Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With particular semiconductor material
Reexamination Certificate
1999-01-07
2001-09-11
Abraham, Fetsum (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With particular semiconductor material
C257S096000, C257S094000, C257S076000, C257S190000
Reexamination Certificate
active
06288417
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention is directed to semiconductor light-emitting devices. More particularly, this invention is directed to semiconductor light-emitting devices that include polycrystalline GaN.
2. Description of Related Art
Group-III nitrides include elements from group III of the periodic table, i.e., Al, Ga and In. These materials are deposited over substrates to form layered structures for optoelectronic devices. The devices can emit visible light over a wide range of wavelengths. GaN and its alloys with InN and AlN can be used in visible light-emitting devices that produce high emission efficiencies. Crystalline heterostructures of these materials are typically deposited epitaxially on single-crystal substrates by vapor phase epitaxy techniques. For example, full-color outdoor displays can be formed by combining existing red emitters and blue and green InGaN/AlGaN light-emitting diodes (LEDs).
LEDs have been produced that can emit all three primary colors (red, green, blue). These devices have potential utility for large-area displays. By mixing two or more colors, a range of intermediate colors can potentially be produced in such displays.
Single crystal group III-nitride LEDs have a high emission efficiency despite having high defect concentrations. These materials can have dislocation densities of~10
10
cm
−2
. These extended defects apparently do not influence carrier flow and recombination in devices that are fabricated from these materials. This insensitivity is surprising in light of the known adverse effects that extended (i.e., one and two-dimensional) lattice defects, such as dislocations and stacking faults, normally have on the optoelectronic properties of semiconducting materials.
SUMMARY OF THE INVENTION
The potential use of known LEDs based on single-crystal LED materials in full-color displays is limited by the need to deposit these materials on single-crystal substrates. Known single crystal substrates including sapphire and silicon carbide have been formed only with limited areas. Accordingly, the size of displays that can be formed by depositing single crystal materials on such single-crystal substrates is limited as well. In addition, the number of suitable materials for forming single-crystal substrates for depositing group III-nitride semiconductor structures is limited.
This invention provides polycrystalline group III-nitride semiconductor materials. This invention separately provides light-emitting diodes (LEDs) and other light-emitting devices that comprise polycrystalline group III-nitride layers.
The polycrystalline group III-nitride materials include GaN and alloys of GaN with other group III-nitrides such as AlN and InN. These materials can be used in visible light-emitting devices to provide efficient light emission.
One exemplary semiconductor structure according to this invention comprises a polycrystalline, substantially non-crystalline or amorphous substrate and at least one polycrystalline group III-nitride layer formed over the substrate.
The polycrystalline group III-nitride layer can be formed on the substrate, i.e. directly upon the substrate. This polycrystalline group III-nitride layer is formed by first depositing amorphous group III-nitride material on the substrate, and then solid-phase crystallizing the amorphous material to form a polycrystalline group III-nitride layer. The amorphous group III-nitride layer is formed by a low temperature deposition technique on the substrate.
Alternatively, polycrystalline group III-nitride layers can be formed over one or more underlying layers formed prior to depositing the group III-nitride layers. These group III-nitride layers are deposited directly as polycrystalline layers without first depositing amorphous material as described above. A wetting (nucleation) layer can be deposited initially on the substrate to enhance deposition of subsequently formed layers over the substrate. The polycrystalline group III-nitride layer can then be formed on the wetting layer, or on other underlying layers such as buffer layers.
The light-emitting devices according to this invention comprise a polycrystalline, substantially non-crystalline or amorphous substrate and p-type and n-type polycrystalline group III-nitride layers formed over the substrate.
The light-emitting devices according to this invention can also comprise an active layer of a suitable polycrystalline group HII-nitride material. This active layer can be deposited between the p-type and n-type polycrystalline group III-nitride layers. This active layer enhances electrical carrier recombination.
To enhance carrier confinement, the light-emitting devices can comprise one or more confinement layers which are formed on the active layer. The confinement layers can comprise a group III-nitride material.
As described above, the polycrystalline p-type and n-type group III-nitride layers and active layer can be initially formed as amorphous layers and subsequently solid-phase crystallized to form polycrystalline material. The low-temperature deposition of the amorphous layers can enhance the incorporation of indium in InGaN active layers, enabling the active layer to emit visible light at the longer wavelengths.
Alternatively, the group III-nitride layers can be formed on the substrate as polycrystalline layers at higher deposition temperatures. In embodiments, a wetting layer can be initially deposited on the substrate to enhance sticking of gallium nitride to the substrate at the higher temperatures.
According to another aspect of this invention, the LEDs be used in large-area color displays. The displays can be monochromatic or multi-color displays. The displays comprise a substrate and a pixel array on the substrate. The substrates are polycrystalline, substantially non-crystalline or amorphous, and can have relatively large areas as compared to single crystal substrates. The polycrystalline group III-nitride layers deposited on the substrates enable enhanced structural flexibility. The pixels each comprise a light-emitting device according to this invention formed on the substrate. The light-emitting devices can emit violet or near-UV light, or alternatively visible light of a selected color.
In multi-color displays according to this invention, each pixel can emit a selected color. The pixels can comprise a red, green or blue phosphor. The phosphors can be formed either over the light-emitting devices or on the opposite surface of the substrate. The displays comprise n-electrodes (address electrode) and a plurality of separately addressable p-electrodes (control electrodes) over the light-emitting devices. The phosphors are each tuned to absorb light emitted by the light-emitting device and to re-emit light at a selected wavelength. Accordingly, the pixels can emit three different primary colors to provide a full-color, large area display.
This invention also provides methods of making the above-described semiconductor structures, light-emitting devices and displays.
These and other features and advantages of this invention are described in, or are apparent from, the following detailed description of the structures, devices and methods according to this invention.
REFERENCES:
patent: 6064078 (2000-03-01), Northrup et al.
S. Nakamura et al., “Candela-class High Brightness InGaN/AIGaN Double-heterostructure Blue-light-emitting Diodes”, Appl. Phys. Lett. 64 (13), 1994, pp. 1687-1689.
S. Nakamura et al., “High-Brightness InGaN Blue, Green and Yellow Light-Emitting Diodes with Quantum Well Structures”, Jpn. J. Appl. Phys. 34, 1995, pp. L797-L799.
S. Nakamura, “Blue-Green Light-Emitting Diodes and Violet Laser Diodes”, MRS Bulletin, 1997, pp. 29-35.
I. Akasaki et al., “Widegap Column-III Nitride Semiconductors for UV/Blue Light Emitting Devices”, J. Electrochem. Soc., 141(8), 1994, pp. 2266-2271.
S. Lester et al., “High Dislocation Densities in High Efficiency GaN-based Light-Emitting Diodes”, Appl. Phys. Lett. 66 (10), 1995, pp. 1249-1251.
D. Bour et al., “Characterization of OMVPE-Grown AIGa
Bour David P.
Mei Ping
Nickel Norbert H.
Van de Walle Christian G.
Abraham Fetsum
Oliff & Berridg,e PLC
Xerox Corporation
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