| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2018) | |
| Plasma Processing | Tuesday Sessions |
| Session PS-TuP |
| Session: | Plasma Processing Poster Session |
| Presenter: | Joon Seop Kwak, Sunchon National University, Republic of Korea |
| Authors: | T.K. Kim, Sunchon National University, Republic of Korea Y.-J. Cha, Sunchon National University, Republic of Korea J.S. Kwak, Sunchon National University, Republic of Korea |
| Correspondent: | Click to Email |
We systematically examined the origin of plasma-induced damage on p-GaN surface during the sputtering of ITO transparent conductive electrodes (TCE) and its effects on the forward voltage and the light output power (LOP) of InGaN/GaN LEDs. Firstly, we investigated the effect of direct current (DC) power in radio frequency (rf) superimposed DC sputtering (RF+DC sputtering) of ITO on the forward voltage and and LOP of InGaN/GaN LEDs and found that the plasma-induced damage was sensitive to the DC power. The forward voltages of the LEDs at 20 mA drastically decreased from over 5 V to 3 V and the LOP of the LEDs was greatly enhanced by more than 20% at 250 mA, when the DC power was changed from negative to positive values. Secondly, electron flux as well as ion flux during the RF+DC sputtering of ITO with the various DC power were calculated based upon the plasma discharge parameters measured by cutoff probe and Langmuir probe. Changing the DC to positive power drastically reduced the electron flux in plasma, suggesting that plasma electrons play an important role in plasma-induced damage of p-GaN surface. Furthermore, the significant increase in forward voltage of the LEDs was observed, when electron-beam irradiation on p-GaN surface was employed. This confirms that the plasma electrons, not ions, can cause the plasma-induced damage on p-GaN during the sputtering of ITO. Lastly, physical mechanism for the generation of plasma-induced damage on p-GaN by the plasma electrons was suggested. The plasma electrons can compensate the deep level defects (DLDs) in the p-GaN surface and reduce the density of DLDs, which increase the effective barrier height at the ITO/DLD band of p-GaN. Furthermore, the plasma electrons yielded the energetic ad-atoms of ITO on p-GaN during sputtering by energy transfer of the electrons to the ad-atoms and increased the plasma-induced damage on p-GaN. We successfully demonstrated the plasma-induced-damage-free ITO TCE on the InGaN/GaN LEDs by sputtering, which showed 20 % improved LOP of the LEDs with comparable forward voltage of 2.9 V at 20 mA to the LEDs with conventional e-beam-evaporated ITO.