United States Patent [191
`Tamaki et al.
`
`lllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll
`US005369289A
`5,369,289
`[11] Patent Number:
`[45] Date of Patent: Nov. 29, 1994
`
`[54] GALLIUM NITRIDE-BASED COMPOUND
`SEMICONDUCfOR LIGHT-EMITTING
`DEVICE AND MEI'HOD FOR MAKING THE
`SAME
`
`[75]
`
`Inventors: Makoto Tamaki, Inazawa; Takahiro
`Kozawa, Owariasahi, both of Japan
`[73] Assignees: Toyoda Gosei Co. Ltd., Nishikasugai;
`Kabushiki Kaisha Toyota Cbuo
`Kenkyusho, Aichi, both of Japan
`
`[21] Appl. No.: 969,769
`Oct. 30, 1992
`[22] Filed:
`[30]
`Foreign Application Priority Data
`Oct. 30, 1991 [JP]
`Japan .................................. 3-313977
`
`[51]
`Int. Cl.s .................... H01L 29/205; HOlL 33/00
`[52] u.s. Cl ......................................... 257/99; 257/94;
`257/103; 257/749; 257/766
`[58] Field of Search ................... 257/94, 101, 99, 102,
`.
`257/103, 749, 766
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`3,409,809 11/1968 Diehl ................................... 257 !766
`3,790,868 2/1974 Soshea ................................. 257/101
`3,849,707 11/1974 Braslau .................................. 257/48
`4,283,118 8/1981 Inoue ................................... 257!766
`4,316,208 2/1982 Kobayashi et al .................... 257/99
`4,408,217 10/1983 Kobayashi et al .................. 257/103
`
`4,495,514 1/1985 Lawrence et al ..................... 257/99
`4,855,249 8/1989 Akasaki et al ...................... 257/103
`4,911,102 3/1990 Manabe et al ...................... 257/103
`4,946,548 8/1990 Kotaki et al ........................ 257/103
`5,122,845 6/1992 Manabe et al ........................ 257/94
`
`Primary Examiner-Jerome Jackson
`Attorney, Agent, or Firm-Cushman, Darby & Cushman
`
`ABSTRACf
`
`[57]
`A light-emitting device comprises an n-type layer made
`of an n-type gallium nitride-based compound of the
`formula A1xGat-xN, wherein O~X<l, and ani-type
`layer formed on the n-type layer and made of a semi(cid:173)
`insulating i-type gallium nitride-based compound semi(cid:173)
`conductor and doped with a p-type impurity for junc(cid:173)
`tion with then-type layer. A first electrode is formed on
`the surface of the i-type layer and made of a transparent
`conductive film and a second electrode is formed to
`connect to the n-type layer through the i-type layer.
`The device is so arranged that light is emitted from the
`side of the i-type layer to the outside. When an electric
`current is supplied to the first electrode from a wire
`contacted thereto, the first electrode is held entirely at
`a uniform potential. Light is emitted from the entire
`interface beneath the first electrode and can thus be
`picked up from the first electrode which is optically
`transparent.
`
`18 Claims, 9 Drawing Sheets
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`Nov. 29, 1994
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`1
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`5,369,289
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`GALLIUM NITRIDE-BASED COMPOUND
`SEMICONDUCI'OR LIGIIT-EMITTING DEVICE
`AND METHOD FOR MAKING THE SAME
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`This invention relates to a gallium nitride-based com(cid:173)
`pound semiconductor light-emitting device which is
`able to emit blue light or light in a short wavelength 10
`spectral range. The invention also relates to a method
`for making the device.
`2. Description of Related Art
`Light-emitting diodes using GaN-based compound
`semiconductors (AlxGa!-xN wherein O~X< 1) are 15
`known as ones which are able to emit blue light or light
`in a short wavelength spectral range. Attention has
`been now directed to the GaN-based compound semi(cid:173)
`conductors because they come in direct transition so
`that a high light emission efficiency is attained, and are 20
`able to emit blue light which is one of the three primary
`colors.
`With such GaN compound semiconductors, low re(cid:173)
`sistance p-type crystals are not obtained. In general, a
`light-emitting diode using a GaN compound semicon- 25
`ductor is arranged to have a so-called MIS structure
`which includes a metal electrode, an i-type layer (insu(cid:173)
`lator) made of semi-insulating GaN and ann layer made
`of n-type GaN. Light emission takes place at a portion
`beneath the electrode (light emission electrode) on the 30
`i-type layer. More particularly, the electrode-forming
`portion has the MIS structure.
