CA2639897A1 - Improved illumination using dilute-nitride layers and devices including dilute-nitride layers - Google Patents

Abstract

Methods and devices for generating light of a controlled color and/or color temperature with a light-emitting device illumination system comprising dilute-nitride based light-emitting diodes (LEDs).

Description

IMPROVED ILLUMINATION USING DILUTE-NITRIDE LAYERS AND DEVICES
INCLUDING DILUTE-NITRIDE LAYERS

FIELD OF THE INVENTION

[0001] This application relates generally to illumination devices made with light-emitting diodes (LEDs). More specifically, this application relates to the utilization of dilute-nitride LEDs with additional LEDs in illumination devices to improve temperature and current stability of the color and/or the color temperature of the devices.

BACKGROUND OF THE INVENTION

[0002] Solid state lighting with light-emitting devices has continued in the last several years to attract much interest in both research and business. Some of the applications for these devices include full-color displays, traffic lights, automotive lights, and backlighting sources for mobile telephones, among a large number of other applications. One objective of research in this area is the production of white LEDs, which could then be used as energy-efficient substitutes for currently widely used incandescent and fluorescent lights.

[0003] Currently, one of the biggest challenges in the LED industry is to produce efficient and cost competitive white LEDs for general illumination.
Utilization of LEDs for general illumination could significantly decrease overall electrical power consumption, as it is estimated that up to 25-30% of all electrical power is used for lighting. LEDs potentially operate at efficiencies of up to 200 lumens per watt (LmMI), which is about 2 to 2.5 times more efficient than fluorescent lamps or about 10 times more efficient than incandescent bulbs.

[0004] According to the American National Standards Institute (ANSI), white light is categorized according to correlated color temperature (CCT): warm white has a CCT
of about 2000 K to 4000 K; neutral white has a CCT of about 4000 K to 5500 K;
and cool white has a CCT of greater than about 5500 K. The CCT categorization ranges are DLMR_528857.4 1 approximate, but provide a rough standard for manufacturers and a basis of comparison for end-users.

[0005] Warm white can be generally described as "yellowish"; cool white can be generally described as "bluish"; and neutral white is in between. People generally prefer to use warm or neutral white for general illumination, as it provides soft white light which does not irritate the human eye. Cool white is generally unpopular for general illumination purposes as it tends to irritate the eye.

[0006] There are three main approaches to the production of white light: (1) using blue light-emitting devices with yellow phosphors; (2) using near ultraviolet (near UV) light-emitting devices with white phosphors; and (3) using tricolor mixing from a set of fundamental colored light-emitting devices such as red, green, and blue light-emitting devices.

[0007] The first two are the more widely used of these techniques. In one example of the first of these techniques, a yellow emitting phosphor is used to absorb a portion of the blue light emitted by the light-emitting device and to emit yellow light. The combination of the unabsorbed portion of the blue light emitted by the light-emitting device and the yellow light emitted from the phosphor is perceived by the human eye as white light. In the second of these techniques, one or more phosphors are utilized that absorb all near UV light emitted by the LED and emit light at a range of longer wavelengths, perceived by the human eye as white light.

[0008] Gallium nitride (GaN)-based LEDs are often used to produce the blue or near UV light, and many different types of phosphors are used for producing white light (or other color light if combined with a portion of the light emitted by the LED to produce white light). Different phosphors have different conversion efficiencies as well as different color and temperature stabilities. As a result, white light illumination devices based on LEDs utilizing phosphors can be produced with CCTs falling anywhere in the range from warm to cool white. However, phosphors used to produce cool white light are more efficient and temperature stable than phosphors used to produce warm white light. Exemplary state-of-the-art efficiency numbers for warm white and cool white DLMR_528857.4 2 devices from a leading white LED manufacturer are: 50-70 Lm/W for warm white and greater than 110 Lm/W for cool white. This represents a problem for the use of these LEDs for general illumination, since the efficiency of these warm white LEDs (50-70 Lm/W) is lower than the efficiency of a fluorescent lamp (typically, 70-80 Lm/W).
Combined with the higher cost of production, LED-phosphor based white light is less attractive for general illumination.

[0009] The last technique, tricolor mixing, is often referred to as the "RGB
approach," making reference to the use of red, green, and blue light-emitting devices to provide the set of fundamental colors. In the RGB approach to the generation of white light, effective tricolor mixing is achieved with light-emitting devices that provide light at approximately 460 nm, 540 nm, and 610 nm. The two shorter wavelengths (460 nm and 540 nm) can be produced using AIGaInN light-emitting devices and the longer wavelength (610 nm) can be produced from AIGaInP light-emitting devices grown on GaAs substrates.

[00010] The current to each LED is controlled either passively or actively to provide the appropriate intensity from each LED to achieve the desired color and color temperature. Such a system can be used to vary the color and/or color temperature to suit different illumination needs. While more flexible, this approach uses a greater quantity of LEDs and more sophisticated drive electronics compared to the LED-phosphor techniques, and is therefore more costly.

[00011] Another major shortcoming with this approach is that different color LEDs have different properties as a function of drive current and temperature.
Specifically the temperature dependence of the output wavelength of red LEDs is typically about 3 to 5 times larger than that of green and blue LEDs. The reason for the disparity is that, as stated above, the different color LEDs are made out of different materials which inherently differ in their brightness dependencies on drive current and temperature.

[00012] For illumination applications where precise color and color temperature control is required, this creates significant problems. If the intensity or ambient temperature of the lighting system changes, the color and/or color temperature will DLMR_528857.4 3 change. This is true whether the system comprises LED(s) emitting in one color or multiple LEDs with different emission wavelengths. The human eye is very sensitive to these changes thus making these changes undesirable for illumination or display applications. Second, a number of lighting applications have standards for colors, for example automotive and traffic illumination, and any lighting system used in these applications must meet these standards.

[00013] A fourth approach has recently been proposed to achieve high efficiency for warm white LED devices for general illumination. The new approach simply combines the above described techniques. A LED-phosphor technique is used to efficiently produce cool white light. This light is combined with light emitted from efficient red LEDs to produce a warm white color. The addition of the light from the red LEDs to the cool white light "warms up" the white light (i.e., decreases the cool color temperature from greater than 6000 K down to about 3000 K). The overall efficiency of such a combination can be greater than 110 Lm/W.

[00014] The red LEDs suggested for this technique are based on the AIInGaP
material system. This material makes an efficient red LED (> 100 Lm/W), but suffers from poor color stability across a range of temperatures and drive currents.
Since white LEDs for general illumination are driven at very high current (in the range of 1-3 A) to produce high luminous flux, a great deal of heat is generated in the p-n junction region(s) of the chips. The heat generated causes the red LED chip peak wavelength to shift with increasing temperature. The wavelength shift dependency on temperature and drive current is different in red LEDs and blue or near UV LEDs, resulting in a change in the overall color appearance of the white light. Additionally, time-dependent degradation in the performance of AllnGaP-based LEDs occurs at a different rate than that of GaN-based LEDs. This also contributes to a color and/or color temperature shift over time.

[00015] In addition to the color temperature, or correlated color temperature, the color rendering index (CRI) is another measure of light quality. The CRI is a quantitative measure of the ability of a light source to reproduce the color of objects DLMR_528857.4 4 faithfully in comparison with an ideal or natural light source. Natural light, for example sunlight, comprises a broad range of wavelengths from the visible spectrum.
Light sources with a high CRI also tend to comprise a broad range of wavelengths from the visible spectrum and are thus reasonably able to faithfully emulate ideal natural light.
Light sources with a low CRI tend to comprise a more narrow range of wavelengths and are less able to emulate ideal or natural light.

[00016] A high CRI may be difficult to achieve with a white light source comprising a plurality of different color LEDs and/or phosphors. The reason for this is that LEDs typically have fairly narrow spectral widths, generally measured as the full width at half maximum (FWHM) of the spectral peak. For typical LEDs the FWHM is on the order of about 10 nm to about 30 nm. The visible spectrum ranges from about 380 nm to about 750 nm. Thus it can be seen that a white light source having relatively few differently colored LEDs may not provide a good approximation to the visible spectrum (natural light) and thus have a low CRI.

[00017] The emission spectra from phosphors have a larger FWHM than LEDs, typically above about 70 nm, and thus may be able to achieve a relatively higher CRI.
However, compared to a LED emitting in the same wavelength range, the phosphor is relatively less efficient because of the loss mechanism inherent in the light conversion process. In other words, a LED emitting in a given wavelength range is more efficient than emission in the same wavelength range from a phosphor excited by a LED.
Thus, while the use of phosphors in a white light system may be able to help in achieving a high CRI, it results in lower overall efficiency as compared to systems without phosphors.

[00018] Problems associated with red AIInGaP-based LEDs are specifically discussed in U.S. Patent Application No. 11/520,622 (Van de Ven), paragraphs on page 2. This patent application describes a complicated system of sensors and reference LEDs combined with control electronics designed to monitor the light output and vary the current of LEDs in order to maintain a specified color and/or color temperature in the face of varying ambient temperature or intensity. Another exemplary DLMR_528857.4 5 control circuit useful for this purpose is described in U.S. Patent No.
7,213,940 (Van de Ven et al., col. 16, line 60 to col. 17, line 45). Inclusion of this type of current control circuitry increases the cost of RGB LED devices.

