Patent Description:
Semiconductor light-emitting diodes and laser diodes (collectively referred to herein as "LEDs") are among the most efficient light sources currently available. The emission spectrum of an LED typically exhibits a single narrow peak at a wavelength determined by the structure of the device and by the composition of the semiconductor materials from which it is constructed. By suitable choice of device structure and material system, LEDs may be designed to operate at ultraviolet, visible, or infrared wavelengths.

LEDs may be combined with one or more wavelength converting materials (generally referred to herein as "phosphors") that absorb light emitted by the LED and in response emit light of a different, typically longer wavelength. For such phosphor-converted LEDs ("pcLEDs"), the fraction of the light emitted by the LED that is absorbed by the phosphors depends on the amount of phosphor material in the optical path of the light emitted by the LED, for example on the concentration of phosphor material in a phosphor layer disposed on or around the LED and the thickness of the layer.

Phosphor-converted LEDs may be designed so that all of the light emitted by the LED is absorbed by one or more phosphors, in which case the emission from the pcLED is entirely from the phosphors. In such cases the phosphor may be selected, for example, to emit light in a narrow spectral region that is not efficiently generated directly by an LED.

Alternatively, pcLEDs may be designed so that only a portion of the light emitted by the LED is absorbed by the phosphors, in which case the emission from the pcLED is a mixture of light emitted by the LED and light emitted by the phosphors. By suitable choice of LED, phosphors, and phosphor composition, such a pcLED may be designed to emit, for example, white light having a desired color temperature and desired color-rendering properties.

Multiple LEDs or pcLEDs can be formed together on a single substrate to form an array. Such arrays can be employed to form active illuminated displays, such as those employed in, e.g., smartphones and smart watches, computer or video displays, augmented- or virtual-reality displays, or signage, or to form adaptive illumination sources, such as those employed in, e.g., automotive headlights, camera flash sources, or flashlights (i.e., torches). An array having one or several or many individual devices per millimeter (e.g., device pitch of about a millimeter, a few hundred microns, or less than <NUM> microns, and spacing between adjacent devices less than <NUM> microns or only a few tens of microns or less) typically is referred to as a miniLED array or a microLED array (alternatively, a µLED array). Such mini- or microLED arrays can in many instances also include phosphor converters as described above; such arrays can be referred to as pc-miniLED or pc-microLED arrays.

<CIT> discloses a display apparatus and method of manufacturing the same. The display apparatus includes a support substrate, a driving layer and a light-emitting layer, wherein the light emitting layer comprising a first semiconductor layer, an active layer and a second semiconductor layer provided on the driving layer, whereas the second semiconductor layer includes a fine pattern structure to increase extraction efficiency.

<CIT> discloses an LED element and manufacturing method for the same. The LED element comprising a sapphire substrate and a semiconductor lamination unit, wherein the semiconductor lamination unit comprising a buffer layer, an N-type layer, including an n-side electrode, a light emitting layer, an electron blocking layer and a P-type layer, including an p-side electrode, whereas a front surface of the sapphire substrate foams a verticalized moth eye surface having a plurality of projection parts, whose period is greater than twice an optical wavelength of light emitted from the light-emitting layer and smaller than coherent length of the light.

<CIT> discloses a device for emitting radiation at a predetermined wavelength, mounted on a carrier substrate, including a cavity with an active layer generating the radiation by charge carrier recombination, whereas a light output window has a textured or roughened surface.

<CIT> discloses an LED including a substrate, first and second semiconductor layers, first and second electrical contacts and a functional stack arranged therebetween, and an internal light-transmissive surface that is patterned proximate to the semiconductor layers.

An inventive semiconductor light-emitting device includes first and second doped semiconductor layers with a junction or active layer between them, first and second sets of electrical contacts, and a set of multiple nanostructured optical elements. The first and second doped semiconductor layers that are arranged for emitting light at a nominal emission vacuum wavelength λ<NUM>; that emission results from carrier recombination at a junction or active layer between the first and second semiconductor layers. The first and second semiconductor layers and the junction or active layer are coextensive over a contiguous area of the device. The first set of one or more electrical contacts is in electrical contact with the first semiconductor layer at its surface opposite the second semiconductor layer; the second set of one or more electrical contacts is in electrical contact with the second semiconductor layer. Each electrical contact of the first set is a composite electrical contact that includes (i) a corresponding electrically conductive layer extending over a corresponding areal region of the first surface of the first semiconductor layer within the contiguous area of the device, (ii) a corresponding substantially transparent dielectric layer between the corresponding conductive layer and the first semiconductor layer, and (iii) one or more corresponding electrically conductive vias through the corresponding dielectric layer, each via providing a localized, circumscribed electrical connection between the corresponding conductive layer and the first semiconductor layer. The set of multiple nanostructured optical elements is arranged at the first surface of the first semiconductor layer with each nanostructured optical element being arranged as one or more volumes of dielectric material protruding into the corresponding dielectric layer of each composite electrical contact. The arrangement of the set of nanostructured optical element results in redirection of at least a portion of light (at the nominal emission vacuum wavelength λ<NUM>) propagating laterally in one or more selected optical modes supported by the first and second semiconductor layers to exit the device through the second semiconductor layer.

The first set of one or more electrical contacts of the inventive light-emitting device can include multiple independent composite electrical contacts. Each corresponding areal region of the first surface of the first semiconductor layer can be a discrete, circumscribed areal region separated from circumscribed areal regions of all other composite contacts of the device, so as to define a corresponding discrete pixel area of the light-emitting device. The set of multiple nanostructured optical elements can be arranged so that, of light emitted within each pixel area at the nominal emission vacuum wavelength λ<NUM> and that exits the device through the second semiconductor layer, (i) at least a specified minimum fraction of the exiting light exits from that pixel area, (ii) at most a specified maximum fraction of the exiting light exits the device from other, different pixel areas, or (iii) a contrast ratio of the fraction of light exiting from that pixel area to the fraction of light exiting one or more adjacent pixel areas exceeds a specified minimum contrast ratio.

The inventive light-emitting device can further include a drive circuit connected to the first and second sets of contacts by the electrically conductive traces or interconnects. The drive circuit can provide electrical drive current that flows through the device and causes the device to emit light, with corresponding portions of the electrical drive current flowing through one or more pixel areas of the device as corresponding pixel currents. Each pixel current magnitude can differ from at least one other pixel current magnitude, or from any other pixel current magnitude. The drive circuit can provide one or more specified spatial distributions across the device of the pixel current magnitudes provided to the corresponding pixel areas of the device. In such examples the spatial distribution of light emission intensity varies across the device according to the arrangement of the pixel areas across the device and the specified distribution among the pixel areas of the pixel current magnitudes provided by the drive circuit.

