Monochromatic emitters on coalesced selective area growth nanocolumns

Abstract

A light emitting structure has quantum wells grown on a coalesced substrate stemming from nanocolumns. The crystal structure is very low in defects and efficiency of light production is good. By growing the nanocolumns at a lower temperature, the quantum well structure is better matched to the coalesced substrate and efficiency is improved.

Claims

1. A method of fabricating light emitting structure comprising an array of negatively-doped or positively-doped GaN nanocolumns having a coalesced substrate, the nanocolumns being grown using molecular beam epitaxy at a low temperature such that the coalesced substrate has an enhanced compatibility with a multiple quantum well structure, multiple quantum wells formed on the coalesced substrate by molecular beam epitaxy by including indium (In), and a layer of positively-doped or negatively-doped GaN formed on the multiple quantum wells using molecular beam epitaxy, the method comprising: providing a growth substrate with a mask defining apertures for the nanocolumns; heating the growth substrate to a first temperature of about 785° C. suitable for reducing defects in the multiple quantum wells formed on said coalesced substrate and; controlling a flux of nitrogen with respect to gallium to grow in the apertures at the first temperature the negatively-doped or positively-doped GaN nanocolumns using molecular beam epitaxy while preventing material from growing on the mask between the apertures until the coalesced substrate is formed; heating the growth substrate and said coalesced substrate to a second temperature of about 650° C. or less suitable for forming the multiple quantum wells with at least indium having an enhanced compatibility with said coalesced substrate; controlling a flux of the indium to form barrier layers of GaN and at least one active layer of InGaN to provide the multiple quantum wells on the coalesced substrate using molecular beam epitaxy; and heating the growth substrate and said coalesced substrate to a third temperature of about 760 to about 785° C.; and forming an upper layer of the positively-doped or negatively-doped GaN on the multiple quantum wells (MQWs).

2. The method of claim 1, wherein the layer of the positively-doped GaN is formed using molecular beam epitaxy.

3. The method of claim 1, wherein the first temperature is in the range of 770° C. and 795° C.

4. The method of claim 1, wherein the positively-doped GaN is Mg-doped GaN.

5. The method of claim 1, wherein the mask is a nitridized titanium mask.

6. The method of claim 1, wherein the mask is processed with one of a lithography and a nanoimprint technology to create the apertures.

7. The method of claim 1, wherein the growth substrate includes a sapphire substrate.

8. The method of claim 1, wherein the growth substrate includes the mask being on a negatively-doped GaN growth layer.

9. The method of claim 8, wherein the negatively-doped GaN growth layer includes Si-doped GaN.

10. The method of claim 1, further comprising growing at least five quantum wells.

11. The method of claim 1, further comprising coating the coalesced substrate, multiple quantum wells, and said upper layer with an isolation layer.

12. The method of claim 11, wherein the isolation layer is a layer of one of a SiNx and a SiO.sub.2.

13. The method of claim 1, further comprising a step of a dry etching process to reveal said upper layer, and a step of subsequently depositing Ni and Au, followed by an annealing process for achieving ohmic contacts.

14. The method of claim 1, further comprising controlling a concentration of In in the multiple quantum wells to determine wavelengths of light emitted by the light emitting structure.

15. The method of claim 1, wherein the MQWs have layers with different bandgaps for emitting light at different wavelengths.

16. The method of claim 15, wherein the different wavelengths combine to provide white light.

17. The method of claim 1, further comprising growing AlxGa1-xN barrier layers with Al content between each GaN quantum well.

18. The method of claim 1, further comprising polishing a back side of a sapphire plane of the growth substrate and adding a micro lens to the back side.

19. The method of claim 1, wherein the coalesced substrate consists of well-ordered semipolar planes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a better understanding of the present technology, as well as other aspects and further features thereof, reference is made to the following description which is to be used in conjunction with the accompanying drawings, where:

(2) FIG. 1 is a perspective view of the growth base having a substrate, a GaN growth layer and a mask with an array of apertures defining the selective area growth in accordance with an embodiment of the present technology;

(3) FIG. 2 is a perspective view of the growth base having of nanocolumns and a coalescent substrate thereon in accordance with an embodiment of the present technology;

(4) FIG. 3 is a schematic view of a cross-sectional portion of the growth base a substrate, a GaN growth layer and a mask with the array of apertures in accordance with an embodiment of the present technology;

(5) FIG. 4 is a schematic illustration of the process of Ga adatoms reaching the mask and diffusing on the mask in accordance with an embodiment of the present technology.

