Polarity control of MOVPE InN on sapphire (0001) was investigated. Two kinds of polarity InN films on sapphire substrate by MOVPE have been prepared by controlling the substrate nitridation process and/or the LT-GaN buffer annealing process. Surface of the nitrided sapphire is a crucial factor in determining the polarity of InN film. N-polarity InN film was grown on the 1000 °C-nitrided substrate without LTGaN buffer; while In-polarity InN film was grown on the 900 °C-nitrided substrate. In the case of InN growth with a LT-GaN buffer, buffer annealing is a crucial issue in determining the polarity of InN film. N-and In-polarity InN films were obtained on the long-time-annealed buffer and the short-time-annealed buffer, respectively.1 Introduction Among the group-III nitrides, InN recently has attracted more attention due to the newly-suggested small band gap of 0.7 eV [1-3], which potentially extends the spectral range covered by group-III nitrides to the infrared. In addition, InN has a very small electron effective mass [4] and a high electron drift velocity [5], which makes the material also promising in high-speed and high-frequency electronic devices. However, the fabrication of InN based devices has been hindered now, due to lack of high quality InN single crystal film. Therefore, growth of high quality InN film is highly required.Polarity is an important property of group-III nitrides with wurtzite structure. The effects of polarity on the growth of InN film by MBE have been reported recently [6,7]. N-(-c) polarity layers could be grown at higher substrate temperature compared with the In-(+c) polarity films; The surface of Npolarity InN film is more smooth than that of In-polarity InN film, and the quality of -c polarity film is better than that of +c polarity film. The situation is very much different from that of other typical IIInitrides of GaN and AlN, where +c polarity is better than -c polarity. This brings us a light to improve the InN film's quality by controlling the polarity. However, it is still not very clear how to control the polarity of InN grown by MOVPE up to now. In this work, we report the growth of -c and +c polarity InN on sapphire substrate by MOVPE.

The growth temperature dependence of the InN film's crystalline quality is reported. InN films are grown on sapphire substrates from 570 to 650°C with low-temperature GaN buffers by metalorganic vapor phase epitaxy ͑MOVPE͒. The X-ray rocking curves and reciprocal space mappings of the symmetric reflection ͑0 0 0 2͒ and asymmetric reflection ͑1 0 1 2͒ are measured with high resolution X-ray diffraction. The results indicate that the crystallinity is sensitive to the growth temperature for MOVPE InN. At growth temperature 580°C, highly crystalline InN film has been obtained, for which the full-width-at-half-maxima of ͑0 0 0 2͒ and ͑1 0 1 2͒ rocking curves are 24 and 28 arcmin, respectively. The crystalline quality deteriorates drastically when the growth temperature exceeds 600°C. Combined with the carrier concentration and mobility, the approach to improve the quality of InN film by MOVPE is discussed. © 2007 International Centre for Diffraction Data.