Inorganic semiconductor light-emitting diodes (LEDs) are environmentally benign and have already found widespread use as indicator lights, large-area displays, and signage applications. In addition, LEDs are very promising candidates for future energy-saving light sources suitable for office and home lighting applications. Today, the entire visible spectrum can be covered by light-emitting semiconductors: AlGaInP and AlGaInN compound semiconductors are capable of emission in the red to yellow wavelength range and ultraviolet (uv) to green wavelength range, respectively. Currently, two basic approaches exist for white light sources: The combination of one or more phosphorescent materials with a semiconductor LED and the use of multiple LEDs emitting at complementary wavelengths. Both approaches are suitable for high efficiency sources that have the potential to replace incandescent and fluorescent lights. In this article, the properties of inorganic LEDs will be presented, including emission spectra, electrical characteristics, and current-flow patterns. Structures providing high internal quantum efficiency, namely, heterostructures and multiple quantum well structures, will be discussed. Advanced techniques enhancing the external quantum efficiency will be reviewed, including resonant-cavities, die shaping (chip shaping), omnidirectional reflectors, and photonic crystals. Different approaches to white LEDs will be presented and figures-of-merit such as the color rendering index, luminous efficacy, and luminous efficiency will be explained. Finally, the packaging of low power and high power LED dies will be discussed.


Keywords:

light-emitting diodes (LEDs);
solid-state lighting;
compound semiconductors;
device physics;
reflectors;
resonant cavity LEDs;
white LEDs;
packaging

Light Emitting Diodes

http://nathan.instras.com/documentDB/paper-69.pdf

Porous silicon: a quantum sponge structure for silicon based optoelectronics

The various arguments for introducing optical interconnections to silicon CMOS chips are summarized, and the challenges for optical, optoelectronic, and integration technologies are discussed. Optics could solve many physical problems of interconnects, including precise clock distribution, system synchronization (allowing larger synchronous zones, both on-chip and between chips), bandwidth and density of long interconnections, and reduction of power dissipation. Optics may relieve a broad range of design problems, such as crosstalk, voltage isolation, wave reflection, impedence matching, and pin inductance. It may allow continued scaling of existing architectures and enable novel highly interconnected or high-bandwidth architectures. No physical breakthrough is required to implement dense optical interconnects to silicon chips, though substantial technological work remains. Cost is a significant barrier to practical introduction, though revolutionary approaches exist that might achieve economies of scale. An Appendix analyzes scaling of on-chop global electrical interconnects, including line inductance and the skin effect, both of which impose significant additional constraints on future interconnects.

/pdf/rationale-and-challenges-for-optical-interconnects-to-5clh2238g9.pdf

Rationale and challenges for optical interconnects to electronic chips

Erbium doped materials are of great interest in thin film integrated optoelectronic technology, due to their Er3+ intra-4f emission at 1.54 μm, a standard telecommunication wavelength. Er-doped dielectric thin films can be used to fabricate planar optical amplifiers or lasers that can be integrated with other devices on the same chip. Semiconductors, such as silicon, can also be doped with erbium. In this case the Er may be excited through optically or electrically generated charge carriers. Er-doped Si light-emitting diodes may find applications in Si-based optoelectronic circuits. In this article, the synthesis, characterization, and application of several different Er-doped thin film photonic materials is described. It focuses on oxide glasses (pure SiO2, phosphosilicate, borosilicate, and soda-lime glasses), ceramic thin films (Al2O3, Y2O3, LiNbO3), and amorphous and crystalline silicon, all doped with Er by ion implantation. MeV ion implantation is a technique that is ideally suited to dope these materials with Er as the ion range corresponds to the typical micron dimensions of these optical materials. The role of implantation defects, the effect of annealing, concentration dependent effects, and optical activation are discussed and compared for the various materials.

