Effect of surface electronic states of p-Type GaN on the blue-light-emitting diodes

The surface electronic states of p-type GaN and its effect on the light-emitting diodes (LEDs) containing such p-GaN layers are studied. The surface band bending of p-GaN layers prepared from different growth conditions are determined by ultraviolet photoemission spectroscopy and X-ray photoemission spectroscopy. By either way, it is found that the surface band bending depends on the growth conditions and is reduced by increasing Mg concentration, growth temperature, and N₂-rich ambient. A further reduction in band bending is found with a postannealing at 750°C in N₂, resulting in a similar reduction of the operation forward voltage of the LED containing such a p-GaN layer. The mechanism involved is discussed.