US20030205718A1 - Light-emitting semiconductor device using group III nitride compound - Google Patents
Light-emitting semiconductor device using group III nitride compound Download PDFInfo
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- US20030205718A1 US20030205718A1 US10/456,509 US45650903A US2003205718A1 US 20030205718 A1 US20030205718 A1 US 20030205718A1 US 45650903 A US45650903 A US 45650903A US 2003205718 A1 US2003205718 A1 US 2003205718A1
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- -1 nitride compound Chemical class 0.000 title claims abstract description 20
- 239000004065 semiconductor Substances 0.000 title claims abstract description 20
- 238000005253 cladding Methods 0.000 claims abstract description 59
- 239000012535 impurity Substances 0.000 claims abstract description 23
- 238000009792 diffusion process Methods 0.000 claims abstract description 7
- JMASRVWKEDWRBT-UHFFFAOYSA-N Gallium nitride Chemical compound [Ga]#N JMASRVWKEDWRBT-UHFFFAOYSA-N 0.000 claims description 19
- 239000011777 magnesium Substances 0.000 claims description 13
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical group [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 6
- 229910052710 silicon Inorganic materials 0.000 claims description 6
- 239000010703 silicon Substances 0.000 claims description 6
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical group [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 claims description 2
- 229910052749 magnesium Inorganic materials 0.000 claims description 2
- 239000000463 material Substances 0.000 claims 1
- 239000000758 substrate Substances 0.000 abstract description 12
- 229910052594 sapphire Inorganic materials 0.000 abstract description 11
- 239000010980 sapphire Substances 0.000 abstract description 11
- 229910002601 GaN Inorganic materials 0.000 description 15
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 8
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 6
- 229910000069 nitrogen hydride Inorganic materials 0.000 description 6
- 230000004888 barrier function Effects 0.000 description 5
- PMHQVHHXPFUNSP-UHFFFAOYSA-M copper(1+);methylsulfanylmethane;bromide Chemical compound Br[Cu].CSC PMHQVHHXPFUNSP-UHFFFAOYSA-M 0.000 description 5
- BLRPTPMANUNPDV-UHFFFAOYSA-N Silane Chemical compound [SiH4] BLRPTPMANUNPDV-UHFFFAOYSA-N 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- 238000000034 method Methods 0.000 description 4
- 229920002120 photoresistant polymer Polymers 0.000 description 4
- 230000008569 process Effects 0.000 description 4
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 3
- 229910052681 coesite Inorganic materials 0.000 description 3
- 239000013256 coordination polymer Substances 0.000 description 3
- 229910052906 cristobalite Inorganic materials 0.000 description 3
- 229910000077 silane Inorganic materials 0.000 description 3
- 239000000377 silicon dioxide Substances 0.000 description 3
- 229910052682 stishovite Inorganic materials 0.000 description 3
- 229910052905 tridymite Inorganic materials 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 2
- 238000001312 dry etching Methods 0.000 description 2
- 230000001747 exhibiting effect Effects 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 238000010030 laminating Methods 0.000 description 2
- 238000002488 metal-organic chemical vapour deposition Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 238000000206 photolithography Methods 0.000 description 2
- PIGFYZPCRLYGLF-UHFFFAOYSA-N Aluminum nitride Chemical compound [Al]#N PIGFYZPCRLYGLF-UHFFFAOYSA-N 0.000 description 1
- 229910015844 BCl3 Inorganic materials 0.000 description 1
- 229910021529 ammonia Inorganic materials 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 239000012159 carrier gas Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- 239000007792 gaseous phase Substances 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- QBJCZLXULXFYCK-UHFFFAOYSA-N magnesium;cyclopenta-1,3-diene Chemical compound [Mg+2].C1C=CC=[C-]1.C1C=CC=[C-]1 QBJCZLXULXFYCK-UHFFFAOYSA-N 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 description 1
- 230000006798 recombination Effects 0.000 description 1
- 238000005215 recombination Methods 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 238000004544 sputter deposition Methods 0.000 description 1
- FAQYAMRNWDIXMY-UHFFFAOYSA-N trichloroborane Chemical compound ClB(Cl)Cl FAQYAMRNWDIXMY-UHFFFAOYSA-N 0.000 description 1
- JLTRXTDYQLMHGR-UHFFFAOYSA-N trimethylaluminium Chemical compound C[Al](C)C JLTRXTDYQLMHGR-UHFFFAOYSA-N 0.000 description 1
- XCZXGTMEAKBVPV-UHFFFAOYSA-N trimethylgallium Chemical compound C[Ga](C)C XCZXGTMEAKBVPV-UHFFFAOYSA-N 0.000 description 1
- IBEFSUTVZWZJEL-UHFFFAOYSA-N trimethylindium Chemical compound C[In](C)C IBEFSUTVZWZJEL-UHFFFAOYSA-N 0.000 description 1
- 238000000927 vapour-phase epitaxy Methods 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
- 238000001039 wet etching Methods 0.000 description 1
Images
Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
- H01L29/12—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
- H01L29/20—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed including, apart from doping materials or other impurities, only AIIIBV compounds
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
- H01L33/26—Materials of the light emitting region
- H01L33/30—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table
- H01L33/32—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table containing nitrogen
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/32—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures
- H01S5/3211—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures characterised by special cladding layers, e.g. details on band-discontinuities
- H01S5/3213—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures characterised by special cladding layers, e.g. details on band-discontinuities asymmetric clading layers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/32—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures
- H01S5/323—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser
- H01S5/32308—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser emitting light at a wavelength less than 900 nm
- H01S5/32341—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser emitting light at a wavelength less than 900 nm blue laser based on GaN or GaP
Definitions
- the present invention relates to a light-emitting semiconductor diode (LED) that uses a Group III nitride compound. More particularly, it relates to an LED having an improved emission efficiency in the ultra violet region.