[00019] Backlighting units for display applications may also use a variety of techniques to produce appropriate wavelengths of light. In simple displays, the backlight may be white light that is filtered through a liquid crystal display (LCD) to achieve a desired color. However, white light-backed LCDs have several potential drawbacks: first, they do not provide a high color saturation or true black;
and second, there is an inherent inefficiency in that power is consumed to generate light that is filtered out by the LCD.

[00020] Another approach uses the above described tricolor mixing of red, green, and blue LEDs. This approach provides relatively better color gamut, saturation, and black rendering. Furthermore, with appropriate processing, it is possible to only generate the desired color, thus eliminating this source of inefficiency.
However, this technique is only as good as the CRI of the backlight light source.

BRIEF SUMMARY OF THE INVENTION

[00021] In the following description and claims, the terms "comprise" and "include,"
along with their derivatives, may be used and are intended as synonyms for each other and mean that addition of unnamed extra elements is not precluded.

[00022] As used herein, the term "connected" may be used to indicate that two or more elements are in direct physical or electrical contact with each other.
The term "coupled" may mean that two or more elements are in direct physical or electrical contact. However, "coupled" may also mean that two or more elements are not in direct contact with each other, but yet still co-operate or interact with each other.
For example, "coupled" may mean that two or more elements do not contact each other but are indirectly joined together via another element or intermediate elements.

[00023] As used herein, the terms "on," "overlying," and "over" may be used in the following description and claims. "On," "overlying," and "over" may be used to indicate DLMR_528857.4 6 that two or more elements are in direct physical contact with each other.
However, "over" may also mean that two or more elements are not in direct contact with each other. For example, "over" may mean that one element is above another element but not contact each other and may have another element or elements in between the two elements. It should be noted that "overlying" and "over" are relative terms that include layers located beneath a substrate when the substrate is turned upside down.

[00024] As used herein, the term "group III" elements indicates the elements found in what is commonly referred to as group III of the periodic table. For example, boron (B), aluminum (AI), gallium (Ga), and indium (In) are group III elements.
Similarly, the term "group V" elements indicates the elements found in what is commonly referred to as group V of the periodic table. For example, nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi) are group V elements.

[00025] A first aspect of the present invention is a method of emitting light with a light-emitting device system, comprising emitting red, orange, or yellow light from one or more dilute-nitride light-emitting diodes (LEDs); emitting light having a color other than red, orange, or yellow from one or more additional LEDs; and combining light emitted by the two types of LEDs. In some embodiments of this aspect, the combined light appears to the human eye as white light, preferably warm white light. In other embodiments, the method has the additional steps of passively or actively controlling the intensity of light emitted by the one or more dilute-nitride LEDs and the light emitted by the one or more additional LEDs so that the color or color temperature of the light emitted by the system is determined by the relative intensities of the combined lights. In some embodiments, the dilute-nitride LEDs comprise AIõIn,nGal_,n,NAsõSbkPl,,k where 0:5 n, m, v, k<_ 1 and 0.001 < c < 0.1. In some embodiments, the dilute-nitride LED is a red LED. In some embodiments, the one or more additional LEDs are one or more blue LEDs and one or more green LEDs. In some embodiments, the one or more additional LEDs are GaN-based LEDs; preferably one or more blue GaN-based LEDs and one or more green GaN-based LEDs.

DLMR_528857.4 7

[00026] Other embodiments of the first aspect of the present invention are light-emitting device based illumination systems comprising one or more red, orange, or yellow emitting dilute-nitride LEDs and one or more additional LEDs. In embodiments of this aspect, the one or more additional LEDs are not red, orange, or yellow LEDs. In some embodiments of this aspect, a combination of light emitted from the one or more dilute-nitride LEDs and light emitted from the one or more additional LEDs appears to the human eye as white light, preferably warm white light. In other embodiments, the systems comprise electronic circuitry to passively or actively control the intensity of light emitted by one or more dilute nitride LEDs, or one or more additional LEDs, or one or more of both types of LEDs. In related embodiments, the color or color temperature of light emitted by a system is determined by the relative intensities of the light emitted by the one or more dilute-nitride LEDs and the one or more additional LEDs. In some embodiments, the dilute-nitride LEDs comprise AIõInmGaj,NAsõSbkP11_õ_k where 0:5 n, m, v, k<_ 1 and 0.001 < c< 0.1.

[00027] A second aspect of the present invention is a method of generating light with a light-emitting device system, comprising emitting red, orange, or yellow light from one or more dilute-nitride light-emitting diodes (LEDs); emitting near ultraviolet (near UV) light or visible light other than red, orange, or yellow light from one or more additional LEDs; absorbing light emitted from the one or more additional LEDs with one or more phosphors; emitting light from the one or more phosphors; and combining light emitted from the one or more dilute-nitride LEDs with light emitted from the one or more phosphors (and, in some embodiments, light emitted from the one or more additional LEDs). In some related embodiments, light emitted from the one or more dilute-nitride LEDs combined with light emitted from the one or more phosphors (and, in some embodiments, light emitted from the one or more additional LEDs) appears to the human eye as white light; preferably warm white light. In some embodiments, the dilute-nitride LEDs comprise AIõIn,,Gal_õ_.,nN,~AsõSbkPl_.c_õ_k where 0:5 n, m, v, k<_ 1 and 0.001 < c< 0.1. In some embodiments, the one or more dilute-nitride LEDs comprise red emitting LEDs; and the one or more additional LEDs comprise one or more blue GaN based LEDs.

DLMR_528857.4 8

[00028] In some embodiments, the one or more phosphors absorb substantially all of the light emitted by the one or more additional LEDs. In these embodiments, the one or more additional LEDs may comprise near UV emitting LEDs, the one or more phosphors may comprise a plurality of phosphors that combined emit white light, and the one or more dilute-nitride LEDs may comprise red light emitting dilute-nitride LEDs.
In some embodiments, the white light emitting phosphor may comprise a mixture of high efficiency europium based red and blue emitting phosphors plus green emitting copper and aluminum doped zinc sulfide (ZnS:Cu,Al). In these embodiments, the light emitted from the white light emitting phosphor may be combined with light emitted from one or more dilute nitride LEDs to achieve light that appears to the human eye as warm white light.

[00029] In alternative embodiments, some of the light emitted by the one or more additional LEDs is transmitted through the phosphor and is combined with light emitted by the phosphor and light emitted by the one or more dilute-nitride LEDs. In these embodiments, the one or more additional LEDs may comprise blue light emitting LEDs, the phosphor may comprise a yellow emitting phosphor, and the one or more dilute-nitride LEDs may comprise red dilute-nitride LEDs. In some embodiments, light emitted from the red dilute-nitride LEDs may be transmitted through the phosphor. In alternative embodiments, the light emitted from the red dilute-nitride LEDs may not be transmitted through the phosphor. In some of these embodiments, the yellow emitting phosphor may comprise Cerium (III)-doped YAG (YAG:Ce3+, or Y3A15O12:Ce3+)

[00030] The two LED/phosphor combinations discussed above (i.e., red LEDs/
near UV LEDs/white phosphors and red LEDs/blue LEDs/yellow phosphors) are not meant to be limiting and other LED/phosphor combinations can be used in embodiments of the present invention to achieve white light; preferably warm white light.

[00031] Other embodiments of the second aspect of the present invention are light-emitting device systems comprising one or more red, orange, or yellow dilute-nitride light-emitting diodes (LEDs); one or more additional LEDs; and one or more phosphors. In embodiments of this aspect, the one or more additional LEDs emit near DLMR_528857.4 9 UV light (i.e., UV radiation) or visible light other than red, yellow, or orange light, such as blue light. In some embodiments, the one or more phosphors absorb at least a portion of the light emitted from the one or more additional LEDs and emit light. In some related embodiments, a combination of light emitted from the one or more dilute-nitride LEDs and light emitted from the one or more additional LEDs and/or phosphors appears to the human eye as white light; preferably warm white light. In some embodiments, the dilute-nitride LEDs comprise AIõInmGaj_,r,nN~AsõSbkP1-'._õ_k where 05 n, m, v, k<_ 1 and 0.001 < c < 0.1. In some embodiments, the one or more dilute-nitride LEDs comprise red emitting LEDs; the one or more additional LEDs comprise blue light emitting LEDs;
the one or more phosphors comprise a yellow emitting phosphor. In some related embodiments, light emitted by the one or more dilute-nitride LEDs is transmitted through the yellow phosphor. In other related embodiments, light emitted by the one or more dilute-nitride LEDs is not transmitted through the yellow phosphor. In other embodiments, the one or more additional LEDs comprise near UV emitting LEDs;
and the one or more phosphors comprise one or more phosphors that in combination emit white light.

