We describe how the material properties of III–V semiconductors, including bandgap, band structure, band offset, refractive index, absorption, and ionization coefficient, are exploited for lasers and photodetectors for fiber-optic communications. The material systems discussed for 1.3 μm and 1.55 μm light emission include the more traditional GaInAsP and AlGaInAs on InP, the more recently investigated GaInAs quantum dots and low-bandgap GaInNAs on GaAs as well as GaAsSb/GaAs Type II structures, and the potentially viable GaN/AlGaN from intersubband transitions (i.e., between quantized conduction-band energy levels). As an example of photodetector applications, GaInAsP/InP and wafer-fused GaInAs/Si are discussed in terms of gain and noise factor for use in avalanche photodiodes with separate absorption and multiplication regions.

Organic light-emitting devices (OLEDs) have attracted considerable interest in the last five years and are now viewed as an important competitor with liquid crystals for a wide variety of display applications. Current research focuses on the use of small-molecule and polymer materials to make organic electroluminescent displays with both passive-and active-matrix technologies. This article will discuss work on the device architecture for a polymer passive-matrix display application, the stability of polymer light-emitting displays, and the use of ink-jet printing for high-resolution patterning of red, green, and blue light-emitting polymers.

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 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.

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.

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.

Optical-fiber sensors can be placed on the skin or inside the human body for the direct measurement of biomedical parameters. This article presents an overview of the most recent applications of optical-fiber sensors for biomedical purposes and those currently under development.