US20100304516A1 - Light-emitting crystal structures - Google Patents
Light-emitting crystal structures Download PDFInfo
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- US20100304516A1 US20100304516A1 US12/852,877 US85287710A US2010304516A1 US 20100304516 A1 US20100304516 A1 US 20100304516A1 US 85287710 A US85287710 A US 85287710A US 2010304516 A1 US2010304516 A1 US 2010304516A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
- H01L33/20—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a particular shape, e.g. curved or truncated substrate
- H01L33/24—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a particular shape, e.g. curved or truncated substrate of the light emitting region, e.g. non-planar junction
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
- H01L33/20—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a particular shape, e.g. curved or truncated substrate
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/005—Processes
- H01L33/0062—Processes for devices with an active region comprising only III-V compounds
- H01L33/0075—Processes for devices with an active region comprising only III-V compounds comprising nitride compounds
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
- H01L33/16—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a particular crystal structure or orientation, e.g. polycrystalline, amorphous or porous
- H01L33/18—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a particular crystal structure or orientation, e.g. polycrystalline, amorphous or porous within the light emitting region
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
- H01L33/26—Materials of the light emitting region
- H01L33/30—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table
- H01L33/32—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table containing nitrogen
Definitions
- the present invention relates to an apparatus having a light emitting diode comprising a structure having a Group III-nitride, and a method of making the apparatus.
- One embodiment is an apparatus comprising a structure comprising a group III-nitride and a junction between n-type and p-type group III-nitride therein, the structure having a pyramidal shape or a wedge shape.
- Another embodiment is an apparatus comprising a light-emitting crystalline structure on a substrate.
- the structure has n-type and p-type barrier regions and a junction there between.
- the junction is located at one or more surfaces of the n-type and the p-type barrier regions that are inclined relative to a planar surface of the substrate.
- Another embodiment is a method manufacturing an apparatus.
- the method comprises forming a light-emitting crystalline structure that includes forming a first barrier region on a substrate, the first barrier region having one or more inclined surfaces relative to a planar surface of the substrate. Forming the structure also includes forming a second barrier region over the first barrier region, to form a junction at the inclined surfaces.
- the first barrier region comprises one of an n-type or p-type semiconductor crystal
- the second barrier region comprises the other of the n-type or p-type semiconductor crystal.
- FIG. 1 illustrates a perspective view of an example apparatus
- FIG. 2 illustrates a perspective view of an alternative example apparatus
- FIG. 3 illustrates a cross-sectional view of a portion of the example apparatus shown in FIG. 1 ;
- FIGS. 4-14 presents cross-sectional and plan views of an example apparatus at selected steps in an example method of manufacture.
- the present invention benefits from the recognition that both the intrinsic and extrinsic efficiency can be improved by forming light-emitting crystalline structures having an inclined surface.
- An improvement in internal efficiency can be achieved by altering the properties of the crystal material itself. Certain crystals, however, have no inversion symmetry along certain crystal axes, which causes the crystal to have an internal electric field. The internal electrical field detrimentally reduces the internal efficiency and can shift the wavelength of light emitted from such structures.
- Forming light emitting components of the structure on an inclined surface can render the structure a semi-polar or non-polar crystal, thereby decreasing or eliminating the internal electric field of the structure. Additionally, forming the structure on an inclined surface reduces the amount of light that gets internally reflected, thereby improving external efficiency.
- FIG. 1 presents a perspective view of an example apparatus 100 , such as an LED or other illuminating apparatus comprising an LED.
- the apparatus 100 comprises a light-emitting crystalline structure 105 having an n-type barrier region 110 and a p-type barrier region 115 .
- junction 120 between the n-type and p-type barrier regions 110 , 115 . Portions of the interior p-type barrier region 115 and junction 120 are shown in a cut-away view in FIG. 1 .
- the junction 120 is located on an inclined surface 125 of one of the n-type or p-type barrier regions 110 , 115 .
- the incline of the surface 125 is relative to a planar surface 127 of a substrate 130 .
- the junction 120 comprises an active region that emits light when a voltage (V) is applied between the n-type and p-type regions 110 , 115 .
- V voltage
- the inclined surface 125 refers to a grown or wet etch-revealed surface of one of the n-type and p-type barrier regions 110 , 115 that deviates from the horizontal planar surface 127 of the substrate 130 that the structure 105 is located on.
- the horizontal plane 127 can correspond to a (0001) or a (000 1 ) plane of a substrate 130 (e.g., an insulating substrate such as sapphire) and the inclined surface 125 can correspond to one of the family of ⁇ 1 1 0 1 ⁇ planes.
- group III-nitride refers to a metal nitride or metal alloy nitride, where the metal comprises one or more atoms from Group III of the Periodic Table of Elements. Examples include aluminum nitride, gallium nitride, indium nitride, or combinations thereof.
- the n-type and p-type barrier regions 110 , 115 include dopants to form an n-type and p-type material. Examples of suitable n-type and p-type dopants include silicon and magnesium, respectively.
- the inclined surface 125 deviates from the horizontal planar surface 127 of the substrate 130 .
- the inclined surface 125 is configured to form an angle 135 that results in the reduction or cancellation of the internal electric field of the n-type or p-type barrier regions 110 , 115 .
- an angle 135 ranging from 55 to 65 degrees, and in some cases 55 to 60 degrees, causes the sum of piezoelectric polarization and spontaneous polarization in the junction 120 to cancel each other, resulting in a substantially zero electric field.
- the structure 105 has a pyramidal shape, and more specifically a hexagonal pyramid.
- the inclined surface 125 corresponds to six facets 140 of the pyramid structure 105 located over the substrate 130 .
- the pyramid structure 105 can be formed using a wet etch process as discussed below.
- the structure 105 has a wedge shape.
- the inclined surface 125 corresponds to the two facets 210 of the wedge structure 105 located over the substrate 130 .
- the inclined surface 125 can correspond to one family of ⁇ 11 2 2 ⁇ planes.
- the wedge structure 105 can be formed by a chemical vapor deposition (CVD), such as described in Srinivasan et al., Applied Physics Letters 87:131911, 2005, which is incorporated by references in its entirety.
- CVD chemical vapor deposition
- the structures 105 it is desirable for the structures 105 to have a plurality of inclined surfaces 125 because this increases the external efficiency of the structure 105 .
- having a plurality of inclined surfaces 125 corresponding to the six facets 140 of the hexagonal pyramid structure 105 ( FIG. 1 ) is preferred over a structure 105 having a plurality of inclined surfaces 125 corresponding to the two facets 210 of the wedge structure 105 ( FIG. 2 ).
