Ultralow threshold blue quantum dot lasers: what’s the true recipe for success?

Alexander Raun,Evelyn Hu

doi:10.1515/nanoph-2020-0382

Abstract

AbstractThe family of III-nitride materials has provided a platform for tremendous advances in efficient solid-state lighting sources such as light-emitting diodes and laser diodes. In particular, quantum dot (QD) lasers using the InGaN/GaN material system promise numerous benefits to enhance photonic performance in the blue wavelength regime. Nevertheless, issues of strained growth and difficulties in producing InGaN QDs with uniform composition and size pose daunting challenges in achieving an efficient blue laser. Through a review of two previous studies on InGaN/GaN QD microdisk lasers, we seek to provide a different perspective and approach in better understanding the potential of QD emitters. The lasers studied in this paper contain gain material where QDs are sparsely distributed, comprise a wide distribution of sizes, and are intermixed with “fragmented” quantum well (fQW) material. Despite these circumstances, the use of microdisk cavities, where a few distinct, high-quality modes overlap the gain region, not only produces ultralow lasing thresholds (∼6.2 μJ/cm2) but also allows us to analyze the dynamic competition between QDs and fQWs in determining the final lasing wavelength. These insights can facilitate “modal” optimization of QD lasing and ultimately help to broaden the use of III-nitride QDs in devices.

Highlights

Microscale light sources have seen impressive advances in sophistication and applicability over the past few decades.The development of increasingly miniaturized light sources has helped realize new technologies across a variety of research fields such as quantum computing, photonic integrated circuits, displays, and biomedicine [1,2,3,4,5,6,7]
The lasers studied in this paper contain gain material where quantum dot (QD) are sparsely distributed, comprise a wide distribution of sizes, and are intermixed with “fragmented” quantum well material
When research into light-emitting diodes (LEDs) and laser diodes (LDs) began, III–V compound semiconductors (i.e., GaAs: gallium arsenide, InP: indium phosphide, GaN: gallium nitride, etc.) emerged as promising candidate materials owing to their direct bandgaps and high carrier mobilities [8, 9]

Summary

Introduction

Microscale light sources have seen impressive advances in sophistication and applicability over the past few decades. When research into light-emitting diodes (LEDs) and laser diodes (LDs) began, III–V compound semiconductors (i.e., GaAs: gallium arsenide, InP: indium phosphide, GaN: gallium nitride, etc.) emerged as promising candidate materials owing to their direct bandgaps and high carrier mobilities [8, 9]. To further improve carrier confinement and material gain, theoretical studies on quantum dots (QDs) began in the early 1980s, and the first GaAs QD laser was shown in 1994 [14,15,16] While these discoveries paved the way for adoption of longer wavelength LEDs and LDs in commercial markets, research into high-power UV/blue light sources lagged. These insights can help improve understanding of the fundamental lasing dynamics of blue QD lasers, advancing a wide variety of applications

Gain material

Modal engineering

Conclusion