Patent Application
20090001389
The present invention relates to solid state lighting and, more particularly, to a hybrid vertical cavity of multiple wavelength Light Emitting Diodes (LEDs).
Solid state lighting devices can provide high brightness and uniform illumination. A solid state lighting device such as a Light Emitting Diode (LED) is a compact element that provides high lighting efficiency. The LED is a semiconductor device that emits light in response to an applied electric current, or field, which constitutes a form of electroluminescence. The color of the emitted light, which depends on the composition and quality of the semi-conducting material used, can be infrared, visible or near-ultraviolet.
In one arrangement, phosphors can be introduced onto the LED to generate light by phosphorescence, which is a sustained glowing after exposure to the applied electric current, or field. A single LED that generates a narrowband light can be coated, or doped, with an active phosphor material to produce wideband light. The phosphors can produce light with colors other than the color of the light produced by the LED. For example, a blue LED that emits a blue light can be coated with a phosphor that absorbs the blue light, and in response, produces red and green light.
It is generally desired for a solid state lighting device used as a flash for a mega-pixel camera phone to produce white light, which is the spectrum of all colors. In practice, white light can be generated from red, green, and blue light. One attempt of the prior art to combine different color LEDs in a single solid state device to produce white light is shown in
As shown in
The parallel approach to combining dual LEDS suffers color breakdown at a far field of the device where the light is emitted. As shown in
One embodiment of the present disclosure is a solid state device that can include a hybrid vertical micro-cavity formed by a cascading of two sub-cavities to share a mirror within the solid state device, wherein the hybrid vertical cavity collimates the first accumulated light and the second accumulated light to increase an efficiency of total emitted light. In one arrangement, the total emitted light can be directed to a phosphor coated on the solid state device to generate a white light. The hybrid vertical cavity can include a first vertical cavity formed between a first filter and the mirror with a first LED between the first filter and the mirror, and the first LED emits a first light with a peak wavelength λ1 that is reflected by the first filter back within the first cavity, wherein the first filter collimates the second light to produce a first accumulated light, and a second vertical cavity formed between a second filter and the mirror with a second LED between the second filter and the mirror, and the second LED emits a second light with a peak wavelength λ2 that is reflected by the second filter back within the second cavity, wherein the second filter collimates the second light to produce a second accumulated light.
In one arrangement, the first filter can be a first Distributed Bragg Grating (DBG) reflector that reflects an optical spectrum with a peak wavelength λ1 of the first light back within the first cavity, and the second filter can be a second Distributed Bragg Grating (DBG) reflector that reflects an optical spectrum with a peak wavelength λ2 of the second light back within the second cavity. The DBR can be fabricated using AlGaN/GaN layers which are p-doped to improve conductivity. The first LED can emit a green light, and the second LED can emit a blue light, wherein a length of the first cavity is longer than a length of the second cavity to accommodate a longer wavelength of the green light. The size, dimension, and position of a LED can vary in accordance with a wavelength of light emitted by the LED. The hybrid vertical can mix the green (and blue), or blue (and UV), respectively, to produce mixed light that is used to pump special designed phosphors coated on the solid state device to collectively produce a white light. The white light can be used for display backlighting, keyboard lighting, camera flash. projector lighting, bio-application, DNA or molecule identification, or optical data storage on a CD or DVD.
Another embodiment of the present disclosure is a solid state device to form a hybrid vertical cavity of multiple wavelength LEDS. The solid state device can include a substrate that is transparent to light, a first filter layered on the first LED to reflect a first light within a first vertical cavity, accumulate the first light within the first cavity, and emit the first light through the substrate, a first LED layered on the substrate to emit the first light, a second filter layered on the first LED to reflect a second light within a second vertical cavity, accumulate the second light within the second cavity, and emit the second light outside of the second vertical cavity through the first LED, the first filter, and the substrate, a second LED layered on the second filter to emit the second light; and a mirror layered on the second LED to reflect the first light within the first cavity and to reflect the second light within the second cavity. The first LED or the second LED can comprise a n-GaN layer, an active region consist of InGaN/GaN multiple quantum well (MQW) layered on the n-GaN layer, and a p-Gan layered on the active region. In other arrangements, at least one more LED and at least one more filter can be inserted to create at least one more vertical cavity within the solid state device.
