Performance Enhancement of Blue InGaN Light-Emitting Diodes with P-GaN/InGaN SPS Last Barrier and P-AlGaN/GaN SPS EBL

Abstract

The numerical simulations of blue InGaN/GaN light-emitting diodes (LEDs) with the combined structures of p-GaN/InGaN shortperiod superlattice (SPS) last barrier (LB) and p-AlGaN/GaN SPS electron blocking layer (EBL) are investigated by the Advance Physical Model of Semiconductor Devices (APSYS) program. The simulation results show that the newly designed LEDs get better performances over the original structure of InGaN/GaN LEDs. This is attributed to the enhancement of the hole injection efficiency and the improvement of the polarization field effect between the InGaN well and the GaN barrier layer in the multiple quantum wells (MQWs). Therefore, the simulation results exhibit a significant increment in radiative recombination rate and about 2.6 times enhancement in the internal quantum efficiency (IQE) at an injection current of 150 mA. More important of all, it also shows that the newly designed structure can obviously reduce the ratio of efficiency droop of the LEDs from 62 to 14.5%.The high-brightness InGaN/GaN LEDs are considered to be the most candidates in the applications on liquid crystal display back lighting, automobile headlamps, and solid-state lighting. However, the efficiency droop is still a serious issue for high-power LEDs applications. It is known that this phenomenon with the significantly reduction of the efficiency of LEDs at high current density has been called the "efficiency droop". Regarding the mechanisms of efficiency droop, several possible causes for the efficiency droop include poor carrier confinement, 1 Auger recombination, 2-4 electron leakage, 5-7 and poor hole injection. 8-10 However, the origin of the efficiency droop mechanism for nitride-based LEDs is still a controversial and uncertain issue until now. Among them, the insufficient hole injection efficiency and the electron overflow effect are very important key issues due to the relatively low mobility of the hole compared with the electron and insufficient potential barrier height for the electron in the conduction band for GaN-based materials. The conventional bulk p-AlGaN EBL between the LB and p-GaN layer acted as a potential barrier for the electron in the conduction band can effectively suppress the electron overflow from the MQWs to the p-GaN layer. However, the conventional bulk p-AlGaN EBL also created a potential barrier for the hole in the valence band, which obstructed the hole injected into the active region. 11 Consequently, some studies have had some specific designs of the LB structure to improve the carrier injection and reduce the efficiency droop in the GaN-based LEDs, such as a p-doped LB and a p-doped SPS LB. 12,13 In addition, several different energy band engineering designs on EBL also have been suggested like as: a graded p-AlGaN EBL, a p-AlGaN/GaN SPS EBL, and a triangle shape pAlGaN/GaN/AlGaN EBL. 14-16 The purposes of these designs are the improvement of the hole concentration and the enhancement of the radiative recombination rate in the MQWs.On the other hand, GaN-based materials generally exis...

Study of GaN/InGaN Light-Emitting Diodes with Specific Zirconium Oxide (ZrO2) Layers

“…[1][2][3][4][5][6][7][8][9] However, based on the remarkable difference in refractive index between the surrounding air (n = 1) and GaN (n = 2.5), the critical angle of total internal reflection (TIR) is only of 23.5°, which seriously suppresses the total light output attributed to the lower light extraction efficiency (LEE) and the lower external quantum efficiency (EQE) of GaN/InGaN LEDs. [10][11][12][13] Recently, various methods, e.g., pattern sapphire substrate, 14 backside reflector, 15 antireflection layer, 16 textured surfaces and sidewalls, 17,18 microhole array, 19 photonic crystal structure, 20 and hybrid surface structure 21 have been reported to upgrade the performance of GaN/InGaN LEDs. Moreover, the current spreading (CS) is an important issue for GaN/InGaN LEDs.…”

GaN-Based Blue Light-Emitting Diodes with an Electron Transmission Layer

“…Regarding the mechanisms of efficiency droop, the main physical explanations have been investigated and proposed such as: carrier delocalization, [1][2][3][4] Auger recombination, [5][6][7][8] junction heating, 9,10 current spreading, 11,12 electron overflow, [13][14][15][16] and poor hole injection. [17][18][19][20] However, the origin of the efficiency droop mechanism for GaN-based LEDs is still a controversial and uncertain issue until now. Yang et al reported that the current dependence of both the quantum efficiency and peak shift appeared to be a strong function of the indium content in the active region.…”