The efficiency droop at higher current injection is still a problem in InGaN blue LEDs and the electron overflow from the active region is one of the probable reasons behind it. The general solution for controlling the electron overflow is to integrate the p-doped AlGaN layer right after the active region. However, it is found that this conventional electron-blocking layer (EBL) fails to prevent electron overflow completely and creates a hole injection problem. We report on the demonstration of a new type of electron overflow controlling system. Here, each GaN/p-Al_xGa_(1-x)N/GaN quantum barrier (QB) in the proposed structure can function as distributed EBL and effectively control the electron overflow.

For this study, the structure was reported by Kuo et al. [1] considered as a reference structure and denoted as LED1. The proposed structure, LED2 is derived from LED1 and doesn’t contain the conventional EBL. Importantly, GaN (5 nm)/p-Al_xGa_(1-x)N (5 nm)/GaN (5 nm) layers are considered as QBs instead of regular GaN (15 nm) QBs in LED2. The x value in all QBs is 0, 0.03, 0.06, 0.09, 0.12, and 0.15. The proposed QBs exhibit progressively increasing conduction band barrier heights, better supply holes due to the p-Al_xGa_(1-x)N layer, avoid the formation of positive sheet polarization at the last QB interface due to the absence of conventional EBL, improved electron confinement, and boosted hole injection. As a result, the output power is increased by ~245%, wall-plug efficiency is improved by ~205% in LED2 compared to the reference structure, LED1 at 150 mA current injection. The current-voltage (I-V), power-current (L-I) characteristics of all LEDs are presented in Fig. 1. All simulations are performed using the Crosslight APSYS tool. We have carefully considered all required material, band parameters and optimize our simulation model. The calculated I-V and L-I curves of LED1 are closest to the results reported by Kuo et al. [1] as shown in Fig. 1, which validates the reliability of our model.