Annealing of an AlN buffer layer in N2-CO for growth of a high-quality AlN film on sapphire

The annealing of an AlN buffer layer in a carbon-saturated N2–CO gas on a sapphire substrate was investigated. The crystal quality of the buffer layer was significantly improved by annealing at 1650–1700 °C. An AlN buffer layer with a thickness of 300 nm was grown by metalorganic vapor phase epitaxy (MOVPE), and was annealed at 1700 °C for 1 h. We fabricated a 2-µm-thick AlN layer on the annealed AlN buffer layer by MOVPE. The full widths at half maximum of the (0002)- and ($10\bar{1}2$)-plane X-ray rocking curves were 16 and 154 arcsec, respectively, and the threading dislocation density was 4.7 × 108 cm−2

Reduction of dislocation density of aluminium nitride buffer layer grown on sapphire substrate

An aluminium nitride (AlN) buffer layer with 200 nm thickness was grown on (0001) sapphire substrate using the metal-organic vapour phase epitaxy (MOVPE) method in a low-pressure furnace, followed by a clean-up treatment of sapphire substrate at 1100°C. Thereafter, the AlN buffer layer was annealed at a high temperature in the range of 1500°C to 1700°C for 2 hours under the atmosphere of N2+CO. The objective of this research is to determine the microstructure changes with different annealing temperatures. Cross-sectional TEM has revealed that, after annealing at 1500°C, two types of defects remained in the AlN buffer layer: inverted cone shape domains and threading dislocations. The former domains were observed in an image taken with diffraction of g=0002, but not in an image with g=1010. The morphology and the diffraction condition for the image contrast strongly, suggesting that the domains are inversion domains. The threading dislocations were invisible in the image taken with the diffraction of g=0002, revealing that they were a-Type dislocations. However, after annealing at 1600oC, the inversion domains coalesced with each other to give a two-layer structure divided by a single inversion domain boundary at the centre of the AlN buffer layer. The density of threading dislocation was roughly estimated to be 5×109 cm-2 after annealing at 1500°C, and to be reduced to 5×108 cm-2 after annealing at 1600°C. These experimental results validate the fact that the annealing temperature around 1600°C is high enough to remove the defects by the diffusion process. Therefore, it was discovered that high temperature annealing is an effective treatment to alter the microstructure of AlN thin films and remove defects by the diffusion process. Annealing at high temperature is recommended to increase the emission efficiency for fabrication of optoelectronic device

Improvements in structural and optical properties of wafer-scale hexagonal boron nitride film by post-growth annealing

Remarkable improvements in both structural and optical properties of wafer-scale hexagonal boron nitride (h-BN) films grown by metal-organic chemical vapor deposition (MOCVD) enabled by high-temperature post-growth annealing is presented. The enhanced crystallinity and homogeneity of the MOCVD-grown h-BN films grown at 1050 degrees C is attributed to the solid-state atomic rearrangement during the thermal annealing at 1600 degrees C. In addition, the appearance of the photoluminescence by excitonic transitions as well as enlarged optical band gap were observed for the post-annealed h-BN films as direct consequences of the microstructural improvement. The post-growth annealing is a very promising strategy to overcome limited crystallinity of h-BN films grown by typical MOCVD systems while maintaining their advantage of multiple wafer scalability for practical applications towards two-dimensional electronics and optoelectronics.11Ysciescopu

Detection of sentinel and non-sentinel lymph node micrometastases by complete serial sectioning and immunohistochemical analysis for gastric cancer

<p>Abstract</p> <p>Background</p> <p>We investigated the presence and distribution of the sentinel and the non-sentinel node micrometastases using complete serial sectioning and immunohistochemical staining (IHC), to inspect whether lymph node micrometastases spread to the sentinel lymph nodes first.</p> <p>Methods</p> <p>A total of 35 patients, who underwent gastrectomy with a sentinel lymph node biopsy for gastric cancer, were enrolled in this study. Total of 1028 lymph nodes of 35 patients having gastric cancer without metastasis of lymph node by permanent section with hematoxylin and eosin staining (H&E) were selected. There were 252 sentinel nodes and the other 776 were non-sentinel nodes. All nodes were sectioned serially and stained alternately with H&E and IHC. Lymph node micrometastases was defined as proving to be positive first either the IHC or the complete serial sectioning.</p> <p>Results</p> <p>Micrometastases were detected in 4 (11%) of the 35 patients, 6 (0.58%) of 1028 nodes. Of these 4 patients, 3 had micrometastases exclusively in sentinel nodes, and the other had micrometastasis in both sentinel and non-sentinel nodes. There was no patient who had the micrometasitases only in non-sentinel nodes.</p> <p>Conclusion</p> <p>These results support the concept that lymph node micrometastasis of gastric cancer spreads first to sentinel nodes.</p

Recent Advances in White LEDs and Solid-State Lighting FOREWORD

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