(12) United States Patent
`Nitta et al.
`
`111111
`
`1111111111111111111111111111111111111111111111111111111111111
`US006258617Bl
`US 6,258,617 Bl
`*Jul. 10, 2001
`
`(10) Patent No.:
`(45) Date of Patent:
`
`(54) METHOD OF MANUFACTURING BLUE
`LIGHT EMITTING ELEMENT
`
`(75)
`
`Inventors: Koichi Nitta; Hidetoshi Fujimoto;
`Masayuki Ishikawa, all of
`Kanagawa-ken (JP)
`
`(73) Assignee: Kabushiki Kaisha Toshiba, Kawasaki
`(JP)
`
`( *) Notice:
`
`This patent issued on a continued pros(cid:173)
`ecution application filed under 37 CFR
`1.53( d), and is subject to the twenty year
`patent term provisions of 35 U.S.C.
`154(a)(2).
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21)
`
`Appl. No.:
`
`08/817,159
`
`(22) PCT Filed:
`
`Aug. 30, 1996
`
`(86) PCT No.:
`
`PCT/JP96/02434
`
`§ 371 Date:
`
`Apr. 15, 1997
`
`§ 102(e) Date: Apr. 15, 1997
`
`(87) PCT Pub. No.: W097/08759
`
`PCT Pub. Date: Mar. 6, 1997
`
`(30)
`
`Foreign Application Priority Data
`
`Aug. 31, 1995
`
`(JP) .............................................. P07-223993
`
`(51)
`
`(52)
`
`(58)
`
`Int. Cl?
`
`......................... HOlL 21!20; HOlL 21/205;
`HOlL 33/00; HOlS 3/18
`U.S. Cl. .............................. 438/46; 438/47; 438/505;
`438/508; 438/509; 438/930
`Field of Search ................................ 257/96, 97, 103;
`372/43, 45; 438/46, 47, 479, 503, 505,
`507, 509, 508, 930
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`5,432,808 * 7/1995 Hatano ................................... 372/45
`5,583,879 * 12/1996 Yamazaki ............................. 257/103
`5,729,029 * 3/1998 Rudaz .................................... 257/13
`5,733,796 * 3/1998 Manabe eta!. .
`5,742,628 * 4/1998 Fujii ....................................... 372/45
`5,747,832 * 5/1998 Nakamura eta!. .................. 257/103
`5,751,013 * 5/1998 Kidoguchi et a!. .................... 257/13
`5,751,021 * 5/1998 Teraguchi ............................. 257/103
`5,753,939 * 5/1998 Sassa et a!. ............................ 257/94
`5,804,834 * 9/1998 Shimoyama eta!. .................. 257/22
`
`FOREIGN PATENT DOCUMENTS
`6-196755 *
`6-232451 *
`8-8460 *
`8-32113 *
`8-115880
`8-125222
`
`7/1994 (JP) . ... ... .... ... ... ... ... .... ... ... ... .. 257/103
`8/1994 (JP) . ... ... .... ... ... ... ... .... ... ... ... .. 257/103
`1!1996 (JP) . ... ... .... ... ... ... ... .... ... ... ... .. 257/103
`2/1996 (JP) . ... ... .... ... ... ... ... .... ... ... ... .. 257/103
`5/1996 (JP) .
`5/1996 (JP) .
`
`* cited by examiner
`
`Primary Examiner-Mary Wilczewski
`(74) Attorney, Agent, or Firm-Foley & Lardner
`
`(57)
`
`ABSTRACT
`
`A gallium-nitride-based blue light emitting element that is
`manufacturable through a small number of processes and a
`method of manufacturing the same are disclosed. A first
`gallium-nitride-based semiconductor layer containing impu(cid:173)
`rities of a first conductivity type, a gallium-nitridebased
`semiconductor active layer that is substantially intrinsic, and
`a second gallium-nitride-based semiconductor layer contain(cid:173)
`ing impurities of a second conductivity type that is opposite
`to the first conductivity type are formed according to a
`thermal CVD method and are left in an inert gas to cool by
`themselves.