The hybrid vertical cavity can serve as a light collimator to increase a light pumping efficiency within a LED. The first filter or the second filter can be Distributed Bragg Grating (DBG) reflectors having a reflectivity index corresponding to a light wavelength of the corresponding first LED or second LED, respectively. The hybrid vertical cavity can be formed by cascading the first vertical cavity with the second vertical cavity to share the mirror. In one arrangement, the first filter can be switched with the mirror to create a top emitting LED device instead of a bottom emitting LED device. In another configuration, a total light can be emitted through the substrate by flip-chip packaging to provide a substrate emitting device.
Yet another embodiment of the present disclosure is a solid state device to emit dual wavelength light within a hybrid vertical cavity. The solid state device can include a first LED that emits a first light with a peak wavelength λ1 within a first vertical cavity which is reflected within the first vertical cavity and accumulated by a first filter that produces a first accumulated light, wherein the first vertical cavity is formed between a first filter and a mirror, and the first light passes through a second filter and a second LED inside the first vertical cavity, and a second LED that emits a second light with a peak wavelength λ2 within a second vertical cavity which is reflected within the second vertical cavity and accumulated by a second filter that produces a second accumulated light, wherein the second vertical cavity is formed between the second filter and the mirror, and the second accumulated light passes through the first LED and the first filter outside of the second vertical cavity. The first filter and the second filter can be composed of aluminum gallium nitride (AlGaN) and GaN and monolithically integrated with the first LED and the second LED to share the mirror. As one example, the first filter can reflect green light, and the second filter can reflects ultraviolet or blue light, yet transmit green light. The first LED can include a first active region consist of InGaN/GaN multiple quantum well to emit a green light in the first vertical cavity, and the second LED can include a second active region consist of InGaN/GaN multiple quantum well to emit a blue light in the second vertical cavity. The first vertical cavity can be longer than the second vertical cavity to accommodate a longer wavelength of the green light. The mirror can be a metal material or a dielectric material.
The terms “a” or “an,” as used herein, are defined as one or more than one. The term “plurality,” as used herein, is defined as two or more than two. The term “another,” as used herein, is defined as at least a second or more. The terms “including” and/or “having,” as used herein, are defined as comprising (i.e., open language). The term “coupled,” as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically.
A “solid state device” can be defined as a packed component comprising at least one semiconductor material. A “cavity” can be defined as a portion of a solid state device to collimate light. The term “collimate” can be defined as aligning a direction of light, for example, within a cavity of a solid state device. A “vertical cavity” can be defined as a vertically oriented cavity in a portion of the solid state device. The term “hybrid cavity” can be defined as at least one cavity within at least one second cavity. A “LED” can be a device that can emit light when electrically biased. The term “emitting” can be defined as generating photons by applying an electric field, or current, to the LED. A “phosphor” can be a substance that exhibits the phenomenon of phosphorescence. The term “pumping” can be defined as impinging a narrowband light, such as that produced by a LED, onto a substance, such as a phosphor, to cause the substance to produce a wideband light. The term “narrowband light” can be defined as light of a wavelength within a predefined color region, such as blue, red, green, or yellow. The term “wideband light” can be defined as light composed of multiple wavelengths of light, such as the combination of red, blue and green light.
The terms “program,” “software application,” “resizing program” and the like as used herein, are defined as a sequence of instructions designed for execution on a computer system. A program, computer program, or software application may include a subroutine, a function, a procedure, an object method, an object implementation, an executable application, an applet, a servlet, a source code, an object code, a shared library/dynamic load library and/or other sequence of instructions designed for execution on a computer system.
Further note, the term “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or designs.
Other embodiments, when configured in accordance with the inventive arrangements disclosed herein, can include a system for performing and a machine readable storage for causing a machine to perform the various processes and methods disclosed herein.
The features of the system, which are believed to be novel, are set forth with particularity in the appended claims. The embodiments herein, can be understood by reference to the following description, taken in conjunction with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which:
While the specification concludes with claims defining the features of embodiments of the invention that are regarded as novel, it is believed that the invention will be better understood from a consideration of the following description in conjunction with the figures, in which like reference numerals are carried forward. Embodiments herein can be implemented in a wide variety of ways using a variety of technologies that enable not only the manufacture of hybrid vertical cavity multiple wavelength LED, but the means of combining light from multiple LEDs.