- the larger number of facets 140 of the pyramid structure 105 provides more surfaces for light to reflect off of at an angle that is below the critical angle of the crystal structure 105 , and therefore a greater number of escape routes from the structure 105 .
- FIG. 3 presents a cross-sectional view along view line 3 - 3 , which traverses through one of the facets 140 shown for the pyramidal-shaped structure 105 depicted in FIG. 1 .
- the cross-sectional view shown in FIG. 3 could also correspond to view line 3 - 3 , as depicted in FIG. 2 , which transverse through a plane perpendicular to the facets 210 of the wedge-shaped structure 105 .
- All three of the n-type region 110 , the p-type region 115 , and the quantum well 305 are pyramid-shaped when the structure 105 is pyramid-shaped. Alternately all three of the n-type region 110 , the p-type region 115 , and the quantum well 305 are wedge-shaped when the structure 105 is wedge-shaped. Having such configurations beneficially improves the internal light emission efficiency because it provides the inclined surface 125 needed to reduce the structure's 105 internal electric field. These configurations also advantageously improve the external light emission efficiency of the structure 105 . That is, there will be less internally reflected light from a quantum well 305 located on the inclined surface 125 compared to light from a quantum well of similar composition, but located on a planar surface.
- the composition of the group III-nitride of the quantum well 305 is different than the compositions of the group III-nitrides of n-type and p-type barrier regions 110 , 115 . It is important to select the compositions of the quantum well 305 and the n-type and p-type barrier regions 110 , 115 so as to configure the n-type and p-type barrier regions 110 , 115 to have a larger band gap than the quantum well 305 .
- Group III-nitrides having aluminum e.g. Al x Ga 1-x N
- a group III-nitride having indium e.g. In y Ga 1-y N
- the n-type and p-type barrier regions 110 , 115 comprises gallium nitride
- the quantum well 305 comprises an alloy of indium and gallium (e.g., indium gallium nitride).
- the n-type and p-type barrier regions 110 , 115 comprise an aluminum gallium alloy (e.g., aluminum gallium nitride) and the quantum well 305 comprises gallium nitride.
- n-type and p-type barrier regions 110 , 115 comprise an aluminum-rich aluminum gallium alloy (e.g., AlGaN having a ratio of Al:Ga:N of about 80:20:100) and the quantum well 305 comprises an aluminum-poor aluminum gallium alloy (e.g., AlGaN having a ratio of Al:Ga:N of about 60:40:100 AlGaN).
- the n-type and p-type barrier regions 110 , 115 comprise indium aluminum nitride or indium gallium aluminum nitride
- the quantum well 305 comprises indium gallium nitride.
- group III-nitrides alloys could be used.
- Each quantum well layer 310 is preferably interposed between barrier layers 315 .
- the quantum well layers 310 are separated from one another by barrier layers with a larger bandgap than the quantum well layers.
- each barrier layer 315 has a thickness 320 of about 10 to 50 Angstroms
- each quantum well layer 310 has a thickness 325 of about 5 to 50 Angstroms.
- the quantum well 305 comprises 1 to 8 quantum well layers 310 . Having multiple quantum well layers 310 beneficially increases the probability of carrier capture into the quantum well 305 . However, if there is too large a number of quantum well layers 310 , then carriers may not be distributed evenly through the different layers 310 .
- the quantum well region 310 and barrier layers 315 can comprise any of the combinations of the material described above for the quantum well 305 and the n-type and p-type regions 110 , 115 , respectively. It is preferable for the compositions of the quantum well region 310 and barrier layers 315 to be configured so that the quantum well region 310 has a narrow band gap and the barrier layers 315 has a wider band gap.
- the quantum well layer 310 can comprise one type of group III-nitride, while the barrier layers 315 can comprise another type of group III-nitride.
- the quantum well layer 310 can comprise InGaN, while the barrier layers 315 comprises GaN.
- the quantum well layer 310 comprises InGaN having a ratio of In:Ga:N ranging from about 15:85:100 to 20:80:100, and even more preferably, about 17:83:100.
- This composition is advantageous because the internal electric fields of the quantum well layers 310 are substantially reduced when located on an inclined surface 120 having an angle 135 of e.g., about 55 to 65° with respect to the substrate 130 . Such angles 135 are attained for the facets 140 , 210 of pyramidal ( FIG. 1 ) or wedge ( FIG. 2 ) shaped structures 105 that comprise, e.g., group III-nitrides.
- the quantum well 305 has a thickness 330 ranging from about 2.5 to 5 nanometers.
- the thickness 330 refers to the sum of the thicknesses of these layers 310 , 315 .
- Thin-film deposition techniques such as molecular beam epitaxy (MBE) can be used, e.g., to fabricate such a low thickness variation layers of quantum well 305 .
- MBE molecular beam epitaxy
- CVD can be used to produce quantum wells 305 whose thickness 330 varies by more than ⁇ 5%.
- the thickness 330 within any one structure 105 can range from about 2.5 to 5 nanometers.
- the p-type barrier region 115 is presented as an outer layer 340 of the structure 105
- the n-type barrier region 110 is shown as an interior region 345 of the structure 105 .
- the n-type barrier region 110 could be the outer layer 340 and the p-type barrier region 115 could be the interior region 345 .
- the junction 120 or optional quantum well 305 , is a middle layer 350 on the inclined surface 125 of the interior region 345 .
- the outer layer 340 comprising either one of an n-type or p-type group III-nitride that has a thickness 355 ranging from about 50 to 500 nanometers.
- the interior region 345 can comprise one or more pyramidal portion 360 located on a base portion 365 .
- the base 365 can be a substantially planar base that is part of the substrate 130 that the structure 105 is located on. For clarity only a single pyramid 360 is depicted in FIGS. 1 and 3 . However, in other embodiments the structure 105 comprises a plurality of pyramids 360 that are on a common base 365 . That is, the pyramids 360 are interconnected via the base 365 .
- Having the pyramids 360 interconnected via the base 365 facilitates the coupling of one of the n- or p-type barrier region 110 , 115 to ohmic contacts 150 , 155 that are in turn coupled to an electrical source 160 configured to apply a voltage (V) between these regions 110 , 115 .
- V voltage
- both the pyramid 360 and the base 365 are covered with the middle layer 350 of the quantum well 305 , and the outer layer 340 of the other of the n-type or p-type barrier regions 110 , 115 .
- the pyramid 360 has a height 370 and width 375 ranging from about 100 nm to 2 microns, and the base 365 has a thickness 380 of about 500 nm to 100 microns. It is desirable for the height 370 of the pyramid 360 to not exceed about 2 microns because taller structures can interfere with the formation of planar photoresist layers in subsequent processing steps.
