Tsukasa Kitano

Microstructure of epitaxial lateral overgrown AlN on trench-patterned AlN template by high-temperature metal-organic vapor phase epitaxy

A high-quality thick AlN layer without cracks was grown on sapphire by the combination of the high-temperature metal-organic vapor phase epitaxial growth and epitaxial lateral overgrowth methods. The dislocation behavior and growth mode of AlN are investigated in detail. The dislocation density of the AlN layer thus grown was less than 107cm−2.

Thermodynamic Aspects of Growth of AlGaN by High-Temperature Metal Organic Vapor Phase Epitaxy

The metalorganic vapor phase epitaxial (MOVPE) growth of AlGaN on AlN-coated sapphire at a temperature higher than 1,200 °C was carried out. Compared with that at a low-temperature growth regime in which alloy composition is determined by the flow rates of metalorganic Ga and Al sources, the solid composition of AlGaN is found to be strongly affected by thermodynamics.

Trench-Shaped Defects on AlGaInN Quantum Wells Grown under Different Growth Pressures

We obtained high-quality AlGaInN/GaN quantum wells (QWs) with a 385 nm emission by adding Al sources to GaInN QWs grown at a low growth pressure of 150 mbar. When AlGaInN QWs were grown at a relatively high growth pressure of 400 mbar, a considerable amount of peculiar trench-shaped defects were observed on the surface of the AlGaInN QWs. We found that the trench defects acted as nonradiative centers, leading to low photoluminescence (PL) intensities. Our experiments reveal that a low growth pressure is effective in suppressing the trench defect formation, resulting in high-quality AlGaInN QWs.

Metal–Organic Vapor Phase Epitaxy Growth of Embedded Gallium Nitride Nanocolumn for Reduction in Dislocation Density

The use of nanocolumn crystals is thought to be effective in producing a low-dislocation-density GaN layers. In this paper, we propose a metal–organic vapor phase epitaxial (MOVPE) growth method for producing uniform GaN nanocolumns using deep through-holes in a thick SiO2 selective growth mask. A SiO2 film with a thickness of 500 nm was deposited by sputtering on an AlN buffer layer/SiC substrate. A nanoimprinting technique was applied to produce dot openings. Then, dry etching with CF4 gas was carried out to form deep through-holes in the SiO2 film. In the second MOVPE growth, individual GaN nanocolumns coalesced into a planarized GaN layer, after thinning the SiO2 mask to 100 nm. A cathode-luminescence image of the GaN layer on a GaN nanocolumn template shows a low dislocation density of 1.3×108 cm-2, while that of a GaN layer directly grown on an AlN buffer layer shows a dislocation density of 9.4×108 cm-2.

Study on Efficiency Component Estimation of 405 nm Light Emitting Diodes from Electroluminescence and Photoluminescence Intensities

The Shockley–Read–Hall (SRH) model was applied to the determination of photoluminescence (PL) and electroluminescence (EL) characteristics. From the ratio of the internal quantum efficiency (IQE) obtained from the PL and EL intensities, the carrier injection efficiencies (CIE) for 405 nm LEDs were derived. All the efficiency components including the IQE, CIE, and light extraction efficiency for 405 nm LEDs were obtained for various structural parameters by fitting the experimental data to theoretical equations of the SRH model.

Group III nitrides grown on 4H-SiC (30 3 8) substrate by metal-organic vapor phase epitaxy

The heteroepitaxial growth of a GaN single crystal by metal-organic vapor phase epitaxy on a 4H-SiC (30 3 8) substrate was demonstrated. The crystallographic orientation of GaN was found to be dependent on growth pressure. When the growth pressure was 1000 hPa, the orientation of the GaN single crystal was consistent with that of the SiC substrate, where the c-plane of the GaN was single crystal tilted 54.7° from the surface plane. Then, we fabricated a violet-light-emitting diode (LED) with a GaInN multiple-quantum-well (QW) active layer grown on the GaN layer, which coherently grew on the 4H-SiC (3038 ) substrate. The blue shift of the peak wavelength with increasing injection current of up to 100 mA was confirmed to be two times smaller than that of a conventional LED on a c-plane sapphire substrate due to a low internal polarization.