Status and future of GaN-based vertical-cavity surface-emitting lasers

Abstract

Vertical-cavity surface-emitting lasers (VCSELs) offer distinct advantages over conventional edge-emitting lasers, including lower power consumption, single-longitudinal-mode operation, circularly symmetric output beams, waferlevel testing, and the ability to form densely packed, two-dimensional arrays. High-performance GaN-based VCSELs are well suited for applications in high-density optical data storage, high-resolution printing, lighting, displays, projectors, miniature atomic clocks, and chemical/biological sensing. Thus far, the performance of these devices has been limited by challenges associated with the formation of high-reflectance distributed Bragg reflectors (DBRs), optical mode confinement, carrier transport, lateral current spreading, polarization-related electric fields, and cavity-length control. This manuscript discusses the state-of-the-art results for electrically injected GaN-based VCSELs and reviews approaches to overcome the key challenges currently preventing higher performance devices. The manuscript also describes the development of nonpolar GaN-based VCSELs on free-standing GaN. Nonpolar orientations exhibit anisotropic optical gain within the quantum well plane and uniquely enable VCSELs with a well-defined and stable polarization state. In addition, a detailed description of a band-gap-selective photoelectrochemical etching (BGS PECE) process for substrate removal and fine cavity length control on free-standing GaN substrates is provided.