Patent Publication Number: US-2021193731-A1

Title: III-Nitride Multi-Wavelength LED Arrays

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation-In-Part of U.S. application Ser. No. 16/725,445, filed Dec. 23, 2019, and claims priority to U.S. Provisional Application Ser. No. 63/055,597, filed Jul. 23, 2020, the entire disclosures of which are hereby incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     Embodiments of the disclosure generally relate to arrays of light emitting diode (LED) devices and methods of manufacturing the same. More particularly, embodiments are directed to arrays of light emitting diode devices comprising III-nitride layers on a wafer which provide microLEDs comprising tunnel junctions. 
     BACKGROUND 
     A light emitting diode (LED) is a semiconductor light source that emits visible light when current flows through it. LEDs combine a P-type semiconductor with an N-type semiconductor. LEDs commonly use a III-group compound semiconductor. A III-group compound semiconductor provides stable operation at a higher temperature than devices that use other semiconductors. The III-group compound is typically formed on a substrate formed of sapphire or silicon carbide (SiC). 
     Various emerging display applications, including wearable devices, head-mounted, and large-area displays require miniaturized chips composed of arrays of microLEDs (μLEDs or uLEDs) with a high density having a lateral dimension down to less than 100 μm×100 μm. MicroLEDs (uLEDs) typically have dimensions of about 50 μm in diameter or width and smaller that are used to in the manufacture of color displays by aligning in close proximity microLEDs comprising red, blue and green wavelengths. Generally, two approaches have been utilized to assemble displays constructed from individual microLED dies. The first is a pick-and-place approach, which comprises picking up and then aligning and attaching each individual blue, green and red wavelength microLED onto a backplane, followed by electrically connecting the backplane to a driver integrated circuit. Due to the small size of each microLED, this assembly sequence is slow and subject to manufacturing errors. Furthermore, as the die size decreases to satisfy increasing resolution requirements of displays, larger and larger numbers of die must be transferred at each pick and place operation to populate a display of required dimensions. 
     Alternatively, to avoid the complicated pick-and-place mass transfer process, a variety of monolithic fabrication methods have been proposed to realize microLED displays. It would be desirable to provide LED devices and methods of making LED devices which provide for monolithic fabrication methods. 
     SUMMARY 
     Embodiments of the disclosure are directed to LED arrays and methods for manufacturing LED arrays. In a first embodiment, a light emitting diode (LED) array comprises a first mesa comprising a top surface, at least a first LED including a first p-type layer, a first n-type layer and a first color active region and a first tunnel junction on the first LED, the top surface of the first mesa comprising a second n-type layer on the first tunnel junction; an adjacent mesa comprising a top surface, the first LED, a second LED including the second n-type layer, a second p-type layer, and a second color active region; a second tunnel junction on the second LED of the adjacent mesa, and a third n-type layer on the second tunnel junction of the adjacent mesa; a first trench separating the first mesa and the adjacent mesa; and anode contacts on the second n-type layer of the first mesa and on the top surface of the adjacent mesa. The LED array further comprises a TFT driver comprising a driving transistor having a first electrode connected to a V DD  line and a second electrode, a capacitor being connected to the second electrode of the driving transistor and a first electrode being connected to a selecting transistor, and the selecting transistor having the first electrode and a second electrode, the second electrode of the selecting transistor being connected to a data line, wherein the selecting transistor is configured to be controlled by a select line, wherein the second electrode of the driving transistor is connected to one of the anode contacts 
     In a second embodiment, the first embodiment is modified so that the top surface of the adjacent mesa comprises the third n-type layer. 
     In a third embodiment, the first embodiment further comprises a third color active region on the n-type layer of the adjacent mesa and the adjacent mesa comprises a top surface including a third p-type layer; a third mesa comprising the first LED, second LED, the second tunnel junction, and the third n-type layer on the second tunnel junction; a second trench separating the adjacent mesa and the third mesa; cathode metallization in the first trench and in electrical contact with the first color active region and the second color active region of the adjacent mesa; cathode metallization in the second trench and in electrical contact with the first color active region and the second color active region of the third mesa and the cathode metallization in the first trench in electrical contact with the first color active region, the second color active region and the third color active region of the adjacent mesa; and an anode contact on the third n-type layer of the third mesa. 
     In a fourth embodiment, the third embodiment includes a feature that the third p-type layer of the adjacent mesa is a non-etched p-type layer. In a fifth embodiment the third or fourth is modified wherein the first color active region is a blue color active region and the second color active region is a green color active region. In a sixth embodiment, the third or fourth embodiment is modified wherein the first color active region is a blue color active region, the second color active region is a green color active region and the third color active region is a red color active region. 
     In a seventh embodiment, any of the first through sixth embodiments are modified so that the first p-type layer, the second p-type layer, the first n-type layer and the second n-type layer comprise a III-nitride material. In an eighth embodiment, the seventh embodiment includes the feature that the III-nitride material comprises GaN. In a ninth embodiment, any of the third through the sixth embodiments include the features that the first p-type layer, the second p-type layer, the third p-type layer, the first n-type layer, the first n-type layer, the second n-type layer and the third n-type layer comprise a III-nitride material. In a tenth embodiment, the ninth embodiment is such that the III-nitride material comprises GaN. 
     In an eleventh embodiment, any of the first through tenth embodiments include the feature that the first mesa has a sidewall and the adjacent mesa has a sidewall and the first mesa sidewall and the adjacent mesa sidewall form an angle with a top surface of a substrate upon which the mesas are formed in a range of from 60 to less than 90 degrees. 
     Another aspect of the disclosure pertains to an electronics system and in a twelfth embodiment, an electronic system comprising the LED array of any of the first through eleventh embodiments and driver circuitry configured to provide independent voltages to one or more anode contacts. In a thirteenth embodiment, the twelfth embodiment includes the feature wherein the electronic system is selected from the group consisting of a LED-based luminaire, a light emitting strip, a light emitting sheet, an optical display, and a microLED display. 
     Another aspect pertains to a method of manufacturing an LED array. In a fourteenth embodiment, a method comprises forming a first mesa comprising a top surface, at least a first LED including a first p-type layer, a first n-type layer and a first color active region and a first tunnel junction on the first LED, the top surface comprising a second n-type layer on the first tunnel junction; forming an adjacent mesa comprising the first LED, a second LED including the second n-type layer, a second p-type layer and a second color active region; forming a second tunnel junction on the second LED of the adjacent mesa, and a third n-type layer on the second tunnel junction of the adjacent mesa p-type layer; forming a first trench separating the first mesa and the adjacent mesa; and forming anode contacts on the second n-type layer of the first mesa and on the third n-type layer of the adjacent mesa. 
