Electrical characteristics of InGaN/GaN light-emitting diodes grown on GaN and sapphire substrates

We report on the electrical characteristics of InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) grown on sapphire and free-standing GaN substrates. As a result of defect reduction, the tunneling current in the homoepitaxially grown LED was remarkably suppressed and diffusion-recombination current dominated at intermediate forward bias. Temperature-dependent measurements showed that the remaining reverse current originated from carrier generation and tunneling associated with deep-level traps. In contrast, the LED on sapphire exhibited dominant tunneling characteristics over a wide range of applied bias. Nanoscale electrical characterization using conductive atomic force microscopy revealed highly localized currents at V-defects, indicating that the associated dislocations are electrically active and likely responsible for the high leakage current in the heteroepitaxially grown LED. (C) 2004 American Institute of Physics.