The crystal quality, electrical, and optical characteristics of GaN-based light-emitting diodes (LEDs) were improved using a sputtered AlN nucleation layer. Replacing the in situ AlN nucleation layer ...with the sputtered AlN nucleation layer reduced the (002) and (102) X-ray rocking curve widths of the GaN layer from 318.0 to 201.1 and 412.5 to 225.0 arcsec, respectively. The -20-V reverse leakage current of the LEDs with the sputtered AlN nucleation layer is about three orders less than that of the LEDs with the in situ AlN nucleation layer. In addition, the LEDs with sputtered AlN nucleation layer could sustain more than 60% passing yield on the ESD test of under a -600-V machine mode, whereas the LEDs with the in situ AlN nucleation layer sustained less than 40% passing yield. Moreover, the 20-mA output power of the LEDs with the sputtered AlN nucleation layer also improved by approximately 5.73% compared with that of the LEDs with the in situ AlN nucleation layer.
We report the fabrication of GaN-based blue light-emitting diodes (LEDs), which separately incorporate the three different electron blocking layers (EBLs), namely, a conventional AlGaN, a uniform ...multiquantum barrier (UMQB), and a chirped multiquantum barrier (CMQB). On the administration of 20 mA injection current, the corresponding LED output powers measured were 27.5, 27.2, and 25.4 mW for CMQB LED, UMQB LED, and LED, respectively, with a conventional AlGaN EBL. It was also found that the LED with CMQB EBL exhibited a significantly lower drooping effect and a smaller forward bias as compared with LEDs with a conventional AlGaN EBL and UMQB EBL.
The optical property and electrostatic discharge (ESD) endurance of GaN-based light-emitting diodes (LEDs) with varied undoped GaN thickness are studied and demonstrated. As the undoped GaN thickness ...increased, the generation of V-shaped defects in the active region was suppressed. Therefore, the output power for a 6-μ.m-thick undoped GaN layer would be enhanced remarkably due to the reduction of nonradiative recombination ratio within the active region. On the other hand, under a reverse ESD pulse voltage of 5.5 kV, the survival rate of the LEDs with an undoped GaN layer thickness of 1.5, 4, and 6 μm were 75%, 65%, and 55%, respectively. It was found that the ESD endurance for a 1.5-μ.m-thick undoped GaN layer with higher internal capacitance was obviously better than others. This could be related to the built-in electric field of LEDs induced by spontaneous polarization field.
The authors report the numerical simulation of GaN-based light-emitting diodes (LEDs) with either a conventional AlGaN electron blocking layer (EBL), uniform multiquantum barrier (UMQB) structure, or ...chirped multiquantum barrier (CMQB) structure. It is found that the 102-meV effective barrier height simulated from the LED with CMQB structure is larger than those simulated from the LEDs with a UMQB structure (90 meV) and with conventional AlGaN EBL (60 meV). With the large effective barrier height, it is found that LEDs with a CMQB structure exhibit smaller leakage current. It is also found that the maximum internal quantum efficiencies are 0.703, 0.842, and 0.887, for the LEDs with conventional EBL, UMQB structure, and CMQB structure, respectively. In addition, it is found that forward voltages simulated from the LEDs with CMQB structure and with UMQB structure are both smaller than that simulated from the LED with conventional AlGaN EBL. These results also agree well with the experimental data.
The authors propose a simple method to enhance current spreading of GaN-based side-view light-emitting diodes (LEDs) by adding a metallic stripe across the long side of the chip. It was found that 20 ...mA output power of the LED could be enhanced from 8.54 to 9.2 mW by adding the metallic stripe. It was also found that further the LED output power could be enhanced to 9.68 mW by partially thinning down the metallic stripe chemically. These improvements could be attributed to the more uniform current distribution across the LED chip.
We present an efficient vertical InGaN light-emitting diode (LED) in which the proposed vertical LEDs were fabricated with patterned sapphire substrates (PSS) using thinning techniques. After the ...thinning of sapphire substrate, selective dry etching process was performed on the remainder sapphire layer to expose the n-GaN contact layer instead of removing the sapphire substrate using the laser lift-off technique. These processes feature the LEDs with a sapphire-face-up structure and vertical conduction property. The PSS was adopted as a growth substrate to mitigate the light-guided effect, and thereby increase the light-extraction efficiency. Compared with conventional lateral GaN LEDs grown on PSS, the proposed vertical LEDs exhibit a higher light output power and less power degradation at a high driving current. This could be attributed to the fact that the vertical LEDs behave in a manner similar to flip-chip GaN/sapphire LEDs with excellent heat conduction.
Vertical GaN-based light-emitting diodes (LEDs) were fabricated with a Si substrate using the wafer-bonding technique. Lapping and dry-etching processes were performed for thinning the sapphire ...substrate instead of removing this substrate using the laser lift-off technique and the thinning process associated with the wafer-bonding technique to feature LEDs with a sapphire-face-up structure and vertical conduction property. Compared with conventional lateral GaN/sapphire-based LEDs, GaN/Si-based vertical LEDs exhibit higher light output power and less power degradation at a high driving current, which could be attributed to the fact that vertical LEDs behave in a manner similar to flip-chip GaN/sapphire LEDs with excellent heat conduction. In addition, with an injection current of 350 mA, the output power (or forward voltage) of fabricated vertical LEDs can be enhanced (or reduced) by a magnitude of 60% (or 5%) compared with conventional GaN/sapphire-based LEDs.
We report the fabrication of InGaN-GaN power flip-chip (FC) light-emitting diodes (LEDs) with a roughened sapphire backside surface prepared by grinding. It was found that we can increase output ...power of the FC LED by about 35% by roughening the backside surface of the sapphire substrate. The reliability of the proposed device was also better, as compared to power FC LEDs with a conventional flat sapphire backside surface.
We present an efficient vertical InGaN light-emitting diode (LED) in which the proposed vertical LEDs were fabricated with patterned sapphire substrates (PSS) using thinning techniques. After the ...thinning of sapphire substrate, selective dry etching process was performed on the remainder sapphire layer to expose the n-GaN contact layer instead of removing the sapphire substrate using the laser lift-off technique. These processes feature the LEDs with a sapphire-face-up structure and vertical conduction property. The PSS was adopted as a growth substrate to mitigate the light-guided effect, and thereby increase the light-extraction efficiency. Compared with conventional lateral GaN LEDs grown on PSS, the proposed vertical LEDs exhibit a higher light output power and less power degradation at a high driving current. This could be attributed to the fact that the vertical LEDs behave in a manner similar to flip-chip GaN/sapphire LEDs with excellent heat conduction.
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