     In a fifteenth embodiment, the fourteenth embodiment further comprises forming a top surface of the adjacent mesa comprising the third n-type. In a sixteenth embodiment, the fourteenth or fifteenth embodiment further comprises forming a third color active region on the n-type layer of the adjacent mesa and the adjacent mesa comprises a top surface including a third p-type layer; forming a third mesa comprising a top surface, the first LED, the second LED, the second tunnel junction, and including the third n-type layer on the second tunnel junction; and the third color active region, the top surface of the third mesa comprising the third n-type layer; forming a second trench separating the adjacent mesa and the third mesa; forming cathode metallization in the first trench which is in electrical contact with the first color active region and the second color active region of the adjacent mesa; forming cathode metallization in the second trench and in electrical contact with the first color active region and the second color active region of the third mesa and the n-type metallization in the first trench in electrical contact with the first color active region, the second color active region and the third color active region of the second adjacent mesa, and the cathode metallization in the first trench in electrical contact with the third color active region; and forming an anode contact on the third n-type layer of the third mesa. The method further comprises forming a TFT driver comprising a driving transistor having a first electrode connected to a V DD  line and a second electrode, a capacitor being connected to the second electrode of the driving transistor and a first electrode being connected to a selecting transistor, and the selecting transistor having the first electrode and a second electrode, the second electrode of the selecting transistor being connected to a data line, wherein the selecting transistor is configured to be controlled by a select line, wherein the second electrode of the driving transistor is connected to one of the anode contacts. 
     In a seventeenth embodiment, the sixteenth embodiment is such that wherein each of the first LED, the second LED and the third LED comprise epitaxially deposited III-nitride material. In an eighteenth embodiment, the first LED, the second LED and the third LED are formed on a substrate. In a nineteenth embodiment, the eighteenth embodiment is such that the first trench and the second trench are formed by etching trenches to form the first mesa, the adjacent mesa and the third mesa. In a twentieth embodiment, the eighteenth or nineteenth embodiment are such that the III-nitride material comprises GaN. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments. The embodiments as described herein are illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements. 
         FIG. 1  illustrates a cross-sectional view of a red, green, and blue LED device including multiple quantum wells according to one or more embodiments; 
         FIG. 2  illustrates sacrificial layers and an etch mask formed over the LED device of  FIG. 1 ; 
         FIG. 3  illustrates the device of  FIG. 2  after an etching process to provide three mesas to form a LED array; 
         FIG. 4  illustrates a conformal dielectric layer on the three mesas of the LED array  FIG. 3 ; 
         FIG. 5  illustrates the LED array of  FIG. 4  after etching openings in the dielectric layer of the device of  FIG. 4 ; 
         FIG. 6  illustrate illustrates the LED array of  FIG. 5  after deposition of cathode metallization in the openings; 
         FIG. 7  illustrates the LED array of  FIG. 6  after electrodeposition of conductive metal; 
         FIG. 8A  illustrates an LED array comprising a first mesa and a second after anode formation; 
         FIG. 8B  illustrates the LED array of  FIG. 7  after p-contact formation; 
         FIG. 9  illustrates the LED array of  FIG. 7  connected to a backplane; 
         FIG. 10  illustrates a top view of an electronic device comprising an LED array configured to emit two or more colors according to an embodiment; 
         FIG. 11  illustrates section A of  FIG. 10 ; 
         FIG. 12  illustrates a side view of an electronic device including an LED array and one or more TFT drivers according to an embodiment; 
         FIG. 13  illustrates an embodiment of an electronic device comprising an LED array and TFT drivers; and 
         FIG. 14  illustrates section B of  FIG. 13 . 
     
    
    
     DETAILED DESCRIPTION 
     Before describing several exemplary embodiments of the disclosure, it is to be understood that the disclosure is not limited to the details of construction or process steps set forth in the following description. The disclosure is capable of other embodiments and of being practiced or being carried out in various ways. 
     The term “substrate” as used herein according to one or more embodiments refers to a structure, intermediate or final, having a surface, or portion of a surface, upon which a process acts. In addition, reference to a substrate in some embodiments also refers to only a portion of the substrate, unless the context clearly indicates otherwise. Further, reference to depositing on a substrate according to some embodiments includes depositing on a bare substrate or on a substrate with one or more layers, films, features or materials deposited or formed thereon. 
     In one or more embodiments, the “substrate” means any substrate or material surface formed on a substrate upon which film processing is performed during a fabrication process. In exemplary embodiments, a substrate surface on which processing is performed includes materials such as silicon, silicon oxide, silicon on insulator (SOI), strained silicon, amorphous silicon, doped silicon, carbon doped silicon oxides, germanium, gallium arsenide, glass, sapphire, and any other suitable materials such as metals, metal nitrides, III-nitrides (e.g., GaN, AlN, InN and other alloys), metal alloys, and other conductive materials, depending on the application. Substrates include, without limitation, light emitting diode (LED) devices. Substrates in some embodiments are exposed to a pretreatment process to polish, etch, reduce, oxidize, hydroxylate, anneal, UV cure, e-beam cure and/or bake the substrate surface. In addition to film processing directly on the surface of the substrate itself, in some embodiments, any of the film processing steps disclosed is also performed on an underlayer formed on the substrate, and the term “substrate surface” is intended to include such underlayer as the context indicates. Thus for example, where a film/layer or partial film/layer has been deposited onto a substrate surface, the exposed surface of the newly deposited film/layer becomes the substrate surface. 
     The term “wafer” and “substrate” will be used interchangeably in the instant disclosure. Thus, as used herein, a wafer serves as the substrate for the formation of the LED devices described herein. 
     Embodiments described herein describe arrays of LED devices and methods for forming arrays of LED devices (or LED arrays). In particular, the present disclosure describes LED devices and methods to produce LED devices which emit multiple colors or wavelengths from a single wafer. The positions and sizes of LED devices which emit multiple colors or wavelengths are controlled by adjusting lithography steps and etching depths in after epitaxial deposition of the materials that form the LED devices. In some embodiments, adjacent LEDs which emit multiple colors or wavelengths use a common n-type electrical contact. In some embodiments, the LEDs can be formed by using a process that does not require substrate removal. One or more embodiments of the disclosure can be used in the fabrication of microLED displays. 
     In one or more embodiments, a less complex microLED manufacturing process is provided by utilization of LED devices and methods for their manufacture which integrate two or more active regions emitting different wavelengths on a single wafer. Devices and methods described according to one or more embodiments utilize III-nitride materials, for example, materials in the AlInGaN materials system, which can be manufactured to form blue, green and red LEDs. Embodiments described herein provide a multi-color device such as a chip, which can be used in microLED display. In one or more embodiments, multiple layers are stacked in a single epitaxial growth process, and the multiple layers are configured to emit at different wavelength. Devices are provided which are configured so that respective emission intensity ratios can be changed between the emitters of different wavelengths. 