- LED light-emitting semiconductor diode
- a known light-emitting semiconductor diode (LED) using a Group III nitride compound comprises an n + -layer comprising GaN, an n layer comprising Al 0.08 Ga 0.92 N, an emission layer comprising In 0.08 Ga 0.92 N, and a p-layer comprising Al 0.08 Ga 0.92 N.
- the known LED's emission mechanism uses inter-band recombination of electrons to obtain ultra violet color light with a peak wavelength of 380 nm or shorter.
- the LED has a low luminous efficiency for several reasons, including a dislocation caused by a mismatch of lattice constants among the n′-layer, the n-layer, and the emission layer which invites poor crystallinity of the emission layer made of InGaN.
- An object of the present invention is, therefore, to improve the luminous efficiency of an LED in the ultraviolet region utilizing a Group III nitride compound.
- a first aspect of the present invention is directed to a Group III nitride compound semiconductor comprising a triple layer structure having an emission layer sandwiched between an n-type cladding layer and a p-type cladding layer.
- the emission layer satisfies the formula Al x1 Ga y1 In 1-x1-y1 N, where 0 ⁇ x 1 ⁇ 1, 0 ⁇ y 1 ⁇ 1, and 0 ⁇ x 1 +y 1 ⁇ 1, and has a thickness wider than the diffusion length of holes.
- the n-type cladding layer satisfies the formula Al x2 Ga y2 In 1-x2-y2 N, where 0 ⁇ x 2 ⁇ 1, 0 ⁇ y 2 ⁇ 1and 0 ⁇ x 2 +y 2 ⁇ 1, and is doped with a donor impurity.
- the lattice constant of the n-type cladding layer is substantially equal to the lattice constant of the emission layer.
- the p-type cladding layer satisfies the formula Al x3 Ga y3 In 1-x3-y3 N, where 0 ⁇ x 3 ⁇ 1, 0 ⁇ y 3 ⁇ 1, and 0 ⁇ x 3 +y 3 ⁇ 1, and is doped with an acceptor impurity.
- the width of the forbidden band of the p-type cladding layer is wider than the width of forbidden band of the emission layer by an amount sufficient to confine electrons injected into the emission layer.
- the emission layer comprises Ga y2 In 1-y2 N, where 0.92 ⁇ y 2 ⁇ 1 and the n-type cladding layer comprises gallium nitride (GaN) doped with a donor impurity.
- GaN gallium nitride
- the n-type cladding layer is formed on another n-type layer, which comprises gallium nitride (GaN) and is doped with a donor impurity at a density relatively higher than the n-type cladding layer.
- GaN gallium nitride
- the donor impurity is silicon (Si).
- the acceptor impurity is magnesium (Mg).
- the emission layer is doped with silicon (Si).
- composition ratio parameters x 2 and y 2 of the n-type cladding layer satisfying the formula Al x2 Ga y2 In 1-x2-y2 N, where 0 ⁇ x 2 ⁇ 1, 0 ⁇ y 2 ⁇ 1, and 0 ⁇ x 2 +y 2 ⁇ 1, is designed that the lattice constant of the n-type cladding layer may be substantially equal to the lattice constant of the emission layer. As a result, crystallinity of the emission layer is improved.
- composition ratio x 3 and y 3 of the p-type cladding layer satisfying the formula Al x3 Ga y3 In 1-x3-y3 N, where 0 ⁇ x 3 ⁇ 1, 0 ⁇ y 3 ⁇ 1, and 0 ⁇ x 3 +y 3 ⁇ 1, is designed to form a forbidden band sufficiently wider than that of the emission layer to confine electrons injected from the n-type cladding layer to the emission layer.
- a barrier between the n-type cladding layer and the emission layer has been made large to confine holes injected from the p-type cladding layer into the emission layer.
- the inventors of the present invention conducted a series of studies and found that when the diffusion length of holes, or life span, is short, i.e., about a 0.1 ⁇ m, compared with thickness of the emission layer, forming a large barrier between the n-type cladding layer and the emission layer is less useful as for its original purpose to confine holes. Therefore, that barrier may be designed to be small.
- the composition ratio x 2 and y 2 of the n-type cladding layer satisfying the formula Al x2 Ga y2 In 1-x2-y2 N, where 0 ⁇ x 2 ⁇ 1, 0 ⁇ y 2 ⁇ 1, and 0 ⁇ x 2 +y 2 ⁇ 1, can be selected so as to minimize lattice mismatching between the n-type cladding layer and the emission layer.
- crystallinity of the emission layer is improved and emission efficiency of the LED in the ultraviolet region is improved.
- the emission layer is comprised of Ga y2 In 1-y2 N (0.92 ⁇ y 2 ⁇ 1)
- the lattice mismatch between the emission layer and the n-type cladding layer is mitigated by forming the n-type cladding layer with GaN for light emission in the ultraviolet region.
- the LED has an AlN buffer layer on a sapphire substrate.
- a highly Si-doped GaN n + -layer of high carrier concentration is formed on the AlN buffer layer.
