Patent Publication Number: US-11387389-B2

Title: Reflective layers for light-emitting diodes

Description:
This application is a 35 U.S.C. § 371 national phase filing of International Application No. PCT/US19/15418, filed Jan. 28, 2019, the disclosure of which is incorporated herein by reference in its entirety. 
     RELATED APPLICATIONS 
     International Application No. PCT/US19/1541 is a continuation-in-part of U.S. patent application Ser. No. 15/882,103, filed Jan. 29, 2018, now U.S. Pat. No. 11,031,527, the disclosure of which is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure relates to solid-state lighting devices including light-emitting diodes and more particularly to light-emitting diodes with reflective layers having high reflectivity. 
     BACKGROUND 
     Solid-state lighting devices such as light-emitting diodes (LEDs) are increasingly used in both consumer and commercial applications. Advancements in LED technology have resulted in highly efficient and mechanically robust light sources with a long service life. Accordingly, modern LEDs have enabled a variety of new display applications and are being increasingly utilized for general illumination applications, often replacing incandescent and fluorescent light sources. 
     LEDs are solid-state devices that convert electrical energy to light and generally include one or more active layers of semiconductor material (or an active region) arranged between oppositely doped n-type and p-type layers. When a bias is applied across the doped layers, holes and electrons are injected into the one or more active layers where they recombine to generate emissions such as visible light or ultraviolet emissions. An active region may be fabricated, for example, from silicon carbide, gallium nitride, gallium phosphide, aluminum nitride, and/or gallium arsenide-based materials and/or from organic semiconductor materials. Photons generated by the active region are initiated in all directions. 
     Typically, it is desirable to operate LEDs at the highest light emission efficiency, which can be measured by the emission intensity in relation to the output power (e.g., in lumens per watt). A practical goal to enhance emission efficiency is to maximize extraction of light emitted by the active region in the direction of the desired transmission of light. Light extraction and external quantum efficiency of an LED can be limited by a number of factors, including internal reflection. According to the well-understood implications of Snell&#39;s law, photons reaching the surface (interface) between an LED surface and the surrounding environment are either refracted or internally reflected. If photons are internally reflected in a repeated manner, then such photons eventually are absorbed and never provide visible light that exits an LED. 
     To increase the opportunity for photons to exit an LED, it has been found useful to pattern, roughen, or otherwise texture the interface between an LED surface and the surrounding environment to provide a varying surface that increases the probability of refraction over internal reflection and thus enhances light extraction. Despite the availability of such methods, their practical employment has been limited in at least certain contexts. For example, mechanical methods may introduce stress in or cause breakage of LED material and may also be limited in terms of the position in a fabrication sequence in which they can be employed. Chemical (e.g., photolithographic etching) methods may also be limited in terms of their position in a fabrication sequence to avoid misalignment or microfeature damage during subsequent LED chip fabrication and/or to avoid chemical incompatibility with LED chip layers if etching is performed after chip fabrication. 
     Another way to increase light extraction efficiency is to provide reflective surfaces that reflect generated light so that such light may contribute to useful emission from an LED chip. In a typical LED package  10  illustrated in  FIG. 1 , a single LED chip  12  is mounted on a reflective cup  13  by means of a solder bond or conductive epoxy. One or more wire bonds  11  can connect the ohmic contacts of the LED chip  12  to leads  15 A and/or  15 B, which may be attached to or integral with the reflective cup  13 . The reflective cup may be filled with an encapsulant material  16 , which may contain a wavelength conversion material such as a phosphor. At least some of light emitted by the LED at a first wavelength may be absorbed by the phosphor, which may responsively emit light at a second wavelength. The entire assembly is then encapsulated in a clear protective resin  14 , which may be molded in the shape of a lens to collimate the light emitted from the LED chip  12 . While the reflective cup  13  may direct light in an upward direction, optical losses may occur when the light is reflected. Some light may be absorbed by the reflector cup due to the less than 100% reflectivity of practical reflector surfaces. Some metals can have less than 95% reflectivity in the wavelength range of interest. 
       FIG. 2  shows another LED package in which one or more LED chips  22  can be mounted onto a carrier such as a printed circuit board (PCB) carrier, substrate, or submount  23 . A metal reflector  24  mounted on the submount surrounds the LED chips  22  and reflects light emitted by the LED chips  22  away from the package  20 . The reflector  24  also provides mechanical protection to the LED chips  22 . One or more wire bond connections  11  are made between ohmic contacts on the LED chips  22  and electrical traces  25 A,  25 B on the submount  23 . The mounted LED chips  22  are then covered with an encapsulant  26 , which may provide environmental and mechanical protection to the chips while also acting as a lens. The metal reflector  24  is typically attached to the carrier by means of a solder or epoxy bond. The metal reflector  24  may also experience optical losses when the light is reflected because it also has less than 100% reflectivity. 
     The reflectors shown in  FIGS. 1 and 2  are arranged to reflect light that escapes from the LED. LEDs have also been developed that have internal reflective surfaces or layers to reflect light internal to the LEDs.  FIG. 3  shows a schematic of an LED chip  30  with an LED  32  mounted on a submount  34  by a metal bond layer  36 . The LED further comprises a p-contact/reflector  38  between the LED  32  and the metal bond  36 , with the p-contact/reflector  38  typically comprising a metal such as silver (Ag). This arrangement is utilized in commercially available LEDs such as those from Cree® Inc., available within the EZBright™ family of LEDs. The p-contact/reflector  38  can reflect light emitted from the LED chip&#39;s active region toward the submount back toward the LED&#39;s primary emitting surface. The reflector also reflects total internal reflection light back toward the LED&#39;s primary emitting surface. Like the metal reflectors above, the p-contact/reflector  38  reflects less than 100% of light and in some cases less than 95%. 
       FIG. 4  shows a graph  40  showing the reflectivity of silver on gallium nitride (GaN) at different viewing angles for light with a wavelength of 460 nm. The refractive index of GaN about 2.4, while the complex refractive index for silver is taken from the technical literature. [See Handbook of Optical Constants of Solids, edited by E. Palik.] The graph shows the p-polarization reflectivity  42 , s-polarization reflectivity  44 , and average reflectivity  46 , with the average reflectivity  46  generally illustrating the overall reflectivity of the metal for the purpose of LEDs where light is generated with random polarization. The reflectivity at 0 degrees is lower than the reflectivity at 90 degrees, and this difference can result in up to 5% or more of the light being lost on each reflection. In an LED chip, in some instances total internal reflection light can reflect off the mirror several times before it escapes and, as a result, small changes in the mirror absorption can lead to significant changes in the brightness of the LED. The cumulative effect of the mirror absorption on each reflection can reduce the light intensity such that less than 75% of light from the LED&#39;s active region actually escapes as LED light. 
     The art continues to seek improved light-emitting diodes and solid-state lighting devices having reduced optical losses and providing desirable illumination characteristics capable of overcoming challenges associated with conventional lighting devices. 
     SUMMARY 
     The present disclosure relates to solid-state lighting devices including light-emitting diodes and more particularly to light-emitting diodes with reflective layers having high reflectivity. 
     In some embodiments, a light-emitting diode (LED) chip includes an active LED structure comprising an active layer between an n-type layer and a p-type layer and a first reflective layer adjacent the active LED structure and comprising a plurality of dielectric layers. The LED chip includes a second reflective layer on the first reflective layer, a barrier layer on the second reflective layer, and a passivation layer on the barrier layer. In some embodiments, each dielectric layer of the plurality of dielectric layers comprises a different thickness. In some embodiments, the plurality of dielectric layers comprises a plurality of first dielectric layers and a plurality of second dielectric layers. In some embodiments, the plurality of dielectric layers comprises an aperiodic Bragg reflector. In some embodiments, the second reflective layer includes an electrically conductive path through the first dielectric layer. 
     In other embodiments, a light-emitting diode (LED) chip includes an active LED structure including an active layer between an n-type layer and a p-type layer, and a first reflective layer adjacent the active LED structure and including a plurality of first dielectric layers and a plurality of second dielectric layers wherein each layer of the plurality of first dielectric layers includes a different thickness. The thickest layer of the plurality of first dielectric layers is between other layers of the plurality of first dielectric layers. 
     In other embodiments, a light-emitting diode (LED) chip includes an active LED structure including an active layer between an n-type layer and a p-type layer and a first reflective layer adjacent the active LED structure and including a plurality of first dielectric layers and a plurality of second dielectric layers. An average thickness of the plurality of first dielectric layers is greater than an average thickness of the plurality second dielectric layers and at least one layer of the plurality of second dielectric layers comprises a thickness greater than at least one layer of the plurality of first dielectric layers. 
     In other embodiments, an LED chip comprises: an active LED structure comprising an active layer between an n-type layer and a p-type layer; a first reflective layer adjacent the active LED structure; a second reflective layer on the first reflective layer; and an adhesion layer between the first reflective layer and the second reflective layer, wherein the adhesion layer comprises a metal oxide. In certain embodiments, the first reflective layer may comprise a plurality of dielectric layers. In certain embodiments, the metal oxide comprises aluminum oxide or anodic aluminum oxide. 
     In another aspect, any one or more aspects, embodiments, or features described herein may be combined with any one or more other aspects or features for additional advantage. 
     Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure and, together with the description, serve to explain the principles of the disclosure. 
         FIG. 1  is a cross-sectional representation of a conventional light-emitting diode (LED). 
         FIG. 2  is a cross-sectional representation of a conventional LED. 
         FIG. 3  is a partial cross-sectional representation of a conventional LED. 
         FIG. 4  is a graph showing the reflectivity of a metal reflector at different viewing angles. 
         FIG. 5A  is a partial cross-sectional representation of an LED according to some embodiments. 
         FIG. 5B  is a partial cross-sectional representation of a reflective layer of an LED according to some embodiments. 
         FIG. 5C  is a partial cross-sectional representation of a reflective layer of an LED according to some embodiments. 
         FIG. 5D  is a partial cross-sectional representation of a reflective layer of an LED according to some embodiments. 
         FIG. 5E  is a partial cross-sectional representation of a reflective layer of an LED according to some embodiments. 
         FIG. 6A  is a graph comparing the percent reflectance over a wide wavelength range at a zero degree angle of incidence for some embodiments. 
         FIG. 6B  is a heat map representation comparing the reflection intensity for a wide angle of incidence (AOI) range and across a wide wavelength range for some embodiments. 
         FIG. 6C  is a heat map representation comparing the reflection intensity for a wide angle of incidence (AOI) range and across a wide wavelength range for some embodiments 
         FIG. 7  is a graph showing the reflectivity of a reflective layer at different viewing angles according to some embodiments. 
         FIG. 8A  is a cross-sectional illustration of an LED according to some embodiments. 
         FIG. 8B  is a cross-sectional illustration of an LED according to some embodiments. 
         FIG. 9A  is a microscopic cross-sectional image of a portion of an LED according to some embodiments. 
         FIG. 9B  is a cross-sectional illustration of a portion of an LED chip that is near an active structure hole according to some embodiments. 
         FIG. 9C  is a cross-sectional illustration of a portion of an LED chip that is near a reflective layer hole according to some embodiments. 
         FIG. 10A  is a cross-sectional illustration of an LED according to some embodiments. 
         FIG. 10B  is a cross-sectional illustration of an LED according to some embodiments. 
         FIG. 11A  is a cross-sectional illustration of an LED according to some embodiments. 
         FIG. 11B  is a cross-sectional illustration of an LED according to some embodiments. 
         FIG. 12A  is a cross-sectional illustration of an LED according to some embodiments. 
         FIG. 12B  is a cross-sectional illustration of an LED according to some embodiments. 
         FIG. 13  is a cross-sectional representation of a packaged LED according to some embodiments. 
         FIG. 14  is a cross-sectional representation of a packaged LED according to some embodiments. 
         FIG. 15  is a cross-sectional representation of a multiple-junction LED chip according to some embodiments. 
         FIG. 16  is a cross-sectional representation of a portion of a lighting fixture according to some embodiments. 
         FIG. 17A  is a scanning electron microscope image of a surface of an Al 2 O 3  film with a magnification of about 10,000×. 
         FIG. 17B  is a scanning electron microscope image of the surface of the Al 2 O 3  film of  FIG. 17A  with a magnification of about 50,000×. 
         FIG. 18A  is a cross-sectional representation that includes an adhesion layer with a controlled morphology or grain structure that is between a first reflective layer and a second reflective layer according to embodiments disclosed herein. 
         FIG. 18B  is a bottom view of a first surface of the adhesion layer of  FIG. 18A  with the first reflective layer removed. 
         FIG. 19A  is a cross-sectional representation that includes an adhesion layer with a different controlled morphology or grain structure that is between a first reflective layer and a second reflective layer according to embodiments disclosed herein. 
         FIG. 19B  is a bottom view of a first surface of the adhesion layer of  FIG. 19A  with the first reflective layer removed. 