[00032] A third aspect of the present invention is a method of emitting light with a light-emitting device system, comprising emitting light from one or more light-emitting diodes (LEDs) with a full width at half maximum (FWHM) within the range of 30 nm and 125 nm, inclusive; emitting light from one or more additional LEDs; and combining light emitted from one or more LEDs with a FWHM within the range of 30 nm and 125 nm and light emitted from one or more additional LEDs. In some embodiments of this aspect, one or more LEDs with a FWHM within the range of 30 nm and 125 nm emit yellow, orange, or red light, and one or more additional LEDs emit visible light of a color other than the color emitted by the one or more LEDs with a FWHM within the range of 30 nm and 125 nm. In some embodiments, one or more LEDs with a FWHM within the range of 30 nm and 125 nm are dilute-nitride LEDs. In some embodiments, the one or more LEDs with a FWHM within the range of 30 nm to 125 nm comprise AIõInmGaj_,~
mNAsõSbkPl,,k where 0 s n, m, v, k<_ 1 and 0.001 < c < 0.1. In some embodiments, one or more LEDs with a FWHM within the range of 30 nm and 125 nm comprise a plurality of active layers interleaved with barrier layers. In related embodiments, at least DLMR_528857.4 10 two active layers may have different compositions, different thicknesses, or both. In additional related embodiments, one or more LEDs with a FWHM within the range of 30 nm and 125 nm may comprise a plurality of barrier layers, at least two of which may have different thicknesses. In some embodiments, one or more LEDs with a FWHM
within the range of 30 nm and 125 nm have a FMHW within the range of 35 nm and nm; preferably within the range of 40 nm and 125 nm; preferably within the range of 50 nm and 125 nm; preferably within the range of 60 nm and 125 nm; preferably within the range of 70 nm and 125 nm; preferably within the range of 75 nm and 125 nm. In some embodiments, the combined light may appear to the human eye as white light;
preferably as warm white light.

[00033] Other embodiments of the third aspect of the present invention are light-emitting device based illumination systems comprising one or more light-emitting diodes (LEDs) with a full width at half maximum (FWHM) within the range of 30 nm to 125 nm;
and one or more additional LEDs. In some embodiments, one or more LEDs with a FWHM within the range of 30 nm to 125 nm comprise red, orange, or yellow LEDs;
and the one or more additional LEDs comprise LEDs that emit visible light of a color other than the color emitted by the one or more LEDs with a FWHM within the range of 30 nm to 125 nm. In some embodiments, one or more LEDs with a FWHM within the range of 30 nm to 125 nm are dilute-nitride LEDs. In some embodiments, the one or more LEDs with a FWHM within the range of 30 nm to 125 nm comprise AIõInmGaj_,rmNAsõSbkP1_ ,õ_k where 0:5 n, m, v, k<_ 1 and 0.001 < c < 0.1. In some embodiments, one or more LEDs with a FWHM within the range of 30 nm to 125 nm comprise a plurality of active layers interleaved with barrier layers. In related embodiments, at least two active layers may have different compositions, different thicknesses, or both. In additional related embodiments, one or more LEDs with a FWHM within the range of 30 nm to 125 nm comprise a plurality of barrier layers, at least two of which have different thicknesses. In some embodiments, one or more LEDs with a FWHM within the range of 30 nm and 125 nm have a FMHW within the range of 35 nm and 125 nm; preferably within the range of 40 nm and 125 nm; preferably within the range of 50 nm and 125 nm;
preferably within the range of 60 nm and 125 nm; preferably within the range of 70 nm and 125 nm; preferably within the range of 75 nm and 125 nm. In some embodiments, DLMR528857.4 11 a combination of light emitted from one or more LEDs with a FWHM within the range of 30 nm to 125 nm and light emitted from the one or more additional LEDs appears to the human eye as white light; preferably warm white light.

[00034] A fourth aspect of the present invention is a method of emitting light with a light-emitting device system, comprising emitting light from one or more light-emitting diodes (LEDs) with a full width at half maximum (FWHM) within the range of 30 nm and 125 nm; emitting light by one or more additional LEDs; absorbing at least a portion of light emitted by one or more additional LEDs with one or more phosphors;
emitting light from the one or more phosphors; and combining light emitted from the one or more phosphors with light emitted from one or more LEDs with a FWHM within the range of 30 nm and 125 nm. In some embodiments, one or more LEDs with a FWHM within the range of 30 nm and 125 nm are red, orange, or yellow LEDs, and the one or more additional LEDs emit near ultraviolet (near UV) light or visible light of a color other than that emitted by LEDs with a FWHM within the range of 30 nm and 125 nm. In some embodiments, one or more LEDs with a FWHM within the range of 30 nm and 125 nm are dilute-nitride LEDs. In some embodiments, the one or more LEDs with a FWHM
within the range of 30 nm to 125 nm comprise AIõIn,nGal_,,nNd4sõSbkPl,,k where n, m, v, k<_ 1 and 0.001 < c< 0.1. In some embodiments, the one or more LEDs with a FWHM within the range of 30 nm to 125 nm comprise AIõInmGal_,~-mNc4sõSbkPl--c_õ_k where 0:5 n, m, v, k<_ 1 and 0.001 < c < 0.1. In some embodiments, one or more LEDs with a FWHM within the range of 30 nm and 125 nm comprise a plurality of active layers interleaved with barrier layers. In related embodiments, at least two active layers may have different compositions, different thicknesses, or both. In additional related embodiments, one or more LEDs with a FWHM within the range of 30 nm and 125 nm may comprise a plurality of barrier layers, at least two of which may have different thicknesses. In some embodiments, one or more LEDs with a FWHM within the range of within the range of 30 nm and 125 nm have a FMHW within the range of 35 nm and 125 nm; preferably within the range of 40 nm and 125 nm; preferably within the range of 50 nm and 125 nm; preferably within the range of 60 nm and 125 nm; preferably within the range of 70 nm and 125 nm; preferably within the range of 75 nm and 125 nm. In some embodiments, a combination of light emitted from one or more LEDs with a DLMR_528857.4 12 FWHM within the range of 30 nm to 125 nm combined with light emitted from the one or more phosphors (and, in some embodiments, light emitted from the one or more additional LEDs) appears to the human eye as white light; preferably warm white light.

[00035] Other embodiments of the fourth aspect of the present invention are light-emitting device based illumination systems, comprising one or more light-emitting diodes (LEDs) with a full width at half maximum (FWHM) within the range of 30 nm and 125 nm; one or more additional LEDs; and one or more phosphors. In some embodiments, one or more LEDs with a FWHM within the range of 30 nm and 125 nm comprise red, orange, or yellow emitting LEDs; and one or more additional LEDs comprise LEDs that emit near ultraviolet (near UV) light or visible light of a color other than the color emitted by one or more LEDs with a FWHM within the range of 30 nm and 125 nm. In some embodiments, one or more LEDs with a FWHM within the range of 30 nm and 125 nm comprise dilute-nitride LEDs. In some embodiments, the one or more LEDs with a FWHM within the range of 30 nm to 125 nm comprise AIõIn,nGal_, ,,,NAsõSbkP11_õ_k where 0:5 n, m, v, k_< 1 and 0.001 < c < 0.1. In some embodiments, one or more LEDs with a FWHM within the range of 30 nm and 125 nm comprise a plurality of active layers interleaved with barrier layers. In related embodiments, at least two active layers may have different compositions, different thicknesses, or both. In additional related embodiments, one or more LEDs with a FWHM within the range of 30 nm and 125 nm comprise a plurality of barrier layers, at least two of which may have different thicknesses. In some embodiments, one or more LEDs with a FWHM
within the range of 30 nm and 125 nm have a FMHW within the range of 35 nm and 125 nm;
preferably within the range of 40 nm and 125 nm; preferably within the range of 50 nm and 125 nm; preferably within the range of 60 nm and 125 nm; preferably within the range of 70 nm and 125 nm; preferably within the range of 75 nm and 125 nm. In some embodiments, a combination of light emitted from one or more LEDs with a FWHM
within the range of 30 nm to 125 nm combined with light emitted from the one or more phosphors (and, in some embodiments, light emitted from the one or more additional LEDs) appears to the human eye as white light; preferably warm white light.

DLMR_528857.4 13

[00036] A fifth aspect of the present invention is a method of emitting light with a light-emitting device system, comprising emitting light from one or more light-emitting diodes (LEDs) that have an emission spectrum with two or more peak wavelengths;
emitting light from one or more additional LEDs; and combining light emitted from one or more LEDs that have an emission spectrum with two or more peak wavelengths and light emitted from one or more additional LEDs. In some embodiments, one or more LEDs that have an emission spectrum with two or more peak wavelengths emit light in the yellow, orange, or red ranges, and one or more additional LEDs emit visible light of a color other than the colors emitted by one or more LEDs that have an emission spectrum with two or more peak wavelengths. In some embodiments, one or more LEDs that have an emission spectrum with two or more peak wavelengths are dilute-nitride LEDs. In some embodiments, the one or more LEDs that have an emission spectrum with two or more peak wavelengths comprise AInInmGaj_,~-mNd4sõSbkP1-.C_v-k where 0:5 n, m, v, k 5 1 and 0.001 < c < 0.1. In some embodiments, one or more LEDs that have an emission spectrum with two or more peak wavelengths comprise a first active region that emits at a first wavelength range and a second active region that emits at a second wavelength range. In some embodiments, the combined light may appear to the human eye as white light; preferably as warm white light.