`In a GaN blue LED having an MIS structure as men(cid:173)
`tioned above, it is important that the device structure
`and the layer arrangement be established firsthand in 35
`order to have light emitted efficiently.
`In light-emitting devices having a pn junction struc(cid:173)
`ture wherein other compound semiconductors of
`groups 111-V, such as AlxGa!-xAs are used, an electric
`current is diffused transversely along the interface of 40
`the junction in the device and, thus, the current passes
`vertically and uniformly with respect to the interface.
`As a consequence, unlike an MIS-type LED wherein
`light is emitted only at a portion beneath the electrode,
`light is emitted from the entire interface irrespective of 45
`the size of the electrode. Because the light is substan(cid:173)
`tially uniformly emitted from the interface, pickup of
`light is easy.
`However, with a GaN blue light LED having an MIS
`structure, little current diffusion along the transverse 50
`direction parallel to the interface takes place in the
`i-type layer beneath the light-emitting electrode. This
`results in a light-emitting portion which is limited only
`to a region beneath the light-emitting electrode. Be(cid:173)
`cause the electrode is generally made of a metal, light 55
`emission is rarely observed from the side of the light
`emission electrode as if disappearing behind the elec(cid:173)
`trode.
`To avoid this, known GaN blue light LEDs make use
`of a sapphire substrate and GaN, both of which are 60
`transparent to emission light. More particularly, it is
`customary to utilize a flip-chip system wherein a light
`emission electrode is provided at the lower side of the
`substrate or, instead, is provided in a system wherein
`light is picked up from the back side through the sub- 65
`strate. To this end, a light emission electrode and an
`electrode electrically connected to an n-type layer (an
`electrode at the side of the n-type layer) are formed on
`
`2
`the surface of a GaN epitaxial layer. These electrodes
`are bonded with a lead frame by means of a solder,
`making it possible to pick up light through the substrate.
`However, when using the flip-chip system wherein a
`5 light emission electrode (i-type layer electrode), an
`n-type layer electrode and a lead frame are bonded
`through a solder, the electric series resistance compo(cid:173)
`nent of the device has to be increased for the following
`reasons:
`(1) Because the distance between the electrodes can(cid:173)
`not be made too narrow in order to prevent short-cir(cid:173)
`cuiting the light emission electrode (i-type layer elec(cid:173)
`trode, n-type layer electrode and the solder), the elec(cid:173)
`tric resistance component becomes large.
`(2) If the light emission electrode (i-type layer elec(cid:173)
`trode) and the n-type layer electrode greatly differ in
`shape under which a solder bump is formed, the solder
`bumps have inevitably different heights, so that a con(cid:173)
`nection failure with the lead frame will be likely to
`occur.
`Accordingly, it is necessary to shape the electrodes so
`as to have substantially the same area. This leads to a
`loss in the degree of design freedom of an electrode
`pattern, further resulting in difficulty in obtaining an
`optimum pattern for reducing the electric resistance
`component. The large electric series resistance compo(cid:173)
`nent not only lowers the light emission efficiency, but
`also unfavorably induces generation of heat in the de(cid:173)
`vice which causes device operation to degrade and light
`emission intensity to become lower.
`
`SUMMARY OF THE INVENTION
`It is accordingly an object of the invention to provide
`a light-emitting device which is improved in light
`pickup efficiency and light emission efficiency while
`suppressing an electric resistance component to an ex(cid:173)
`tent as low as possible.
`It is another object of the invention to provide a
`method for making a light-emitting device of the type
`mentioned above.
`The above object can be achieved, according to the
`invention, by a gallium nitride-based compound semi(cid:173)
`conductor light emission device of the type which com(cid:173)
`prises an n-type layer made of ann-type gallium nitride(cid:173)
`based compound semiconductor of the formula Alx(cid:173)
`Ga!-xN wherein O~X<l, and ani-type layer formed
`on the n-type layer and made of a gallium nitride-based,
`semi-insulating gallium nitride-based compound semi(cid:173)
`conductor of the formula AlxGa1-xN wherein O~X < 1
`which is doped with a p-type impurity for junction with
`the n-type layer.
`The device also includes a ftrst electrode formed on
`one side of the i-type layer and formed of a transparent
`conductive fllm, and a second electrode connected to
`the n-type layer through the i-type layer, light being
`emitted from the i-type layer to the outside.
