Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure
Reexamination Certificate
2000-06-26
2002-07-16
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
C257S085000, C438S022000
Reexamination Certificate
active
06420732
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the field of light emitting diodes. More particularly, the invention relates to light emitting diode structures which provide improved current blocking and/or light extraction properties.
BACKGROUND OF THE INVENTION
AlInGaP alloys have been used for making bright light emitting diodes (LEDs), wherein the light wavelength produced by an AlInGaP alloy LED is determined by the aluminum to gallium ratio of the alloy within the active region of the LED. The wavelength produced by an AlInGaP alloy LED is typically varied, from about 550 nanometers to about 680 nanometers.
A conventional AlInGaP LED typically contains a double heterostructure AlInGaP device, in which a first confining layer, such as an n-type AlInGaP, is formed on an n-type substrate, such as GaAs. An active layer or region of undoped. AlInGaP is then formed on the first layer, and a p-type AlInGaP confining layer is formed upon the active layer. Metalorganic vapor phase epitaxy (MOVPE) processes are typically used to grow the AlInGaP substrates for this double heterostructure device.
Various light emitting diodes have been disclosed in the prior art, which describe various LED structures, materials, and manufacturing processes. N. Hosoi, K. Fujii, A. Yamauchi, H. Gotoh, and Y. Sato,
Semiconductor Light Emitting Devices,
European Patent Application No. EP 0 702 414 A2 (filed Jan. 9, 1995) disclose various semiconductor light emitting device structures.
A. Dutta,
Surface
-
Emission Type Light
-
Emitting Diode and Fabricating process Therefor
U.S. Pat. No. 5,972,731 (Oct. 26, 1999), and U.S. Pat. No. 5,821,569 (Oct. 13, 1998), discloses “An n-type GaAs layer as a buffer layer, an n-type (Al
0.7
Ga
0.3
)
0.5
In
0.5
P layer, an active layer, a p-type (Al
0.7
Ga
0.3
)
0.5
In
0.5
P layer, a thin layer of Al
x
Ga
1−x
As layer (x≧0.9), an Al
0.7
Ga
0.3
As layer as a current spreading layer and a high doped p-type GaAs cap layer are sequentially grown on an n-type GaAs layer of a substrate. As the active layer, an (Al
x
Ga
1−x
)
0.5
In
0.5
P based bulk or multi-quantum well is employed. As the current spreading layer, an Al
x
Ga1-xAs (x≧0.7) is employed. The current spreading layer is a p-type III-IV compound semiconductor having wider band gap than a band gap of a material used for forming the active layer, and being established a lattice matching with the lower layer. After mesa etching up to the cladding layer, growth of selective oxide is performed at a part of the AlGaAs layer. By this, a block layer (selective oxide of AlGaAs) is formed. By this blocking layer, a light output power and a coupling efficiency are improved”.
K. Shimoyama, N. Hosoi, K. Fujii, A. Yamauchi, H. Gotoh and Y. Sato,
Semiconductor Light
-
Emitting Devices,
U.S. Pat. No. 5,811,839 (Sep. 22, 1998) disclose “a semiconductor light-emitting device including a first clad layer comprising a first conductive type of AlGaAsP compound, a second clad layer that is located next to the first clad layer, comprises a first conductive type of AlGaInP compound and has a thickness of up to 0.5 &mgr;m, an active layer that is located next to the second clad layer and comprises a first or second conductive type AlGaInP or GalnP, a third clad layer that is located next to the active layer, comprises a second conductive type of AlGaInP compound and has a thickness of up to 0.5 &mgr;m, and a fourth clad layer that is located next to the third clad layer and comprises a second conductive type of AlGaAsP compound, and/or a light-extracting layer that comprises a second conductive type AlGaP or GaP and has a thickness of 1 &mgr;m to 100 &mgr;m.”