     According to one or more embodiments, devices and methods provide multiple quantum wells (MQW) configured to emit red, green, and blue light within a single active region, namely between the p- and n-layers of one p-n junction. In one or more embodiments, two or more pixels of different wavelengths in the same LED device are formed which comprise several p-n junctions on the same epitaxial wafer. By etching mesas using multiple steps as described further herein, embodiments provide the formation of independent electrical contacts to each of the p-n junctions. According to one or more embodiments, one or more emitter layers of different wavelengths are embedded in separate p-n junctions with separate current paths so the wavelength and radiance are controlled independently. 
       FIG. 3  shows exemplary embodiment of a LED array configured to emit two or more different colors adjacent to each other on the same wafer. Several p-n junctions and active regions are stacked on top of each other, which in some embodiments are made by an epitaxial growth sequence in which unnecessary layers are removed by post-growth etching. In one or more embodiments, methods are provided which utilize dry etching to open trenches for contacting buried layers. However, it has been discovered that the process of dry etching introduces atomic level damage to the III-nitride crystal structure of the epitaxial layers, which changes conductivity type of p-type layers to n-type layers. 
     Due to this conductivity type conversion during dry etching, it is not possible to obtain ohmic contact of low resistance to a buried p-type nitride surface that has been exposed by dry etching. Thus, in a LED array  109  of the type shown in  FIG. 3  processed by dry etching resulting in damage to the p-GaN surface, the non-ohmic contact to the dry etched p-GaN surface results in a forward voltage penalty of one volt or more for the blue and green active regions. Even if the voltage penalty was acceptable to a device manufacturer, the p-GaN layers would have to be grown much thicker than is optimal in order to provide a sufficient margin for error in controlling the etch rate to ensure that the etch stops in the p-GaN layer. 
     According to one or more embodiments, by incorporating tunnel junctions into the epitaxial layer, the functionality shown in  FIG. 3  is achieved, but without the difficulties associated with trying to make electrical contacts to etched p-GaN surfaces. In specific embodiments, electrical contacts are made to n-type GaN layers, which can be grown to fairly high thickness without damaging the active region or inducing optical absorption losses. Embodiments of the lithography and etching methods described herein allow for the manufacture of LEDs configured to emit different colors at adjacent locations on the same wafer. A common n-type electrical contact is made to a group of different LED colors without requiring substrate removal. 
     According to one or more embodiments, LED arrays and processes for their manufacture are provided that result in a reduced number of separate epitaxy recipes which must be manufactured to produce source die for microLED displays compared to existing methods. The reduced number of epitaxy recipes reduces cost and complexity in the epitaxial manufacturing stage of LED array manufacture. Existing methods require production of separate blue, green, and red epitaxy recipes. In one or more embodiments, the number of pick and place operations required to populate a display is reduced, since arrays of pixels can be transferred together, instead of only one pixel at a time. Fewer pick and place operations will lead to cost and throughput improvements at the display assembly stage. In some embodiments, the need for pick and place operations is entirely eliminated and embodiments instead allow whole wafer-level transfer of pixels onto a display since each wafer can contain all three required colors (red, blue and green). In such embodiments, the entire processed wafer or a large piece of it could be incorporated directly into the display. According to one or more embodiments, the problem of having to make an ohmic electrical contact to etched p-GaN surfaces is avoided, making possible lower operating voltage and higher wall-plug efficiency. In some embodiments, restrictions on control of the etching rate are relaxed since all etched contacts in the tunnel junction are made to n-GaN layers which can be grown much thicker than p-GaN layers while maintaining high LED efficiency. 
     Thus, one or more embodiments provide a III-nitride based LED, such as a GaN-based LED wafer that contains two or more separate active regions configured to emit different colors, the active regions grown sequentially and connected by tunnel junctions. Embodiments provide a multi-level mesa etching process that allows independent electrical contacts to be made to each of the separate active regions producing LEDs of two or three different colors in close proximity to each other on the same wafer. One or more embodiments include an n-type electrical contact made to the sidewalls of the etched mesas, instead of the contact made to planar n-type III-nitride (e.g., GaN) surfaces. A common n-contact, made from the side of the wafer opposite the substrate side, may be used for the entire array of red, green, and blue LED mesas. 
     An aspect of the disclosure pertains to a method of manufacturing a LED array. Referring first to  FIG. 1 , a LED device  100  is manufactured by forming a plurality of III-nitride layers on a substrate  101  to form a plurality of LEDs on the substrate including color-active regions. The color active regions include a first color active region  124 , a second color active region  114  and a third color active region  104 . While any order of stacking the different color active regions is within the scope of the disclosure, in specific embodiments, for a device emitting toward the substrate  101  from which the layers are formed, the color active region of shortest emission wavelength is the first color active region grown in the sequence of forming two or more color active regions. Accordingly in one or more embodiments, the first color active region  124  is formed on the substrate first and is a blue color active region, and then the second color active region  114  is formed, which is a green color active region, and then the third color active region  104 , which is a read color active region, is formed. This sequence in which the first color active region  124  is blue, the second color active region  114  is green and the third color active region  104  is red avoids internal absorption of the emission from the blue color active region  124  by the color active regions of longer wavelengths. 
     Therefore, according to certain specific embodiments, the LED device  100  comprises a first LED including a first n-type layer  126  formed on the substrate, a first p-type layer  122  formed on the first n-type layer  126 , and a first color active region  124  between the first n-type layer  126  and the first p-type layer  122 . In one or more embodiments, the first color active region  124  is a blue color active region. In the embodiment shown, there is a first tunnel junction  120  on the first LED, in particular on the first p-type layer  122 . A tunnel junction is a structure that allows electrons to tunnel from the valence band of a p-type layer to the conduction band of an n-type layer in reverse bias. The location where a p-type layer and an n-type layer abut each other is called a p/n junction. When an electron tunnels, a hole is left behind in the p-type layer, such that carriers are generated in both regions. Accordingly, in an electronic device like a diode, where only a small leakage current flows in reverse bias, a large current can be carried in reverse bias across a tunnel junction. A tunnel junction comprises a particular alignment of the conduction and valence bands at the p/n tunnel junction. This can be achieved by using very high doping (e.g., in the p++/n++ junction). In addition, III-nitride materials have an inherent polarization that creates an electric field at heterointerfaces between different alloy compositions. This polarization field can also be utilized to achieve band alignment for tunneling. 
