Light-emitting diode array with anti-reflection coating providing reduced internal reflection

Claim 2

An LED array, comprising: a semiconductor substrate of a first conductive type; an insulating film formed on one surface of said semiconductor substrate, having a plurality of windows; a plurality of diffusion regions of a second conductive type disposed below respective windows, formed by diffusion of an impurity through said windows into said semiconductor substrate; and an anti-reflection coating covering exposed portions of said diffusion regions in said windows, consisting of at least a first thin film of phospho-silicate glass and a second thin film of aluminum oxide.

Claim 3

The array of claim 1, wherein said diffusion regions have a refractive index n, said first thin film has a first thickness d 1 and a first refractive index n 1 , said second thin film has a second thickness d 2 and a second refractive index n 2 , air having a refractive index n 0 , and said first thickness d 1 and said second thickness d 2 are selected to maximize a transmittance T defined as follows: T=1-(r×r*) where r is a complex number, r*, is the complex conjugate of r, and r is equal to: ##EQU2## r 1 being a reflectivity at an interface between said p-type diffusion regions and said first thin film, calculated as r 1 =(n-n 1 )/(n+n 1 ); r 2 being a reflectivity at an interface between said first thin film and said second thin film, calculated as r 2 =(n 2 -n 1 )/(n 2 +n 1 ); r 3 being a reflectivity at an interface between said second thin film and air, calculated as r 3 =(n 2 -n 1 )/(n 2 +n 1 ); δ 1 being a phase shift of light in transit through said first thin film, calculated as δ 1 =4πn 1 d 1 /λ; δ 2 being a phase shift of light in transit through said second thin film, calculated as δ 2 =4πn 2 d 2 /λ; and λ being a wavelength of light emitted from said diffusion regions.

Claim 4

The LED array of claim 1, further comprising a plurality of electrodes disposed over said insulating film, extending to respective windows, and making electrical contact with said diffusion regions in said windows, wherein: said anti-reflection coating has contact holes through which said electrodes make said electrical contact with said diffusion regions; and said anti-reflection coating extends between said electrodes and said insulating film.

Claim 5

The LED array of claim 1, wherein said insulating film comprises a film of Al 2 O 3 .

Claim 6

The LED array of claim 2, further comprising a plurality of electrodes disposed over said insulating film, extending to respective windows, and making electrical contact with said diffusion regions in said windows, wherein: said anti-reflection coating has contact holes through which said electrodes make said electrical contact with said diffusion regions; and said anti-reflection coating extends between said electrodes and said insulating film.

Claim 7

The LED array of claim 2, wherein said insulating film comprises a film of Al 2 O 3 .

Claim 8

The LED array of claim 2, wherein λ is approximately 740 nm, n is approximately 3.5, n 0 is 1.0, n 1 is approximately 1.4, n 2 is approximately 1.6, d 1 is approximately 20 nm, and d 2 is approximately 100 nm.

Claim 9

The LED array of claim 2, wherein λ is approximately 740 nm, n is approximately 3.5, n 0 is 1.0, n 1 is approximately 1.4, n 2 is approximately 1.6, d 1 is in a range from 10 nm to 20 nm, and d 2 is in a range from 150 nm to 250 nm.

Claim 10

The LED array of claim 1, wherein said substrate comprises a GaAsP epitaxial layer, wherein said insulating film comprises a film of Al 2 O 3 of approximately 200 nm thickness, wherein said first thin film of phospho-silicate glass is approximately 20 nm thick, and wherein said second thin film comprises a film of Al 2 O 3 of approximately 100 nm thickness.

Claim 11

The LED array of claim 2, wherein said substrate comprises a GaAsP epitaxial layer, wherein said insulating film comprises a film of Al 2 O 3 of approximately 200 nm thickness, wherein said first thin film of phospho-silicate glass is approximately 20 nm thick, and wherein said second thin film comprises a film of Al 2 O 3 of approximately 100 nm thickness.