Referring to
Referring to
Briefly, the mirror 350 reflects the first light 211 to produce a first reflected light 213 which travels back through the first cavity 210 to the first filter 312. The first filter 311 collimates the light from the first LED 322 within the first cavity 210 by accumulating the first light 211 and the reflected first light 213. Similarly, the mirror 350 reflects the second light 222 to produce a second reflected light 223 which travels back through the second cavity 220 to the second filter 322. The second filter 322 collimates the light from the second LED 332 within the second cavity 220 by accumulating the second light 222 and the reflected second light 223. The first filter 311 is transparent to the second light thus allowing the second light to pass through un-accumulated. The second filter 332 is transparent to the first light thus allowing the first light to pass through un-accumulated. The substrate 310 is transparent to light emitted by the first LED 322 and the second LED 341, and the light reflected off the mirror 350. The light emitted from the solid state device 200 is collimated as a result of the filtering process, which aligns the direction of light and suppresses internal reflection to increase a lighting efficiency.
It should be noted that the first light 211 and second light 222 can fill both the first cavity 210 and the second cavity 220. The first cavity 210 and the second cavity 220 establish how light is collimated within the solid state device 200. More specifically, the first cavity 210 channels light between the first filter 311 and the mirror 350, and the second cavity 220 channels light between the second filter 332 and the mirror 350. The respective LEDs are positioned between the filters and the mirror to collimate the light. This allows the filters to accumulate light associated with the respective LED. For example, as shown in
The vertical aspects of the cavities and the positions of the LEDs can also be adjusted based on the wavelength of light emitted. For instance, the first cavity 210 can be lengthened longer than the length of the second cavity 220 to accommodate light of a longer wavelength. As an example, the first cavity can 210 collimate a green light, and the second cavity 220 can collimate blue light, since green light has a longer wavelength than blue light. As shown, the first filter 311 and the mirror 350 form the first vertical cavity 210 for collimating green light, and the second filter 322 and the mirror 350 from the second vertical cavity 220 for collimating blue light. In such a configuration, light traveling within the first cavity travels a longer distance within the solid state device 200 than the smaller path of travel of the second cavity 220.
Referring to
The method 410 can start at state 411, in which the first LED 321 emits the first light 211 in multiple directions, which can include an upward direction towards the first filter 311 and a downward direction towards the second filter 322. As shown in
At step 414, the mirror 350 reflects the first light 211 to produce a first reflected light 213, which travels back through the second LED 332, the second filter 322, and the first LED 321 to the first filter 311 through the first vertical cavity 210. The mirror 350 can also reflect non-direct light such as that generated from refraction within the solid state device 200.
At step 415, the first filter 311 reflects a portion of both the first light 211 and first reflected light 213 back within the first cavity 210. In this case, a first portion of the light is directed out towards the substrate 310, and a second portion of the light is kept within the first cavity 210. The first filter 311 has a reflectivity corresponding to a wavelength of the first light 211 emitted by the first LED 311. More specifically, the first filter is a first Distributed Bragg Grating (DBG) reflector that reflects an optical spectrum with a peak wavelength λ1 of the first light back within the first cavity.
Referring to
The mirror 350 reflects the second light 222 back through the second LED 322 in vertical cavity 220 to produce second reflected light 224. The mirror 350 can also reflect non-direct light such as that generated from refraction within the solid state device 200. Both the second light 222 directly emitted by the second LED 332 and the second reflected light 223 travel upward towards the second filter 322. At step 423, the second filter 322 can reflect a portion of both the second light 222 and the second reflected light 223 back within vertical cavity 220. The second filter 322 has a reflectivity corresponding to a wavelength of the second light 222 emitted by the second LED 332. More specifically, the second filter is a second Distributed Bragg Grating (DBG) reflector that reflects an optical spectrum with a peak wavelength λ2 of the second light back within the second cavity.
In this step, the second filter 322 also accumulates the light reflected within the vertical cavity 220 to produce second accumulated light 224. Notably, the first LED 321 can pass the second accumulated light 224 unobstructed through both the first LED 321 at step 424, and the first filter 311 at step 425. At step 426, the second filter 332 emits the second accumulated light 224 through the substrate 310, which is transparent to the emitted light.
Referring to
The solid state device 200 includes the mirror 350 (shown at top) positioned above the second LED 332, that is positioned above the first filter 322, that is positioned above the first LED 321, that is positioned above the first filter 311, that is positioned above the substrate 310.
The first filter 311 is a Distributed Bragg Grating (DBG) reflector that has reflectivity index corresponding to the first LED 321. The first filter 311 can include a composition of aluminium gallium nitride (AlGaN) and GaN. The first LED 321 includes a n-GaN layer 610, a second n-GaN layer 611, a first active region 612 consisting of InGaN/GaN multiple quantum well (MQW) layered on the n-GaN layer 611, and a p-GaN layer 614. The first active region 612 emits green light in response to an electric voltage applied across n-GaN layer 610 and p-GaN layer 614.