`
`23 Claims, 4 Drawing Sheets
`
`20
`
`/
`
`TEMPERATURE ( oC)
`
`1200
`1100
`
`900
`
`TIME
`
`Vizio EX1015 Page 0001
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`U.S. Patent
`
`Jul. 10, 2001
`
`Sheet 1 of 4
`
`US 6,258,617 Bl
`
`FIG.l
`
`r---107
`-----106
`
`---105
`
`---104
`
`---103
`
`r---1 08
`
`102
`
`101
`
`-----...__
`
`---
`
`.--.....__.. 100
`
`Vizio EX1015 Page 0002
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`U.S. Patent
`
`Jul. 10, 2001
`
`Sheet 2 of 4
`
`US 6,258,617 Bl
`
`FIG.2
`
`20
`
`~
`
`23
`
`FIG.3
`TEMPERATURE ( oC)
`
`1200 --
`1100
`
`900
`
`TIME
`
`Vizio EX1015 Page 0003
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`U.S. Patent
`
`Jul. 10, 2001
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`Sheet 3 of 4
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`US 6,258,617 Bl
`
`512
`
`I
`
`FIG.4
`510
`
`I
`
`r-- 506
`--505
`
`500
`)
`
`512
`
`I
`
`511
`504
`503
`502
`501
`
`f-.-
`
`r--
`
`r--
`
`1--
`
`\
`
`FIG.5
`711
`'/~ r------710
`r---708
`r---706
`r---704
`
`----
`709
`----
`707
`705
`
`........__
`
`r---
`
`r--
`
`1--
`
`703
`702
`701
`
`Vizio EX1015 Page 0004
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`U.S. Patent
`
`Jul. 10, 2001
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`Sheet 4 of 4
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`US 6,258,617 Bl
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`FIG.6
`
`/ / /
`
`/1
`
`-r-- 800
`
`FIG.7
`
`204
`A
`
`205
`
`---203 A
`
`r-- 803
`802
`801
`
`r---
`
`r--- 202
`
`r--- 201
`
`r--- 200
`
`Vizio EX1015 Page 0005
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`US 6,258,617 Bl
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`1
`METHOD OF MANUFACTURING BLUE
`LIGHT EMITTING ELEMENT
`
`TECHNICAL FIELD
`
`The present invention relates to a blue light em1ttmg
`element employing a gallium-nitride-based compound semi(cid:173)
`conductor and a method of manufacturing the same.
`
`BACKGROUND ART
`
`2
`high-intensity light and low power consumption and a
`method of manufacturing the same.
`In order to accomplish the objects, the present invention
`provides a blue light emitting element consisting of a first
`5 gallium-nitride-based semiconductor layer containing impu(cid:173)
`rities of a first conductivity type, a gallium-nitride-based
`semiconductor active layer that is substantially intrinsic, and
`a second gallium-nitride-based semiconductor layer contain(cid:173)
`ing impurities of a second conductivity type that is opposite
`10 to the first conductivity type. The first and second gallium(cid:173)
`nitride-based semiconductor layers and gallium-nitride(cid:173)
`based semiconductor active layer are formed according to a
`thermal CVD method and are left in an inert gas to cool by
`themselves, so that seven percent or more of the impurities
`15 are activated.
`The present invention also provides a method of manu(cid:173)
`facturing a blue light emitting element including the steps of
`forming, according to a thermal CVD method in a vacuum
`chamber, a first gallium-nitride-based semiconductor layer
`20 containing impurities of a first conductivity type, a gallium(cid:173)
`nitride-based semiconductor active layer that is substantially
`intrinsic, and a second gallium-nitride-based semiconductor
`layer containing impurities of a second conductivity type
`that is opposite to the first conductivity type, and leaving the
`25 layers in an inert gas so that the layers may cool by
`themselves.
`The present invention involves simple processes without
`thermal annealing and improves yield. The gallium-nitride(cid:173)
`based compound semiconductor blue light emitting element
`of the present invention realizes high-intensity light with
`small power consumption.
`
`Gallium-nitride-based compound semiconductor such as
`GaN, InGaN, and GaAlN is drawing attention as material for
`fabricating blue light emitting diodes (LEDs) and blue laser
`diodes (LDs) . This kind of compound semiconductor is
`capable. of emitting blue light of sufficient intensity hardly
`realized so far.
`A blue light emitting element employing the gallium(cid:173)
`nitride-based compound semiconductor is disclosed in, for
`example, Japanese Unexamined Patent Publication No.
`4-321280. FIG. 7 shows the basic structure of a blue light
`emitting element 2 according to a prior art. On a sapphire
`substrate 200, a buffer layer 201 is formed. On the buffer
`layer 201, an n-type GaN semiconductor layer 202 and a
`p-type GaN semiconductor layer 203 are formed. Between
`the layers 202 and 203, there is a depletion layer to which
`carriers are injected to emit light.
