(12) United States Patent
`(10) Patent N0.:
`US 6,791,119 B2
`
`Slater, Jr. et al.
`(45) Date of Patent:
`Sep. 14, 2004
`
`USOO6791119BZ
`
`(54) LIGHT ElVIITTING DIODES INCLUDING
`
`(75)
`
`MODIFICATIONS FOR LIGHT
`EXTRACTION
`Inventors: David B. Slater, Jr., Raleigh, NC (US);
`Robert C. Glass, Chapel H111, NC
`(US); Charles M. Swoboda,
`Morrisville, NC (US); Bernd Keller,
`Golcta, CA (US); James Ibbetson,
`(Foleta, CA (USE; Brian Thibeault,
`Santa Barbara, CA (U5); Eric J- Tarsa,
`G016”, CA (US)
`
`(73) Assignee: Cree, Inc., Durham, NC (US)
`( * ) Notice:
`Subject to any disclaimer, the term of this
`‘
`'
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(2]) Appl. NO‘: 10/0579821
`(22)
`Filed:
`Jan. 25, 2002
`(65)
`Prior Publication Data
`US 2002/0123164 A1 Sep. 5, 2002
`_
`_
`Related U-S- Application Data
`PIOViSiOIlfll apfllication NO; 69/307235; filed on JUL 23;
`2001, and prov1s10nal application No. 60/265,707, filed on
`Feb. 1 2001.
`’
`-
`Int. CL/ ------------------------------------------------ H0111 33/00
`(51)
`(52) US. Cl.
`.............................. 257/99; 257/95; 257/98
`(58) Field of Search ............................... 257/95, 98, 99
`
`(60)
`
`(56)
`
`References Cited
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`
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`
`EP
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`l'
`a;
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`
`FOREIGN PATENT DOCUMENTS
`/
`51982
`0 051 172
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`'
`(ill
`(l
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`£22 :36 22
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`a e)
`(List continued on next
`P g ‘
`*
`OTHER PUBLICATIONS
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`Craford, Outlook for AllnGaP Technology, Presentation,
`Strategies in light 2000.
`Krames et al., HighiPower TruncatedilnvertediPyramid
`(441»???159051nosP/GHP
`Light—Entittirlg
`‘ Diodes
`Exhibiting > 55External Quantum Efi‘iczency, Applied Phys-
`ics Letters, vol. 75, No. 16, Oct. 18, 1999, pp. 2365—2367.
`(List continued on next page.)
`Primary Examiner—Jerome Jackson
`(74) Attorney, Agent, or Firirt%yers Bigel Sibley &
`Sajovec
`(57)
`
`ABSTRACT
`
`Light emitting diodes include a substrate having first and
`second opposing faces and that is transparent to optical
`radiation in a predetermined wavelength range and that is
`aatterncd tohdcfinc, in cross-section, a plurality of pedestals
`hat extend into the substrate from the first face towards the
`second face. Adiode region on the second face is configured
`0 emit light in the predetermined wavelength range, into the
`substrate upon application of voltage across the diode
`region. Amounting support on the diode region, opposite the
`substrate is configured to support the diode region, such that
`he light
`that
`is emitted from the diode region into the
`substrate, is emitted from the first face upon application of
`voltage across the diode region. The first face of the sub-
`strate may include therein a plurality of grooves that define
`he plurality of triangular pedestals in the substrate. The
`.
`-
`,
`grooves may include tapered sidewalls and/or a beveled
`’oor. The first face of the substrate also may include therein
`an array of via holes. The via holes may include tapered
`sidewalls and/or a floor-
`104 Claims, 15 Drawing Sheets
`
`
`
`1750
`1738
`
`\f
`bonding
`1735
`
`
`barrier
`adhesmn
`i700 1754
`Ohmic/reflector
`\ 1732
`1310a
`1310
`1722
`
`1730
`
`‘ 1724
`
`
`
`
`
`
`x740
`
`1725
`
`210/
`
`
`1310b \{ /
`
`1320
`'
`Ohmic
`m4
`\
`/
`1743
`
`reflector
`barrier#__t
`‘ 1745
`\1 74B ——
`bondiHi
`
`
`
`|
`
`
`
`L
`
`Cree Ex. 1012
`
`Page 1
`
`Cree Ex. 1012
`
`Page 1
`
`