[00037] Other embodiments of the fifth aspect of the present invention are light-emitting device based illumination systems, comprising one or more light-emitting diodes (LEDs) that have an emission spectrum with two or more peak wavelengths; and one or more additional LEDs. In some embodiments, one or more LEDs that have an emission spectrum with two or more peak wavelengths emit light in the yellow, orange, or red ranges; and one or more additional LEDs comprise LEDs that emit visible light of a color other than the colors emitted by one or more LEDs that have an emission spectrum with two or more peak wavelengths. In some embodiments, one or more LEDs that have an emission spectrum with two or more peak wavelengths are dilute-nitride LEDs. In some embodiments, the one or more LEDs that have an emission spectrum with two or more peak wavelengths comprise AIõlnmGaj_,~mNoAsõSbkP1..,-"
where 0< n, m, v, k 5 1 and 0.001 < c < 0.1. In some embodiments, one or more LEDs that have an emission spectrum with two or more peak wavelengths comprise a first DLMR_528857.4 14 active region that emits at a first wavelength range and a second active region that emits at a second wavelength range. In some embodiments, a combination of light emitted from one or more LEDs that have an emission spectrum with two or more peak wavelengths and light emitted from the one or more additional LEDs appears to the human eye as white light; preferably warm white light.

[00038] A sixth aspect of the present invention is a method of emitting light with a light-emitting device system, comprising emitting light from one or more light-emitting diodes (LEDs) that have an emission spectrum with two or more peak wavelengths;
emitting light by one or more additional LEDs; absorbing at least a portion of light emitted by one or more additional LEDs with one or more phosphors; emitting light from one or more phosphors; and combining light emitted from one or more phosphors with light emitted from one or more LEDs that have an emission spectrum with two or more peak wavelengths. In some embodiments, one or more LEDs that have an emission spectrum with two or more peak wavelengths emit light in the yellow, orange, or red ranges, and one or more additional LEDs emit near ultraviolet (near UV) light or visible light of a color other than the colors emitted by one or more LEDs that have an emission spectrum with two or more peak wavelengths. In some embodiments, one or more LEDs that have an emission spectrum with two or more peak wavelengths are dilute-nitride LEDs. In some embodiments, the one or more LEDs that have an emission spectrum with two or more peak wavelengths comprise AIõInmGaj_,,...mNAsõSbkP1,,-k where 0:5 n, m, v, k<_ 1 and 0.001 < c < 0.1. In some embodiments, one or more LEDs that have an emission spectrum with two or more peak wavelengths comprise a first active region that emits at a first wavelength range and a second active region that emits at a second wavelength range. In some embodiments, a combination of light emitted from one or more LEDs that have an emission spectrum with two or more peak wavelengths combined with light emitted from the one or more phosphors (and, in some embodiments, light emitted from the one or more additional LEDs) appears to the human eye as white light; preferably warm white light.

[00039] Other embodiments of the sixth aspect of the present invention are light-emitting device based illumination systems, comprising one or more light-emitting DLMR 528857.4 15 diodes (LEDs) that have an emission spectrum with two or more peak wavelengths; one or more additional LEDs; and one or more phosphors. In some embodiments, one or more LEDs that have an emission spectrum with two or more peak wavelengths comprise red, orange, or yellow emitting LEDs; and one or more additional LEDs comprise LEDs that emit near ultraviolet (near UV) light or visible light of a color other than the colors emitted by one or more LEDs that have an emission spectrum with two or more peak wavelengths. In some embodiments, one or more LEDs that have an emission spectrum with two or more peak wavelengths comprise dilute-nitride LEDs. In some embodiments, the one or more LEDs that have an emission spectrum with two or more peak wavelengths comprise AIõIn,nGaj_õ_,nNd4sõSbkP11õ_k where 0:5 n, m, v, k<_ 1 and 0.001 < c < 0.1. In some embodiments, one or more LEDs that have an emission spectrum with two or more peak wavelengths comprise a first active region that emits at a first wavelength range and a second active region that emits at a second wavelength range. In some embodiments, a combination of light emitted from one or more LEDs that have an emission spectrum with two or more peak wavelengths combined with light emitted from the one or more phosphors (and, in some embodiments, light emitted from the one or more additional LEDs) appears to the human eye as white light;
preferably warm white light.

BRIEF DESCRIPTION OF THE DRAWINGS

[00040] A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings wherein like reference numerals are used throughout the several drawings to refer to similar components.

[00041] Figure 1 is a plot demonstrating the dependence of the peak wavelength shift versus temperature for AIInGaP-based LEDs and for dilute-nitride-based LEDs.

[00042] Figure 2 is a plot demonstrating a comparison of saturation current densities for dilute-nitride-based LEDs with 300 pm and 400 pm die and typical values for AIInGaP LEDs (shown as the region bounded by vertical dashed lines).

DLMR_528857.4 16

[00043] Figures 3A-C are schematic illustrations of embodiments of the present invention in which light emitted from dilute-nitride LEDs is combined with light emitted from one or more phosphors (Figure 3A), or combined with light emitted from one or more phosphors and one or more additional LEDs (Figures 3B and C).

[00044] Figure 4 shows photoluminescence spectra from exemplary AIInGaP and dilute nitride LEDs.

[00045] For simplicity of illustration and ease of understanding, elements in the various figures are not necessarily drawn to scale, unless explicitly so stated. In some instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present disclosure. The following detailed description is merely exemplary in nature and is not intended to limit the disclosure of this document and uses of the disclosed embodiments. Furthermore, there is no intention that the appended claims be limited by the title, technical field, background, or abstract.

DETAILED DESCRIPTION OF THE INVENTION

[00046] LEDs capable of emitting light in the red-orange-yellow wavelength ranges using dilute-nitride semiconductors are described in U.S. Patent Application No.
11/576,992 (filed April 10, 2007), hereby incorporated by reference in its entirety. LEDs described in these applications are based on dilute-nitride semiconductor materials of the general formula AIõIn,nGaj_n_mNAsvSbkP1,_õ_k where 0:5 n, m, c, v, k<_1 and have greatly improved color and brightness stability as a function of temperature and drive current compared to conventional AIInGaP-based LEDs. Dilute-nitride LEDs envisioned for use in the present invention utilize dilute-nitride semiconductor active layers with the general formula AIõIn,,,Gal_õ_n,NAsõSbkPl,õ_k where 0:5 n, m, v, k_1 and 0.001< c <0.1. One skilled in the art would readily recognize that in dilute-nitride semiconductors of this general formula, 0:5 n + m<_1, 0.001< c <0.1, and 0.001< v + k + c<_1.
The present invention is directed to the use of these dilute-nitride based LEDs in illumination systems to provide improved color control.

DLMR_528857.4 17

[00047] As used herein, the term "white light" refers to light that lies on the well known Black Body Locus ("BBL") line on a CIE chromaticity diagram. Light that lies along the BBL obeys Planck's equation: E(A)=AA-5/(e(B'fO-1), where E is the emission intensity, \ is the emission wavelength, T is the color temperature of the black body, and A and B are constants.

[00048] As used herein, the term "light that appears to the human eye as white light" refers to light that approximates light that falls on the BBL on a CIE
chromaticity diagram. That is, in order to appear to the human eye as a white light, the light must fall on, or near, the BBL on a CIE chromaticity diagram.

[00049] As used herein, the term "warm white light" is used to indicate white light with a correlated color temperature (CCT) of about 2000 K to 4000 K; the term "neutral white light" to indicate white light with a CCT of about 4000 K to 5500 K; and the term "cool white light" to indicate white light with a CCT of greater than about 5500 K.

[00050] As used herein, the term "red" is used to describe light indicates a portion of the electromagnetic spectrum with wavelengths about 700 nm to about 630 nm.
Similarly, the terms "orange," "yellow," "green," blue," and "near ultraviolet" (or "near UV") are used to indicate a portion of the electromagnetic spectrum with wavelength ranges of about 630 nm to about 590 nm, about 590 nm to about 560 nm, about 560 nm to about 490 nm, about 490 nm to about 450 nm, and about 400 nm to about 300 nm, respectively. Use of any of these terms to describe a LED or phosphor indicates that light emitted from that LED or phosphor falls within the above described ranges. For example, a red LED emits light with a wavelength in the range of about 700 nm to about 630 nm.

[00051] The terms "about" and "similar" as used herein as related to a numerical value represents the value +/- 10% thereof.

[00052] Figure 1 shows the dependence of the peak wavelength shift versus temperature for AlInGaP-based LEDs and for dilute-nitride-based LEDs. The plot shows that across a temperature range of 25 C to 125 C, conventional AllnGaP-based DLMR_528857.4 18 LEDs suffer a peak wavelength shift of 15 nm versus a mere 3 nm shift for dilute-nitride LEDs. Dilute-nitride LEDs thus provide much better overall color stability at their peak emitting wavelength.

