期刊
MICROMACHINES
卷 12, 期 6, 页码 -出版社
MDPI
DOI: 10.3390/mi12060676
关键词
GaN; III-nitrides; VCSEL; distributed Bragg reflector; carrier aperture; polarization
类别
资金
- Ministry of Science and Technology in TAIWAN [MOST 109-2221-E-009-150, MOST 109-2124-M-009-005]
This article reviews the key challenges and solutions for III-nitride VCSELs, including polarization effects, DBR fabrication difficulties, and anti-guiding effects. By developing alternative cavity structures and processing technologies, these challenges have been overcome, leading to improved performance of VCSELs.
Since the first demonstration of (Al, In, Ga)N-based blue vertical-cavity surface-emitting lasers (VCSELs) in 2008, the maximum output power (P-max) and threshold current density (J(th)) has been improved significantly after a decade of technology advancements. This article reviewed the key challenges for the realization of VCSELs with III-nitride materials, such as inherent polarization effects, difficulties in distributed Bragg's reflectors (DBR) fabrication for a resonant cavity, and the anti-guiding effect due to the deposited dielectrics current aperture. The significant tensile strain between AlN and GaN hampered the intuitive cavity design with two epitaxial DBRs from arsenide-based VCSELs. Therefore, many alternative cavity structures and processing technologies were developed; for example, lattice-matched AlInN/GaN DBR, nano-porous DBR, or double dielectric DBRs via various overgrowth or film transfer processing strategies. The anti-guiding effect was overcome by integrating a fully planar or slightly convex DBR as one of the reflectors. Special designs to limit the emission polarization in a circular aperture were also summarized. Growing VCSELs on low-symmetry non-polar and semipolar planes discriminates the optical gain along different crystal orientations. A deliberately designed high-contrast grating could differentiate the reflectivity between the transverse-electric field and transverse-magnetic field, which restricts the lasing mode to be the one with the higher reflectivity. In the future, the III-nitride based VCSEL shall keep advancing in total power, applicable spectral region, and ultra-low threshold pumping density with the novel device structure design and processing technologies.
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