(6) FIG. 5 is a schematic illustration of the process of the Ga adatoms reaching the apertures in the mask and starting to form the bases of the nanocolumns in accordance with an embodiment of the present technology;

(7) FIG. 6 is a schematic illustration of some of Ga adatoms migrating to the sidewalls of nanocolumns for lateral growth and other Ga adatoms migrating to tops of the nanocolums for vertical growth;

(8) FIG. 7 is a schematic illustration of two nanostructures selectively grown on a growth base, the nanostructures including n-doped GaN, MQWs active region and p-doped GaN in accordance with an embodiment of the present technology;

(9) FIG. 8: is a schematic illustration of two nanostructures selectively grown on a growth base, the nanostructures including n-doped GaN, MQWs active region, p-doped GaN, a layer of insulation and an n-contact connected to the n-doped GaN in accordance with an embodiment of the present technology;

(10) FIG. 9 is a schematic illustration of two nanostructures selectively grown on a growth base, the nanostructures including n-doped GaN, MQWs active region, p-doped GaN, a layer of insulation, an n-contact connected to the n-doped GaN and a p-contact connected to the p-doped GaN in accordance with an embodiment of the present technology;

(11) FIG. 10 is a schematic illustration of two nanostructures selectively grown on a growth base, the nanostructures including n-doped GaN, MQWs active region, p-doped GaN, a layer of insulation, an n-contact connected to the n-doped GaN, a p-contact connected to the p-doped GaN and a layer of Aluminum reflector deposited conformally in accordance with an embodiment of the present technology;

(12) FIG. 11 is a schematic illustration of two nanostructures selectively grown on a growth base, the nanostructures including n-doped GaN, MQWs active region, p-doped GaN, a layer of insulation, an n-contact connected to the n-doped GaN, a p-contact connected to the p-doped GaN, a layer of Aluminum reflector deposited conformally, and a thick metal stack Ti/Au deposited as contact pads for bonding purpose in accordance with an embodiment of the present technology;

(13) FIG. 12 is a schematic illustration of two nanostructures selectively grown on a growth base, the nanostructures including n-doped GaN, MQWs active region, p-doped GaN, a layer of insulation, an n-contact connected to the n-doped GaN, a p-contact connected to the p-doped GaN, a layer of Aluminum reflector deposited conformally, a thick metal stack Ti/Au deposited as contact pads for bonding purpose, and the growth base having micro-lenses attached thereto in accordance with an embodiment of the present technology;

(14) FIG. 13 is a schematic illustration of a conventional thin film fabricated light emitting device in accordance with an embodiment of the present technology;

(15) FIG. 14 is a schematic illustration of a coalesced nanocolumns fabricated light emitting device in accordance with an embodiment of the present technology;

(16) FIG. 15 is schematic representation of the steps a method of fabricating a light emitting device using coalesced nanocolumns process in accordance with an embodiment of the present technology.

DETAILED DESCRIPTION

(17) Reference will now be made in detail to some specific examples of the embodiments of the invention including some modes of carrying out the invention that are contemplated by the inventors to be suitable for understanding the technology. Examples of the specific embodiments are illustrated in the accompanying drawings. While the technology is described in conjunction with these specific embodiments, it will be understood that it is not intended to limit the invention to the described embodiments. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the scope of the invention as defined by the appended claims.

(18) In the following description, specific details are set forth in order to provide a thorough understanding of the present technology. Particular example embodiments of the present technology may be implemented without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present technology.

(19) Various techniques and mechanisms of the present technology will sometimes be described in singular form for clarity. However, it should be noted that some embodiments include multiple iterations of a technique or multiple instantiations of a mechanism unless noted otherwise.

(20) Furthermore, the techniques and mechanisms of the present technology will sometimes describe a connection between two entities. It should be noted that a connection between two entities does not necessarily mean a direct, unimpeded connection, as a variety of other entities may reside between the two entities. Consequently, a connection does not necessarily mean a direct, unimpeded connection unless otherwise noted.

(21) FIGS. 1 and 2 illustrate schematically the nanocolumn selective area growth process in accordance with the present technology.

