Vertical-Cavity Surface-Emitting Lasers
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Vertical-Cavity
Surface-Emitting Lasers
Kevin L. Lear and Eric D. Jones, Guest Editors Abstract This issue of MRS Bulletin presents a review of the progress that vertical-cavity surface-emitting lasers (VCSELs) have made throughout the wavelength spectrum. A VCSEL is a semiconductor laser diode in which light propagates normal to the epitaxial layers. In its older cousin, the Fabry–Pérot laser, light propagates in the plane of the epitaxial layers and reflects from mirrors formed by cleaving a crystal facet across the active layers. No cleaving is required for VCSEL mirrors, which are formed from multiple layers of epitaxially grown or otherwise-deposited thin films. The simple twist in the direction of the laser beam with respect to the epitaxial layers is responsible for most of the unique attributes of VCSELs, which arise from their short cavity length, their completely lithographically defined cross section, and their reliance on only wafer-scale processes for device fabrication. The articles in this issue cover a range of topics, including blue devices, short-wavelength communications lasers, recent advances in 1.3-m VCSELs, fundamental materials issues related to distributed Bragg reflectors, theoretical quantum-well gain calculations, and work on quantum-dot VCSELs. Keywords: distributed Bragg reflectors, gallium nitride (GaN), indium gallium arsenide nitride (InGaAsN), quantum-dot lasers, quantum-well gain regions, semiconductor diode lasers, vertical-cavity surface-emitting lasers (VCSELs).
Introduction The success of laser diodes has always been critically dependent on semiconductor material properties. Material selection during design, well-controlled epitaxial growth with sufficient material versatility, and property modification using microfabrication techniques are key issues for semiconductor lasers ranging from the conventional Fabry–Pérot lasers used in compact-disc systems to the distributed-feedback lasers used in high-end fiber communications systems. For vertical-cavity surface-emitting lasers (VCSELs), reviewed in this issue of MRS Bulletin, materials issues are no less important. The commercial progress of VCSELs is closely tied to the availability of appropriate semiconductor alloy systems that can be combined to realize mirrors and gain (amplifying) regions at the desired lasing wavelength. A VCSEL (pronounced “vik-sell”) is a semiconductor laser diode in which light
T T hh ee MRS BULLETIN/JULY 2002
propagates normal to the epitaxial layers. In its older cousin, the Fabry–Pérot laser, light propagates in the plane of the epitaxial layers and reflects from mirrors formed by cleaving a crystal facet across the active layers. No cleaving is required for VCSEL mirrors, which are formed from multiple layers of epitaxially grown or otherwise deposited thin films. The simple twist in the direction of the laser beam with respect to the epitaxial layers is responsible for most of the unique attributes of VCSELs, which arise from their short cavity length, their completely lithographically defi
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