In this chapter, we propose a hole accelerator, which is made of a polarization mismatched p-electron-blocking layer (EBL)/p-GaN/p-Al _x Ga_1−x N heterojunction. By setting III-nitride-based blue light-emitting diodes (LEDs) as examples, the effectiveness of the hole accelerator with different designs (i.e., the AlN composition in the p-Al _x Ga_1−x N layer and the thickness for the p-GaN layer and p-Al _x Ga_1−x N layer) on the hole injection is probed. According to our findings, the energy that the holes obtain does not monotonically increase as the AlN incorporation in the p-Al _x Ga_1−x N layer increases. Meanwhile, for x > 15% in our case, the energy that the holes gain increases and then reaches a saturation level as increasing the p-GaN layer or p-Al _x Ga_1−x N layer thickness. Therefore, the hole injection efficiency and device efficiency are very sensitive to the p-EBL/p-GaN/p-Al _x Ga_1−x N design, and the hole accelerator can effectively increase the hole injection if properly designed.