         FIG. 20  is a plot representing ellipsometry measurements for an Al 2 O 3  film. 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that when an element such as a layer, region, or substrate is referred to as being “on” or extending “onto” another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or extending “directly onto” another element, there are no intervening elements present. Likewise, it will be understood that when an element such as a layer, region, or substrate is referred to as being “over” or extending “over” another element, it can be directly over or extend directly over the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly over” or extending “directly over” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. 
     Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “vertical” may be used herein to describe a relationship of one element, layer, or region to another element, layer, or region as illustrated in the Figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including” when used herein specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     The present disclosure is directed to solid-state emitters having internal or integral reflective surfaces/layers arranged to increase the emission efficiency of the emitters. The present disclosure is described herein with reference to light-emitting diodes (LEDs), but it is understood that it is equally applicable to other solid-state emitters. Devices of the present disclosure can be used as a reflector in conjunction with one or more contacts or can be used as a reflector separate from the contacts. 
     As described above, different embodiments of LED chips according to the present disclosure comprise an active LED structure having an active layer between two oppositely doped layers. It is understood that the active LED structure may include many additional layers, and the active layer may include a plurality of layers, and two oppositely doped layers may also include a plurality of layers. A first reflective layer can be provided adjacent to one of the oppositely doped layers, with the first layer comprising a material with a different index of refraction from the active LED structure. In some embodiments, the first reflective layer can comprise a layer with an index of refraction that is primarily lower at or near its interface with the active LED structure. Stated differently, when the layer comprises a number of materials, some embodiments of the layer can have an average index of refraction lower than that of the active LED structure. In still other embodiments, the portion of the reflective layer closest to the active LED structure should be less than that of the active LED structure. 
     The difference in index of refraction between the active LED structure and the first reflective layer increases the amount of total internal reflection (TIR) light at this interface. In embodiments in which the first reflective layer has an index of refraction lower than that of the active LED structure, the lower index of refraction material provides a step down in the index of refraction that increases the amount of light that can experience TIR. Some embodiments of LED chips according to the present disclosure can also comprise a second reflective layer or metal layer that can be on and used in conjunction with the first reflective layer such that light passing through the first reflective layer (e.g., not experiencing TIR) can be reflected by the second reflective layer. 
     These internal or integral reflective layers can reduce optical emission losses that can occur by light being emitted in an undesirable direction where it can be absorbed. Light that is emitted from the emitter&#39;s active LED structure in a direction away from useful light emission, such as toward the substrate, submount, or metal bonding layers, can instead be reflected by the first reflective layer. The reflective surfaces can be positioned to reflect this light so that it emits from the LED chip in a desirable direction. Embodiments of the present disclosure provide one or a plurality of layers and materials that can cooperate to efficiently reflect light in the desired directions so that it can contribute to the emitter&#39;s useful emission. 
     The first reflective layer can comprise many different materials including silicon nitride (SiN, SiNx, Si 3 N 4 ), silicon (Si), germanium (Ge), silicon oxide (SiO 2 , SiOx), titanium oxide (TiO 2 ), indium tin oxide (ITO), magnesium oxide (MgOx), zinc oxide (ZnO), and combinations thereof. In some embodiments, the first reflective layer comprises dielectric materials such as silicon dioxide (SiO 2 ) and/or silicon nitride (SiN, Si 3 N 4 ). It is understood that many other materials can be used with refractive indexes that are lower or higher, with some material having an index of refraction that is up to approximately 50% smaller than that of the LED&#39;s active structure material. In other embodiments the index of refraction of the first reflective material can be up to approximately 40% smaller than that of the active structure material, while in other embodiments it can be up to approximately 30% smaller, while in still other embodiments it can be up to approximately 20% smaller. For example, in some embodiments the GaN material of the active structure has an index of refraction of about 2.4, and the reflective material includes one or more layers of silicon dioxide material with an index of refraction of about 1.46 and one or more layers of silicon nitride with an index of refraction of about 1.9. 
     Many conventional LEDs rely primarily on a metal reflector layer made of different material such as silver (Ag), Ag alloys, gold (Au), and Au alloys. As described above, there can be losses with each reflection off metal reflectors, and these losses can be significant, particularly for light making multiple passes and reflections in the LED. There are no optical losses in light reflected by TIR, so that when more light is reflected using TIR, the emission efficiency of the LED can increase. Other conventional LEDs chips have relied on internal multiple layer reflectors, such as distributed Bragg reflectors (DBRs). A conventional DBR, such as a quarter-wave reflector, includes multiple pairs of layers with different indexes of refraction. The multiple pairs are arranged sequentially to provide multiple interfaces with index of refraction gradients. Each interface between the two layers contributes a Fresnel reflection; however, this occurs only for a particular angle of incidence range. 
     Different embodiments of emitters according to the present disclosure can also utilize other structures, layers, or features that allow for efficient and reliable LED operation. In some embodiments, a current-spreading layer can be included in proximity to the reflective layer to provide for spreading of current into the one or more layers of the active LED structure. In other embodiments, materials can be included to provide for reliable adhesion between different layers, such as between the low index of refraction layer and the metal reflective layer. Different embodiments of the disclosure also provide having conductive via or path arrangements that provide conductive paths through the low index of refraction reflective layer. This allows an electric signal to pass through the low index of refraction layer along the vias so that the composite layer can be used as an internal layer, where an electrical signal can pass through the low index of refraction layer during operation. This via arrangement can take many different shapes and sizes as described in detail below. 
     The present disclosure is described herein with reference to certain embodiments, but it is understood that the disclosure can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In particular, the lower index of refraction first reflective layer can comprise many different material layers and can have many different thicknesses beyond those described herein. Some embodiments can have layers having layers or materials with an index of refraction higher than that of the active LED structure, but these layers can be thin enough to have minimal optical impact. The first reflective layer can also be in many different locations on different solid-state emitters beyond those described herein and can be used on different devices beyond solid-state emitters. Further, the first reflective layer can be provided with or without conductive structures to allow electrical signals to pass through. It is understood that LEDs according to the present disclosure can also utilize the first reflective layer in conjunction with other reflectors including metal and other dielectric reflective layers. The first reflective layer is arranged to increase the amount of light reflected by TIR while at the same time maintaining a simple, efficient, and cost-effective reflecting system. 
     Embodiments of the disclosure are described herein with reference to cross-sectional view illustrations that are schematic illustrations of embodiments of the disclosure. As such, the actual thickness of the layers can be different, and variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are expected. For example, a region illustrated or described as square or rectangular can have rounded or curved features, and regions shown as straight lines may have some irregularity. Thus, the regions illustrated in the figures are schematic and their shapes are not intended to illustrate the precise shape of a region of a device and are not intended to limit the scope of the disclosure. 
       FIG. 5A  illustrates a sectional view of an LED chip  50  according to some embodiments. The LED chip  50  includes reflective structures that allow for LED chip operation with increased emission efficiency. Although the present disclosure is described with reference to fabrication of a single LED chip, it is understood that the present disclosure can also be applied to wafer-level LED chip fabrication, fabrication of groups of LED chips, or fabrication of packaged LED chips. The wafer LEDs or groups of LEDs can then be separated into individual LED chips using known singulation or dicing methods. The present disclosure can also be used in different LEDs having different geometries, such lateral geometry or vertical geometry. The present disclosure can also be used in LEDs compatible with flip-chip mounting and in those that are arranged for non-flip-chip mounting. 
     The LED chip  50  comprises an active LED structure  52  or region that can have many different semiconductor layers arranged in different ways. The fabrication and operation of LEDs and their active structure are generally known in the art and are only briefly discussed herein. The layers of the active LED structure  52  can be fabricated using known processes with a suitable process being fabrication using metal organic chemical vapor deposition. The layers of the active LED structure  52  can comprise many different layers and generally comprise an active layer sandwiched between n-type and p-type oppositely doped epitaxial layers, all of which are formed successively on a growth substrate. It is understood that additional layers and elements can also be included in the active LED structure  52 , including but not limited to, buffer layers; nucleation layers; super lattice structures; un-doped layers; cladding layers; contact layers; and current-spreading layers and light extraction layers and elements. The active layer can comprise single quantum well, multiple quantum well, double heterostructure, or super lattice structures. 
     The active LED structure  52  can be fabricated from different material systems, with some material systems being Group III nitride-based material systems. Group III nitrides refer to those semiconductor compounds formed between nitrogen and the elements in the Group III of the periodic table, usually aluminum (Al), gallium (Ga), and indium (In). Gallium nitride (GaN) is a common binary compound. The term also refers to ternary and quaternary compounds such as aluminum gallium nitride (AlGaN), indium gallium nitride (InGaN), and aluminum indium gallium nitride (AlInGaN). For Group III nitrides, silicon (Si) is a common n-type dopant and magnesium (Mg) is a common p-type dopant. Accordingly, the active layer, n-type layer, and p-type layer may include one or more layers of GaN, AlGaN, InGaN, and AlInGaN that are either undoped or doped with Si or Mg for a material system based on Group III nitrides. Other material systems include silicon carbide, organic semiconductor materials, and other Group III-V systems such as gallium phosphide, gallium arsenide, and related compounds. 
     The active LED structure  52  may be grown on a growth substrate (not shown in  FIG. 5A ). Growth substrates can be made of many materials such as sapphire, silicon carbide, aluminum nitride (AlN), GaN, with a suitable substrate being a 4H polytype of silicon carbide, although other silicon carbide polytypes can also be used including 3C, 6H, and 15R polytypes. Silicon carbide has certain advantages, such as a closer crystal lattice match to Group III nitrides than other substrates and results in Group III nitride films of high quality. Silicon carbide also has a very high thermal conductivity so that the total output power of Group III nitride devices on silicon carbide is not limited by the thermal dissipation of the substrate. Sapphire is another common substrate for Group III nitrides and also has certain advantages, including being lower cost, having established manufacturing processes, and having good light transmissive optical properties. 
     Different embodiments of the active LED structure  52  can emit different wavelengths of light depending on the composition of the active layer and n-type and p-type layers. In some embodiments, the active LED structure  52  emits a blue light in the peak wavelength range of approximately 430 nm to 480 nm. In other embodiments, the active LED structure  52  emits green light in a peak wavelength range of 500 nm to 570 nm. In other embodiments, the active LED structure  52  emits red light in a peak wavelength range of 600 to 650 nm. The LED chip  50  can also be covered with one or more lumiphors or other conversion materials, such as phosphors, such that at least some of the light from the LED passes through the one or more phosphors and is converted to one or more different wavelengths of light. In one embodiment, the LED chip emits a white light combination of light from the LED&#39;s active structure and light from the one or more phosphors. The one or more phosphors may include yellow (e.g., YAG:Ce), green (LuAg:Ce), and red (Ca i-x-y Sr x Eu y AlSiN 3 ) emitting phosphors, and combinations thereof. 
     As mentioned above, different layers can be included to allow for efficient operation of the LED chip  50 . For some semiconductor materials, such as some Group III nitride material systems, current does not effectively spread through the p-type layer. In these embodiments, a current-spreading layer  54  can be on the active LED structure  52  in a location to aid in current-spreading into the p-type layer. In some embodiments the current-spreading layer  54  can cover some or the entire p-type layer, and in some embodiments the current-spreading layer  54  helps spread current from a p-type contact across the surface of the p-type layer as described in more detail below. This helps to provide improved current-spreading across the p-type layer with a corresponding improvement in current injection from the p-type layer. 
     The current-spreading layer  54  can comprise many different materials and is typically a transparent conductive oxide such as ITO or a metal such as platinum (Pt), although other materials can also be used. The current-spreading layer can have many different thicknesses, with the present disclosure having a thickness small enough to minimize absorption of light from the active structure that passes through the current-spreading layer. Some embodiments of current-spreading layer  54  comprising ITO can have thicknesses less than 1000 angstroms (Å), while other embodiments can have a thickness less than 700 Å. Still other embodiments can have a thickness less than 500 Å. Still other embodiments can have a thickness in the range of 50 Å to 300 Å, with some of these embodiments having a current-spreading layer with a thickness of approximately 200 Å. The current-spreading layer  54  and the reflective layers described below can be deposited using known methods. It is understood that in embodiments where current spreading is not a concern, the LED chips can be provided without a current-spreading layer. 
     The LED chip  50  can also comprise a first reflective layer  56  that can be formed on the active LED structure  52 , and in the embodiment shown is formed on the current-spreading layer  54  with current-spreading layer  54  between a first reflective layer  56  and the active LED structure  52 . The first reflective layer  56  can comprise many different materials and preferably comprises a material that presents an index of refraction step with the material comprising the active LED structure  52 . Stated differently, the first reflective layer  56  should have an index of refraction that is smaller than that of the active LED structure  52  to promote TIR of active structure light-emitting toward the first reflective layer  56 , as shown by first light trace  58 . Light that experiences TIR is reflected without experiencing absorption or loss, and TIR allows for the efficient reflection of active structure light so that it can contribute to useful or desired LED chip emission. In embodiments that rely solely on metal layers to reflect light, the light experiences loss with each reflection (as described above), which can reduce overall LED chip emission efficiency. 
