WO2006022423A1 - Germanium-adding source for compound semiconductor, production method of compound semiconductor using the same and compound semiconductor - Google Patents

Germanium-adding source for compound semiconductor, production method of compound semiconductor using the same and compound semiconductor Download PDF

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WO2006022423A1
WO2006022423A1 PCT/JP2005/015834 JP2005015834W WO2006022423A1 WO 2006022423 A1 WO2006022423 A1 WO 2006022423A1 JP 2005015834 W JP2005015834 W JP 2005015834W WO 2006022423 A1 WO2006022423 A1 WO 2006022423A1
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germanium
layer
compound semiconductor
compound
group iii
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French (fr)
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Mineo Okuyama
Hideki Tomozawa
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Showa Denko K.K.
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Definitions

  • the present invention relates to a material, used as a germanium-adding source, for obtaining a low-resistance n-type compound semiconductor by adding germanium to a compound semiconductor. Also, it relates to a method for obtaining a low-resistance n-type compound semiconductor by adding germanium using the material, and a compound semiconductor produced by the method.
  • a Group III nitride semiconductor formed on a substrate has been used as a functional material for fabricating pn-junction Group III nitride semiconductor light-emitting devices which emit visible light of a short wavelength such as light-emitting diodes (LEDs) and laser diodes (LDs) (see, for example, Japanese Patent Application Laid-Open (kokai) No. 2000-332364) .
  • LEDs light-emitting diodes
  • LDs laser diodes
  • an n-type or a p- type Group III nitride semiconductor layer serving as a cladding layer is joined to a light-emitting layer in order to fabricate a light-emitting member having a hetero-junction structure for attaining high emission intensity.
  • an n-type Group III nitride semiconductor layer interposed between, for example, a substrate and a light-emitting layer is usually formed from a silicon (Si) -doped Group III nitride semiconductor.
  • germanium adding source the only known material which can be used as a germanium adding source is the highly-toxic germane gas (GeH 4 ) .
  • germaneH 4 highly-toxic germane gas
  • An object of the present invention is to provide a germanium-adding source which can be easily handled when used for adding germanium to a compound semiconductor and, especially, for obtaining a low-resistance germanium-doped n-type compound semiconductor.
  • the present invention provides following inventions.
  • a germanium-adding source for a compound semiconductor comprising an organic germanium compound.
  • the organic germanium compound comprises at least one selected from a group consisting of tetramethyl germanium ((CHa) 4 Ge)) and tetraethyl germanium ((C 2 Hs) 4 Ge)) .
  • a light-emitting device comprising a compound semiconductor according to any one of above (4) to (6) .
  • germanium is required for obtaining a low-resistance mirror-surfaced n-type group III nitride semiconductor layer and thereby obtaining a group III nitride semiconductor light-emitting device with high emission intensity
  • germanium adding source by using an organic germanium compound for the germanium adding source, production using an easily handled germanium source becomes possible.
  • Fig. 1 is schematic cross-section of a stacked structure fabricated in Example 1.
  • Fig. 2 is schematic cross-section of a Group III nitride semiconductor light-emitting device fabricated in
  • an impurity-adding source for a semiconductor is that it is preferably decomposed under a growth condition of the semiconductor, and favorably added into the semiconductor.
  • MOCVD method metal organic chemical vapor deposition method
  • an organic Ga compound as an example of a group III source, and ammonia, as an example of a nitrogen source, are fed onto a heated substrate, to thereby decompose an organic group (for example, an alkyl group) and ammonia on the substrate, and carry out crystal growth of GaN by taking Ga and N into a crystal structure of GaN
  • an organic Ge compound is similarly fed onto the heated substrate, to thereby decompose an organic group (for example, an alkyl group) on the substrate and let Ge taken into the GaN crystal.
  • the decomposition temperature of an organic Ge compound (under a predetermined pressure) varies depending on an added organic group. Accordingly, an organic group of an organic Ge compound to be preferably decomposed and favorably added to GaN can be selected freely, in accordance with a used growth temperature (normally 500 to 1200 0 C) and a growth pressure (normally 1 to 30OkPa) . As shown in the examples below, inventors of the present invention found that Ge can be effectively taken into a group III nitride semiconductor using an organic Ge compound. Also, the organic Ge compound has higher vapor pressure compared to a simple metal element.
  • high temperature heating at a material part is not especially required, unlike the MBE (molecular beam epitaxy) method, and the supply amount of the material can be controlled by only controlling a flow rate of the gas. Thus, it can be easily handled compared to germane gas (GeH 4 ) .
  • germane gas GeH 4
  • a favorable organic group can be freely selected in accordance with a condition.
  • the organic Ge compound containing an alkyl group having a higher molecular weight has a higher decomposition temperature and a lower vapor pressure.
  • the decomposition temperature can be represented by "one with a methyl group” ⁇ "one with an ethyl group” ⁇ "one with a butyl group”.
  • this is not always true because it may vary depending on a structure of the organic group (For example, a case of a linear alkyl group and a case of a branched alkyl group are different, even though they have the same molecular weight. If it has a ⁇ bond in addition to a sigma bond, the difference becomes larger) .
  • the kind of compound to be used may be decided considering a growth condition of a semiconductor.
  • a sufficient carrier concentration that is, a high carrier concentration of, for example, about 10 15 to 10 21 cm “3 can be obtained as a result of taking in the impurity.
  • a high carrier concentration of, for example, about 10 15 to 10 21 cm “3 can be obtained as a result of taking in the impurity.
  • inventors of the present invention found that, by doping Ge to a group III nitride semiconductor using the organic Ge compound, a high carrier concentration of about 10 16 to 10 20 cm "3 can be achieved.
  • the impurity adding source is also important. Especially, the contents of water, oxygen, carbon and heavy metal element, etc., must be small. Also, for the impurity source for a group III nitride semiconductor, the contents of a group II element and a group VI element, etc., must also be small.
  • Measuring Device AA Shimazu AA-8500
  • ICP-MS Seiko SPQ-9000
  • the toxicity is low.
  • Gerber G. B. and Leonard A. described in "Mutagenicity, Carcinogenicity and Teratogenicity of Germanium Compounds" (Mutation Research, 387(3), 141-146 (1997)) that "Germane gas (GeH 4 ) has strong toxicity at concentration of lOOppm, and at concentration of 150ppm, it is lethal due to hemolysis and disorder of cardiovascular system, liver and kidney. Except for tetrahydride german, general toxicity of germanium is low ", and this suggests that an organic germanium compound has low toxicity compared to germane gas. As mentioned above, inventors of the present invention found that an organic germanium compound is useful as a germanium adding source for various compound semiconductors.
