Abstract We observed killer defects that served as reverse leakage current paths for halide vapor phase epitaxial (001) β -Ga 2 O 3 Schottky barrier diodes, which resulted in a leakage current of −0.46 μ A at reverse bias of −100 V. Synchrotron X-ray topography revealed comet-shaped contrasts extending along [010] which are induced from the strain field surrounding the defects. They consisted of perfect (100)-cracks and horizontal-oriented (001) cracks. The cross-sectional scanning transmission electron microscopy observation showed (100)-cracks on the surface and dislocations along [100] beneath the surface. This defect was speculated to be generated from damage during the chemical-mechanical polishing.
Epitaxial growth of an AlGaN/GaN high-electron mobility trainsistor (HEMT) structure on a diamond (111) substrate was investigated. Due to the misorientation of the diamond (111) surface, the AlGaN/GaN HEMT structure showed the macro-step surface. Using diamond surfaces with two different misorientation angles (3 and 0.5°), we found that the one with the small misorientation angle is effective for obtaining a flat AlGaN/GaN HEMT surface. Threading dislocation density of the AlGaN/GaN HEMT structure grown on the diamond (111) surface was evaluated from cross-sectional transmission electron microscope images. The densities of pure-screw-, pure-edge- and mixed-type threading dislocation were 0.3×10 9 , 4.1×10 9 , and 4.5×10 9 cm -2 , respectively. The AlGaN/GaN HEMT eptaxially grown on the diamond (111) substrate showed the maximum drain current of 800 mA/mm with little self-heating effect.
In order to make MPPT control of PCS effective, strings of almost same maximum power should be connected in parallel to the PCS. We have collected a big data of string powers measured in Yoshinogari mega solar power plant (MSPP) in Japan for two years. The data shows that string powers depend on height in the array. The average power of strings at the highest position in the array was greater approximately 7 than strings at the lowest positon. Several causes of this dependence are analyzed quantitatively.
We report on the electron field emission (FE) from heavily Si-doped AlN grown by metalorganic vapor phase epitaxy. We found that, as the Si-dopant density increases, the threshold electric field decreases and, consequently, the FE current from AlN increases drastically. We show that heavily Si-doped (2.5×1020 cm−3) AlN has a threshold electric field of 34 V/μm, a maximum FE current density of 4.8 mA/cm2, and stable FE current (fluctuation: 3%).
Direct bonding of diamond and Cu was successfully conducted by the surface activated bonding method at room temperature. The structure of the diamond/Cu bonding interface was investigated by transmission electron microscopy and electron energy-loss spectroscopy. The effect of heat treatment temperature on the interface structure was also investigated. A 4-nm-thick damaged layer was formed at the as-bonded interface, and the damaged layer's thickness decreased with an annealing temperature rise. It was found that the atomic ratio of sp2 bonding in the bonding interface was larger than that of the diamond separated from the interface by approximately 50 nm, which indicates that the damaged layer was composed of amorphous carbon or graphite and diamond. After annealing at 700 °C, a composite layer about 2 nm thick was observed at the interface. There were no nano-voids or micro-cracks observed at the interface with annealing at a temperature as high as 700 °C. These results indicate that the diamond/Cu bonding interface has high thermal stability and can withstand the temperature rise of power devices during operation.