     Still referring to  FIG. 1 , the LED device  100  further comprises a second LED including a second n-type layer  116  on the first tunnel junction  120 , a second p-type layer  112  formed on the second n-type layer  116 , and a second color active region  114  between the second n-type layer  116  and the second p-type layer  112 . In one or more embodiments, the second color active region  114  is a green color active region. In the embodiment shown, there is a second tunnel junction  110  on the second LED, in particular on the second p-type layer  112 . The LED device  100  further comprises a third LED including a third n-type layer  106  formed on the second tunnel junction  110 , a third p-type layer  102  formed on the third n-type layer  106 , and a third color active region  104  between the third n-type layer  106  and the third color active region. In one or more embodiments, the third color active region  104  is a green color active region. 
     The substrate  101  may be any substrate known to one of skill in the art which is configured for use in the formation of III-nitride LED devices. In one or more embodiments, the substrate comprises one or more of sapphire, silicon carbide, silica (Si), quartz, magnesium oxide (MgO), zinc oxide (ZnO), spinel, and the like. In specific embodiments, the substrate  101  comprises sapphire. In one or more embodiments, the substrate  101  is not patterned prior to formation of the LEDs on a top surface  101   t  of the substrate  101 . Thus, in some embodiments, the substrate is  101  not patterned and can be considered to be flat or substantially flat. In other embodiments, the substrate  101  is a patterned substrate. 
     In one or more embodiments, the n-type layers and p-type layers of each of the first LED, the second LED and the third LED each comprise a layer of III-nitride material. In some embodiments, the III-nitride material comprises one or more of gallium (Ga), aluminum (Al), and indium (In). Thus, in some embodiments, the n-type and p-type layers of the respective LEDs comprise one or more of gallium nitride (GaN), aluminum nitride (AlN), indium nitride (InN), gallium aluminum nitride (GaAlN), gallium indium nitride (GaInN), aluminum gallium nitride (AlGaN), aluminum indium nitride (AlInN), indium gallium nitride (InGaN), indium aluminum nitride (InAlN), and the like. In specific embodiments, the n-type and p-type layers of the respective LEDs comprise n-doped and p-doped GaN. 
     In one or more embodiments, the layers of III-nitride material which form the first LED, the second LED and the third LED are deposited by one or more of sputter deposition, atomic layer deposition (ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD), plasma enhanced atomic layer deposition (PEALD), and plasma enhanced chemical vapor deposition (PECVD). 
     “Sputter deposition” as used herein refers to a physical vapor deposition (PVD) method of thin film deposition by sputtering. In sputter deposition, a material, e.g. a III-nitride, is ejected from a target that is a source onto a substrate. The technique is based on ion bombardment of a source material, the target. Ion bombardment results in a vapor due to a purely physical process, i.e., the sputtering of the target material. 
     As used according to some embodiments herein, “atomic layer deposition” (ALD) or “cyclical deposition” refers to a vapor phase technique used to deposit thin films on a substrate surface. The process of ALD involves the surface of a substrate, or a portion of substrate, being exposed to alternating precursors, i.e. two or more reactive compounds, to deposit a layer of material on the substrate surface. When the substrate is exposed to the alternating precursors, the precursors are introduced sequentially or simultaneously. The precursors are introduced into a reaction zone of a processing chamber, and the substrate, or portion of the substrate, is exposed separately to the precursors. 
     As used herein according to some embodiments, “chemical vapor deposition” refers to a process in which films of materials are deposited from the vapor phase by decomposition of chemicals on a substrate surface. In CVD, a substrate surface is exposed to precursors and/or co-reagents simultaneous or substantially simultaneously. As used herein, “substantially simultaneously” refers to either co-flow or where there is overlap for a majority of exposures of the precursors. 
     As used herein according to some embodiments, “plasma enhanced atomic layer deposition (PEALD)” refers to a technique for depositing thin films on a substrate. In some examples of PEALD processes relative to thermal ALD processes, a material may be formed from the same chemical precursors, but at a higher deposition rate and a lower temperature. A PEALD process, in general, a reactant gas and a reactant plasma are sequentially introduced into a process chamber having a substrate in the chamber. The first reactant gas is pulsed in the process chamber and is adsorbed onto the substrate surface. Thereafter, the reactant plasma is pulsed into the process chamber and reacts with the first reactant gas to form a deposition material, e.g. a thin film on a substrate. Similarly to a thermal ALD process, a purge step maybe conducted between the delivery of each of the reactants. 
     As used herein according to one or more embodiments, “plasma enhanced chemical vapor deposition (PECVD)” refers to a technique for depositing thin films on a substrate. In a PECVD process, a source material, which is in gas or liquid phase, such as a gas-phase III-nitride material or a vapor of a liquid-phase III-nitride material that have been entrained in a carrier gas, is introduced into a PECVD chamber. A plasma-initiated gas is also introduced into the chamber. The creation of plasma in the chamber creates excited radicals. The excited radicals are chemically bound to the surface of a substrate positioned in the chamber, forming the desired film thereon. 
     In one or more embodiments, a LED device  100  which is to form a LED array is manufactured by placing the substrate  101  in a metalorganic vapor-phase epitaxy (MOVPE) reactor so that the LED device layers are grown epitaxially. The first n-type layer  126  comprises one or more layers of semiconductor material that include different compositions and dopant concentrations. In specific embodiments, the first n-type layer  126  is formed by growing an epitaxial layer of a III-nitride, for example, n-GaN. The first p-type layer  122  comprises one or more layers of semiconductor material that include different compositions and dopant concentrations. In specific embodiments, the first p-type layer  122  is formed by growing an epitaxial layer of a III-nitride, for example, p-GaN. In use, an electrical current is caused to flow through the p-n junction in the first color active region  124 , and the first color active region  124  generates light of a first wavelength determined in part by the bandgap energy of the materials. In some embodiments, the first LED comprising the first n-type layer  126 , the first p-type layer  122 , and the first color active region  124  includes one or more quantum wells. In one or more embodiments, the first color active region  124  is configured to emit blue light. 
     In specific embodiments, after completing formation of the first p-type layer  122  comprising the p-GaN layer of the blue LED, epitaxial growth conditions are then modified to grow the first tunnel junction  120 . Then the second LED is formed, comprising the second n-type layer  116 , the second p-type layer  112  and the second color active region  114  between the second n-type layer  116  and the second p-type layer  112 . The second n-type layer  116  is formed by growing an epitaxial layer of a III-nitride, for example, n-GaN. The second p-type layer  112  comprises one or more layers of semiconductor material that include different compositions and dopant concentrations. In specific embodiments, the second p-type layer  112  is formed by growing an epitaxial layer of a III-nitride, for example, p-GaN. In use, an electrical current is caused to flow through the p-n junction in the second color active region  114 , and the second color active region  114  generates light of a second wavelength determined in part by the bandgap energy of the materials. In some embodiments, the second LED comprising the second n-type layer  116 , the second p-type layer  112 , and the second color active region  114  includes one or more quantum wells. In one or more embodiments, the second color active region  114  is configured to emit green light. Formation of the second LED according to some embodiments includes changes to the thickness and/or growth conditions of the second n-type layer  116 . 