`The blue light emitting element is manufactured by grow(cid:173)
`ing crystals on a sapphire substrate according to a CVD
`method and by forming gallium nitride semiconductor layers
`on the substrate. The substrate is properly cut into chips. 30
`Each chip is connected to a wire frame, and wiring is made
`to complete a device.
`A natural cooling process in an inert gas is disclosed in
`Japanese Unexamined Patent Publication No. 8-125222. To
`replace an atmospheric gas at room temperature with an 35
`inert gas, the disclosure vacuums a reactive tube under a
`high temperature. This high temperature may grow a sub(cid:173)
`strate. When vacuuming the reactive tube, the grown crys(cid:173)
`tals may evaporate. As a result, no grown crystals may be
`left, or the crystallized film may be thinned.
`In the gallium-nitride-based blue light emitting element of
`the prior art, impurities in the semiconductor layers are not
`sufficiently activated. Accordingly, the prior art needs an
`after-treatment of thermal annealing.
`The thermal annealing increases the number of processes
`and processing time. Since the gallium nitride semiconduc-
`tor is exposed to a high temperature of 600° C. or over for
`a long time, nitrogen may escape from crystals and deterio(cid:173)
`rate surface homology. This results in changing semicon(cid:173)
`ductor properties and deteriorating blue light emitting effi(cid:173)
`ciency and yield.
`
`BRIEF DESCRIPTION OF DRAWINGS
`FIG. 1 is a sectional view showing the structure of a
`gallium-nitride-based compound semiconductor blue light
`emitting diode chip according to the present invention;
`FIG. 2 is a schematic view showing a CVD apparatus for
`forming a gallium-nitride-based compound semiconductor
`40 blue light emitting diode chip according to the present
`invention;
`FIG. 3 is a graph showing temperature changes when
`manufacturing a gallium-nitride-based compound semicon(cid:173)
`ductor blue light emitting diode according to the present
`45 invention;
`FIG. 4 shows a gallium-nitride-based compound semi(cid:173)
`conductor blue light emitting diode according to another
`embodiment of the present invention;
`FIG. 5 shows a gallium-nitride-based compound semi-
`50 conductor blue light emitting diode employing a semicon(cid:173)
`ductor laser according to the present invention;
`FIG. 6 shows another gallium-nitride-based semiconduc(cid:173)
`tor blue light emitting diode employing a semiconductor
`55 laser according to the present invention; and
`FIG. 7 is a sectional view showing the structure of a
`gallium-nitride-based compound semiconductor blue light
`emitting diode chip according to a prior art.
`
`DISCLOSURE OF INVENTION
`
`An object of the present invention is to provide a gallium(cid:173)
`nitride-based blue light emitting element involving a small
`number of manufacturing processes and a method of manu(cid:173)
`facturing the same.
`Another object of the present invention is to provide a
`gallium-nitride-based blue light emitting element realizing 60
`high yield and a method of manufacturing the same.
`Still another object of the present invention is to provide
`a gallium-nitride-based blue light emitting element proper
`for mass-production and a method of manufacturing the
`same.
`Still another object of the present invention is to provide
`a gallium-nitride-based blue light emitting element realizing
`
`BEST MODE FOR CARRYING OUT THE
`INVENTION
`
`A method of manufacturing a gallium-nitride-based com(cid:173)
`pound semiconductor blue light emitting diode according to
`the present invention will be explained with reference to
`65 FIG. 1.
`The gallium-nitride-based compound semiconductor blue
`light emitting diode 1 has a sapphire substrate 100. On the
`
`Vizio EX1015 Page 0006
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`

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`US 6,258,617 Bl
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`20
`
`30
`
`3
`substrate 100, a gallium-nitride-based semiconductor buffer
`layer 101 and a gallium-nitride-based n-type semiconductor
`contact layer 102 are formed. On the layer 102, a gallium(cid:173)
`nitride-based n-type semiconductor clad layer 103, a
`gallium-nitride-based semiconductor active layer 104, a 5
`gallium-nitride-based p-type semiconductor clad layer 105,
`and a gallium-nitride-based p-type semiconductor contact
`layer 106 are formed. An electrode 108 is formed in contact
`with the layer 102. An electrode 107 is formed in contact
`with the layer 105.