     In some embodiments, the first reflective layer  56  comprises a material with an index of refraction lower than the index of refraction of the active LED structure  52  material, with the lower index of refraction material providing for increased TIR of light from the active LED structure  52 . The first reflective layer  56  may comprise many different materials, with some having an index of refraction less than 2.3, while others can have an index of refraction less than 2.15, less than 2.0, and less than 1.5. In some embodiments the first reflective layer  56  comprises a dielectric material, with some embodiments comprising silicon dioxide and/or silicon nitride. It is understood that many dielectric materials can be used such as SiN, SiNx, Si 3 N 4 , Si, Ge, SiO 2 , SiOx, TiO 2 , Ta 2 O 5 , ITO, MgOx, ZnO, and combinations thereof. 
     As mentioned above, some Group III nitride materials such as GaN can have an index of refraction of approximately 2.4, and silicon dioxide can have an index of refraction of approximately 1.48, and silicon nitride can have an index of refraction of approximately 1.9. Embodiments with an active LED structure  52  comprising GaN and the first reflective layer  56  that comprises silicon dioxide can have a sufficient index of refraction step between the two to allow for efficient TIR of light at the junction between the two as shown by first light trace  58 . The first reflective layer  56  can have different thicknesses depending on the type of materials used, with some embodiments having a thickness of at least 0.2 microns (μm). In some of these embodiments it can have a thickness in the range of 0.2 μm to 0.7 μm, while in some of these embodiments it can be approximately 0.5 μm thick. 
     As light experiences TIR at the junction with the first reflective layer  56 , an evanescent wave with exponentially decaying intensity can extend into the first reflective layer  56 . This wave is most intense within approximately one third of the light wavelength from the junction (about 0.3 μm for 450 nm light in silicon dioxide). If the thickness of the first reflective layer  56  is too thin, such that significant intensity remains in the evanescent wave at the interface between the first reflective layer  56  and a second reflective layer  60 , a portion of the light can reach the second reflective layer  60 . This in turn can reduce the TIR reflection at the first interface. For this reason, in some embodiments the first reflective layer  56  should have a thickness of at least 0.3 μm. 
     As mentioned above, an LED chip  50  according to some embodiments can also utilize the second reflective layer  60 , such as a metal layer, on the first reflective layer  56  to reflect any light that may pass through the first reflective layer  56 . An example of the light reflected at the second reflective layer  60  is shown by second light trace  62 , which passes first through the first reflective layer  56  before being reflected at the second reflective layer  60 . The second reflective layer  60  can comprise many different materials such as Ag, Au, Al, or combinations thereof, with the present embodiment being Ag. Some embodiments may also comprise an adhesion layer  64  between the first reflective layer  56  and the second reflective layer  60  to promote adhesion between the two. Many different materials can be used for the adhesion layer  64 , such as titanium oxide (TiO, TiO 2 ), titanium oxynitride (TiON, Ti x O y N) tantalum oxide (TaO, Ta 2 O 5 ), tantalum oxynitride (TaON), aluminum oxide (AlO, Al x O y ) or combinations thereof, with a preferred material being TiON, AlO, or Al x O y . In this regard, the adhesion layer  64  may comprise a metal oxide. The adhesion layer  64  may have many different thicknesses from just a few angstroms to thousands of angstroms. In some embodiments it can be less than 160 Å, while in other embodiments it can be less than 100 Å, while in other embodiments it can be less than 50 Å. In some of these embodiments, it can be approximately 20 Å thick. The thickness of the adhesion layer  64  and the material used should minimize the absorption of light passing to minimize losses of light reflecting off the second reflective layer  60 . For example, TiON provides good adhesion between the first reflective layer  56  and the second reflective layer  60 , but TiON has a high extinction coefficient and is absorbing for wavelengths around 450 nm. In this regard, in embodiments where the adhesion layer  64  comprises TiON, the thickness of the adhesion layer  64  may be less than 50 Å, or about 20 Å to provide good adhesion while reducing absorption of light from the active LED structure  52 . Al x O y  has a lower extinction coefficient for wavelengths around 450 nm and is thereby less absorbing for light generated from the active LED structure  52 . In this regard, in embodiments where the adhesion layer  64  comprises Al x O y , the adhesion layer  64  may comprise a thickness in a range from about 60 Å to about 160 Å, or in a range from about 90 Å to about 120 Å, or in a range from about 100 Å to about 110 Å. At thicknesses below about 60 Å, certain Al x O y  materials may provide reduced adhesion. At thickness above about 160 Å, certain Al x O y  materials may provide a refractive index interface that alters the reflective properties provided by the first reflective layer  56  and the second reflective layer  60 . In certain embodiments, the adhesion layer  64  comprises Al x O y , where 1≤x≤4 and 1≤y≤6. In certain embodiments, the adhesion layer  64  comprises Al x O y , where x=2 and y=3, or Al 2 O 3 . In certain embodiments, the adhesion layer  64  comprises Al x O y , where a majority of the Al x O y  comprises Al 2 O 3  and the remainder of the Al x O y  comprises other x and y values. The adhesion layer  64  may be deposited by electron beam deposition that may provide a smooth, dense, and continuous layer without notable variations in surface morphology. The adhesion layer  64  may also be deposited by sputtering, chemical vapor deposition, or plasma enhanced chemical vapor deposition. 
     As stated above, the interface between the first reflective layer  56  and the active LED structure  52  includes an index of refraction step to promote TIR of light, as shown by first light trace  58 . However, depending on the angle of incidence, some light may still pass through the first reflective layer  56  before being reflected at the second reflective layer  60 , as depicted by the second light trace  62 .  FIG. 5B  illustrates a sectional illustration of the first reflective layer  56  according to some embodiments. The first reflective layer  56  includes a plurality of layers ( 56 - 1 ,  56 - 2 ,  56 - 3 ,  56 - 4 ,  56 - 5 ,  56 - 6 , and  56 - 7 ) configured to provide a plurality of different interfaces between them. Additionally, layer  56 - 1  forms an interface with the active LED structure  52  and layer  56 - 7  forms an interface with either the adhesion layer  64  or the second reflective layer  60  of  FIG. 5A . Each different interface promotes TIR of light having a different angle of incidence range and accordingly, the total amount of light reflected by the first reflective layer  56  is increased, and the amount of light reaching the second reflective layer  60  is reduced. 
     A different interface may be formed from materials having different indexes of refraction. For example, layer  56 - 1  may include silicon dioxide and layer  56 - 2  may include silicon nitride. Accordingly, the interface between layer  56 - 1  and the active LED structure  52  is different from the interface between layer  56 - 1  and layer  56 - 2 . If two interfaces are provided between the same two materials, then the interfaces may be different by varying the optical thickness of each layer. Optical thickness can be defined as the product of the refractive index of the material and the geometric length the path of light travels. Accordingly, the optical thickness of a layer of material may be changed by increasing or decreasing the actual layer thickness. A layer with a larger optical thickness will generally promote TIR of light having shallower angles of incidence than another layer with a smaller optical thickness. Accordingly, a plurality of layers with varying optical thicknesses allow some layers to reflect more light of shallower angles of incidence while having other layers that reflect more light at greater angles of incidence, thus providing the plurality of layers with increased total reflection over all angles. 
     In some embodiments, the first reflective layer  56  includes a plurality of first dielectric layers  56 - 1 ,  56 - 3 ,  56 - 5 , and  56 - 7  of a first material and a plurality of second dielectric layers  56 - 2 ,  56 - 4 , and  56 - 6  of a second material that is different from the first material. If the thickness of each of the plurality of first dielectric layers  56 - 1 ,  56 - 3 ,  56 - 5 , and  56 - 7  is varied, then each of the interfaces, that is,  56 - 1  and  56 - 2 ,  56 - 2  and  56 - 3 ,  56 - 3  and  56 - 4 ,  56 - 4  and  56 - 5 , and  56 - 5  and  56 - 6 , will be different, and accordingly, each interface may promote TIR of light having different angle of incidence ranges. In some embodiments, the thickness of each of the plurality of second dielectric layers  56 - 2 ,  56 - 4 , and  56 - 6  may also be varied. In some embodiments, the first material is silicon dioxide and the second material is silicon nitride. In other embodiments, the first and second material may be any combination of SiN, SiNx, Si 3 N 4 , Si, Ge, SiO 2 , SiOx, TiO 2 , Ta 2 O 5 , ITO, MgOx, ZnO, or related materials. As illustrated in  FIG. 5B , some embodiments include an uneven number of first dielectric layers and an even number of second dielectric layers. In other embodiments, the number of the first dielectric layers is equal to the number of the second dielectric layers. The thickness of the plurality of first dielectric layers  56 - 1 ,  56 - 3 ,  56 - 5 , and  56 - 7  may be varied in different configurations within the first reflective layer  56 . For example, the thickness of each layer of the plurality of first dielectric layers  56 - 1 ,  56 - 3 ,  56 - 5 , and  56 - 7  may increase or decrease sequentially within the first reflective layer  56 . In other embodiments, a thickest layer (illustrated as layer  56 - 3  in  FIG. 5B ) of the plurality of first dielectric layers  56 - 1 ,  56 - 3 ,  56 - 5 , and  56 - 7  is between other layers ( 56 - 1 ,  56 - 5 , and  56 - 7 ) of the plurality of first dielectric layers  56 - 1 ,  56 - 3 ,  56 - 5 , and  56 - 7 . The thickest layer (layer  56 - 3  in  FIG. 5B ) has the longest optical thickness and is good for promoting TIR of light having the shallowest angles of incidence, such as 0 to 15 degrees, compared with the other layers (layers  56 - 1 ,  56 - 5 , and  56 - 7 ). By placing the thickest layer (layer  56 - 3 ) between the other layers (layers  56 - 1 ,  56 - 5 , and  56 - 7 ), at least some light with greater angles of incidence, such as greater than 15 degrees, may be reflected earlier without potentially being lost to absorption within the first reflective layer  56 . In  FIG. 5B , the thickest layer of the plurality of first dielectric layers  56 - 1 ,  56 - 3 ,  56 - 5 , and  56 - 7  is illustrated as layer  56 - 3 ; however, layer  56 - 5  could also be the thickest layer without deviating from the principles of these embodiments. 
     Accordingly, some embodiments disclosed herein include an LED chip that includes a first reflective layer that includes a plurality of dielectric layers with varying optical thicknesses. In some embodiments, an LED chip comprising an active structure comprising an active layer between an n-type layer and a p-type layer; a first reflective layer adjacent the active LED structure and comprising a plurality of first dielectric layers and a plurality of second dielectric layers wherein each layer of the plurality of first dielectric layers comprises a different thickness; wherein a thickest layer of the plurality of first dielectric layers is between other layers of the plurality of first dielectric layers. 
     In some embodiments, an average thickness of the plurality of first dielectric layers  56 - 1 ,  56 - 3 ,  56 - 5 , and  56 - 7  is greater than an average thickness of the plurality of second dielectric layers  56 - 2 ,  56 - 4 , and  56 - 6 . However, in some embodiments, at least one layer of the plurality of second dielectric layers  56 - 2 ,  56 - 4 , and  56 - 6  has a thickness greater than at least one of the plurality of first dielectric layers  56 - 1 ,  56 - 3 ,  56 - 5 , and  56 - 7 . For example, the plurality of first dielectric layers  56 - 1 ,  56 - 3 ,  56 - 5 , and  56 - 7  may comprise silicon dioxide, and the plurality of second dielectric layers  56 - 2 ,  56 - 4 , and  56 - 6  comprise silicon nitride, and the thickness of layer  56 - 1  is from 190 nm to 200 nm, the thickness of layer  56 - 2  is from 50 nm to 60 nm, the thickness of layer  56 - 3  is from 335 nm to 345 nm, the thickness of layer  56 - 4  is from 55 nm to 65 nm, the thickness of layer  56 - 5  is from 75 nm to 85 nm, the thickness of layer  56 - 6  is from 60 nm to 70 nm, and the thickness of layer  56 - 7  is from 45 nm to 55 nm. In some embodiments, the average thickness of the plurality of first dielectric layers is greater than the average thickness of the plurality of second dielectric layers by at least a factor of 2. In other embodiments, the average thickness of the plurality of first dielectric layers is greater than the average thickness of the plurality of second dielectric layers by at least a factor of 3. 
