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-μm VCSELs, fundamental materials issues related to distributed Bragg reflectors, theoretical quantum-well gain calculations, and work on quantum-dot VCSELs.

Vertical-cavity surface-emitting lasers (VCSELs) based on gallium nitride semiconductor heterostructures represent a contemporary focus of research, the aim of which is to develop a new class of planar microdevices in the blue, violet, and near-ultraviolet ranges. We review recent progress in this exploratory area, to highlight the challenges and scientific excitement associated with the efforts that are under way to create flexible, short-wavelength sources for applications expected to range from biomedical diagnostics to solid-state displays and lighting.

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 device-fabrication 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.

Optical components based on vertical-cavity surface-emitting lasers (VCSELs) are moving from 850-nm wavelengths to 1.31-μm and 1.55-μm wavelengths. These long-wavelength devices, enabled by new developments in materials technology, will compete directly with distributed-feedback (DFB) and Fabry-Pérot (FP) laser technologies in fiber-optic markets. In addition, the unique properties of VCSELs are opening up a new category of optically integrated components that are not possible with traditional edge-emitting laser source technologies. These VCSEL structures, such as linear and two-dimensional arrays, have the potential to dramatically reduce the cost structure of traditional optical networking equipment and provide a path for rapid growth in optical bandwidth.

Distributed Bragg reflectors (DBRs) not only serve as high-reflectance mirrors to define the laser cavity of a vertical-cavity surface-emitting laser (VCSEL), but they also must conduct electricity, confine currents, and provide a single-crystal template for the gain region of the laser. Basic optical and electrical properties of DBRs are presented in this article. Three examples of DBR structures used in VCSEL applications from the ultraviolet to the infrared are given to illustrate the complexity and range of materials science issues that are encountered in DBR growth. Fabrication issues are also discussed.

The development of vertical-cavity surface-emitting lasers (VCSELs) relies on an understanding of gain-medium physics, more so than in edge-emitting lasers. An important tool in the investigation of semiconductor gain behavior is a theory that provides a systematic account of the interaction between the laser field and the electron–hole plasma, the influence of the band structure, and the many-body effects due to Coulomb interactions among carriers. This article describes a semiclassical approach that is based on the semiconductor Bloch equations, with carrier correlation effects described at the level of quantum kinetic theory. To illustrate its application, we discuss research activities involving the development of gain media for long-wavelength VCSELs.

GaAs-based continuous-wave quantum-dot vertical-cavity surface-emitting lasers (VCSELs) operating at 1.3 μm at 20°C with output power of 1.2 mW have been realized. Threshold currents approach 1–1.5 mA for 8-μm oxide apertures. Operating voltages are ∼2 V. Long operation lifetimes in excess of 5000 h at 50°C without degradation have been achieved. This article describes these breakthroughs, which are based on our development of complex self-organized growth technologies for defect-free stacked quantum dots.

The following article is based on the presentation given by Simon C. Moss (University of Houston), recipient of the 2001 MRS Von Hippel Award, the Materials Research Society's highest honor, at the 2001 MRS Fall Meeting on November 28 in Boston. Moss was cited for “consistently timely and essential contributions to identifying and understanding the atomic-level structure of almost every new type of material discovered in the last 30 years.” The main unifying thread in his work is the use of diffuse scattering of x-rays and neutrons from disordered and defective solids to study their structure as well as the effects that defects have on phase transitions, whose intrinsic disorder makes them both “real” and challenging.