`The present invention employs InAlGaN compound semi(cid:173)
`conductor as the gallium-nitride-based semiconductor. This
`semiconductor is capable of emitting a wide range of blue
`light by adjusting the composition thereof. Examples of
`compositions will be explained. The composition of InAl- 15
`GaN compound semiconductor is expressed as In(x)Al(y)
`Ga(1-x-y)N, where 0<=X<=1, 0<=y<=1, and x+y<=l.
`The gallium-nitride-based n-type semiconductor buffer
`layer 101 relaxes lattice unconformity between the gallium(cid:173)
`nitride-based semiconductor contact layer 102 and the sap(cid:173)
`phire substrate 100. Values for the parameters of In(x)Al(y)
`Ga(1-x-y)N are, for example, 0<=X<=1 and 0<=y<=1,
`preferably, 0<=X<=0.5 and 0<=y<=0.5.
`The gallium-nitride-based n-type semiconductor contact
`layer 102 serves a contact surface for the electrode 108.
`Values for the parameters of In(x)Al(y)Ga(1-x-y)N for the
`layer 102 are, for example, 0<=X<=1 and 0<=y<=1,
`preferably, 0<=X<=0.3 and 0<=y<=0.3. To make the layer be
`of n-type, impurities such as silicon and selenium are added
`thereto at an impurity concentration of6 x1018 cm-3
`.
`The gallium-nitride-based n-type semiconductor clad
`layer 103 forms then side of a pin junction that forms a light
`emitting region. Values for the parameters of In(x)Al(y)Ga
`(1-x-y)N are properly adjusted according to a required 35
`wavelength of light and are, for example, 0<=X<=1 and
`0<=y<=1, preferably, 0<=X<=0.3 and 0.1<=y<=l. To make
`the layer be of n-type, impurities such as silicon and
`selenium are added thereto at an impurity concentration of
`3x1018 cm-3
`.
`The gallium-nitride-based semiconductor active layer 104
`is substantially an intrinsic semiconductor layer that forms a
`main part of the light emitting region. Values for the
`parameters of In(x)Al(y)Ga(1-x-y)N are properly adjusted
`according to a required wavelength of light and are, for
`example, 0<=X<=1 and 0<=y<=1, preferably, 0<=X<=0.6
`and 0<=y<=0.5.
`The gallium-nitride-based p-type semiconductor clad
`layer 105 forms the p side of the pin junction that forms the
`light emitting region. Values for the parameters of In(x)Al 50
`(y)Ga(1-x-y)N are properly adjusted according to a
`required wavelength of light and the gallium-nitride-based
`n-type semiconductor clad layer 103 and gallium-nitride(cid:173)
`based semiconductor active layer 104 and-are, for example,
`0<=X<=1 and 0<=y<=1, preferably, 0<=X<=0.3 and 0.1<= 55
`y<=l.O. To make the layer be of p-type, impurities such as
`magnesium, beryllium, and zinc are added thereto at an
`impurity concentration of 3x1018 cm-3
`.
`The gallium-nitride-based p-type semiconductor contact
`layer 106 serves a contact surface for the electrode 107. 60
`Values for the parameters of In(x)Al(y)Ga(1-x-y)N are, for
`example, 0<=X<=1 and 0<=y<=1, preferably, 0<=X<=0.3
`and 0<=y<=0.3. To make the layer be of p-type, impurities
`such as magnesium, beryllium, and zinc are added thereto at
`an impurity concentration of 8x1018 cm-3
`.
`The electrode 107 is a transparent electrode with respect
`to the gallium-nitride-based semiconductor active layer 104.
`
`4
`More precisely, 1t 1s a compound of metal such as ITO
`(indium tin oxide) and oxygen, or it may be a very thin film
`of metal such as Al and Ni.
`The other electrode 108 is not necessarily transparent. It
`may be made of metal such as Ti, Al, and Ni.
`The values mentioned above for the parameters of In(x)
`Al(y)Ga(1-x-y)N are set so that the band gap of each of the
`gallium-nitride-based n-type semiconductor clad layer 103
`and gallium-nitride-based p-type semiconductor clad layer
`10 105 is larger than that of the gallium-nitride-based semicon(cid:173)
`ductor active layer 104. This results in increasing the amount
`of carriers injected into the layer 104, to further improve the
`intensity of emitted light.
`These gallium-nitride-based semiconductor layers are
`formed on the sapphire substrate according to, for example,
`the thermal CVD method. FIG. 2 shows a CVD apparatus.
