We have succeeded in distinguishing the polarities of InN by wet etching using KOH solution for the first time. We found N‐polar InN was etched roughly, and hexagonal pyramids surrounded by {10$\bar 1 \bar 1$} facets appeared after etching for 60 min. On the other hand, In‐polar InN was etched smoothly in shorter term of etching. These features observed are very similar to those reported for GaN. After longer term of exposure to the KOH solution over 60 min, however, hexagonal and dot type etch pits appeared on the surface of In‐polar InN. The densities of hexagonal and dot type etch pits were 3 ∼ 5 × 109 cm–2 and 1 ∼ 3 × 1010 cm–2, respectively. Since the densities of these etch pits almost correspond to the dislocation densities of InN, it is considered that the etch pit formation is related to the threading dislocations. In this study, it was also found for the first time that InN layers grown on (0001) sapphire substrates using a low‐temperature GaN buffer layer had In‐polarity. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Recent developments on RF‐MBE growth of InN and InGaN and their structural and property characterizations are reviewed. For successful growth of high quality InN, (1) nitridation of the sapphire substrates, (2) two‐step growth, (3) precise control of V/III ratio and (4) selection of optimum growth temperature are found to be essential. Characterization using XRD, TEM, EXAFS and Raman scattering have clearly demonstrated that InN films have ideal hexagonal wurtzite structure. It is also found that the film has N‐polarity. Studies on optimum growth condition dependence on substrate polarity using C and Si face SiC substrates and Ga and N face free‐standing GaN substrates are also demonstrated. The result explains why high‐quality InN grown by RF‐MBE has N‐polarity. PL and CL studies on these well‐characterized high‐quality InN have shown luminescence peaks at approximately 0.75 eV at 77K. These values, however, change slightly depending on measurement temperatures and probably on the residual carrier concentrations. InGaN with full compositional range are also successfully grown on sapphire substrates and band gap energies of these alloys are also studied using PL and CL. Based on these results, true band gap energies of InN are discussed. This paper also includes latest study on single crystalline InN growth on Si (111) substrates. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

No abstract

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.

This paper describes studies on high-quality InN growth on sapphire by RF-MBE. Critical procedures to obtain high-quality InN films were investigated and (1) nitridation process of sapphire substrates prior to growth, (2) precise control of V/III ratio and (3) selection of optimum growth temperature were found to be essential. Detailed structural characterizations by XRD, TEM, Raman scattering and EXAFS indicate that InN films obtained in this study have ideal hexagonal wurtzite structure. FWHMs of ω-2θ mode XRD and E 2 (high)-phonon-mode of Raman scattering are as small as 28.9 arcsec and 3.2 cm -1 , respectively. True band gap energy of InN is also discussed based on optical characterization results obtained from well-characterized hexagonal InN grown in this study. PbS, instead of InGaAs, was used as a detector for PL study in order to solve the problem coming from the cut-off wavelength of InGaAs detector. Based on these systematic studies on structural and optical property characterizations using high-quality InN, true band-gap energy of InN is suggested to be less than 0.67 eV and approximately 0.65 eV at room temperature. Single-crystalline InN films are also successfully grown on Si substrates by a brief nitridation of the Si substrates. Significant improvement of InN crystal quality on Si substrates by the insertion of an AlN buffer layer is also demonstrated.