Objects and advantages pertaining to LEDs, pcLEDs, miniLED arrays, pc-miniLED arrays, microLED arrays, and pc-microLED arrays may become apparent upon referring to the examples illustrated in the drawings and disclosed in the following written description or appended claims.

The examples depicted are shown only schematically; all features may not be shown in full detail or in proper proportion; for clarity certain features or structures may be exaggerated or diminished relative to others or omitted entirely; the drawings should not be regarded as being to scale unless explicitly indicated as being to scale. For example, individual LEDs may be exaggerated in their vertical dimensions or layer thicknesses relative to their lateral extent or relative to substrate or phosphor thicknesses. "Vertical" and "lateral" directions are defined only relative to a substrate or a layer structure, with "vertical" being perpendicular to the substrate or layers and "lateral" being parallel to them; they do not indicate any absolute direction in space or relative to any surrounding structure. "Transverse" is defined only relative to a light propagation direction, and so can be either vertical or lateral for laterally propagating light. Note that when a first structure or layer is described as "on" another, that encompasses arrangements with or without one or more intervening structures or layers. One structure or layer described as "directly on" another indicates that there is no intervening layer or structure. Any units or scales of any graphs or plots are arbitrary unless specifically indicated otherwise. The examples shown should not be construed as limiting the scope of the present disclosure or appended claims.

The following detailed description should be read with reference to the drawings, in which identical reference numbers refer to like elements throughout the different figures. The drawings, which are not necessarily to scale, depict selective examples and are not intended to limit the scope of the invention.

<FIG> shows an example of an individual pcLED <NUM> comprising a semiconductor diode structure <NUM> disposed on a substrate <NUM>, together considered herein an "LED" or "semiconductor LED", and a wavelength converting structure (e.g., phosphor layer) <NUM> disposed on the semiconductor LED. Semiconductor diode structure <NUM> typically comprises an active region disposed between n-type and p-type layers. Application of a suitable forward bias across the diode structure <NUM> results in emission of light from the active region. The wavelength of the emitted light is determined by the composition and structure of the active region.

The LED may be, for example, a III-Nitride LED that emits blue, violet, or ultraviolet light. LEDs formed from any other suitable material system and that emit any other suitable wavelength of light may also be used. Suitable material systems may include, for example, various III-Nitride materials, various III-Phosphide materials, various III-Arsenide materials, and various II-VI materials.

Any suitable phosphor materials may be used for or incorporated into the wavelength converting structure <NUM>, depending on the desired optical output from the pcLED.

<FIG> show, respectively, cross-sectional and top views of an array <NUM> of pcLEDs <NUM>, each including a phosphor pixel <NUM>, disposed on a substrate <NUM>. Such an array may include any suitable number of pcLEDs arranged in any suitable manner. In the illustrated example the array is depicted as formed monolithically on a shared substrate, but alternatively an array of pcLEDs may be formed from separate individual pcLEDs. Substrate <NUM> may optionally include electrical traces or interconnects, or CMOS or other circuitry for driving the LED, and may be formed from any suitable materials.

Individual pcLEDs <NUM> may optionally incorporate or be arranged in combination with a lens or other optical element located adjacent to or disposed on the phosphor layer. Such an optical element, not shown in the figures, may be referred to as a "primary optical element". In addition, as shown in <FIG>, a pcLED array <NUM> (for example, mounted on an electronics board) may be arranged in combination with secondary optical elements such as waveguides, lenses, or both for use in an intended application. In <FIG>, light emitted by each pcLED <NUM> of the array <NUM> is collected by a corresponding waveguide <NUM> and directed to a projection lens <NUM>. Projection lens <NUM> may be a Fresnel lens, for example. This arrangement may be suitable for use, for example, in automobile headlights. In <FIG>, light emitted by pcLEDs of the array <NUM> is collected directly by projection lens <NUM> without use of intervening waveguides. This arrangement may particularly be suitable when pcLEDs can be spaced sufficiently close to each other, and may also be used in automobile headlights as well as in camera flash applications. A miniLED or microLED display application may use similar optical arrangements to those depicted in <FIG>, for example. Generally, any suitable arrangement of optical elements may be used in combination with the pcLEDs described herein, depending on the desired application.

Although <FIG> show a 3x3 array of nine pcLEDs, such arrays may include for example on the order of <NUM><NUM>, <NUM><NUM>, <NUM><NUM>, <NUM><NUM>, or more LEDs, e.g., as illustrated schematically in <FIG>. Individual LEDs <NUM> (i.e., pixels) may have widths w<NUM> (e.g., side lengths) in the plane of the array <NUM>, for example, less than or equal to <NUM> millimeter (mm), less than or equal to <NUM> microns, less than or equal to <NUM> microns, or less than or equal to <NUM> microns. LEDs <NUM> in the array <NUM> may be spaced apart from each other by streets, lanes, or trenches <NUM> having a width w<NUM> in the plane of the array <NUM> of, for example, hundreds of microns, less than or equal to <NUM> microns, less than or equal to <NUM> microns, less than or equal to <NUM> microns, less than or equal to <NUM> microns, or less than or equal to <NUM> microns. The pixel pitch D<NUM> is the sum of w<NUM> and w<NUM>. Although the illustrated examples show rectangular pixels arranged in a symmetric matrix, the pixels and the array may have any suitable shape or arrangement, whether symmetric or asymmetric. Multiple separate arrays of LEDs can be combined in any suitable arrangement in any applicable format to form a larger combined array or display.

LEDs having dimensions w<NUM> in the plane of the array (e.g., side lengths) of less than or equal to about <NUM> millimeters microns are typically referred to as microLEDs, and an array of such microLEDs may be referred to as a microLED array. LEDs having dimensions w<NUM> in the plane of the array (e.g., side lengths) of between about <NUM> millimeters and about <NUM> millimeters are typically referred to as miniLEDs, and an array of such miniLEDs may be referred to as a miniLED array.