`This apparatus has a vacuum chamber 20, a substrate holder
`21 disposed in the chamber, a reactive gas introducing pipe
`22, an evacuation pipe 23, and a high-frequency coil (not
`shown) for heating a substrate set on the holder 21.
`At first, a sapphire substrate 100 is set on the substrate
`holder 21. The vacuum chamber 20 is evacuated from 760
`to 1 Torr. Then, high-frequency heating is started, and a
`25 reactive gas containing organic metal is introduced. The
`reactive gas may contain Ga(CH3 ) 3 , In(CH3 ) 3 , Al(CH3 ) 3 ,
`and NH3 and is introduced with a carrier gas containing
`hydrogen and nitrogen. A reaction pressure is about 760
`Torr.
`In this way, gallium-nitride-based semiconductor is
`formed. The composition of the reactive gas is properly
`changed to adjust the composition of each layer to form.
`Impurities are added by properly introducing SiH4 and
`CP2Mg.
`FIG. 3 shows temperature changes in the vacuum cham(cid:173)
`ber 20 when forming the gallium-nitride-based semiconduc(cid:173)
`tor. The temperature of the substrate is increased to 1000° C.
`to 1400° C., for example, 1200° C. to form a gallium-nitride(cid:173)
`based semiconductor buffer layer. The temperature is
`40 dropped by 50° C. to 200° C. down to 800° C. to 1200° C.
`For example, the temperature is dropped from 1200° C. to
`1100° C. to form an n-type contact layer and an n-type clad
`layer by adding proper impurities. To form an active layer,
`the temperature is dropped by 300° C. to 600° C. For
`45 example, the temperature is dropped from 1100° C. to 900°
`C. to 600°0 C. Lastly, the temperature of the substrate is
`increased to the first temperature, for example, 1100° C. to
`form a p-type clad layer and a p-type contact layer, thereby
`completing the element.
`The present invention completely replaces the reactive
`gas in the vacuum chamber 20 with an inert gas. The inert
`gas is preferably nitrogen, or may be He or Ar.
`After the vacuum chamber 20 is filled with the inert gas,
`the pressure of the chamber is adjusted to 600 to 900 Torr,
`for example, 760 Torr. This state is maintained for two to
`three hours. Then, the temperature of the substrate drops to
`room temperature, for example, 25° C. The sapphire sub(cid:173)
`strate is removed from the vacuum chamber 20.
`The sapphire substrate removed from the vacuum cham(cid:173)
`ber 20 is properly cut by diamond cutter into many chips.
`Each chip forms a blue light emitting element that emits
`light having sufficient intensity. Accordingly, there is no
`need of an after-treatment of thermal annealing.
`Since there is no need of carrying out the after-treatment
`of thermal annealing on the sapphire substrate taken out of
`the vacuum chamber 20, the present invention simplifies
`
`65
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`US 6,258,617 Bl
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`5
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`5
`manufacturing processes and shortens a manufacturing time.
`The intensity of light emitted from the produced element is
`higher than that of the prior art.
`The reason of this will be explained. The prior art
`activates impurities by thermal annealing. Actual measure(cid:173)
`ments on the prior art tell, however, only about one percent
`of the impurities are activated. The remaining 99 percent are
`not only useless but also interfering because they cause
`lattice defects to act as carrier traps. Namely, injected
`carriers are mostly trapped thereby and do not work to emit
`light.
`On the other hand, actual measurements on the present
`invention tell seven percent or more, usually about 10
`percent of injected carriers are activated. In this way, the
`present invention activates many carriers and reduces resis(cid:173)
`tance to drop power consumption.
`FIG. 4 is a sectional view showing the structure of a light
`emitting diode 500 according to another embodiment of the
`present invention. A method of manufacturing the light
`emitting diode 500 will be explained with reference to the
`figure.
`A sapphire substrate 501 having a plane c as a principal
`plane is cleaned for organic and acid matter. The substrate is
`set on a susceptor to be heated in an MOCVD apparatus.
`Heating is carried out by a resistive or inductive heater.
`Oxygen is supplied to the sapphire substrate 501 at a rate
`of 10 L/min, and the substrate is heat-treated at 1100° C. for
`about 10 minutes to remove process damage and oxides
`from the surface thereof.
`The temperature is dropped to 550° C., and hydrogen at 30
`15 L/min, nitrogen at 5 L/min, ammonia at 10 L/min, and
`TMG (trimethyl gallium) at 25 cc/min are supplied for four
`minutes to form a GaN buffer layer 502 of 30 nm thick.