`In the device of the invention, on the semi-insulating
`i-type layer, the first electrode made of a transparent
`conductive fllm is formed. Light is emitted through the
`first electrode. The light emission area is defined by the
`area of the first electrode. The first electrode is conduc(cid:173)
`tive in nature, so that even if an electric current is only
`partially supplied to the first electrode, the ftrst elec(cid:173)
`trode is entirely held at a uniform potential, thereby
`causing light to be emitted from the entire lower surface
`of the ftrst electrode.
`
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`3
`As stated above, the gallium nitride-based compound
`semiconductor light emitting device of the invention
`makes use of a transparent conductive film as the first
`electrode (light emission electrode). Needless to say, the
`transparent conductive film is transparent to visible 5
`light, making it possible to pick up light from the side of
`the light emission electrode. This ensures a number of
`significant effects as follows.
`1. The electrode can be mounted as an uppermost
`layer and can be connected through an ordinary wire 10
`bonding method without use of any solder. If a lead
`wire is spot connected to the first electrode, an electric
`current can be diffused in parallel directions owing to
`the conductivity of the first electrode. The uniform
`potential of the first electrode is ensured. This would 15
`possibly narrow a wire bonding pad with respect to the
`first electrode. This allows the first electrode (light
`emission electrode) and the second electrode (n-type
`electrode) to be kept at a distance therebetween suffi(cid:173)
`cient to prevent short-circuiting in device fabrication 20
`processes such as photolithography, etching, lift-off and
`the like.
`In the known flip-chip system, the two electrodes
`should be kept away from each other at a distance much
`longer than a limited distance created by the litho- 25
`graphic or etching technique so as to prevent short-cir(cid:173)
`cuiting between solders for the two electrodes. This in
`turn prevents the area of the first electrode from being
`widened.
`In the practice of the invention, the ratio of the first 30
`electrode area to the total chip area can be increased,
`resulting in an improvement of the light emission effi(cid:173)
`ciency. The distance between the two electrodes can be
`made significantly smaller than that selected in a flip(cid:173)
`chip system. This leads to a reduction of the electric 35
`resistance component of the device.
`2. Although the flip-chip system requires a first elec(cid:173)
`trode (light emission electrode) and a second electrode
`(n-type layer electrode) which have the same pattern, it
`is possible in the present invention to design an optimum 40
`pattern for reducing the electric resistance component
`of the device owing to an increasing degree of freedom
`of design of the two electrode patterns.
`3. Because of the small distance between the first
`electrode (light emission electrode) and the second 45
`electrode (n-type layer electrode) and the increase in
`the degree of freedom of design of the electrode pat(cid:173)
`tern, it is possible to miniaturize the chip size relative to
`the light emission area and enlarge the light emission
`area, resulting in the economic fabrication of the device. 50
`4. The device of the invention can be assembled into
`a hybrid unit with other light emission devices such as
`AlGaAs red light LED, within the same lead frame,
`making it easy to fabricate a light emission device of
`multi-colors such as light, green and red colors.
`
`55
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a schematic sectional view showing a chip
`structure of a light-emitting device according to one
`embodiment of the invention;
`FIG. 2 is a schematic sectional view of a light emit-
`ting diode structure using the chip structure;
`FIGS. 3 to 9 are, respectively, a schematic sectional
`view showing a fabrication sequence of the light-emit-
`ting diode of FIG. 1;
`FIG. 10 is a schematic sectional view showing a light-
`emitting diode according to another embodiment of the
`invention;
`
`5,369,289
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`4
`FIG. 11 is a schematic sectional view showing a light(cid:173)
`emitting diode according to a further embodiment of
`the invention;
`FIGS. 12-15 are, respectively, schematic sectional
`views of a wafer during the fabrication process of the
`light-emitting diode of FIG. 11;
`FIG. 16 is a schematic sectional view of a light-emit(cid:173)
`ting diode according to a still further embodiment of the
`invention; and
`FIG. 17 is a plan view of the light-emitting diode of
`FIG. 16.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`The following specific embodiments of the present
`invention are described with reference to the accompa(cid:173)
`nying drawings.
`FIG. 1 shows a light-emitting diode to which a gal(cid:173)
`lium nitride-based compound semiconductor device of
`the invention is applied.
