Analysis of the Thickness Effect of Undoped Electron-Blocking Layer in Ultraviolet LEDs

In this paper, the thickness effect of an undoped Al_0.23Ga_0.77N inserted in the Mg-doped Al_0.23Ga_0.77N electron-blocking layer (EBL) on the characteristics of the ultraviolet light-emitting diodes (UV-LEDs) was analyzed. The results of secondary-ion-mass spectrometry clearly show that the concentration of Mg back-diffusion from the p-GaN and the Mg-doped EBL decreases with the thickness of an undoped EBL. The radiative recombination rate in the multiple quantum wells (MQWs) can be obviously enhanced after inserting an undoped EBL from the simulated results, and the sample with a 6-nm-thick undoped EBL has the highest radiative recombination rate. It is worth noticing that the hole carrier concentration in the MQWs increases with increasing the thickness of an undoped EBL. The UV-LED possesses 400% enhancement in the output power (at 20 mA) by inserting a 6-nm-thick undoped EBL. The significant enhancement is ascribed to the decrease of nonradiative recombination defects formed by Mg atoms and the increase of hole concentration in the MQWs.