An array of LEDs, miniLEDs, or microLEDs, or portions of such an array, may be formed as a segmented monolithic structure in which individual LED pixels are electrically isolated from each other by trenches and or insulating material. <FIG> shows a perspective view of an example of such a segmented monolithic LED array <NUM>. Pixels in this array (i.e., individual semiconductor LED devices <NUM>) are separated by trenches <NUM> which are filled to form n-contacts <NUM>. The monolithic structure is grown or disposed on the substrate <NUM>. Each pixel includes a p-contact <NUM>, a p-GaN semiconductor layer 102b, an active region 102a, and an n-GaN semiconductor layer 102c; the layers 102a/102b/102c collectively form the semiconductor LED <NUM>. A wavelength converter material <NUM> may be deposited on the semiconductor layer 102c (or other applicable intervening layer). Passivation layers <NUM> may be formed within the trenches <NUM> to separate at least a portion of the n-contacts <NUM> from one or more layers of the semiconductor. The n-contacts <NUM>, other material within the trenches <NUM>, or material different from material within the trenches <NUM> may extend into the converter material <NUM> to form complete or partial optical isolation barriers <NUM> between the pixels.

<FIG> is a schematic cross-sectional view of a close packed array <NUM> of multi-colored, phosphor converted LEDs <NUM> on a monolithic die and substrate <NUM>. The side view shows GaN LEDs <NUM> attached to the substrate <NUM> through metal interconnects <NUM> (e.g., gold-gold interconnects or solder attached to copper micropillars) and metal interconnects <NUM>. Phosphor pixels <NUM> are positioned on or over corresponding GaN LED pixels <NUM>. The semiconductor LED pixels <NUM> or phosphor pixels <NUM> (often both) can be coated on their sides with a reflective mirror or diffusive scattering layer to form an optical isolation barrier <NUM>. In this example each phosphor pixel <NUM> is one of three different colors, e.g., red phosphor pixels 106R, green phosphor pixels <NUM>, and blue phosphor pixels 106B (still referred to generally or collectively as phosphor pixels <NUM>). Such an arrangement can enable use of the LED array <NUM> as a color display.

The individual LEDs (pixels) in an LED array may be individually addressable, may be addressable as part of a group or subset of the pixels in the array, or may not be addressable. Thus, light-emitting pixel arrays are useful for any application requiring or benefiting from fine-grained intensity, spatial, and temporal control of light distribution. These applications may include, but are not limited to, precise special patterning of emitted light from pixel blocks or individual pixels, in some instances including the formation of images as a display device. Depending on the application, emitted light may be spectrally distinct, adaptive over time, and/or environmentally responsive. The light-emitting pixel arrays may provide preprogrammed light distribution in various intensity, spatial, or temporal patterns. The emitted light may be based at least in part on received sensor data and may be used for optical wireless communications. Associated electronics and optics may be distinct at a pixel, pixel block, or device level.

<FIG> are examples of LED arrays <NUM> employed in display applications, wherein an LED display includes a multitude of display pixels. In some examples (e.g., as in <FIG>), each display pixel comprises a single semiconductor LED pixel <NUM> and a corresponding phosphor pixel 106R, <NUM>, or 106B of a single color (red, green, or blue). Each display pixel only provides one of the three colors. In some examples (e.g., as in <FIG>), each display pixel includes multiple semiconductor LED pixels <NUM> and multiple corresponding phosphor pixels <NUM> of multiple colors. In the example shown each display pixel includes a 3X3 array of semiconductor pixels <NUM>; three of those LED pixels have red phosphor pixels 106R, three have green phosphor pixels <NUM>, and three have blue phosphor pixels 106B. Each display pixel can therefore produce any desired color combination. In the example shown the spatial arrangement of the different colored phosphor pixels <NUM> differs among the display pixels; in some examples (not shown) each display pixel can have the same arrangement of the different colored phosphor pixels <NUM>.

As shown in <FIG>, a pcLED array <NUM> may be mounted on an electronics board <NUM> comprising a power and control module <NUM>, a sensor module <NUM>, and an LED attach region <NUM>. Power and control module <NUM> may receive power and control signals from external sources and signals from sensor module <NUM>, based on which power and control module <NUM> controls operation of the LEDs. Sensor module <NUM> may receive signals from any suitable sensors, for example from temperature or light sensors. Alternatively, pcLED array <NUM> may be mounted on a separate board (not shown) from the power and control module and the sensor module.

In many previous examples (including some of those shown above), multiple individual LED devices <NUM> are formed monolithically on a common layered semiconductor structure by etching trenches to form mesa-like structures separated by the trenches (e.g., as in <FIG>). Each mesa forms a separate LED device or pixel <NUM>, with the trenches extending through at least one (and sometimes both) of the doped semiconductor layers and the junction or active layer between them. In the example of <FIG>, trenches extend entirely through the p-type semiconductor layer 102b and the active layer 102a, but only partly through the n-type semiconductor layer 102c. In this common arrangement the partly etched layer 102c holds the multiple LED devices <NUM> together in a monolithically integrated array <NUM>. Drive current can be directed through each mesa independently of the others, laterally confined by the surrounding trench walls, so that the corresponding pixel <NUM> is independently addressable. However, as pixel sizes or spacings get smaller, a number of factors limit light output from each pixel, contrast between adjacent pixels <NUM>, or both.

One such factor is decreased internal quantum efficiency of light emission due to non-radiative carrier recombination at defect sites at the etched sidewalls. Such defects are an unavoidable byproduct of the etch process, and their relative importance increases with decreasing pixel size; as transverse pixel size decreases, sidewall perimeter decreases linearly while emission area decreases quadratically. For pixel sizes greater than, e.g., <NUM> or <NUM> across, the effect of recombination at sidewall defects is relatively unimportant, or at least tolerable. As pixel size shrinks to <NUM>, <NUM>, or even less, a greater fraction of overall carrier recombination is non-radiative recombination at the sidewalls, and internal quantum efficiency suffers accordingly.

Another factor is increasingly difficult light extraction as pixel size decreases. A common method for increasing light extraction from a semiconductor LED is to provide texturing of the light-exit surface of the device. Such texturing can be formed by growing the semiconductor layers on a substrate having corrugations or other similar surface structural features, or by depositing a layer of scattering particles on the light-exit surface. However, the resulting structures typically have feature sizes of at least several microns or several tens of microns, and so cannot be readily implemented on an LED pixel that is too small, e.g., less than <NUM> or <NUM> across. Even if structurally realizable at such small pixel sizes, such light-extraction surface features would severely degrade contrast between adjacent pixels. The common arrangement of <FIG>, with inter-pixel trenches extending only partly through one of the semiconductor layers, also permits light emitted from one pixel <NUM> to propagate into end exit the array from a different pixel <NUM>, as indicated by some of the heavy arrows in <FIG>.