[00053] Another important advantage of illumination devices with dilute-nitride LEDs is higher saturation current densities. While all LEDs have relatively high efficiency, efficiency decreases at high current densities. Furthermore, higher current densities than are attainable in conventional LEDs are desired to achieve high absolute brightness to allow for illumination with fewer LEDs. Thus operation at high current densities is desirable to achieve high brightness at lower cost.

[00054] The saturation current densities of conventional AIInGaP LEDs are several times smaller than those of dilute-nitride based LEDs, due to smaller conduction band offsets (about 2 to 3 times) and smaller electron effective mass (about 3 to 5 times).
Figure 2 shows a comparison of saturation current densities for dilute-nitride-based LEDs with two different size die (300 pm and 400 pm) and typical values for AIInGaP
LEDs (region bounded by vertical dashed lines).

[00055] One aspect of the present invention includes LED systems comprising one or more red, orange, or yellow dilute-nitride LEDs and one or more additional LEDs that are not red, orange, or yellow LEDs. The operation of these systems involves emitting light from the one or more dilute-nitride LEDs; emitting light from the one or more additional LEDs; and combining the emitted lights. LEDs may be selected for use in these systems so that depending on the current in each of the one or more red, orange, or yellow dilute nitride LEDs and the one or more additional LEDs that are not red, orange, or yellow, the combined emitted lights appear virtually any color and/or color temperature to the human eye.

[00056] In one embodiment, the one or more additional LEDs may be one or more green LEDs and one or more blue LEDs. This allows the system to utilize a tricolor mixing technique to produce light that appears to the human eye as white light, preferably warm white light. In a tricolor mixing technique, light of three primary colors is emitted by LEDs in the system and combined to produce light that appears to the DLMR_528857.4 19 human eye as white light. Emission of light that appears to the human eye as white light (preferably warm white light) by tricolor mixing may be achieved with LED systems of the present invention by using LEDs that emit blue, green, and red lights.
The blue and green light can be emitted by AIGaInN LEDs (i.e., GaN-based LEDs) having different active layer compositions and the red light can be emitted from one or more dilute-nitride LEDs. Incorporation of red dilute-nitride LEDs into tricolor mixing systems provides several advantages over similar systems utilizing conventional red AlInGaP
LEDs. First, the stability of the light color and/or color temperature is improved as a function of temperature and brightness because the emission properties of red dilute-nitride LEDs are better matched to the GaN-based LEDs than are those of red AIInGaP
LEDs. A second advantage is that fewer red dilute-nitride LEDs may be required to achieve a high brightness because dilute-nitride LEDs may be driven to higher current densities than red AIInGaP LEDs without suffering from a large shift in emission wavelength. This reduces the cost of the light fixture. Additionally, as the emission properties of red dilute-nitride LEDs are better matched with the emission properties of the GaN-based LEDs, electronic circuitry for passively or actively adjusting the relative currents in the one or more dilute-nitride and one or more additional LEDs (and thereby controlling the intensity of light emitted from the LEDs) to maintain a desired color and/or color temperature may be simplified or eliminated.

[00057] However, in some embodiments of the present invention, electronic circuitry for passively or actively controlling the intensity of light emitted from the one or more dilute-nitride and one or more additional LEDs is included and used to select and maintain the color and/or color temperature of emitted light. Full color displays or illumination systems often use a mixture of red/green/blue (RGB) LEDs. Other systems may use additional or fewer different color LEDs. The illumination or display color is determined by the relative light outputs of different color LEDs, which is directly controlled by the current driven through each color LED. As discussed above, a further complication of such a system utilizing red AIInGaP LEDs is that the display color may change with changes in the ambient temperature or the drive current of the LEDs. In addition to the problems discussed above, color is particularly important for brand identification in signage applications. Complicated control systems are required in DLMR_528857.4 20 systems utilizing red AIInGaP LEDs in order to correct for these problems because of the difference in wavelength shift with temperature and/or drive current for the different materials that comprise the active regions of blue, green, and red LEDs.

[00058] Embodiments of this aspect of the present invention reduce or eliminate these problems. Because peak wavelength shift of dilute-nitride based LEDs has reduced dependence on temperature or drive current, incorporation of dilute-nitride based LEDs into RGB LED devices allows for simplified control circuitry in systems where generation of a custom color is desired. Thus, in certain embodiments, dilute-nitride LEDs are used together with one or more blue, green, and/or yellow LEDs in a multicolor display or illumination system.

[00059] In embodiments of another aspect of the present invention, a LED-phosphor technique is used to efficiently produce light that appears to the human eye to be white light, preferably warm white light. Embodiments of this aspect include LED
systems comprising one or more red, orange, or yellow dilute-nitride LEDs; one or more additional LEDs; and one or more phosphors. The one or more additional LEDs may emit near UV light or visible light other than red, orange, or yellow light, such as blue light. In embodiments of this aspect, light emitted by the one or more dilute-nitride LEDs is combined with light emitted by the one or more phosphors (or light emitted by the one or more phosphors and light emitted by the one or more additional LEDs). In preferred embodiments, the combined light appears to the human eye as white light, more preferably warm white light.

[00060] In some embodiments, the one or more phosphors absorb substantially all of the light emitted by the one or more additional LEDs. In these embodiments, the one or more additional LEDs may comprise near UV emitting LEDs, the one or more phosphors may comprise a plurality of phosphors that together emit white light (i.e., whose light outputs in combination appear as white light), and the one or more dilute-nitride LEDs may comprise red light emitting dilute-nitride LEDs. In some embodiments, the white light emitting phosphor may comprise a mixture of high efficiency europium DLMR_528857.4 21 based red and blue emitting phosphors plus green emitting copper and aluminum doped zinc sulfide (ZnS:Cu,Al).

[00061] Figure 3A is a schematic illustration of an exemplary red LED/near UV
LED/white phosphor system. As seen in Figure 3A, one or more near UV emitting LEDs 16 emit light that is absorbed by one or more white emitting phosphors 18. The one or more white emitting phosphors 18 may comprise a plurality of phosphors that combined emit white light. This plurality of phosphors may comprise a mixture of high efficiency europium based red and blue emitting phosphors plus green emitting copper and aluminum doped zinc sulfide (ZnS:Cu,Al). This mixture may be incorporated into an encapsulating matrix that is applied over the one or more near UV emitting LEDs 16.
The one or more white emitting phosphors 18 absorb substantially all of the near UV
light emitted by the near UV LEDs 16 and emit white light 20 that is combined with red light 12 emitted from one or more red dilute-nitride LEDs 4. When observed by the human eye, the combined light 22 preferably appears as warm white light.

[00062] In alternative embodiments, some of the light emitted by the one or more additional LEDs is transmitted through the phosphor and is combined with light emitted by the one or more phosphors and light emitted by the one or more dilute-nitride LEDs.
In these embodiments, the one or more additional LEDs may comprise blue light emitting LEDs, the one or more phosphors may comprise a yellow emitting phosphor, and the one or more dilute-nitride LEDs may comprise red dilute-nitride LEDs.
In some of these embodiments, the yellow emitting phosphor may comprise Cerium (III)-doped YAG (YAG:Ce3+, or Y3AI5012:Ce3+)

[00063] In some embodiments, the light emitted from the red dilute-nitride LEDs is not transmitted through the phosphor. This may occur, for example, in systems where LEDs in the system are individually encapsulated, allowing for an encapsulating matrix that contains the yellow emitting phosphor to be selectively applied over the one or more blue LEDs. Figure 3B is a schematic illustration of an exemplary red LED/blue LED/yellow phosphor system in which the red light emitted from the one or more red dilute-nitride LEDs is not transmitted through the phosphor. As seen in this figure, one DLMR_528857.4 22 or more blue LEDs 2 emit light that is partially absorbed by a yellow emitting phosphor 6. Yellow light 10 is emitted by the phosphor 6 and combined with blue light 8 transmitted through the phosphor 6, and red light 12 emitted from the one or more red dilute-nitride LEDs 4. When observed by the human eye, the combined light 14 preferably appears as warm white light.

[00064] In some embodiments, light emitted from the red dilute-nitride LEDs may be transmitted through the phosphor. This may occur, for example, in systems where the LEDs are encapsulated as a panel, with the phosphor containing encapsulation matrix applied to both blue light emitting and red light emitting LEDs. Figure 3C is a schematic illustration of a red LED/blue LED/yellow phosphor system in which the red light emitted from the one or more red dilute-nitride LEDs is transmitted through the phosphor. As seen in this figure, one or more blue LEDs 2 emit light that is partially absorbed by a yellow emitting phosphor 6. Yellow light 10 is emitted by the phosphor 6 and combined with blue light 8 transmitted through the phosphor 6. Light emitted from the one or more red dilute-nitride LEDs 4 is transmitted through the phosphor 6. This red light 12 passes through the phosphor 4 and is combined with yellow light 10 and blue light 8. When observed by the human eye, the combined light 14 preferably appears as warm white light.

[00065] The three LED/phosphor combinations discussed above and presented in Figures 3A-C are not meant to be limiting and other LED/phosphor combinations can be used in embodiments of the present invention. Similarly, warm white light generated by the three combinations discussed above is not meant to be a limitation, as light of other temperatures or colors may be achieved with other LED/phosphor combinations.