(22) Particularly, FIG. 1 shows an embodiment where a growth base 100 consists of a sapphire substrate 101. The sapphire substrate 101 is covered by a n-doped GaN growth layer 106, which is covered by a mask 102 that has apertures 103 therethrough exposing the growth layer 106 through the mask 102. While in the Figures, the base and nanocolumns are n-GaN with p-GaN provided on top of the MQWs, it will be appreciated that p-GaN can be used for the base and nanocolumns with n-GaN provided on top of the MQWs.

(23) In this exemplary embodiment, the sapphire substrate 101 is polished flat to an RMS of 1-2 nanometres (hereinafter: nm) on the side 107 that is used for forming the n-doped GaN growth layer 106 thereon, and the opposite side 108 of the substrate 101 may be coated with 2 microns of molybdenum or another high heat conductive material. In embodiments when a material alternative to sapphire is used for the growth base 100 substrate 101, such a substrate 101 would typically be also polished or otherwise processed/treated to create a sufficiently smooth surface for forming a n-doped GaN growth layer 106 thereon on one side 107 and may be coated with a heat resistant conductive material on the side 108. The molybdenum or another high heat conductive material may be deposited onto the side 108 of the sapphire substrate 101 by any suitable technological process, for example, sputtering or evaporation. Alternative materials to sapphire may include Si, GaN.

(24) The n-doped GaN growth layer 106 may be a thin layer of about 2 microns, however, it is understood by a person skilled in the art, that the n-doped GaN growth layer 106 may have a thickness of about 2 to 5 microns. Typically, the thickness of the growth layer 106 is determined by the specific characteristics of the production facility used to fabricate the light emitting devices and the desired characteristics of the manufacturer. The n-doped GaN growth layer 106 may be grown on the sapphire substrate 101 using any suitable process known in the art, for example, by molecular beam epitaxy, MOCVD or other epitaxy process.

(25) The side 107 of the sapphire substrate 101 that is coated with the n-doped GaN growth layer 106 is may also be coated with about 10 nm of titanium and then processed with lithography to create apertures 103, thus creating the mask 102.

(26) As shown in FIG. 2, the apertures 103 are defined to create selected areas for the formation of the base 109 of the nanocolumns 104 of the coalesced substrate 105. The array of nanoscale apertures 103 may be performed by top-down fabrication process on the Ti mask 102.

(27) FIG. 2 shows the nanostructure 111 grown on the growth base 100. The nanostructure 111 is an example of a type of nanostructure that may be grown using by molecular beam epitaxy by the selective area growth technique. The nanocolumns 104 are shown to extend from the growth base 100 from the apertures 103. The nanocolumns 104 coalesce at a specific height forming the coalesced substrate 105. The coalesced substrate 105 is shown to have other layers grown thereon, these layers may be a layer 112 of one or more quantum wells and a layer of p-doped GaN 113.

(28) It is understood that the nanostructure 111 may have less or more nanocolumns 104, the nanocolumns 104 may be of any suitable height, the coalesced substrate 105 may be of any suitable height, the quantum wells layer 112 may thicker should it include a large number of quantum wells, and the p-doped GaN layer 113 may be of any suitable thickness.

(29) FIG. 2 also illustrates that the top surface 114 of the structure 111 consists of well-ordered semipolar planes. The shape of the surface 114 is dictated by the crystalline shape of the coalesced substrate 105 of the n-doped GaN NCs 104, as the coalesced substrate 105 has a surface consisting of the same well-ordered semipolar planes (not shown on FIG. 1B).

(30) FIGS. 1 and 2 show that the selected growth areas are placed at a distance relative to each other, whereby the distance is small enough, such that when the n-doped GaN nanocolumns 104 grow both in height and laterally, they coalesce at a certain height, thus forming a common canopy, which is the coalesced substrate 105.

(31) FIG. 3 shows a portion of the growth base 100 particularly a portion of a cross-section of the growth base 100. The portion of the cross-section of the growth base 100 has a sapphire substrate 101, a n-doped GaN growth layer 106 and the mask 102 with the array of apertures 103. It may be seen that apertures 103 protrude through the mask 102 exposing the n-doped GaN growth layer 106. The n-doped GaN growth layer 106 covers the entirety of the sapphire substage 101 surface, which is the opposite surface to the bottom surface 108.

