In this paper, we discusse the origin of basal-plane stacking faults (BSFs) generated in the homoepitaxial hydride vapor phase epitaxy (HVPE) growth of m-plane gallium nitride (GaN). We investigated the effects of seed quality, especially dislocation density, on BSF generation during homoepitaxy. The results clearly identify basal-plane dislocation in the seed as a cause of BSF generation. We realized high-quality m-plane GaN substrates with a 2-in. diameter using HVPE on low-dislocation-density m-plane seeds. (C) 2016 The Japan Society of Applied Physics

A new theoretical model has been proposed to explain the origin of the double-peak emission observed characteristically in m-plane InGaN quantum wells (QWs). Although the emission spectrum with a double-peak structure is generally regarded as evidence of In compositional phase separation or extended crystal defects that generate localized energy states, such crystal irregularities cannot be observed by transmission electron microscopy or three-dimensional atom probe in the QWs. It has been clarified, by our model, that only the slowly decaying tailing of the density of states can cause the double-peak structure. This is consistent with experimental results, and furthermore, the measured temperature and In composition dependences of photoluminescence spectra with the double-peak emission can also be successfully reproduced by theoretical calculation based on our model. (C) 2016 The Japan Society of Applied Physics

We carried out the selective-area growth of GaN and fabricated InGaN/GaN MQWs on non- and semi-polar bulk GaN substrates by MOVPE. The differences in the GaN structures and the In incorporation of InGaN/GaN MQWs grown on non- and semi-polar GaN substrates were investigated. In the case of selective-area growth, different GaN structures were obtained on GaN, GaN, and GaN substrates. A repeating pattern of and facets appeared on GaN. Then, we fabricated InGaN/GaN MQWs on the facet structures on GaN. The emission properties characterized by cathodoluminescence were different for and facets. On the other hand, for InGaN/GaN MQWs on non- and semi-polar GaN substrates, steps along the a-axis were observed by AFM. In particular on GaN, undulations and undulation bunching appeared. Photoluminescence characterization indicated that In incorporation increased with the off-angle from the m-plane and also depended on the polarity.

We carried out the selective area growths of GaN on semipolar (201), (20), and related non- and semi-polar GaN substrates by metalorganic vapor phase epitaxy. By changing the growth parameters and directions of the SiO2 stripe mask, the differences in GaN structures between the growths on the different substrates were investigated. In the case of the stripes ∥ a-axis, anisotropic GaN structures with (000) and (101) facets were obtained for all the non- and semi-polar GaN substrates. On the other hand, in the case of the stripes ⊥ a-axis, isotropic GaN structures were obtained for the (201) and (20) GaN substrates. However, the GaN structures between them were quite different. After 120 min of growth, {110} and (20) facets markedly expanded for the (20) and (20) GaN substrates, respectively. Moreover, by exploiting the effect of growth temperature, the growth of a continuous (20) GaN layer with voids was realized.

We carried out the selective area growths of GaN on semipolar (20 (2) over bar1), (20 (2) over bar(1) over bar), and related non- and semi-polar GaN substrates by metalorganic vapor phase epitaxy. By changing the growth parameters and directions of the SiO2 stripe mask, the differences in GaN structures between the growths on the different substrates were investigated. In the case of the stripes parallel to a-axis, anisotropic GaN structures with (000 (1) over bar) and (10 (1) over bar1) facets were obtained for all the non- and semi-polar GaN substrates. On the other hand, in the case of the stripes perpendicular to a-axis, isotropic GaN structures were obtained for the (20 (2) over bar1) and (20 (2) over bar(1) over bar) GaN substrates. However, the GaN structures between them were quite different. After 120 min of growth, {11 (2) over bar0} and (20 (2) over bar(1) over bar) facets markedly expanded for the (20 (2) over bar1) and (20 (2) over bar(1) over bar) GaN substrates, respectively. Moreover, by exploiting the effect of growth temperature, the growth of a continuous (20 (2) over bar(1) over bar) GaN layer with voids was realized. (C) 2013 The Japan Society of Applied Physics