     In specific embodiments, after completing formation of the second p-type layer  112  comprising the p-GaN layer of the green LED, epitaxial growth conditions are then modified to grow the second tunnel junction  110 . Then the third LED is formed, comprising the third n-type layer  106 , the third p-type layer  102  and the third color active region  104  between the third n-type layer  106  and the third p-type layer  102 . The third n-type layer  106  is formed by growing an epitaxial layer of a III-nitride, for example, n-GaN. The third p-type layer  102  comprises one or more layers of semiconductor material that include different compositions and dopant concentrations. In specific embodiments, the third p-type layer  102  is formed by growing an epitaxial layer of a III-nitride, for example, p-GaN. In use, an electrical current is caused to flow through the p-n junction in the third color active region  104 , and the third color active region  104  generates light of a third wavelength determined in part by the bandgap energy of the materials. In some embodiments, the third LED comprising the third n-type layer  106 , the third p-type layer  102 , and the third color active region  104  includes one or more quantum wells. In one or more embodiments, the third color active region  104  is configured to emit red light. Formation of the third LED according to some embodiments includes changes to the thickness and/or growth conditions of the third n-type layer  106 . 
     The disclosure is not limited to any particular epitaxial designs of the first tunnel junction  120  and the second tunnel junction  110  or the LED color active regions. After epitaxial growth, of the first LED, the second LED and the third LED, a series of photolithography and dry etch processes are utilized to form a LED array  109  according to one or more embodiments, as shown in  FIGS. 2-8 . The end result of the photolithography and dry etch processes is an array of mesas with different heights as shown in  FIG. 8 . Quantum wells and p-n junctions not required for a particular emission color are etched away in some of the mesas, which results in mesas having a different height. 
     According to embodiments, a variety of options can be used in the photolithography and dry etch processes as will be discussed below. Routine processing steps such as photoresist exposure, development, strip and clean steps have been omitted from  FIGS. 2-8 . In one embodiment of an etch process, a first sacrificial layer  125   a  is patterned over a portion of the third p-type layer  102  where a mesa having the greatest height is desired as shown in  FIG. 2 . A second sacrificial layer  125   b  is patterned of a portion of the third type p-type layer  102  where an adjacent mesa having a height that is greater than the height of the first mesa. The first sacrificial layer  125   a  has a height that is greater than the second sacrificial layer  125   b.    
     After formation of the first sacrificial layer  125   a  and the second sacrificial layer  125   b , an etch mask layer  127  is deposited over the third p-type layer  102  not covered by the first sacrificial layer  125   a  and the second sacrificial layer  125  as well as over the first sacrificial layer  125   a  and the second sacrificial layer as shown in  FIG. 2 . In the embodiment shown, neither the material that forms the etch mask layer  127  nor the material that forms the first sacrificial layer  125   a  and the second sacrificial layer  125   b  is impervious to the dry etch chemistry. Therefore, for etch times long enough to etch through the etch mask layer  127  and/or the sacrificial layers, the depth etched into the epitaxial wafer depends on the thickness of the etch mask layer and the sacrificial layers. Adjacent mesas with different heights can then be obtained with a single dry etch step using the thickness of sacrificial layers and the differences in etch rates between sacrificial layers, the etch mask layer, and epitaxially formed layers of the first LED, the second LED and the third LED to control the height of each of the mesas. A first mesa  103  has a first height denoted by H, an adjacent mesa  105  has a second height, and a third mesa  107  has a third height. In the embodiment shown, the first height H of the first mesa  103  is less than a second height of the adjacent mesa  105 , and a third height of the third mesa  107 . The second height of the adjacent mesa  105  is greater than the third height of the third mesa  107 . Thus, the first mesa  103  is the shortest of the three mesas. First trench  111  separates the first mesa  103  and the adjacent mesa  105 , and second trench  113  separates the adjacent mesa  105  and the third mesa  107 . The first mesa  103  has a sidewall  103   s,  the adjacent mesa  105  has a sidewall  105   s,  and the third mesa  107  has a sidewall  107   s.  In one or more embodiments, the sidewalls  103   s,    105   s  and  107   s  are angled with respect to a top surface  101   t  of the substrate. The sidewall  103   s  of the first mesa  103 , the sidewall  105   s  of the adjacent mesa  105  and the sidewall  107   s  of the third mesa  107  each form an angle “a” with the top surface  101   t  of the substrate  101  in a range of from 75 to less than 90 degrees. 
     In some embodiments, which will be discussed with respect to  FIG. 8A , there is a first mesa  103  and an adjacent mesa  105 . Thus, in such embodiments, only a first sacrificial layer is utilized and only a first trench is formed during the manufacturing process. 
     At the first trench  111  and the second trench  113 , the etching process effectively stops at the substrate  101 , as the substrate is nearly impervious to etching under conditions used to etch the III-nitride epitaxial layers. In one or more embodiments, the etch mask layer  127 , the first sacrificial layer  125   a  and the second sacrificial layer  125   b  are comprised of the same material or different materials. Photoresists or dielectric materials such as silicon dioxide and silicon nitride can be used as suitable etch mask materials for the masking and etching processes. 
     In alternative embodiments of the etch process, first mesa  103 , the adjacent mesa  105 , and the third mesa  107  each having different heights are processed in separate dry etching steps. In a first etch step, mesas of equal heights are produced. The first etch step is stopped and some mesas are re-masked to prevent their heights from being reduced in subsequent etching steps. The mask layer is not completely etched through during the process and in some embodiments comprises a material that is impervious to the etch chemistry. This alternative embodiment exhibits a slower manufacturing throughput than the embodiment described in the previous paragraph, but exhibits less stringent control of parameters such as mask and sacrificial layer thickness and etch rate selectivity. 
     Following the end of the mesa etch process shown in  FIG. 3  and suitable cleaning steps, activation of buried p-type layers is accomplished by laterally diffusing hydrogen through etched sidewalls of the buried p-type layers. According to one or more embodiments, the mesas are annealed after mesa etch rather than earlier in the process because the spaces in between the mesas allow for an efficient path for lateral diffusion and escape of hydrogen from the p-type layers. The annealing may be similar to those of a conventional LED or may use higher temperatures and/or longer times. 
     Referring now to  FIG. 4 , after the p-type layer activation anneal, a conformal coating of a dielectric layer  130 , for example, silicon dioxide is deposited over the mesas and their sidewalls using a method such as plasma-enhanced chemical vapor deposition, atomic layer deposition, or sputtering. The dielectric layer  130  isolates metal contacts from each other will be fabricated in later process steps. 