- the pyramid 360 formed by a partial wet etch of the base 365 can be designed to remove material from a specific surface of crystal structures to reveal the pyramid 360 . Examples of such wet-etch processes are presented in U.S. Pat. No. 6,986,693 to Chowdhury et al., which is incorporated by reference herein in its totality.
- N-polar nitrogen-polar
- M-polar metal-polar
- N-polar surface refers to a face of a Group III-nitride Wurtzite structure having a straight bond (in a tetragonal bonding configuration) from a Nitrogen atom to a Group III metal atom.
- An M-polar surface refers to a face having the straight bond from a Group III metal atom to the Nitrogen atom.
- the base wet etch etches the ⁇ 1 1 0 1 ⁇ planes of a Group III-nitride crystal (e.g., GaN) to produce a hexagonal-shaped pyramidal structure 105 ( FIG. 1 ).
- the hexagonal pyramidal structure 105 has six facets 140 of the ⁇ 1 1 0 1 ⁇ family.
- the hexagonal-shaped pyramidal shaped structure 105 has a base-to-facet angle 135 of about 58.4 degrees.
- the p-ohmic contact 150 touches the p-type barrier region 115 and the n-ohmic contact 155 touches the n-type barrier region 110 .
- the ohmic contacts 150 , 155 comprise one or more layers of conductive material such as titanium, aluminum, nickel, platinum, gold or alloys thereof.
- the electrical source 160 is configured to apply a voltage (e.g., V of about 0.5 to 10 Volts, in some embodiments) to the ohmic contacts 150 , 155 so as to cause the structure 105 to emitting light.
- FIGS. 4-20 show cross-sectional views of selected steps in an example method of manufacturing an apparatus 400 . Any of the embodiments of the example apparatuses depicted in FIGS. 1 and 3 could be manufactured by the method.
- FIGS. 4-8 show selected steps in forming a light-emitting crystalline structure 405 of the apparatus 400 .
- Forming the structure includes forming a first barrier region on a substrate, the first barrier region having one or more inclined surfaces relative to a planar surface of the substrate.
- FIG. 4-7 illustrate selected steps in forming the first barrier region.
- FIG. 4 shows the apparatus 400 after forming a barrier region seed layer 407 on a substrate 410 .
- Sapphire is a preferred substrate 410 because it facilitates formation of a subsequently grown N-polar barrier region on the substrate 410 .
- Forming the barrier region seed layer 407 can comprise growing, via MBE, an AlN seed layer 415 (thickness 417 of about 20 nm) on the substrate 410 and a group III-nitride (e.g., GaN) seed layer 420 (thickness 422 of about 50 nm) on the AlN seed layer 415 .
- the AlN seed layer 415 is preferred because it facilitates the growth of a subsequently grown M-polar barrier region on the substrate 410 .
- FIG. 4 also illustrates the apparatus 400 after depositing a photoresist layer 425 , e.g., by spin coating, and patterning the photoresist layer 425 to form one or more openings 430 .
- the openings 430 define locations on the substrate 410 where light-emitting crystalline structures 405 are formed.
- FIG. 6 shows the apparatus after forming a layer of first barrier region 605 on the substrate 410 and on the group III-nitride seed layer 420 .
- MBE can be used to grow a layer of first barrier region 605 that comprises a group III-nitride and has a thickness 607 ranging from about 1 to 5 micron.
- the group III-nitride of the first barrier region 605 can be substantially similar in composition to the group III-nitride seed layer 420 of the seed layer 407 .
- the first barrier region 605 and group III-nitride seed layer 420 can both comprise GaN.
- the first barrier region 605 comprises one of an n-type or p-type semiconductor crystal to thereby form an n-type barrier region or p-type barrier region.
- suitable n-type or p-type dopants such as silicon or magnesium, respectively, can be included during the MBE growth of the first barrier region 605 .
- Preferred embodiments of the layer of first barrier region 605 comprise a grown M-polar surface 610 and a grown N-polar surface 615 . That is, the layer of first barrier region 605 grown on the barrier region seed layer 407 has the M-polar surface 610 , while the layer of first barrier region 605 grown on the substrate 410 that is exposed in the opening 430 has the N-polar surface 615 . It is advantageous for the first barrier region 605 to have both the M-polar and N-polar surfaces 610 , 615 because this allows one to predefine the location on the substrate 410 where the inclined surface of the first barrier region 605 will be formed.
- an inclined surface 705 can be formed by wet etching the N-polar surfaces 615 , e.g., with a base as discussed above and in U.S. Pat. No. 6,986,693.
- the M-polar surface 610 of the first barrier region 605 is comparatively unaffected by the wet etch.
- the first barrier region 605 comprises Group III-nitrides (e.g., GaN)
- wet etching the N-polar surfaces 615 causes rapid etching of the family of ⁇ 1 1 0 1 ⁇ planes to form one or more hexagonal pyramid 710 .
- the inclined surfaces 705 comprise facets 715 of the pyramid 710 .
- the inclined surface 705 can form an angle 720 ranging from about 55 to 65° with respect to a horizontal planar surface 725 of the substrate 410 .
- the wet etching can form a plurality of interconnected pyramids 710 on a base portion 730 of the first barrier region 605 .
- the pyramids 710 and the base portion 730 both comprise a same material of the first barrier region 605 .
- FIG. 8 shows the apparatus 100 after forming a second barrier region 805 over the first barrier region 605 , thereby forming a junction 810 at the inclined surfaces 705 .
- the second barrier region 805 comprises the other of the n-type or p-type semiconductor crystal that the first barrier region 605 does not comprise.
- Preferred embodiments of the second barrier region 805 comprise a group III-nitride.
- MBE can be used to grow a layer of the second barrier region 805 that comprises a group III-nitride having a thickness 815 ranging from about 50 to 500 nanometers. MBE is preferred because it can form the second barrier region 805 with a minimum variation in the thickness 815 .
- the second barrier region 805 is deposited over, and in some cases on, the plurality of interconnected pyramids 710 on a base portion 730 .
- a quantum well 820 can be formed on the first barrier region 605 before forming the second barrier region 805 .
- the junction 810 comprises the quantum well 820 .
- the quantum well 820 comprising a group III-nitride can be formed, e.g., via MBE on the plurality of interconnected pyramids 710 on a base portion 730 , and then the second barrier region 805 is formed on the quantum well 820 .
- FIGS. 9-13 show selected steps in forming contacts to the first and second barrier regions 605 , 805 .
- FIG. 9 shows the apparatus 100 after filling the opening 430 , with second photoresist 905 .
