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Vertical-Cavity

Surface-Emitting Lasers: Light for the Information Age Kent D. Choquette

Abstract The emergence of miniature light sources such as the vertical-cavity surface-emitting laser (VCSEL) is poised to advance the information age. The development of VCSELs has stimulated a wide range of materials research into epitaxial growth and devicefabrication technologies. In this article, current and emerging applications that are guiding the commercial development of VCSELs are first considered, followed by discussions of the VCSEL epitaxial structure and fabrication technologies. This brief overview will also mention recent efforts aimed at achieving long-wavelength VCSELs grown on GaAs substrates, as well as approaches for achieving a high modulation rate. Keywords: compound semiconductors, ion implantation, optoelectronic materials, selective oxidation, vertical-cavity surface-emitting lasers (VCSELs).

Introduction The infrastructure of the information age has relied upon advances in microelectronics to produce integrated circuits that are ever smaller, better performing, and less expensive than their predecessors. The emergence of photonics, where light rather than electricity is manipulated, is poised to further advance the information age. Central to the photonic revolution is the development of miniature light sources such as the vertical-cavity surface-emitting laser, or VCSEL. Today, VCSEL manufacturing has become well established in serving communications and telecommunications applications and markets. The development of VCSELs during the past two decades has stimulated a wide range of research, from basic studies of microcavity and semiconductor physics, to advances in epitaxial growth and device fabrication technologies.1 The first VCSEL was reported in Japan in 1979,2 although it was not until the latter part of the 1980s that VCSEL research became prominent in the United States and Europe. Since the middle of the 1990s, numerous companies have begun to manufacture VCSELs, and several applications have penetrated the marketplace.

MRS BULLETIN/JULY 2002

The dependence of VCSEL development upon compound-semiconductor epitaxial growth and fabrication advances continues today. A key VCSEL device innovation is the semiconductor distributed Bragg reflector (DBR) mirror, composed of alternating high- and low-refractive-index layers that enable a monolithic epitaxial structure. Thus, the development of activeregion materials that emit at the desired

wavelength can be complicated by the demand of lattice-matching to the DBR mirror materials. Similarly, the device structure and fabrication processes that are employed influence VCSEL performance characteristics (e.g., threshold current and voltage, efficiency, modulation response, etc.). In this review, we examine the VCSEL epitaxy and device processing that impact this optoelectronic technology. We start by considering the present and emerging VCSEL applications that are guiding commercial development. We then review the VCSEL epitaxial structure and ment