(Invited) the Progress and Outlook of GaN Laser Devices
Authors: Han Jung 
Published: February 2020

GaN laser diodes are considered the next frontier for high performance GaN optoelectronics. Currently, GaN edge-emitting laser diodes are finding specific applications in optical information storage, in large-area projection, and in automobile headlights. It is widely anticipated that further advances in GaN laser diodes could enable a much broader range of applications in lighting and display.
The purpose of this presentation is to provide a high-level analysis of the state of two types of GaN laser diodes; one is the edge-emitting laser (EEL) and the other is the vertical cavity surface emitting laser (VCSEL). Commercial GaN EEL has been available for more than 15 years but the performance (wall-plug efficiency) is limited to ~35%[1]. For GaN VCSELs, in spite of various laboratory demonstrations in the past 10 years, there has not been any commercial product as a result of complexity involved in the growth and fabrication.
For the discussion of GaN EELs we will analyze the factors that define and limit the contemporary GaN EELs. New approaches such as using non-polar/semipolar planes [2], quantum-dot active regions [3], higher power operation [4], and our unique approach of engineering the optical cavity confinement [5] will be discussed.
Concerning GaN VCSELs, the technological bottleneck has been the formation of distributed Bragg reflectors (DBRs) for a planar microcavity. We will review the pros and cons of several approaches including epitaxial DBRs (AlGaN [6] or AlInN [7]), dielectric DBRs involving layer separation and transfer [8]–[10], and later overgrowth on dielectric DBRs [11]. Special emphasis will be given to our effort in using a nanoporous medium to form an epitaxial, conductive, and highly reflective DBRs for VCSELs [12], [13].
This work is supported the National Science Foundation (NSF) under Award ECCS-1709149 and by DARPA MTO of the United States. The facilities used were supported by the Yale SEAS cleanroom, YINQE, and NSF MRSEC DMR-1119826.

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