  • An organic germanium compound having a vapor pressure, at around room temperature, of lOPa to IMPa is preferable. Concretely, it may be tetramethyl germanium ((CHs) 4 Ge)), tetraethyl germanium ((C 2 H 5 J 4 Ge), tetrapropyl germanium ((CaH 7 J 4 Ge), tetrabutyl germanium
  • a production method of a Ge-doped compound semiconductor layer according to the present invention will be explained below using a group III nitride semiconductor and a light-emitting device using same, as examples.
  • Group III nitride semiconductor layers which contain a layer doped with Ge of the present invention, are stacked on a substrate which may have a comparatively high melting point (i.e., high heat resistance) .
  • the material of the substrate include oxide single crystal materials such as sapphire (CI-AI 2 O 3 single crystal) , zinc oxide (ZnO) , and gallium lithium oxide (LiGa ⁇ 2 ) , and Group IV semiconductor single crystals such as a silicon single crystal and cubic or hexagonal silicon carbide (SiC) .
  • a group III-V compound semiconductor single crystal material such as gallium phosphide (GaP) may also be employed as a substrate material.
  • An optically transparent single- crystal material, through which light emitted from the light-emitting layer can be transmitted, is advantageously employed for a substrate material.
  • the layer is preferably stacked by the mediation of a low- temperature buffer layer or a high-temperature buffer layer which mitigates mismatch and provides a Group III nitride semiconductor layer of high crystallinity.
  • a method for increasing doping efficiency of a group III nitride semiconductor layer to which germanium of the present invention is added, and obtaining a low- resistance n-type group III nitride semiconductor layer, while preventing generation of small holes destroying smoothness on the surface although germanium is doped in high concentration a method for forming a region whose germanium atom concentration is periodically changed can be used, as mentioned above.
  • the method is not limited thereto.
  • the region whose germanium atom concentration is periodically changed is formed by periodically changing a supply amount of the organic Ge compound, which acts as a Ge doping source, to a vapor-phase growth reaction system at the time of vapor-phase growth of the group III nitride semiconductor layer.
  • a supply amount of the organic Ge compound which acts as a Ge doping source
  • an undoped thin layer is formed without supplying the organic Ge compound to the vapor-phase growth region.
  • a growing condition such as a ratio of group V element / groupXlII element, etc.
  • a thin layer containing Ge atoms in low concentration is formed on the layer having high Ge atom concentration.
  • a growing condition such as a ratio of group V element / groupXlII element, etc.
  • MOCVD metal- organic chemical vapor deposition
  • HVPE hydrogen vapor phase epitaxy
  • MBE molecular beam epitaxy
  • H 2 hydrogen
  • N 2 nitrogen
  • trimethylgallium (TMG) or triethylgallium (TEG) is employed as a Ga (Group III element) source
  • trimethylaluminum (TMA) or triethylaluminum (TEA) is employed as an Al (Group III element) source
  • trimethylindium (TMI) or triethylindium (TEI) is employed as an In (Group III element) source
  • ammonia (NH 3 ) , hydrazine (N 2 H 4 ) , or the like is employed as an N (Group V element) source.
  • an organic germanium compound serving as a Ge source is employed as an n-type dopant
  • bis (cyclopentadienyl)magnesium (Cp 2 Mg) or bis (ethylcyclopentadienyl)magnesium ((EtCp) 2 Mg) serving as an Mg source is employed as a p-type dopant.
  • a n-type gallium nitride layer including a region whose germanium atom concentration is periodically changed is formed on a sapphire substrate using (CHs) 4 Ge at 900 0 C or higher and 125O 0 C or lower.
  • the higher concentration layer preferably has a Ge atom concentration of 5 x 10 17 cm “3 to 5 x 10 19 cm “3 , more preferably 1 x 10 18 cm “3 to 3 x 10 19 cm “3 , particularly preferably 3 x 10 18 cm “3 to 2 x 10 19 cm “3 .
  • concentration is lower than 5 x 10 17 cm “3 , resistance of the entire Ge-doped n-type semiconductor layer increases, and production of an LED exhibiting low forward voltage becomes difficult.
  • the Ge atom concentration is 5 x 10 19 cm “3
  • the Ge-doped n-type semiconductor layer has a carrier concentration of about 3 x 10 19 cm “3 to 4 x 10 19 cm “3 .
  • the Ge atom concentration is more than 5 x 10 19 cm “3 , the surface pit density steeply increases, which is not preferred.
  • the lower concentration layer has a Ge atom concentration which is lower than that of the higher concentration layer and which is equal to or less than 2 x 10 19 cm “3 .
  • the Ge atom concentration is more preferably 1 x 10 19 cm “3 or less, particularly preferably 5 x 10 18 cm “3 or less.
  • the lower limit of the concentration is as low as possible, and the lower concentration layer is not intentionally doped with Ge atom.
  • the Ge atom concentration may be determined through, for example, secondary ion mass spectrometry (SIMS) , which is a technique which includes irradiating a surface of a sample with a primary ion beam and analyzing the released ionized elements through mass analysis.
  • SIMS secondary ion mass spectrometry
  • the technique enables quantification of a specific element and observation of a concentration distribution profile of the element in the depth direction.
  • the Ge atom present in the Group III nitride semiconductor layer can be effectively quantified through the technique. In the analysis, the thickness of each layer can be also calculated.
  • the region whose Ge atom concentration is periodically changed can be arranged in any place within the group III nitride semiconductor layer.
  • it can be provided in direct contact with a surface of a crystal substrate.
  • it can be provided in contact with a buffer layer provided on a surface of the crystal substrate. If the region whose Ge atom concentration is periodically changed is provided in the vicinity of the crystal substrate or the buffer layer, etc., a group III nitride semiconductor layer having superior crystallinity can be obtained. This is because, by providing the region whose Ge atom concentration is periodically changed, no propagation, to the upper layer side, of misfit dislocations, etc., due to lattice mismatch with the crystal substrate, occurs.
  • the periodic layer can have a thickness of 0.5 ⁇ m to 5 ⁇ m.
  • compositions represented by the above formula including known ones, and doped with a p-type dopant such as Mg, Zn, etc., can be used, without limitation.
  • a positive electrode (p-type ohmic electrode) and a negative electrode (n-type ohmic electrode) are formed at predetermined positions.
  • a positive electrode and a negative electrode for the compound semiconductor light- emitting device various constitutions and structures are known. Including these known positive electrodes and negative electrodes, positive electrodes and negative electrodes having various constitutions and structures can be used without limitation. Also, for the production method thereof, any known method such as a vacuum vapor deposition method, a sputtering method, etc., can be used without limitation. Examples
  • Fig. 1 schematically shows a cross-section of a stacked structure containing a Ge-doped n-type Group III nitride semiconductor layer fabricated in Example 1.
  • a stacked structure including a sapphire substrate and Group III nitride semiconductor layers successively stacked on the substrate was formed by means of conventional reduced-pressure MOCVD through the following procedure.