`

`US 6,791,119 32
`
`Page 2
`
`US. PATENT DOCUMENTS
`
`WO
`W0
`
`WO 00/33365
`WO 01/47039 A1
`
`6/2000
`(5/2001
`
`OTHER PUBLICATIONS
`Lambrecht et al., Band Structure Interpretation of the Opti-
`cal Transztzons Between low—Lying Conduction Bands in
`n—Type Doped SiC Polytypes, Materlals Sc1ence Forum,
`V015~ 264-268, 1998, pp- 271-274-
`Craford, Overview of Device Issues in High—Brightness
`Light—Emitting Diodes, Chapter 2, High Brightness Light
`Emitting Diodes: Semiconductors and Semimetals, vol. 48,
`S ringfellow et al. ed., Academic Press, 1997, pp. 47—63.
`Yoo ct al., Bulk Crystal Growth of 6H—SiC on Polytype—
`Controlled Substrates Through Vapor Phase and Charac-
`.
`.
`.
`terization, Journal of Crystal Growth, vol. 115, vol. 1991,
`P? 733—739
`,
`,
`'
`,
`B1ederman, The OpticalAbsorptionBands and TheirAnisot-
`ropy in the Wirious Modifications of SiC, Solid State Com—
`munications, vol. 3, 1965, pp. 343—346.
`LS. application Ser. No. 09/154,363, entitled Vertical
`Geometry InGaN LED.
`L.S. application Ser. \Io. 60,411,980, filed Sep. 19, 2002,
`Phosphor—Coated Light Emitting Diodes Including Tapered
`S‘dewallsi “”4 Fabm‘lm" Metho‘is‘
`LS. application Ser. \Io. 10/003,331, filed Oct. 31, 2001,
`Low Temperature Formation of Backside Ohmic Contacts
`for Vertical Devices.
`LS. application Ser. No. 60/294,445, filed May 30, 2001,
`1 ulti—Quantum Well Light Emitting Diode Structure.
`LS. application Ser. \10. 60/294,378, filed May 30, 2001,
`Light Emitting Diode Structure With Multi—Quantum Well
`and Superlattice Structure.
`,
`.
`.
`,
`,
`L..S. applicahon Ser. No 60/294,308, filed May 30, 2001,
`Light Emitting Diode Structure With Superlatiice Structure.
`LS. application Ser. \Io. 09/787,189, filed Mar. 15, 2001,
`Low Temperature Formation of Backside Ohmic Contacts
`for Vertical Devices.
`Invitation to Pay Addi ional Fccs, Annex to Form PCT/ISA/
`206, Communication Relating to the Results of the Partial
`International Search, PCT/USOZ/02849, Aug. 26, 2002.
`International Search Report, PCT/USO2/02849, Dec. 2,
`2002.
`
`
`
`
`
`Mensz et al., InxGAlflN/AlvG/llivN Violet Light Emitting
`Diodes with Reflective p—Contacts for High Single Sided
`Light Extraction, Electronics Letters, VOl. 33, No. 24, Nov.
`20, 1997, pp. 2066—2068.
`Honina et al., Evaluation ofBarrierIl/[etals ofSolder Bumps
`for Flip—Chip Interconnection, Electronic Manufacturing
`Technology Symposium, 1995, Proceedings of 1995 Japan
`International, 18’” IEEE/CPMT, Dec. 4, 1995, pp. 113—116.
`Lcc ct al., Bonding ofInP LaserDiodes byAu—Sn Solder and