H. Sugawara, M. Ishikawa, Y. Kokubun, Y. Nishikawa, S. Naritsuka, K. ltaya, G. Hatakoshi, and M. Suzuki,
Semiconductor Light Emitting Device,
U.S. Pat. No. 5,153,889 (Oct. 6, 1992) disclose “a semiconductor light emitting device, comprising a semiconductor substrate, a double hetero structure portion formed on the front surface of the substrate and consisting of an InGaAlP active layer and lower and upper clad layers having the active layer sandwiched therebetween, a first electrode formed in a part of the surface of the double hetero structure portion, and a second electrode formed on the back surface of the substrate. A current diffusion layer formed of GaAIAs is interposed between the double hetero structure portion and the first electrode, said current diffusion layer having a thickness of 5 to 30 microns and a carrier concentration of 5×10
17
cm
−3
to 5×10
18
cm
−3
.”
J. Ming-Jiunn, B. Lee, and J. Tarn,
Light Emitting Diode With Asymmetrical Energy Band Structure,
U.S. Pat. No. 5,917,201 (Jun. 29, 1999) disclose a high bandgap material “used as a cladding layer to confine the carrier overflow in a aluminum-gallium-indium-phosphide light emitting diode. The quantum efficiency is improved. The use of this high bandgap material as a window material also prevents current crowding. The efficiency can further be improved by using a Distributed Bragg Reflector in the structure to reflect light, and a buffer layer to reduce interface dislocation.”
Y.
Liu, Gallium Aluminum Arsenide Graded Index Waveguide,
U.S. Pat. No. 4,152,044 (May 1, 1979) discloses a “double heterostructure light emitting device has a graded index optical waveguide formed integrally therein. The integrally formed waveguide collects light from the heterojunction and directs the light in a distinct light pattern on one surface of the device. The rate of variation of the index gradient within the waveguide region determines the geometry of the light pattern. The light output pattern can be conveniently tailored to match the geometry of a wide variety of optical fiber dimensions”.
H. Abe,
Semiconductor Light
-
Emitting Element with Light
-
Shielding Film,
U.S. Pat. No. 5,192,985 (Mar. 9, 1993) discloses a semiconductor light-emitting element, which “includes a current pinching type semiconductor light-emitting element main body, which utilizes light extracted from a surface parallel to a light-emitting layer, and a light-shielding film, which is locally or entirely coated on a side surface of the semiconductor light-emitting element main body to be electrically insulated therefrom. A method of manufacturing a semiconductor light-emitting element, includes the steps of preparing a wafer by sequentially stacking and forming a current blocking layer, a first cladding layer, an active layer, a second cladding layer, and a first ohmic electrode on one surface of a substrate, and forming a second ohmic electrode on the other surface of the substrate, forming a resist film on the major surface of the wafer, forming a plurality of grooves reaching at least the first cladding layer at predetermined positions on the resist layer, coating an electrical insulating film on the resist film including the grooves, and coating a light-shielding layer on the electrical insulating film, removing the electrical insulating film, the light-shielding film, and the resist film so as to leave the electrical insulating film and the light-shielding film in portions of the grooves, and cutting the wafer at the portions of the grooves.”
A. Cho, E. Schubert, L. Tu, and G. Zydzik,
Light Emitting Diode,
U.S. Pat. No. 5,226,053 (Jul. 6, 1993) disclose an LED in which: “an optical cavity of the LED, which includes an active layer (or region) and confining layers, is within a resonant Fabry-Perot cavity. The LED with the resonant cavity, hereinafter called Resonant Cavity LED or RCLED, has a higher spectral purity and higher light emission intensity relative to conventional LEDs. The Fabry-Perot cavity is formed by a highly reflective multilayer distributed Bragg reflector (DBR) mirror (R
B
≧0.99) and a mirror with a low to moderate reflectivity (R
T
~0.25-0.99). The DBR mirror, placed in the RCLED structure between the substrate and the confining bottom layer, is used as a bottom mirror. Presence of the less reflective top mirror above the active region leads to an unexpected improvement in
Devito Mark
Kung Hsing
Tu Chin-Wang
Glenn Michael A.
Hendricks Don
Huynh Andy
Luxnet COrporation
Nelms David
LandOfFree
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