[en] The designs of magnet components, vacuum system and buncher and their measurement results of ECR-SFC axial injection beam line are described

[en] The ultraviolet (UV) emitting AlGaN/GaN multiple quantum wells (MQWs) were grown on low dislocation density AlN/sapphire templates by metal-organic chemical vapor deposition (MOCVD). The impact of the purg time on the interface quality of the AlGaN/GaN quantum well was studied. The high resolution x-ray diffraction (XRD) measurement results demonstrate that the density of dislocations was reduced significantly with the purge time after growth of AlGaN barrier layer and GaN well layer was determined to be 4 min and 2 min, respectively. The mechanism of defect formation in quantum wells was investigated by scanning electron microscope (SEM) measurement. (paper)

[en] The MgN/AlGaN insertion layers were applied for the first time in the growth of non-polar a -plane AlGaN epi-layers by metal organic chemical vapor deposition technology. The full-width-at-half-maximum value of X-ray rocking curve for the a -plane AlGaN epi-layer was decreased by approximately 50.6% and the root-mean-square value of the surface was reduced by 74% by inserting the MgN/AlGaN insertion layers with optimized number of insertion pairs, which revealed that the compressive strain within the a -plane AlGaN epi-layers was effectively reduced, leading to significant improvements in crystalline quality and surface morphology, which is very helpful to fabricate high quality AlGaN-based ultraviolet light-emitting-diodes. (paper)

[en] Highlights: • The non-polar a-plane Mg-delta-doped p-AlGaN epi-layers with various Al compositions were successfully grown for the first time on the semi-polar r-plane sapphire substrates with metal organic chemical vapor deposition technology. • An evident enhancement in electrical properties has been realized due to the significant improvements in crystalline quality and surface morphology for the non-polar p-AlGaN epi-layers grown with the newly-developed pulsed mass flow supply technique. -- Abstract: We report on the successful growth of non-polar a-plane p-type Mg-doped AlGaN epi-layers with various Al compositions by metal organic chemical vapor deposition (MOCVD). The p-AlGaN epi-layers with the Al composition varied from 0 to 0.41 were studied comprehensively. In particular, a novel MOCVD growth process featured with pulsed mass flow supply (PMFS) of the metal organic-source was applied for the fabrication of the Mg-doped AlGaN with various Al compositions. It was revealed that a significant enhancement in electrical conductivity was induced owing to the application of the newly-developed PMFS technique during the growth of the Mg-doped AlGaN. In fact, a hole concentration up to 7.0 × 10¹⁶ cm⁻³ was realized for the p-Al_0.41Ga_0.59N epi-layer sample grown with the PMFS technique.

No abstract available

[en] Highlights: • Investigation of optical properties of Al_xGa_1-xN (x = 0.35–0.75) films by SE. • Temperature-dependent (300–823 K) refractive index and bandgap are obtained. • The refractive index increase in the transparent region with rising temperature. • The reduction of bandgap with temperature is more pronounced for higher Al content. • The quantitative analysis of refractive index and bandgap with T are proposed. - Abstract: A series of Al_xGa_1-xN/AlN/Sapphire films with x = 0.35–0.75 and different thickness of epi-layer were prepared by metalorganic chemical vapor deposition (MOCVD). Spectroscopic ellipsometry (SE) was used to study the temperature-dependent refractive indices and optical bandgaps of the Al_xGa_1-xN films ranging from 300 to 823 K. Parametric semiconductor (PSEMI) models were used to describe the dielectric functions of AlGaN/AlN layers. The fitting results of refractive index, energy bandgap, thickness and surface roughness at 300 K are in good agreement with photoluminescence (PL), scanning electron microscopy (SEM) measurements and the existing literature. Our finding indicates that the crystal quality of the samples with x = 0.47 and 0.60 are better than those with x = 0.35 and 0.75. As the temperature rises, the increasing of refractive index for the low Al content Al_xGa_1-xN layers is stronger than that of high Al content in the transparent region, and the reduction of bandgap with high Al content is larger than that of low Al content. For all the samples (x = 0.35–0.75), an analytical expression for temperature-dependent refractive index in the wavelength range of 195–1650 nm was obtained using the Sellmeier law, and the quantitative analysis of the SE-derived temperature-dependent bandgap was conducted by using the Bose-Einstein equation.