RESUMEN
The fabrication and feasibility assessment of n-side up, thin-epilayer, AlGaInP-based vertical light-emitting-diodes (LEDs; emitting area: 1 mm × 1 mm) with a copper-invar-copper-composite metal (CIC) substrate was obtained by wafer bonding and epilayer transferring technologies. The structure of CIC substrate is a top Cu layer of 20 µm, a middle Invar layer of 64 µm, and a bottom Cu layer of 20 µm. The invar layer consists of Fe and Ni at a ratio of 70% to 30%. The coefficient of thermal expansion for CIC is about 6.1 × 10-6 /K, which is similar to that of the GaAs substrate (5.7 × 10-6 /K) and AlGaInP epilayers. Due to the high thermal conductivity (160 W/m-K) of 104-µm-thick CIC, the high performances of the packaged LEDs are obtained. They present a low red shift phenomenon (from 623 to 642 nm for 100 mA to 1 A) and a high output power 212 mW at 800 mA. The CIC substrate can be extended to fabricate high-efficiency thin film LEDs with conventional vertical electrodes.
RESUMEN
Single-crystalline ZnO nanorod arrays (ZNRs) were grown by metalorganic chemical vapor deposition on ZnO buffer/sapphire substrate without using any metal catalyst. The density of vertically aligned ZNRs was found to govern by the morphology and thickness of buffer layer. That is to say, the ZnO buffer layer can be used as the nucleation template to control the growth direction and density of the ZNRs. In addition, by controlling the diethyl zinc flow rate, we can manipulate the size, crystal, and optical quality of ZNRs. Finally, the possible growth mechanism of ZNRs was discussed in detail.
RESUMEN
ZnO was grown on sapphire substrate by metal-organic chemical vapor deposition using the diethylzinc (DEZn) and oxygen (O(2)) as source chemicals at 500 degrees C. Influences of the chamber pressure and O(2)/DEZn ratio on the ZnO structural properties were discussed. It was found that the chamber pressure has significant effects on the morphology of ZnO and could result in various structures of ZnO including pyramid-like, worm-like, and columnar grain. When the chamber pressure was kept at 10 Torr, the lowest full width at half-maximum of ZnO (002) of 175 arc second can be obtained. On the other hand, by lowering the DEZn flow rate, the crystal quality of ZnO can be improved. Under high DEZn flow rate, the ZnO nanowall-network structures were found to grow vertically on the sapphire substrate without using any metal catalysts. It suggests that higher DEZn flow rate promotes three-dimensional growth mode resulting in increased surface roughness. Therefore, some tip on the ZnO surface could act as nucleation site. In this work, the growth process of our ZnO nanowall networks is said to follow the self-catalyzed growth mechanism under high-DEZn flow rate.
RESUMEN
Uniformly distributed ZnO nanowall network structures were grown at 550 degrees C by organometallic chemical vapor deposition technique on the GaN/sapphire substrate without using any catalysts. In this research, we discussed the nanostructures and optical properties of ZnO samples grown under the same conditions but on different underlying materials (GaN/sapphire and sapphire). By adjusting the growth parameters, ZnO nanowall networks with a honeycomb-like pattern without using any metal catalysts were successfully fabricated on the GaN/sapphire and sapphire substrates. Since the lattice mismatch between ZnO and GaN is only about 1.8% while the lattice mismatch between ZnO and sapphire is about 18.4%. Lattice mismatch may not be the decisive factor in the formation process of ZnO nanowall networks. The ZnO grown on GaN epilayer had smaller full width at half maximum value than that of ZnO grown under the same growth condition on the sapphire substrate, indicating a higher crystal quality in the sample of ZnO on GaN. The room temperature PL measurement of both ZnO nanostructures grown on GaN and sapphire show strong ultraviolet peak intensity and high intensity ratio of the near band emission to the deep-level emission in a PL spectrum.