- An n-type cladding layer is formed on the n + -layer which leads current to the n-type cladding layer. Because the n-type cladding layer is comprised of GaN, the lattice constant of the n + -layer and that of the n-type cladding layer precisely match each other. Accordingly, lattice mismatching is not transferred to an emission layer formed on the n-type cladding layer, and crystallinity of the emission layer is improved.
- FIG. 1 is a diagram showing the structure of an LED in the example set forth below.
- FIGS. 2 through 5 are sectional views illustrating a process for manufacturing the LED in the example.
- FIG. 1 shows an Example LED 100 .
- the illustrated LED 100 has a sapphire (Al 2 O 3 ) substrate 1 upon which an aluminum nitride (AlN) buffer layer 2 having a thickness generally of 500 ⁇ is formed.
- AlN aluminum nitride
- two n-type layers are formed on the AlN buffer layer 2 : a silicon (Si) doped GaN n ⁇ -layer 3 of high carrier concentration, having a thickness generally of 5.0 ⁇ m and having a Si concentration of 5 ⁇ 10 18 /cm 3 and having an electron concentration of 2.5 ⁇ 10 18 /cm 3 ; and a Si-doped GaN cladding layer 4 having a thickness generally of 0.5 ⁇ m and having a Si concentration of 1 ⁇ 10 18 /cm 3 and having an electron concentration of 5 ⁇ 10 17 /cm 3 .
- An emission layer 5 comprised of In 0.07 Ga 0.93 N and having a thickness of generally 0.5 ⁇ m, is formed on the cladding layer 4 .
- an Mg-doped p-type cladding layer 61 comprised of Al 0.08 Ga 0.92 N, having a thickness generally of 0.5 ⁇ m and having a hole concentration of 5 ⁇ 10 17 /cm 3 , and an Mg concentration of 5 ⁇ 10 20 /cm 3 ; and an Mg doped GaN p-typo layer 62 functioning as a contact layer, having a hole concentration of 7 ⁇ 10 18 /cm 3 , and having an Mg concentration of 5 ⁇ 10 21 /cm 3 .
- Nickel electrodes 7 and 8 are each connected to the contact layer 62 and the n ⁇ -layer 3 , respectively.
- Band gap of the GaN cladding layer 4 is 3.4 eV and its lattice constant is 3.160 ⁇ .
- Band gap of the emission layer 5 of In 0.07 Ga 0.93 N is 3.22 eV and its lattice constant is 3.187 ⁇ .
- Band gap of the cladding layer 61 of Al 0.08 Ga 0.92 N is 3.54 eV and its lattice constant is 3.156 ⁇ .
- the composition ratios of the cladding layer 4 and the emission layer 5 are designed to make misfit between them 0.85%.
- the illustrated LED 100 is produced by gaseous phase epitaxial growth, called metal organic vapor phase epitaxy, referred to as MOVPE hereinafter.
- MOVPE metal organic vapor phase epitaxy
- the gases employed in this process are ammonia (NH 3 ), a carrier gas (H 2 or N 2 ), trimethyl gallium (Ga(CH 3 ) 3 ) (hereinafter TMG), trimethyl aluminum (Al(CH 3 ) 3 ) (hereinafter TMG), trimethyl indium (In(CH 3 ) 3 ) (hereinafter TMI), silane (SiH 4 ), and biscyclopentadienyl magnesium (Mg(C 5 H 5 ) 2 ) (hereinafter CP 2 Mg).
- NH 3 ammonia
- TMG trimethyl gallium
- Al(CH 3 ) 3 ) hereinafter TMG
- TMI trimethyl indium
- SiH 4 silane
- Mg(C 5 H 5 ) 2 ) biscyclopentadienyl magnesium
- the single crystalline sapphire substrate 1 has a thickness of about 100 ⁇ m to 400 ⁇ m. After having its main surface ‘a’ cleaned by an organic washing solvent and heat treatment, the sapphire substrate 1 was placed on a susceptor in a reaction chamber for the MOVPE treatment. Then the sapphire substrate 1 was baked at 1100° C. by H 2 vapor fed into the chamber at a flow rate of 2 liter/min. under normal pressure for a period of 30 min.
- a 500 ⁇ thick AlN buffer layer 2 was formed on the surface ‘a’ of the baked sapphire substrate 1 under conditions controlled by lowering the temperature in the chamber to 400° C., keeping the temperature constant, and concurrently supplying for a period of 90 sec. H 2 at a flow rate of 20 liter/min., NH 3 at 10 liter/min., and TMA at 1.8 ⁇ 10 ⁇ 5 mol/min.
- Si-doped GaN was formed on the buffer layer 2 , as an n ⁇ -layer 3 of high carrier concentration with a Si concentration of about 5 ⁇ 10 18 /cm 3 and an electron concentration of about 2.5 ⁇ 10 18 /cm 3 , under conditions controlled by keeping the temperature of the sapphire substrate 1 at 1150° C. and concurrently supplying for 30 min. H 2 at a flow rate of 20 liter/min., KH 3 at 10 liter/min., TMG at 1.7 ⁇ 10 ⁇ 4 mol/min., and silane diluted to 0.86 ppm by H 2 at 200 ml/min.