       FIG. 5C  illustrates a sectional illustration of the first reflective layer  56  according to other embodiments. In  FIG. 5C , the first reflective layer  56  includes a plurality of layers ( 56 - 1 ,  56 - 2 ,  56 - 3 ,  56 - 4 ,  56 - 5 ,  56 - 6 ,  56 - 7 ,  56 - 8 ,  56 - 9 ,  56 - 10 ,  56 - 11 ,  56 - 12 ,  56 - 13 ) configured to provide a plurality of different interfaces between them. Layer  56 - 1  forms an interface with the active LED structure  52  of  FIG. 5A  and layer  56 - 7  forms an interface with either the adhesion layer  64  or the second reflective layer  60  of  FIG. 5A . Each different interface promotes TIR of light having a different angle of incidence range, and accordingly, the total amount of light reflected by the first reflective layer  56  is increased and the amount of light reaching the second reflective layer  60  is reduced. In some embodiments, the first reflective layer  56  includes a plurality of first dielectric layers  56 - 1 ,  56 - 3 ,  56 - 5 ,  56 - 7 ,  56 - 9 ,  56 - 11 , and  56 - 13  of a first material and a plurality of second dielectric layers  56 - 2 ,  56 - 4 ,  56 - 6 ,  56 - 8 ,  56 - 10 , and  56 - 12  of a second material that is different from the first material. The first material and the second material may be any material or any combination of the materials described above for  FIG. 5B . The thicknesses of each layer of the plurality first dielectric layers and each layer of the plurality of second dielectric layers may be varied as described above for  FIG. 5B . 
     In  FIG. 5C , the thickest layer is illustrated as layer  56 - 1 , which forms an interface with the active LED structure of  FIG. 5A . As described above for  FIG. 5B , the thickest layer (layer  56 - 1  in  FIG. 5C ) has the longest optical thickness and is good for promoting TIR of light having the shallowest angles of incidence, such as 0 to 15 degrees, compared with the other layers. In order to reduce the chances that light of greater angles of incidence, such as greater than 15 degrees, is lost to absorption, additional layers (layers  56 - 8 ,  56 - 9 ,  56 - 10 ,  56 - 11 ,  56 - 12 , and  56 - 13  when compared with  FIG. 5B ) with different optical thicknesses are provided. In some embodiments, the thickest layer (layer  56 - 1 ) is at least 5 times thicker than any other layer of the plurality of first dielectric layers (layers  56 - 3 ,  56 - 5 ,  56 - 7 ,  56 - 9 ,  56 - 11 , and  56 - 13 ) and the plurality of second dielectric layers (layers  56 - 2 ,  56 - 4 ,  56 - 6 ,  56 - 8 ,  56 - 10 , and  56 - 12 ). In some embodiments, the thinnest layer (layer  56 - 13 ) of the plurality of first dielectric layers forms an interface with either the adhesion layer  64  or the second reflective layer  60  of  FIG. 5A . 
     In some embodiments, an average thickness of the plurality of first dielectric layers (layers  56 - 1 ,  56 - 3 ,  56 - 5 ,  56 - 7 ,  56 - 9 ,  56 - 11 , and  56 - 13 ) is at least 2 times greater than an average thickness of the plurality of second dielectric layers (layers  56 - 2 ,  56 - 4 ,  56 - 6 ,  56 - 8 ,  56 - 10 , and  56 - 12 ). In further embodiments, at least one layer of the plurality of second dielectric layers (layers  56 - 2 ,  56 - 4 ,  56 - 6 ,  56 - 8 ,  56 - 10 , and  56 - 12 ) is at least 2 times thicker than the thinnest layer ( 56 - 13 ) of the plurality of first dielectric layers (layers  56 - 1 ,  56 - 3 ,  56 - 5 ,  56 - 7 ,  56 - 9 ,  56 - 11 , and  56 - 13 ). In some embodiments, the plurality of first dielectric layers (layers  56 - 1 ,  56 - 3 ,  56 - 5 ,  56 - 7 ,  56 - 9 ,  56 - 11 , and  56 - 13 ) comprises silicon dioxide, and the plurality of second dielectric layers (layers  56 - 2 ,  56 - 4 ,  56 - 6 ,  56 - 8 ,  56 - 10 , and  56 - 12 ) comprises silicon nitride, and the thickness of layer  56 - 1  is from 480 nm to 490 nm, the thickness of layer  56 - 2  is from 80 nm to 90 nm, the thickness of layer  56 - 3  is from 50 nm to 60 nm, the thickness of layer  56 - 4  is from 55 nm to 65 nm, the thickness of layer  56 - 5  is from 65 nm to 75 nm, the thickness of layer  56 - 6  is from 60 nm to 70 nm, the thickness of layer  56 - 7  is from 65 nm to 75 nm, the thickness of layer  56 - 8  is from 55 nm to 65 nm, the thickness of layer  56 - 9  is from 50 nm to 60 nm, the thickness of layer  56 - 10  is from 70 nm to 80 nm, the thickness of layer  56 - 11  is from 80 nm to 90 nm, the thickness of layer  56 - 12  is from 65 nm to 75 nm, and the thickness of layer  56 - 13  is from 45 nm to 55 nm. 
       FIG. 5D  illustrates a sectional illustration of the first reflective layer  56  according to other embodiments. The embodiments of  FIG. 5D  are similar to the embodiments of  FIG. 5C . Accordingly, the description of  FIG. 5C  also applies to  FIG. 5D  with differences provided below. 
     In  FIG. 5D , the thickest layer is also illustrated as layer  56 - 1 , which forms an interface with the active LED structure  52  of  FIG. 5A . The second thickest layer is illustrated as layer  56 - 3  and both layers  56 - 1  and  56 - 3  are notably thicker than any other layer of the first reflective layer  56 . Accordingly, layers  56 - 1  and  56 - 3  have the largest two optical thicknesses and promote TIR of light having shallower angles of incidence than the other layers. Layer  56 - 3  has a different optical thickness than layer  56 - 1  and will trade off some shallow angle reflection to increase reflection at greater angles, thus helping increase the total reflection over all angles. In some embodiments, the thickest layer (layer  56 - 1 ) is at least 2 times thicker than the second thickest layer (layer  56 - 3 ) and at least 5 times thicker than any other layer of the plurality of first dielectric layers (layers  56 - 5 ,  56 - 7 ,  56 - 9 ,  56 - 11 , and  56 - 13 ). Additionally, the thickest layer (layer  56 - 1 ) is at least 6 times thicker than any of the plurality of second dielectric layers (layers  56 - 2 ,  56 - 4 ,  56 - 6 ,  56 - 8 ,  56 - 10 , and  56 - 12 ). When the first reflective layer  56  of  FIG. 5A  is configured as illustrated in  FIG. 5D , layers  56 - 1  and  56 - 3  are closer to the active LED structure  52  than any other layer of the plurality of first dielectric layers ( 56 - 5 ,  56 - 7 ,  56 - 9 ,  56 - 11 , and  56 - 13 ). Accordingly, more light with shallow angles of incidence are reflected earlier than the embodiments described for  FIG. 5C . In turn, at least one other layer of the plurality of first dielectric layers (layers  56 - 5 ,  56 - 7 ,  56 - 9 ,  56 - 11 , and  56 - 13 ) is much thinner than any other layer. In  FIG. 5D , the thinnest layer is illustrated as layer  56 - 7 , but it is understood in various embodiments that the thinnest layer could be any of layers (layers  56 - 5 ,  56 - 7 ,  56 - 9 ,  56 - 11 , and  56 - 13 ). In some embodiments, the thickest layer (layer  56 - 1 ) is at least 10 times thicker than the thinnest layer (layer  56 - 7 ) of the plurality of first dielectric layers and in further embodiments, the thickest layer (layer  56 - 1 ) is at least 16 times thicker than the thinnest layer (layer  56 - 7 ). Additionally, the thickest layer (layer  56 - 4 ) of the plurality of second dielectric layers is at least 2 times thicker than the thinnest layer (layer  56 - 7 ) of the plurality of first dielectric layers, and the thinnest layer (layer  56 - 6 ) of the plurality of second dielectric layers is at least one and a half times thicker than the thinnest layer (layer  56 - 7 ). 
     In some embodiments, the plurality of first dielectric layers (layers  56 - 1 ,  56 - 3 ,  56 - 5 ,  56 - 7 ,  56 - 9 ,  56 - 11 , and  56 - 13 ) comprises silicon dioxide, and the plurality of second dielectric layers (layers  56 - 2 ,  56 - 4 ,  56 - 6 ,  56 - 8 ,  56 - 10 , and  56 - 12 ) comprises silicon nitride, and the thickness of layer  56 - 1  is from 490 nm to 510 nm, the thickness of layer  56 - 2  is from 60 nm to 70 nm, the thickness of layer  56 - 3  is from 195 nm to 205 nm, the thickness of layer  56 - 4  is from 70 nm to 80 nm, the thickness of layer  56 - 5  is from 90 nm to 100 nm, the thickness of layer  56 - 6  is from 40 nm to 50 nm, the thickness of layer  56 - 7  is from 25 nm to 35 nm, the thickness of layer  56 - 8  is from 70 nm to 80 nm, the thickness of layer  56 - 9  is from 70 nm to 80 nm, the thickness of layer  56 - 10  is from 65 nm to 75 nm, the thickness of layer  56 - 11  is from 80 nm to 90 nm, the thickness of layer  56 - 12  is from 60 nm to 70 nm, and the thickness of layer  56 - 13  is from 55 nm to 65 nm. 
       FIG. 5E  illustrates a sectional illustration of the first reflective layer  56  according to other embodiments. The embodiments of  FIG. 5E  are similar to the embodiments of  FIG. 5B . Accordingly, the description of  FIG. 5B  also applies to  FIG. 5E  with differences provided below. In  FIG. 5E , the first reflective layer  56  includes a plurality of dielectric layers ( 56 - 1 ,  56 - 2 ,  56 - 3 ,  56 - 4 ,  56 - 5 ) configured to provide a plurality of different interfaces between them. Layer  56 - 1  forms an interface with the active LED structure  52  of  FIG. 5A  and layer  56 - 5  forms an interface with either the adhesion layer  64  or the second reflective layer  60  of  FIG. 5A . Each different interface promotes TIR of light having a different angle of incidence range, and accordingly, the total amount of light reflected by the first reflective layer  56  is increased and the amount of light reaching the second reflective layer  60  is reduced. In some embodiments, the first reflective layer  56  includes a plurality of first dielectric layers  56 - 1 ,  56 - 3 , and  56 - 5  of a first material that alternate with a plurality of second dielectric layers  56 - 2  and  56 - 4  of a second material that is different from the first material. The first material and the second material may be any material or any combination of the materials described above for  FIG. 5B . The thicknesses of each layer of the plurality of first dielectric layers and each layer of the plurality of second dielectric layers may be varied as described above for  FIG. 5B . In certain embodiments the plurality of first dielectric layers  56 - 1 ,  56 - 3 , and  56 - 5  comprises silicon dioxide and the plurality of second dielectric layers  56 - 2  and  56 - 4  comprises silicon nitride. As previously described, silicon nitride may have a refractive index of about 1.9. Depending on the growth conditions and composition of the silicon nitride, the refractive index may include a range from about 1.8 to about 2.2. In certain embodiments disclosed herein, the plurality of second dielectric layers  56 - 2  and  56 - 4  may comprise silicon nitride that has been formed with growth conditions such as hotter growth temperatures or different deposition rates that are configured to provide a higher refractive index, such as a refractive index in a range from about 2.0 to about 2.2. In this regard, each interface between certain ones of the first dielectric layers  56 - 1 ,  56 - 3 , and  56 - 5  and certain ones of the second dielectric layers  56 - 2  and  56 - 4  may have increased refraction or reflection of light. Accordingly, the total number of dielectric layers ( 56 - 1 ,  56 - 2 ,  56 - 3 ,  56 - 4 ,  56 - 5 ), e.g. five in  FIG. 5E , may be reduced compared to previous embodiments. 
     Accordingly, the first reflective layer  56  of  FIG. 5A  may comprise a plurality of dielectric layers. The plurality of dielectric layers may comprise embodiments in which each dielectric layer of the plurality of dielectric layers comprises a different thickness. In some embodiments, the first reflective layer  56  comprises from 7 to 13 dielectric layers. In some embodiments, the first reflective layer  56  comprises a plurality of alternating first dielectric layers and second dielectric layers. The first dielectric layers may have a different index of refraction than the second dielectric layers. In some embodiments, the plurality of first dielectric layers comprises silicon dioxide and the plurality of second dielectric layers comprises silicon nitride, although other material combinations are possible as described above. In some embodiments, the first reflective layer  56  comprises an uneven number of first dielectric layers and second dielectric layers, while in other embodiments, the first reflective layer  56  comprises an even number of first dielectric layers and of second dielectric layers. In some embodiments, the first reflective layer  56  comprises an aperiodic Bragg reflector. In some embodiments, the first reflective layer  56  comprises a plurality of dielectric layers in which the thickest dielectric layer of the plurality of dielectric layers is spaced from the active layer by at least one thinner dielectric layer. In other embodiments, the thickest dielectric layer is adjacent the active LED structure and in further embodiments, the second thickest dielectric layer is adjacent the thickest dielectric layer when compared with other layers of the plurality of first dielectric layers. In some embodiments, the first reflective layer  56  comprises a plurality of first dielectric layers having an average thickness that is greater than an average thickness of a plurality of second dielectric layers, and at least one layer of the plurality of second dielectric layers has a thickness greater than at least one layer of the plurality of first dielectric layers. In some embodiments, the thickest layer of the plurality of first dielectric layers is at least 10 times thicker than the thinnest layer of the plurality of first dielectric layers, and in further embodiments, the thickest layer of the plurality of first dielectric layers is at least 16 times thicker than the thinnest layer of the plurality of first dielectric layers. 