`A light-emitting diode 10 has a sapphire substrate 1
`and a 500 angstrom thick AIN buffer layer 2 formed
`thereon. An approximately 2.5 J.Lm thick n-type layer 4
`made of n-type GaN is formed on buffer layer 2. In
`addition, an approximately 0.2 J.Lm thick i-type layer 5
`made of semi-insulating GaN is formed on n-type layer
`4. A recess 21 which reaches n-type layer 4 through
`i-type layer 5 is also formed. A second electrode 8 made
`of a metal material is formed to fill recess 21 for connec(cid:173)
`tion with n-type layer 4.
`Further, a first electrode 7 which is kept away from
`second electrode 8 is formed on i-type layer 5. First
`electrode 7 is a transparent conductive film made of
`tin-added indium oxide (hereinafter abbreviated as
`ITO). First electrode 7 has terminal electrode 9 formed
`at a corner portion thereof. Terminal electrode 9 is
`constituted of two layers including an Ni layer 9a and
`an Au layer 9b. The second electrode 8 is constituted of
`three layers including an AI layer Sa connected to n(cid:173)
`type layer 4, an Ni layer 8b and an Au layer Sc. In this
`type of light-emitting diode 10, sapphire substrate 1 has
`an AI reflection film 13 vacuum deposited on the oppo(cid:173)
`site side of the sapphire substrate 1.
`Light-emitting diode 10 is mounted on a substrate 40
`as shown in FIG. 2 and is electrically connected to lead
`pins 41, 42 provided vertically to the substrate 40. More
`particularly, the Au layer 9b of the terminal electrode 9
`connected to the first electrode 7 is connected to the
`lead pin 41 through an Au wire 43. The Au layer 8c of
`the second electrode 8 and the lead pin 42 are connected
`to each other through an Au wire 44.
`Fabrication of the light-emitting diode as set out here(cid:173)
`inabove is described with reference to FIGS. 3 to 9.
`The light-emitting diode 10 is fabricated by vapor
`phase growth according to a metal organic vapor phase
`epitaxy technique (hereinafter referred to MOVPE).
`The gases used include NH3, an H2 carrier gas, tri-
`methyl gallium (Ga(CH3)3) (hereinafter referred to
`simply as TMG), trimethyl aluminum (Al(CH3)3, here-
`60 inafter referred to simply as TMA), silane (Sili4) and
`diethyl zinc (hereinafter referred to simply as DEZ).
`A single crystal sapphire substrate 1 having a surface
`oriented to the direction (1120), i.e., "a"-surface, sub-
`jected to organic washing and thermal treatment, is set
`65 on a susceptor which is mounted in a reaction chamber
`of a MOVPE apparatus.
`While passing H2 to the reaction chamber at a flow
`rate of 2 liters/minute at normal pressures, the sapphire
`
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`5
`electrode 8 are to be formed, respectively. As a result, a
`substrate 1 is subjected to vapor phase etching at 1200°
`photoresist layer 31 is formed except for the portions
`C. for 10 minutes.
`where the terminal electrode 9 and the second electrode
`Thereafter, the temperature is lowered to 400° C.,
`8 are to be formed.
`followed by feeding H2 at 20 liters/minute, NH3 at 10
`liters/minute and TMA at a rate of 1.8 X 10-5 moles/- 5 As shown in FIG. 9, aNi layer 32 and an Au layer 33
`minute to form a AlN buffer layer 2 with a thickness of
`are, successively, formed over the entire upper surface
`500 angstroms.
`of the sample in thicknesses of about 500 angstroms and
`about 3000 angstroms, respectively.
`While keeping the sapphire substrate 1 at a tempera-
`ture of 1150° C., 20 liters/minute ofH2, 10 liters/minute
`The photoresist 31 is removed by means of acetone to
`of NH3 and 1. 7 X IQ-4 moles/minute of TMG are fed 10 remove the Ni layer 32 and the Au layer 33 formed on
`the photoresist 31, thereby forming a Ni layer 9a and an
`for 30 minutes to form a 2.5 p.m n-type layer 4 consisting
`of GaN having a carrier concentration of 1 X 1Ql5fcm3.
`Au layer 9b of the terminal electrode 9 for the first
`electrode 7 and a Ni layer 8b and an Au layer 8c for the
`The sapphire substrate 1 is then heated to 900° C.,
`followed by feeding 20 liters/minute of H2, 10 liters/mi-
`second electrode 8.