- n + -layer 3 As an n-type cladding layer 4 with a Si concentration of about 1 ⁇ 10 18 /cm 3 and an electron concentration of about 5 ⁇ 10 17 /cm 3 , under conditions controlled by keeping the temperature of the sapphire substrate 1 at 1100° C. and concurrently supplying for 30 min. H 2 or N 2 at a flow rate of 10 liter/min., NH 3 at 10 liter/min., TMG at 1.12 ⁇ 10 ⁇ 4 mol/min., and silane diluted to 0.86 ppm by H 2 at 10 ⁇ 10 ⁇ 9 mol/min.
- Mg-doped Al 0.08 Ga 0.92 N p-type cladding layer 61 was formed on the omission layer 5 under conditions controlled by keeping the temperature of the sapphire substrate 1 at 1100° C. and concurrently supplying for 60 min. N 2 or H 2 at a flow rate of 20 liter/min., NH 3 at 10 liter/min., TMG at 1.12 ⁇ 10 ⁇ 4 mol/min., TMA at 0.47 ⁇ 10 ⁇ 4 mol/min., and CP 2 Mg at 2 ⁇ 10 ⁇ 4 mol/min.
- the resistivity of the cladding layer 61 was 10 8 ⁇ cm or more, exhibiting insulating characteristics.
- the impurity concentration of Mg doped into the cladding layer 61 was 1 ⁇ 10 20 /cm 3 .
- Mg-doped GaN serving as a contact layer 62
- a contact layer 62 was formed on the cladding layer 61 under conditions of keeping the temperature of the sapphire substrate 1 at 1100° C. and concurrently supplying for 4 min. N 2 or H 2 at a flow rate of 20 liter/min. , NH 3 at 10 liter/min., TMG at 1.12 ⁇ 10 ⁇ 4 mol/min., and CP 2 Mg at 4 ⁇ 10 ⁇ 4 mol/min.
- the resistivity of the contact layer 62 was 10 8 ⁇ cm or more, exhibiting insulating characteristics.
- the impurity concentration of Mg doped into the contact layer 62 was 2 ⁇ 10 20 /cm 3 .
- the exposed part of the successive layers, from the surface of the device, or the p-type contact layer 62 , to the n-type cladding layer 4 were removed by dry etching, or by supplying a high-frequency power density of 0.44 W/cm 2 and BCl 3 gas of 10 ml/min. at a vacuum degree of 0.04 Torr. After that, dry etching was carried out with argon (Ar) on the exposed surface of the n + layer 3 . Consequently, a hole A was formed for forming an electrode extending in the n + -layer 3 as shown in FIG. 5.
- electrodes 7 and 8 were formed respectively connected to the p-type contact layer 62 and bottom of the hole A or the exposed part of the n + -layer 3 .
- the wafer treated with the above-mentioned process was divided or diced to form separate chips or elements including an LED 100 as shown in FIG. 1.
- the obtained LED 100 was found to have a luminous intensity of 1 mW and a peak wavelength of 380 nm in the luminous spectrum at a driving current of 20 mA.
- the luminous efficiency was 1.5% which is 5 folds that of a conventional LED.
- both the n + -layer 3 and the n-type cladding layer 4 were formed of GaN, no lattice mismatching occurred between the layers. Accordingly, any mismatching (misfit) of lattice constant was transferred to the emission layer 5 comprising In 0.07 Ga 0.93 N. Further, the degree of mismatching between the lattice constants of GaN and In 0.07 Ga 0.93 N was small. As a result, the crystallinity of the emission layer 5 was improved.
- the thickness of the emission layer 5 which is about 0.5 ⁇ m in the illustrated Example, was longer than the diffusion length, or life span, of holes injected from the p-type cladding layer, so that the luminous efficiency could be maintained despite the small barrier between the n-type cladding layer 4 and the emission layer 5 .
- the luminous efficiency in the ultraviolet region was improved compared with a conventional LED.
- the misfit ratio between the cladding layer 4 and the emission layer 5 in the illustrated example is 0.85%. Preferable misfit ratio between then is within 1%.
- GaN and In 0.07 Ga 0.93 N are used as an example of four element compounds of Al x Ga y In 1-x-y N.
- a lattice constant and a band gap of the Al x Ga y In 1-x-y N is determined according to mixed crystal ratio of GaN, InN, and AlN whose lattice constants are respectively 3.160 ⁇ , 3.544 ⁇ , and 3.110 ⁇ and whose band gaps are respectively 3.4 eV, 1.95 eV, and 6.0 eV.
- the LED 100 has a double-hetero junction structure.
- Another junction structure may be used, such as a single-hetero junction structure.
- heat treatment was used to obtain p-type conduction, electron irradiation can be used as an alternate.
- the emission layer 5 in the illustrated Example is not doped with any impurities.
- the emission layer 5 may be doped with a donor impurity such as silicon (Si) and an acceptor impurity such as (Zn).
- the emission layer 5 in the illustrated Example has a thickness of 0.5 ⁇ m.
- Preferable thickness of the emission layer 5 ranges from 0.1 ⁇ m to 1.0 ⁇ m. It is not preferable that the emission layer is thinner than 0.1 ⁇ m, because barrier between the emission layer 5 and the n-type cladding layer 4 is small and unable to confine holes effectively. It is not preferable that the emission layer is thicker than 1.0 ⁇ m, because confining electrons whose diffusion length are 1 ⁇ m becomes less effective.
- a laser diode can be provided as an alternate.