`Tungsten—Based Barrier Illetallization Schemes, Semicon-
`ductor Science and Technology, vol. 9, No. 4, Apr. 1994, pp.
`379—386.
`
`* cited by examiner
`
`............... 372/45
`
`307/86
`' 323:3:
`257/76
`. 257/77
`. 257/77
`, 437/22
`. 438/33
`. 117/84
`-- 257/103
`
`
`
`-
`
`
`
`9/ 993 Okazaki et a].
`5,247,533 A
`8/ 994 Lezan et a1.
`5,338,994 A
`1;; 23: 31:31::dire:
`233335: 1’:
`5/ 995 Edmond et all
`5’4161342 A
`6/ 996 Edmond et a1.
`5:523:589 A
`12/ 996 Tischler .......
`5,585,648 A
`2/ 997 deond et a],
`5,604,135 A
`5/ 997 Negley ........
`5,631,190 A
`2/ 998 Carter et a1.
`.
`5,718,760 A
`4/ 998 Edmond Ct 31-
`5:739:54 A
`(7/ 998 Yang et 31-
`5:7“):‘379 A
`6/ 998 Nakamura et a1. """
`" 252/749
`5’267’381 A
`7/ 998 Nakamura et a1.
`. 257/96
`5,/77,350 A
`
`
`7/ 998 Krames et a1.
`. 216/24
`5,779,924 A
`5,846,694 A * 12/ 998 Strand et al.
`430/321
`5,912,477 A
`6/ 999 Negley .....
`. 257/95
`5,917,202 A
`6/ 999 Hafiz et a1,
`, 257/93
`5,952,681 A
`9/ 999 Chen ...........
`. 257/89
`
`6,015,719 A
`1/2000 Kish, Jr. ct a1.
`. 438/29
`
`
`6,031,243 A *
`2/2000 Taylor ...............
`257/98
`
`6,046,465 A
`4/2000 Wang cl al~
`~~~~~
`257/98
`1 353/3:
`gggifiii :
`3:888 3:341
`
`.
`6:118:259 A
`9/2000 Bucks et a1.
`323/312
`
`9/2000 Edmond a a1.
`6,120,600 A
`. 117/89
`6,121,636 A
`9/2000 Morita et a].
`. 257/99
`
`
`9/2000 Isokawa ct a1.
`.
`6,121,637 A
`257/99
`
`.. 257/103
`6,133,589 A
`10/2000 Krames et a1.
`6,139,166 A
`10/2000 Marshall et a1
`362/231
`
`691477453 A
`11/2000 BUCKS 6131‘
`325/225
`621691294 B1
`U2001 Biinngye et “1'
`' 237/79
`
`1/2001 L1nthlcum et a1.
`6,177,688 B1
`. 257/77
`2/2001 Edmond et al.
`.
`6,187,606 B1
`. 438/46
`
`.,
`6 194 742 131
`2/2001 Kern et a1.
`. 257/94
`
`6:201:264 B1
`3/2001 Khare et a].
`. 257/97
`6,204,523 B1
`3/2001 Carey et a1.
`. 257/98
`
`4/2001 Carter-Comm] et a],
`,,,,,, 257/98
`6,222,207 B1
`
`.
`6,229,160 B1
`5/2001 Krames et a1.
`257/94
`6,455,878 B1
`9/2002 Bhat et al.
`. 257/99
`
`
`1/2003 Emerson et 31-
`-~ 257/79
`2003/0006418 A1
`2003/0025212 A1
`2/2003 Bhat et al.
`FOREIGN PATENT DOCUMENTS
`6 1 1 10476
`1-225377
`06-232510
`07-235729
`08621660
`9-82587
`09-223846
`10-163530
`10-233549
`107256604
`11 -150302
`11 -191641
`1 1 220168
`2000777713 A
`2000-195827
`
`
`
`5/1986
`9/1989
`8/1994
`9/1995
`12/1996
`3/1997
`8/1997
`6/1998
`9/1998
`9/1998
`6/1999
`7/1999
`8/1999
`3/2000
`7/2000
`
`A A
`
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`
`Cree Ex. 1012
`
`Page 2
`
`Cree Ex. 1012
`
`Page 2
`
`