     As used herein, the term “dielectric” refers to an electrical insulator material that can be polarized by an applied electric field. In one or more embodiments, the dielectric layer includes, but is not limited to, oxides, e.g., silicon oxide (SiO 2 ), aluminum oxide (Al 2 O 3 ), nitrides, e.g., silicon nitride (Si 3 N 4 ). In one or more embodiments, the dielectric layer comprises silicon nitride (Si 3 N 4 ). In one or more embodiments, the dielectric layer comprises silicon oxide (SiO 2 ). In some embodiments, the dielectric layer composition is non-stoichiometric relative to the ideal molecular formula. For example, in some embodiments, the dielectric layer includes, but is not limited to, oxides (e.g., silicon oxide, aluminum oxide), nitrides (e.g., silicon nitride (SiN)), oxycarbides (e.g. silicon oxycarbide (SiOC)), and oxynitrocarbides (e.g. silicon oxycarbonitride (SiNCO)). 
     In one or more embodiments, the dielectric layer  130  is deposited by one or more of sputter deposition, atomic layer deposition (ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD), plasma enhanced atomic layer deposition (PEALD), and plasma enhanced chemical vapor deposition (PECVD). 
     Referring now to  FIG. 5 , subsequently portions of the mesas are masked with resist and openings are dry etched in the dielectric layer  130 . As shown in  FIG. 5 , the dielectric layer  130  only covers the sidewall  105   s  of the adjacent mesa  105  at the third p-type layer  102  and the third color active region  104  (red color active region) of the adjacent mesa  105 . On the third mesa  107 , the dielectric layer  130  extends over the sidewall  107   s  at only the third n-type layer  106 , the second tunnel junction  110 , the second p-type layer  112  and the second color active region  114  (green color active region). On the first mesa  103 , the dielectric layer  130  covers only the sidewall  103   s  at the second n-type layer  116 , the first tunnel junction  120 , the first p-type layer  122  and the first color active region  124  (blue color active region). 
     Referring now to  FIG. 6 , a cathode metallization layer  132  is deposited in the open areas left by the dry-etching step shown in  FIG. 5 . In one or more embodiments, the cathode metallization layer  132  comprises an aluminum-containing metal layer and is deposited by physical vapor deposition and patterned as shown in  FIG. 6 . The n-contact metallization layer  132  covers sidewall over the n-type layer  126  of the first mesa  103  and the adjacent mesa  105 . The n-contact metallization layer  132  extends to and covers the sidewall of the third n-type layer  106  of adjacent mesa  105 . The n-contact metallization layer  132  extends to and covers the sidewall of the third mesa  107  to the second n-type layer  116 . 
     Referring now to  FIG. 7 , the first trench  111  and the second trench  113  between adjacent mesas are partially filled using solution-based electrodeposition of a metal such as copper using the previously deposited aluminum-containing metal as a seed layer. If needed, the electrodeposited metal may be planarized in a subsequent processing step using chemical-mechanical planarization. 
     Referring now to  FIG. 8B , after cleaning, the LED array  109  is masked again and a set of openings for anode metallization contacts is patterned and another set of openings etched in the dielectric layer  130 . Then, an anode metallization contact comprising a conductive metal such as silver is patterned into the openings as shown in  FIG. 8B . Optionally the patterning shown in  FIG. 8B  can be performed in separate photolithography and deposition steps if it is desired to use different contact metals for the electrode contact on the third p-type layer  102  (red LED) on the first mesa  103  and the p-type metallization contacts  136  on the n-GaN tunnel junction contacts of the blue LED of the third mesa  107  and the green LED of the adjacent mesa  105 . 
     In  FIG. 8B , the cathode metallization layer  132  of the green LED third mesa  107  also contacts layers of the blue LED in the third mesa  107 , and the cathode metallization layer  132  of the red LED first mesa  103  also contacts layers of the green and blue LEDs in that mesa. This contact, however, does not prevent independent operation of adjacent LEDs sharing a common cathode. The bias voltage in typical applications would not exceed 4V, which is insufficient to inject holes beyond the active region closest to the anode even if the cathode metal contacts layers deeper within the epitaxy structure. The dashed arrows  150  in  FIG. 8B  show the path of the current for typical bias of less than 4V. 
     Another aspect of the disclosure pertains to a LED array shown in  FIGS. 8A and 8B . In a first embodiment shown in  FIG. 8A  a LED array  109   a  comprises a first mesa  103  comprising a top surface  103   t,  at least a first LED including a first p-type layer  122 , a first n-type layer  126  and a first color active region  124  and a first tunnel junction  120  on the p-type layer  122  of the first LED, the top surface  103   t  of the first mesa  103  comprising a second n-type layer  116  on the first tunnel junction  120 . Still referring to  FIG. 8A , there is an adjacent mesa  150  comprising a top surface  105   t,  the first LED, a second LED including the second n-type layer  116 , a second p-type layer  112 , and a second color active region  114 . There is a second tunnel junction  110  on the second LED of the adjacent mesa  105 , and a third n-type layer  106  on the second tunnel junction  110  of the adjacent mesa  105 . There is a first trench  111  separating the first mesa  103  and the adjacent mesa  105 . There is cathode metallization  134  in the first trench  111  and in electrical contact with the first color active region  124  and the second color active region  114  of the adjacent mesa  105 . There are anode metallization contacts  136  on the second n-type layer  116  of the first mesa  103  and on the third n-type layer  106  of the adjacent mesa  105 . In the embodiment shown in  FIG. 8A , the top surface  105   t  of the adjacent mesa  105  comprises the third n-type layer  106 . 
     The LED array  109   a  shown in  FIG. 8  therefor comprises a single color (blue) LED formed by the first mesa  103  and a two color LED (glue and green) formed by the adjacent mesa  105 ). 
       FIG. 8B  shows another embodiment of an LED array  109 B comprising a first mesa  103  comprising a top surface  103   t,  at least a first LED including a first p-type layer  122 , a first n-type layer  126  and a first color active region  124  and a first tunnel junction  120  on the p-type layer  122  of the first LED, the top surface  103   t  of the first mesa  103  comprising a second n-type layer  116  on the first tunnel junction  120 . An adjacent mesa  105  comprises a top surface  105   t , the first LED, a second LED including the second n-type layer  116 , a second p-type layer  112 , and a second color active region  114 . There is a second tunnel junction  110  on the second LED of the adjacent mesa  105 , namely on the p-type layer  112 , and a third n-type layer  106  on the second tunnel junction  110  of the adjacent mesa  105 . There is a first trench  111  separating the first mesa  103  and the adjacent mesa  105 . There is n-type metallization  134  in the first trench  111  and in electrical contact with the first color active region  124  and the second color active region  114  of the adjacent mesa  104 . There are p-type metallization contacts  136  on the second n-type layer of the first mesa and on the top surface  105   t  of the adjacent mesa  105 . 