- the photoresist 905 thereby covers portions of the first barrier region 605 , the second barrier region 805 and optional quantum well 820 that are located inside the opening 430 .
- FIG. 10 illustrates the apparatus 100 after exposing the M-polar surface 610 of the first barrier region 605 .
- a plasma etch comprising Ar and Cl can be used to remove the portions of the second barrier region 805 and the optional quantum well 820 , that are outside of the opening 430 and not covered with the photoresist 905 .
- the photoresist 905 protects the first barrier region 605 , the second barrier region 805 and optional quantum well 820 in the opening 430 from being etched. Thereafter, the photoresist 905 is removed.
- FIG. 11 depicts the apparatus 100 after depositing a first ohmic contact 1105 on the M-polar surface 610 of the first barrier region 605 .
- the first ohmic contact 1105 can be formed by a conventional metal lift-off process.
- a third photoresist 1110 can be deposited and patterned to form an opening 1115 to the barrier region 605 and located around the light-emitting crystal structure 405 .
- the material of the first contact 1105 e.g., aluminum, titanium, gold
- first contact 1105 comprises four consecutively deposited layers of titanium, aluminum, titanium, and gold on the first barrier region 605 configured as an n-type barrier region.
- FIG. 12 shows the apparatus 100 after depositing a second ohmic contact 1205 on the second barrier region 805 .
- a fourth photoresist 1210 can be deposited and patterned to form an opening 1215 to the second barrier region 805 and located within the light-emitting crystal structure 405 .
- the second barrier region 805 is located over or on the N-polar surface 615 of the first barrier region 605 and the second contact 1205 is over or on the second barrier region 805 .
- the second ohmic contact 1205 comprises a different material than the first contact 1105 .
- second contact 1205 comprises two consecutively deposited layers of nickel and gold on the second barrier region 805 configured as a p-type barrier region.
- FIG. 13 depicts the apparatus 100 after lifting-off the photoresist layer 1210 ( FIG. 12 ).
- FIG. 14 shows a plan view of the apparatus 100 such as depicted in FIG. 13 .
- the first contact 1105 need not cover the entire M-polar surface 610 . This follows because the portion of the first barrier region 605 having the M-polar surface 610 is in electrical contact with portion of the first barrier region 605 having the N-polar surface 615 . E.g., the base 730 below the pyramids 710 touches the first barrier region 605 that is under the M-polar surface 610 . Therefore, the first contact 1105 is also in electrical contact with the inclined surfaces 705 and the junction 810 of the structure 405 .
- the second contact 1205 does not need to cover the entire second barrier region 805 formed on each inclined surface 705 of the structure.
- the second barrier region 805 forms a uniform coating over interconnected pyramids 710 and the base 730 of the first barrier region 605
- a second contact 1205 touching any portion of the second barrier region 805 is also in electrical contact with the inclined surfaces 705 and the junction 810 of the structure 405 .
- Having the structure 405 comprise a uniform coating of second barrier region 805 over a plurality interconnected pyramids 710 advantageously allows one more flexibility as to the placement of the second contact 1205 . This avoids the need to align the second contact 1205 with a specific location on each pyramid 710 , which can problematic because the exact location of where a pyramid 710 will form by the wet etch process can be unpredictable.
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Abstract
A method of manufacturing an apparatus, comprising forming a light-emitting crystalline structure. Forming the light-emitting crystalline structure includes forming a first barrier region on a substrate, the first barrier region having one or more inclined surfaces relative to a planar surface of the substrate. Forming the light-emitting crystalline structure also includes forming a second barrier region over the first barrier region, to form a junction at the inclined surfaces, wherein the first barrier region comprises one of an n-type or p-type semiconductor crystal, and the second barrier region comprises the other of the n-type or p-type semiconductor crystal.
Description
- This Application is a Divisional of U.S. application Ser. No. 11/456,428 filed on Jul. 10, 2006, to Hock Min Ng, entitled “LIGHT-EMITTING CRYSTAL STRUCTURES,” currently allowed; commonly assigned with the present invention and incorporated herein by reference in it entirety.
- The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of DAAE 30-03-D-1013 awarded by the U.S. Army ARD (Picatinny Arsenal).
- The present invention relates to an apparatus having a light emitting diode comprising a structure having a Group III-nitride, and a method of making the apparatus.
- It is desirable to improve the efficiency of light-emitting crystal structures, such as light-emitting diodes (LEDs), because this would increase their scope of use in commercial applications. Efficiency can be improved in two ways: increase the external efficiency or increase the internal efficiency.
- An improvement in external efficiency is achieved by extracting more light out of the structure. As well known by those skilled in the art light-emitting crystal structures have a critical angle where light reflected beyond that angle gets reflected internally and does not exit the structure. E.g., only about 5 percent of the light generated in conventional planar LED passes out of the LED, the rest being internally reflected. Efforts to extract more light include texturing planar LEDs to reduce the amount of internally reflected light.
- One embodiment is an apparatus comprising a structure comprising a group III-nitride and a junction between n-type and p-type group III-nitride therein, the structure having a pyramidal shape or a wedge shape.
- Another embodiment is an apparatus comprising a light-emitting crystalline structure on a substrate. The structure has n-type and p-type barrier regions and a junction there between. The junction is located at one or more surfaces of the n-type and the p-type barrier regions that are inclined relative to a planar surface of the substrate.
- Another embodiment is a method manufacturing an apparatus. The method comprises forming a light-emitting crystalline structure that includes forming a first barrier region on a substrate, the first barrier region having one or more inclined surfaces relative to a planar surface of the substrate. Forming the structure also includes forming a second barrier region over the first barrier region, to form a junction at the inclined surfaces. The first barrier region comprises one of an n-type or p-type semiconductor crystal, and the second barrier region comprises the other of the n-type or p-type semiconductor crystal.
- The invention is best understood from the following detailed description, when read with the accompanying FIGUREs. Various features may not be drawn to scale and may be arbitrarily increased or reduced in size for clarity of discussion. Reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
-
FIG. 1 illustrates a perspective view of an example apparatus; -
FIG. 2 illustrates a perspective view of an alternative example apparatus; -
FIG. 3 illustrates a cross-sectional view of a portion of the example apparatus shown inFIG. 1 ; and -
FIGS. 4-14 presents cross-sectional and plan views of an example apparatus at selected steps in an example method of manufacture. - The present invention benefits from the recognition that both the intrinsic and extrinsic efficiency can be improved by forming light-emitting crystalline structures having an inclined surface. An improvement in internal efficiency can be achieved by altering the properties of the crystal material itself. Certain crystals, however, have no inversion symmetry along certain crystal axes, which causes the crystal to have an internal electric field. The internal electrical field detrimentally reduces the internal efficiency and can shift the wavelength of light emitted from such structures. Forming light emitting components of the structure on an inclined surface can render the structure a semi-polar or non-polar crystal, thereby decreasing or eliminating the internal electric field of the structure. Additionally, forming the structure on an inclined surface reduces the amount of light that gets internally reflected, thereby improving external efficiency.
