We report improvement of improvement effectiveness of the light extraction efficiency of 10 W operated InGaN-based vertical light-emitting diodes via n-GaN surface roughening, using a commercial photoresist (PR) developer as an etching solution, which was compared with a conventional KOH-based solution. With the conventional KOH-based solution for n-GaN surface roughening, although both the depth and density of the etch pyramid initially increased with etching time, the depth eventually decreased and the density also decreased gradually, resulting in degradation in improvement effectiveness of extraction efficiency. Using the commercial PR developer for etching, however, after an initial increase in both the depth of the etch pyramid and its density, the depth and density were maintained without degradation, confirming the improvement in improvement effectiveness of extraction efficiency as well as the improvement in run to run fabrication uniformity. This may be due that with developer the GaN surface is etched only along the dislocation and is not etched over the non-defect region even as etching time goes on.
We propose a nanoscale Ni-embedded single-wall carbon nanotube (SWCNT) composite for transparent conductive electrodes (TCEs) of AlGaN-based ultraviolet light-emitting diodes (UV LEDs). TCEs specifically for the ultraviolet region were developed using Ni selectively electroless-plated SWCNTs. The nanoscale Ni of TCEs improved electrical conductivity and formed ohmic contact with p-GaN while minimizing transmittance loss. We applied Ni-embedded SWCNTs, SWCNTs, and Ni/Au to the TCEs of 375 nm UV LEDs. UV LEDs with Ni-embedded SWCNTs showed a 32% higher output power than UV LEDs with conventional Ni/Au TCEs.
The band-edge potential and photocurrent density of N-face GaN were experimentally determined to be more negative and greater than those of Ga-face GaN, respectively, in this photoelectrochemical experiment. These results indicate that the N-face GaN could generate much more hydrogen than Ga-face GaN. Although the time dependence of the photocurrent density of N-face GaN was almost constant, that of Ga-face GaN stabilized only after 260 min of reaction time. From these results, we conclude that N-face GaN, which has a more negative band-edge potential and a more stable photocurrent density, could be suitable for higher-photocurrent generation than Ga-face GaN.
The effects of annealing with H2 and N2 on the photoelectrochemical (PEC) properties of annealed Nb-doped TiO2 (ann-TNO) film were investigated. The photocurrent density of the ann-TNO film was 2 to 3 orders of magnitude higher than that of u-TiO2 film. To understand this phenomenon, ann-TNO film was investigated by comparing u-TiO2 and Nb-doped TiO2 (TNO) films. An investigation was conducted using Hall effect estimation, photoluminescence (PL) analysis, and band-gap calculation.
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