High-power and reliable operation of vertical light-emitting diodes on bulk GaN

$\mathrm{In}\mathrm{Ga}\mathrm{N}∕\mathrm{Ga}\mathrm{N}$ light-emitting diodes (LEDs) with lateral and vertical geometries have been fabricated on free-standing GaN substrates. Current spreading was significantly enhanced in the vertical LED, leading to a reduced series resistance of $7\Omega$ compared to 12.2 and $14.2\Omega$ for the lateral LEDs on GaN and sapphire, respectively. As a result, the light output and power conversion efficiency of the vertical LED on GaN were greatly improved at high injection currents. The vertical LED was subjected to a stress test at $400\mathrm{mA}$ and showed minimal degradation of optical power, whereas the same stress resulted in the destruction of the lateral LED on sapphire due to increased current crowding and self-heating. However, lateral LEDs on sapphire with optimized current spreading exhibited excellent reliability, indicating the presence of a high density of dislocations $(\sim {10}^9{\mathrm{cm}}^{-2})$ in the heteroepitaxial device does not accelerate LED degradation at current densities up to $700\mathrm{A}∕{\mathrm{cm}}^2$ .