Accordingly, it would be desirable to provide a light-emitting device that exhibits adequate, desirable, or improved levels of internal quantum efficiency or light extraction. It would be desirable to provide a monolithic array of LED pixels, including arrays having pixels sizes less than <NUM>, <NUM>, or even <NUM>, while maintaining such levels of internal quantum efficiency or light extraction, or adequate, desirable, or improved levels of pixel contrast.

Examples of inventive light-emitting devices <NUM> are illustrated schematically in <FIG> and <FIG>. Each includes first and second doped semiconductor layers <NUM> and <NUM> with a junction or active layer <NUM> between them, first and second sets of electrical contacts <NUM> and <NUM>, and a set of multiple nanostructured optical elements <NUM>. The first and second doped semiconductor layers <NUM> and <NUM> are arranged for emitting light at a nominal emission vacuum wavelength λ<NUM> that results from carrier recombination at the junction or active layer <NUM>. The first and second semiconductor layers <NUM> and <NUM>, as well as the junction or active layer <NUM>, are coextensive over a contiguous area of the device <NUM>, i.e., not divided by any trench within that contiguous area. In some examples each of the semiconductor layers <NUM> and <NUM> can include one or more III-V semiconductor materials, or alloys, derivatives, or mixtures thereof. In some common examples various doped GaN-type materials can be employed, or various derivatives or alloys thereof; in some other common examples various doped GaAs-type or InP-type materials, or various derivatives or alloys thereof, can be employed. In many common examples the device <NUM> includes one or more quantum wells or multi-quantum wells as the active layer <NUM> between the semiconductor layers <NUM>. Such active layers can be tuned to emit light at a selected nominal emission vacuum wavelength λ<NUM> (e.g., emission typically in a band perhaps <NUM> to <NUM> wide that includes λ<NUM>). The nominal emission vacuum wavelength typically can be in the near-UV, visible, or near-IR portions of the electromagnetic spectrum, e.g., between about <NUM> and about <NUM>, between about <NUM> and about <NUM>, or between about <NUM> and about <NUM>.

The one or more electrical contacts <NUM> of the first set are in electrical contact with the first semiconductor layer <NUM> at its first surface opposite the second semiconductor layer <NUM> (meaning that the semiconductor layer <NUM> is between the contacts <NUM> and the semiconductor layer <NUM>). As a result of that arrangement, light emitted by the device <NUM> mostly exits through the second semiconductor layer <NUM>. Each of the electrical contacts <NUM> is a composite electrical contact that includes a corresponding electrically conductive layer <NUM>, a corresponding substantially transparent dielectric layer <NUM> between the corresponding conductive layer <NUM> and the first semiconductor layer <NUM>, and one or more corresponding electrically conductive vias <NUM>. "Substantially transparent" in this context indicates that, over at least the range of wavelengths of the emitted light that includes λ<NUM>, a fraction of light is transmitted that is sufficiently large for the light-emitting device <NUM> to function as needed, intended, or desired. Each contact <NUM> extends over a corresponding areal region of the first surface of the first semiconductor layer <NUM> within the contiguous area of the device <NUM>. Each via <NUM> extends through the corresponding dielectric layer <NUM> and provides a localized, circumscribed electrical connection between the corresponding conductive layer <NUM> and the first semiconductor layer <NUM>. In some examples the electrically conductive layer <NUM> or the vias <NUM>, or both, of each composite contact <NUM> can include one or more metals or metal alloys. In some examples the dielectric layer <NUM> of each composite contact <NUM> can include doped or undoped silica, one or more doped or undoped metal or semiconductor oxides, nitrides, or oxynitrides, or combinations or mixtures thereof. The composite contacts <NUM> can and typically do act as optical reflectors that redirect incident light to propagate generally toward the second semiconductor layer <NUM> and an exit surface of the device <NUM>.

In some examples, the vias <NUM> connect the conductive layers <NUM> directly to the first semiconductor layer <NUM>, and the dielectric layers <NUM> are in direct contact with the semiconductor <NUM>. In other examples, each composite electrical contact <NUM> further includes a corresponding substantially transparent electrode layer <NUM> between the corresponding dielectric layer <NUM> and the first semiconductor layer <NUM>; the electrode <NUM> is in direct contact with the semiconductor layer <NUM>. In such examples each via <NUM> provides an electrical connection between the corresponding conductive layer <NUM> and the first semiconductor layer <NUM> by providing an electrical connection between the corresponding conductive layer <NUM> and the corresponding electrode layer <NUM>. Suitable materials for forming the electrode layer <NUM> can include one or more of indium tin oxide, indium zinc oxide, one or more other transparent conductive oxides, or combinations or mixtures thereof.

The second set of one or more electrical contacts <NUM> is in electrical contact with the second semiconductor layer <NUM>, and can be of any suitable type or arrangement. In some examples the contacts <NUM> can include any one or more of, e.g., (i) one or more substantially transparent electrodes at the surface of the second semiconductor layer <NUM> opposite the first semiconductor layer <NUM> (i.e., at the exit surface of the device <NUM>), (ii) one or more secondary vias (not shown) passing through and electrically insulated from the first semiconductor layer <NUM> and the junction or active layer <NUM>, (iii) one or more edge contacts, or (iv) one or more peripheral areal contacts.

Light emitted at the junction or active layer <NUM> can propagate generally toward the exit surface of the device <NUM> or generally toward the contacts <NUM> to be reflected generally toward the exit surface of the device <NUM> (as indicated by some of the heavy arrows in <FIG> and <FIG>), or can propagate laterally within the semiconductor layers <NUM> and <NUM> (as indicated by the lighter arrows in <FIG> and <FIG>). The semiconductor layers <NUM> and <NUM> can act as a waveguide supporting optical modes confined vertically (i.e., in a direction perpendicular to the layers <NUM> and <NUM>) in which light can propagate laterally (i.e., parallel to the layers <NUM> and <NUM>). Light propagating laterally in such supported modes is undesirable because it represents lost emission intensity, and because it can propagate into adjacent pixels of a light-emitting array and degrade pixel contrast. The multiple nanostructured optical elements <NUM> are positioned at the first surface of the first conductive layer <NUM> (e.g., as in <FIG>) or at the device exit surface (e.g., as in <FIG>, with the surface of the second semiconductor layer <NUM> opposite the first semiconductor layer <NUM> acting as the exit surface). The nanostructured optical elements <NUM> are arranged to redirect at least a portion of light (at the nominal emission vacuum wavelength λ<NUM>), that propagates laterally in one or more of the supported optical modes, to exit the device <NUM> through the second semiconductor layer <NUM> and the device exit surface (as indicated by some of the heavy arrows in <FIG> and <FIG>).