- One embodiment of the invention is an apparatus.
FIG. 1 presents a perspective view of anexample apparatus 100, such as an LED or other illuminating apparatus comprising an LED. Theapparatus 100 comprises a light-emittingcrystalline structure 105 having an n-type barrier region 110 and a p-type barrier region 115. There isjunction 120 between the n-type and p-type barrier regions type barrier region 115 andjunction 120 are shown in a cut-away view inFIG. 1 . Thejunction 120 is located on aninclined surface 125 of one of the n-type or p-type barrier regions surface 125 is relative to aplanar surface 127 of asubstrate 130. As well understood to those skilled in the art, thejunction 120 comprises an active region that emits light when a voltage (V) is applied between the n-type and p-type regions - The
inclined surface 125 refers to a grown or wet etch-revealed surface of one of the n-type and p-type barrier regions planar surface 127 of thesubstrate 130 that thestructure 105 is located on. E.g., for n-type and p-type barrier regions horizontal plane 127 can correspond to a (0001) or a (0001 ) plane of a substrate 130 (e.g., an insulating substrate such as sapphire) and theinclined surface 125 can correspond to one of the family of {11 01 } planes. - The term group III-nitride as used herein refers to a metal nitride or metal alloy nitride, where the metal comprises one or more atoms from Group III of the Periodic Table of Elements. Examples include aluminum nitride, gallium nitride, indium nitride, or combinations thereof. In some cases, the n-type and p-
type barrier regions - The examples to follow feature Wurtzite crystal structures comprising group III-nitrides. However, one skilled in the art would appreciate that the invention could be applied to any light emitting crystal structure having non-inversion symmetry. Examples of other light-emitting crystal structures having non-inversion symmetry include Group II-VI compounds, such as Zinc Oxide (ZnO), Magnesium Zinc Oxide (MgZnO), Cadmium Zinc Oxide (CdZnO) and combinations thereof.
- As illustrated in
FIG. 1 , theinclined surface 125 deviates from the horizontalplanar surface 127 of thesubstrate 130. In some preferred embodiments theinclined surface 125 is configured to form anangle 135 that results in the reduction or cancellation of the internal electric field of the n-type or p-type barrier regions type barrier regions angle 135 ranging from 55 to 65 degrees, and in some cases 55 to 60 degrees, causes the sum of piezoelectric polarization and spontaneous polarization in thejunction 120 to cancel each other, resulting in a substantially zero electric field. - It is advantageous to form
structures 105 that provide one or moreinclined surface 125 having the desiredangle 135. In some preferred embodiments, theapparatus 100 can comprise astructure 105 comprising group III-nitrides and ajunction 120 between n-type and p-type group III-nitrides therein 110, 115, thestructure 105 having a pyramidal shape or a wedge shape. - In some embodiments, such as shown in
FIG. 1 , thestructure 105 has a pyramidal shape, and more specifically a hexagonal pyramid. In this case, theinclined surface 125 corresponds to sixfacets 140 of thepyramid structure 105 located over thesubstrate 130. Thepyramid structure 105 can be formed using a wet etch process as discussed below. - In other embodiments, such as shown in
FIG. 2 (using the same reference numbers asFIG. 1 ) thestructure 105 has a wedge shape. In this case, theinclined surface 125 corresponds to the twofacets 210 of thewedge structure 105 located over thesubstrate 130. Theinclined surface 125 can correspond to one family of {112 2} planes. Thewedge structure 105 can be formed by a chemical vapor deposition (CVD), such as described in Srinivasan et al., Applied Physics Letters 87:131911, 2005, which is incorporated by references in its entirety. - It is desirable for the
structures 105 to have a plurality ofinclined surfaces 125 because this increases the external efficiency of thestructure 105. For instance, having a plurality ofinclined surfaces 125 corresponding to the sixfacets 140 of the hexagonal pyramid structure 105 (FIG. 1 ) is preferred over astructure 105 having a plurality ofinclined surfaces 125 corresponding to the twofacets 210 of the wedge structure 105 (FIG. 2 ). The larger number offacets 140 of thepyramid structure 105 provides more surfaces for light to reflect off of at an angle that is below the critical angle of thecrystal structure 105, and therefore a greater number of escape routes from thestructure 105. -
FIG. 3 presents a cross-sectional view along view line 3-3, which traverses through one of thefacets 140 shown for the pyramidal-shapedstructure 105 depicted inFIG. 1 . The cross-sectional view shown inFIG. 3 , however, could also correspond to view line 3-3, as depicted inFIG. 2 , which transverse through a plane perpendicular to thefacets 210 of the wedge-shapedstructure 105. - As further illustrated in
FIG. 3 , to improve the amount of light being emitting from thestructure 105, it is desirable for thejunction 120 to include aquantum well 305. Some embodiments of the quantum well 305 comprise a group III-nitride. - All three of the n-
type region 110, the p-type region 115, and the quantum well 305 are pyramid-shaped when thestructure 105 is pyramid-shaped. Alternately all three of the n-type region 110, the p-type region 115, and the quantum well 305 are wedge-shaped when thestructure 105 is wedge-shaped. Having such configurations beneficially improves the internal light emission efficiency because it provides theinclined surface 125 needed to reduce the structure's 105 internal electric field. These configurations also advantageously improve the external light emission efficiency of thestructure 105. That is, there will be less internally reflected light from a quantum well 305 located on theinclined surface 125 compared to light from a quantum well of similar composition, but located on a planar surface. - The composition of the group III-nitride of the
quantum well 305 is different than the compositions of the group III-nitrides of n-type and p-type barrier regions quantum well 305 and the n-type and p-type barrier regions type barrier regions quantum well 305. Group III-nitrides having aluminum (e.g. AlxGa1-xN) will cause these materials to have a wider band gap, while a group III-nitride having indium (e.g. InyGa1-yN) causes these materials to have a narrower band gap. - For example, in some preferred embodiments, the n-type and p-
type barrier regions quantum well 305 comprises an alloy of indium and gallium (e.g., indium gallium nitride). In other embodiments, the n-type and p-type barrier regions quantum well 305 comprises gallium nitride. In still other embodiments, n-type and p-type barrier regions quantum well 305 comprises an aluminum-poor aluminum gallium alloy (e.g., AlGaN having a ratio of Al:Ga:N of about 60:40:100 AlGaN). In still other cases, the n-type and p-type barrier regions quantum well 305 comprises indium gallium nitride. One skilled in the art would appreciate that other combinations of group III-nitrides alloys could be used. - As further illustrated in