`

`US. Patent
`
`Sep. 14, 2004
`
`Sheet 1 of 15
`
`US 6,791,119 B2
`
`100
`
`FIG.1
`
`170
`
`140
`
`130
`
`120
`
`110
`
`\
`
`160
`
`110a
`
`FIG. 2
`
`
`
`
`Cree Ex. 1012
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`

`

`US. Patent
`
`Sep. 14, 2004
`
`Sheet 2 of 15
`
`US 6,791,119 B2
`
`
`
`Cree Ex. 1012
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`Cree Ex. 1012
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`

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`US. Patent
`
`Sep. 14, 2004
`
`Sheet 3 of 15
`
`US 6,791,119 B2
`
`400
`
`FIG. 4
`
`210
`
`
`1100
`
`5°°\
`
`FIG. 5
`
`Cree Ex. 1012
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`

`

`US. Patent
`
`Scp.14,2004
`
`Shcct4 0f15
`
`US 6,791,119 132
`
`0.0E
`
`01-1411
`
`ImL?
`
`QITIV1.!
`
`
`
`I...
`
`4:4n4n4I4-4-4i4l4l414..4446444444
`
`til-r
`lulu-
`
`0mm00m03.00¢0mm
`
`AEEr3566;
`
`NA
`
`GA
`
`v.0
`
`Nd
`
`0d
`
`3.8534.
`
`3.3
`
`Cree Ex. 1012
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`Page 6
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`Cree Ex. 1012
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`
`

`

`US. Patent
`
`Sep. 14, 2004
`
`Sheet 5 of 15
`
`US 6,791,119 B2
`
`FIG. 7A
`
`72°\
`
`722
`V
`
`710a
`
`78
`‘5‘
`
`73'
`1‘
`
`7108
`
`720
`
`FIG. 7B
`
`700
`
`/
`
`Cree Ex. 1012
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`Page 7
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`
`