[00066] As used herein, the term "phosphor" is used to indicate a substance that absorbs light of a first wavelength range and emits light of a second wavelength range.
The process of light absorption and emission by phosphors is not intended to be limited to any particular mechanism. For example, phosphors may absorb and emit light by phosphorescence, fluorescence, or by scintillation. Examples of phosphors include Cerium(III)-doped YAG (YAG:Ce3+, or Y3AI5O12:Ce3+), which absorbs blue light and DLMR_528857.4 23 emits yellow light; and a mixture of high efficiency europium based red and blue emitting phosphors plus green emitting copper and aluminum doped zinc sulfide (ZnS:Cu,Al), which absorbs near UV light and emits white light. Many other phosphors are well known in the art and can be used in the present invention.

[00067] Use of red, orange, or yellow dilute-nitride LEDs in embodiments of this aspect solves or reduces the severity of several problems associated with red AIInGaP
LED systems. As discussed above, dilute-nitride LEDs have significantly increased color stability across a range of temperatures and drive currents thus allowing for much greater color stability at the high luminous flux required for general illumination purposes.

[00068] As discussed above, the color rendering index (CRI) is another measure of light quality and a high CRI may be difficult to achieve with a white light source comprising a plurality of different color LEDs and/or phosphors. The reason for this is that LEDs typically have fairly narrow spectral widths, generally measured as the full width at half maximum (FWHM) of the spectral peak. For typical LEDs, the FWHM
is on the order of about 10 nm to about 30 nm.

[00069] In some embodiments of the present invention, LEDs with a spectral FWHM larger than conventional AIInGaP LEDs of about the same color range and peak wavelength may be used in the above described RGB and phosphor methods and systems. LEDs with a large spectral FWHM may have a FWHM between 30 nm and 125 nm; preferably between 35 nm and 125 nm; preferably between 40 nm and 125 nm;
preferably between 50 nm and 125 nm; preferably between 60 nm and 125 nm;
preferably between 70 nm and 125 nm; preferably between 75 nm and 125 nm.

[00070] The spectrum of one exemplary LED with a large spectral FWHM is shown in Figure 4. Spectrum 410 in FIG. 4 is from a representative dilute nitride LED
while spectrum 420 is from a representative AlInGaP LED. As can be seen, the FWHM
of the dilute-nitride LED is significantly larger than that of the AIInGaP
LED. In this example, the spectral FWHM of the AlInGaP LED is about 15 nm while that of the dilute-nitride LED is about 75 nm. The broader FWHM LED, when incorporated in a DLMR_528857.4 24 light emitting device system, provides relatively more spectral coverage than AIInGaP
LEDs in the same wavelength range, therefore providing a higher CRI.

[00071] Incorporation of several types of structural features into LEDs may give rise to broadening of the spectral output. For example, in some embodiments, the LEDs with a large FWHM may comprise an active region which comprises a plurality of active layers interleaved with one or more barrier layers. The active layers may be selected such that the emission wavelength of each active layer may be slightly larger than that of the previous active layer (i.e., active layers closer to LED
emission surface emit shorter wavelength radiation). In some embodiments, the plurality of active layers may comprise the same material. Alternatively, in some embodiments, two or more active layers may comprise compositionally distinct materials. In some embodiments, at least two of the plurality of active layers may have different thicknesses. In some embodiments, the LEDs may have a plurality of barrier layers, of which two or more barrier layers may have different thicknesses. In preferred embodiments, up to about 15, most preferably about 5, active layers having a thickness ranging from about 0.1 nm to about 100 nm are interleaved with barrier layers having a thickness ranging from about 0.1 nm to about 100 nm.

[00072] Another means to increase the CRI of light emitted by methods and devices of the present invention is through the incorporation of LEDs that emit in a plurality of spectral ranges into the above described RGB and phosphor methods and systems. LEDs whose emission spectrum has two or more peaks may comprise a plurality of active regions, each of which emits at a different peak wavelength. Each active region may comprise a plurality of active layers interleaved with barrier layers. In one embodiment, the LED comprises a first active region that emits at a first wavelength positioned below a second active region that emits at a second wavelength, where the first wavelength is relatively longer than the second wavelength. In this arrangement, the second active region is relatively transparent to the light emitted from the first active region and wavelengths from both active regions may exit the LED structure through the second active region, thus providing spectral output with two peak wavelengths from a LED that emits light away from the substrate. In an alternative embodiment, the LED
DLMR_528857.4 25 may be configured to emit light through the substrate. In such an embodiment, the relative positions of the first and second active regions are reversed. That is, the second active region is positioned closer to the substrate.

[00073] In one embodiment, the above LED is designed to emit two spectral ranges within the red wavelength range. For example, the two active regions could be designed so that the first active region emits a spectrum with a peak wavelength in the range of about 650 nm to about 675 nm, and the second active region emits a spectrum with a peak wavelength in the range of about 600 nm to about 630 nm. In one embodiment, the LED may comprise dilute nitride semiconductors, for example GaNXPj_ X where 0.001< x <0.1, GaNXAsyP,_x_y where 0.001< x <0.1 and 0:5 y<_1, InaGal_aNXP,_X
where 05 a s1 and 0.001 < x<0.1, or more generally AIrInmGaj_n_mNc4sõSbkP1_c_õ_k where O5 n, m, v, k<_1 and 0.001< c <0.1. These materials may be used in embodiments of the present invention by varying the elemental composition of active layers within the active region, for example by varying the nitrogen and/or arsenic and/or antimony content of one active region relative to another to create active regions with differing band gaps within the LED. It should be noted that while the examples provided above are for LEDs emitting in the red spectral region, this concept may be applied to LEDs emitting in any spectral region, such as for example yellow or orange.

[00074] It will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the invention. Accordingly, the above description should not be taken as limiting the scope of the invention, which is defined in the following claims.

DLMR_528857.4 26

Claims (110)

WHAT IS CLAIMED IS:

1. A method of emitting light with a light-emitting device system, said method comprising:

emitting red, orange, or yellow light from one or more dilute-nitride light-emitting diodes (LEDs);

emitting light having a color other than red, orange, or yellow from one or more additional LEDs; and combining light emitted from the one or more dilute-nitride LEDs and light emitted from the one or more additional LEDs.

2. The method of claim 1, wherein the combined light appears to a human eye as white light.

3. The method of claim 1, wherein the combined light appears to a human eye as warm white light.

4. The method of claim 1, further comprising:

passively or actively controlling the intensity of light emitted from one or more dilute nitride LEDs, or one or more additional LEDs, or one or more of both types of LEDs;

wherein, a color or color temperature of the combined light is determined by relative intensities of light emitted from the one or more dilute-nitride LEDs and light emitted from the one or more additional LEDs.

5. The method of claim 1, wherein the one or more dilute-nitride LEDs comprise Al n In m Ga1-n-m N c As v Sb k P1-c-v-k where 0 <= n, m, v, k <= 1 and 0.001 < c < 0.1.

6. The method of claim 1, wherein the one or more dilute-nitride LEDs emit red light.

7. The method of claim 1, wherein the one or more additional LEDs comprise GaN-based LEDs.

8. The method of claim 1, wherein the one or more additional LEDs comprise one or more blue GaN based LEDs and one or more green GaN based LEDs.

9. A light-emitting device based illumination system, said system comprising:
one or more dilute-nitride light-emitting diodes (LEDs); and one or more additional LEDs;

wherein one or more dilute-nitride LEDs are red, orange, or yellow LEDs;
and the one or more additional LEDs are not red, orange, or yellow LEDs.

10. The system of claim 9, wherein light emitted from the one or more dilute-nitride LEDs combined with light emitted from the one or more additional LEDs results in light that appears to a human eye as white light.

11. The system of claim 9, wherein light emitted from the one or more dilute-nitride LEDs combined with light emitted from the one or more additional LEDs results in light that appears to a human eye as warm white light.

12. The system of claim 9, further comprising:

electronic circuitry to control intensity of light emitted by at least one of a group consisting of a dilute-nitride LED and an additional LED.

13. The system of claim 9, wherein the one or more dilute-nitride LEDs comprise Al n In m Ga1-n-m N c As v Sb k P1-c-v-k where 0 <= n, m, v, k <= 1 and 0.001 < c < 0.1.

14. The system of claim 9, wherein the one or more dilute-nitride LEDs comprise red emitting LEDs; and the one or more additional LEDs comprise one or more blue GaN based LEDs and one or more green GaN based LEDs.

15. A method of emitting light with a light-emitting device system, said method comprising:

emitting red, orange, or yellow light from one or more dilute-nitride light-emitting diodes (LEDs);

emitting near ultraviolet (near UV) light or visible light other than red, orange, or yellow light from one or more additional LEDs;

absorbing at least a portion of light emitted by the one or more additional LEDs with one or more phosphors;

emitting light from the one or more phosphors; and combining light emitted from the one or more phosphors with light emitted from the one or more dilute-nitride LEDs.

16. The method of claim 15, wherein the combined light appears to a human eye as white light.

17. The method of claim 15, wherein the combined light appears to a human eye as warm white light.

18. The method of claim 15, wherein the one or more dilute-nitride LEDs comprise Al n In m Ga1-n-m N c As v Sb k P1-c-v-k where 0 <= n, m, v, k <= 1 and 0.001 < c < 0.1.

