Growth and characterization of blue and near-ultraviolet light-emitting diodes on bulk GaN

Abstract

Blue and near-ultraviolet (UV) InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) were grown on GaN and sapphire substrates using metalorganic chemical vapor deposition. The homoepitaxial LEDs exhibited greatly improved microstructural and electrical properties compared to the devices grown on sapphire. As a result of defect reduction, the reverse-bias leakage current was reduced by more than six orders of magnitude. At forward bias, thermally activated current rather than carrier tunneling was dominant in the LEDs on GaN. The improvement of optical characteristics was found to be a strong function of In content in the active region. At low and intermediate injection levels, the internal quantum efficiency of the UV LED on GaN was much higher compared to that on sapphire, whereas the performance of the blue LEDs was found to be comparable. At high injection currents, both the blue and UV LEDs on GaN greatly outperformed their counterparts on sapphire. The homoepitaxial LEDs with a vertical geometry had a much smaller series resistance and were capable of operating at 600 A/cm 2 in cw mode due to uniform current spreading and efficient heat dissipation.