Blue and Near-Ultraviolet Vertical-Cavity Surface-Emitting Lasers
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Blue and Near-
Ultraviolet Vertical-Cavity Surface-Emitting Lasers Arto Nurmikko and Jung Han
Abstract 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. Keywords: semiconductor light-emitters, blue light-emitting diodes, gallium nitride (GaN), nitride semiconductors, vertical-cavity surface-emitting lasers (VCSELs), widebandgap semiconductors.
Introduction Vertical-cavity surface-emitting lasers (VCSELs) from the infrared to the red wavelength ranges have leapfrogged from a laboratory curiosity to a position of technological importance, if not dominance, in many areas of contemporary semiconductor optoelectronics. There are ample reasons to pursue the extension of VCSELs, resonantcavity light-emitting diodes (RCLEDs), and related planar devices to the shortwavelength edge of the visible spectrum and on to the ultraviolet, as they have significant application potential for optical storage, projection-based displays, chip-scale biochemical/biological analysis, lithography, printing, and semiconductor-based solid-state lighting. In this article, we examine recent research employing III–V nitride semiconductor heterostructures, the goal of which is the development of blue, violet, and ultraviolet high-performance directional and monochromatic light-emitters that are compatible with high-density multielement array fabrication. Although there are no viable 502
VCSELs in this arena as of this writing, good progress has been made in the past two years to develop some of the key concepts and building blocks for future devices. It is important to highlight the differences and juxtapose the challenges posed by the nitride microcavity emitters against the arsenide- and phosphide-based VCSELs at longer wavelengths. First, vertical-cavity nitride emitters are being pursued hot on the heels of the only very recently developed blue edge-emitting diode lasers and high-power LEDs.1 Therefore, they lack the springboard of the long development history that had brought the material and device sciences of ”conventional” III–V semiconductors to a significant technological maturity more than a decade ago when early work on GaAs-based VCSELs and RCLEDs began. Second, due to the fundamental differences in the basic physical properties between wide-bandgap (such as nitrides) and other semiconductors, the material and device sciences of the nitrides has demanded much innovation and fre-
quently an idiosyncratic approach to problem solving. (For example, the basic difficulties of electrical control in wide-gap semiconductors were so s
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