Optimization of electrode shape for high power GaN-based light-emitting diodes

Abstract

Because the polarization effect influences the distribution of the carriers in the multiple quantum wells of the light-emitting diodes (LEDs), the light-emitting efficiency is also affected. The influence of the polarization effect on GaN-based LEDs' performance is simulated. By simulating four different types of electrode shapes, it's found that the electrode shape influences not only the photoelectric characteristics but also the optical absorption by the semiconductor. Through the optimization of the electrode shape, the I-V characteristic is improved, and the series resistance is lowered. The optical absorption by the semiconductor is decreased and then the heat generated in the LEDs is lowered. As a result, both the photoelectric conversion efficiency and the stability are improved.GaN-based light emitting-diodes have a variety of applications such as backlighting in flat-panel displays, traffic signals, full-color displays, automotive lighting and the realization of white LED [1,2] . This is due to their many distinctive advantages, such as fast response, long life, small size, low power consumption and high reliability. However, because a GaN-based LED generally grows on the sapphire substrate which is an insulator, we need to etch a mesa on the LED chip in order to get N-contact. The current distribution is not uniform due to the mesa structure, which results in the current crowding effect [3] as shown in Fig.1. And the situation is worse for a high power GaN-based LED with a large mesa area. In addition, the photons generated within the active region can't entirely escape out of the LED. On one hand, the photons can exit from the semiconductor only if their angles of incidence are less than the critical angle. On the other hand, the semiconductor itself will absorb the photons. Through the simulation of electrode shape, it , s found that the electrode structure influences light extraction and optical absorption of the semiconductor. There are many ways to improve the optical and electrical characteristics of LED, such as adopting photonic crystal structure [4] , introducing distributed Bragg reflectors [5] , using short-period-superlattice and an ITO transparent contact [6] , and optimizing electron blocking layer [7] . In this paper, the characteristics of LED are improved by the optimization of electrode shape. Fig.1 The structure and current crowding of the GaNbased LEDMany papers have reported that the optimization of electrode shape can make the current distribution more uniform. For example, J B Zhang et al. [8] used METALAB software to simulate the current distribution of AlGaInP LED and found that the LED with a Wan Zi type electrode possessed more uniform current distribution and higher light extraction efficiency. However, the structure of GaN-based LED is not simple as that of AlGaInP LED, and its mesa structure makes the carriers distribution more complex. In this paper, we use

Modulation Performance of Blue Ingan Light-Emitting Diodes with P-Type Electron-Blocking Layer and N-Type Hole-Blocking Layer

“…[1][2][3][4] However, blue LEDs suffer from a rapid efficiency droop with increasing injection current, [5,6] which is detrimental to their high-brightness applications. The published simulations show that the electron leakage may play an important role in the efficiency droop.…”