Role of Intrinsic Surface States in Efficiency Attenuation of GaN-Based Micro-Light-Emitting-Diodes

The effects of an intrinsic nonpolar surface on internal quantum efficiency (IQE) are numerically investigated for gallium nitride (GaN)-based micro-light emitting-diodes (mu-LEDs). It is found that due to the modulation of the surface density of states, the surface energy band bends upward, and valence band holes are naturally pushed toward the surface and are accumulated at the surface, resulting in significant nonradiative recombination. Consequently, the intrinsic surface states remarkably affect the IQE of mu-LEDs with a size of less than 30 mu m due to the large surface-to-volume ratio, whereas the IQE of devices with a size of more than 30 mu m is relatively insensitive to the intrinsic surface states. IQE starts to decrease for devices with a size of 30 mu m, even without considering sidewall damage. In particular, starting from a size of 10 mu m, mu-LEDs suffer a significant efficiency loss and the peak current density shifts to a higher value. The results open the way to improving device performance of mu-LEDs down to 1 mu m and beyond, by incorporating surface band engineering combined with surface passivation over the full range of microdisplay applications.