ABSTRACT
Group ΙΠ nitride semiconductors are very promising materials because of their potential for use in optoelectronic and high-power microwave devices. Among ΙΠ-Ν semiconductors, InN has a relatively small direct band gap of ~1.9 eV; hence, visible-light emitting diodes can be made out of continuous alloys with InN. In addition, InN has the smallest effective mass [ 1 ] and the highest electron drift velocity of all ΙΠ-Ν semiconductors [2]. Therefore, InN is expected to be a good material for a channel layer of high-frequency electronic devices such as a heterostructure field-effect transistor (HFET) [3]. However, the growth of InN has been more difficult than the growth of other ΙΠ-Ν semiconductors because of its low dissociation temperature and the relatively high equilibrium N2 vapor pressure over InN films [4]. Recently, epitaxial growths of high mobility InN films with a nitridation and a buffer layer were reported [5,6]. However, the growth mechanisms of InN, especially that for the nitridation and the buffer layer, are not fully clarified. In regard to the nitridation, Tsuchiya et al. [7] reported that the InN films grown without nitridation on sapphire were always polycrystalline. They recently solved this problem by the use of MgAl204 instead of sapphire as a substrate [8 ]. In the meantime, we have clarified the problem for the InN films grown without nitridation [9]. InN films of mostly c-axis orientation were grown on sapphire substrates both with and without nitridation. However InN films grown without
nitridation have a tendency to form the multi-domain structures due to the in-plane rotation. Therefore, it is an important thing to control the multi-domain structures in the InN films grown without nitridation.
