The influence of Si doping to the characteristics of AlGaAs / AlAs distributed Bragg reflectors

Abstract

Many researches have been devoted to enhance the light extraction of light emitting diodes (LED). In some designs of LEDs, an absorbing substrate cannot be avoided. To prevent the emitted light from being absorbed by the substrate, a highly reflective mirror called distributed Bragg reflectors (DBR) is employed between the substrate and the active layers. In addition, the DBR layers are doped to conduct current. In our study, we have n-GaAs as the substrate, n-AlGaAs / AlAs as the DBR, multiple quantum wells (MQW) as the active layers, p-GaP as the window layer. The choices of the dopant for the DBR are Si and Te. However, the resultant LEDs have different performance. The one doped with Si in DBR (DBR:Si) performs poorly. Our investigation shows that the optical properties of DBR:Si degrade dramatically because of the existence of AlGaInP (part of MQW) layer above and the subsequent high temperature annealing in p-GaP layer growth. Either condition alone cannot yield the degradation. Conversely, the optical properties of DBR:Te do not change significantly even though it undergoes the same processes to grow the subsequent layers. The result indicates a sophisticated interaction between DBR:Si and AlGaInP layers during the high temperature annealing process for the growth of p-GaP. The study provides the insight on the influence of the dopant to the optical properties of DBR in LED devices.