| AVS 62nd International Symposium & Exhibition | |
| Electronic Materials and Processing | Tuesday Sessions |
| Session EM-TuP |
| Session: | Electronic Materials and Processing Poster Session |
| Presenter: | Hyunsoo Kim, Chonbuk National University, Republic of Korea |
| Authors: | K. Kim, Chonbuk National University, Republic of Korea H. Kim, Chonbuk National University, Republic of Korea |
| Correspondent: | Click to Email |
A key technology to fabricate highly efficient and reliable GaN-based light-emitting diodes (LEDs) is transparent conductive electrodes (TCEs), which are used as the Ohmic contact to p-GaN and the current spreader. Indeed, a lot of attempts have been made to fabricate better TCEs with high optical transmittance, low sheet resistance, and low contact resistance by employing Pt, oxidized Ni/Au, indium tin oxide (ITO), zinc oxide (ZnO), carbon nanotubes, graphene, et c. Among these TCEs, ITOs are the best in terms of their high optical transmittance in the visible wavelength range, low sheet resistances, feasible Ohmic contact to p-GaN, and guaranteed robustness, enabling them to be practically used in commercial products. Unfortunately, however, the sputtering process, which can produce the best quality of ITO films, cannot be used for the deposition of ITO film to p-GaN, associated with the sputtering damage of p-GaN surface. As an alternative, therefore, the e-beam evaporation technique, which is a representative physical vapor deposition technique free of ion damage, has been used for the ITO deposition. However, the evaporated ITO films were relatively poorer than the sputtered films due to the lack of stoichiometry and insufficient crystallinity of the ITO.
Metallic Pt thin film was shown to act as efficient current spreader in the GaN-based LEDs due to its low Rsh value and feasible Ohmic contact associated with its large work function (5.65 eV). More interestingly, Pt thin film has a distinctive feature of agglomeration upon thermal annealing, a so-called Ostwald ripening, leading to the formation of Pt islands or nanoclusters. This feasibility suggests that the combination of sputtered ITO or ZnO films and Pt nanoclusters, namely, hybrid TCEs, may be successful for fabricating novel TCEs for GaN-based LEDs since Pt nanoclusters are expected to act as the preventer of ion damage or an Ohmic patch. In this regard, hybrid TCEs were investigated by combining Pt nanoclusters and sputtered films. Notably, hybrid ITO TCEs fabricated by combining interfacial Pt nanoclusters with a coverage ratio of 23.7 % (acting as an Ohmic patch) and a 100-nm thick sputtered ITO film yielded a low specific contact resistance of ~1.3x10-2 Ωcm2, a sheet resistance of 24 Ω/sq, and a high optical transmittance of 90 % at 450 nm. LEDs fabricated with the hybrid ITO TCEs showed a 17.2 % brighter light output power compared to reference LEDs. This indicates that the high-quality sputtered ITO film can be practically used in LEDs by embedding Pt nanoclusters.