`The TMG is stopped, and the temperature is increased up
`to 1100° C. at a speed of 50° C./min or slower. If the 35
`temperature increasing speed is faster than 50° C., the
`surface of the buffer layer 502 will be roughened to form
`irregularities on the surface of a monocrystalline layer.
`The temperature is kept at 1100° C., and hydrogen at 15
`L/min, nitrogen at 5 L/min, ammonia at 10 L/min, and TMG 40
`at 100 cc/min are supplied to form a gallium-nitride-based
`monocrystalline semiconductor (GaN) buffer layer 503 of
`1.8 ,urn thick.
`The temperature is kept at 1100° C., and a silane gas is
`added at 10 cc/min for 130 minutes to the material gas, to
`form an n-type GaN contact injection layer 504 of 4 ,urn
`thick.
`The TMG, silane gas, and hydrogen are stopped, and the
`temperature is dropped down to 780° C.
`The temperature is kept at 780° C., and nitrogen at 20
`L/min, hydrogen at 100 cc/min, ammonia at 10 L/min, TMG
`at 12 cc/min, TMI (trimethyl indium) at 150 cc/min, silane
`gas at 3 cc/min, and DMZ (dimethyl zinc) at 20 cc/min are
`supplied for six minutes to form an InGaN semiconductor 55
`active layer 505 of 0.2 ,urn thick serving as a light emitting
`layer.
`Nitrogen at 20 L/min, hydrogen at 100 cc/min, and
`ammonia at 10 L/min are supplied, and the temperature is
`increased up to 1100° C.
`The temperature is kept at 1100° C., and nitrogen at 20
`L/min, hydrogen at 150 cc/min, ammonia at 10 L/min, TMG
`at 100 cc/min, and Cp2Mg ( cyclopentadienyl magnesium) at
`50 cc/min are supplied for 10 minutes to form a p-type GaN
`contact injection layer 506 of 0.3 ,urn thick.
`Although the p-type layer is single in this embodiment, it
`is possible to separately form a contact layer and an injection
`
`6
`layer. In this case, the contact layer is made from GaN and
`the injection layer fromAlGaN so that the contact layer may
`have a higher carrier concentration than the injection layer.
`The supplied gas is switched to nitrogen at 30 L/min, and
`the temperature is dropped to room temperature. As a result,
`the p-type GaN layer shows an activation ratio of 8% with
`respect to an Mg concentration of 3x1019 cm-3
`. The acti(cid:173)
`vation ratio is obtained by standardizing an acceptor con(cid:173)
`centration according to an Mg concentration. If the tempera-
`10 ture is dropped to 400° C. with nitrogen at 20 L/min and
`ammonia at 10 L/min, and from 400° C. to room temperature
`with only nitrogen at 30 L/min, an activation ratio of 7% or
`greater is secured.
`Generally, gallium-nitride-based semiconductor has the
`15 problem of denitrification. To prevent the problem, a com(cid:173)
`pound that produces nitrogen ions instead of nitrogen itself
`is effective. This is the reason why ammonia is used in
`addition to nitrogen. If the ammonia is too much, hydrogen
`will reversely affect strongly. According to experiments, a
`20 preferable ratio of nitrogen to ammonia is 2:1.
`The layer structure thus formed is heat-treated at 750° C.
`for one minute to further increase a carrier concentration in
`the p-type layer 506 and realize p-type crystals of 2x1017
`cm-3
`.
`The layer structure is patterned with the use of, for
`example, Si02 and is etched according to a reactive ion
`etching (RIE) method using Cl2 and BC13 to expose a part
`of the n-type GaN layer 504.
`An electrode for the p-type layer 506 is formed by
`depositing Ni for 20 nm and gold for 400 nm (510 in FIG.
`4) according to a known vacuum deposition method and
`spattering method. An electrode for the n-type layer 504 is
`formed by depositing Ti for 20 nm and gold for 400 nm (511
`in FIG. 4). The electrode for the p-type layer may be not only
`the laminated structure of Ni/ Au but also a monolayer of Pd,
`Ti, Pt, or In, a laminated structure thereof with Ni and Au,
`or an alloy thereof. The electrode for the n-type layer may
`be made of Ti and Au, a monolayer of Al or In, a laminated
`structure including Ti and Au, or an alloy thereof.
`On the p-type electrode 510, a protection film of Si02 is
`formed, to complete the element.