`

`US. Patent
`
`Sep. 14, 2004
`
`Sheet 6 0f 15
`
`US 6,791,119 B2
`
`710a'
`
`720
`
`FIG. 7C
`
`700'\
`
`\
`
`13—0
`
`724'
`\710'
`
`72
`
`722'
`
`722'
`
`710'
`
`740
`
`FIG. 8C
`
`810a'
`
`/
`
`Cree Ex. 1012
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`Page 8
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`
`

`

`US. Patent
`
`Sep. 14, 2004
`
`Sheet 7 of 15
`
`US 6,791,119 B2
`
`
`
`810a
`
`820
`
`FIG. 88
`
`
`
`Cree Ex. 1012
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`Page 9
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`Cree Ex. 1012
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`

`

`US. Patent
`
`Sep. 14, 2004
`
`Sheet 8 of 15
`
`US 6,791,119 B2
`
`FIG. 9
`
`7103‘
`
`720
`
`900
`
`
`
`Cree Ex. 1012
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`Page 10
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`
`

`

`US. Patent
`
`Sep. 14, 2004
`
`Sheet 9 of 15
`
`US 6,791,119 B2
`
`FIG. 11
`
`710a
`
`720
`
`
`220
`
`840
`
`412
`
`414
`
`155
`
`Cree Ex. 1012
`
`Page 11
`
`810a
`
`820
`
`1200
`
`810
`
`Cree Ex. 1012
`
`Page 11
`
`

`

`US. Patent
`
`Sep. 14, 2004
`
`Sheet 10 of 15
`
`US 6,791,119 B2
`
`710a
`
`720
`
`FIG. 14A
`
`
`
`
`
`Cree Ex. 1012
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`Page 12
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`

`

`US. Patent
`
`Sep. 14, 2004
`
`Sheet 11 0f 15
`
`US 6,791,119 B2
`
`FIG. 15A
`
`
`
`Cree Ex. 1012
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`

`

`US. Patent
`
`Sep. 14, 2004
`
`Sheet 12 of 15
`
`US 6,791,119 B2
`
`FIG. 16
`
`1600
`
`282
`
`280
`
`Active
`
`$C
`
`1620
`
`150
`
`
`240 I._ ,/
`170 no I.—120 .
`
`
`
`110
`
`
`
`
`
`—_
`
`
`
`
`
`270
`
`260
`
`Cree Ex. 1012
`
`Page 14
`
`Cree Ex. 1012
`
`Page 14
`
`

`

`US. Patent
`
`Sep. 14, 2004
`
`Sheet 13 of 15
`
`US 6,791,119 B2
`
`FIG. 17B
`
`
`
`1750
`
`
`
`
`
`FIG. 17A
`
`1730
`
`
`
`
`
`1738
`
`1734
`
`1700
`\ 1732
`
`Ohmic/ reflector
`
`
`
`1726
`
`1724
`
`A
`
`1742 l
`_
`
`
`1746
`
`
`
`
`
`
`bonding
`
`
`Cree Ex. 1012
`
`Page 15
`
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`
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`
`

`

`US. Patent
`
`Sep. 14, 2004
`
`Sheet 14 of 15
`
`US 6,791,119 B2
`
`FIG. 18
`
`1840
`
`1800
`
`1824
`
`1822
`
`1826
`
`1828
`
`1830
`
`
`
`
`
`
`1320
`
`
`
`
`
`
`
`1820
`
`
`
`
`
`
`
`
`
`1810
`
`Cree Ex. 1012
`
`Page 16
`
`Cree Ex. 1012
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`
`

`

`US. Patent
`
`Sep. 14, 2004
`
`Sheet 15 of 15
`
`US 6,791,119 B2
`
`FIG. 19
`
`LED Manufacturing
`
`
`
`Fabricate diode region on
`silicon carbide substrate
`
`Form grooves and/ or
`via holes
`
`
`
`Form semi—transparent
`electrode and/or reflector
`
`Dice
`
`
`Join
`
`
`1910
`
`1920
`
`1930
`
`1940
`
`1950
`
`1960
`
`End
`
`Cree Ex. 1012
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`Page 17
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`