     The LED array  109   b  shown in  FIG. 8B  further comprises a third color active region  104  on the n-type layer  106  of the adjacent mesa  105  and the adjacent mesa comprises a top surface  105   t  including a third p-type layer  102 . The LED array  109   b  further comprises a third mesa  107  comprising the first LED, the second LED, the second tunnel junction  110 , and the third n-type layer  106  on the second tunnel junction  110 . There is a second trench  113  separating the adjacent mesa  105  and the third mesa  107 . There is cathode metallization  134  in the second trench  113  and in electrical contact with the first color active region  124  and the second color active region  114  of the third mesa  107  and the cathode metallization  134  in the first trench  111  in electrical contact with the first color active region  124 , the second color active region  114  and the third color active region  104  of the adjacent mesa  105 . In addition, there is an anode metallization contact  136  on the third n-type layer  106  of the third mesa  107 . 
     In some embodiments, the third p-type layer  102  of the adjacent mesa  105  is a non-etched p-type layer. In some embodiments, the first color active region  124  is a blue color active region and the second color active region  114  is a green color active region. In some embodiments, the first color active region  124  is a blue color active region, the second color active region  114  is a green color active region and the third color active region  104  is a red color active region. 
     In embodiments in which light is emitted toward the substrate side of the structure the heights of the mesas increase in the order of increasing emission wavelength (red&gt;green&gt;blue in this example). 
     Referring now to  FIG. 9 , an electronic system or device  200  is shown comprising the LED array  109  of  FIG. 8 , and driver circuitry configured to provide independent voltages to one or more of the anode contacts  136  of the first mesas,  103 , the adjacent mesa  105  and the third mesa. This can be achieved by a backplane  190 , such as a CMOS backplane  190  connected to the anode contacts  136  by metal  192 , such as metal solder bumps. In one or more embodiments, the electronic system is selected from the group consisting of a LED-based luminaire, a light emitting strip, a light emitting sheet, an optical display, and a microLED display. 
     Referring now to  FIGS. 10 through 15 , an electronic device  800  comprising thin film transistor (TFT) drive circuitry is shown comprising an LED array  809  integrated with one or more TFT drivers  850 . In one or more embodiments, the TFT drive circuitry including the one or more TFT drivers  850  are incorporated with any of the embodiments of LED arrays described herein. 
     A partial top view of the LED array  809  configured to emit two or more colors is shown in  FIG. 10 . The partial top view of  FIG. 10  shows the LED array  809  including a section of a TFT matrix grid  802  having a plurality of rows and columns. In the embodiment shown, the section of the grid  802  has three rows and three columns for a total of nine cells, with each row of three cells arranged in a pattern of blue ( 854 B) columns, red ( 854 R) columns, and green ( 854 G) columns of LEDs to provide a plurality of rows (a top row  855 A, a middle row  855 B and bottom row  855 C). Each cell comprises an electrode contact  853  electrically connected to an anode metallization contact  836  (shown in cross-section in  FIGS. 12-14 ) disposed on a mesa of an LED of any of the embodiments described herein. Each electrode contact  853  of each of the cells is surrounded by an n-type material  852  (e.g., n-type GaN). 
     The grid  802  further comprises at least a plurality of select lines  856  running parallel to each of the rows  855 A,  855 B,  855 C and a plurality of V DD  lines  858  and a plurality of data lines  860  running perpendicular to each of the rows. The plurality of V DD  lines  858  and plurality of data lines  860  are deposited at least one layer above the select line  856 , as described in further detail below. In one or more embodiments, each of the plurality of V DD  lines  858  supplies constant voltage above the threshold “on” voltage for each of the LEDs. There is one select line  856  for each row of the display and one V DD  line  858  for each display column, but all connect to a one common external power supply. There is one data line  860  for each column driver connected to external CMOS column drivers (on per display column). A LED common cathode is connected to a ground external to a device such as a display. 
       FIG. 11  illustrates a schematic of the one or more TFT drivers  850 , as indicated by section A depicted by the dotted line in  FIG. 10 . For purposes of clarity, insulator materials are not depicted. As illustrated, each of the TFT drivers  850  comprises at least two transistors, a capacitor, one of the select lines  856 , one of the V DD  lines  858  and one of the data lines  860 . The V DD  line  858  is connected to a first electrode  868  of a driving transistor  865 , the driving transistor  865  being configured as a gate for the device. The driving transistor  865  is connected to a capacitor  864 , which in turn is connected to a first electrode  867  of a selecting transistor  863 . A second electrode  869  of the selecting transistor  863  is connected to the data line  860 . A second electrode  866  of the driving transistor  865  is connected to the anode metallization contact  836  (shown in  FIGS. 12-14 ) of each mesa powering the LED. 
     According to one or more embodiments, the V DD  line  858  is configured as a source providing a constant power supply voltage above a turn-on threshold of each LED, and the select line  856  is configured as a drain. The data line  860  is configured to charge the capacitor  864  to a desired voltage, and the select line  856  is configured to open the driving transistor  865 . In operation, the V DD  line  858  provides a constant power supply voltage. Cycle voltage to the select line  856  opens the selecting transistor  863 , and voltage to the data line  860  charges the capacitor  864 . The current through each LED is controlled by voltage stored within the capacitor  864 . In one or more embodiments, an exemplary voltage is 3.5V. 
       FIG. 12  illustrates the LED array  809  similar to the LED array shown in  FIG. 8B  and comprising a first mesa  803  comprising a top surface  803   t,  at least a first LED including a first p-type layer  822 , a first n-type layer  826  and a first color active region  824  and a first tunnel junction  820  on the p-type layer  822  of the first LED, the top surface  803   t  of the first mesa  803  comprising a second n-type layer  816  on the first tunnel junction  820 . An adjacent mesa  805  comprises a top surface  805   t,  the first LED, a second LED including the second n-type layer  816 , a second p-type layer  812 , and a second color active region  814 . There is a second tunnel junction  810  on the second LED of the adjacent mesa  805 , namely on the p-type layer  812 , and a third n-type layer  806  on the second tunnel junction  810  of the adjacent mesa  805 . There is a first trench separating the first mesa  803  and the adjacent mesa  805 . There is n-type metallization  834  in the first trench and in electrical contact with the first color active region  824  and the second color active region  814  of the adjacent mesa  804 . There are anode metallization contacts  836  on the second n-type layer of the first mesa and on the top surface  805   t  of the adjacent mesa  805 . Common ground electrodes  847  are deposited above the first and second trenches, and in contact with the cathode metallization  834 . 