     Accordingly, some embodiments disclosed herein include an LED chip comprising an active LED structure comprising an active layer between an n-type layer and a p-type layer, and a first reflective layer adjacent the active LED structure and comprising a plurality of first dielectric layers and a plurality of second dielectric layers, wherein an average thickness of the plurality of first dielectric layers is greater than an average thickness of the plurality second dielectric layers, and wherein at least one layer of the plurality of second dielectric layers comprises a thickness greater than at least one layer of the plurality of first dielectric layers. 
     As discussed above, in some embodiments, the first reflective layer  56  comprises a plurality of alternating first and second dielectric layers of varying materials with different indexes of refraction and thicknesses that promote TIR over a wide range of angles of incidence. Accordingly, the first reflective layer  56  may be referred to as an aperiodic Bragg reflector. In contrast, a periodic Bragg reflector typically consists of multiple pairs of two materials with alternating higher and lower indexes of refraction. The thickness of each material is chosen so that reflected waves are in constructive interference, and the thickness of each material is kept constant among the repeating pairs. Periodic Bragg reflectors offer improved reflectivity over single dielectric reflectors or metal reflectors, but the improved reflectivity is limited to a particular angle of incidence range. 
       FIG. 6A  is a graph comparing the percent reflectance over a wide wavelength range at a zero degree angle of incidence for some embodiments. Each embodiment includes a first reflective layer and a second reflective layer on an active LED structure. Line  66  represents an embodiment in which the first reflective layer is a single dielectric layer of silicon dioxide and the second reflective layer is silver. Line  68  represents an embodiment in which the first reflective layer comprises a plurality of first and second dielectric layers including silicon dioxide and silicon nitride with compositions and thicknesses as described above, and the second reflective layer is silver. Line  68  has noticeably higher reflectivity at most wavelengths. For example, the reflectivity is at least 2% higher at some wavelengths above 450 nm and about 5% higher at some wavelengths from 500 nm to 530 nm. 
       FIG. 6B  and  FIG. 6C  are heat map representations comparing reflection intensity across a wide angle of incidence (AOI) range and across a wide wavelength range. As with  FIG. 6A , the embodiments represented by  FIG. 6B  and  FIG. 6C  both include a first reflective layer and a second reflective layer on an active LED structure.  FIG. 6B  represents an embodiment in which the first reflective layer comprises a plurality of first and second dielectric layers including silicon dioxide and silicon nitride with compositions and thicknesses as described above, and the second reflective layer is silver, as for example, the LED chip of  FIG. 5A  with the first reflective layer  56  of  FIG. 5D .  FIG. 6C  represents an embodiment in which the first reflective layer is a single dielectric layer of silicon dioxide and the second reflective layer is silver. Notably, the percent reflectance improvements illustrated in  FIG. 6A  for zero angle of incidence are also realized across a wide angle of incidence range. For example, at a most wavelengths from 400 nm to 650 nm, the embodiment of  FIG. 6B  has greater reflection intensity (represented as darker regions) than the embodiment of  FIG. 6C  across the most angles of incidence. 
       FIG. 7  is a graph representing the reflectivity percent (%) of a sample including a first reflective layer and a second reflective layer on an active LED structure. The first reflective layer comprises a plurality of first and second dielectric layers including silicon dioxide and silicon nitride with compositions and thicknesses as described above, and the second reflective layer is silver, as for example, the LED chip of  FIG. 5A  with the first reflective layer  56  of  FIG. 5D . The reflectivity percent (y-axis) is plotted at different angles of incidence (x-axis) for light with a wavelength of 460 nm. The graph shows the p-polarization reflectivity  70 , s-polarization reflectivity  72 , and average reflectivity  74 , with the average reflectivity  74  generally illustrating the overall reflectivity of the first reflective layer for the purpose of LEDs in which light is generated with random polarization. Notably, the reflectivity is substantially improved when compared with the similar graph of  FIG. 4  that represents only a silver reflective layer on GaN. For example, the average reflectivity  74  at zero degrees is at least 93% and exceeds 94% for most angles from about 15 degrees to over 50 degrees. 
     It is understood that the first reflective layer  56  arrangements described above can be used in many different LED chips according to the present disclosure.  FIG. 8A  illustrates some embodiments of an LED chip  80  having a lateral geometry and arranged for flip-chip mounting. The LED chip  80  comprises an active LED structure  82  comprising a p-type layer  84 , n-type layer  86 , and an active layer  88  formed on a substrate  91 . In some embodiments, the n-type layer  86  is between the active layer  88  and the substrate  91 . In other embodiments, the p-type layer  84  is between the active layer  88  and the substrate  91 . The substrate  91  can comprise many different materials such as silicon carbide or sapphire and can have one or more surfaces that are shaped, textured, or patterned to enhance light extraction. 
     The LED chip  80  also comprises a current-spreading layer  90  that is between the active LED structure  82  and a first reflective layer  92 . The current-spreading layer  90  can have the same thickness and can comprise the same materials as the current-spreading layer  54  shown in  FIG. 5A  and described above. In LED chip  80 , the current-spreading layer  90  can comprise ITO and is on the p-type layer  84  to spread current into the p-type layer  84 . The first reflective layer  92  is arranged on the current-spreading layer  90  and adjacent the p-type layer  84  and can have any of the embodiments with a plurality of layers previously described for the first reflective layer  56 , for example, as described for  FIG. 5B . For example, in LED chip  80  the first reflective layer  92  may comprise a plurality of dielectric layers. The plurality of dielectric layers may comprise embodiments in which each dielectric layer of the plurality of dielectric layers comprises a different thickness. In some embodiments, the first reflective layer  92  comprises from 7 to 13 dielectric layers. In some embodiments, the first reflective layer  92  comprises a plurality of alternating first dielectric layers and a plurality of alternating second dielectric layers. The plurality of first dielectric layers may have a different index of refraction than the plurality second dielectric layers. In further embodiments, the plurality of first dielectric layers comprises silicon dioxide and the plurality of second dielectric layers comprises silicon nitride, although other material combinations are possible as described above. In some embodiments, the first reflective layer  92  comprises an uneven number of first dielectric layers and second dielectric layers, while in other embodiments, the first reflective layer  92  comprises an even number of first dielectric layers and of second dielectric layers. In some embodiments, the first reflective layer  92  comprises an aperiodic Bragg reflector. In some embodiments, the first reflective layer  92  comprises a plurality of dielectric layers in which the thickest dielectric layer of the plurality of dielectric layers is spaced from the active layer by at least one thinner dielectric layer. In some embodiments, the first reflective layer  92  comprises a plurality of first dielectric layers having an average thickness that is greater than an average thickness of a plurality of second dielectric layers, and at least one layer of the plurality of second dielectric layers has a thickness greater than at least one layer of the plurality of first dielectric layers. All other embodiments described for the first reflective layer  56  ( FIG. 5B ) are also applicable to the first reflective layer  92 . 
     A second reflective layer  94  and an adhesion layer  96  are included on the first reflective layer  92 , with the adhesion layer  96  sandwiched between and providing adhesion between the second reflective layer  94  and first reflective layer  92 . These layers can comprise the same material and can have the same thickness as the second reflective layer  60  and adhesion layer  64  described above for  FIG. 5A . For example, in some embodiments, the second reflective layer  94  comprises an electrically conductive material, such as silver or other metals. 
     The LED chip  80  further comprises reflective layer holes  98  that can pass through the adhesion layer  96  and the first reflective layer  92  to the current-spreading layer  90 . The holes  98  can then be filled or partially filled when the second reflective layer  94  is deposited. Accordingly, the second reflective layer  94  is formed on the first reflective layer  92  and comprises vias  100  to the current-spreading layer  90 . As described in more detail below, second reflective layer  94 , by way of vias  100 , provides an electrically conductive path through the first reflective layer  92 , between a p-contact  110  and the current-spreading layer  90 . In some embodiments, the second reflective layer  94  completely fills the holes  98 . In other embodiments, the second reflective layer  94  only partially fills the holes  98 . When the second reflective layer  94  only partially fills the holes  98 , then a barrier layer  102  and a passivation layer  106  may fill the remaining portion of the vias. 
     The holes  98  can be formed using many known processes such as conventional etching processes or mechanical processes such as microdrilling. The holes  98  can have many different shapes and sizes, with the holes  98  in the embodiment shown having angled or curved side surfaces and a circular cross-section with a diameter of less than 20 μm. In some embodiments, the holes  98  can have a diameter of approximately 8 μm, with others having a diameter down to 1 μm. Adjacent holes  98  can be less than 100 μm apart, with the embodiment shown having a spacing of 30 μm from edge to edge. In still other embodiments, the holes  98  can have a spacing of as small as 10 μm or less. It is understood that the holes  98  (and resulting vias  100 ) can have cross-section with different shapes such as square, rectangular, oval, hexagon, and pentagon. In other embodiments the holes are not uniform size and shapes, and there can be different or non-uniform spaces between adjacent holes. 
     In other embodiments, different structures can be used to provide a conductive path between the p-contact  110  and the current-spreading layer  90 . Instead of holes  98 , an interconnected grid can be formed through the first reflective layer  92 , with a conductive material then being deposited in the grid to form the conductive path to the current-spreading layer  90 . The grid can take many different forms, with portions of the grid interconnecting at different angles in different embodiments. An electrical signal applied to the grid can spread throughout and along the interconnected portions. It is further understood that in different embodiments a grid can be used in combination with holes, while other embodiments can provide other conductive paths. In some embodiments one or more conductive paths can run outside the LED chip&#39;s active layer, such as along a side surface of the LED chip. 
     The LED chip  80  can also comprise a barrier layer  102  on the second reflective layer  94  to prevent migration of the second reflective layer  94  material, such as Ag, to other layers. Preventing this migration helps the LED chip  80  maintain efficient operation through its lifetime. Accordingly, the barrier layer  102  is also part of the conductive path from the p-contact  110  to the current-spreading layer  90 . In some embodiments, the barrier layer  102  is a single layer, and in other embodiments, the barrier layer  102  comprises a plurality of layers. Suitable materials for the barrier layer  102  include but are not limited to sputtered Ti/Pt followed by evaporated Au bulk material or sputtered Ti/Ni followed by a evaporated Ti/Au bulk material. 
     An active structure hole  104  can be included passing through the adhesion layer  96 , the first reflective layer  92 , and p-type layer  84  to expose the n-type layer  86 . A passivation layer  106  is included on the barrier layer  102  and the side surfaces of the active structure hole  104 . The passivation layer  106  protects and provides electrical insulation between the contacts and the layers below as described in more detail below. The passivation layer  106  can comprise many different materials, such as a dielectric material. In some embodiments, the passivation  106  is a single layer, and in other embodiments, the passivation layer  106  comprises a plurality of layers. A suitable material for the passivation layer  106  includes but is not limited to silicon nitride. 
     Passivation layer hole  108  can be formed through the passivation layer  106  to the barrier layer  102  and/or the second reflective layer  94 . The p-contact  110  can then be deposited in the passivation layer hole  108 . In operation, an electrical signal applied to the p-contact passes through the barrier layer  102 , through the second reflective layer  94  and the vias  100 , and to the current-spreading layer  90  through which it is spread to the p-type layer  84 . Similarly, an n-contact  112  is formed on the passivation layer  106  and through the active structure hole  104 , with the n-contact  112  providing an electrical path for an electrical signal to be applied to the n-type layer  86 . In operation, a signal applied across the p-contact  110  and the n-contact  112  is conducted to the p-type layer  84  and the n-type layer  86 , causing the LED chip  80  to emit light from its active layer  88 . 
     The p-contact  110  and the n-contact  112  can comprise many different materials such as Au, copper (Cu), nickel (Ni), In, Al, Ag, tin (Sn), Pt, or combinations thereof. In still other embodiments they can comprise conducting oxides and transparent conducting oxides such as ITO, nickel oxide, zinc oxide, cadmium tin oxide, indium oxide, tin oxide, magnesium oxide, ZnGa 2 O 4 , ZnO 2 /Sb, Ga 2 O 3 /Sn, AgInO 2 /Sn, In 2 O 3 /Zn, CuAlO 2 , LaCuOS, CuGaO 2 , and SrCu 2 O 2 . The choice of material used can depend on the location of the contacts and on the desired electrical characteristics, such as transparency, junction resistivity, and sheet resistance. 