`US 6,791,119 B2
`
`1
`LIGHT EMITTING DIODES INCLUDING
`MODIFICATIONS FOR LIGHT
`EXTRACTION
`
`CROSS-REFERENCE TO PROVISIONAL
`APPLICATIONS
`
`This application claims the benefit of Provisional Appli-
`cation Serial No. 60/265,707, filed Feb. 1, 2001 entitled
`Light Emitting Diode With Optically Transparent Silicon
`Carbide Substrate, and Provisional Application Serial No.
`60/307,235,
`filed Jul. 23, 2001, entitled Light Emitting
`Diodes Including Modifications for Light Extraction and
`Alanafizcturingill/[ethods Therefor, the disclosures of both of
`which are hereby incorporated herein by reference in their
`entirety as if set forth fully herein.
`STATEMENT OF FEDERAL SUPPORT
`
`This invention was made possible with government sup—
`port under grant number 70NANB8H4022 from the
`National Institute of Standards and Technology (Advanced
`Technology Program). The United States government has
`certain rights to this invention.
`FIELD OF TIIE INVENTION
`
`This invention relates to microelectronic devices and
`fabrication methods therefor, and more particularly to light
`emitting diodes (LEDs) and manufacturing methods there-
`for.
`
`BACKGROUND OF THE INVENTION
`
`
`
` iciency of LEDs is the cost per lumen.
`
`Light emitting diodes are widely used in consumer and
`commercial applications. As is well known to those having
`skill in the art, a light emitting diode generally includes a
`diode region on a microelectronic substrate. The microelec-
`tronic substrate may comprise,
`for example, gallium
`arsenide, gallium phosphide, alloys thereof, silicon carbide
`
`
`and/or sapphire. Continued developments in LEDs have
`
`
`resulted in highly e 'icient and mechanically robust light
`sources that can cover the visible spectrum and beyond.
`These attributes, coupled with the potentially long service
`life of solid state cevices, may enable a variety of new
`display applications, and may place LEDs in a position to
`compete with the we l entrenched incandescent and fluores-
`cent lamps,
`One measure of e
`The cost per lumen for an LED may be a function of the
`manufacturing cost per LED chip,
`the internal quantum
`efficiency of the LED material and the ability to couple or
`extract the generatec light out of the device. An overview of
`light extraction issues may be found in the textbook entitled
`High BrightnessLight EmittingDiodes to Stringfellow et al.,
`Academic Press, 1997, and particularly Chapter 2, entitled
`Overview of Device Issues in High-Brightness Light Entit-
`ting Diodes, to Craford, at pp. 47—63.
`Light extraction has been accomplished in many ways,
`depending, for example, on the materials that are used to
`fabricate the diode region and the substrate. For example, in
`gallium arsenide and gallium phosphide material systems, a
`thick, p—type, topside window layer may be used for light
`extraction. The p—type window layer may be grown because
`high epitaxial growth rates may be possible in the gallium
`arsenide/gallium phosphide material systems using liquid
`and/or vapor phase epitaxy. Moreover, current spreading
`may be achieved due to the conductivity of the p-type
`topside window layer. Chemical etching with high etch rates
`
`10
`
`15
`
`
`
`
`
`2
`and high etch selectivity also may be used to allow the
`removal of at least some of the substrate if it is optically
`absorbent. Distributed Bragg reflectors also have been
`grown between an absorbing substrate and the diode region
`0 decouple the emitting and absorbing regions,
`Other approaches for
`light extraction may involve
`mechanical shaping or texturing of the diode region and/or
`he substrate. However, it may be desirable to provide other
`
`ight extraction techniques that can allow further improve-
`
`
`
`ments in extraction e iciency. Moreover, it may be desirable
`0 increase the area of an LED chip from about 0.1 mm2 to
`
`
`arger areas, to thereby provide larger LEDs. Unfortunately,
`
`he e ectiveness of these shaping techniques may not be
`maintained as the chip dimensions are scaled tip for higher
`aower/intensity and/or other applications.
`Much development
`interest and commercial activity
`recen ly has focused on LEDs that are fabricated in or on
`silicon carbide, because these LEDs can emit radiation in the
`alue/green portions of the visible spectrum. See,
`for
`exam ale, U.S. Pat. No. 5,416,342 to Edmond et al., entitled
`Blue Light-Emitting Diode With High External Quantum
`Efi‘iciency, assigned to the assignee of the present
`application, the disclosure of which is hereby incorporated
`herein by reference in its entirety as if set forth frilly herein.
`There also has been much interest in LEDs that include
`gallium nitride-based diode regions on silicon carbide
`substrates, because these devices also may emit light with
`high efficiency. See, for example, US. Pat. No. 6,177,688 to
`Linthicum et al., entitled Pendeoepitaxial Gallium Nitride
`. Semiconductor Layers 0n Silicon Carbide Substrates, the
`disclosure of which is hereby incorporated herein by refer-
`ence in its entirety as if set forth fully herein.
`In such silicon carbide LEDs or gallium nitride LEDs on
`silicon carbide,
`it may be difficult
`to use conventional
`
`techniques for light extraction, For example,
`it may be
`
`
`di icult to use thick p-type window layers because of the
`re atively low growth rate of gallium nitride. Also, although
`
`
`such LEDs may benefit from the use of Bragg reflectors
`
`
`and/or substrate removal techniques, it may be di
`icult to
`fabricate a reflector between the substrate and the gallium
`ni ride diode region and/or to etch away at least part of the
`silicon carbide substrate.
`
`35
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`US. Pat. No. 4,966,862 to Edmond, entitled Method of
`Production of Light Emitting Diodes, assigned to the
`assignee of the present application, the disclosure of which
`is hereby incorporated herein by reference in its entirety as
`if set forth fully herein, describes a method for preparing a
`alurality of light emitting diodes on a single substrate of a
`semiconductor material. The method is used for structures
`where the substrate includes an epitaxial layer of the same
`semiconductor material
`that
`in turn comprises layers of
`a-type and n-type material that define a p-n junction ther-
`ebetween. The epitaxial layer and the substrate are etched in
`a predetermined pattern to define individual diode
`arecursors, and deeply enough to form mesas in the epitaxial
`ayer that delineate the p—n junctions in each diode precursor
`rom one another. The substrate is then grooved from the
`side of the epitaxial layer and between the mesas to a
`aredetermined depth to define side portions of diode pre-
`cursors in the substrate while retaining enough of the
`substrate beneath the grooves to maintain its mechanical
`stability. Ohmic contacts are added to the epitaxial layer and
`o the substrate and a layer of insulating material is formed
`on the diode precursor. The insulating layer covers the
`aortions of the epitaxial layer that are not covered by the
`ohmic contact, any portions of the one surface of the
`substrate adjacent the mesas, and the side portions of the
`
`
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`Cree Ex. 1012
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`