`Although the embodiment relates to a light emitting
`diode, the gist of the present invention is the method of
`manufacturing a p-type layer. Accordingly, the present
`invention is applicable to a semiconductor laser employing
`GaN-based semiconductor.
`FIG. 5 shows the structure of a blue light emitting element
`50 employing such a semiconductor laser.
`On a sapphire substrate 701, there are formed a gallium(cid:173)
`nitride-based semiconductor buffer layer 702, a gallium(cid:173)
`nitride-based n-type semiconductor contact layer 703, a
`gallium-nitride-based n-type semiconductor layer 704, a
`gallium-nitride-based n-type semiconductor clad layer 705,
`a gallium-nitride-based semiconductor active layer 706, a
`gallium-nitride-based p-type semiconductor clad layer 707,
`a gallium-nitride-based p-type semiconductor layer 708, a
`gallium-nitride-based p-type semiconductor layer 709, and a
`60 gallium-nitride-based p-type semiconductor contact layer
`710.
`Similar to the embodiment of FIG. 4, a part of the
`structure is etched according to the reactive ion etching
`method to partly expose the surface of the gallium -nitride-
`65 based n-type semiconductor contact layer 703. On the
`exposed surface, Ti, Au, Ti, and Au are laminated in this
`order to form an n-type electrode. The thicknesses there of
`
`25
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`45
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`Vizio EX1015 Page 0008
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`US 6,258,617 Bl
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`15
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`7
`are 200 ,urn, 4000 angstroms, 200 ,urn, and 1 ,urn, respec(cid:173)
`tively. A p-type electrode 711 may be formed by laminating
`Pd, Ti, Pt, and Ti in this order. The thicknesses thereof are
`200 ,urn, 4000 angstroms, 200 ,urn, and 1 ,urn, respectively.
`The gallium-nitride-based semiconductor active layer 706 5
`is made of In(x)Ga(1-x)N compound semiconductor having
`a quantum well structure. The layer is made by alternately
`laminating a film of 25 angstroms thick with x=O.OS and
`y=0.95 and a film of 25 angstroms thick with x=0.20 and
`y=0.80 about 20 times, to form a multilayer quantum well. 10
`Any other gallium-nitride-based semiconductor layer is
`basically made of GaN. Examples of thicknesses are 70 ,urn
`for the sapphire substrate 701, 500 angstroms for the
`gallium-nitride-based semiconductor buffer layer 702, 4 ,urn
`for the gallium-nitride-based n-type semiconductor contact
`layer 703, 0.3 ,urn for the gallium-nitride-based n-type
`semiconductor layer 704, 0.2 ,urn for the gallium-nitride(cid:173)
`based n-type semiconductor clad layer 705, 0.2 ,urn for the
`gallium-nitride-based p-type semiconductor clad layer 707,
`0.3 ,urn for the gallium-nitride-based p-type semiconductor
`layer 708, 0.9 ,urn for the gallium-nitride-based p-type
`semiconductor layer 709, and 0.1 ,urn for the gallium-nitride(cid:173)
`based p-type semiconductor contact layer 710.
`Examples for impurity concentrations are 2x1018 cm-3
`for the gallium-nitride-based n-type semiconductor contact 25
`layer 703, 5x1017 cm-3 for the gallium-nitride-based n-type
`semiconductor layer 704, 5x1017 cm-3 for the gallium(cid:173)
`nitride-based n-type semiconductor clad layer 705, 5x1017
`cm-3 for the gallium-nitride-based p-type semiconductor
`clad layer 707, 5x1017 cm-3 for the gallium-nitride-based 30
`p-type semiconductor layer 708, 3x1018 cm-3 for the
`gallium-nitride-based p-type semiconductor layer 709, and
`2x1019 cm-3 for the gallium-nitride-based p-type semicon(cid:173)
`ductor contact layer 710.
`After the gallium-nitride-based p-type semiconductor 35
`layer 708 is formed, the reactive ion etching method may be
`used to etch up to the gallium-nitride-based n-type semi(cid:173)
`conductor contact layer 703. The etched part is filled with a
`GaN layer of high resistance with Zn, to limit a resonance
`part. An example of this kind of structure is shown in FIG. 40
`6. A high-resistance GaN layer 800 contains Zn of 2x1018
`cm-3 in concentration.