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Abstract
A Group III nitride compound semiconductor includes a multiple layer structure having an emission layer between an n-type cladding layer and a p-type cladding layer. The n-type cladding layer may be below the emission layer, having been formed on another n-type layer which was formed over a buffer layer and a sapphire substrate. The emission layer has a thickness which is wider than the diffusion length of holes within the emission layer. The n-type cladding layer is doped with a donor impurity and has a lattice constant substantially equal to a lattice constant of the emission layer. The p-type cladding layer is doped with an acceptor impurity and has a forbidden band sufficiently wider than the forbidden band of the emission layer in order to confine electrons injected into the emission layer.
Description
- 1. Field of the Invention
- The present invention relates to a light-emitting semiconductor diode (LED) that uses a Group III nitride compound. More particularly, it relates to an LED having an improved emission efficiency in the ultra violet region.
- 2. Description of the Background Information
- A known light-emitting semiconductor diode (LED) using a Group III nitride compound comprises an n+-layer comprising GaN, an n layer comprising Al0.08Ga0.92N, an emission layer comprising In0.08Ga0.92N, and a p-layer comprising Al0.08Ga0.92N. The known LED's emission mechanism uses inter-band recombination of electrons to obtain ultra violet color light with a peak wavelength of 380 nm or shorter.
- However, the LED has a low luminous efficiency for several reasons, including a dislocation caused by a mismatch of lattice constants among the n′-layer, the n-layer, and the emission layer which invites poor crystallinity of the emission layer made of InGaN.
- An object of the present invention is, therefore, to improve the luminous efficiency of an LED in the ultraviolet region utilizing a Group III nitride compound.
- A first aspect of the present invention is directed to a Group III nitride compound semiconductor comprising a triple layer structure having an emission layer sandwiched between an n-type cladding layer and a p-type cladding layer.
- The emission layer satisfies the formula Alx1Gay1In1-x1-y1N, where 0≦x1≦1, 0≦y1≦1, and 0≦x1+y1≦1, and has a thickness wider than the diffusion length of holes. The n-type cladding layer satisfies the formula Alx2Gay2In1-x2-y2N, where 0≦x2≦1, 0≦y2≦1and 0≦x2+y2≦1, and is doped with a donor impurity. The lattice constant of the n-type cladding layer is substantially equal to the lattice constant of the emission layer. The p-type cladding layer satisfies the formula Alx3Gay3In1-x3-y3N, where 0≦x3≦1, 0≦y3≦1, and 0≦x3+y3≦1, and is doped with an acceptor impurity. The width of the forbidden band of the p-type cladding layer is wider than the width of forbidden band of the emission layer by an amount sufficient to confine electrons injected into the emission layer.
- According to a second aspect of the invention, the emission layer comprises Gay2In1-y2N, where 0.92≦y2≦1 and the n-type cladding layer comprises gallium nitride (GaN) doped with a donor impurity.
- According to a third aspect of the invention, the n-type cladding layer is formed on another n-type layer, which comprises gallium nitride (GaN) and is doped with a donor impurity at a density relatively higher than the n-type cladding layer.
- According to a fourth aspect of the invention, the donor impurity is silicon (Si).
- According to a fifth aspect of the invention, the acceptor impurity is magnesium (Mg).
- According to a sixth aspect of the invention, the emission layer is doped with silicon (Si).
- The composition ratio parameters x2 and y2 of the n-type cladding layer satisfying the formula Alx2Gay2In1-x2-y2N, where 0≦x2≦1, 0≦y2≦1, and 0≦x2+y2≦1, is designed that the lattice constant of the n-type cladding layer may be substantially equal to the lattice constant of the emission layer. As a result, crystallinity of the emission layer is improved.
- Further, the composition ratio x3 and y3 of the p-type cladding layer satisfying the formula Alx3Gay3In1-x3-y3N, where 0≦x3≦1, 0≦y3≦1, and 0≦x3+y3≦1, is designed to form a forbidden band sufficiently wider than that of the emission layer to confine electrons injected from the n-type cladding layer to the emission layer.
- Conventionally, a barrier between the n-type cladding layer and the emission layer has been made large to confine holes injected from the p-type cladding layer into the emission layer. The inventors of the present invention conducted a series of studies and found that when the diffusion length of holes, or life span, is short, i.e., about a 0.1 μm, compared with thickness of the emission layer, forming a large barrier between the n-type cladding layer and the emission layer is less useful as for its original purpose to confine holes. Therefore, that barrier may be designed to be small. Accordingly, the composition ratio x2 and y2 of the n-type cladding layer satisfying the formula Alx2Gay2In1-x2-y2N, where 0≦x2≦1, 0≦y2≦1, and 0≦x2+y2≦1, can be selected so as to minimize lattice mismatching between the n-type cladding layer and the emission layer. As a result, crystallinity of the emission layer is improved and emission efficiency of the LED in the ultraviolet region is improved.
- When the emission layer is comprised of Gay2In1-y2N (0.92≦y2≦1), the lattice mismatch between the emission layer and the n-type cladding layer is mitigated by forming the n-type cladding layer with GaN for light emission in the ultraviolet region.
- The LED has an AlN buffer layer on a sapphire substrate. A highly Si-doped GaN n+-layer of high carrier concentration is formed on the AlN buffer layer. An n-type cladding layer is formed on the n+-layer which leads current to the n-type cladding layer. Because the n-type cladding layer is comprised of GaN, the lattice constant of the n+-layer and that of the n-type cladding layer precisely match each other. Accordingly, lattice mismatching is not transferred to an emission layer formed on the n-type cladding layer, and crystallinity of the emission layer is improved.
