Phone: þ81 22 215 2281, Fax: þ81 22 215 2302Cleaved ScAlMgO 4 (SCAM) substrates with small lattice mismatch of 1.8% to GaN were used for metalorganic vapor phase epitaxial (MOVPE) growth of GaN. A single crystalline GaN film with a flat surface was obtained on a cleaved substrate without peeling off of the film, which is contrast to the growth on ZnO substrate with comparably small lattice mismatch to GaN. Polarity of the film was proven to be Ga polarity and an interface model was proposed based on the topmost surface structure of the cleaved SCAM. The effect of substrate-cleaning and growth conditions on the surface morphology, crystallographic orientation relationship with the substrate, threading dislocation densities, small residual strains, and small background carrier density of GaN have been studied. To discuss the residual strains, thermal expansion coefficient of SCAM has also been measured.

Due to the huge bandgap-bowing, a red shift of the band gap energy with increasing nitrogen content is expected for the InAsN alloy. However, a blue shift of the fundamental absorption edge has been observed in a recent study. This result seems to be significantly affected by the Burstein-Moss effect because the InAsN alloy has a large carrier concentration. The Burstein-Moss effect should be ruled out in order to characterize the real band gap energy. In this paper, Hall effect measurements were performed to estimate the carrier concentration of the InAsN alloy films and the Burstein-Moss shift energy was evaluated. Excluding the Burstein-Moss shift energy, a red shift of the real band-gap energy with increasing nitrogen content was observed.1 Introduction The InAsN alloy has attractive potentials for infrared optical applications due to the huge bandgap-bowing [1] which is specific to the III-V-N-type ternary alloys. In our recent study, the InAsN epilayers were successfully grown on GaAs (001) substrates with a ~0.8 µm InAs buffer layer by RF-MBE, and the nitrogen content was estimated to be 0.09-1.69% [2]. Contrary to the theoretical prediction, a blue shift of the fundamental absorption edge was observed [3]. The result seems to be significantly affected by the Burstein-Moss (BM) effect because the InAsN alloy has a large carrier concentration due to its narrow bandgap. It will easily raise the absorption edge to higher energy than the real band gap energy. The BM shift energy (∆E BM ) should be excluded for determining the real band gap energy of InAsN.For this reason, we have attempted to evaluate the carrier concentration of the InAsN alloy films, which is the most important factor to estimate ∆E BM . The conductive buffer layer, such as a thick InAs buffer layer, is unfavourable for Hall effect measurements because it may cause carrier parallel conduction and conceal the information about the InAsN epilayers. In this work, the InAsN alloy films were grown directly on semi-insulating GaAs (001) substrates by RF-MBE. Next, the nitrogen content of all the samples was estimated by HR-XRD. The Hall effect measurements were carried out to characterize the carrier transport property and the FT-IR absorption measurements were performed to obtain the optical absorption spectra.

N-polar (−c-plane) InGaN light-emitting diodes with emission wavelengths ranging from blue to green to red were fabricated on a c-plane sapphire substrate by metalorganic vapor phase epitaxy. The optimization of growth conditions for −c-plane InGaN/GaN multiple quantum wells was performed. As a result, the extension of the emission wavelength from 444 to 633 nm under a constant current of 20 mA was achieved by changing the growth temperature of quantum wells from 880 to 790 °C.

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