`
`8
`stopping the introduction of the n-type dopant gas and
`lowering said temperature of the substrate by from 300
`to 600° C. to form an active layer of a gallium-nitride(cid:173)
`based semiconductor;
`heating said substrate to a temperature of from 1000 to
`1400° C. to form a p-type cladding layer of a gallium(cid:173)
`nitride-based semiconductor and then a p-type contact
`layer of a gallium-nitride-based semiconductor by
`introducing a p-type dopant gas in addition to said
`carrier gas, ammonia (NH3 ) and said gas comprising
`the Group III element
`terminating the introduction of the gas containing the
`Group III element and increasing the flow rate of said
`inert gas immediately after the completion of the lami(cid:173)
`nated structure of said p-type contact layer; and
`cooling said substrate by itself with said inert gas being
`introduced in the increased flow rate together with said
`ammoma.
`2. The method of manufacturing a semiconductor device
`as claimed in claim 1 wherein said inert gas is introduced in
`excess of hydrogen, whose flow ratio to said inert gas is not
`smaller than 0.75%, in the step of forming said p-type
`cladding layer and said p-type contact layer.
`3. The method of manufacturing a semiconductor device
`as claimed in claim 2 wherein at least one of said n-type
`contact layer, said the n-type cladding layer, said the active
`layer, said the p-type cladding layer and said the p-type
`contact layer is represented by formula In(x)Al(y)Ga(1-x(cid:173)
`y)N(x+y~1, O~x~1, O~y~1).
`4. The method of manufacturing a semiconductor device
`as claimed in claim 2 wherein the step of cooling said
`substrate by itself comprises a step of adjusting the internal
`pressure of said vacuum chamber to from 600 Torr to 900
`Torr with said inert gas being introduced in the increased
`flow rate and leaving said substrate with the internal pres-
`sure being maintained at the adjusted pressure.
`5. The method of manufacturing a semiconductor device
`as claimed in claim 2 wherein, in the step of increasing the
`flow rate of said inert gas, the flow ratio of said inert gas to
`said ammonia (NH3 ) is set to 2:1.
`6. The method of manufacturing a semiconductor device
`as claimed in claim 2 wherein said inert gas is one of
`Nitrogen (N2), Helium (He) and Argon (Ar).
`7. The method of manufacturing a semiconductor device
`as claimed in claim 2 wherein said buffer layer is composed
`45 of GaN.
`8. The method of manufacturing a semiconductor device
`as claimed in claim 2 wherein said buffer layer is composed
`of AlaGal-aN (O~a~1).
`9. The method of manufacturing a semiconductor device
`as claimed in claim 2 wherein said gas containing the Group
`III element is composed of an organic metal gas.
`10. The method of manufacturing a semiconductor device
`as claimed in claim 1 wherein the step of forming said buffer
`layer is performed by introducing hydrogen (H2) and an
`55 inert gas into said vacuum chamber as a carrier gas in order
`that hydrogen is introduced in excess of the inert gas, and
`wherein the method further comprises the step of forming a
`buffer layer by introducing ammonia (NH3 ) and a gas
`comprising a Group III element in addition to the carrier gas.
`11. The method of manufacturing a semiconductor device
`as claimed in claim 1 wherein at least one of said n-type
`contact layer, said the n-type cladding layer, said the active
`layer, said the p-type cladding layer and said the p-type
`contact layer is represented by formula In(x)Al(y)Ga(1-x-
`65 y)N(x+y~1, O~x~1, O~y~1).
`12. The method of manufacturing a semiconductor device
`as claimed in claim 11 wherein the step of cooling said
`
`20
`
`INDUSTRIAL APPLICABILITY
`As explained above, the present invention provides a
`gallium-nitride-based compound semiconductor blue light
`emitting element that is manufactured through simple pro(cid:173)
`cesses at high yield.
`The gallium-nitride-based compound semiconductor blue
`light emitting element of the present invention provides 50
`high-intensity light at low power consumption.
`What is claimed is:
`1. A method of manufacturing a semiconductor device
`comprising the steps of:
`disposing a substrate in a vacuum chamber;
`heating said substrate to a temperature of from 1000 to
`1400° C. to form a buffer layer of a gallium-nitride(cid:173)
`based semiconductor;
`lowering said temperature of the substrate is by 50 to 200°
`C., after the completion of forming said gallium- 60
`nitride-based semiconductor buffer layer;
`forming ann-type contact layer of a gallium-nitride-based
`semiconductor and then forming an n-type cladding
`layer by introducing ammonia (NH3 ), a gas comprising
`a Group III element and a