(32) The apertures 103 are nanoscale apertures. In cases when the mask 102 is a titanium mask, the apertures 103 may be created using standard electron beam lithography process or nanoimprint technology, followed by a dry etch process. It is important to create apertures that expose the n-doped GaN growth layer 106 from under the titanium mask 102 while preventing damaging the n-doped GaN growth layer 106 exposing the sapphire substrate 101.

(33) The n-doped GaN growth layer 106 is required for forming the base 109 of the nanocolumns 104.

(34) To initiate the forming by molecular beam epitaxy of the base 109 of the n-doped GaN nanocolumns 104 and the growth by molecular beam epitaxy of the n-doped GaN nanocolumns 104, the growth base 100 must be heated to a first temperature in the range of 760 to 795 degrees C. and a source of nitrogen and gallium must be supplied.

(35) In the prior art, Sekiguchi and Kishino's group are pioneers in growing GaN NCs using SAG techniques on Ti mask. In their studies, the growth temperatures (Tg) are always above 900° C. Under 900° C., no SAG occurred. [1-10] At the low Tg of 880° C., the desorption and diffusion of Ga were sufficiently suppressed; thus, crystal nucleation occurred on the space between the nanoholes. The lowest Tg ever reported by this group is 880° C. However, it was measured using a pyrometer with lack of accuracy. [5]

(36) Also in the prior art, Kristine Bertness, Norman Sanford, and John Schlager from National Institute of Standards and Technology (NIST) reported SAG GaN NCs grown on Si template under the Tg of 835° C.-844° C. However, the NCs crystal quality is low with numbers of pores and defects in the structure. [11] Additionally, in the prior art, E. Calleja and his colleagues initially grew SAG GaN NCs at very high Tg of 900° C.-960° C. [12, 13] Later on, by improving the growth techniques, the lowest Tg achieved by this group is 840° C.-880° C.[14-22]. Furthermore, in the prior art, Zetian Mi's group has also demonstrated the low-defect GaN NCs using SAG technique. The Tg is in rage of 850° C.-1030° C.[23-27]. Also, in the prior art, Yong Ho Ra et al. from Korea Institute of Ceramic Engineering & Technology has reported SAG GaN NCs successfully grown at Tg as high as 920° C.-1010° C. Finally, in the prior art, Songui Zhao from McGill University is able to grow SAG GaN NCs with reasonable morphology and crystal quality at 865° C. [28]

(37) The Applicants discovered that using a substantively different range first temperatures as mentioned above is required for producing a nanostructure 111 having minimal crystalline defects.

(38) After the growth base 100 is heated to the first temperature in the range of 760 to 795 degrees C., the MBE process is initiated and the nitrogen flux is supplied and is controlled relative to the gallium supplied to the growth base 100, the Ga adatoms 400 will reach the mask 102 and will diffuse thereon, as shown in FIG. 4. Due to the first temperature and the control of nitrogen flux relative to gallium conditions, the Ga adatoms 400 will dwell mostly in the apertures 103 and react with N to form GaN that will bond to the GaN substrate, thus starting to form the base 109 of the n-doped GaN nanocolumns. In this way, GaN does not get deposited onto the mask 102. If the N flux is too great, the Ga adatoms may begin to react while they are briefly on the mask surface, and selective area growth or SAG can be disrupted.

(39) Then while maintaining the first temperature in the required the range of 760 to 795 degrees C. and continuing the MBE process of growing the nanostructure 111, as shown in FIG. 5, Ga adatoms 400, which include impinging and diffused atoms, will react with N (and some Si) to form the base 109 that will extend above the mask 102 top surface 107. The base 109 of the n-doped GaN nanocolumns 104 will have minimal defects if the first temperature and the control of nitrogen flux conditions are maintained. If the N flux is high enough, the Ga adatoms may begin to react to form GaN while they are still on the side of the nanocolumns and migrating to the top surface, and widening of the nanocolumn ensues.

(40) FIG. 5 shows that as the MBE growth process progresses, the Ga adatoms 400, which include impinging and diffused atoms, migrate onto the sidewalls 402 of the n-doped GaN nanocolumns 104, thus enhancing the lateral growth of the n-doped GaN nanocolumns 104, while other Ga adatoms 400, which include impinging and diffused atoms will contribute to the vertical growth of the n-doped GaN nanocolumns 104. Maintaining the first temperature and the control of nitrogen flux conditions keeps preventing the Ga adatoms 400 from reacting with N while onto the top surface 107 of the mask 102, while growing the nanocolumns 104 having minimal crystalline defects.