19. The method of claim 15, wherein the one or more dilute-nitride LEDs emit red light.

20. The method of claim 15, wherein red light is emitted from the one or more dilute-nitride LEDs; blue light is emitted by the one or more additional LEDs;
the one or more phosphors comprise a yellow emitting phosphor; the one or more phosphors absorb less than all of the blue light emitted by the one or more blue emitting LEDs; and blue light not absorbed by the phosphors, yellow light emitted from the yellow emitting phosphor, and red light emitted by the one or more dilute-nitride LEDs are combined.

21. The method of claim 20, wherein the red light emitted by the one or more dilute-nitride LEDs is not transmitted through the yellow phosphor.

22. The method of claim 20, wherein all, substantially all, or a portion of the red light emitted by the one or more dilute-nitride LEDs is transmitted through the yellow phosphor.

23. The method of claim 15, wherein near UV light is emitted by the one or more additional LEDs; the one or more phosphors comprise a white emitting phosphor;
the one or more phosphors absorb substantially all of the near UV light emitted by the one or more near UV emitting LEDs; white light emitted from the white emitting phosphor and light emitted by the one or more dilute-nitride LEDs are combined to achieve light that appears to a human eye as warm white light.

24. A light-emitting device based illumination system, said system comprising:

one or more dilute-nitride light-emitting diodes (LEDs);

one or more additional LEDs; and one or more phosphors;

wherein one or more dilute-nitride LEDs comprise red, orange, or yellow emitting LEDs; and the one or more additional LEDs comprise near ultraviolet (near UV) emitting LEDs or visible light other than red, orange, or yellow light emitting LEDs.

25. The system of claim 24, wherein the one or more phosphors absorb at least a portion of the light emitted from the one or more additional LEDs and emit light.

26. The system of claim 24, wherein the one or more dilute-nitride LEDs comprise Al n In m Ga1-n-m N c As v Sb k P1-c-v-k where 0 <= n, m, v, k <= 1 and 0.001 < c < 0.1.

27. The system of claim 25, wherein light emitted from the one or more dilute-nitride LEDs combined with light emitted from the one or more phosphors and light emitted from the one or more additional LEDs appears to a human eye as white light.

28. The system of claim 25, wherein light emitted from the one or more dilute-nitride LEDs combined with light emitted from the one or more phosphors and light emitted from the one or more additional LEDs appears to a human eye as warm white light.

29. The system of claim 24, wherein the one or more dilute-nitride LEDs comprise red emitting LEDs; the one or more additional LEDs comprise blue light emitting LEDs; the one or more phosphors comprise a yellow emitting phosphor.

30. The system of claim 29, wherein light emitted by the one or more dilute-nitride LEDs is transmitted through the yellow phosphor.

31. The system of claim 29, wherein light emitted by the one or more dilute-nitride LEDs is not transmitted through the yellow phosphor.

32. The system of claim 25, wherein light emitted from the one or more dilute-nitride LEDs combined with light emitted from the one or more phosphors appears to a human eye as white light.

33. The system of claim 25, wherein light emitted from the one or more dilute-nitride LEDs combined with light emitted from the one or more phosphors appears to a human eye as warm white light.

34. The system of claim 24, wherein the one or more additional LEDs comprise near UV emitting LEDs; and the one or more phosphors comprise one or more phosphors that in combination emit white light.

35. A method of emitting light with a light-emitting device system, said method comprising:

emitting light from one or more light-emitting diodes (LEDs) with a full width at half maximum (FWHM) within the range of 30 nm to 125 nm;

emitting light from one or more additional LEDs;

and combining light emitted from the one or more LEDs with a FWHM
within the range of 30 nm to 125 nm and light emitted from the one or more additional LEDs.

36. The method of claim 35, wherein one or more LEDs with a FWHM within the range of 30 nm to 125 nm emits yellow, orange, or red light, and one or more additional LEDs emits visible light of a color other than the color emitted by the one or more LEDs with a FWHM within the range of 30 nm to 125 nm.

37. The method of claim 35, wherein one or more LEDs with a FWHM within the range of 30 nm to 125 nm are dilute-nitride LEDs.

38. The method of claim 35, wherein one or more LEDs with a FWHM within the range of 30 nm to 125 nm comprise Al n In m Ga1-n-m N c As v Sb k P1-c-v-k where 0 <= n, m, v, k <= 1 and 0.001 < c < 0.1.

39. The method of claim 35, wherein one or more LEDs with a FWHM within the range of 30 nm to 125 nm comprise a plurality of active layers interleaved with barrier layers.

40. The method of claim 38, wherein at least two of said plurality of active layers have a different composition from each other.

41. The method of claim 38, wherein at least two of said plurality of active layers have a different thickness from each other.

42. The method of claim 38, wherein one or more LEDs with a FWHM within the range of 30 nm to 125 nm comprise a plurality of barrier layers, at least two of which have a different thickness from each other.

43. The method of claim 35, wherein one or more LEDs with a FWHM within the range of 30 nm to 125 nm have a FWHM within the range of 75 nm to 125 nm.

44. The method of claim 35, wherein the combined light appears to a human eye as white light.

45. The method of claim 35, wherein the combined light appears to a human eye as warm white light.

46. A light-emitting device based illumination system, said system comprising:

one or more light-emitting diodes (LEDs) with a full width at half maximum (FWHM) within the range of 30 nm to 125 nm; and one or more additional LEDs.

47. The system of claim 46, wherein one or more LEDs with a FWHM within the range of 30 nm to 125 nm comprise red, orange, or yellow LEDs; and the one or more additional LEDs comprise one or more LEDs that emit visible light of a color other than the color emitted by the one or more LEDs with a FWHM within the range of 30 nm to 125 nm.

48. The system of claim 46, wherein one or more LEDs with a FWHM within the range of 30 nm to 125 nm are dilute-nitride LEDs.

49. The system of claim 46, wherein one or more LEDs with a FWHM within the range of 30 nm to 125 nm comprise Al n In m Ga1-n-m N c As v Sb k P1-c-v-k where 0 <= n, m, v, k <= 1 and 0.001 < c < 0.1.

50. The system of claim 46, wherein one or more LEDs with a FWHM within the range of 30 nm to 125 nm comprise a plurality of active layers interleaved with barrier layers.

51. The system of claim 50, wherein at least two of said plurality of active layers have a different composition from each other.

52. The system of claim 50, wherein at least two of said plurality of active layers have a different thickness from each other.

53. The system of claim 50, wherein one or more LEDs with a FWHM within the range of 30 nm to 125 nm comprise a plurality of barrier layers, at least two of which have a different thickness from each other.

54. The system of claim 46, wherein one or more LEDs with a FWHM within the range of 30 nm to 125 nm have a FWHM within the range of 75 nm to 125 nm.

55. The system of claim 46, wherein light emitted from the one or more LEDs with a FWHM within the range of 30 nm to 125 nm combined with light emitted from the one or more additional LEDs results in light that appears to a human eye as white light.

56. The system of claim 46, wherein light emitted from the one or more LEDs with a FWHM within the range of 30 nm to 125 nm combined with light emitted from the one or more additional LEDs results in light that appears to a human eye as warm white light.

57. A method of emitting light with a light-emitting device system, said method comprising:

emitting light from one or more light-emitting diodes (LEDs) with a full width at half maximum (FWHM) within the range of 30 nm to 125 nm;

emitting light by one or more additional LEDs;

absorbing at least a portion of light emitted by the one or more additional LEDs with one or more phosphors;

emitting light from the one or more phosphors; and combining light emitted from the one or more phosphors with light emitted from the one or more LEDs with a FWHM within the range of 30 nm to 125 nm.

58. The method of claim 57, wherein LEDs with a FWHM within the range of 30 nm to 125 nm are red, orange, or yellow LEDs, and the one or more additional LEDs emit near ultraviolet (near UV) light or visible light of a color other than that emitted by LEDs with a FWHM within the range of 30 nm to 125 nm.

59. The method of claim 57, wherein the LEDs with a FWHM within the range of 30 nm to 125 nm are dilute-nitride LEDs.

60. The method of claim 57, wherein one or more LEDs with a FWHM within the range of 30 nm to 125 nm comprise Al n In m Ga1-n-m N c As v Sb k P1-c-v-k where 0 <= n, m, v, k <= 1 and 0.001 < c < 0.1.

61. The method of claim 57, wherein one or more LEDs with a FWHM within the range of 30 nm to 125 nm comprise a plurality of active layers interleaved with barrier layers.

62. The method of claim 61, wherein at least two of said plurality of active layers have a different composition from each other.

63. The method of claim 61, wherein at least two of said plurality of active layers have a different thickness from each other.

64. The method of claim 61, wherein one or more LEDs with a FWHM within the range of 30 nm to 125 nm comprise a plurality of barrier layers, at least two of which have a different thickness from each other.

65. The method of claim 58, wherein one or more LEDs with a FWHM within the range of 30 nm to 125 nm have a FWHM within the range of 75 nm to 125 nm.