Erbium implanted thin film photonic materials

We review the family of optoelectronic devices whose performance is enhanced by placing the active device structure inside a Fabry‐Perot resonantmicrocavity. Such resonantcavity enhanced (RCE) devices benefit from the wavelength selectivity and the large increase of the resonant optical field introduced by the cavity. The increased optical field allows RCE photodetector structures to be thinner and therefore faster, while simultaneously increasing the quantum efficiency at the resonant wavelengths. Off‐resonance wavelengths are rejected by the cavity making RCE photodetectors promising for low crosstalk wavelength division multiplexing(WDM) applications. RCE optical modulators require fewer quantum wells so are capable of reduced voltage operation. The spontaneous emission spectrum of RCE light emitting diodes(LED) is drastically altered, improving the spectral purity and directivity. RCE devices are also highly suitable for integrated detectors and emitters with applications as in optical logic and in communication networks. This review attempts an encyclopedic overview of RCE photonicdevices and systems. Considerable attention is devoted to the theoretical formulation and calculation of important RCE device parameters. Materials criteria are outlined and the suitability of common heteroepitaxial systems for RCE devices is examined. Arguments for the improved bandwidth in RCE detectors are presented intuitively, and results from advanced numerical simulations confirming the simple model are provided. An overview of experimental results on discrete RCE photodiodes, phototransistors, modulators, and LEDs is given. Work aimed at integrated RCE devices,optical logic and WDM systems is also covered. We conclude by speculating what remains to be accomplished to implement a practical RCE WDM system.

Resonant cavity enhanced photonic devices

One-dimensional microcavities are optical resonators with coplanar reflectors separated by a distance on the order of the optical wavelength. Such structures quantize the energy of photons propagating along the optical axis of the cavity and thereby strongly modify the spontaneous emission properties of a photon-emitting medium inside a microcavity. This report concerns semiconductor light-emitting diodes with the photon-emitting active region of the light-emitting diodes placed inside a microcavity. These devices are shown to have strongly modified emission properties including experimental emission efficiencies that are higher by more than a factor of 5 and theoretical emission efficiencies that are higher by more than a factor of 10 than the emission efficiencies in conventional light-emitting diodes.

https://science.sciencemag.org/content/sci/265/5174/943.full.pdf

Highly efficient light-emitting diodes with microcavities

The spontaneous emission lifetime and intensity of Er implanted into ${\mathrm{SiO}}_{2}$ is modified by a Si/${\mathrm{SiO}}_{2}$ planar microcavity. The cavity strongly affects the coupling of the optically excited ${\mathrm{Er}}^{3+}$ to the radiative and waveguiding modes of the system, resulting in a spontaneous lifetime of 14.8 ms for a cavity off-resonance with the ${\mathrm{Er}}^{3+}$ versus a lifetime of 9.1 ms for an on-resonance cavity. The observed spontaneous emission lifetime changes agree well with calculated values based on a computation method which is also presented.

Controlled atomic spontaneous emission from Er3+ in a transparent Si/SiO2 microcavity.

We describe the first integration of vertical-cavity surface-emitting laser arrays with gigabit-per-second CMOS circuits via flip-chip bonding.

Vertical-cavity surface-emitting lasers flip-chip bonded to gigabit-per-second CMOS circuits

Under pulsed operation, gain guided surface emitting lasers have exhibited long delay times and higher threshold current than for CW operation. This phenomenon is explained by assuming that adiabatic heating of the active region results in time evolution of the transverse mode guiding. Our theory suggests that a built in index guiding greater than 10 −2 will stabilise the fundamental mode and improve the temporal performance of surface emitting lasers

George J. Zydzik

Papers

Highly efficient light-emitting diodes with microcavities

Controlled atomic spontaneous emission from Er3+ in a transparent Si/SiO2 microcavity.

Vertical-cavity surface-emitting lasers flip-chip bonded to gigabit-per-second CMOS circuits

Anomalous temporal response of gain guided surface emitting lasers

Thermal expansion — An empirical correlation