  • a (0001) -sapphire substrate 1 was placed on a high-purity graphite susceptor (for semiconductors) to be heated at a film formation temperature by a high-frequency (RF) induction heater.
  • the sapphire substrate placed on the susceptor was placed in a stainless steel-made vapor growth reactor furnace, and the reactor furnace was purged with nitrogen. After passage of nitrogen in the vapor growth reactor furnace for 8 minutes, the substrate 1 was heated over 10 minutes from room temperature to 600°C by means of the induction heater.
  • the surface of the substrate 1 was thermally cleaned by allowing the substrate to stand for 2 minutes under the temperature/pressure conditions. After completion of thermal cleaning, the supply of nitrogen gas was stopped, but hydrogen was continuously supplied to the reactor furnace.
  • the substrate 1 was heated to l,120°C under hydrogen.
  • hydrogen gas containing trimethylaluminum (TMA) vapor was supplied to the vapor growth reactor furnace for 8 minutes and 30 seconds.
  • TMA trimethylaluminum
  • the supplied TMA was caused to react with N atoms which had been released through decomposition of nitrogen-containing deposits on an inner wall of the reactor furnace, thereby depositing a high- temperature buffer layer 2 composed of an aluminum nitride (AlN) thin film having a thickness of some nm on the sapphire substrate 1.
  • AlN aluminum nitride
  • ammonia (NH 3 ) gas was supplied to the vapor growth reactor furnace.
  • the susceptor temperature was lowered to l,040°C under an ammonia flow.
  • TMG trimethylgallium
  • the substrate 1 was heated to l,120°C. After confirmation that a constant temperature of l,120°C was attained, tetramethylgermanium ( (CH 3 ) 4 Ge) was supplied for 18 seconds, followed by stopping the supply for 18 seconds. The cycle was repeated 100 times, to thereby form a Ge-doped n-type GaN layer 4 having a thickness of 2.0 ⁇ m in which the Ge concentration periodically varied.
  • tetramethylgermanium (CH 3 ) 4 Ge
  • the substrate 1 was allowed to cool to room temperature over about 20 minutes through stopping the current supply to the induction heater. During cooling, the inside atmosphere of the vapor growth reactor furnace was formed solely of nitrogen. After confirmation that the substrate 1 was cooled to room temperature, the stacked structure was removed from the vapor growth reactor furnace to the outside.
  • the Ge-doped n-type GaN layer 4 of the thus-produced stacked structure was found to have a carrier concentration, as measured on the basis of the Hall effect, of 7 x 10 18 cm "3 .
  • the n-type GaN layer 4 had a remarkably flat surface having a pit density of 200/cm 2 or less.
  • each higher concentration layer was found to have a Ge atom concentration of 1.2 x 10 19 cm “3 and a thickness of 10 nm
  • each lower concentration layer was found to have a Ge atom concentration of 1 x 10 18 cm “3 and a thickness of 10 nm.
  • SIMS analysis was carried out under the following conditions: primary ion species of Cs + , acceleration voltage of 14.5 keV, ionic current of 40 nA, raster area of 100 um 2 , and analysis area of 30 ⁇ m 2 .
  • Example 2 The procedure of Example 1 was repeated, except that a Ge-doped n-type GaN layer 4 having a thickness of 2.0 ⁇ m was formed through supplying (CH 3 ) 4 Ge for 9 seconds, followed by stopping supply for 9 seconds, and repeating the cycle 200 times, to thereby form a stacked structure.
  • the Ge-doped n-type GaN layer 4 of the thus-produced stacked structure was found to have a carrier concentration, as measured on the basis of Hall effect, of 7 x 10 18 cm "3 , which is equivalent to that obtained in Example 1.
  • each higher concentration layer was found to have a Ge atom concentration of 1.2 x 10 19 cm “3 and a thickness of 5 nm, and each lower concentration layer was found to have a Ge atom concentration of 1 x 10 18 cm “3 and a thickness of 5 nm.
  • the n-type GaN layer 4 had a surface having a pit density of 4,000/cm 2 . Although the pit density is slightly higher than that obtained in Example 1, the surface was very flat as compared with a conventional Ge- doped n-type semiconductor layer.
  • a Group III nitride semiconductor light-emitting device was fabricated through further stacking a Group
  • FIG. 2 schematically shows a cross-section of a Group III nitride semiconductor light- emitting device fabricated in Example 3.
  • the procedure of Example 1 was repeated, to thereby form a Ge-doped n-type GaN layer 4.
  • an undoped n-type Alo.o 7 Gao. 9 3N cladding layer 5 having a thickness of 12.5 nm was stacked on the GaN layer at l,060°C.
  • the substrate 1 was cooled to 730 0 C and, on the undoped n-type Alo.o 7 Gao.
  • a light- emitting layer 6 having a multiple (5 cycles) quantum well structure including Alo. 03 Gao. 97 N barrier layers 6a and Ino. 25 Gao. 75 N well layers 6b was provided.
  • an Alo.o 3 Gao. 97 N barrier layer 6a was joined to the undoped n-type Alo.o 7 Gao. 93 N cladding layer 5.
  • the Alo.o 3 Gao. 97 N barrier layers 6a were grown in an undoped state by use of trimethylaluminum (TMA) as an aluminum source and triethylgallium (TEG) as a gallium source, and each layer had a thickness of 8 nm.
  • TMA trimethylaluminum
  • TEG triethylgallium
  • TMI trimethylindium
  • a magnesium (Mg) -doped p-type Alo. 0 7Gao. 93 N cladding layer 7 having a thickness of 10 nm was formed on the light-emitting layer 6 having a multiple quantum well structure.
  • Mg-doped p-type GaN contact layer 8 was formed on the p-type Alo. 07 Gao. 93 N cladding layer 7, an Mg-doped p-type GaN contact layer 8 was formed.
  • Biscyclopentadienyl Mg was employed as an Mg dopant source.
  • Mg was added in such an amount that the p-type GaN contact layer 8 had a hole concentration of 8 x 10 17 cm "3 .
  • the p-type GaN contact layer 8 had a thickness of 100 nm.
  • the substrate 1 was allowed to cool to room temperature over about 20 minutes through stopping the current supply to the induction heater. During cooling, the inside atmosphere of the vapor growth reactor furnace was formed solely of nitrogen. After confirmation that the substrate 1 was cooled to room temperature, the stacked structure was removed from the vapor growth reactor furnace to the outside. At this instance, the p- type GaN contact layer 8 exhibited p-type conductivity, even though the layer had undergone no annealing to electrically activate the p-type carrier (Mg) .
  • Mg p-type carrier
  • the high-Ge-concentration layer of the Ge-doped n-type GaN layer 4 was exposed exclusively in an area where an n- type Ohmic electrode 9 was to be formed.