Thickness of the dielectric layers <NUM> is typically sufficiently large so as to reduce spatial overlap of the laterally propagating modes with the conductive layer <NUM>, to reduce or eliminate absorption loss due to that layer. In some examples thickness of the dielectric layer <NUM> can be greater than <NUM>, greater than <NUM>, greater than <NUM>, or greater than <NUM>, in some examples thickness of the dielectric layer can be about <NUM>.

For purposes of this disclosure, those propagating optical modes supported by the semiconductor layer structure of the device <NUM> that have qualitatively similar vertical intensity profiles (e.g., same numbers of peaks and nodes), regardless of lateral propagation direction or lateral intensity profile, shall be referred to collectively as only one mode among the supported optical modes. Typical conventional light-emitting devices typically have semiconductor layers, with a junction or active layer between them, having a total thickness greater than <NUM>, <NUM>, <NUM>, or even larger. Such thick semiconductor structures can in some instances support more than <NUM>, more than <NUM>, or even more propagating optical modes. With light propagating in so many different optical modes in a conventional, relatively thick light-emitting device, achieving efficient redirection using nanostructured optical elements is problematic. Typically the size, shape, and arrangement of such nanostructured elements can be optimized simultaneously for only a few optical modes (e.g., <NUM> or fewer). If too many different modes are present, there is an inherent limit to the fraction of laterally propagating light that can be redirected to exit the device, because a significant fraction of that light propagates in optical modes that are not efficiently redirected by the nanostructured optical elements.

Accordingly, in some examples of the inventive light-emitting device <NUM>, the total thickness of the semiconductor layers <NUM> and <NUM>, and the junction or active layer <NUM> between them, can be reduced to reduce the number of different laterally propagating modes supported by the semiconductor layer structure of the light-emitting device <NUM>. In some examples the semiconductor layer structure can support at most <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> laterally propagating optical modes. To achieve that, in some examples the non-zero total thickness of the first and second semiconductor layers <NUM> and <NUM>, and the junction or active layer <NUM> between them, can be less than about <NUM>, less than about <NUM>, less than about <NUM>, less than about <NUM>, or less than about <NUM>. With the number of supported optical modes thus reduced, the nanostructured optical elements <NUM> can be optimized for redirecting light propagating in the correspondingly reduced number of optical modes, so that a higher overall fraction of laterally propagating light can be redirected to exit the device <NUM>. <FIG> shows plots of calculated extraction efficiency for two different devices <NUM> with nanostructured optical elements <NUM> and total thickness of the semiconductor layers <NUM> and <NUM> and the junction or active layer <NUM> of <NUM> and <NUM> compared to a reference device having an overall thickness of <NUM> and no elements <NUM>. Extraction efficiency is plotted as a function of thickness of the semiconductor layer <NUM> (discussed further below), and shows significant enhancement of extraction efficiency for the thinner devices <NUM>.

In addition to increasing extraction efficiency (and therefore overall emission efficiency), the reduction in the number of laterally propagating modes also enables at least some degree of optimization of the nanostructured optical elements <NUM> to achieve, or at least approximate, a desired distribution of propagation directions for light exiting the device <NUM> (e.g., to achieve an angular distribution narrower than a Lambertian distribution typical of many conventional light-emitting devices). In some examples an angular distribution of emission intensity can be generated that is narrower than, e.g., a commonly occurring Lambertian distribution. Typically, a narrower or more well-defined angular distribution of emission can be obtained as thickness of the semiconductor layer structure of the light-emitting device <NUM> decreases and fewer laterally propagating optical modes are supported.

Overall efficiency of emission can also be increased by selection of a thickness of the first semiconductor layer <NUM>. A resonator-like structure is formed by the composite contacts <NUM> (acting as a backside reflector) and the semiconductor layers <NUM> and <NUM> with the junction or active layer <NUM> between them. Proper tuning of the position of the junction or active layer <NUM> within that resonator-like structure, by selection of the relative thicknesses of the layers <NUM> and <NUM>, can result in enhancement of the device's Purcell factor and a concomitant increase in the internal quantum efficiency of the device <NUM> (i.e., fraction of injected charge carriers converted to photons emitted at the junction or active layer <NUM>). Calculated Purcell factors are plotted in <FIG> for the same three devices as in <FIG> as a function of thickness of the semiconductor layer <NUM>. A product of the calculated extraction efficiency and calculated Purcell factor are plotted in <FIG>, and show clear enhancement of overall emission efficiency for the inventive device <NUM> with reduced thickness of the semiconductor layer structure and the nanostructured optical elements <NUM>. In some examples of an inventive device <NUM>, non-zero thickness of the semiconductor layer <NUM> can be less than about <NUM>, less than about <NUM>, less than about <NUM>, or less than about <NUM>, and can be selected to result in an adequate, desirable, or improved extraction efficiency, internal quantum efficiency, Purcell factor, or overall emission efficiency. In some examples the semiconductor layer <NUM> can be a p-doped semiconductor layer while the semiconductor layer <NUM> can be an n-doped semiconductor layer.

Although <FIG> and <FIG> show multiple discrete contacts <NUM>, the inventive arrangements and advantages thereof described above are applicable to a single, contiguous light-emitting device <NUM> for providing improved or enhanced emission efficiency or directionality of emission. However, when implemented as shown in <FIG> and <FIG> to form an array of independent light-emitting pixels on the device <NUM>, additional advantages can be realized. In some examples of an inventive light-emitting device <NUM>, the electrical contacts <NUM> can include multiple independent composite electrical contacts <NUM>. "Independent" here indicates that there is no direct electrically conductive path between different composite contacts <NUM>; the only connections between different contacts <NUM> in such examples are indirect, e.g., by two different contacts <NUM> both being connected to the semiconductor layer <NUM>, or by both being connected to a common drive circuit <NUM> by separate traces or interconnects <NUM>. In some examples each composite contact <NUM> can be connected to a single corresponding one of the traces or interconnects <NUM> that is different from a corresponding trace or interconnect <NUM> connected to at least one other composite contact <NUM> (i.e., there are at least two independent groups of contacts <NUM>). In some examples each composite contact <NUM> can be connected to a single corresponding one of the traces or interconnects <NUM> that is different from a corresponding trace or interconnect <NUM> connected to any other composite contact <NUM> (i.e., every contact <NUM> is independent of every other contact <NUM>).