(41) FIG. 6 shows that during the MBE process, the n-doped GaN NCs 104 will eventually coalesce under controlled size, diameter and orientation forming the coalesced substrate 105 of the nanostructure 111. The first temperature and the control of nitrogen flux conditions must maintained at least to the moment of the NCs 104 coalescence. The resulting coalesced substrate to eliminate defects at the boundary of the coalesced substrate 105.

(42) In an exemplary embodiment of the MBE process in accordance with the present technology, the lateral growth of the n-doped GaN NCs 104 was is caused by Ga adatoms starting to react with N and stick to the side walls of the nanocolumns in a nitrogen rich conditions with the growth base 100 heated to 785 degrees C.

(43) In another exemplary embodiment, high quality SAG n-doped GaN NCs 104 are grown at first temperature of 780° C. to 790° C. The growth conditions of the SAG n-doped GaN NCs 104 may consist of Ga flux of 17 nm/min (about 1.1×10.sup.15 atoms/cm.sup.2/s), N flux of 5 nm/min (˜3.7×10.sup.14 atoms/cm.sup.2/s), first temperature of 790° C.

(44) The (S)TEM studies show that GaN NCs grown by MBE exhibit nearly defect-free structure. Structural defects including strain, threading dislocation and boundary defects due to lattice mismatch are bended and terminated towards the n-doped GaN nanocolumn's 104 sidewalls 402.

(45) When the N flux relative to the Ga flux in the MBE process of forming n-GaN nanocolumns is too low, there is failure of GaN formation and the nanocolumns do not form. When the N flux relative to the Ga flux in the MBE process of forming nanocolumns is too great, GaN forms too quickly and selective growth in the apertures is lost because GaN forms on the mask as well. The rate of GaN formation is also slower at a temperature of 790° C. instead of 900° C., so the relative flux of N to Ga needs to be increased at the lower temperature of growing the NCs.

(46) Referring now to FIGS. 4, 5, and 6 the rate of epitaxial growth of the n-doped GaN NCs 104 in both directions may be controlled such that all the n-doped GaN NCs 104 grown simultaneously on the growth base 100 as group meet at the top of the n-doped GaN NCs 104, i.e. coalesce, forming a continuous horizontal film of n-doped GaN with extremely high purity, i.e. the coalesced substrate 105. The coalesced substrate 105 of the n-doped GaN NCs 104 is disassociated from the lattice mismatch problems encountered in all other epitaxial growth approaches known in the art, which leads to forming a defect-free or quasi defect-free base for the MQWs to be formed on.

(47) In one embodiment, each of the grown n-doped GaN nanocolumns 104 has a largest diameter or width of about 200 nm. These n-doped GaN nanocolumns 104 are grown from apertures 103 that are spaced apart at a distance of about 50 nm. It is understood by a person skilled in that art that other dimensions are within the scope of the present technology, for example, the distance between the apertures 103 may be anywhere in the range of 50 nm to 100 nm, the largest diameter of each n-doped GaN nanocolumn may be in the range of 200 nm to 400 nm and the height of the n-doped GaN nanocolumns may be in the range of 300 nm to 600 nm.

(48) In another embodiment, each of the grown n-doped GaN nanocolumns 104 has been grown to 500 nm in height and had a smaller diameter than 200 nm. It is understood by a person skilled in the art that the dimensions of the epitaxially grown n-doped GaN NCs 104 depend on the exact growth conditions.

(49) Growth conditions that have proven to be effective for giving the desired results to the Applicants are shown in the Table 1 below. The Table 1 shows the exemplary epitaxial growth conditions for the UVA n-doped GaN nanocolumns 104 having high EQE UVA emission characteristics.

