Influence of Quantum-Well Number and an AlN Electron Blocking Layer on the Electroluminescence Properties of AlGaN Deep Ultraviolet Light-Emitting Diodes

Shuxin Tan,Takashi Egawa,Gang Chen,Jicai Zhang

doi:10.3390/app8122402

Abstract

The influence of quantum-well (QW) number on electroluminescence properties was investigated and compared with that of AlN electron blocking layer (EBL) for deep ultraviolet light-emitting diodes (DUV-LEDs). By increasing the QW number, the band emission around 265 nm increased and the parasitic peak around 304 nm was suppressed. From the theoretical calculation, the electron current overflowing to the p-type layer was decreased as the QW number increased under the same injection. Correspondingly, the light output power also increased. The increment of output power from 5 QWs to 10 QWs was less than that from 10 QWs to 40 QWs, which was very different from what has been reported for blue and near-UV LEDs. The parasitic peak was still observed even when the QW number increased to 40. However, it can be suppressed efficiently by 1 nm AlN EBL for LEDs with 5 QWs. The simulation showed that the insertion of a thin EBL increased the barrier height for electron overflow and the electron current in p-type layers decreased significantly. The results contributed to the understanding of behavior of electron overflow in DUV-LEDs.

Highlights

GaN and AlN alloys have attracted more and more attention as candidate materials for realizing ultraviolet (UV) optoelectronics [1,2,3,4,5]
When the wavelength was less than 300 nm, the external quantum efficiency (EQE) and output power were far lower than those of
We found that the electron overflow was partly suppressed and the relative output power continued to increase as the QW number increased up to 40

Summary

Introduction

GaN and AlN alloys have attracted more and more attention as candidate materials for realizing ultraviolet (UV) optoelectronics [1,2,3,4,5]. There are several factors responsible for the lower EQE and power, such as the lack of high-quality AlN substrate or an AlGaN template with low threading dislocation density, the difficulty in obtaining high conductivity in p-type layers [6,7,8], and the excessive self-heating effect of these devices under direct current operation [2,3]. The large spontaneous and piezoelectric fields in group III nitrides will result in the tilted band structure diagrams of multiple quantum wells (MQWs) [9,10] and reduce overlap of electron and hole wave functions, which will decrease the internal quantum efficiency of DUV-LEDs. Due to the lack of high-quality AlN substrate, a high-quality AlN template on sapphire is usually used for DUV-LEDs. It is well known that the weak surface migration of Al adatoms on the growth front limited the improvement of crystal quality. We found that the electron overflow was partly suppressed and the relative output power continued to increase as the QW number increased up to 40

Experiment

The quantum-well structures forfor all all thethe deep

Results

Simulation and Discussion

Conclusions