Over the past decade, advances in LEDs have enabled the potential for wide-scale replacement of traditional lighting with solid-state light sources. If LED performance targets are realized, solid-state lighting will provide significant energy savings, important environmental benefits, and dramatically new ways to utilize and control light. In this paper, we review LED performance targets that are needed to achieve these benefits and highlight some of the remaining technical challenges. We describe recent advances in LED materials and novel device concepts that show promise for realizing the full potential of LED-based white lighting.

LEDs for Solid-State Lighting: Performance Challenges and Recent Advances

Blue light-emitting diodes with a light extraction efficiency of 73% are reported. The InGaN–GaN devices use a photonic-crystal structure for superior optical mode control; their performance has been characterized experimentally and modelled theoretically.

III -nitride photonic-crystal light-emitting diodes with high extraction efficiency

Provided is a light emitting diode (LED) manufactured by using a wafer bonding method and a method of manufacturing a LED by using a wafer bonding method. The wafer bonding method may include interposing a stress relaxation layer (33) formed of a metal between a semiconductor layer (20) and a bonding substrate (31). When the stress relaxation layer is used, stress between the bonding substrate and a growth substrate may be offset due to the flexibility of metal, and accordingly, bending or warpage of the bonding substrate may be reduced or prevented.

Light-emitting device and method of manufacturing the same

In this article, we review current understanding of the reliability of organic field-effect transistors, with a particular focus on degradation of device characteristics under bias stress conditions. We discuss the various factors that have been found to influence the operational stability of different material systems, including dependence on stress voltage and duty cycle, gate dielectric, environmental conditions, light exposure, and contact resistance. A key question concerns the role of extrinsic factors, such as oxidation or presence of moisture, and that of intrinsic factors, such as the inherent structural and electronic disorder that is present in thin organic semiconductor films. We also review current understanding of the microscopic defects that could play a role in charge trapping in organic semiconductors.

Reliability of Organic Field‐Effect Transistors

Optimization of internal quantum efficiency (IQE) for InGaN quantum wells (QWs) light-emitting diodes (LEDs) is investigated. Staggered InGaN QWs with large electron-hole wavefunction overlap and improved radiative recombination rate are investigated for nitride LEDs application. The effect of interface abruptness in staggered InGaN QWs on radiative recombination rate is studied. Studies show that the less interface abruptness between the InGaN sub-layers will not affect the performance of the staggered InGaN QWs detrimentally. The growths of linearly-shaped staggered InGaN QWs by employing graded growth temperature grading are presented. The effect of current injection efficiency on IQE of InGaN QWs LEDs and other approaches to reduce dislocation in InGaN QWs LEDs are also discussed. The optimization of both radiative efficiency and current injection efficiency in InGaN QWs LEDs are required for achieving high IQE devices emitting in the green spectral regime and longer.

Approaches for high internal quantum efficiency green InGaN light-emitting diodes with large overlap quantum wells

We relate the currently limited efficiency of photonic crystal (PhC)-assisted gallium nitride light-emitting diodes (LEDs) to the existence of unextracted guided modes. To remedy this, we introduce epitaxial structures which modify the distribution of guided modes. LEDs are fabricated according to this concept, and the tailored band structure is determined experimentally. We investigate theoretically the consequences of this improvement, which significantly enhances the potential for efficient light extraction by PhCs.

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Photonic-crystal GaN light-emitting diodes with tailored guided modes distribution

Limitations in extraction efficiency of gallium nitride (GaN) photonic crystal (PhC) light emitting diodes (LEDs) are addressed by implementing an LED design using both two-dimensional PhCs in-plane and index guiding layers (IGLs) in the vertical direction. The effects of PhCs on light extraction and emission directionality from GaN LEDs are studied experimentally. Angular-resolved electroluminescence clearly shows the combined effect of controlling the vertical mode profile with the IGLs and tailoring the emission profile with the periodicity of the PhC lattice. Increases in directional emission as high as 3.5 times are achieved by taking advantage of this directionality and guided mode control.

https://hal-iogs.archives-ouvertes.fr/hal-00818799/document

Directional emission control and increased light extraction in GaN photonic crystal light emitting diodes

GaN nanopillar and nanostripe arrays with embedded InGaN∕GaN multi-quantum wells (MQWs) were fabricated by holographic lithography and subsequent reactive ion etching. Etch related damage of the nanostructures was successfully healed through annealing in NH3∕N2 mixtures under optimized conditions. The nanopatterned samples exhibited enhanced luminescence in comparison to the planar wafers. X-ray reciprocal space maps recorded around the asymmetric (101¯5) reflection revealed that the MQWs in both nanopillars and nanostripes relaxed after nanopatterning and adopted a larger in-plane lattice constant than the underlying GaN layer. The pillar relaxation process had no measurable effect on the Stokes shift typically observed in MQWs on c-plane GaN, as evaluated by excitation power dependent photoluminescence (PL) measurements. Angular-resolved PL measurements revealed the extraction of guided modes from the nanopillar arrays.

Optical and structural properties of GaN nanopillar and nanostripe arrays with embedded InGaN∕GaN multi-quantum wells

Photonic crystal membrane cavities play a key role as building blocks in the realization of several applications, including quantum information and photonic circuits. Thus far, there has been no work on defect cavities with active layers emitting in the UV to green range of the spectrum based on the (Al,In,Ga)N material system. While this material system has great potential for a new generation of optoelectronic devices, there are several obstacles for the fabrication of GaN-based membrane cavities, including the absence of a conventional selective chemical wet etch. Here, we demonstrate the first fabrication of fully undercut GaN photonic crystal membranes containing an InGaN multiquantum well layer, fabricated using band-gap-selective photoelectrochemical etching. A postfabrication coating of Ta2O5 is used to tune the cavity modes into resonance with the quantum well emission, and the fabricated membranes exhibit resonant modes with Q=300.

Visible resonant modes in GaN-based photonic crystal membrane cavities

We introduce GaN∕InGaN light emitting diodes with a dielectric photonic crystal embedded in the epitaxial layer by lateral epitaxial overgrowth on a patterned GaN template. Overgrowth, coalescence, and epitaxial growth of the pn junction within a thickness of 500nm is obtained using metal-organic chemical vapor deposition. This design strongly modifies the distribution of guided modes, as confirmed by angle-resolved measurements. The regime of operation and potential efficiency of such structures are discussed.

/pdf/gan-ingan-light-emitting-diodes-with-embedded-photonic-3kf069axrw.pdf

Kelly McGroddy

Papers

Photonic-crystal GaN light-emitting diodes with tailored guided modes distribution

Directional emission control and increased light extraction in GaN photonic crystal light emitting diodes

Optical and structural properties of GaN nanopillar and nanostripe arrays with embedded InGaN∕GaN multi-quantum wells

Visible resonant modes in GaN-based photonic crystal membrane cavities

GaN/InGaN light emitting diodes with embedded photonic crystal obtained by lateral epitaxial overgrowth