Each independent contact <NUM> is positioned on a corresponding areal region of the semiconductor layer <NUM> (i.e., a contact area) that is a discrete, circumscribed areal region separated from circumscribed areal regions of all other composite contacts <NUM> by gaps between the contacts <NUM>. Each contact area defines a corresponding discrete pixel area of the inventive light-emitting device <NUM>; the pixel area typically can be somewhat larger than the corresponding contact area due to lateral spreading of current flowing from the electrode <NUM> to the junction or active layer <NUM> through the semiconductor layer <NUM> and lateral propagation of emitted output light. Although <FIG> and <FIG> show only three contacts <NUM> defining three corresponding pixel areas, an inventive light-emitting device <NUM> can include any suitable number or arrangement of contacts <NUM> defining corresponding pixel areas of the device, for example on the order of <NUM><NUM>, <NUM><NUM>, <NUM><NUM>, <NUM><NUM>, or more contacts <NUM>. Corresponding conductive layers <NUM> of adjacent contacts <NUM> can be separated from one another by vacuum, air, or inert gas, or by a liquid or solid electrically insulating material in the gaps between them, so that direct electrical conduction between adjacent composite contacts <NUM> is substantially prevented. If the contacts <NUM> include corresponding transparent electrode layers <NUM>, those too can be separated from one another by vacuum, air, inert gas, or by a liquid or solid electrically insulating material.

Emitted light propagating laterally in one or more optical modes could potentially propagate from a pixel area where it was emitted to a different pixel area. If such emitted light were to exit the device <NUM> from that different pixel area, pixel contrast ratio of the device <NUM> would be degraded. The set of multiple nanostructured optical elements <NUM> can be arranged so that, of the light that is emitted within each pixel area at the nominal emission vacuum wavelength λ<NUM> and that exits the device <NUM> through the semiconductor layer <NUM>, (i) at least a specified minimum fraction of the exiting light exits from that pixel area where it was emitted, (ii) at most a specified maximum fraction of the exiting light exits the device from other, different pixel areas, or (iii) a contrast ratio of the fraction of light exiting from the emitting pixel area to the fraction of light exiting one or more adjacent pixel areas exceeds a specified minimum contrast ratio.

So in addition to enhancing overall extraction efficiency from the device <NUM>, the nanostructured optical elements <NUM> can be arranged to also provide redirection of laterally propagating light emitted in the given pixel area to exit the device <NUM> from that pixel area, thereby providing contrast between adjacent pixel areas even without any trenches or other structures separating corresponding areas of the semiconductor layer <NUM>, the junction or active layer <NUM>, or the semiconductor layer <NUM>. As noted above, such trenches, typically formed by etching, unavoidably include defect sites that result in non-radiative carrier recombination and concomitant decrease of internal quantum efficiency. The fraction of drive current lost to such non-radiative recombination increases with decreasing pixel area, which decreases quadratically while the pixel perimeter (where etch defects are located) decreases only linearly. Defining distinct, discrete pixel areas using discrete contacts <NUM> and the nanostructured optical elements <NUM>, while the semiconductor layers <NUM> and <NUM>, and the junction or active layer <NUM> between them, remain coextensive over a contiguous area of the device <NUM>, eliminates that source of non-radiative recombination. In addition, fabrication of light-emitting devices <NUM> can be simpler, less expensive, and higher-yield when fabrication steps related to forming inter-pixel trenches are omitted.

In some examples, each electrode area can have a non-zero transverse size (i.e., largest transverse dimension, e.g., longest side of a rectangular or triangular contact, diameter of a circular contact, major axis of an elliptical contact, and so forth) that is less than about <NUM>, less than about <NUM>, less than about <NUM>, less than about <NUM>, less than about <NUM>, less than about <NUM>, or less than about <NUM>. In some examples, non-zero separation between adjacent composite electrical contacts <NUM> can be less than about <NUM>, less than about <NUM>, less than about <NUM>, less than about <NUM>, less than about <NUM>, less than about <NUM>, or less than about <NUM>. In some examples, particularly for smaller contacts <NUM>, the separation between adjacent contacts <NUM> can be about equal to their transverse size. There is no minimum required separation between adjacent contacts <NUM>, except that the separation must be sufficiently large so that there is no direct electrical contact between adjacent, independent contacts <NUM>.

The reduced overall thickness of the semiconductor layers <NUM> and <NUM> and the junction or active layer <NUM> between them, as noted above, reduces the number of laterally propagating optical modes supported by the semiconductor layer structure of the device <NUM>, so that the nanostructured optical elements <NUM> can be more effectively optimized for redirecting such laterally propagating light to exit the device <NUM> through the semiconductor layer <NUM>. In addition to increased extraction efficiency as described above, that more effective optimization also reduces or substantially eliminates lateral propagation of emitted light into adjacent pixel areas. Because any light that does reach a different pixel area necessarily was not very efficiently redirected by the nanostructured optical elements <NUM> within the emitting pixel area, it is also unlikely to be so redirected in any other pixel area, and so is less likely to degrade contrast between pixel areas.

In some examples, arrangement of the multiple nanostructured optical elements <NUM> can result in at least the specified minimum fraction of light emitted within each pixel area exiting the device <NUM> from that pixel area. In some of those examples, the specified minimum fraction can be greater than about <NUM>%, greater than about <NUM>%, greater than about <NUM>%, greater than about <NUM>%, greater than about <NUM>%, or greater than about <NUM>%. In some examples, arrangement of the multiple nanostructured optical elements <NUM> can result in at most the specified maximum fraction of light emitted within each pixel area exiting the device <NUM> from other, different pixel areas. In some of those examples, the specified maximum fraction can be less than about <NUM>%, less than about <NUM>%, less than about <NUM>%, less than about <NUM>%, less than about <NUM>%, or less than about <NUM>%. In some examples, arrangement of the multiple nanostructured optical elements <NUM> can result in the contrast ratio of the fraction of light exiting from that pixel area where it was emitted to the fraction of that light exiting one or more adjacent pixels areas exceeds the specified minimum contrast ratio. In some of those examples, the specified minimum contrast ratio is greater than about <NUM>:<NUM>, greater than about <NUM>:<NUM>, greater than about <NUM>:<NUM>, greater than about <NUM>:<NUM>, or greater than about <NUM>:<NUM>.