  • an n- type Ohmic electrode titanium (semiconductor side) /gold
  • the chip exhibited a forward voltage of 3.5 V at a forward current of 20 mA.
  • the emission center wavelength of the band of blue light emission at a forward current of 20 mA was found to be 460 ran.
  • a Group III nitride semiconductor light-emitting device attaining high emission intensity was successfully fabricated.
  • Example 4 A group III nitride semiconductor light-emitting device was produced by the same method as Example 3, except that, upon growing a barrier layer 6a of a multiple quantum well structure light-emitting layer 6, tetraethyl germanium is used as a Ge dopant source in addition to an aluminum source made of TMA and a gallium source made of TEG, so as to make the barrier layer 6a to be a Ge-doped Alo.o 3 Gao. 97 N barrier layer.
  • the obtained light-emitting device was evaluated the same as Example 3. Although the emission intensity was decreased a little to 4.8mW, the forward voltage was
  • the carrier concentration thereof was 1 x 10 17 cm "3 .
  • a Ge-doped compound semiconductor can be produced without using a germane gas that is hard to handle.
  • the utility value in industry is large.

Abstract

An object of the present invention is to provide a germanium-adding source which can be easily handled when used for adding germanium to a compound semiconductor and, especially, for obtaining a low-resistance germanium-doped n-type compound semiconductor. The inventive germanium adding source for a compound semiconductor comprises an organic germanium compound.

Description

DESCRIPTION
GERMANIUM-ADDING SOURCE FOR COMPOUND SEMICONDUCTOR, PRODUCTION METHOD OF COMPOUND SEMICONDUCTOR USING THE SAME AND COMPOUND SEMICONDUCTOR
Cross Reference to Related Application
This application is an application filed under 35
U. S.C. §111 (a) claiming benefit, pursuant to 35 U.S.C. §119 (e) (1), of the filing date of the Provisional
Application No.60/605, 163 filed on August 30, 2004, pursuant to 35 U.S.C. §111 (b) .
Technical Field The present invention relates to a material, used as a germanium-adding source, for obtaining a low-resistance n-type compound semiconductor by adding germanium to a compound semiconductor. Also, it relates to a method for obtaining a low-resistance n-type compound semiconductor by adding germanium using the material, and a compound semiconductor produced by the method.
Background Art
Conventionally, a Group III nitride semiconductor formed on a substrate has been used as a functional material for fabricating pn-junction Group III nitride semiconductor light-emitting devices which emit visible light of a short wavelength such as light-emitting diodes (LEDs) and laser diodes (LDs) (see, for example, Japanese Patent Application Laid-Open (kokai) No. 2000-332364) .
For example, in the fabrication of an LED emitting near- UV rays, blue light, or green light, n-type or p-type aluminum gallium nitride (AlxGaYN, 0<X, Y≤l, X + Y = 1) is employed to form a cladding layer (see, for example, Japanese Patent Application Laid-Open (kokai) No. 2003-
229645) . Similarly, gallium indium nitride (GaYInzN, 0<Y, Z≤l, Y + Z = 1) is employed for fabricating a light- emitting layer (see, for example, Japanese Patent Publication {kokoku) No. 55-3834) .
Generally, in conventional Group III nitride semiconductor light-emitting devices, an n-type or a p- type Group III nitride semiconductor layer serving as a cladding layer is joined to a light-emitting layer in order to fabricate a light-emitting member having a hetero-junction structure for attaining high emission intensity. For example, in order to fabricate a light- emitting member having a doublehetero-junction structure, the light-emitting layer is composed of a semiconductor such as GayInzN (O≤Y, Z≤l, Y + Z = 1) , to which an n-type or a p-type Group III nitride semiconductor layer serving as a cladding layer is joined (see, for example, a book written and edited by Isamu AKASAKI, "Group III-V Compound Semiconductors," published Baifukan Co., Ltd., Chapter 13, May 20 (1995)) .
Conventionally, an n-type Group III nitride semiconductor layer interposed between, for example, a substrate and a light-emitting layer, is usually formed from a silicon (Si) -doped Group III nitride semiconductor. In this connection, a semiconductor layer; for example, an Si-doped n-type AlχGaγN (0<X, Y<1, X + Y = 1) layer having a resistivity controlled through modification of the amount of silicon (Si) as a dopant, is employed (see, for example, Japanese Patent No. 3383242) .
However, when a large amount of silicon is added during vapor growth of a low-resistive n-type Group III nitride semiconductor layer, problematic cracks are generated in the layer. In other words, even when conventional technical means; i.e., doping with silicon, is employed, a low-resistive and continuous n-type Group III nitride semiconductor layer has not been reliably obtained. On the other hand, as an n-type impurity other than silicon, germanium (Ge) is known. However, compared to Si, doping efficiency is low (for example, see Jpn. J. Appl. Phys., Vol. 31(9A), p. 2883, (1992)), and thus, it is regarded unsuitable for use in obtaining a low- resistance n-type group III nitride semiconductor layer. Also, the only known material which can be used as a germanium adding source is the highly-toxic germane gas (GeH4) . Thus, sufficient attention to safety and various facilities for preventing leakage, etc., are required for use, especially for industrial use and, thus, the handling thereof is difficult.
Also, there is a drawback that, if Ge is doped in high concentration, small holes (pits) , which prevent smoothness, are generated on a surface of an n-type group III nitride semiconductor layer, to thereby deteriorate the crystallinity of a semiconductor layer laminated thereon (for example, see Book "Group III Nitride Semiconductor Compounds", published CLARENDON Press. (OXFORD), p. 104, (1998)). Accordingly, for an n-type doping material, only Si has been used industrially, and Ge has not been used.
Disclosure of Invention An object of the present invention is to provide a germanium-adding source which can be easily handled when used for adding germanium to a compound semiconductor and, especially, for obtaining a low-resistance germanium-doped n-type compound semiconductor. The present invention provides following inventions.
(1) A germanium-adding source for a compound semiconductor comprising an organic germanium compound.
(2) A germanium-adding source according to (1) above, wherein the organic germanium compound comprises at least one selected from a group consisting of tetramethyl germanium ((CHa)4Ge)) and tetraethyl germanium ((C2Hs)4Ge)) . (3) A production method for a compound semiconductor containing germanium as an impurity, wherein an organic germanium compound is used as an impurity source.
(4) A Ge-doped compound semiconductor produced by the production method according to (3) above.
(5) A Ge-doped compound semiconductor according to (4) above, wherein the compound semiconductor is n-type.
(6) A Ge-doped compound semiconductor according to above (4) or (5), wherein the compound semiconductor is a group III nitride semiconductor.
(7) A light-emitting device comprising a compound semiconductor according to any one of above (4) to (6) .
