The fabrication process and performance characteristics of a vertical-structured GaN-based light-emitting diode (VM-LED) employing nickel electroplating and patterned laser liftoff techniques are presented. As compared to regular LED, the forward voltage drop of the VM-LED at 20–80 mA is about 10%–21% lower, while the light output power (Lop) is more than twice in magnitude. Especially, the Lop exhibits no saturation or degradation at an injection current up to 520 mA which is about 4.3 times higher than that of the regular one. Substantial improvements in the VM-LEDs performances are mainly attributed to the use of metallic substrate which results in less current crowding, larger effective area, and higher thermal conductivity.
The self-synthesis of tungsten oxide
(W18O49)
nanowires on sputter-deposited W films prepared under different
O2/Ar
flow rate ratios (OAFRRs) in the sputtering gas is reported. After thermally annealing at
700–850 °C
in N2
ambient for 15 min, dense and well crystalline
W18O49
(010) nanowires or nanobelts were obtained depending on the oxygen content in the sputtering
gas. Experimental results show that the annealing temperature required for the full growth of
W18O49
nanowires reduced when the OAFRR in the sputtering gas was increased. It is found that
the oxygen absorbed in the surface region is responsible for the growth of nanowires. As the
OAFRR was increased to (8 sccm)/(24 sccm), which resulted in a saturated oxygen
content of about 55 at.% inside the W film, large-scale nanobelts or nanosheets of
W18O49
were grown. The possible growth mechanism which governs the evolution from nanowires to
nanobelts as the OAFRR was changed is also discussed.
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