The III-nitride light-emitting diodes (LEDs) have popularly penetrated into the market of the visible light communication, lighting, sensing, and display illumination. The electrons are supplied by the n-GaN layer, while the holes are injected from the p-GaN layer. It is well known that electrons and holes are not synchronized in the transport due to the fact that electrons are more mobile than holes. The layer that can make electrons "cold" is named as the electron cooler (EC), electron injector or electron reservoir layer. The hole injection is also affected by the doping efficiency of the p-GaN layer. To increase the hole concentration in the p-GaN layer, we have also proposed a hole modulator. Insufficient hole injection is also reflected by the nonuniform hole distribution in the multiple quantum wells. A most effective way to reduce the valence band discontinuity between the quantum well and the quantum barrier is to replace the GaN quantum barriers with InGaN quantum barriers.