- The above and other objects, features, advantages, and characteristics of the present invention are further described in the following detailed description with reference to the accompanying drawings by way of non-limiting exemplary embodiments of the present invention, wherein like reference numerals represent similar parts of the embodiments throughout the several views.
- In the accompanying drawings:
- FIG. 1 is a diagram showing the structure of an LED in the example set forth below; and
- FIGS. 2 through 5 are sectional views illustrating a process for manufacturing the LED in the example.
- The invention will be more fully understood by reference to the following example.
- FIG. 1 shows an
Example LED 100. The illustratedLED 100 has a sapphire (Al2O3)substrate 1 upon which an aluminum nitride (AlN)buffer layer 2 having a thickness generally of 500 Å is formed. Consecutively, two n-type layers are formed on the AlN buffer layer 2: a silicon (Si) doped GaN n−-layer 3 of high carrier concentration, having a thickness generally of 5.0 μm and having a Si concentration of 5×1018/cm3 and having an electron concentration of 2.5×1018/cm3; and a Si-dopedGaN cladding layer 4 having a thickness generally of 0.5 μm and having a Si concentration of 1×1018/cm3 and having an electron concentration of 5×1017/cm3. Anemission layer 5, comprised of In0.07Ga0.93N and having a thickness of generally 0.5 μm, is formed on thecladding layer 4. Two p-layers are formed on the emission layer 5: an Mg-doped p-type cladding layer 61, comprised of Al0.08Ga0.92N, having a thickness generally of 0.5 μm and having a hole concentration of 5×1017/cm3, and an Mg concentration of 5×1020/cm3; and an Mg doped GaN p-typo layer 62 functioning as a contact layer, having a hole concentration of 7×1018/cm3, and having an Mg concentration of 5×1021/cm3.Nickel electrodes contact layer 62 and the n−-layer 3, respectively. - Band gap of the GaN
cladding layer 4 is 3.4 eV and its lattice constant is 3.160 Å. Band gap of theemission layer 5 of In0.07Ga0.93N is 3.22 eV and its lattice constant is 3.187 Å. Band gap of thecladding layer 61 of Al0.08Ga0.92N is 3.54 eV and its lattice constant is 3.156 Å. The composition ratios of thecladding layer 4 and theemission layer 5 are designed to make misfit between them 0.85%. - The illustrated
LED 100 is produced by gaseous phase epitaxial growth, called metal organic vapor phase epitaxy, referred to as MOVPE hereinafter. - The gases employed in this process are ammonia (NH3), a carrier gas (H2 or N2), trimethyl gallium (Ga(CH3)3) (hereinafter TMG), trimethyl aluminum (Al(CH3)3) (hereinafter TMG), trimethyl indium (In(CH3)3) (hereinafter TMI), silane (SiH4), and biscyclopentadienyl magnesium (Mg(C5H5)2) (hereinafter CP2Mg).
- The single
crystalline sapphire substrate 1 has a thickness of about 100 μm to 400 μm. After having its main surface ‘a’ cleaned by an organic washing solvent and heat treatment, thesapphire substrate 1 was placed on a susceptor in a reaction chamber for the MOVPE treatment. Then thesapphire substrate 1 was baked at 1100° C. by H2 vapor fed into the chamber at a flow rate of 2 liter/min. under normal pressure for a period of 30 min. - A 500 Å thick
AlN buffer layer 2 was formed on the surface ‘a’ of thebaked sapphire substrate 1 under conditions controlled by lowering the temperature in the chamber to 400° C., keeping the temperature constant, and concurrently supplying for a period of 90 sec. H2 at a flow rate of 20 liter/min., NH3 at 10 liter/min., and TMA at 1.8×10−5 mol/min. - About 5.0 μm in thickness of Si-doped GaN was formed on the
buffer layer 2, as an n−-layer 3 of high carrier concentration with a Si concentration of about 5×1018/cm3 and an electron concentration of about 2.5×1018/cm3, under conditions controlled by keeping the temperature of thesapphire substrate 1 at 1150° C. and concurrently supplying for 30 min. H2 at a flow rate of 20 liter/min., KH3 at 10 liter/min., TMG at 1.7×10−4 mol/min., and silane diluted to 0.86 ppm by H2 at 200 ml/min. - About 0.5 μm in thickness of Si-doped GaN was formed on the n+-
layer 3, as an n-type cladding layer 4 with a Si concentration of about 1×1018/cm3 and an electron concentration of about 5×1017/cm3, under conditions controlled by keeping the temperature of thesapphire substrate 1 at 1100° C. and concurrently supplying for 30 min. H2 or N2 at a flow rate of 10 liter/min., NH3 at 10 liter/min., TMG at 1.12×10−4 mol/min., and silane diluted to 0.86 ppm by H2 at 10×10−9 mol/min. - About 0.5 μm in thickness of In0.07Ga0.93N was formed on the n-
type cladding layer 4 asemission layer 5 under conditions controlled by keeping the temperature of thesapphire substrate 1 at 850° C. and concurrently supplying for 60 min. H2 at a flow rate of 20 liter/min. NH3 at 10 liter/min., TMG at 1.53×10−4 mol/min., and TMI at 0.02×10−4 mol/min. - About 1.0 μm in thickness of Mg-doped Al0.08Ga0.92N p-
type cladding layer 61 was formed on theomission layer 5 under conditions controlled by keeping the temperature of thesapphire substrate 1 at 1100° C. and concurrently supplying for 60 min. N2 or H2 at a flow rate of 20 liter/min., NH3 at 10 liter/min., TMG at 1.12×10−4 mol/min., TMA at 0.47×10−4 mol/min., and CP2Mg at 2×10−4 mol/min. The resistivity of thecladding layer 61 was 108 Ω·cm or more, exhibiting insulating characteristics. The impurity concentration of Mg doped into thecladding layer 61 was 1×1020/cm3. - About 0.2 μm in thickness of Mg-doped GaN, serving as a