FIG. 3 , the quantum well 305 can have one or more quantum well layers 310 and one or more barrier layers 315 therein. Example quantum well layers 310 andbarrier layers 315 are presented in U.S. Pat. No. 6,891,187 to Cho et al., which is incorporated by reference herein in its entirety. - Each
quantum well layer 310 is preferably interposed between barrier layers 315. In cases where there is more than onequantum well layer 310, the quantum well layers 310 are separated from one another by barrier layers with a larger bandgap than the quantum well layers. In some preferred embodiments, eachbarrier layer 315 has a thickness 320 of about 10 to 50 Angstroms, and eachquantum well layer 310 has a thickness 325 of about 5 to 50 Angstroms. In some preferred embodiments thequantum well 305 comprises 1 to 8 quantum well layers 310. Having multiple quantum well layers 310 beneficially increases the probability of carrier capture into thequantum well 305. However, if there is too large a number of quantum well layers 310, then carriers may not be distributed evenly through thedifferent layers 310. - The
quantum well region 310 andbarrier layers 315 can comprise any of the combinations of the material described above for thequantum well 305 and the n-type and p-type regions quantum well region 310 andbarrier layers 315 to be configured so that thequantum well region 310 has a narrow band gap and the barrier layers 315 has a wider band gap. - The
quantum well layer 310 can comprise one type of group III-nitride, while the barrier layers 315 can comprise another type of group III-nitride. E.g., thequantum well layer 310 can comprise InGaN, while the barrier layers 315 comprises GaN. In some preferred embodiments, thequantum well layer 310 comprises InGaN having a ratio of In:Ga:N ranging from about 15:85:100 to 20:80:100, and even more preferably, about 17:83:100. This composition is advantageous because the internal electric fields of the quantum well layers 310 are substantially reduced when located on aninclined surface 120 having anangle 135 of e.g., about 55 to 65° with respect to thesubstrate 130.Such angles 135 are attained for thefacets FIG. 1 ) or wedge (FIG. 2 ) shapedstructures 105 that comprise, e.g., group III-nitrides. - In some embodiments, the
quantum well 305 has athickness 330 ranging from about 2.5 to 5 nanometers. In cases where the quantum well comprises a plurality of quantum well layers 310 andbarrier layers 315, thethickness 330 refers to the sum of the thicknesses of theselayers thickness 330 of the quantum well 305 (or its component layers 310, 315) throughout theentire structure 105 to be about ±5% or less. This low thickness variation is desirable because it minimizes the range of wavelengths of light emitted from thestructure 105. Thin-film deposition techniques such as molecular beam epitaxy (MBE) can be used, e.g., to fabricate such a low thickness variation layers ofquantum well 305. In other cases, however, where a broader range of emitted wavelengths is desired, other techniques, such CVD can be used to producequantum wells 305 whosethickness 330 varies by more than ±5%. E.g., thethickness 330 within any onestructure 105 can range from about 2.5 to 5 nanometers. - In the above discussion of the examples shown in
FIGS. 1-3 , the p-type barrier region 115 is presented as anouter layer 340 of thestructure 105, and the n-type barrier region 110 is shown as aninterior region 345 of thestructure 105. In other embodiments, however, the n-type barrier region 110 could be theouter layer 340 and the p-type barrier region 115 could be theinterior region 345. Thejunction 120, or optional quantum well 305, is amiddle layer 350 on theinclined surface 125 of theinterior region 345. - In some embodiments, the
outer layer 340, comprising either one of an n-type or p-type group III-nitride that has athickness 355 ranging from about 50 to 500 nanometers. - As further illustrated in
FIG. 3 , theinterior region 345 can comprise one or morepyramidal portion 360 located on abase portion 365. The base 365 can be a substantially planar base that is part of thesubstrate 130 that thestructure 105 is located on. For clarity only asingle pyramid 360 is depicted inFIGS. 1 and 3 . However, in other embodiments thestructure 105 comprises a plurality ofpyramids 360 that are on acommon base 365. That is, thepyramids 360 are interconnected via thebase 365. Having thepyramids 360 interconnected via thebase 365 facilitates the coupling of one of the n- or p-type barrier region ohmic contacts electrical source 160 configured to apply a voltage (V) between theseregions - As shown in
FIG. 3 , both thepyramid 360 and the base 365 are covered with themiddle layer 350 of thequantum well 305, and theouter layer 340 of the other of the n-type or p-type barrier regions pyramid 360 has aheight 370 andwidth 375 ranging from about 100 nm to 2 microns, and thebase 365 has athickness 380 of about 500 nm to 100 microns. It is desirable for theheight 370 of thepyramid 360 to not exceed about 2 microns because taller structures can interfere with the formation of planar photoresist layers in subsequent processing steps. - The
pyramid 360 formed by a partial wet etch of thebase 365. Wet etch processes can be designed to remove material from a specific surface of crystal structures to reveal thepyramid 360. Examples of such wet-etch processes are presented in U.S. Pat. No. 6,986,693 to Chowdhury et al., which is incorporated by reference herein in its totality. For example, the nitrogen-polar (N-polar) surface of a Group III-nitrides crystal is more susceptible to a base wet etch than a metal-polar (M-polar) surface. One skilled in the art would understand that N-polar surface refers to a face of a Group III-nitride Wurtzite structure having a straight bond (in a tetragonal bonding configuration) from a Nitrogen atom to a Group III metal atom. An M-polar surface refers to a face having the straight bond from a Group III metal atom to the Nitrogen atom. The base wet etch etches the {11 01 } planes of a Group III-nitride crystal (e.g., GaN) to produce a hexagonal-shaped pyramidal structure 105 (FIG. 1 ). The hexagonalpyramidal structure 105 has sixfacets 140 of the {11 01 } family. In some preferred embodiments, the hexagonal-shaped pyramidal shapedstructure 105 has a base-to-facet angle 135 of about 58.4 degrees. - As further illustrated in
FIGS. 1 and 3 , the p-ohmic contact 150 touches the p-type barrier region 115 and the n-ohmic contact 155 touches the n-type barrier region 110. Theohmic contacts electrical source 160 is configured to apply a voltage (e.g., V of about 0.5 to 10 Volts, in some embodiments) to theohmic contacts structure 105 to emitting light. - Another aspect of the invention is a method of manufacturing an apparatus.
