This work establishes the relationship between the electron energy and the electron concentration within the multiple quantum wells (MQWs) for AlGaN based deep ultraviolet light-emitting diodes (DUV LEDs). The electron energy of different values can be obtained by modulating the Si doping concentration in the n-AlGaN layer and/or engineering the polarization induced interface charges. The modulated Si doping concentration in the n-AlGaN layer will cause the interface depletion region within which the electric field can be generated and then tunes the electron energy. The polarization induced charges and the polarization induced electric field can be obtained by stepwisely reducing the AlN composition for the n-AlGaN layer along the  orientation. We find that the electron concentration in the MQWs can be increased once the electron energy is reduced to a proper level, which correspondingly improves the external quantum efficiency (EQE) for DUV LEDs. According to our investigations, it is more advisable to adopt the n-AlGaN layer with the stepwise AlN composition, which can make both the EQE and the wall plug efficiency high.