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 performance of vertical-structure metallic-substrate GaN-based light-emitting diodes (VM-LEDs) with a patterned SiO2 film as the current-blocking layer (CBL) was investigated. From theoretical calculations of current and light distributions and experimental results on current–voltage (I–V) and light output power–current (L–I) characteristics, we found that SiO2 CBL inserted under the n-pad electrode increases light output power by 35.4% at 20 mA as compared with VM-LEDs without CBL. Such an improvement is attributed to the insulated CBL structure, which provides better current spreading and less photon absorption and/or reflection at the n-electrode.
Large-area (0.6 ×0.6 and 1 ×1 mm2) highly-efficient GaN-based light-emitting diodes (LEDs) with a vertical-conducting structure (VM-LEDs), using a patterned laser lift-off technique and a Ni electroplating process as well as a surface treatment of the top n-GaN epilayer by plasma and chemical etching, were successfully fabricated and investigated. Compared to regular LEDs of the same size, both the forward voltage drop and the light output power (Lop) of the VM-LED were substantially improved. With inductively coupled plasma (ICP) etching followed by an additional KOH etching and an HF/HCl treatment on the n-GaN layer, an increase in Lop by 227% (195%) at 350 (800) mA has been achieved for the (1 ×1 mm2)-sized VM-LEDs.
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