| AVS 54th International Symposium | |
| Electronic Materials and Processing | Monday Sessions |
| Session EM+NS-MoA |
| Session: | Semiconductor Nanostructures for Electronics and Optoelectronics I |
| Presenter: | F. Ren, University of Florida |
| Authors: | L. Stafford, University of Florida L.F. Voss, University of Florida S.J. Pearton, University of Florida H.T. Wang, University of Florida F. Ren, University of Florida |
| Correspondent: | Click to Email |
InGaN/GaN multiple quantum well light-emitting diodes (MQW-LEDs) are commercially available in a broad range of wavelengths for use in applications such as full color displays, traffic signals, and exterior lighting. There is also interest in shorter wavelength LEDs with AlGaN active regions which can be used in conjunction with down conversion phosphors to produce white light, and hold significant promise for next generation lighting technology. Nevertheless, to compete with fluorescent and other high-efficiency lighting sources, it is essential to drive GaN-based LEDs at very high current densities to maximize light output. One drawback of the high current densities is self-heating of the heterostructure. This can produce either indiffusion of the Ohmic contact elements, leading to an electrical short of the pn junction, or intermixing of the contact scheme, producing very rough surface morphology. One possible way to prevent excessive Ohmic contact degradation is to use a high-melting-point diffusion barrier in the contact stack. TiB2, with a melting temperature of ~3000°C, reasonable electrical resistivity (28 μΩ.cm) and thermal conductivity (26 W.m-1.K-1), and heat of formation comparable to those for silicides or nitrides, shows promise as a diffusion barrier. In this work, we report on the long-term annealing characteristics at 200-350°C of InGaN/GaN MQW-LEDs with TiB2- and Ir-based p-Ohmic contacts. This high-temperature stress stimulates accelerated aging of GaN-based LEDs and gives an idea of the expected reliability of the Ohmic contacts. By comparison with companion devices with conventional Ni/Au Ohmic contacts fabricated on the same wafer, MQW-LEDs with TiB2- and Ir-based Ohmic metallization schemes showed superior long-term thermal stability after 45 days at 200°C and 350°C, as judged by the change in turn-on voltage, leakage current, and output power. This is a promising result for applications where high-temperature operation is required.