`US 6,791,119 B2
`
`3
`substrate. As a result, the junction and the side portions of
`the substrate of each diode are insulated from electrical
`contact other than through the ohmic contacts. When the
`diodes are separated they can be conventionally mounted
`with the junction side down in a conductive epoxy without
`concern that the epoxy will short circuit the resulting diode.
`See the abstract of US, Pat, No. 4,966,862.
`US. Pat. No. 5,210,051 to Carter, Jr., entitled High
`Efficiency Light Emitting Diodes From Bipolar Gallium
`Nitride, assigned to the assignee of the present application,
`the disclosure of which is hereby incorporated herein by
`reference in its entirety as if set forth fully herein, describes
`a method of growing intrinsic, substantially undoped single
`crystal gallium nitride with a donor concentration of 7x1017
`cm3 or less. The method comprises introducing a source of
`nitrogen into a reaction chamber containing a growth surface
`while introducing a source of gallium into the same reaction
`chamber and while directing nitrogen atoms and gallium
`atoms to a growth surface upon which gallium nitride will
`grow. The method further comprises concurrently maintain—
`ing the growth surface at a temperature high enough to
`provide sufficient surface mobility to the gallium and nitro-
`gen atoms that strike the growth surface to reach and move
`into proper lattice sites,
`thereby establishing good
`erystallinity,
`to establish an effective sticking coefficient,
`and to thereby grow an epitaxial layer of gallium nitride on
`the growth surface, but low enough for the partial pressure
`of nitrogen species in the reaction chamber to approach the
`equilibrium vapor pressure of those nitrogen species over
`gallium nitride under the other ambient conditions of the
`chamber to thereby minimiae the loss of nitrogen from the
`gallium nitride and the nitrogen vacancies in the resulting
`epitaxial layer. See the abstract of US. Pat. No. 5,210,051.
`In view of the above discussion, improved light extraction
`techniques may be desirable for LEDs, especially LEDs that
`are fabricated from silicon carbide, that are fabricated from
`gallium nitride on silicon carbide and/or that have a rela-
`tively large area.
`SUMMARY OF THE INVENTION
`
`Light emitting diodes according to some embodiments of
`the invention include a substrate having first and second
`opposing faces that is transparent to optical radiation in a
`predetermined wavelength range and that
`is patterned to
`define, in cross-section, a plurality of pedestals that extend
`into the substrate from the first face towards the second face.
`As used herein, the term “transparent” refers to an element,
`such as a substrate, layer or region that allows some or all
`optical radiation in a predetermined wavelength range to
`pass therethrough, i.e., not opaque. A diode region on the
`second face is configured to emit light in the predetermined
`wavelength range, into the substrate upon application of
`voltage across the diode region. In other embodiments, a
`mounting support on the diode region, opposite the substrate
`is configured to support the diode region, such that the light
`that is emitted from the diode region into the substrate, is
`emitted from the first face upon application of voltage across
`the diode region. In some embodiments, the light emitting
`diode on a transparent substrate with pedestals is flip-
`mounted on a mounting support, with the diode region
`adjacent to the mounting support and a substrate opposite
`the mounting support, for light emission through the sub—
`strate. In other embodiments, the light emitting diode on a
`transparent substrate with pedestals is mounted on a mount-
`ing support, with the substrate adjacent to the mounting
`support and the diode region opposite the mounting support.
`Thus, non—flip—chip mounting also may be provided.
`
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`4
`In yet other embodiments of the invention, a reflector also
`is provided between the mounting support and the diode
`region or the substrate. The reflector may be configured to
`reflect
`light
`that
`is emitted from the diode region back
`through the diode region, through the substrate and from the
`pedestals, upon application of voltage across the diode
`region. In other embodiments, a transparent electrode also
`may be provided between the diode region and the reflector.
`In still other embodiments, a solder preform and/or other
`bonding region may be provided between the reflector and
`the mounting support and/or an optical element such as a
`window or lens may be provided adjacent the first face
`opposite the diode region. In yet other embodiments, the
`diode region includes a peripheral portion and at least one
`central portion that is enclosed by the peripheral portion, and
`the light emitting diode further comprises at
`least one
`electrode on the diode region, that is confined to within the
`at least one central portion and does not extend onto the
`peripheral portion. It will be understood that the central
`portion need not be centered on the diode region.
`In other embodiments of the invention, a contact structure
`for the substrate and/or the diode region of an LED includes
`a transparent ohmic region, a reflector, a barrier region and
`a bonding region. The transparent ohmic region provides
`electrical contact and/or current spreading. The reflector
`reflects at least some incident radiation and also may provide
`current spreading. The barrier region protects the reflector
`and/or the ohmic region. The bonding region bonds the LED
`Jackage to a mounting support. In some embodiments, the
`unctionality of the transparent ohmic region and the reflec-
`or can be combined in a single ohmic and reflector region.
`Contact structures according to these embodiments of the
`invention also may be used with conventional silicon car-
`3ide LEDs, gallium nitride on silicon carbide LEDs and/or
`other LEDs.
`
`In still other embodiments of the present invention, the
`1rst face of the substrate may include therein at least one
`groove that defines a plurality of pedestals, such as trian-
`gular pedestals, in the substrate. The grooves may include
`apered sidewalls and/or a beveled floor. The first and second
`aces of the substrate may have square perimeters, and/or the
`1rst face of the substrate may be textured. The light emitting
`diode may further include a plurality of emission regions
`and/or electrodes on the diode region, a respective one of
`which is confined to within a respective one of the pedestals
`and does not extend beyond the respective one of the
`pedestals.
`In yet other embodiments of the present invention, the
`first face of the substrate includes therein an array of via
`holes. The via holes may include tapered sidewalls and/or a
`floor. The via holes preferably extend only part way through
`the substrate, but in other embodiments they can extend all
`the way through the substrate. The first and second substrate
`faces may have square perimeters, and/or the first face may
`be textured. The light emitting diodes may further include at
`least one electrode on the diode region that does not overlap
`the array of via holes.
`The pedestals and/or array of via holes also may be used
`with light emitting diodes that include silicon carbide or
`non-silicon carbide substrates,
`to allow improved light
`extraction therefrom. Moreover, electrodes as described
`above also may be used with light emitting diodes that
`include a non-silicon carbide substrate. For example, when
`the first face of the substrate has smaller surface area than
`the second face, and the diode region is on the second face,
`an emission region may be provided on the diode region that
`is confined to within the smaller surface area of the first face.
`
`
`
`Cree Ex. 1012
`
`Page 19
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`Cree Ex. 1012
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`