`nute of NH3, 1.7X 10-4 moles/minute of TMG and 15 As shown in FIG. 1, AI is vacuum deposited on the
`1.5 X 10-4 moles/minute of DEZ for two minutes,
`entire opposite side of the sapphire substrate 1 in a
`thereby forming a 0.2 p.m thick i-type layer 5 made of
`thickness of about 2000 angstroms to form a reflection
`fllm 13.
`GaN.
`Thus, there is obtained a LED wafer having a multi-
`The resultant wafer is diced into individual chips.
`layer structure as shown in FIG. 3.
`20 The LED chip is fixed on a lead frame 40 as shown in
`As shown in FIG. 4, a Si02layer 11 is formed in a
`FIG. 2. The lead pin 41 and the Au layer 9b of the
`thickness of 1 p.m over the entire upper surface ofi-type
`terminal electrode 9 for the first electrode 7 are con-
`layer 5 by a sputtering technique. A photoresist 12 is
`nected by Au wire 43. The lead pin 42 and the Au layer
`8c of the second electrode 8 are connected by Au wire
`then formed on Si02layer 11, followed by photolithog-
`raphy to form an intended pattern such that a portion of 25 44.
`photoresist 12, corresponding to a portion where a sec-
`In this manner, a light-emitting diode having a MIS
`ond electrode 8 is to be formed, is removed.
`(metal-insulator-semiconductor) structure can be fabri-
`Thereafter, as shown in FIG. 5, the resultant exposed
`cated.
`portion of the Si02 layer 11 is etched by means of a
`When a voltage is applied such that the first transpar-
`hydrofluoric acid etchant through the mask of the pho- 30 ent conductive electrode 7 becomes positive in potential
`relative to the second electrode 8, light is emitted at
`toresist 12.
`As shown in FIG. 6, a recess 21 which reaches the
`i-type layer 5 provided beneath first electrode 7. The
`n-type layer 4 through i-type layer 5 is formed by reac-
`light can be directly picked up through first transparent
`tive ion etching through the masks of the photoresist 12
`electrode 7. Moreover, the light reflected from the
`and the Si02layer 11 while feeding CChF2 gas at a rate 35 reflection film 13 formed on the opposite side of the
`of 10 ml/minute under conditions of a degree of vac-
`sapphire substrate 1 is obtained through first transparent
`uum of 0.04 Torr., and high frequency power of 0.44
`electrode 7.
`W /cm2. After completion of the etching, dry etching
`This light emitting diode makes use of a transparent
`with Ar is effected.
`conductive film as the first electrode 7. Thus, the area of
`The photoresist 12 and the SiO layer 11 are removed 40 the first electrode 7 is enlarged. This makes a small
`series resistance between the first electrode 7 and the
`by means of hydrofluoric acid.
`Subsequently, an approximately 1000 angstrom thick
`second electrode 8, thereby suppressing generation of
`transparent conductive ITO layer is formed over the
`heat.
`entire surface by ion plating. A photoresist is applied
`This reflects on the current-voltage characteristic in
`onto the ITO layer. The photoresist is formed into a 45 which the threshold Voltage at a current of 10 mA is 6
`desired pattern by photolithography while leaving the
`volts. With a light-emitting diode having a known struc-
`photoresist at a portion at which first electrode 7 is to be
`ture (i.e. LED using an aluminum electrode as the first
`electrode), the threshold voltage at a current of 10 mA
`formed.
`The exposed portion of the ITO layer is etched
`is 8 volts. Thus, the threshold voltage is reduced to
`through the photoresist mask. Thereafter, the photore- 50 about ! of that in conventional diodes, thus lowering
`sist is removed. By this operation, the first electrode
`the drive voltage.
`consisting of the ITO layer left after the etching is
`In the light emitting diode 10 of the above embodi-
`formed as shown in FIG.7.
`ment, n-type layer 4 has a single-layer structure. As
`Subsequently, an AI layer is formed over the entire
`shown in FIG. 10, a light-emitting diode lOa may have
`surface of the sample in a thickness of approximately 55 a double-layer n-type structure which includes a 1.5 p.m
`2000 angstroms. A photoresist is applied onto the AI
`thick lower carrier concentration n-type layer 4a con-
`layer, followed by photolithography to form an in-
`nected to the i-type layer 5 and a 2.2 p.m thick high
`tended pattern of the photoresist so that a portion corre-
`carrier concentration n+-type layer 3.
