PACS 71.20.Nr, 78.20.Ci, 78.55.Cr InN crystals are grown on sapphire substrates by a plasma assisted MBE system. The carrier concentration of the samples are 2×10 18 −1×1019 cm -3. Optical transmission and reflectance measurements are performed on these samples in a temperature range of 8 -300 K. The resultant spectra are analysed by theoretical spectra based on a LO-phonon plasmon coupling scheme for phonon related factor and nonparabolic conduction band structure for electronic transition factor. The observed absorption edge is estimated to mainly originate from the valence band to conduction band transition rather than defect or impurity related transition on the basis of the electron concentration dependence of the momentum matrix element. The bandgap energy is about 0.63 eV, and increases with the temperature decrease.

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Molecular-beam epitaxial growth of InN was investigated on Ga-and N-polar GaN templates. It was found that InN layers could be grown at higher temperature on N-polar GaN than on Ga-polar one, on which InN films succeeded the cation-or anion-polarity, respectively. The growth temperature of In-polar InN was limited below 500 °C; while that of N-polar InN could be as high as 600 °C. In the upper-limit growth temperature range for N-polar InN, atomic-height growth steps could be observed on the surface. The possible mechanisms for the polarity dependence of InN growth behaviors were also discussed.

InN crystals with the electron concentration N e of 4 -11 × 10 18 cm -3 are grown on sapphire substrates by molecular beam epitaxy. Optical reflectance and transmission measurements are performed in a temperature range of 5 to 296 K. The reflectance spectra are analysed by simulation including the longitudinal optical phonon -plasmon coupling scheme. At a N e value of 4 × 10 18 cm -3, the electronic states are found to be still degenerated. An anomalous temperature dependence of the bandgp energy E g is found; with decreasing temperature E g increases, and then decreases below 50 K. This decrease is smaller for samples with smaller N e . In spite of this energy shift the decrease of N e is too small to be detected. The effective electron mass of the intrinsic region is estimated to be 0.1m 0 .

Subject classification: 73.61.Ey; 81.15.Kk; S7.14 One-, two-and three-flow metalorganic vapor phase epitaxy (MOVPE) methods have been compared in GaN growth, and each growth is analyzed by computational fluid dynamics (CFD). It is found that two-flow method shows better growth condition for achieving high quality layers compared to one-and three-flow methods. A GaN layer with high Hall mobility of 360 cm 2 /Vs is obtained by two-flow MOVPE growth despite no low-temperature buffer layer. The V/III decomposition ratio of NH 2 /GaCH 3 is calculated by CFD simulation in gas phase just on substrate surface. The V/III ratio is in a narrow region to get high-mobility samples.