GaN based LED lighting extraction efficiency using digital diffractive phase grating
First Claim
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1. A light emitting diode comprising:
- (a) a stacked structure having a top surface, a bottom surface, edges extending between said top and bottom surfaces and an emitting junction extending generally in a horizontal plane above the bottom surface, said emitting junction having an emission wavelength;
said stacked structure having vertical directions normal to the emitting junction, and (b) a reflective periodic diffraction grating disposed below said emitting junction on or in said stacked structure, said grating including a plurality of elements periodically spaced apart from one another in a repeat direction defining a set of first regions and second regions having different vertical elevations, such that said first regions project below said second regions by a predetermined distance, said first and second regions arranged to reflect light at phases differing by π
, the periodic spacing of the first and second regions of said grating being operative to diffract light at said emission wavelength directed vertically downwardly from said emission layer so that a substantial portion of such light is reflectively diffracted in major diffraction directions oblique to the vertical and intersecting the edges of the structure.
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Abstract
A light emitting diode incorporating an active emitting layer (14) overlying a transparent substrate (10) is provided with a reflective diffraction grating (30) on the bottom surface of the substrate. Emitted light passing downwardly through the substrate is diffracted outwardly toward edges (21) of the substrate and passes out of the die through the edges. This effect enhances the external quantum efficiency of the diode.
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18 Claims
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1. A light emitting diode comprising:
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(a) a stacked structure having a top surface, a bottom surface, edges extending between said top and bottom surfaces and an emitting junction extending generally in a horizontal plane above the bottom surface, said emitting junction having an emission wavelength;
said stacked structure having vertical directions normal to the emitting junction, and(b) a reflective periodic diffraction grating disposed below said emitting junction on or in said stacked structure, said grating including a plurality of elements periodically spaced apart from one another in a repeat direction defining a set of first regions and second regions having different vertical elevations, such that said first regions project below said second regions by a predetermined distance, said first and second regions arranged to reflect light at phases differing by π
, the periodic spacing of the first and second regions of said grating being operative to diffract light at said emission wavelength directed vertically downwardly from said emission layer so that a substantial portion of such light is reflectively diffracted in major diffraction directions oblique to the vertical and intersecting the edges of the structure. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A light emitting diode comprising:
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a light emissive stacked structure including;
(i) a substrate having top and bottom principal surfaces transverse to a vertical direction, and (ii) a light emissive stack disposed on the top principal surface of the substrate, the light emissive stacked structure having light transmitting edges spaced apart by a horizontal dimension in a horizontal direction transverse to the vertical direction; and a reflective periodic diffraction grating disposed on or in the bottom principal surface of the substrate and having a grating period in the horizontal direction defining selected non-zeroeth order diffraction directions, the horizontal dimension, a thickness of the light emissive stacked structure, and the grating period being selected such that a substantial portion of vertically oriented light diffracted by the diffraction grating into the selected non-zeroeth order diffraction directions exits the light emissive stacked structure via the light transmitting edges, the reflective periodic diffraction grating including;
first regions and second regions alternating along the horizontal direction to define the grating period, the first and second regions having different vertical elevations, such that the first regions project below the second regions by a predetermined distance selected so that the first and second regions reflect light at phases differing by π
.- View Dependent Claims (14, 15, 16, 17, 18)
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Specification