     A conformal coating of a dielectric layer  830 , for example, silicon dioxide, is deposited over the mesas and their sidewalls using a method such as plasma-enhanced chemical vapor deposition, atomic layer deposition, or sputtering. The dielectric layer  830  isolates metal contacts from each other will be fabricated in later process steps. Planarization material  845  (which in some embodiments comprises dielectric material) is deposited above the dielectric layer  830 , the mesas and the common ground electrodes  847 . Electrical contacts extend through the planarization material  845 , which connect the p-type metallization contacts  836  of the first mesa  803 , adjacent mesa  805  and third mesa  807  to the second electrode  866  of the driving transistor  865  of the one or more TFT drivers  850 , powering the LEDs. 
       FIGS. 13 and 14  illustrate the stacked layers comprising the one or more TFT drivers  850 , with  FIG. 14  illustrating the stacked layers in greater detail, as indicated by dotted line B in  FIG. 13 . For ease of reference all of the details of  FIG. 12  of the LEDs are not repeated in  FIGS. 13 and 14 . It will be appreciated that the capacitor  864  shown in  FIG. 12  is not visible in the cross-sectional views shown in  FIGS. 13 and 14 . Deposited over the planarization material  845  is a TFT lower dielectric layer  870 , which in some embodiments functions as an insulator for the capacitor and gate of the selecting transistor  863 . There is also a lower level TFT metallization layer  872  comprising a first portion  872   a,  a second portion  872   b  and a third portion  872   c.  In some embodiments, these first, second and third portions of the lower TFT metallization layer  872  function as a gate of the selecting transistor  863  and the source and drain of the driving transistor  865 . The selecting transistor  863  comprises semiconductor material  863 S on the TFT lower dielectric layer  870  as shown in  FIGS. 13 and 14 . The driving transistor  865  comprises semiconductor material  865 S on the second portion  872   b  and third portion  872   c  of the lower TFT metallization layer  872 . There is an upper level TFT metallization layer  877  comprising a first portion  877   a,  a second portion  877   b,  and third portion  877   c,  which in some embodiments respectively function as a gate of the selecting transistor and the source and drain of the driving transistor  865 . There is a TFT upper dielectric layer  879 , which on the semiconductor material  865 S of the driving transistor  865 , which in some embodiments functions as an insulator for the gate of the driving transistor  865 . There is also an upper level TFT metallization layer  881  comprising a first portion  881   a,  a second portion  881   b  and a third portion  881   c,  which in some embodiments, respectively function as a source ( 881   a ) and a drain ( 881   b ) of the selecting transistor  863  and the gate ( 881   c ) of the driving transistor  865 . While not shown in the cross-section of  FIGS. 13 and 14 , the third portion  872   c  of the lower metallization layer is connected to the bottom the capacitor  864 , and the first portion  872   a  of the lower metallization layer is connected to the select line  856 . The electronic device  800  comprising the LED array  809  and the driver circuitry configured to provide independent voltages to one or more of the anode metallization contacts  836  of the first mesas,  803 , the adjacent mesa  805  and the third mesa  807 . This can be achieved by the TFT circuitry shown and described herein according to one or more embodiments. In one or more embodiments, the electronic device  800  is selected from the group consisting of a LED-based luminaire, a light emitting strip, a light emitting sheet, an optical display, and a microLED display. 
     According to embodiments provided herein, CMOS gate and column drivers take a video input signal and convert the video input signal to voltages on data lines which program the LED to emit the light level needed to produce an image. In embodiments described herein, operation of device  800  is divided between “program” and “display” cycles. In a “program” cycle, voltage to a select line opens select transistors along a specified row, and voltages to data lines charge each capacitor on the column at a desired voltage. In one or more embodiments, programming of the device  800  proceeds one row at a time. In “display” cycle the current through each LED is controlled by voltage stored on capacitor in “program” cycle. 
     According to embodiments, the transistor is an amorphous silicon N-channel transistor. The source and drain contacts can be separately deposited amorphous silicon film with high n-type (phosphorous) doping. Non-source and drain semiconductor area is unintentionally doped amorphous Si with weak p-type conductivity. In some embodiments, applied gate voltage inverts the p-type material under the gate to n-type, switching ON current flow in a lateral direction. In some embodiments, dielectric materials are SiN x  fabricated by plasma-enhanced chemical vapor deposition, which is also the method used to deposit amorphous Si. Metals of some embodiments are typically Cr or Mo and deposited by e-beam evaporation or sputtering. 
     In one or more embodiments, semiconductor materials that could be used to fabricate TFTs, that have process temperatures suitable for a LED wafer include amorphous silicon, laser-crystallized polycrystalline silicon, amorphous conducting oxides such as indium gallium zinc oxide, or II-VI compounds such as CdS. TFTs in general can be N-channel or P-channel, but amorphous Si transistors are always N-channel (due to poor hole mobility). In some embodiments, polycrystalline Si may allow smaller physical dimensions of the TFTs allowing smaller pixel pitches. Also, polycrystalline Si has better long-term reliability and may improve electrical efficiency of the display. 
     Simpler embodiments of the disclosure comprise the epitaxial growth sequence features only one tunnel junction (instead of two tunnel junctions) and active regions of only two colors (instead of three colors). While the figures show architectures where the substrate remains attached in the finished device, in some embodiments laser liftoff or other epitaxial film separation processes could be applied so that substrate is removed in the finished device. Photoelectrochemical etching could be applied after the substrate is removed to roughen the exposed GaN surface and improve light extraction efficiency. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the materials and methods discussed herein (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the materials and methods and does not pose a limitation on the scope unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the disclosed materials and methods. 
     Reference throughout this specification to the terms first, second, third, etc. may be used herein to describe various elements, and these elements should not be limited by these terms. These terms may be used to distinguish one element from another. 
     Reference throughout this specification to a layer, region, or substrate as being “on” or extending “onto” another element, means that it may be directly on or extend directly onto the other element or intervening elements may also be present. When an element is referred to as being “directly on” or extending “directly onto” another element, there may be no intervening elements present. Furthermore, when an element is referred to as being “connected” or “coupled” to another element, it may be directly connected or coupled to the other element and/or connected or coupled to the other element via one or more intervening elements. When an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present between the element and the other element. It will be understood that these terms are intended to encompass different orientations of the element in addition to any orientation depicted in the figures. 
     Relative terms such as “below,” “above,” “upper,”, “lower,” “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 are intended to encompass different orientations of the device in addition to the orientation depicted in the figures. 
     Reference throughout this specification to “one embodiment,” “certain embodiments,” “one or more embodiments” or “an embodiment” means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. Thus, the appearances of the phrases such as “in one or more embodiments,” “in certain embodiments,” “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment of the disclosure. In one or more embodiments, the particular features, structures, materials, or characteristics are combined in any suitable manner. 
     Although the disclosure herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present disclosure. It will be apparent to those skilled in the art that various modifications and variations can be made to the method and apparatus of the present disclosure without departing from the spirit and scope of the disclosure. Thus, it is intended that the present disclosure include modifications and variations that are within the scope of the appended claims and their equivalents.