Reduced thickness of the semiconductor layer structure of the device <NUM> can enhance contrast between adjacent pixel areas in other ways. Decreased thickness of the semiconductor layer <NUM> results in less lateral spread of drive current injected via the contacts <NUM> before reaching the junction or active layer <NUM>. As a result, leakage of current injected in one pixel area is less likely to result in radiative recombination and light emission from an adjacent pixel area. The generally lower conductivity of a p-type semiconductor layer <NUM> can enhance that effect. In addition, light propagating generally toward the contact <NUM> or the exit surface of the device <NUM>, but off normal, travels a smaller lateral distance before encountering a surface (reflective or transmissive), and is therefore more likely to exit the device <NUM> within or near the pixel area from which it was emitted, compared to a device with thicker semiconductor layers.

In some examples (with or without discrete pixel areas), the set of multiple nanostructured optical elements <NUM> can be positioned at the first surface of the semiconductor layer <NUM>, i.e., near the contacts <NUM> (e.g., as in <FIG>). Each nanostructured optical element <NUM> in such examples can be arranged as one or more volumes of dielectric material protruding into the semiconductor layer <NUM> or into the corresponding dielectric layer <NUM> of each composite electrical contact <NUM> (e.g., as in <FIG>). In some examples the set of multiple nanostructured optical elements <NUM> can be positioned at the surface of the semiconductor layer <NUM> opposite the semiconductor layer <NUM>, i.e., at the exit surface of the device <NUM> (e.g., as in <FIG>). Each nanostructured optical element <NUM> in such examples can be arranged as one or more volumes of dielectric material protruding into the semiconductor layer <NUM> or into a dielectric layer or medium on the surface of the semiconductor layer <NUM>. In some examples, corresponding arrays of nanostructured optical elements <NUM> can be positioned at both of those locations. The nanostructured optical elements <NUM> can be characterized by an element size relative to the nominal emission vacuum wavelength λ<NUM> and by an element shape, and the set of multiple nanostructured optical elements <NUM> can be arranged as an array of elements characterized by at least one element spacing relative to the nominal emission vacuum wavelength λ<NUM>. The at least one element spacing can be sub-wavelength or larger than the nominal vacuum wavelength λ<NUM>. The element size and shape and the at least one element spacing are selected so as to result in the redirection of laterally propagating emitted light at the nominal emission vacuum wavelength λ<NUM> so that a fraction of that light exits the device through the second semiconductor layer.

In some examples the nanostructured optical elements <NUM> can include doped or undoped silica, one or more doped or undoped metal or semiconductor oxides, nitrides, or oxynitrides, or combinations or mixtures thereof. In some examples, the nanostructured optical elements <NUM> can be formed as voids in the dielectric layer <NUM>, semiconductor layer <NUM>, or semiconductor layer <NUM>. In some examples the dielectric material of the nanostructured optical elements <NUM> can differ, with respect to refractive index, from the corresponding dielectric layer <NUM> of each composite electrical contact, or from a dielectric layer or medium on the surface of the semiconductor layer <NUM>. That need not be the case in examples wherein the nanostructured optical elements <NUM> extend into the semiconductor layer <NUM> or <NUM>. In some examples the nanostructured optical elements are characterized by an element height between about <NUM> and about <NUM> or an element width between about <NUM> and about <NUM>. In some examples the element shape can include one or more of: right or oblique, circular or elliptical cylindrical (e.g., as in <FIG>); right or oblique conical or frusto-conical (e.g., as in <FIG>); right or oblique pyramidal or frusto-pyramidal; right or oblique polygonal prismatic; polyhedral; or vertical, horizontal, or coaxial dimers (e.g., as in <FIG>). In some examples, at least one element spacing is between about <NUM> and about <NUM>, or between about <NUM> and about <NUM>. In some examples, the set of nanostructured optical elements <NUM> can be arranged as a trigonal, rectangular, or hexagonal grid or in an aperiodic, irregular, or random arrangement. The example shown in <FIG> includes right circular cylindrical elements <NUM> in a regular hexagonal grid arrangement; other suitable shapes and arrangements of elements <NUM> can be employed.

Typically, calculation or computer simulation is required to achieve at least a preliminary design for the set of nanostructured optical elements <NUM>; in some instances, a final design can be achieved by iterative experimental optimization of the various parameters by fabricating and characterizing test devices. Note that a set of nanostructured optical elements <NUM> that is not necessarily fully optimized can nevertheless provide an adequate level of redirection to provide the desired behavior of the light-emitting device <NUM>. Such partly optimized sets of elements <NUM> fall within the scope of the present disclosure or appended claims. Examples of suitable nanostructured optical elements <NUM> can be found in, e.g., (i) <CIT>, (ii) <CIT>, (iii) <NPL>), (iv) <NPL>), (v) <NPL>), and (vi) <NPL>).

In some examples, the exit surface of the light-emitting device <NUM> can include an anti-reflection coating on the surface of the semiconductor layer <NUM> opposite the semiconductor layer <NUM>. Any suitable anti-reflection coating can be employed, e.g., a single quarter-wave layer, a multilayer dielectric stack, a so-called moth's-eye structure, and so forth.

An inventive light-emitting device <NUM> can be connected to a drive circuit <NUM> connected to the first and second sets of contacts <NUM>/<NUM> by corresponding electrical traces or interconnects <NUM>. The traces or interconnects <NUM> that connect independent contacts <NUM> to the drive circuit <NUM> are themselves also independent of one another ("independent" as defined above). Note that in some examples multiple contacts <NUM> can be connected to a single, common trace or interconnect <NUM>; in such an instance those commonly connected contacts <NUM> act collectively as a single contact, that is independent of other contacts <NUM> not connected to the same trace <NUM>. Perhaps more typically, in some examples each contact <NUM> and its corresponding pixel area can be connected to a trace or interconnect <NUM> that is independent of all others, so that each pixel area is addressable independently of any other pixel area. The drive circuit <NUM> can be arranged in any suitable way and can include any suitable set of components or circuit elements, including but not limited to analog components, digital components, active components, passive components, ASICs, computer components (e.g., processors, memory, or storage media), analog-to-digital or digital-to-analog converters, and so forth. The drive circuit <NUM> provides electrical drive current that flows through the device <NUM> and causes it to emit light. The drive circuit <NUM> can be further structured and connected so that (i) corresponding portions of the electrical drive current flow through one or more of the contacts <NUM> and their corresponding pixel areas as corresponding pixel currents, and (ii) each pixel current magnitude can differ from the corresponding pixel current magnitude of at least one other pixel area, or any other pixel area. In other words, the pixel current magnitudes can differ among the different contacts <NUM> and corresponding pixel areas, and the spatial distribution of those pixel current magnitudes determines the spatial distribution of light emission intensity across the different pixel areas of the inventive deice <NUM>.

