Efficiency enhancement in ultraviolet light-emitting diodes by manipulating polarization effect in electron blocking layer

The characteristics of the ultraviolet light-emitting diode (LED) with conventional and specifically designed electron blocking layers (EBLs) are investigated numerically and experimentally in this work. Simulation results show that delicately designed EBLs can not only capably perform the electron blocking function but also eliminate the incidental drawback of obstruction of hole injection caused by the nature of the large polarization field at the c-plane nitride heterojunction. It is shown that the polarization induced downward band bending can be mitigated when the portion of conventional EBL lying adjacent to the active region is replaced by a graduated AlGaN layer. The conduction band profile indicates that this replacement structure could have the capability of electron confinement similar to the conventional structure, and the valence band profile indicates that the spike induced by the polarization field is simultaneously eliminated, assisting the process of hole injection and distribution in the active region. Electron leakage over the EBL is thus obviously reduced, and the consumption efficiency of the injection carriers is improved, as expressed in the distribution of the electron current density. The experimental results show that the light output power can be significantly enhanced from 29.3 mW for the conventional device to 54.7 mW for the LED with the redesigned EBL structure. (C) 2013 AIP Publishing LLC.