(50) TABLE-US-00001 TABLE 1 Length Plasma N flow CAR Al flux Ga flux Mg Si Stage (nm) (W) (sccm) (° C.) (Torr) (Torr) (° C.) (° C.) n-GaN 500 350 0.33 920  4E−7 1180 Al.sub.0.09Ga.sub.0.91N - (×5)  3-4 350 0.33 940 1.1E−8  4E−7 GaN - (×5) 2-3 350 0.33 940  4E−7 p-GaN  50 350 0.33 960 2.5E−7  340

(51) The table 1 also shows the variable additional materials that may be included into the nanostructure grown by MBE depending on the desired characteristics of a light emitting device fabricated using the technology taught in the present specification. For example, the nanostructures may consist of Si-doped and Mg-doped GaN segments, which may serve as n- and p-contact layers, respectively.

(52) FIG. 7 shows a nanostructure 700 consisting of the growth base 100 that has the n-doped GaN nanocolumns 104 grown thereon. The growth base 100 has a GaN-on-sapphire substrate 101 that has the n-doped GaN growth layer 106 exposed through the mask 102. The base 109 of the n-doped GaN nanocolumns 104 is formed on the n-doped GaN growth layer 106 of the GaN-on-sapphire substrate 101. The n-doped GaN nanocolumns 104 coalesce to form the coalesced substrate 105. Multiple quantum wells 701 are grown on the coalesced substrate 105 of the n-doped GaN nanocolumns 104. The MQWs 701 are sandwiched between the coalesced substrate 105 of the n-doped GaN nanocolumns 104 and the p-doped GaN layer 113. The p-doped GaN layer 113 has a top surface 114. The top surface 114 is adapted to having other layers formed thereon as described in more detail below.

(53) FIG. 7 also shows barrier layers 702 that may be sandwiched between each quantum well 701. For example, the barrier layers 702 may include GaN (undoped), AlxGa1-xN layers with Al content xAl of ˜9-15%, or other forms of GaN.

(54) In accordance with the present technology, the MQW 701, the barrier layers 702 and the p-doped GaN layer 113 are grown by molecular beam epitaxy.

(55) At least one of the MQWs 701 have In added to the GaN. The level of In affects the wavelength of the light emitted. Al can also be added, in particular to emit shorter wavelengths. When the level of Al is increased, as mentioned above, the AlGaN can form a barrier instead of an active layer.

(56) The MBE growth process of the active and barrier layers can be repeated a number of times, preferably between three to eight times, to form the MQW region on top of the coalesced substrate 105. The layer of p-doped GaN may have thickness of 50 nm and may be grown by doping it with magnesium as per Table 1 above. AlGaN QWs will emit UV wavelength, the exact wavelength will depend on the concentration of Al in the AlGaN and this can be controlled through the density of the flux of each component. For visible light the QW material can be InGaN where the wavelength will depend on the ratio of In to Ga in the flux of each material.

(57) It is understood by a person skilled in the art that the thickness of each QW 701, of the barrier layer 702 and of the p-doped GaN layer 113 may differ in accordance with required design characteristics of the fabrication process of the nanostructure 700.

(58) It is also understood that a different number of MQWs 701 grown in the nanostructure 700 may give other suitable results and is within the scope of the present technology. For example, the nanostructure 700 may have one quantum well 701, two quantum wells 701, three quantum wells 701 and so on up to about 10 quantum wells.

(59) It is also understood that different growth bases 100 having different templates of substrates 101 and mask 102 may give other suitable results and are within the scope of the present technology.

(60) The fabrication process defined in this specification can fabricate light emitters of different diameters. The diameters are defined by a group of nanocolumns 104 that coalesce into one coalesced substrate 105 or into multiple coalesced substrates 105 grown together forming a grouped common canopy with layered multiple quantum wells 701 on each or most of the coalesced substrates 105.

(61) Once the MQWs are formed, a further barrier of AlGaN can be added by MBE to prevent electron leakage.

(62) On the MQWs, p-GaN is grown. As described above, the temperature for growing the p-GaN 113 can be higher as long as the InGaN is not disrupted by the heat. While MBE is efficient to grow the p-GaN 113, MOCVD can also be used.

(63) FIG. 8 shows that the nanostructure 700 may be coated with an isolation or insulation layer 800. The insulation layer 800 be include SiNx or SiO.sub.2 or any other suitable material that is deposited on the n-doped GaN nanocolumns 104, the MQWs portion 701, the p-doped GaN layer 112 and the mask 102 of the nanostructure 700. In some embodiments, the deposited insulation layer 800 may be planarized to form a planar surface. The insulation layer 800 is covering every group of n-doped nanocolumns 104 forming the coalesced substrate 105 and the mask 102 between each such group. It is understood that the process of depositing the insulation layer 800 is used from any of those available in the art.