A method for using the inventive light-emitting device <NUM> comprises:.

A method for making an inventive light-emitting device <NUM> comprises:.

In addition to the preceding, the following example embodiments fall within the scope of the present disclosure or appended claims:.

This disclosure is illustrative and not limiting. Further modifications will be apparent to one skilled in the art in light of the present disclosure and are intended to fall within the scope of the present disclosure or appended claims. It is intended that equivalents of the disclosed example embodiments and methods, or modifications thereof, shall fall within the scope of the present disclosure or appended claims.

In the foregoing Detailed Description, various features may be grouped together in several example embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that any claimed embodiment requires more features than are expressly recited in the corresponding claim. Rather, as the appended claims reflect, inventive subject matter may lie in less than all features of a single disclosed example embodiment.

The following interpretations shall apply for purposes of the present disclosure and appended claims. The words "comprising," "including," "having," and variants thereof, wherever they appear, shall be construed as open ended terminology, with the same meaning as if a phrase such as "at least" were appended after each instance thereof, unless explicitly stated otherwise. The article "a" shall be interpreted as "one or more" unless "only one," "a single," or other similar limitation is stated explicitly or is implicit in the particular context; similarly, the article "the" shall be interpreted as "one or more of the" unless "only one of the," "a single one of the," or other similar limitation is stated explicitly or is implicit in the particular context. The conjunction "or" is to be construed inclusively unless: (i) it is explicitly stated otherwise, e.g., by use of "either. or," "only one of," or similar language; or (ii) two or more of the listed alternatives are understood or disclosed (implicitly or explicitly) to be incompatible or mutually exclusive within the particular context. In that latter case, "or" would be understood to encompass only those combinations involving non-mutually-exclusive alternatives. In one example, each of "a dog or a cat," "one or more of a dog or a cat," and "one or more dogs or cats" would be interpreted as one or more dogs without any cats, or one or more cats without any dogs, or one or more of each. In another example, each of "a dog, a cat, or a mouse," "one or more of a dog, a cat, or a mouse," and "one or more dogs, cats, or mice" would be interpreted as (i) one or more dogs without any cats or mice, (ii) one or more cats without and dogs or mice, (iii) one or more mice without any dogs or cats, (iv) one or more dogs and one or more cats without any mice, (v) one or more dogs and one or more mice without any cats, (vi) one or more cats and one or more mice without any dogs, or (vii) one or more dogs, one or more cats, and one or more mice. In another example, each of "two or more of a dog, a cat, or a mouse" or "two or more dogs, cats, or mice" would be interpreted as (i) one or more dogs and one or more cats without any mice, (ii) one or more dogs and one or more mice without any cats, (iii) one or more cats and one or more mice without and dogs, or (iv) one or more dogs, one or more cats, and one or more mice; "three or more," "four or more," and so on would be analogously interpreted.

For purposes of the present disclosure, when terms are employed such as "about equal to," "substantially equal to," "greater than about," "less than about," and so forth, in relation to a numerical quantity, standard conventions pertaining to measurement precision and significant digits shall apply, unless a differing interpretation is explicitly set forth. For null quantities described by phrases such as "substantially prevented," "substantially absent," "substantially eliminated," "about equal to zero," "negligible," and so forth, each such phrase shall denote the case wherein the quantity in question has been reduced or diminished to such an extent that, for practical purposes in the context of the intended operation or use of the disclosed or claimed apparatus or method, the overall behavior or performance of the apparatus or method does not differ from that which would have occurred had the null quantity in fact been completely removed, exactly equal to zero, or otherwise exactly nulled.

Claim 1:
A semiconductor light-emitting device (<NUM>) comprising:
first (<NUM>) and second doped semiconductor layers (<NUM>) that are arranged for emitting light at a nominal emission vacuum wavelength λ<NUM> resulting from carrier recombination at a junction or active layer (<NUM>) between the first (<NUM>) and second semiconductor layers (<NUM>), the first (<NUM>) and second semiconductor layers (<NUM>) and the junction or active layer (<NUM>) being coextensive over a contiguous area of the device (<NUM>);
a first set of one or more electrical contacts (<NUM>) in electrical contact with the first semiconductor layer (<NUM>) at a first surface thereof opposite the second semiconductor layer (<NUM>), each electrical contact of the first set (<NUM>) being a composite electrical contact comprising (i) a corresponding electrically conductive layer (<NUM>) extending over a corresponding areal region of the first surface of the first semiconductor layer (<NUM>) within the contiguous area of the device (<NUM>), (ii) a corresponding transparent dielectric layer (<NUM>) between the corresponding conductive layer and the first semiconductor layer, and (iii) one or more corresponding electrically conductive vias (<NUM>) through the corresponding dielectric layer (<NUM>), each via providing a localized, circumscribed electrical connection between the corresponding conductive layer (<NUM>) and the first semiconductor layer (<NUM>);
a second set of one or more electrical contacts (<NUM>) in electrical contact with the second semiconductor layer (<NUM>); and
a set of multiple nanostructured optical elements (<NUM>) being positioned at the first surface of the first semiconductor layer (<NUM>), with each nanostructured optical element (<NUM>) being arranged as one or more volumes of dielectric material protruding into the corresponding dielectric layer (<NUM>) of each composite electrical contact (<NUM>),
wherein the set of multiple nanostructured optical elements (<NUM>) is arranged so as to redirect at least a portion of light at the nominal emission vacuum wavelength λ<NUM> propagating laterally in one or more selected optical modes supported by the first (<NUM>) and second semiconductor layers (<NUM>) to exit the device (<NUM>) through the second semiconductor layer (<NUM>).