Influence of quantum well design on light polarization switching in AlGaN ultraviolet emitters

Cheng Liu,Jing Zhang

doi:10.1063/1.5048597

Abstract

Polarization properties from AlGaN quantum well (QW) strongly determine the efficiency of deep ultraviolet (UV) light-emitting diodes (LEDs), hence knowing the critical Al-content at which the light polarization switches is essential for high-efficiency deep UV LED designs. This work theoretically investigates the influence of QW design on the light polarization switching in AlGaN-based UV LEDs. The physics analysis by using the self-consistent 6-band k·p model shows that the Al-content for valence subbands crossover presents an increasing trend as AlGaN QW thickness increases with consideration of polarization electric field, carrier screening effect and strain state. On the other hand, the critical Al-content where the transverse-electric-polarized spontaneous emission recombination rate (Rsp) is equal to the transverse-magnetic-polarized Rsp has the maximum value at the QW thickness of ∼1.5 nm. The difference between the two types of critical Al-contents can be explained by the quantum confined stark effect and the band mixing effect. The light polarization properties from reported AlGaN-based UV emitters show a similar trend to our theoretical results on critical Al-contents, indicating the importance on the understanding of QW design for high-efficiency deep-UV emitters.

Highlights

AlGaN-based deep ultraviolet (UV) light-emitting diodes (LEDs) and lasers are demonstrated to be ideal candidates for a variety of applications such as water/air purification, sterilization and highdensity optical recording.[1]
Those photons emitted at large angle will be trapped and absorbed in the LED structure more which results in a low ηLEE
It is very important to understand the physics of AlGaN quantum wells (QWs) design on the influence of optical polarization switching point, which has not been reported yet

Summary

Introduction

AlGaN-based deep ultraviolet (UV) light-emitting diodes (LEDs) and lasers are demonstrated to be ideal candidates for a variety of applications such as water/air purification, sterilization and highdensity optical recording.[1]. For AlGaN quantum wells (QWs), the emitted photons switch from TE-polarization to difficult-escaped TM-polarization as the Al-composition increases because of the remarkable difference of the crystal-field splitting energies (∆CR) between AlN (-169 meV) and GaN (10 meV) which changes the order of valence subbands.[4] Note that the light polarization change in the AlGaN QW does limit the ηLEE, and strongly influence spontaneous emission rate and internal quantum efficiency as well.[5] it is essential to investigate and predict the critical Al-content at which the switching from TE to TM occurs for efficient deep-UV active region design.

Results

Conclusion