Despite tremendous progress, the optoelectronic properties of GaN and related compounds still pose a rich field for scientific research. The aim of this session is to bring together leading experts on materials, characterization, and theory in order to discuss the physics of group-III nitride-based heterostructures and various approaches to realize future optoelectronic devices. Open questions are in particular the socalled *green gap* describing lower efficiency in GaN based green light emitters as opposed to their blue and ultraviolet counterparts, polarization of the crystal structure, as well as high-In containing alloys for light emitters in the entire visible range. (Organizers: Bernd Witzigmann, University of Kassel and Frank Bertram, University of Magdeburg)

The current–voltage characteristics of Schottky barrier diodes formed on GaN(0001) free-standing substrates with net donor concentrations of 7.6×1015–1.4×1017 cm-3 are discussed. The substrates were grown by hydride vapor phase epitaxy. Ni Schottky contacts were directly formed on chemical–mechanical-polished Ga-polar faces of the substrates. Nearly ideal characteristics for both directions were obtained. The ideality factors for forward characteristics are 1.02–1.05, very close to unity. The reverse characteristics agree well with calculations based on thermionic-field emission theory without any fitting parameter.

We succeeded in preparing very thick c-plane bulk gallium nitride (GaN) crystals grown by hydride vapor phase epitaxy. Growth of the bulk GaN crystals was performed on templates with 3 μm GaN layer grown by metal organic chemical vapor deposition on (0 0 0 1) sapphire substrates. Colorless freestanding bulk GaN crystals were obtained through self-separation processes. The crystal's diameter and thickness were about 52 and 5.8 mm, respectively. No surface pits were observed within an area of 46 mm diameter of the bulk GaN crystal. The dislocation density decreased with growth direction (from N-face side to Ga-face side) and ranged from 5.1×106 cm−2 near the N-face surface to 1.2×106 cm−2 near the Ga-face. A major impurity was Si, and other impurities (O, C, Cl, H, Fe, Ni and Cr) were near or below the detection limits by SIMS measurements.

The authors have grown high‐quality m ‐plane In0.36Ga0.64N (1$ \bar 1 $00) films on ZnO (1$ \bar 1 $00) substrates at room temperature (RT) by pulsed laser deposition (PLD) and have investigated their structural properties. m ‐plane InGaN films grown on ZnO substrates at RT possess atomically flat surfaces with stepped and terraced structures, indicating that the film growth proceeds in a two‐dimensional mode. X‐ray diffraction measurements have revealed that the m ‐plane InGaN films grow without phase separation reactions at RT. The full‐width at half‐maximum values of the 1$ \bar 1 $00 X‐ray rocking curves of films with X‐ray incident azimuths perpendicular to the c ‐ and a‐axis are 88 arcsec and 78 arcsec, respectively. Reciprocal space‐mapping has revealed that a 50 nm thick m ‐plane In0.36Ga0.64N film grows coherently on the ZnO substrate, which can probably explain the low defect density that is observed in the film. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Recently, an innovative method of fabricating vertical light-emitting diode (LED) was introduced by the chemically lift-off (CLO) process. Such fabrication of the vertical LED could be realized by inserting the CrN interlayer between sapphire substrate and gallium nitride (GaN) layer. In this paper, by using off-cut sapphires, we tried to find out the influence of off-angles on the overgrown GaN films with respect to crystal quality and surface roughness. The CrN is formed by nitridizing the deposited Cr layer on the sapphire substrate at 1080°C, and then GaN was grown on the nitrided Cr. By X-ray diffraction system (XRD) measurements, the crystal quality tendency of the GaN film on the variation of the off-angles was similar with that of the CrN interlayer. Through high-resolution transmission electron microscopy (HRTEM) measurement, it was found out that AlN layer with a thickness of a few nanometers also formed between sapphire and CrN during the nitridation treatment of Cr layer. Compared with the previous reports, such tendency of the crystal quality for the vicinal sapphires with CrN interlayer was well matched with the tendency of the previous results in the vicinal sapphire without the CrN interlayer. Therefore, it can be surmised that the AlN layer between sapphire and CrN was precedently influenced by the vicinal substrate and then, the AlN layer had an influence on the upper layers of GaN as well as CrN. In addition, it was found that the vicinal sapphires with the off-angles of 0.2–0.3° had the minimum full-width at half-maximum (FWHM) values by XRD measurements, which were lower by 20% than the others.