Investigation of the Optimum Mg Doping Concentration in p-Type-Doped Layers of InGaN Blue Laser Diode Structures

Chibuzo Onwukaeme,Han-Youl Ryu

doi:10.3390/cryst11111335

Abstract

In GaN-based laser diode (LD) structures, Mg doping in p-type-doped layers has a significant influence on the device performance. As the doping concentration increases, the operation voltage decreases, whereas the output power decreases as a result of increased optical absorption, implying that optimization of the Mg doping concentration is required. In this study, we systematically investigated the effect of the Mg doping concentration in the AlGaN electron-blocking layer (EBL) and the AlGaN p-cladding layer on the output power, forward voltage, and wall-plug efficiency (WPE) of InGaN blue LD structures using numerical simulations. In the optimization of the EBL, an Al composition of 20% and an Mg doping concentration of 3 × 1019 cm−3 exhibited the best performance, with negligible electron leakage and a high WPE. The optimum Mg concentration of the p-AlGaN cladding layer was found to be ~1.5 × 1019 cm−3, where the maximum WPE of 38.6% was obtained for a blue LD with a threshold current density of 1 kA/cm2 and a slope efficiency of 2.1 W/A.

Highlights

After the first development of nitride laser diodes (LDs) in 1996 [1] and first demonstration of blue LDs in 2001 [2] by Nichia, the performance of blue LDs has improved considerably
We investigated the optimum Mg doping concentrations in the p-type AlGaN electron-blocking layer (EBL) and cladding layers of InGaN blue LD structures using numerical simulations
The LD epitaxial layer structures were composed of a 1-μm thick n-Al0.04Ga0.95N cladding layer, an n-In0.02Ga0.98N lower waveguide (LWG), MQW active region, an In0.02Ga0.98N upper waveguide (UWG), a 15-nm thick p-AlGaN EBL, a 0.6-μm thick pAl0.04Ga0.95N cladding layer, and a 20-nm thick p-GaN contact layer grown on a GaN substrate

Summary

Introduction

After the first development of nitride laser diodes (LDs) in 1996 [1] and first demonstration of blue LDs in 2001 [2] by Nichia, the performance of blue LDs has improved considerably. High-power operation of InGaN blue LDs with >5 W output power in a single chip has been demonstrated, mainly by company research groups such as Nichia, Osram, and Sony [3,4,12]. They reported the low-threshold and high-efficiency operation of blue LDs with a threshold current density (Jth) < 1 kA/cm, slope efficiency (SE) > 2 W/A, and wall-plug efficiency (WPE) > 40% [3,12]. The low conductivity of the p-type layers is one of the main reasons limiting the WPE of GaN-based LDs [17,18]

Methods

Results

Conclusion