Abstract
This paper reviews past research and the current state-of-the-art concerning gallium nitride-based vertical-cavity surface-emitting lasers (GaN-VCSELs) incorporating distributed Bragg reflectors (DBRs). This paper reviews structures developed during the early stages of research into these devices, covering both major categories of GaN-based VCSELs: hybrid-DBR and all-dielectric-DBR. Although both types exhibited satisfactory performance during continuous-wave (CW) operation in conjunction with current injection as early as 2008, GaN-VCSELs have not yet been mass produced for several reasons. These include the difficulty in controlling the thicknesses of nitride semiconductor layers in hybrid-DBR type devices and issues related to the cavity dimensions in all-dielectric-DBR units. Two novel all-dielectric GaN-based VCSEL concepts based on different structures are examined herein. In one, the device incorporates dielectric DBRs at both ends of the cavity, with one DBR embedded in n-type GaN grown using the epitaxial lateral overgrowth technique. The other concept incorporates a curved mirror fabricated on (000-1) GaN. Both designs are intended to mitigate challenges regarding industrial-scale processing that are related to the difficulty in controlling the cavity length, which have thus far prevented practical applications of all-dielectric GaN-based VCSELs.
Highlights
For more than two decades, gallium nitride (GaN) has attracted interest with regard to applications in a wide range of optical devices, such as light-emitting diodes (LEDs) and laser diodes (LDs) [1,2]
All-dielectric-distributed Bragg reflectors (DBRs) vertical-cavity surface-emitting lasers (VCSELs) reported in the early stage of research into such devices are examined, after which the latest progress in other types of all-dielectric-DBR VCSELs based on epitaxial lateral overgrowth [14,15] and curved mirrors [16,17] is summarized
As an alternative to the approach reported by Higuchi et al, in which a lapping process is used to provide a basal plane for dielectric DBR deposition, a thinning technique based on photoelectrochemical (PEC) etching [24] was found to result in an operable GaN-VCSEL with a short cavity of 1.2 μm
Summary
For more than two decades, gallium nitride (GaN) has attracted interest with regard to applications in a wide range of optical devices, such as light-emitting diodes (LEDs) and laser diodes (LDs) [1,2]. GaN-based vertical-cavity surface-emitting lasers (VCSELs) have received considerable attention as a result of their superior characteristics, including low threshold currents, array formation capability, applicability to high-frequency operation, low manufacturing costs and high efficiencies [3,4,5,6,7,8,9,10,11,12,13]. Due to these advantages, GaN-based VCSELs have the potential to replace conventional LEDs and edge emitting LDs as light sources for optical storage, laser printers, projectors, displays, solid state lighting, optical communications, biosensors and many other applications. All-dielectric-DBR VCSELs reported in the early stage of research into such devices are examined, after which the latest progress in other types of all-dielectric-DBR VCSELs based on epitaxial lateral overgrowth [14,15] and curved mirrors [16,17] is summarized
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