     As described above, the LED chip  80  is arranged for flip-chip mounting. In operation, the p-contact  110  and n-contact  112  are bonded to a surface, such as a printed circuit board, with electrical paths for applying an electrical signal to the LED chip  80 . In most cases, the p-contact  110  and n-contact  112  are on the bottom surface, and light that is emitted toward the bottom of the LED chip risks being at least partially absorbed, such as by the printed circuit board. The first reflective layer  92  and the second reflective layer  94  are arranged below the active layer  88  so that light emitted toward the bottom is reflected back up to contribute to useful LED chip emission. The first reflective layer  92  reflects most light by TIR, with the majority of the remainder of the light being reflected by the second reflective layer  94 . 
       FIG. 8B  illustrates some embodiments of an LED chip  113  having a lateral geometry and arranged for flip-chip mounting. The LED chip  113  comprises an active LED structure  82  comprising the p-type layer  84 , the n-type layer  86 , and the active layer  88  formed on the substrate  91  as previously described. The substrate  91  can comprise many different materials such as silicon carbide or sapphire and may comprise a patterned surface  105  that is shaped, textured, or patterned to enhance light extraction. The LED chip  113  additionally includes the first reflective layer  92 , the second reflective layer  94 , the adhesion layer  96 , the reflective layer holes  98 , the vias  100  to the current spreading layer  90 , the barrier layer  102 , the active structure hole  104  to the n-type layer  86 , the passivation layer  106 , the passivation layer hole  108 , the p-contact  110 , and the n-contact  112  as previously described. In some embodiments, the passivation layer  106  includes a metal-containing interlayer  122  arranged therein, wherein the interlayer  122  may comprise Al or another suitable metal. Notably, the interlayer  122  is embedded within the passivation layer  106  and is electrically isolated from the rest of the LED chip  113 . In application, the interlayer  122  may function as a crack stop layer for any cracks that may propagate through the passivation layer  106 . Additionally, the interlayer  122  may reflect at least some light that may pass through both the first reflective layer  92  and the second reflective layer  94 . In  FIG. 8B , the first reflective layer  92  is illustrated as a single layer; however, the first reflective layer  92  may include any of the multiple layer reflective combinations as previously described, for example as described for the first reflective layer  56  of  FIG. 5B ,  FIG. 5C ,  FIG. 5D , and  FIG. 5E . Additionally, the first reflective layer  92  includes portions that are proximate to the active LED structure  82  and “wraparound” peripheral portions of the active LED structure  82  (including the n-type layer  86 , the active layer  88 , and the p-type layer  84 ). In this regard, wraparound portions  92 ′ of the first reflective layer  92  extends on sidewalls of the p-type layer  84 , the active layer  88 , and the n-type layer  86 , as well as laterally on a portion of the n-type layer  86  that is registered with the active structure hole  104 . Accordingly, the peripheral portions of the LED active structure  82  have improved reflectivity and more light may be redirected toward the substrate  91  and out of the LED chip  113 . In certain embodiments, the second reflective layer  94  does not include a wraparound portion that extends along sidewalls of the active LED structure  82 . For embodiments where the second reflective layer  94  comprises a metal, the absence of the second reflective layer  94  on sidewalls of the active LED structure  82  may reduce migration of metal that could otherwise contact sidewalls of the p-type layer  84 , the active layer  88 , and the n-type layer  86  and thereby cause electrical shorting. 
     As described above, the actual thickness of the layers can be different, and variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are expected. A region illustrated or described as square or rectangular can have rounded or curved features, and regions shown as straight lines may have some irregularity. For example,  FIG. 9A  is a microscopic cross-sectional image of a portion of an LED chip according to some embodiments, that is near an individual reflective layer hole  98  of  FIG. 8A . In particular,  FIG. 9A  is a focused ion beam image along a portion of the reflective layer hole  98 . In  FIG. 9A , the active LED structure  82 , current-spreading layer  90 , first reflective layer  92 , reflective layer hole  98 , second reflective layer  94 , barrier layer  102 , and passivation layer  106  are visible. As shown in the image, the second reflective layer  94 , barrier layer  102 , and passivation layer  106  are on the first reflective layer  92  and are conformal to the first reflective layer  92  through the hole. The second reflective layer  94  partially fills the reflective layer hole  98  with the remaining portion of the reflective layer hole  98  filled by the barrier layer  102  and the passivation layer  106 . 
       FIG. 9B  is a cross-sectional illustration of a portion of an LED chip according to some embodiments, that is near the active structure hole  104  of  FIG. 8B . As shown in the illustration of  FIG. 9B , the n-contact  112  is configured to extend into the active structure hole  104  to provide an electrical connection with the n-type layer  86 . As shown, the n-contact  112  is illustrated as two conformal layers, however the n-contact  112  may include a multiple layer stack of conductive materials. For example, the first and thinnest layer of the n-contact  112  illustrated in  FIG. 9B  may include an ohmic layer followed by one or more migration barrier layers, and the thickest layer of the n-contact  112  illustrated in  FIG. 9B  may include one or more bulk contact layers. The ohmic layer may be conformally coated on the passivation layer  106  and directly on the surface of the n-type layer  86 . The ohmic layer may include one or more layers of Al, chromium (Cr), Ti, ZnO, and Ag. The migration barrier layers may be conformally coated over the ohmic layer and may include one or more combinations of Ti, Au, Pt, Ni, titanium tungsten (TiW), and titanium nitride (TiN). The bulk contact layers may be conformally coated on the migration barrier layers and may include one or more combinations of gold tin (AuSn) and titanium nickel gold (TiNiAu). To the left of the illustration, the wraparound portion  92 ′ (of the first reflective layer  92  of  FIG. 8B ) extends laterally along a portion of the n-type layer  86  that is registered with the active structure hole  104 . The adhesion layer  96  is barely visible on the wraparound portion  92 ′. Additionally, the passivation layer  106  conformally covers the adhesion layer  96 , the wraparound portion  92 ′, and extends laterally along a portion of the n-type layer  86  that is between the wraparound portion  92 ′ and the n-contact  112 .  FIG. 9C  is a microscopic cross-sectional image of a portion of an LED chip according to some embodiments, that is near an individual reflective layer hole  98  of  FIG. 8B . In particular,  FIG. 9C  is a cross-sectional illustration of a portion of an LED chip that is near a portion of the reflective layer hole  98 . As shown in the illustration of  FIG. 9C , the current spreading layer  90  is barely visible on the p-type layer  84 . Portions of the first reflective layer  92  are visible to the left and right of the image, with the reflective layer hole  98  formed therebetween. The second reflective layer  94  extends on the first reflective layer  92  as well as along portions of the current spreading layer  90  that are registered with the reflective layer hole  98 . The adhesion layer  96  is provided between portions of the first reflective layer  92  and the second reflective layer  94 . The barrier layer  102 , which may include a multiple layer stack as previously described, is shown extending along the second reflective layer  94 . The passivation layer  106  includes the interlayer  122 , and the passivation layer  106  is configured to cover the barrier layer  102  entirely across the reflective layer hole  98 , thereby providing electrical insulation for the n-contact  112  that extends along a portion of the passivation layer  106 . 
     Accordingly, some embodiments disclosed herein include an LED chip comprising an active LED structure comprising an active layer between an n-type layer and a p-type layer; a first reflective layer adjacent the active LED structure and comprising a plurality of dielectric layers; a second reflective layer on the first reflective layer; a barrier layer on the second reflective layer; and a passivation layer on the barrier layer. 
       FIG. 10A  illustrates an LED chip  114  similar to the embodiments described above for  FIG. 8A  and  FIG. 8B . In  FIG. 10A , the LED chip  114  is in a flip-chip orientation and includes an active LED structure  82 , a substrate  91 , a first reflective layer  92 , a second reflective layer  94 , a barrier layer  102 , a passivation layer  106 , vias  100 , active structure holes  104 , a p-contact  110 , and an n-contact  112  similar to those described in  FIG. 8 . The substrate  91  is light transmissive (preferably transparent) and includes an outer major surface  118 , side surfaces  120 , and an internal surface  116 . The internal surface  116  is proximate the active LED structure  82  and includes a patterned surface  105  adjacent the active LED structure  82  having multiple recessed and/or raised features. In some embodiments, the patterned surface  105  is adjacent an n-layer of the active LED structure  82 . A patterned surface  105  is particularly useful in embodiments in which the substrate  91  comprises sapphire in order to promote extraction of light through the interface between the active LED structure  82  and the substrate  91 . In some embodiments, the passivation layer  106  includes the metal-containing interlayer  122  arranged therein, wherein the interlayer  122  may comprise Al or another suitable metal. Notably, the interlayer  122  is embedded within passivation layer  106  and is electrically isolated from the rest of the LED chip  114 . In application, the interlayer  122  may function as a crack stop layer for any cracks that may propagate through the passivation layer. Additionally, the interlayer  122  may reflect at least some light that may pass through both the first reflective layer  92  and the second reflective layer  94 . 
       FIG. 10B  illustrates the LED chip  114  of  FIG. 10A  mounted to a submount  124  and covered with a layer of at least one lumiphoric material  126 . The submount  124  includes a first contact pad  128  and a second contact pad  130  arranged proximate to the p-contact  110  and n-contact  112  of the LED chip  114 , respectively. Solderless, soldered flux, direct attach, or other conventional attachment means may be used to establish conductive electrical communication between the first contact pad  128  and the p-contact  110  and the second contact pad  130  and the n-contact  112 . As illustrated in  FIG. 10B , the layer of at least one lumiphoric material  126  is arranged to cover the outer major surface  118 , side surfaces  120 , and at least a portion of the submount  124 . 
     Lumiphoric materials as described herein may be or include one or more of a phosphor, a scintillator, a lumiphoric ink, a quantum dot material, a day glow tape, and the like. Lumiphoric materials may be provided by any suitable means, for example, direct coating on one or more surfaces of an LED, dispersal in an encapsulant material configured to cover one or more LEDs, and/or coating on one or more optical or support elements (e.g., by powder coating, inkjet printing, or the like). In certain embodiments, lumiphoric materials may be downconverting or upconverting, and combinations of both downconverting and upconverting materials may be provided. In certain embodiments, multiple different (e.g., compositionally different) lumiphoric materials arranged to produce different peak wavelengths may be arranged to receive emissions from one or more LED chips. In some embodiments, one or more phosphors may include yellow phosphor (e.g., YAG:Ce), green phosphor (LuAg:Ce), and red phosphor (Ca i-x-y Sr x Eu y AlSiN 3 ) and combinations thereof. 
     One or more lumiphoric materials may be provided on one or more portions of a flip-chip LED and/or a submount in various configurations. In certain embodiments, one or more surfaces of flip-chip LEDs may be conformally coated with one or more lumiphoric materials, while other surfaces of such LEDs and/or associated submounts may be devoid of lumiphoric material. In certain embodiments, a top surface of a flip-chip LED may include lumiphoric material, while one or more side surfaces of a flip-chip LED may be devoid of lumiphoric material. In certain embodiments, all or substantially all outer surfaces of a flip-chip LED (e.g., other than contact-defining or mounting surfaces) are coated or otherwise covered with one or more lumiphoric materials. In certain embodiments, one or more lumiphoric materials may be arranged on or over one or more surfaces of a flip-chip LED in a substantially uniform manner; in other embodiments, one or more lumiphoric materials may be arranged on or over one or more surfaces of a flip-chip LED in a manner that is non-uniform with respect to one or more of material composition, concentration, and thickness. In certain embodiments, the loading percentage of one or more lumiphoric materials may be varied on or among one or more outer surfaces of a flip-chip LED. In certain embodiments, one or more lumiphoric materials may be patterned on portions of one or more surfaces of a flip-chip LED to include one or more stripes, dots, curves, or polygonal shapes. In certain embodiments, multiple lumiphoric materials may be arranged in different discrete regions or discrete layers on or over a flip-chip LED. 
     In certain embodiments, a lumiphoric material may be arranged over a light-transmissive surface of the substrate, and the substrate may comprise a thickness of at least 120 μm, at least 150 μm, at least 170 μm, at least 200 μm, at least 230 μm, at least 250 μm (with the preceding minimum thickness values optionally bounded at the upper end by any of the foregoing thickness values), or another thickness threshold specified herein. Without intending to be limited by any specific theory of operation, it is currently believed that providing a relatively thick substrate according to one or more of the preceding thickness thresholds may enhance conversion efficiency of a lumiphor-converted flip-chip LED due to one or more of the following phenomena: (i) increasing physical separation (distance) between an outer major (e.g., top) surface of a substrate and the multi-layer mirror, and (ii) reducing luminous flux on lumiphoric material arranged on or over an outer surface of the substrate. 
