Double mesa large area AlInGaBN LED design for deep UV and other applications

Abstract

Methods are provided for forming AlInGaBN material. The method can include growing an AlInGaBN layer on a substrate; removing a portion of the AlInGaBN layer from the substrate to define a plurality of AlInGaBN islands on the substrate; and growing a highly doped-AlInGaBN layer on each of the AlInGaBN islands.

Claims

1. A method of forming an Al.sub.xIn.sub.yGa.sub.zB.sub.1-x-y-zN (0x+y+z1) material having a double mesa structure, the method comprising: growing an Al.sub.xIn.sub.yGa.sub.zB.sub.1-x-y-zN (0x+y+z1) layer on a substrate; removing a portion of the Al.sub.xIn.sub.yGa.sub.zB.sub.1-x-y-zN (0x+y+z1) layer to define a plurality of Al.sub.xIn.sub.yGa.sub.zB.sub.1-x-y-zN (0x+y+z1) islands on the substrate, wherein each of the Al.sub.xIn.sub.yGa.sub.zB.sub.1-x-y-zN (0x+y+z1) islands has an area between 0.5 millimeters by 0.5 millimeters and 2 millimeters by 2 millimeters; and growing an n-doped Al.sub.xIn.sub.yGa.sub.zB.sub.1-x-y-zN (0x+y+z1) layer on each of the Al.sub.xIn.sub.yGa.sub.zB.sub.1-x-y-zN (0x+y+z1) islands, wherein the n-doped Al.sub.xIn.sub.yGa.sub.zB.sub.1-x-y-zN (0x+y+z1) layer grown on each of the Al.sub.xIn.sub.yGa.sub.zB.sub.1-x-y-zN (0x+y+z1) islands has an area that is less than the area of each of the Al.sub.xIn.sub.yGa.sub.zB.sub.1-x-y-zN (0x+y+z1) islands.

2. The method as in claim 1, further comprising: growing a multiple quantum well (MQW) active region on the n-doped Al.sub.xIn.sub.yGa.sub.zB.sub.1-x-y-zN (0x+y+z1) layer.

3. The method as in claim 2, further comprising: forming a p-Electron block on the MQW active region.

4. The method as in claim 3, further comprising: forming a p-Al.sub.xGa.sub.1-xN (0x1)-p-GaN layer on the p-Electron block.

5. The method of claim 1, wherein a buffer layer is positioned between the Al.sub.xIn.sub.yGa.sub.zB.sub.1-x-y-zN (0x+y+z1) layer and the substrate such that the Al.sub.xIn.sub.yGa.sub.zB.sub.1-x-y-zN (0x+y+z1) layer is grown on the buffer layer.

6. The method of claim 1, wherein the substrate is a sapphire substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) A full and enabling disclosure of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in the remainder of the specification, which includes reference to the accompanying figures, in which:

(2) FIG. 1 shows a cross-sectional view of an exemplary AlInGaBN layer formed on a substrate;

(3) FIG. 2a shows a cross-sectional view of an exemplary AlInGaBN island on a first selective area of a substrate;

(4) FIG. 2b shows a top-down view of an exemplary AlInGaBN layer, such as in FIG. 2a, with a plurality of AlInGaBN islands on the substrate;

(5) FIG. 3a shows a cross-sectional view of an exemplary highly doped-AlInGaBN layer on the AlInGaBN island of FIG. 2a; and

(6) FIG. 3b shows a top-down view of an exemplary highly doped-AlInGaBN layer on each of the AlInGaBN islands of FIG. 2b.

DEFINITIONS

(7) Chemical elements are discussed in the present disclosure using their common chemical abbreviation, such as commonly found on a periodic table of elements. For example, hydrogen is represented by its common chemical abbreviation H; helium is represented by its common chemical abbreviation He; and so forth.

(8) In the present disclosure, when a layer is being described as on or over another layer or substrate, it is to be understood that the layers can either be directly contacting each other or have another layer or feature between the layers, unless expressly stated to the contrary. Thus, these terms are simply describing the relative position of the layers to each other and do not necessarily mean on top of since the relative position above or below depends upon the orientation of the device to the viewer.

DETAILED DESCRIPTION

(9) Reference now will be made to the embodiments of the invention, one or more examples of which are set forth below. Each example is provided by way of an explanation of the invention, not as a limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as one embodiment can be used on another embodiment to yield still a further embodiment. Thus, it is intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents. It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied exemplary constructions.

(10) Generally speaking, the present invention relates to the development of highly stable deep ultra-violet light emitting diodes (LEDs) and improving the power-lifetime performance of UV light emitting diodes (LEDs) for commercial applications. More specifically, a new Double Mesa Large Area LED Design is generally provided for avoiding the current crowding issue that limits the maximum area of deep UV LEDs. The methods generally described herein avoid the growth limitations previously seen by growing the relevant active layers in a selective area.