Although addition of germanium is required for obtaining a low-resistance mirror-surfaced n-type group III nitride semiconductor layer and thereby obtaining a group III nitride semiconductor light-emitting device with high emission intensity, by using an organic germanium compound for the germanium adding source, production using an easily handled germanium source becomes possible.
Brief Description of the Drawings
Fig. 1 is schematic cross-section of a stacked structure fabricated in Example 1. Fig. 2 is schematic cross-section of a Group III nitride semiconductor light-emitting device fabricated in
Example 3.
Best Mode for Carrying Out the Invention One property required for an impurity-adding source for a semiconductor is that it is preferably decomposed under a growth condition of the semiconductor, and favorably added into the semiconductor. For example, when a group III nitride semiconductor is grown by a metal organic chemical vapor deposition method (MOCVD method) , it is normally carried out at a temperature of 500 to 1200°C and a pressure of 1 to 30OkPa. Addition of Ge, using an organic Ge compound, to a group III nitride semiconductor, for example GaN, under such conditions, is carried out as follows.
While an organic Ga compound, as an example of a group III source, and ammonia, as an example of a nitrogen source, are fed onto a heated substrate, to thereby decompose an organic group (for example, an alkyl group) and ammonia on the substrate, and carry out crystal growth of GaN by taking Ga and N into a crystal structure of GaN, an organic Ge compound is similarly fed onto the heated substrate, to thereby decompose an organic group (for example, an alkyl group) on the substrate and let Ge taken into the GaN crystal.
The decomposition temperature of an organic Ge compound (under a predetermined pressure) varies depending on an added organic group. Accordingly, an organic group of an organic Ge compound to be preferably decomposed and favorably added to GaN can be selected freely, in accordance with a used growth temperature (normally 500 to 12000C) and a growth pressure (normally 1 to 30OkPa) . As shown in the examples below, inventors of the present invention found that Ge can be effectively taken into a group III nitride semiconductor using an organic Ge compound. Also, the organic Ge compound has higher vapor pressure compared to a simple metal element. Accordingly, high temperature heating at a material part is not especially required, unlike the MBE (molecular beam epitaxy) method, and the supply amount of the material can be controlled by only controlling a flow rate of the gas. Thus, it can be easily handled compared to germane gas (GeH4) . As the vapor pressure varies depending on an organic group of the organic Ge compound, a favorable organic group can be freely selected in accordance with a condition.
In general, when organic Ge compounds, containing an alkyl group having a similar structure, are compared, the organic Ge compound containing an alkyl group having a higher molecular weight has a higher decomposition temperature and a lower vapor pressure. For example, the decomposition temperature can be represented by "one with a methyl group" < "one with an ethyl group" < "one with a butyl group". However, this is not always true because it may vary depending on a structure of the organic group (For example, a case of a linear alkyl group and a case of a branched alkyl group are different, even though they have the same molecular weight. If it has a π bond in addition to a sigma bond, the difference becomes larger) . The kind of compound to be used may be decided considering a growth condition of a semiconductor.
Another important property required for the impurity adding source for the semiconductor is that a sufficient carrier concentration, that is, a high carrier concentration of, for example, about 1015 to 1021 cm"3 can be obtained as a result of taking in the impurity. As mentioned in the examples below, inventors of the present invention found that, by doping Ge to a group III nitride semiconductor using the organic Ge compound, a high carrier concentration of about 1016 to 1020 cm"3 can be achieved.
Further, in order to obtain a semiconductor achieving a high carrier concentration and stable with no deterioration over time, purity of the impurity adding source is also important. Especially, the contents of water, oxygen, carbon and heavy metal element, etc., must be small. Also, for the impurity source for a group III nitride semiconductor, the contents of a group II element and a group VI element, etc., must also be small.
Of course, if there is a problem in purity, various purification means are known for each substance (element) . The element in question can be removed using a known purification mean. As a result of analysis by
Fourier transform infrared spectroscopy (FTIR), however, each content of water, oxygen and carbon within tetramethyl germanium, which is used in the Example below, was 0.05 % or less by weight, which is the detection limit. The impurity metal concentration was shown in Table 1.
Note that the metal analysis was carried out as follows. 10ml of 1.9 mol/litre HNO3 was introduced into a 100 ml plastic bottle and was cooled with ice water. After sampling and weighing a sample, the sample was added to the plastic bottle, and then, heated on a hot plate. After being adjusted to be 25g using pure water, analysis was carried out. Five samplings were carried out for one sample. An average value of three of them, excluding the maximum value and the minimum value, is shown in Table 1. Each sampled amount was 2.46g, 2.4Ig, 2.46g, 2.45g and 2.43g.
Table 1: Result of Impurity Metal Analysis of Tetramethyl Germanium Used in Example
Figure imgf000008_0001
Measuring Device AA: Shimazu AA-8500, ICP-MS: Seiko SPQ-9000
As is apparent from Table 1, the purity of the tetramethyl germanium was sufficiently satisfactory. Also, as can been seen from favorable results of the examples below, it is apparent that a commercially available organic germanium compound has a sufficient purity as a germanium adding source for a compound semiconductor.
Also, for industrial use, it is preferable that the toxicity is low. Gerber G. B. and Leonard A. described in "Mutagenicity, Carcinogenicity and Teratogenicity of Germanium Compounds" (Mutation Research, 387(3), 141-146 (1997)) that "Germane gas (GeH4) has strong toxicity at concentration of lOOppm, and at concentration of 150ppm, it is lethal due to hemolysis and disorder of cardiovascular system, liver and kidney. Except for tetrahydride german, general toxicity of germanium is low ", and this suggests that an organic germanium compound has low toxicity compared to germane gas. As mentioned above, inventors of the present invention found that an organic germanium compound is useful as a germanium adding source for various compound semiconductors. An organic germanium compound having a vapor pressure, at around room temperature, of lOPa to IMPa is preferable. Concretely, it may be tetramethyl germanium ((CHs)4Ge)), tetraethyl germanium ((C2H5J4Ge), tetrapropyl germanium ((CaH7J4Ge), tetrabutyl germanium
((C3Hg)4Ge) and tetraallyl germanium ((CaHs)4Ge), but it is not limited to these. Among these, tetramethyl germanium ((CHa)4Ge)) and tetraethyl germanium ((C2H5)4Ge) are especially preferable. As mentioned above, there is a drawback that, if Ge is doped, in high concentration, to a compound semiconductor, small holes (pits) which destroy smoothness are generated on a surface of the compound semiconductor layer, to thereby deteriorate the crystallinity of a semiconductor layer laminated thereon. However, it was found that by periodically changing the Ge atom concentration so as to obtain a Ge atom high concentration layer and a Ge atom low concentration layer alternatively and periodically, a Ge-doped n-type semiconductor layer having a very smooth mirror surface can be obtained.
A production method of a Ge-doped compound semiconductor layer according to the present invention will be explained below using a group III nitride semiconductor and a light-emitting device using same, as examples.