(64) The n-contact 802 may be defined with a photolithographic step. The n-contact 802 may be defined proximate the mask 102 on the n-doped GaN growth layer 106. The arrow 801 indicates where a p-contact may be defined on the nanostructure 700.

(65) As illustrated in FIG. 9, on each group of n-doped GaN nanocolumns 104 that are grown on the growth base 100 of the nanostructure 700 of the light emitting device, a p-contact 900 may be fabricated. In order to add the p-contact 900 to the p-doped GaN layer 113, the insulation 800 must be removed from the top surface 114 of the p-doped GaN layer 113. This may be done by etching or any other suitable approach known in the art. After exposing the top surface 114 of the p-doped GaN layer 113, the p-contact may be created by depositing about 3 nm of nickel and about 3 nm of gold, and then the nanostructure 700 can be annealed at about 450 degrees C. for about ten minutes.

(66) The p-contact 900 described herein may have a high transparency for UVA (for example, >92%). It may also be an ohmic contact. It should be noted that in certain conditions, thicknesses of the p-contact 900 that are significantly greater than 3 nm may encourage non-linearly higher absorption for UVA. Additionally, p-contact 900 having thicknesses of significantly greater than 3 nm may compromise the efficiency and/or presence of the ohmic contact required for high efficiency conversion from electrical energy to light in the light emitting nanostructure 700.

(67) As illustrated in FIG. 7, on top of the insulation layer 800 and the p-contact layer 900, a reflective layer 1000 is deposited. The reflective layer may consist of about 50 nm thick of reflective material for 365 nm. The reflective material may be Al or any suitable reflective material known in the art. It is understood that various thicknesses of reflective material layer 1000 are contemplated within the scope of this technology and include thicknesses much greater or smaller than about 50 nm.

(68) The reflective layer 1000 reflects the light generated within the nanostructure 700 of the light emitting device through the p-contact 900. All other light that is bounced off the reflective layer 1000 may also find its way to the bottom of the light emitting device, i.e. through the nanocolumns 104 to and through the growth base 100 the substrate 101, e.g., the sapphire substrate 101.

(69) In some embodiments, the nanostructure 700, consisting of the growth base 100 (the GaN substrate 101 and mask 101), a of plurality of n-doped GaN nanocolumns 104 that create one or more canopies of coalesced substrates 105 with MQW 701 layered thereon, covered with p-doped GaN layer 113, a p-contact layer 900 and a reflective layer 1000, may be at least in part covered by an isolation and transparent layer on which there is a reflective layer and then another isolation layer (not shown). This last isolation layer (not shown) may serve two purposes, one may be to protect all the conductive surface from creating electrical shorts with other structure in final packaging and the other may be to provide a surface to put the n-pad 1102 (FIG. 11) and p-pad 1101 (FIG. 11), which must be at a higher level than the nanostructure 700 for the packaging purposes of a commercial light emitting device.

(70) The light in the nanostructure 700 is emitted by the MQWs 701 in all directions. The emitted light is reflected down from the reflective layer 1000 towards the bottom surface 108 of the emitter. The light going to the side walls 1001 may be reflected off the reflective layer 1000, bouncing within the nanostructure 700 until it is reflected such that it passes through the bottom surface 108, and/or it may be absorbed internally by the nanostructure 700. All light emission may then take place through the bottom surface 108 of the substrate 101 of the growth base 100.

(71) In embodiments that have an additional layer of insulation, for example a SiO.sub.2 layer of insulation, (not shown) on top of the reflective layer 1000, the additional layer of insulation may be etched to reveal the underlying p-contact 900. A metal layer 1100 forming the traces to connect the p-contact 900 to the associated p-pad 1101 may then be deposited. FIG. 11 shows the metal layer 1100 connected to the p-pad 1101 and to the p-contact 900.

(72) The n-contact 800 is connected to the bottom n-doped GaN growth layer 106 and it connected to the n-pad 1102, for example, by running metallic traces from a common layer between the n-contact 800 to the n-pad 1102 as shown in FIG. 11.

(73) Driving each such p-pad 1101 while connecting the n-pad 1102 to negative, the differential being above the forward drop of the light emitting device having the nanostructure 700 may induce emission in the light emitting device.