The second filter 322 is a Distributed Bragg Grating (DBG) reflector that has reflectivity index corresponding to the second LED 332. The second filter 311 can also include a composition of AlGaN/GaN though is not limited to this composition. The second LED 33 includes a n-GaN layer 620, a second active region 621 consisting of InGaN/GaN multiple quantum well (MQW) layered on the n-GaN layer 620, a p-GaN layer 622, and a second p-GaN layer 623. The second active region 621 emits blue light in response to an electric voltage applied across n-GaN layer 620 and p-GaN layer 623.
The solid state device 200 includes a p-contact terminal 601 (i.e. positive) and a n-contact (i.e. negative) terminal 602. The p-contact terminal 601 can comprise a separate Ni/Au ring contact, and can be incorporated into the mirror 350. The mirror can be a metal, such as silver, or a dielectric material, such as SiO2/Ti O2. In the case of a dielectric material the light generated within the vertical hybrid micro-cavity can also exit from the top in addition to the direction of the substrate 310. The n-contact terminal 602 can be a Ti/Al depositing after partial etching of the n-GaN layers (610 and 620). A power supply can be applied to the p-contact terminal 601 and the negative terminal 602 to source a current of electrons. The electrons can travel through the various layers in an arrangement that produces and collimates light as previously described.
For each LED, the current flows from the p-side, or anode, to the n-side, or cathode, but not in the reverse direction. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon. When the voltage is applied across n-GaN layer 610 and p-GaN 614 of the first LED 321, UV light is produced that strikes the a first active region 612 and which produces green light of wavelength 505-530 nm. Similarly, when the voltage is applied across n-GaN layer 620 and p-GaN 623 of the second LED 332, UV light is produced that strikes the second active region 621 and which produces blue light of wavelength of 450-470 nm. The tunnel junction 6187 electrically separates the first LED 321 from the second LED 332. It serves as an electron current spreading layer for the first LED 321, and which allows the p-type connection for the first LED 321.
It should be noted that phosphors are not included within the solid state device 200. More specifically, the two active regions serve to produce blue and green light independently which are collimated in the vertical hybrid micro-cavity. Also, the DBG filter are monolithically integrated with the corresponding LEDs to create a hybrid vertical cavity of dual wavelength LEDs. Moreover, the entire cavity of the solid state device 200 includes two cascaded sub-cavities (first cavity 210, and second cavity 220) that share the single mirror 350. The vertical integration of the first LED 321 and the second LED 332 also mitigates a halo effect generally introduce in multi-chip LEDS exhibiting a lateral (e.g. side by side) or stacked (e.g. layer on layer) LED configuration. It should also be noted that the effective area of the DBR is determined by the size of the mirror 350, which can be metal or dielectric. The arrangement of layers can be extended to create additional layers to provide multiple wavelengths. In such regard, the solid state device 200 is a fully integrated package of multiple LEDs that emits multiple wavelengths. As illustrated in
Referring to
Upon reviewing the aforementioned embodiments, it would be evident to an artisan with ordinary skill in the art that said embodiments can be modified, reduced, or enhanced without departing from the scope and spirit of the claims described below. There are numerous configurations for peer to peer authentication that can be applied to the present disclosure without departing from the scope of the claims defined below. For example, at least one more LED and at least one more filter can be inserted in the sold state device to create at least one more vertical cavity within the solid state device. The solid state device can include additional active regions and filters for various colors besides green and blue. These are but a few examples of modifications that can be applied to the present disclosure without departing from the scope of the claims stated below. Accordingly, the reader is directed to the claims section for a fuller understanding of the breadth and scope of the present disclosure.
While the invention has been described in conjunction with specific embodiments, it is evident that many alternatives, modifications, permutations and variations will become apparent to those of ordinary skill in the art in light of the foregoing description. Accordingly, it is intended that the present invention embrace all such alternatives, modifications, permutations and variations as fall within the scope of the appended claims. While the preferred embodiments of the invention have been illustrated and described, it will be clear that the embodiments of the invention are not so limited. Numerous modifications, changes, variations, substitutions and equivalents will occur to those skilled in the art without departing from the spirit and scope of the present embodiments of the invention as defined by the appended claims.
