surface depends on H2 partial pressure.

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