contact layer 62, was formed on thecladding layer 61 under conditions of keeping the temperature of thesapphire substrate 1 at 1100° C. and concurrently supplying for 4 min. N2 or H2 at a flow rate of 20 liter/min. , NH3 at 10 liter/min., TMG at 1.12×10−4 mol/min., and CP2Mg at 4×10−4 mol/min. The resistivity of thecontact layer 62 was 108 Ω·cm or more, exhibiting insulating characteristics. The impurity concentration of Mg doped into thecontact layer 62 was 2×1020/cm3. - Then, heat treatment was uniformly carried out on the wafer at 450° C. for a period of 45 min. The heat treatment changed the
insulative contact layer 62 and the insulative cladding layer 81 to each be a p-type conductive semiconductors with respective hole concentrations of 7×1017/cm3 and 5×1017/cm3 and respective resistivities of 2 Ω·cm and 0.8 Ω·cm. As a result, a wafer with a multiple layer structure was obtained as shown in FIG. 2. - As shown in FIG. 3, about 2000 Å in thickness of SiO2 was deposited by sputtering to form a
layer 11 on thecontact layer 62. Then, the SiO2 layer 11 was coated with aphotoresist layer 12. A selected part or area of thephotoresist layer 12, named A′, which corresponds to an electrode forming part, was removed by photolithography as shown in FIG. 3. Part of the SiO2 layer 11 which was not covered with thephotoresist layer 12 was then etched off by an etching liquid such as hydrofluoric acid as shown in FIG. 4. - Then, the exposed part of the successive layers, from the surface of the device, or the p-
type contact layer 62, to the n-type cladding layer 4, were removed by dry etching, or by supplying a high-frequency power density of 0.44 W/cm2 and BCl3 gas of 10 ml/min. at a vacuum degree of 0.04 Torr. After that, dry etching was carried out with argon (Ar) on the exposed surface of the n+ layer 3. Consequently, a hole A was formed for forming an electrode extending in the n+-layer 3 as shown in FIG. 5. - Then, through processes including laminating a Ni layer, laminating a photoresist layer, carrying out photolithography, and wet etching,
electrodes type contact layer 62 and bottom of the hole A or the exposed part of the n+-layer 3. The wafer treated with the above-mentioned process was divided or diced to form separate chips or elements including anLED 100 as shown in FIG. 1. - The obtained
LED 100 was found to have a luminous intensity of 1 mW and a peak wavelength of 380 nm in the luminous spectrum at a driving current of 20 mA. The luminous efficiency was 1.5% which is 5 folds that of a conventional LED. - Because both the n+-
layer 3 and the n-type cladding layer 4 were formed of GaN, no lattice mismatching occurred between the layers. Accordingly, any mismatching (misfit) of lattice constant was transferred to theemission layer 5 comprising In0.07Ga0.93N. Further, the degree of mismatching between the lattice constants of GaN and In0.07Ga0.93N was small. As a result, the crystallinity of theemission layer 5 was improved. The thickness of theemission layer 5, which is about 0.5 μm in the illustrated Example, was longer than the diffusion length, or life span, of holes injected from the p-type cladding layer, so that the luminous efficiency could be maintained despite the small barrier between the n-type cladding layer 4 and theemission layer 5. As a result of the above identified features, the luminous efficiency in the ultraviolet region was improved compared with a conventional LED. - While the invention has been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements such as those included within the spirit and scope of the appended claims. Some examples of such modification may include the following.
- The misfit ratio between the
cladding layer 4 and theemission layer 5 in the illustrated example is 0.85%. Preferable misfit ratio between then is within 1%. - In the illustrated Example, GaN and In0.07Ga0.93N are used as an example of four element compounds of AlxGayIn1-x-yN. In general, a lattice constant and a band gap of the AlxGayIn1-x-yN is determined according to mixed crystal ratio of GaN, InN, and AlN whose lattice constants are respectively 3.160 Å, 3.544 Å, and 3.110 Å and whose band gaps are respectively 3.4 eV, 1.95 eV, and 6.0 eV.
- In the illustrated Example, the
LED 100 has a double-hetero junction structure. Another junction structure may be used, such as a single-hetero junction structure. In addition, for example, although heat treatment was used to obtain p-type conduction, electron irradiation can be used as an alternate. - The
emission layer 5 in the illustrated Example is not doped with any impurities. Theemission layer 5 may be doped with a donor impurity such as silicon (Si) and an acceptor impurity such as (Zn). - Further, the
emission layer 5 in the illustrated Example has a thickness of 0.5 μm. Preferable thickness of theemission layer 5 ranges from 0.1 μm to 1.0 μm. It is not preferable that the emission layer is thinner than 0.1 μm, because barrier between theemission layer 5 and the n-type cladding layer 4 is small and unable to confine holes effectively. It is not preferable that the emission layer is thicker than 1.0 μm, because confining electrons whose diffusion length are 1 μm becomes less effective. - Although the illustrated Example provides an LED, a laser diode can be provided as an alternate.