66. The method of claim 58, wherein the combined light appears to a human eye as white light.

67. The method of claim 58, wherein the combined light appears to a human eye as warm white light.

68. A light-emitting device based illumination system, said system comprising:

one or more light-emitting diodes (LEDs) with a full width at half maximum (FWHM) within the range of 30 nm to 125 nm;

one or more additional LEDs; and one or more phosphors.

69. The system of claim 68, wherein one or more LEDs with a FWHM within the range of 30 nm to 125 nm comprise red, orange, or yellow emitting LEDs;
and the one or more additional LEDs comprise one or more LEDs that emit near ultraviolet (near UV) light or visible light of a color other than the color emitted by the one or more LEDs with a FWHM within the range of 30 nm to 125 nm.

70. The system of claim 68, wherein one or more LEDs with a FWHM within the range of 30 nm to 125 nm comprise dilute-nitride LEDs.

71. The system of claim 68, wherein one or more LEDs with a FWHM within the range of 30 nm to 125 nm comprise Al n In m Ga1-n-m N c As v Sb k P1-c-v-k where 0 <= n, m, v, k <= 1 and 0.001 < c < 0.1.

72. The system of claim 68, wherein one or more LEDs with a FWHM within the range of 30 nm to 125 nm comprise a plurality of active layers interleaved with barrier layers.

73. The system of claim 72, wherein at least two of said plurality of active layers have a different composition from each other.

74. The system of claim 72, wherein at least two of said plurality of active layers have a different thickness from each other.

75. The system of claim 72, wherein one or more LEDs with a FWHM within the range of 30 nm to 125 nm comprise a plurality of barrier layers, at least two of which have a different thickness from each other.

76. The system of claim 68, wherein one or more LEDs with a FWHM within the range of 30 nm to 125 nm have a FWHM within the range of 75 nm to 125 nm.

77. The system of claim 68, wherein light emitted from the one or more LEDs with a FWHM within the range of 30 nm to 125 nm combined with light emitted from the one or more phosphors and light emitted from the one or more additional LEDs appears to a human eye as white light.

78. The system of claim 68, wherein light emitted from the one or more LEDs with a FWHM within the range of 30 nm to 125 nm combined with light emitted from the one or more phosphors and light emitted from the one or more additional LEDs appears to a human eye as warm white light.

79. The system of claim 68, wherein light emitted from the one or more LEDs with a FWHM within the range of 30 nm to 125 nm combined with light emitted from the one or more phosphors appears to a human eye as white light.

80. The system of claim 68, wherein light emitted from the one or more LEDs with a FWHM within the range of 30 nm to 125 nm combined with light emitted from the one or more phosphors appears to a human eye as warm white light.

81. A method of emitting light with a light-emitting device system, said method comprising:

emitting light from one or more light-emitting diodes (LEDs) that have an emission spectrum with two or more peak wavelengths;

emitting light from one or more additional LEDs;

and combining light emitted from the one or more LEDs that have an emission spectrum with two or more peak wavelengths and light emitted from the one or more additional LEDs.

82. The method of claim 81, wherein one or more LEDs that have an emission spectrum with two or more peak wavelengths emit light in the yellow, orange, or red ranges, and one or more additional LEDs emits visible light of a color other than the colors emitted by the one or more LEDs that have an emission spectrum with two or more peak wavelengths.

83. The method of claim 81, wherein one or more LEDs that have an emission spectrum with two or more peak wavelengths are dilute-nitride LEDs.

84. The method of claim 81, wherein one or more LEDs that have an emission spectrum with two or more peak wavelengths comprise Al n In m Ga1-n-m N c As v Sb k P1-c-v-k where 0 <= n, m, v, k <= 1 and 0.001 < c < 0.1.

85. The method of claim 81, wherein one or more LEDs that have an emission spectrum with two or more peak wavelengths comprise a first active region that emits radiation having a peak in a first wavelength range and a second active region that emits radiation having a peak in a second wavelength range.

86. The method of claim 81, wherein the combined light appears to a human eye as white light.

87. The method of claim 81, wherein the combined light appears to a human eye as warm white light.

88. A light-emitting device based illumination system, said system comprising:

one or more light-emitting diodes (LEDs) that have an emission spectrum with two or more peak wavelengths; and one or more additional LEDs.

89. The system of claim 88, wherein one or more LEDs that have an emission spectrum with two or more peak wavelengths emit light in the yellow, orange, or red ranges; and the one or more additional LEDs comprise LEDs that emit visible light of a color other than the colors emitted by the one or more LEDs that have an emission spectrum with two or more peak wavelengths.

90. The system of claim 88, wherein one or more LEDs that have an emission spectrum with two or more peak wavelengths are dilute-nitride LEDs.

91. The system of claim 88, wherein one or more LEDs that have an emission spectrum with two or more peak wavelengths comprise Al n In m Ga1-n-m N c As v Sb k P1-c-v-k where 0 <= n, m, v, k <= 1 and 0.001 < c < 0.1.

92. The system of claim 88, wherein one or more LEDs that have an emission spectrum with two or more peak wavelengths comprise a first active region that emits radiation having a peak in a first wavelength range and a second active region that emits radiation having a peak in a second wavelength range.

93. The system of claim 88, wherein light emitted from the one or more LEDs that have an emission spectrum with two or more peak wavelengths combined with light emitted from the one or more additional LEDs results in light that appears to a human eye as white light.

94. The system of claim 88, wherein light emitted from the one or more LEDs that have an emission spectrum with two or more peak wavelengths combined with light emitted from the one or more additional LEDs results in light that appears to a human eye as warm white light.

95. A method of emitting light with a light-emitting device system, said method comprising:

emitting light from one or more light-emitting diodes (LEDs) that have an emission spectrum with two or more peak wavelengths;

emitting light by one or more additional LEDs;

absorbing at least a portion of light emitted by the one or more additional LEDs with one or more phosphors;

emitting light from the one or more phosphors; and combining light emitted from the one or more phosphors with light emitted from the one or more LEDs that have an emission spectrum with two or more peak wavelengths.

96. The method of claim 95, wherein one or more LEDs that have an emission spectrum with two or more peak wavelengths emit light in the yellow, orange, or red ranges, and the one or more additional LEDs emit near ultraviolet (near UV) light or visible light of a color other than the colors emitted by the one or more LEDs that have an emission spectrum with two or more peak wavelengths.

97. The method of claim 95, wherein one or more LEDs that have an emission spectrum with two or more peak wavelengths are dilute-nitride LEDs.

98. The method of claim 95, wherein one or more LEDs that have an emission spectrum with two or more peak wavelengths comprise Al n In m Ga1-n-m N c As v Sb k P1-c-v-k where 0 <= n, m, v, k <= 1 and 0.001 < c < 0.1.

99. The method of claim 95, wherein one or more LEDs that have an emission spectrum with two or more peak wavelengths comprise a first active region that emits radiation having a peak in a first wavelength range and a second active region that emits radiation having a peak in a second wavelength range.

100. The method of claim 95, wherein the combined light appears to a human eye as white light.

101. The method of claim 95, wherein the combined light appears to a human eye as warm white light.

102. A light-emitting device based illumination system, said system comprising:
one or more light-emitting diodes (LEDs) that have an emission spectrum with two or more peak wavelengths;

one or more additional LEDs; and one or more phosphors.

103. The system of claim 102, wherein one or more LEDs that have an emission spectrum with two or more peak wavelengths comprise red, orange, or yellow emitting LEDs; and the one or more additional LEDs comprise LEDs that emit near ultraviolet (near UV) light or visible light of a color other than the colors emitted by the one or more LEDs that have an emission spectrum with two or more peak wavelengths.

104. The system of claim 102, wherein one or more LEDs that have an emission spectrum with two or more peak wavelengths comprise dilute-nitride LEDs.

105. The system of claim 102, wherein one or more LEDs that have an emission spectrum with two or more peak wavelengths comprise Al n In m Ga1-n-m N c As v Sb k P1-c-v-k where 0 <= n, m, v, k <= 1 and 0.001 < c < 0.1.

106. The system of claim 102, wherein one or more LEDs that have an emission spectrum with two or more peak wavelengths comprise a first active region that emits radiation having a peak in a first wavelength range and a second active region that emits radiation having a peak in a second wavelength range.

107. The system of claim 102, wherein light emitted from the one or more LEDs that have an emission spectrum with two or more peak wavelengths combined with light emitted from the one or more phosphors and light emitted from the one or more additional LEDs appears to a human eye as white light.

108. The system of claim 102, wherein light emitted from the one or more LEDs that have an emission spectrum with two or more peak wavelengths combined with light emitted from the one or more phosphors and light emitted from the one or more additional LEDs appears to a human eye as warm white light.

109. The system of claim 102, wherein light emitted from the one or more LEDs that have an emission spectrum with two or more peak wavelengths combined with light emitted from the one or more phosphors appears to a human eye as white light.

110. The system of claim 102, wherein light emitted from the one or more LEDs that have an emission spectrum with two or more peak wavelengths combined with light emitted from the one or more phosphors appears to a human eye as warm white light.