`

`US 6,791,119 B2
`
`6
`textured. An electrode may be formed on the diode region
`that does not overlap the array of via holes.
`Sawing a plurality of intersecting grooves and/0r reactive
`etching an array of via holes into the first face may be used
`for light emitting diodes that include a silicon carbide or
`non—silicon carbide substrate to allow improved light extrac—
`tion therefrom. Moreover,
`the formation of an emission
`region on the diode region that is confined to within the
`smaller surface area of the first face also may be used for
`other conventional light emitting diodes, to allow improved
`light extraction therefrom.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIGS. 1—5 are cross-sectional views of light emitting
`diodes according to embodiments of the present invention.
`FIG. 6 graphically illustrates absorption of light versus
`wavelength for silicon carbide at various doping levels.
`FIG. 7A is a top view and FIGS. 7B and 7C are cross-
`sectional views along the line 7B—7B' of FIG. 7A, of ight
`emitting diodes according to other embodiments of the
`present invention.
`FIG. 8A is a top View and FIGS. 8B and 8C are cross-
`sectional views along the line SB—SB‘ of FIG. 8A, of ight
`emitting diodes according to other embodiments of the
`present invention.
`FIGS. 9—13 are cross-sectional views of light emi ting
`diodes according to yet other embodiments of the present
`invention.
`
`FIG. 14A a cross—sectional View taken along the lines
`14A714A' of FIG. 14B, which is a bottom view of
`ight
`emitting diodes according to still other embodiments o the
`aresent invention.
`
`
`
`5
`light
`invention,
`In other embodiments of the present
`emitting diodes include a compensated, colorless silicon
`carbide substrate having first and second opposing faces and
`a gallium nitride-based diode region on the second face that
`is configured to emit light into the substrate upon application
`of voltage across the diode region. Mounting supports,
`reflectors, contact structures, grooves, pedestals, texturing
`and/or confined emission areas/electrodes may be provided
`according to any of the embodiments that were described
`above.
`
`Accordingly, many of the above-described embodiments
`comprise embodiments of means for extracting from the
`substrate at least some of the light that is emitted into the
`substrate by the diode region. Examples of these means for
`extracting include compensating dopants in the silicon car-
`bide substrate to provide a colorless silicon carbide
`substrate, patterning the substrate to define, in cross-section,
`a plurality of pedestals that extend into the substrate from the
`first face toward the second face and/or many of the other
`embodiments that were described above, including mount-
`ing supports,
`reflectors, contact structures, grooves,
`pedestals,
`texturing and/or confined emission areas/
`electrodes.
`
`Light emitting diodes may be manufactured, according to
`some embodiments of the invention, by forming a diode
`region that is configured to emit light in a predetermined
`wavelength range on a second face of a substrate having first
`and second opposing faces, and that is transparent to the
`optical radiation in the predetermined wavelength range.
`The substrate is patterned before, during and/or after form-
`ing the diode region to define, in cross-section, a plurality of
`pedestals that extend into the substrate from the first face
`towards the second face. In other embodiments, the diode
`region is mounted onto a mounting substrate that is config-
`ured to support the diode region such that the light that is
`emitted from the diode region into the substrate is emitted
`from the first face upon application of voltage across the
`diode region. The mounting may be preceded by forming a
`reflector on the diode region such that
`the reflector is
`configured to reflect light that is emitted from the diode
`region back into the diode region through the substrate and
`from the first face, upon application of voltage across the
`diode region. Prior to forming the reflector, a transparent
`ohmic electrode also may be formed on the diode region
`opposite the substrate. A barrier region and/or an adhesion
`region also may be formed after forming the reflector. In
`other embodiments, a mounting support is placed adjacent
`the reflector with the barrier region and/or the adhesion
`region therebetween, and the LED is joined to the mounting
`support. In still other embodiments, an electrode is formed
`on the diode region that is confined to within the central
`portion thereof and does not extend onto the peripheral
`portion thereof.
`Other method embodiments include forming a plurality of
`intersecting grooves into the first face of the substrate to
`define the plurality of pedestals, such as triangular pedestals,
`in the substrate. The grooves may include tapered sidewalls
`and/or a beveled floor. The first face of the substrate also
`may be textured. A plurality of electrodes also may be
`formed on the diode region. In some embodiments, a respec-
`tive one of the electrodes is confined to within a respective
`one of the pedestals and does not extend beyond the respec-
`tive one of the pedestals.
`Still other method embodiments according to the present
`invention include reactive ion etching an array of via holes
`in the first face of the substrate. The via holes may include
`tapered sidewalls and/or a floor. The first face also may be
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`FIG. 15A a cross-sectional View taken along the lines
`15A—15A‘ of FIG. 15B, which is a bottom view of
`ight
`emitting diodes according to yet other embodiments o i the
`aresent invention.
`FIGS. 16, 17A and 18 are cross—sectional views of
`emitting diodes according to still other embodiments o
`aresent invention.
`
`ight
`the
`
`FIG. 17B is a top view of FIG. 17A according to embodi-
`ments of the present invention.
`FIG. 19 is a flowchart illustrating manufacturing methods
`or light emitting diodes according to embodiments of the
`aresent invention.
`
`DETAILED DESCRIPTION OF PREFERRED
`EMBODIMENTS
`
`The present invention now will be described more fully
`hereinafter with reference to the accompanying drawings, in
`which preferred embodiments of the invention are shown.
`This invention may, however, be embodied in many dilferent
`forms and should not be construed as limited to the embodi—
`ments set forth herein. Rather, these embodiments are pro—
`vided so that this disclosure will be thorough and complete,
`and will fully convey the scope of the invention to those
`skilled in the art. In the drawings, the thickness of layers and