Group III nitride semiconductor layers, which contain a layer doped with Ge of the present invention, are stacked on a substrate which may have a comparatively high melting point (i.e., high heat resistance) . Examples of the material of the substrate include oxide single crystal materials such as sapphire (CI-AI2O3 single crystal) , zinc oxide (ZnO) , and gallium lithium oxide (LiGaθ2) , and Group IV semiconductor single crystals such as a silicon single crystal and cubic or hexagonal silicon carbide (SiC) . Alternatively, a group III-V compound semiconductor single crystal material such as gallium phosphide (GaP) may also be employed as a substrate material. An optically transparent single- crystal material, through which light emitted from the light-emitting layer can be transmitted, is advantageously employed for a substrate material.
The Group III nitride semiconductor layers, which contain a layer doped with Ge and are stacked on a crystal substrate, are formed from a Group III nitride semiconductor represented by a formula: AlxGaYInzNi-aiyia (0 < X < 1, O ≤ Y ≤ l, O ≤ Z ≤ l, X + Y + Z = 1, and 0 < a < 1, wherein M represents a non-nitrogen Group V element) . When the substrate is lattice-mismatched with the Group III nitride semiconductor layer formed thereon, the layer is preferably stacked by the mediation of a low- temperature buffer layer or a high-temperature buffer layer which mitigates mismatch and provides a Group III nitride semiconductor layer of high crystallinity. Such a buffer layer may be composed of aluminum gallium nitride (AlxGaYInzN: 0 < X, Y, Z < 1, X + Y + Z = 1) . As a method for increasing doping efficiency of a group III nitride semiconductor layer to which germanium of the present invention is added, and obtaining a low- resistance n-type group III nitride semiconductor layer, while preventing generation of small holes destroying smoothness on the surface although germanium is doped in high concentration, a method for forming a region whose germanium atom concentration is periodically changed can be used, as mentioned above. However, the method is not limited thereto.
The region whose germanium atom concentration is periodically changed is formed by periodically changing a supply amount of the organic Ge compound, which acts as a Ge doping source, to a vapor-phase growth reaction system at the time of vapor-phase growth of the group III nitride semiconductor layer. For example, after forming a thin layer containing Ge atoms in high concentration by instantly supplying a large amount of organic Ge compound to a vapor-phase growth region, an undoped thin layer is formed without supplying the organic Ge compound to the vapor-phase growth region. By increasing or decreasing the amount of the organic Ge compound to be supplied to the vapor-phase growth reaction system, a region whose germanium atom concentration is periodically changed can be formed. Also, after growing a layer having nigra. Ge atom concentration, the growth is stopped until a growing condition, such as a ratio of group V element / groupXlII element, etc., is adjusted suitable for adding Ge atoms in low concentration, and then, a thin layer containing Ge atoms in low concentration is formed on the layer having high Ge atom concentration. No particular limitation is imposed on the method for growing these group III nitride semiconductors, and there may be employed any known method for growing a Group III nitride semiconductor, such as MOCVD (metal- organic chemical vapor deposition) , HVPE (hydride vapor phase epitaxy) , or MBE (molecular beam epitaxy) . From the viewpoints of layer thickness controllability and mass productivity, MOCVD is preferably employed. In the case of MOCVD, hydrogen (H2) or nitrogen (N2) is employed as a carrier gas, trimethylgallium (TMG) or triethylgallium (TEG) is employed as a Ga (Group III element) source, trimethylaluminum (TMA) or triethylaluminum (TEA) is employed as an Al (Group III element) source, trimethylindium (TMI) or triethylindium (TEI) is employed as an In (Group III element) source, and ammonia (NH3) , hydrazine (N2H4) , or the like is employed as an N (Group V element) source. In addition, an organic germanium compound serving as a Ge source is employed as an n-type dopant, whereas bis (cyclopentadienyl)magnesium (Cp2Mg) or bis (ethylcyclopentadienyl)magnesium ((EtCp)2Mg) serving as an Mg source is employed as a p-type dopant. In the MOCVD method, for example, a n-type gallium nitride layer including a region whose germanium atom concentration is periodically changed is formed on a sapphire substrate using (CHs)4Ge at 9000C or higher and 125O0C or lower. The higher concentration layer preferably has a Ge atom concentration of 5 x 1017 cm"3 to 5 x 1019 cm"3, more preferably 1 x 1018 cm"3 to 3 x 1019 cm"3, particularly preferably 3 x 1018 cm"3 to 2 x 1019 cm"3. When the concentration is lower than 5 x 1017 cm"3, resistance of the entire Ge-doped n-type semiconductor layer increases, and production of an LED exhibiting low forward voltage becomes difficult. When the Ge atom concentration is 5 x 1019 cm"3, the Ge-doped n-type semiconductor layer has a carrier concentration of about 3 x 1019 cm"3 to 4 x 1019 cm"3. When the Ge atom concentration is more than 5 x 1019 cm"3, the surface pit density steeply increases, which is not preferred.
Preferably, the lower concentration layer has a Ge atom concentration which is lower than that of the higher concentration layer and which is equal to or less than 2 x 1019 cm"3. When the Ge atom concentration is in excess of 2 x 1019 cm"3, surface pit density steeply increases, which is not preferred. Thus, the Ge atom concentration is more preferably 1 x 1019 cm"3 or less, particularly preferably 5 x 1018 cm"3 or less. Preferably, the lower limit of the concentration is as low as possible, and the lower concentration layer is not intentionally doped with Ge atom.
The Ge atom concentration may be determined through, for example, secondary ion mass spectrometry (SIMS) , which is a technique which includes irradiating a surface of a sample with a primary ion beam and analyzing the released ionized elements through mass analysis. The technique enables quantification of a specific element and observation of a concentration distribution profile of the element in the depth direction. The Ge atom present in the Group III nitride semiconductor layer can be effectively quantified through the technique. In the analysis, the thickness of each layer can be also calculated.
The region whose Ge atom concentration is periodically changed can be arranged in any place within the group III nitride semiconductor layer. For example, it can be provided in direct contact with a surface of a crystal substrate. Also, it can be provided in contact with a buffer layer provided on a surface of the crystal substrate. If the region whose Ge atom concentration is periodically changed is provided in the vicinity of the crystal substrate or the buffer layer, etc., a group III nitride semiconductor layer having superior crystallinity can be obtained. This is because, by providing the region whose Ge atom concentration is periodically changed, no propagation, to the upper layer side, of misfit dislocations, etc., due to lattice mismatch with the crystal substrate, occurs. In this case, the periodic layer can have a thickness of 0.5μm to 5μm.
