Fabrication And Band Calculation Of Photonic Crystal On The Surface Of Light Emitting Diodes

GaN-based light-emitting diodes (LEDs) have been intensively developed and utilized for various applications with its advantages of high efficiency and low power, such as illumination and color displays and so on, but one of the biggest problems in limiting the brightness of GaN-based LEDs is the poor light extraction efficiency. This problem was solved in this paper by fabricating photonic crystal (PhC) pattern on the surface of LEDs.First of all, the band structures of different kinds of PhC patterns were calculated by Rsoft program, we did analysis and comparison with the results to get the change rule between band structures and different PhC patterns. In the experimental stage, we fabricated two-dimensional PhC pattern on the p-GaN layer and indium tin oxide layer respectively by using nanoimprint lithography. The pattern of nickel template consists of a periodic array of holes of245nm diameter and465nm period. Because of using soft template during nanoimprint lithography, we got PhC pattern on the surface of experiment sample with great integrity and accuracy. After the preparation of electrode, these three kinds of specimens were tested in electrical characteristics, electroluminescence spectra and relative luminous intensity. The results are as follow:(1)Compared to ITO PhC LED and Non-PhC LED, p-GaN PhC LED got a higher forward voltage. Under10mA forward current, p-GaN PhC LED’s forward voltage is8V, and the voltage of Non-PhC LED is3V. The possible reason is that p-GaN layer got damage during the etching process by the reactant gas.(2)We found that two-dimensional PhC pattern on the surface could affect the spectrum of the samples. Compared to the peak of Non-PhC LED’ spectrum, a redshift of6nm was observed in p-GaN LED’s spectrum, and the spectrum of ITO PhC LED also showed a slight shift. In our opinion, it’s due to the PhC’s modulation of light. We think that a specific PhC pattern will mainly increase the extraction of light with specific wavelength, that’s why the spectral peak of LED with PhC may shift compared to the LED without PhC.(3)According to the results of relative luminous intensity test on these samples, p-GaN PhC LED’s relative luminous intensity was1.39times higher than the Non-PhC LED under60mA forward current, but the test results of ITO PhC LED didn’t show any different compared with the non-PhC LED because of the location of ITO PhC pattern and the annealing progress.