(74) FIG. 12 shows that one or more micro-lenses 1200 may be added to the bottom surface 108 of the substrate 101 of the growth base 100. The micro-lenses 1200 may enhance the light emitting characteristics of the nanostructure 700 of the light emitting device The presence of a micro-lens 1200 may further enhance the emission and to guide the light for certain applications such as imaging on photosensitive materials such as lithography. The micro-lens 1200 may be etched by plasma on the emission side of the sapphire substrate 101. It is understood that the micro-lenses 1200 may be added to the bottom surface 108 by any other technique known in the art.

(75) FIGS. 13 and 14 provide an illustration of types of nanostructures that may be grown using known techniques (FIG. 13) and the process outlined herein (FIG. 14).

(76) FIG. 13 shows a nanostructure 1300 that has a surface 1306 of a nanostructure 1304 on which a QW 1305 is formed. The nanostructure 1304 has a diameter d that is equal to the diameter of the aperture 1307 of the mask 1302. The nanostructure 1304 is grown on a substrate 1301.

(77) FIG. 14 shows a nanostructure 1400 that has a surface 1406 of a coalesced substrate 1405 on which the QW 1407 are formed. The coalesced substrate 1405 has a diameter d, however, the coalesced substrate 1405 is grown on nanocolumns 1404 that extend from the base 1404 from the apertures 1408 that have a much smaller diameter each.

(78) For the same diameter d of the structures 1300 and 1400, the surface 1406 is larger than the surface 1306. This provides for a QMs 1407 that generate more light than the QM 1305. The coalesced substrate 1405 consist of tops of nanocolumns 1403, as such the crystalline structure of each nanocolumn 1403 is able to correct many defects during vertical growth that may exist at the substrate 1401 and the base 1403 junction of each nanocolumn 1404. The nanostructure 1304 often lacks the ability to correct many similar defects.

(79) The structure obtained from the above method displays higher EQE compared to present thin film methods, or high luminosity per area, at the same or lower cost (due to fewer fabrication steps) is known from the following significant achievements of the method described above: 1 The GaN nanocolumns on which the QW are constructed are of very low lattice discontinuities, resulting in higher EQE. This results from growing the GaN columns on top of a thin film GaN layer on the sapphire substrate. 2 Due to the absence of plasma ion etching in thin film emitters, because of which the EQE lessens as the emitter size reduces, nanocolumn emitters do not show lessening of EQE as the emitter size reduces.

(80) The top of the nanocolumns is not flat (see FIG. 10) but have a semipolar plane. This makes the top of the coalesced structure to be non-planer. This increases the area of the emitter as compared to thin film emitters. The increase in area can be computed as;
A.sub.flat=A.sub.semipolar×cos θ

(81) Where θ is the inclination angles of a semipolar plane in a wurtzite GaN lattice as shown in FIG. 14.

(82) Depend on growth conditions, θ varies in range of 30°-58°, corresponding to an increase in active area of 25%-100%

(83) Thus, the total emissions per area of the emitter will be higher than thin film devices.

(84) FIG. 15 illustrates steps of a method 1500 of a fabrication of a light emitting device in accordance with the present technology.

(85) In the above description, numerous specific details are set forth, but embodiments of the invention may be practiced without these specific details. Well-known circuits, structures and techniques have not been shown in detail to avoid obscuring an understanding of this description. “An embodiment”, “various embodiments” and the like indicate embodiment(s) so described may include particular features, structures, or characteristics, but not every embodiment necessarily includes the particular features, structures, or characteristics. Some embodiments may have some, all, or none of the features described for other embodiments. “Connected” may indicate elements are in direct physical or electrical contact with each other and “coupled” may indicate elements co-operate or interact with each other, but they may or may not be in direct physical or electrical contact. Also, while similar or same numbers may be used to designate same or similar parts in different figures, doing so does not mean all figures including similar or same numbers constitute a single or same embodiment.

(86) Some of these steps are well known in the art and, as such, have been omitted in certain portions of this description for the sake of simplicity.

(87) Modifications and improvements to the above-described implementations of the present technology may become apparent to those skilled in the art. The foregoing description is intended to be exemplary rather than limiting. The scope of the present technology is therefore intended to be limited solely by the scope of the appended claims.