FIGS. 4-20 show cross-sectional views of selected steps in an example method of manufacturing anapparatus 400. Any of the embodiments of the example apparatuses depicted inFIGS. 1 and 3 could be manufactured by the method. -
FIGS. 4-8 show selected steps in forming a light-emittingcrystalline structure 405 of theapparatus 400. Forming the structure includes forming a first barrier region on a substrate, the first barrier region having one or more inclined surfaces relative to a planar surface of the substrate.FIG. 4-7 illustrate selected steps in forming the first barrier region. -
FIG. 4 . shows theapparatus 400 after forming a barrierregion seed layer 407 on asubstrate 410. Sapphire is apreferred substrate 410 because it facilitates formation of a subsequently grown N-polar barrier region on thesubstrate 410. Forming the barrierregion seed layer 407 can comprise growing, via MBE, an AlN seed layer 415 (thickness 417 of about 20 nm) on thesubstrate 410 and a group III-nitride (e.g., GaN) seed layer 420 (thickness 422 of about 50 nm) on theAlN seed layer 415. TheAlN seed layer 415 is preferred because it facilitates the growth of a subsequently grown M-polar barrier region on thesubstrate 410. The group III-nitride layer 420 protects theAlN seed layer 415 from oxidation until the M-polar barrier region is formed.FIG. 4 also illustrates theapparatus 400 after depositing aphotoresist layer 425, e.g., by spin coating, and patterning thephotoresist layer 425 to form one ormore openings 430. Theopenings 430 define locations on thesubstrate 410 where light-emittingcrystalline structures 405 are formed. -
FIG. 5 shows theapparatus 400 after removing portions of the barrierregion seed layer 407 that are exposed in theopening 430, and then removing the photoresist layer 425 (FIG. 4 ). E.g., a plasma etch comprising Cl and Ar can be used to remove the exposed portions of barrierregion seed layer 407 to extend theopening 430 down to thesubstrate 410. E.g., the gas composition can comprise 30 sccm Cl and 10 sccm Ar. Thephotoresist 425 is then removed by a conventional process, such as immersion in acetone, followed by 10:1 (by volume) H2SO4:H2O2. -
FIG. 6 shows the apparatus after forming a layer offirst barrier region 605 on thesubstrate 410 and on the group III-nitride seed layer 420. E.g., MBE can be used to grow a layer offirst barrier region 605 that comprises a group III-nitride and has athickness 607 ranging from about 1 to 5 micron. The group III-nitride of thefirst barrier region 605 can be substantially similar in composition to the group III-nitride seed layer 420 of theseed layer 407. E.g., thefirst barrier region 605 and group III-nitride seed layer 420 can both comprise GaN. Thefirst barrier region 605 comprises one of an n-type or p-type semiconductor crystal to thereby form an n-type barrier region or p-type barrier region. E.g., suitable n-type or p-type dopants, such as silicon or magnesium, respectively, can be included during the MBE growth of thefirst barrier region 605. - Preferred embodiments of the layer of
first barrier region 605 comprise a grown M-polar surface 610 and a grown N-polar surface 615. That is, the layer offirst barrier region 605 grown on the barrierregion seed layer 407 has the M-polar surface 610, while the layer offirst barrier region 605 grown on thesubstrate 410 that is exposed in theopening 430 has the N-polar surface 615. It is advantageous for thefirst barrier region 605 to have both the M-polar and N-polar surfaces substrate 410 where the inclined surface of thefirst barrier region 605 will be formed. - For instance, as shown in
FIG. 7 , aninclined surface 705 can be formed by wet etching the N-polar surfaces 615, e.g., with a base as discussed above and in U.S. Pat. No. 6,986,693. As illustrated inFIG. 7 , the M-polar surface 610 of thefirst barrier region 605 is comparatively unaffected by the wet etch. When thefirst barrier region 605 comprises Group III-nitrides (e.g., GaN), wet etching the N-polar surfaces 615 causes rapid etching of the family of {11 01 } planes to form one or morehexagonal pyramid 710. Theinclined surfaces 705 comprisefacets 715 of thepyramid 710. In some cases, theinclined surface 705 can form an angle 720 ranging from about 55 to 65° with respect to a horizontalplanar surface 725 of thesubstrate 410. As shown inFIG. 7 , the wet etching can form a plurality ofinterconnected pyramids 710 on abase portion 730 of thefirst barrier region 605. Thepyramids 710 and thebase portion 730 both comprise a same material of thefirst barrier region 605. -
FIG. 8 shows theapparatus 100 after forming asecond barrier region 805 over thefirst barrier region 605, thereby forming ajunction 810 at the inclined surfaces 705. Thesecond barrier region 805 comprises the other of the n-type or p-type semiconductor crystal that thefirst barrier region 605 does not comprise. Preferred embodiments of thesecond barrier region 805 comprise a group III-nitride. MBE can be used to grow a layer of thesecond barrier region 805 that comprises a group III-nitride having athickness 815 ranging from about 50 to 500 nanometers. MBE is preferred because it can form thesecond barrier region 805 with a minimum variation in thethickness 815. In some cases, thesecond barrier region 805 is deposited over, and in some cases on, the plurality ofinterconnected pyramids 710 on abase portion 730. - As further illustrated in
FIG. 8 , a quantum well 820 can be formed on thefirst barrier region 605 before forming thesecond barrier region 805. In such instances, thejunction 810 comprises thequantum well 820. The quantum well 820 comprising a group III-nitride can be formed, e.g., via MBE on the plurality ofinterconnected pyramids 710 on abase portion 730, and then thesecond barrier region 805 is formed on thequantum well 820. -
FIGS. 9-13 show selected steps in forming contacts to the first andsecond barrier regions FIG. 9 shows theapparatus 100 after filling theopening 430, withsecond photoresist 905. Thephotoresist 905 thereby covers portions of thefirst barrier region 605, thesecond barrier region 805 and optional quantum well 820 that are located inside theopening 430. -
FIG. 10 illustrates theapparatus 100 after exposing the M-polar surface 610 of thefirst barrier region 605. E.g., a plasma etch comprising Ar and Cl can be used to remove the portions of thesecond barrier region 805 and the optional quantum well 820, that are outside of theopening 430 and not covered with thephotoresist 905. Thephotoresist 905 protects thefirst barrier region 605, thesecond barrier region 805 and optional quantum well 820 in theopening 430 from being etched. Thereafter, thephotoresist 905 is removed. -
FIG. 11 depicts theapparatus 100 after depositing a firstohmic contact 1105 on the M-polar surface 610 of thefirst barrier region 605. The firstohmic contact 1105 can be formed by a conventional metal lift-off process. E.g., athird photoresist 1110 can be deposited and patterned to form anopening 1115 to thebarrier region 605 and located around the light-emittingcrystal structure 405. The material of the first contact 1105 (e.g., aluminum, titanium, gold) can be deposited in theopening 1115 on the M-polar surface 610 of thefirst barrier region 605 using conventional metal deposition technique such as electron beam deposition. In some preferred embodiments,first contact 1105 comprises four consecutively deposited layers of titanium, aluminum, titanium, and gold on thefirst barrier region 605 configured as an n-type barrier region. -
