Photonic crystals (PhCs) were typically fabricated on the light emitting surface of light emitting
diodes (LEDs) to improve light extraction, which is regarded as the weak coupling between the
laterally propagated light in the epi-layers and the surface nanostructure. This work demonstrates
GaN-based LEDs with the PhC structure on the mesa surface and nanohole arrays surrounding the light
emitting mesa. Our new device (SHLED) shows a 56% higher optical output power than the planar
structure (PLED), as compared with the 40% improvement of the surface PhC device (SLED) over
PLED. The output power of SHLED is higher than that of SLED due to the enhanced diffraction of low
order modes propagated in the lateral direction, in addition to the higher order mode light diffraction
from the surface PhCs. From the relative angular spectra, the interaction of in-plane optical wave with
the nanoholes (which are etched through MQWs) is much stronger than that with surface PhCs,
suggesting an efficient light diffraction to the surface normal by nanoholes.
We propose an on-wafer heat relaxation technology by selectively ion-implanted in part of the p-type GaN to decrease
the junction temperature in the LED structure. The Si dopant implantation energy and concentration are characterized to
exhibit peak carrier density 1×1018 cm-3 at the depth of 137.6 nm after activation in nitrogen ambient at 750 °C for 30
minutes. The implantation schedule is designed to neutralize the selected region or to create a reverse p-n diode in the p-GaN layer, which acts as the cold zone for heat dissipation. The cold zone with lower effective carrier concentration and
thus higher resistance is able to divert the current path. Therefore, the electrical power consumption through the cold
zone was reduced, resulting in less optical power emission from the quantum well under the cold zone. Using the diode
forward voltage method to extract junction temperature, when the injection current increases from 10 to 60 mA, the
junction temperature of the ion-implanted LED increases from 34.3 °C to 42.3 °C, while that of the conventional one
rises from 30.3 °C to 63.6 °C. At 100 mA, the output power of the ion-implanted device is 6.09 % higher than that of the
conventional device. The slight increase of optical power is due to the increase of current density outside the cold zone
region of the implanted device and reduced junction temperature. The result indicates that our approach improves
thermal dissipation and meanwhile maintains the linearity of L-I curves.
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