(11) The LEDs of the present invention can be formed by growing a group-III nitride template on a UV-light transparent substrate (e.g., a sapphire, aluminum gallium nitride substrate) and then flip-chip mounting the LED electrodes such that the UV light is emitted through the UV-light transparent substrate. Group III nitride refers to those semiconducting compounds formed between elements in Group III of the periodic table and nitrogen. More preferably the Group III element is selected from the group consisting of aluminum (Al), gallium (Ga), and indium (In). As is well understood in the art, the Group III elements can combine with nitrogen to form binary compounds (e.g., GaN, AlN and InN), ternary compounds (e.g., AlGaN, AlInN, and GaInN), and quaternary compounds (i.e., AlInGaN). However, the inclusion of indium in layers of the LED can cause a shift in wavelength of the emitted light to the visible and out of the ultraviolet. Thus, in one embodiment, the nitride layers of the LED of the present invention can be substantially free of indium.

(12) One exemplary embodiment is schematically shown in FIGS. 1-3. FIG. 1 shows an exemplary substrate 10 defining a first surface 11 and an opposite surface 9. The substrate 10 can be any suitable substrate for hosting a LED, including but not limited to sapphire, aluminum gallium nitride, silicon carbide, boron nitride, silicon, etc.

(13) A buffer layer 12 is optionally positioned on the first surface 11 of the substrate 10. In turn, the buffer layer 12 defines a buffer surface 13. In certain embodiments, the buffer layer 12 includes an AlN/AlInGaBN superlattice template 22 or an AlNAlN/AlInGaBN superlattice template 22.

(14) An AlInGaBN layer 14 is also formed over the substrate 10. In the shown embodiment, the AlInGaBN layer 14 is formed on the buffer surface 13 of the buffer layer 12 such that the buffer layer 12 is positioned between the substrate 10 and the AlInGaBN layer 14. However, in other embodiments, the AlInGaBN layer 14 can be positioned directly on the substrate 10.

(15) The AlInGaBN layer 14 is a n.sup.+-AlInGaBN layer in one particular embodiment, This layer 14 can also be comprised of a superlattice that includes n+AlInGaBN.

(16) The AlInGaBN layer 14 is grown on the substrate 10 (i.e., the buffer layer 12 when present) using any suitable technique, including but not limited to, metalorganic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE), molecular beam epitaxy (MBE), metalorganic hydride vapor phase epitaxy (MOHVPE), pulsed atomic layer epitaxy (PALE) growth technique, pulsed lateral overgrowth techniques (PLOG) (useful for growth of a group III nitride epilayer on a patterned wafer), or any combination of any of the deposition methods.

(17) After the AlInGaBN layer 14 is formed, a portion of the AlInGaBN layer 14 is removed such that a plurality of AlInGaBN islands 20 are defined over the substrate 10, as shown in FIGS. 2a and 2b. Thus, the buffer surface 13 is exposed in the areas where the AlInGaBN layer 14 is removed. In one embodiment, the AlInGaBN islands 20 have at least one dimension with a size ranging from about 0.5 mm to about 2 mm (e.g., about 0.50.5 mm to about 22 mm if square), though larger islands 20 could be formed if desired.

(18) In one embodiment, the portion of the AlInGaBN layer 14 is removed utilizing a SiO.sub.2 masking process. The area not to be removed is covered by a masking material (e.g., SiO.sub.2) that has a reactive-ion etch rate less than AlInBGaN. Then, a reactive ion-etching process is used to remove the AlInBGaN layer from uncovered and exposed areas.

(19) As shown in FIGS. 3a and 3b, a highly doped n.sup.+-AlInGaBN layer 30 is then grown on the surface 15 of the AlInGaBN islands 20 to serve as n.sup.+-templates for subsequent growth of the MQW active region 32 and the p-Electron block 34 and the p-AlGaN-p-GaN layer 36. The etched portions can also be covered with SiO.sub.2 by using a masking process followed by sputtering or e-beam evaporation of SiO.sub.2 or any other chemical process.

(20) The doped n.sup.+-AlInGaBN layer 30 generally includes a n.sup.+-AlInGaBN material doped with Si, Ge, O.sub.2, or other n-type dopants. The doping concentrations can vary from about 110.sup.16/cm.sup.3 to about 110.sup.20/cm.sup.3.

(21) The n+-AlInBGaN layer thickness can vary from 0.5 m to 5 m. Subsequently, the MQW region 32, the p-Electron block layer 34 and the p-AlGaN-p-GaN layer 36 are then deposited using MOCVD.

(22) It is to be understood that when reciting nitrides, a sum of group Ill elements in any nitride composition shall be greater than or equal to zero and less than or equal to 1, e.g. AlInGaBN is understood as Al.sub.xIn.sub.yGa.sub.zB.sub.1-x-y-zN, where 0x+y+z1, and AlGaN is understood as Al.sub.xGa.sub.1-xN, where 0x1.

(23) These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention, which is more particularly set forth in the appended claims. In addition, it should be understood the aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention so further described in the appended claims.