In the region whose Ge atom concentration is periodically changed, no propagation of dislocation from lower side to the upper layer takes place. Thus, if the region whose Ge atom concentration is periodically changed is provided on the upper side of the n-type group III nitride semiconductor layer, as a base layer for forming a light-emitting layer, a light-emitting layer having superior crystallinity can be effectively formed. This makes it possible to obtain a group III nitride semiconductor light-emitting device having high emission intensity.
When a group III nitride semiconductor light- emitting device is produced using the Ge-doped n-type group III nitride semiconductor layer produced according to the present invention, light-emitting layers having various compositions represented by AlχGaγInzNi-aMa (wherein O≤X≤l, O≤Y≤l, O≤Z≤l, X+Y+Z=l, and 0 < a < 1, wherein M represents a non-nitrogen Group V element) and having a single quantum well structure or a multiple quantum well structure, etc., including known ones, can be used, without limitation, for a light-emitting layer made of the group III nitride semiconductor. Also, for the p- type group III nitride semiconductor layer for constituting a light-emitting part having a double hetero structure, compositions represented by the above formula, including known ones, and doped with a p-type dopant such as Mg, Zn, etc., can be used, without limitation.
After laminating the Ge-doped n-type semiconductor layer, the light-emitting layer, and the p-type semiconductor layer on the substrate in this order, a positive electrode (p-type ohmic electrode) and a negative electrode (n-type ohmic electrode) are formed at predetermined positions. For a positive electrode and a negative electrode for the compound semiconductor light- emitting device, various constitutions and structures are known. Including these known positive electrodes and negative electrodes, positive electrodes and negative electrodes having various constitutions and structures can be used without limitation. Also, for the production method thereof, any known method such as a vacuum vapor deposition method, a sputtering method, etc., can be used without limitation. Examples
The present invention will next be described in more detail by way of Examples, which should not be construed as limiting the invention. <Example 1>
Fig. 1 schematically shows a cross-section of a stacked structure containing a Ge-doped n-type Group III nitride semiconductor layer fabricated in Example 1.
A stacked structure including a sapphire substrate and Group III nitride semiconductor layers successively stacked on the substrate was formed by means of conventional reduced-pressure MOCVD through the following procedure. Firstly, a (0001) -sapphire substrate 1 was placed on a high-purity graphite susceptor (for semiconductors) to be heated at a film formation temperature by a high-frequency (RF) induction heater. The sapphire substrate placed on the susceptor was placed in a stainless steel-made vapor growth reactor furnace, and the reactor furnace was purged with nitrogen. After passage of nitrogen in the vapor growth reactor furnace for 8 minutes, the substrate 1 was heated over 10 minutes from room temperature to 600°C by means of the induction heater. While the substrate 1 was maintained at 600°C, hydrogen gas and nitrogen gas were caused to flow in the vapor growth reactor furnace so as to adjust the pressure inside the furnace to 1.5 x 104 Pa. The surface of the substrate 1 was thermally cleaned by allowing the substrate to stand for 2 minutes under the temperature/pressure conditions. After completion of thermal cleaning, the supply of nitrogen gas was stopped, but hydrogen was continuously supplied to the reactor furnace.
Subsequently, the substrate 1 was heated to l,120°C under hydrogen. After confirmation that a constant temperature of l,120°C was attained, hydrogen gas containing trimethylaluminum (TMA) vapor was supplied to the vapor growth reactor furnace for 8 minutes and 30 seconds. Through this step, the supplied TMA was caused to react with N atoms which had been released through decomposition of nitrogen-containing deposits on an inner wall of the reactor furnace, thereby depositing a high- temperature buffer layer 2 composed of an aluminum nitride (AlN) thin film having a thickness of some nm on the sapphire substrate 1. The supply of hydrogen gas containing TMA vapor into the vapor growth reactor furnace was stopped, thereby completing growth of AlN.
The conditions were maintained for 4 minutes, whereby the TMA vapor remaining in the furnace was completely removed.
Subsequently, ammonia (NH3) gas was supplied to the vapor growth reactor furnace. Four minutes after the start of supply of ammonia gas, the susceptor temperature was lowered to l,040°C under an ammonia flow. After confirmation that the susceptor temperature was lowered to l,040°C and the susceptor maintained a constant temperature of 1,0400C,, supply of trimethylgallium (TMG) into the vapor growth reactor furnace was started, and a base layer 3 composed of undoped GaN was grown for one hour. The thickness of the base layer 3 was adjusted to
2 μm. Subsequently, the substrate 1 was heated to l,120°C. After confirmation that a constant temperature of l,120°C was attained, tetramethylgermanium ( (CH3) 4Ge) was supplied for 18 seconds, followed by stopping the supply for 18 seconds. The cycle was repeated 100 times, to thereby form a Ge-doped n-type GaN layer 4 having a thickness of 2.0 μm in which the Ge concentration periodically varied.
After completion of the growth of the Ge-doped n- type GaN layer 4, the substrate 1 was allowed to cool to room temperature over about 20 minutes through stopping the current supply to the induction heater. During cooling, the inside atmosphere of the vapor growth reactor furnace was formed solely of nitrogen. After confirmation that the substrate 1 was cooled to room temperature, the stacked structure was removed from the vapor growth reactor furnace to the outside. The Ge-doped n-type GaN layer 4 of the thus-produced stacked structure was found to have a carrier concentration, as measured on the basis of the Hall effect, of 7 x 1018 cm"3. The n-type GaN layer 4 had a remarkably flat surface having a pit density of 200/cm2 or less. Through SIMS analysis, each higher concentration layer was found to have a Ge atom concentration of 1.2 x 1019 cm"3 and a thickness of 10 nm, and each lower concentration layer was found to have a Ge atom concentration of 1 x 1018 cm"3 and a thickness of 10 nm. SIMS analysis was carried out under the following conditions: primary ion species of Cs+, acceleration voltage of 14.5 keV, ionic current of 40 nA, raster area of 100 um2, and analysis area of 30 μm2. <Example 2> The procedure of Example 1 was repeated, except that a Ge-doped n-type GaN layer 4 having a thickness of 2.0 μm was formed through supplying (CH3) 4Ge for 9 seconds, followed by stopping supply for 9 seconds, and repeating the cycle 200 times, to thereby form a stacked structure. The Ge-doped n-type GaN layer 4 of the thus-produced stacked structure was found to have a carrier concentration, as measured on the basis of Hall effect, of 7 x 1018 cm"3, which is equivalent to that obtained in Example 1. Through SIMS analysis, each higher concentration layer was found to have a Ge atom concentration of 1.2 x 1019 cm"3 and a thickness of 5 nm, and each lower concentration layer was found to have a Ge atom concentration of 1 x 1018 cm"3 and a thickness of 5 nm. The n-type GaN layer 4 had a surface having a pit density of 4,000/cm2. Although the pit density is slightly higher than that obtained in Example 1, the surface was very flat as compared with a conventional Ge- doped n-type semiconductor layer. <Example 3>
A Group III nitride semiconductor light-emitting device was fabricated through further stacking a Group
III nitride semiconductor layer on the stacked structure produced in Example 1. Fig. 2 schematically shows a cross-section of a Group III nitride semiconductor light- emitting device fabricated in Example 3. The procedure of Example 1 was repeated, to thereby form a Ge-doped n-type GaN layer 4. After formation of the Ge-doped n-type GaN layer 4, an undoped n-type Alo.o7Gao.93N cladding layer 5 having a thickness of 12.5 nm was stacked on the GaN layer at l,060°C. The substrate 1 was cooled to 7300C and, on the undoped n-type Alo.o7Gao.93N cladding layer 5, a light- emitting layer 6 having a multiple (5 cycles) quantum well structure including Alo.03Gao.97N barrier layers 6a and Ino.25Gao.75N well layers 6b was provided. In the fabrication of the light-emitting layer 6 having a multiple quantum well structure, an Alo.o3Gao.97N barrier layer 6a was joined to the undoped n-type Alo.o7Gao.93N cladding layer 5.