`sponding to second electrode 8 to be formed is left.
`In this light-emitting diode lOa, an electric current
`The exposed portion of the AI layer is etched through 60 passes through the high carrier concentration n+ type
`layer 3 in a horizontal direction. Thus, the resistance
`the photoresist mask, after which the photoresist is
`removed. By this operation, an AI layer 8a which is
`between electrodes can be further reduced.
`used as second electrode 8 for connection to then-type
`The high carrier concentration n+-type layer 3 is
`layer 4 is formed as shown in FIG. 8.
`formed by keeping the temperature of the sapphire
`A photoresist is applied over the entire upper surface 65 substrate at 1150° C. and feeding 20 liters/minute ofH2,
`10 liters/minute of NH3, 1. 7 X 10-4 moles/minute of
`of the sample, followed by photolithography to remove
`the photoresist at portions where the terminal electrode
`TMG, and 200 ml/minute of silane (Sili4) diluted with
`9 for the first electrode 7 made of ITO and the second
`H2 to 0.86 ppm for 30 minutes thereby providing a fllm
`
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`25
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`7
`with a thickness of 2.2 iJ-m and a carrier concentration
`of l.SX 1Q18jcm3.
`A further embodiment is shown in FIG. 11, wherein
`a light-emitting diode lOb includes a first electrode 7
`which is provided at the center of the chip and made of 5
`a transparent conductive film and a second electrode 8
`provided around the first electrode 7 and connected to
`n+-type layer 3.
`In this arrangement, an Allayer which is the lower(cid:173)
`most layer of the second electrode 8 may be provided as 10
`a reflection layer, resulting in an improvement of light
`emission efficiency.
`The light-emitting diode lOb can be fabricated by the
`steps shown in FIGS. 12-15.
`As shown in FIG. 12, a AlN buffer layer 2, a high 15
`carrier concentration n+-type layer 3, a low carrier
`concentration n-type layer 4a and an i-type layer 5 are
`successively formed on a sapphire substrate 1 according
`to the procedure set out hereinabove.
`As shown in FIG. 13, the resultant multi-layered 20
`wafer is diced by the use of a thick blade having, for
`example, a thickness of 250 iJ-m, and cross cut to an
`extent reaching the upper surface of the sapphire sub(cid:173)
`strate 1 from the i-type layer 5 through the lower car-
`rier concentration n-type layer 4a, high carrier concen(cid:173)
`tration n+-type layer 3 and buffer layer 2.
`In the same manner as in FIGS. 7 and 8, a first elec(cid:173)
`trode 7 consisting of ITO and a second electrode 8a are
`formed as shown in FIG. 14.
`According to the procedure shown in FIG.9, Ni
`layer 9a and Au layer 9b of the terminal electrode 9, and
`Ni layer 8b and Au layer 8c of the second electrode 2
`are formed as shown in FIG. 15.
`As shown in FIG. 15, the wafer is diced by means of 35
`a thin blade having a thickness, for example, of 150 1-Lm
`to cut off the sapphire substrate 1 into pieces at the
`half-cut portions where the second electrode 8 has been
`cross cut.
`In this manner a light-emitting diode lOb having such 40
`a structure as shown in FIG. 11 is fabricated.
`Further, as shown in FIG. 16, a light-emitting diode
`lOc may be fabricated as follows: a small-size hole
`which extends to the n+-type is formed at a central
`portion of i-type layer 5, and a second electrode 8 is 4S
`formed in the hole, about which a first transparent con(cid:173)
`ductive electrode 7 is formed.
`In light-emitting diodes lOb, lOc having such struc(cid:173)
`tures as stated hereinabove, second electrode 8 for the
`high carrier concentration n+-type layer 3 has a sym- so
`metric positional relation with first electrode 7 for i(cid:173)
`type layer 5.
`Accordingly, the electric current passing between
`these electrodes is substantially uniform irrespective of
`the position of the i-type layer 5. Accordingly, uniform ss
`light emission in the blue light-emitting region of the
`diodes is ensured with an improved light emission inten(cid:173)
`sity.
`While this invention has been described in connection
`with what is presently considered to be the most practi- 60
`cal and preferred embodiments, it is to be understood
`that the invention is not limited to the disclosed embodi(cid:173)
`ments, but, on the contrary, is intended to cover various
`modifications and equivalent arrangements included
`within the spirit and scope of the appended claims.