     Benefits of reduced optical losses may be more pronounced and significant with larger LED die sizes (e.g., with substrate widths of at least about 1.2 mm, at least about 1.4 mm, at least about 2 mm, or larger). Larger die have a greater dependency on internal reflectivity due to more interaction of light with the internal reflector layers before the light escapes the LED. Benefits of reduced optical losses may also be more pronounced in producing warm white (versus cool white) emitters, since warm white emitters typically involve a greater amount of back reflection into a LED chip (e.g., due to conversion by multiple phosphor materials or material layers, such as a yellow layer and a red layer). As described above, the first reflective layer  92  includes improved reflectivity across a wide wavelength range and across a wide angle of incidence range and is therefore additionally well suited for larger LED die and/or LED die with multiple lumiphors that convert light from the active LED structure  82  to multiple other colors. Additionally, the first reflective layer  92  in combination with any or all of the second reflective layer  94 , the interlayer  122 , the patterned surface  105 , and the light transmissive or transparent substrate  91  reduces optical losses within the LED chip  114  providing an increase in brightness or luminous flux. 
       FIG. 11A  illustrates an LED chip  132  according other embodiments. In  FIG. 11A , an active LED structure  82 , a substrate  91 , a first reflective layer  92 , a second reflective layer  94 , a barrier layer  102 , a passivation layer  106 , vias  100 , active structure holes  104 , a p-contact  110 , and an n-contact  112  are similar to those described in  FIG. 10A . Additionally, the first reflective layer  92  and the second reflective layer  94  include portions that are proximate to the active LED structure  82  and “wraparound” peripheral portions of the active LED structure  82  (including the n-type layer, active layer, and p-type layer). As shown in  FIG. 11A , the active LED structure  82  extends away from the substrate  91  and forms a mesa  134  with a mesa sidewall  134 ′ that is laterally bounded by at least one recess  136  at the periphery of the LED chip  132 . The at least one recess  136  includes a peripheral wraparound portion  92 ′ of the first reflective layer  92  that bounds peripheral portions of the active LED structure  82  forming the mesa  134 . Additionally, the at least one recess  136  includes a peripheral wraparound portion  94 ′ of the second reflective layer  94  that is arranged in contact with a portion of a wraparound portion  92 ′ of the first reflective layer  92 . Within the at least one recess  136 , the wraparound portion  92 ′ and peripheral wraparound portion  94 ′ are peripherally bounded by passivation material of the passivation layer  106 . Accordingly, the active LED structure  82  comprise a mesa sidewall  134 ′ and the first reflective layer  92  extends along the mesa sidewall  134 ′. 
     As with previous embodiments, the first reflective layer  92  may comprise a plurality of first and second dielectric layers with different materials, such as silicon dioxide and silicon nitride, and the wraparound portion  92 ′ would therefore also comprise silicon dioxide and silicon nitride. Accordingly, the peripheral portions of the LED active structure  82  have improved reflectivity and more light may be redirected toward the substrate  91  and out of the LED chip  132 . The presence of silicon nitride in the wraparound portion  92 ′ of the first reflective layer  92  serves to provide passivation to the side of the mesa  134  of active LED structure  82 . In particular, the presence of silicon nitride in the wraparound portion  92 ′ may serve to protect the active LED structure  82  from migration of metals, such as silver, from the second reflective layer  94 . Any metal migrating along the mesa  134  edge may contact both the n-layer and the p-layer of the active LED structure  82  and provide an electrical short that would cause failure of operation of the LED chip  132 . Additionally, the presence of silicon nitride in the passivation layer  106  within the recess  136  may serve to block potential paths for moisture to be drawn into contact with metal-containing portions of the second reflective layer  94 , which would be expected to lead to detrimental chemical interaction. Accordingly, the LED chip  132  is expected to have improved lumen maintenance, or less light loss over time, in all operating conditions. 
       FIG. 11B  illustrates the LED chip  132  of  FIG. 11A  mounted to a submount  124  and covered with a layer of at least one lumiphoric material  126  similar to that of  FIG. 10B . The submount  124  includes a first contact pad  128  and a second contact pad  130  arranged proximate to the p-contact  110  and n-contact  112 , respectively. Solderless, soldered flux, direct attach, or other conventional attachment means may be used to establish conductive electrical communication between the first contact pad  128  and the p-contact  110  and the second contact pad  130  and the n-contact  112 . As illustrated in  FIG. 11B , the layer of at least one lumiphoric material  126  is arranged to cover an outer major surface  118  of the substrate  91  and one or more side surfaces  120  of the substrate  91  as well as the at least a portion of the submount  124 . 
       FIG. 12A  illustrates another embodiment of a LED chip  138  according to the present invention that is flip-chip mounted onto a submount or substrate for use. The LED chip has many layers similar to those in the embodiment shown in  FIG. 8 ,  FIG. 10A , and  FIG. 10B  and described above, including an active LED structure  140  comprising an p-type layer  142 , n-type layer  144 , and an active layer  146 . A current-spreading layer  148  is included on the p-type layer  142  to spread current to the p-type layer  142  during operation. A first reflective layer  150  is included on the current-spreading layer  148 , and a second reflective layer  152  is included on the first reflective layer  150  with an adhesion layer  154  between the two. 
     The first reflective layer  150  is arranged on the current-spreading layer  148  and adjacent the p-type layer  142  and can have any of the embodiments with a plurality of layers previously described for the first reflective layer  56  as described for  FIG. 5B  or the first reflective layer  92  as described for  FIG. 8 . For example, in LED chip  138 , the first reflective layer  150  may comprise a plurality of dielectric layers. The plurality of dielectric layers may comprise embodiments in which each dielectric layer of the plurality of dielectric layers comprises a different thickness. In some embodiments, the first reflective layer  150  comprises from 7 to 13 dielectric layers. In some embodiments, the first reflective layer  150  comprises a plurality of alternating first dielectric layers and second dielectric layers. The plurality first dielectric layers may have a different index of refraction than the plurality of second dielectric layers. In further embodiments, the plurality of first dielectric layers comprises silicon dioxide and the plurality of second dielectric layers comprises silicon nitride, although other material combinations are possible as described above. In some embodiments, the first reflective layer  150  comprises an uneven number of first dielectric layers and second dielectric layers, while in other embodiments, the first reflective layer  150  comprises an even number of first dielectric layers and of second dielectric layers. In some embodiments, the first reflective layer  150  comprises an aperiodic Bragg reflector. In some embodiments, the first reflective layer  150  comprises a plurality of dielectric layers in which the thickest dielectric layer of the plurality of dielectric layers is spaced from the active layer by at least one thinner dielectric layer. In some embodiments, the first reflective layer  150  comprises a plurality of first dielectric layers having an average thickness that is greater than an average thickness of a plurality of second dielectric layers, and at least one layer of the plurality of second dielectric layers has a thickness greater than at least one layer of the plurality of first dielectric layers. All other embodiments described for the first reflective layer  56  of  FIGS. 5A-5E  and the first reflective layer  92  of  FIG. 8A  and  FIG. 8B  are also applicable to the first reflective layer  150  of  FIG. 12A . 
     The LED chip  138  further comprises reflective layer holes  156  that can pass through the adhesion layer  154  and the first reflective layer  150  to the current-spreading layer  148 . The reflective layer holes  156  can then be filled or partially filled when the second reflective layer  152  is deposited. Accordingly, the second reflective layer  152  is formed on the first reflective layer  150  and comprises vias  158  to the current-spreading layer  148  as previously described for  FIG. 8 . 
     In  FIG. 12A , a passivation layer  160  and a barrier layer  162  extend beyond the edge of the active LED structure  140  where a p-contact  164  can be formed on the barrier layer  162 . It is understood that the passivation layer  160  may include a metal interlayer as described in  FIG. 10A . An active structure hole  166  is included through the adhesion layer  154 , the first reflective layer  150 , the current-spreading layer  148 , the p-type layer  142 , and the active layer  146 . The passivation layer  160  is included on the barrier layer  162  and the side surfaces of the active structure hole  166 , and an n-contact via or n-contact  168  is included in the active structure hole  166  for applying an electrical signal to the n-type layer  144 . An electrical signal applied to the p-contact  164  is conducted to the p-type layer  142  through the barrier layer  162 , the second reflective layer  152 , and the current-spreading layer  148 . Accordingly, an electrical signal applied across the p-contact  164  and the n-contact  168  is conducted to the p-type layer  142  and the n-type layer  144 , causing the active layer  146  to emit light. 
     In  FIG. 12A , the growth substrate for LED chip  138  has been removed, and the top surface  170  of the n-type layer  144  is textured for light extraction. To provide mechanical stabilization, the LED chip  138  is flip-chip mounted to a submount  172 , with a bond metal layer  174  and blanket mirror layer  176  between the submount  172  and the active LED structure  140 . Accordingly, the p-type layer  142  is between the submount  172  and the active layer  146 . The submount  172  can be made of many different materials, with a suitable material being silicon. The blanket mirror layer  176  can be made of many different materials, with a suitable material being Al. The blanket mirror layer  176  helps to reflect LED light that escapes reflection by the first reflective layer  150  and the second reflective layer  152 , such as light that may passes through the active structure hole  166 . In some embodiments, the first reflective layer  150  may wrap around and extend on the side of the active LED structure  140  within the active structure hole  166 . 
       FIG. 12B  illustrates the LED chip  138  of  FIG. 12A  covered with a layer of at least one lumiphoric material  178 . The lumiphoric material  178  may be any material or combination of materials as described for the layer of at least one lumiphoric material  126  of  FIG. 10B . In  FIG. 12B , the layer of at least one lumiphoric material  178  may be deposited on top of active LED structure  140  while leaving the p-contact  164  exposed. As with the embodiments of  FIG. 12A , the active LED structure  140  includes an n-type layer  144 , an active layer  146 , and a p-type layer  142 . In some embodiments, the layer of at least one lumiphoric material  178  is on the n-type layer  144 . As described above, the first reflective layer  92  includes improved reflectivity across a wide wavelength range and across a wide angle of incidence range. In operation, light of various wavelengths is emitted omnidirectionally from the active layer  146  and/or converted omnidirectionally by the layer of at least one lumiphoric material  178  and may be reflected by the first reflective layer  150 , the second reflective layer  152  or the blanket mirror layer  176  and extracted from the textured top surface  170 . Accordingly, the first reflective layer  150  in combination with any or all of the second reflective layer  152 , the blanket mirror layer  176 , and the textured top surface  170  reduces optical losses within the LED chip  138 , providing an increase in brightness or luminous flux. 
     In addition to the LED chip embodiments previously described, reflective layers described herein may also provide reflectivity improvements in other configurations. For example,  FIG. 13  is a cross-sectional representation of a packaged LED  180  according to some embodiments. In  FIG. 13 , at least one light source  182 , such as an LED chip, mounted on a submount  184 . The submount  184  may include any number of materials, including but not limited to, alumina, AlN, silicon, and printed circuit boards. In some embodiments, a first reflective layer  186  is on the submount  184  and between the at least one light source  182  and the submount  184 . In further embodiments, the first reflective layer  186  extends on the submount  184  beyond where the at least light source  182  is mounted. In other embodiments, the first reflective layer  186  may only be on portions of the submount  184  in areas outside of where the at least one light source  182  is mounted. The packaged LED  180  may further include a lumiphoric layer  188  and an encapsulant  190 . The lumiphoric layer  188  may include any of the lumiphoric materials previously described, for example as described for  FIG. 10A , and the encapsulant  190  may include an optically transmissive material such as silicone or glass that may be molded in the shape of a lens. In some embodiments, the lumiphoric layer  188  is on the first reflective layer  186  outside of where the at least one light source  182  is mounted. In some embodiments, the lumiphoric layer  188  and the encapsulant  190  may be combined, for example a silicone material acting as a binder for lumiphoric materials. The first reflective layer  186  may be any of the multiple layer reflective combinations as previously described, for example as described for the first reflective layer  56  of  FIG. 5B ,  FIG. 5C ,  FIG. 5D , and  FIG. 5E . Accordingly, the first reflective layer  186  is in an optical path of the at least one light source  182 . For example, light emitted by the at least one light source  182  and light converted by the lumiphoric layer  188  toward the submount  184  may be reflected by the first reflective layer  186  in locations between the at least one light source  182  and the submount  184  as well as locations on the submount  184  outside of where the at least light source  182   182  is mounted. 