The Alo.o3Gao.97N barrier layers 6a were grown in an undoped state by use of trimethylaluminum (TMA) as an aluminum source and triethylgallium (TEG) as a gallium source, and each layer had a thickness of 8 nm. The Ino.25Gao.75N well layers 6b were grown in an undoped state by use of triethylgallium (TEG) as a gallium source and trimethylindium (TMI) as an indium source, and each layer had a thickness of 2.5 nm.
On the light-emitting layer 6 having a multiple quantum well structure, a magnesium (Mg) -doped p-type Alo.07Gao.93N cladding layer 7 having a thickness of 10 nm was formed. On the p-type Alo.07Gao.93N cladding layer 7, an Mg-doped p-type GaN contact layer 8 was formed. Biscyclopentadienyl Mg was employed as an Mg dopant source. Mg was added in such an amount that the p-type GaN contact layer 8 had a hole concentration of 8 x 1017 cm"3. The p-type GaN contact layer 8 had a thickness of 100 nm. After completion of growth of the p-type GaN contact layer 8, the substrate 1 was allowed to cool to room temperature over about 20 minutes through stopping the current supply to the induction heater. During cooling, the inside atmosphere of the vapor growth reactor furnace was formed solely of nitrogen. After confirmation that the substrate 1 was cooled to room temperature, the stacked structure was removed from the vapor growth reactor furnace to the outside. At this instance, the p- type GaN contact layer 8 exhibited p-type conductivity, even though the layer had undergone no annealing to electrically activate the p-type carrier (Mg) .
Subsequently, through a known photolithographic technique and a conventional dry etching technique, the high-Ge-concentration layer of the Ge-doped n-type GaN layer 4 was exposed exclusively in an area where an n- type Ohmic electrode 9 was to be formed. On the thus- exposed surface of the high-Ge-concentration layer, an n- type Ohmic electrode (titanium (semiconductor side) /gold)
9 was formed. On the entire surface of the p-type GaN contact layer 8 serving as the remaining surface of the stacked structure, nickel and gold were successively stacked through a conventional vacuum vapor deposition means, a known photolithographic means, and other means, thereby forming a p-type Ohmic electrode 10. Thereafter, the stacked structure was cut into LED chips of a square shape (350 μm x 350 μm) , and each chip was placed on a lead frame which was bonded to a gold wire to allow device operating current to flow from the lead frame to the LED chip. Upon passage of forward device operating current between the n-type and the p-type Ohmic electrodes 9 and
10 via the lead frame, the chip exhibited a forward voltage of 3.5 V at a forward current of 20 mA. The emission center wavelength of the band of blue light emission at a forward current of 20 mA was found to be 460 ran. The emission intensity of the light emitted from the chip, as determined through a typical integrating sphere, was 5 mW. Thus, a Group III nitride semiconductor light-emitting device attaining high emission intensity was successfully fabricated. <Example 4> A group III nitride semiconductor light-emitting device was produced by the same method as Example 3, except that, upon growing a barrier layer 6a of a multiple quantum well structure light-emitting layer 6, tetraethyl germanium is used as a Ge dopant source in addition to an aluminum source made of TMA and a gallium source made of TEG, so as to make the barrier layer 6a to be a Ge-doped Alo.o3Gao.97N barrier layer.
The obtained light-emitting device was evaluated the same as Example 3. Although the emission intensity was decreased a little to 4.8mW, the forward voltage was
3.2V, and thus, a superior light-emitting device having an extremely low operating voltage was obtained.
Also, when a Ge-doped Alo.o3Gao.9-7N layer having a thickness of lOOnm was produced under the same condition as the growth of the barrier layer 6a, the carrier concentration thereof was 1 x 1017 cm"3.
Industrial Applicability
According to the present invention, a Ge-doped compound semiconductor can be produced without using a germane gas that is hard to handle. The utility value in industry is large.

Claims

1. A germanium-adding source for a compound semiconductor comprising an organic germanium compound.
2. A germanium-adding source according to claim 1, wherein the organic germanium compound comprises at least one selected from a group consisting of tetramethyl germanium ((CHs)4Ge)) and tetraethyl germanium ((C2Hs)4Ge)) .
3. A production method for a compound semiconductor containing germanium as an impurity, wherein an organic germanium compound is used as an impurity source.
4. A Ge-doped compound semiconductor produced by the production method according to claim 3.
5. A Ge-doped compound semiconductor according to claim 4, wherein the compound semiconductor is n-type.
6. A Ge-doped compound semiconductor according to claim 4 or 5, wherein the compound semiconductor is a group III nitride semiconductor.
7. A light-emitting device comprising a compound semiconductor according to any one of claims 4 to 6.
PCT/JP2005/015834 2004-08-25 2005-08-24 Germanium-adding source for compound semiconductor, production method of compound semiconductor using the same and compound semiconductor WO2006022423A1 (en)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH07249796A (en) * 1994-03-09 1995-09-26 Toshiba Corp Semiconductor light emitting element
JPH08139361A (en) * 1994-11-08 1996-05-31 Toshiba Corp Compound semiconductor light emitting device
JP2005129923A (en) * 2003-10-02 2005-05-19 Showa Denko Kk Nitride semiconductor, light emitting element using it, light emitting diode, laser element, lamp, and manufacturing method for those

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH07249796A (en) * 1994-03-09 1995-09-26 Toshiba Corp Semiconductor light emitting element
JPH08139361A (en) * 1994-11-08 1996-05-31 Toshiba Corp Compound semiconductor light emitting device
JP2005129923A (en) * 2003-10-02 2005-05-19 Showa Denko Kk Nitride semiconductor, light emitting element using it, light emitting diode, laser element, lamp, and manufacturing method for those

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