`What is claimed is:
`1. A semiconductor light-emitting device which com(cid:173)
`prises:
`
`8
`an n-type layer made of an n-type gallium nitride(cid:173)
`based compound semiconductor of the formula
`AlxGat-xN, wherein O:§X< 1;
`an i-type layer formed on the n-type layer and made
`of a semi-insulating i-type gallium nitride-based
`compound semiconductor of the formula Alx.
`Gat-xN, wherein O:§X<l, and doped with a p(cid:173)
`type impurity for junction with the n-type layer;
`a first electrode formed on the surface of the i-type
`layer and made of a transparent conductive ftlm;
`and
`a second electrode formed to connect to the n-type
`layer wherein light is emitted from the side of the
`i-type layer to the outside,
`wherein said first electrode is formed at a central
`portion of said i-type layer and said second elec(cid:173)
`trode is provided around said first electrode and
`connected to a side wall of said n-type layer.
`2. A semiconductor light-emitting device according
`to claim 1, wherein said second electrode is formed to
`connect with said n-type layer by making cross-cut
`grooves from a side of said i-type layer to the surface of
`said sapphire substrate depending on the chip size of a
`light-emitting device, and a metal material, filling said
`grooves and separating said sapphire substrate along
`said cross-cut grooves.
`3. A semiconductor light-emitting device according
`to claim 1, further comprising a sapphire substrate on
`which said n-type layer is formed, said sapphire sub(cid:173)
`strate having a reflection layer on a side opposite to said
`n-type layer.
`4. A semiconductor light-emitting device according
`to claim 3, further comprising a frame substrate to
`which said reflection layer is connected.
`5. A semiconductor light-emitting device according
`to claim 1, wherein said transparent conductive film
`consists of tin-added indium oxide (ITO).
`6. A semiconductor light-emitting device according
`to claim 1, further comprising a terminal electrode
`formed at one corner of said first electrode and having
`a nickel lowermost layer.
`7. A semiconductor light-emitting device according
`to claim 1, wherein said second electrode has a three
`layer structure consisting of aluminum, nickel and gold
`layers formed in this order from a side contacting the
`n-type layer.
`8. A semiconductor light-emitting device according
`to claim 1, wherein said n-type layer is of double-layer
`structure including an n-layer of low carrier concentra(cid:173)
`tion and an n+-layer of high carrier concentration, the
`former being adjacent to said i-layer.
`9. A semiconductor light-emitting device according
`to claim 3, further comprising a buffer layer formed on
`said sapphire substrate.
`10. A semiconductor light-emitting device which
`comprises:
`an n-type layer made of an n-type gallium nitride(cid:173)
`based compound semiconductor of the formula
`AlxGat-xN, wherein O:§X< 1;
`an i-type layer formed on the n-type layer and made
`of a semi-insulating i-type gallium nitride-based
`compound semiconductor of the formula Alx.
`Gat-xN, wherein O:§X< 1, and doped with a p(cid:173)
`type impurity for junction with the n-type layer;
`a first electrode formed on the surface of the i-type
`layer and made of a transparent conductive film;
`and
`
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`5,369,289
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`9
`a second electrode formed to connect to the n-type
`layer through the i-type layer, wherein light is
`emitted from the side of the i-type layer to the
`outside,
`wherein said second electrode is connected to said 5
`n-type layer at a central portion of said i-type layer
`through said i-type layer and said flrst electrode is
`formed on said i-type layer around said second
`electrode and in spaced relation to said second
`electrode.
`11. A semiconductor light-emitting device according
`to claim 10, further comprising a sapphire substrate on
`which said n-type layer is formed, said sapphire sub(cid:173)
`strate having a reflection layer on a side opposite to said
`n-type layer.
`12. A semiconductor light-emitting device according
`to claim 10, further comprising a reflection film and a
`frame substrate to which said reflection fllm is con(cid:173)
`nected.
`13. A semiconductor light-emitting device according 20
`to claim 10, wherein said transparent conductive fllm of
`said first electrode consists of tin-added indium oxide
`(ITO).
`
`10
`14. A semiconductor light-emitting device according
`to claim 10, further comprising a terminal electrode
`formed at one corner of said first electrode and having
`a nickel lowermost layer.
`15. A semiconductor light-emitting device according
`to claim 10, wherein said second electrode has a three
`layer structure consisting of alumi