Claims (13)
1. A Group III nitride compound semiconductor comprising:
a triple layer structure having an emission layer sandwiched between an n-type cladding layer and a p-type cladding layer;
said emission layer satisfying the formula Alx1Gay1In1-x1-y1N, where 0≦x1≦1, 0≦y1≦1, and 0≦x1+y1≦1, and having a thickness larger then diffusion length of holes;
said n-type cladding layer satisfying the formula Alx2Gay2In1-x2-y2N, where 0≦x2≦1, 0≦y2≦1and 0≦x2+y2≦1, being doped with a donor impurity, and having a lattice constant substantially equal to a lattice constant of said emission layer: and
said p-type cladding layer satisfying the formula Alx3Gay3In1-x3-y3N, where 0≦x3≦1, 0≦y3≦1, and 0≦x3+y3≦1, being doped with an acceptor impurity, having a forbidden band sufficiently wider than a forbidden band of said emission layer to confine electrons injected into said emission layer.
2. The Group III nitride compound semiconductor according to claim 1 , wherein said emission layer comprises Gay2In1-y2N, ,where 0.92≦y2≦1, and wherein said n-type cladding layer comprises gallium nitride (GaN) doped with a donor impurity.
3. The Group III nitride compound semiconductor according to claim 2 , wherein said n-type cladding layer is formed on a lower n type layer comprising gallium nitride (GaN), said lower n-type layer being doped with a donor impurity and comprising a donor impurity density higher than a donor impurity density of said n-type cladding layer.
4. The Group III nitride compound semiconductor according to claim 1 , wherein said donor impurity is silicon (Si).
5. The Group III nitride compound semiconductor according to claim 1 , wherein said acceptor impurity is magnesium (Mg).
6. The Group III nitride compound semiconductor according to claim 1 , wherein said emission layer is doped with silicon (Si).
7. The Group III nitride compound semiconductor comprising:
a multiple layer structure including an emission layer sandwiched between an n-type layer and a p-type layer:
said emission layer comprising a semiconductor material satisfying the formula Alx1Gay1In1-x1-y1N, where 0≦x1≦1, 0≦y1≦1, and 0≦x1+y1≦1, said emission layer having a thickness significantly larger than a diffusion length of holes within said emission layer:
said n-type cladding layer satisfying the formula Alx2Gay2In1-x2-y2N, where 0≦x2≦1, 0≦y2≦1and 0≦x2+y2≦1, being doped with a donor impurity; and
said p-type layer satisfying the formula Alx3Gay3In1-x3-y3N, where 0≦x3≦1, 0≦y3≦1, and 0≦x3+y3≦1, being doped with an acceptor impurity.
8. The Group III nitride compound semiconductor according to claim 7 , wherein said n-type layer has a lattice constant substantially equal to a lattice constant of said emission layer.
9. The Group III nitride compound semiconductor according to claim 8 , wherein said p-type layer comprises a forbidden band sufficiently wider than a forbidden band of said emission layer to confine electrons injected into said emission layer.
10. The Group III nitride compound semiconductor according to claim 1 , wherein misfit ratio between said lattice constant of said n-type cladding layer and said lattice constant of said emission layer is within 1%.
11. The Group III nitride compound semiconductor according to claim 8 , wherein misfit ratio between said lattice constant of said n-type cladding layer and said lattice constant of said emission layer is within 1%.
12. The Group III nitride compound semiconductor according to claim 1 , wherein said emission layer has a thickness of 0.1 μm to 1.0 μm.
13. The Group III nitride compound semiconductor according to claim 7 , wherein said emission layer has a thickness of 0.1 μm to 1.0 μm.
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US10/456,509 US20030205718A1 (en) | 1995-07-24 | 2003-06-09 | Light-emitting semiconductor device using group III nitride compound |
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JP20918195A JP3564811B2 (en) | 1995-07-24 | 1995-07-24 | Group III nitride semiconductor light emitting device |
JP209181/1995 | 1995-07-24 | ||
US08/681,412 US7045829B2 (en) | 1995-07-24 | 1996-07-23 | Light-emitting semiconductor device using Group III nitride compound |
US10/456,509 US20030205718A1 (en) | 1995-07-24 | 2003-06-09 | Light-emitting semiconductor device using group III nitride compound |
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US10/456,509 Abandoned US20030205718A1 (en) | 1995-07-24 | 2003-06-09 | Light-emitting semiconductor device using group III nitride compound |
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US20070090390A1 (en) * | 2005-10-20 | 2007-04-26 | Formosa Epitaxy Incorporation | Light emitting diode chip |
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KR100506077B1 (en) * | 2000-04-15 | 2005-08-04 | 삼성전기주식회사 | Method for making high quality group-Ⅲ nitride thin film by metal organic chemical vapor deposition |
JP5511395B2 (en) * | 2010-01-06 | 2014-06-04 | セイコーインスツル株式会社 | Semiconductor device |
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KR970008639A (en) | 1997-02-24 |
TW419832B (en) | 2001-01-21 |
KR100468320B1 (en) | 2006-05-11 |
JPH0936421A (en) | 1997-02-07 |
US7045829B2 (en) | 2006-05-16 |
US20030057433A1 (en) | 2003-03-27 |
JP3564811B2 (en) | 2004-09-15 |
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