FIG. 12 shows theapparatus 100 after depositing a secondohmic contact 1205 on thesecond barrier region 805. E.g., afourth photoresist 1210 can be deposited and patterned to form anopening 1215 to thesecond barrier region 805 and located within the light-emittingcrystal structure 405. As illustrated, thesecond barrier region 805 is located over or on the N-polar surface 615 of thefirst barrier region 605 and thesecond contact 1205 is over or on thesecond barrier region 805. In some preferred embodiments, the secondohmic contact 1205 comprises a different material than thefirst contact 1105. E.g., in some preferred embodiments,second contact 1205 comprises two consecutively deposited layers of nickel and gold on thesecond barrier region 805 configured as a p-type barrier region. -
FIG. 13 depicts theapparatus 100 after lifting-off the photoresist layer 1210 (FIG. 12 ).FIG. 14 shows a plan view of theapparatus 100 such as depicted inFIG. 13 . As illustrated for the embodiments shown inFIGS. 13 and 14 , thefirst contact 1105 need not cover the entire M-polar surface 610. This follows because the portion of thefirst barrier region 605 having the M-polar surface 610 is in electrical contact with portion of thefirst barrier region 605 having the N-polar surface 615. E.g., thebase 730 below thepyramids 710 touches thefirst barrier region 605 that is under the M-polar surface 610. Therefore, thefirst contact 1105 is also in electrical contact with theinclined surfaces 705 and thejunction 810 of thestructure 405. - Similarly, the
second contact 1205 does not need to cover the entiresecond barrier region 805 formed on eachinclined surface 705 of the structure. When thesecond barrier region 805 forms a uniform coating overinterconnected pyramids 710 and thebase 730 of thefirst barrier region 605, then asecond contact 1205 touching any portion of thesecond barrier region 805 is also in electrical contact with theinclined surfaces 705 and thejunction 810 of thestructure 405. Having thestructure 405 comprise a uniform coating ofsecond barrier region 805 over a plurality interconnectedpyramids 710 advantageously allows one more flexibility as to the placement of thesecond contact 1205. This avoids the need to align thesecond contact 1205 with a specific location on eachpyramid 710, which can problematic because the exact location of where apyramid 710 will form by the wet etch process can be unpredictable. - Although the embodiments have been described in detail, those of ordinary skill in the art should understand that they could make various changes, substitutions and alterations herein without departing from the scope of the invention.
Claims (9)
1. A method of manufacturing an apparatus, comprising:
forming a light-emitting crystalline structure including:
forming a first barrier region on a substrate, the first barrier region having one or more inclined surfaces relative to a planar surface of the substrate; and
forming a second barrier region over the first barrier region, to form a junction at the inclined surfaces, wherein the first barrier region comprises one of an n-type or p-type semiconductor crystal, and the second barrier region comprises the other of the n-type or p-type semiconductor crystal.
2. The method of claim 1 , wherein the first barrier region comprises an M-polar surface located over a seed barrier layer comprising an AlN layer on the substrate, and an N-polar surface located on the substrate comprising sapphire, and the inclined surfaces are formed by wet etching the N-polar surface of the first barrier region.
3. The method of claim 1 , wherein forming the first barrier region comprises forming a plurality of interconnected pyramidal-shaped portions on a base portion, the pyramidal-shaped portions and the base portion comprising a same material of the first barrier region.
3. The method of claim 1 , wherein forming the first barrier region comprises forming a plurality of interconnected wedge-shaped portions on a base portion, the wedge-shaped portions and the base portion comprising a same material of the first barrier region.
4. The method of claim 1 , wherein forming the light-emitting crystalline structure further includes:
depositing a quantum well layer on the plurality of interconnected portions of the first barrier region; and
depositing the second barrier region on the quantum well layer that covers the plurality of interconnected portions.
5. The method of claim 1 , further comprising forming contacts to the first and second barrier regions, including:
depositing a first ohmic contact on a M-polar surface of the first barrier region; and
depositing a second ohmic contact on the second barrier region, wherein the second barrier region is located over an N-polar surface of the first barrier region.
6. The method of claim 1 , wherein one of the n-type or p-type barrier regions comprises one or more of the inclined surfaces that are interconnected through a base portion on the substrate, and the other of the n-type or p-type barrier regions comprises an outer layer that continuously coats the inclined surfaces.
7. The method of claim 1 , wherein the inclined surfaces comprise the facets of the structures, the structures having pyramidal shapes.
8. The method of claim 1 , wherein the inclined surfaces comprise the facets of the structures, the structures having wedge shapes.
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US12/852,877 US20100304516A1 (en) | 2006-07-10 | 2010-08-09 | Light-emitting crystal structures |
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US20040189173A1 (en) * | 2003-03-26 | 2004-09-30 | Aref Chowdhury | Group III-nitride layers with patterned surfaces |
US6986693B2 (en) * | 2003-03-26 | 2006-01-17 | Lucent Technologies Inc. | Group III-nitride layers with patterned surfaces |
US20050061074A1 (en) * | 2003-08-13 | 2005-03-24 | Markus Sonnemann | Analyzer unit for the measuring signal of a micromechanical sensor |
US20050285132A1 (en) * | 2004-06-28 | 2005-12-29 | Matsushita Electric Industrial Co., Ltd. | Semiconductor light emitting element, semiconductor light emitting device, and method for fabricating semiconductor light emitting element |
US7915622B2 (en) * | 2004-09-28 | 2011-03-29 | Nanogan Limited | Textured light emitting diodes |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
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US20100216270A1 (en) * | 2009-02-20 | 2010-08-26 | Cheng-Yi Liu | Method for manufacturing light emitting diode |
US8168455B2 (en) * | 2009-02-20 | 2012-05-01 | Cheng-Yi Liu | Method for manufacturing light emitting diode |
Also Published As
Publication number | Publication date |
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JP2009543372A (en) | 2009-12-03 |
EP2041803A1 (en) | 2009-04-01 |
US20080006831A1 (en) | 2008-01-10 |
WO2008008097A1 (en) | 2008-01-17 |
CN101490859A (en) | 2009-07-22 |
US7952109B2 (en) | 2011-05-31 |
KR20090018721A (en) | 2009-02-20 |
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