       FIG. 14  is a cross-sectional representation of a packaged LED  192  according to some embodiments that is similar to the packaged LED  180  of  FIG. 13 , but is illustrated with a plurality of light sources  194 , such as LED chips. Notably, a first reflective layer  195  is on a submount  196  and is in an optical path of the plurality of light sources  194  and is configured to reflect light emitted by the plurality of light sources  194 . The first reflective layer  195  may be any of the multiple layer reflective combinations as previously described, for example as described for the first reflective layer  56  of  FIG. 5B ,  FIG. 5C ,  FIG. 5D , and  FIG. 5E . An encapsulant  198  may be provided over the plurality of LED chips  194  and may comprise many shapes, for example but not limited to, a square or rectangular cubic shape, a hemispherical-shaped lens, or a hemispherical-shaped lens with planar side surfaces. In some embodiments, the encapsulant may be dispensed on the submount  196  inside of a retention material (not shown) that surrounds the plurality of light sources  194 . 
       FIG. 15  is a cross-sectional representation of a multiple-junction LED chip  200  according to some embodiments. The multiple-junction LED chip  200  includes a substrate  204 , at least one n-type layer  206 , at least one active layer  208 , and at least one p-type layer  210 . Individual junctions  218  are provided by isolation trenches  216  that extend through the at least one p-type layer  210  and the at least one active layer  208  to the at least one n-type layer  206 . In some embodiments, the isolation trenches  216  extend to the substrate  204 . In some embodiments, the isolation trenches  216  extend completely through the substrate  204  as illustrated by the vertical dashed lines in  FIG. 15 . In embodiments where the substrate  204  is removed, the isolation trenches  216  may extend through the at least one n-type layer  206 . Individual junctions  218  are individually addressable by way of a separate first contact  212  and a separate second contact  214  for each of the individual junctions  218 . For example, the multiple-junction LED chip  200  may be mounted on a submount (not shown) that includes corresponding electrical connections for the first contact  212  and the second contact  214 . The submount may be a printed circuit board with electrical traces or any other type of submount with corresponding electrical connections. The multiple-junction LED chip  200  further includes a first reflective layer  202  that may be on the at least one p-type layer  210  of the individual junctions  218 . The first reflective layer  202  may be any of the multiple layer reflective combinations as previously described, for example as described for the first reflective layer  56  of  FIG. 5B ,  FIG. 5C ,  FIG. 5D , and  FIG. 5E . The first reflective layer  202  is in an optical path of the multiple-junction LED chip  200 . The multiple-junction LED chip  200  may be a flip-chip LED similar to the embodiments previously described for  FIG. 8 ,  FIG. 10A ,  FIG. 10B ,  FIG. 11A , and  FIG. 11B . In other embodiments, the multiple-junction LED chip  200  may be similar to the embodiment previously described for  FIG. 12A  and  FIG. 12B . The first reflective layer  202  may be on each of the individual junctions  218  and the isolation trenches  216  may extend through the first reflective layer. In other embodiments, the first reflective layer  202  may be a continuous layer across all of the individual junctions  218  as shown by the horizontal dashed lines in  FIG. 15 . For example, the isolation trenches  216  may be formed from the substrate or the at least one n-type layer  206  toward but not through the first reflective layer  202 . 
     In other embodiments, reflective layers described herein may also provide reflectivity improvements in system level configurations. For example,  FIG. 16  is a cross-sectional representation of a portion of a lighting fixture  220  according to some embodiments. In  FIG. 16 , a lighting fixture  220  includes a light source  222 . The light source  222  may be a single light source or a plurality of light sources and may include a packaged LED, a semiconductor-based LED chip, an organic LED chip, a laser, a fluorescent light source, and an incandescent light source among others. The light source  222  is mounted or supported to a housing  224  of the light fixture  220 . A first reflective layer  226  is on the housing and may be located between the light source  222  and the housing  224  as well as in locations outside of where the light source  222  is supported by the housing  224 . In some embodiments, the first reflective layer  226  is only in locations outside of where the light source  222  is supported by the housing  224 . The first reflective layer  226  may be any of the multiple layer reflective combinations as previously described, for example as described for the first reflective layer  56  of  FIG. 5B ,  FIG. 5C ,  FIG. 5D , and  FIG. 5E . The lighting fixture  220  may further include a light-transmissive cover  228 . Accordingly, the first reflective layer  226  is in an optical path of the light source  222 . For example, light emitted by the light source  222  may be reflected by the first reflective layer  226  on the housing  224  before exiting the lighting fixture  220  through the light-transmissive cover  228 . 
     Accordingly, some embodiments described herein include a device comprising a light source and a first reflective layer in an optical path of the light source. The first reflective layer comprises a plurality of first dielectric layers and a plurality of second dielectric layers and an average thickness of the plurality of first dielectric layers is greater than an average thickness of the plurality second dielectric layers. At least one layer of the plurality of second dielectric layers comprises a thickness greater than at least one layer of the plurality of first dielectric layers. Additionally, the reflective layer may comprise any of the embodiments described above for  FIG. 5B ,  FIG. 5C ,  FIG. 5D , and  FIG. 5E . Other embodiments described herein include a device comprising a light source and a first reflective layer in an optical path of the light source. The first reflective layer comprises a plurality of first dielectric layers and a plurality of second dielectric layers wherein each layer of the plurality of first dielectric layers comprises a different thickness. A thickest layer of the plurality of first dielectric layers is between other layers of the plurality of first dielectric layers. Additionally, the reflective layer may comprise any of the embodiments described above for  FIG. 5B ,  FIG. 5C ,  FIG. 5D , and  FIG. 5E . 
     As previously described, the adhesion layer may be configured between the first reflective layer and the second reflective layer to promote adhesion between the two. Many different materials can be used for the adhesion layer, such as titanium oxide (TiO, TiO 2 ), titanium oxynitride (TiON, Ti x O y N) tantalum oxide (TaO, Ta 2 O 5 ), tantalum oxynitride (TaON), aluminum oxide (AlO, Al x O y ) or combinations thereof. In certain embodiments, it may be desirable to form the adhesion layer with a smooth surface on which the second reflective layer may be formed. If the adhesion layer included a surface with rough surface morphology, then unwanted light scattering sites may be introduced between the adhesion layer and the second reflective layer. Additionally, a rough surface morphology could negatively impact film quality of subsequently formed layers. In certain embodiments, the adhesion layer comprises aluminum oxide, such as Al x O y  or Al 2 O 3 , which may be formed by electron beam deposition to provide a dense and continuous film with smooth surfaces and without notable surface morphology. In this regard, a film of Al 2 O 3  was formed by electron beam deposition with a thickness of about 105 Å and viewed with a scanning electron microscope.  FIG. 17A  is a scanning electron microscope image of a surface of the Al 2 O 3  film with a magnification of about 10,000×. As shown, there is no notable surface morphology visible in the Al 2 O 3  film at 10,000×.  FIG. 17B  is a scanning electron microscope image of a surface of the Al 2 O 3  film from  FIG. 17A  with a magnification of about 50,000×. Again, no notable surface morphology is visible in the Al 2 O 3  film at 50,000×. In this regard, an adhesion layer comprising Al 2 O 3  that is formed by electron beam deposition may form a smooth surface on which the second reflective layer may be formed. Accordingly, an interface between the adhesion layer and the second reflective layer may have reduced scattering sites and improved layer quality. 
     In certain embodiments, it may be desirable to form the interface between the adhesion layer and the second reflective layer with a controlled morphology or grain structure. For example, a pattern or array of complete or partial openings within the adhesion layer may provide improved adhesion between the second reflective layer and the first reflective layer with reduced optical losses. In this regard,  FIG. 18A  is a cross-sectional representation that includes the adhesion layer  96  with a controlled morphology or grain structure between the first reflective layer  92  and the second reflective layer  94 . The first reflective layer  92  and the second reflective layer  94  may be configured as previously described. As illustrated, the adhesion layer  96  is configured to form a plurality of openings  96 ′ that extend between the first reflective layer  92  and the second reflective layer  94 . In particular, one or more of the openings of the plurality of openings  96 ′ extend through an entire thickness of the adhesion layer  96 . In certain embodiments, the adhesion layer  96  comprises aluminum oxide, such as Al x O y  or Al 2 O 3 , as previously described. In further embodiments, the adhesion layer  96  comprises anodic aluminum oxide (Al x O y  or Al 2 O 3 ). In order to form the adhesion layer  96  with anodic aluminum oxide, a layer of aluminum may first be formed or deposited on the first reflective layer  92 . The layer of aluminum may subsequently be subjected to an anodizing process with an electrolytic solution. During the anodizing process, the electrochemical conversion of the aluminum film to anodic aluminum oxide may form pores, nanopores, or the openings  96 ′ across the film of anodic aluminum oxide. In  FIG. 18A , the adhesion layer  96  comprises a first surface  230  that contacts the first reflective layer  92 . In certain embodiments, the adhesion layer  96  comprises anodic aluminum oxide that forms pores, nanopores, or the openings  96 ′ that extend entirely between the first reflective layer  92  and the second reflective layer  94 . In other embodiments, the adhesion layer  96  may comprise other anodic metal oxides. One or more openings of the plurality of openings  96 ′ may be at least partially filled by the second reflective layer  94 . In this regard, portions of the second reflective layer  94  may completely fill one or more openings of the plurality of openings  96 ′ and contact portions of the first reflective layer  92 . Accordingly, the surface area between the second reflective layer  94  and the adhesion layer  96  is increased, which may promote improved adhesion. Additionally, at least some light that passes through the first reflective layer  92  may be reflected by the second reflective layer  94  without passing through the adhesion layer  96 , which may reduce some optical losses. In other embodiments, the second reflective layer  94  may only partially fill the openings  96 ′, while in still further embodiments, the second reflective layer  94  may not fill the openings  96 ′.  FIG. 18B  is a bottom view of the first surface  230  of the adhesion layer  96  of  FIG. 18A  with the first reflective layer  92  removed. As shown in  FIG. 18B , the openings  96 ′ of the adhesion layer  96  may form a pattern or array across the adhesion layer  96 . As previously described, the openings  96 ′ may extend entirely through the adhesion layer  96  and accordingly, portions of the second reflective layer  94  are visible. 
       FIG. 19A  is a cross-sectional representation that includes the adhesion layer  96  with a different controlled morphology or grain structure between the first reflective layer  92  and the second reflective layer  94 . As illustrated in  FIG. 19A , the plurality of openings  96 ′ extend through less than an entire thickness of the adhesion layer  96  between the second reflective layer  94  and the first reflective layer  92 . In particular, the plurality of openings  96 ′ extend from the second reflective layer  94  toward the first reflective layer  92 . Restated, the plurality of openings  96 ′ extend through a boundary between the second reflective layer  94  and the adhesion layer  96 , but do not extend through a boundary between the adhesion layer  96  and the first reflective layer  94 . In this regard, the first surface  230  of the adhesion layer  96  may form a continuous interface with the first reflective layer  92 . As previously described, the adhesion layer  96  may comprise an anodic metal oxide, such as anodic aluminum oxide. To form the adhesion layer  96  illustrated in  FIG. 19A , the anodizing process is stopped before the pores, nanopores, or openings  96 ′ are able to extend completely through the adhesion layer  96 . In this manner, the surface area between the second reflective layer  94  and the interface between the adhesion layer  96  may be increased while continuous contact is maintained between the adhesion layer  96  and the first reflective layer  92 .  FIG. 19B  is a bottom view of the first surface  230  of the adhesion layer  96  of  FIG. 19A  with the first reflective layer  92  removed. As shown in  FIG. 19B , the first surface  230  of the adhesion layer  96  is continuous and the openings  96 ′ of  FIG. 19A  are not visible. 
     Forming the adhesion layer  96  with an anodized metal oxide as illustrated in  FIGS. 18A-19B  provides the ability to tailor the refractive index of the adhesion layer  96 . In particular, altering electrochemical conditions of the anodizing process, such as one or more of electrolyte concentrations, acidity, solution temperature, current, and anodizing time may alter the widths of the openings  96 ′. Different widths of the openings  96 ′ may provide films with different indexes of refraction. In particular, larger widths of the openings  96 ′ may increase the index of refraction of the adhesion layer  96  while smaller widths of the openings  96 ′ may decrease the index of refraction of the adhesion layer  96 . For example, in embodiments where the adhesion layer  96  comprises anodized aluminum oxide (Al x O y  or Al 2 O 3 ), tailoring the widths of the openings  96 ′ can provide a refractive index of the adhesion layer  96  in a range from about 1.4 to about 2.1. 
     As previously described, aluminum oxide films have lower extinction coefficients for wavelengths around 450 nm and are thereby less absorbing for light generated from the active LED structures.  FIG. 20  is a plot representing ellipsometry measurements for an Al 2 O 3  film. For the measurements, the Al 2 O 3  film was formed by electron beam deposition with a thickness of about 105 Å. Psi and Delta data for angles of 55°, 65°, and 75° were collected and plotted across the range of wavelengths represented by the x-axis. A model analysis of the ellipsometry data plotted in  FIG. 20  calculated an index of refraction of about 1.7 and an extinction coefficient less than about 0.001, thereby demonstrating adhesion layers that comprise aluminum oxide provide reduced absorption of light generated from active LED structures. 
     Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.