WO2013165134A1 - Method for fabricating p-type aluminum gallium nitride semiconductor - Google Patents

Method for fabricating p-type aluminum gallium nitride semiconductor Download PDF

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WO2013165134A1
WO2013165134A1 PCT/KR2013/003658 KR2013003658W WO2013165134A1 WO 2013165134 A1 WO2013165134 A1 WO 2013165134A1 KR 2013003658 W KR2013003658 W KR 2013003658W WO 2013165134 A1 WO2013165134 A1 WO 2013165134A1
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substrate
type
aluminum
alc
semiconductor layer
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French (fr)
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Shiro Sakai
Hee Sub Lee
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Seoul Opto Device Co., Ltd.
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Priority claimed from JP2012104734A external-priority patent/JP5844685B2/en
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Publication of WO2013165134A1 publication Critical patent/WO2013165134A1/en

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    • H—ELECTRICITY
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    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
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    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02436—Intermediate layers between substrates and deposited layers
    • H01L21/02439—Materials
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    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
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    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
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    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
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    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02518—Deposited layers
    • H01L21/0257—Doping during depositing
    • H01L21/02573—Conductivity type
    • H01L21/02579—P-type
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    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02612—Formation types
    • H01L21/02617—Deposition types
    • H01L21/0262—Reduction or decomposition of gaseous compounds, e.g. CVD
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    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02612—Formation types
    • H01L21/02617—Deposition types
    • H01L21/02636—Selective deposition, e.g. simultaneous growth of mono- and non-monocrystalline semiconductor materials
    • H01L21/02639—Preparation of substrate for selective deposition
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    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/005—Processes
    • H01L33/0062—Processes for devices with an active region comprising only III-V compounds
    • H01L33/0066—Processes for devices with an active region comprising only III-V compounds with a substrate not being a III-V compound
    • H01L33/007—Processes for devices with an active region comprising only III-V compounds with a substrate not being a III-V compound comprising nitride compounds
    • H—ELECTRICITY
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    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier 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 with at least one potential-jump barrier or surface barrier 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 system
    • H01L33/32—Materials of the light emitting region containing only elements of group III and group V of the periodic system containing nitrogen

Definitions

  • the present invention relates to a method for fabricating a p-type aluminum gallium nitride semiconductor. More particularly, the present invention relates to a method for fabricating a carbon-doped p-type aluminum gallium nitride semiconductor.
  • a light emitting diode (hereinafter referred to as "LED") using gallium nitride (GaN) based semiconductor is applied to various devices such as signals or backlights for liquid crystal panels.
  • GaN gallium nitride
  • the AlGaN based LED has only 8% of external light extraction efficiency in a wavelength range of 300 to 350 nm and also has no practical use since it has only less than 1% of external light extraction efficiency in a wavelength range of 280 nm or less (See Non-patent document 1).
  • Activation energy of a donor and an acceptor in an AlGaN semiconductor layer is dependent on the mole fraction of AlN in AlGaN.
  • a high free electron concentration can be maintained to a high AlN mole fraction.
  • the mole fraction of AlN in AlGaN was hard to exceed 0.2 in a case where previously used magnesium (Mg) was used as p-type impurities. Accordingly, it was difficult to improve external light extraction efficiency in a wavelength range of less than 330 nm.
  • an LED using conventional p-type AlGaN semiconductor layers doped with Mg and the like requires a high resistance and a high voltage of 20 V or higher since an energy level is too deep (See Non-patent document 2).
  • a p-type Al x Ga 1-x N (x ⁇ 0.2) or Schottky barrier was used to obtain light in a wavelength range of less than 330 nm.
  • both of the p-type Al x Ga 1-x N (x ⁇ 0.2) and Schottky barrier allow AlGaN not to exhibit its light-emitting capability and cause the efficiency to drop in a high current region, and thus, it is expected to develop a new p-type AlGaN semiconductor layer even in view of energy efficiency.
  • Non-patent documents 3 and 4 Recently, results of studies on a carbon (C) doped AlGaN semiconductor layer have been presented (See Non-patent documents 3 and 4). It is described in these documents to form a p-type AlGaN semiconductor layer of high AlN mole fraction using carbon tetrabromide (CBr 4 ) as impurities.
  • CBr 4 carbon tetrabromide
  • the semiconductor layer is grown by metal organic chemical vapor deposition (MOCVD) while supplying CBr 4 .
  • MOCVD metal organic chemical vapor deposition
  • CBr 4 is a toxic chemical compound, and thus, if CBr 4 can be replaced by more inexpensive source materials, it is expected that an LED using a carbon doped p-type AlGaN semiconductor layer can be put in practical use.
  • the present invention aims to provide a method for fabricating a p-type aluminum gallium nitride semiconductor using new source materials.
  • a method for fabricating a p-type aluminum gallium nitride semiconductor which comprises disposing a material piece having aluminum carbide on a first face of a substrate, supplying a gas containing aluminum, a gas containing gallium, and a gas containing nitrogen from a first direction perpendicular to the first face of the substrate, and forming an aluminum gallium nitride semiconductor comprising carbon on the first face of the substrate.
  • the material piece having aluminum carbide may comprise a sapphire substrate and an aluminum carbide layer disposed on the sapphire substrate.
  • An aluminum gallium nitride semiconductor layer is formed on the first face of the substrate, the material piece having aluminum carbide may be disposed on the aluminum gallium nitride semiconductor layer such that the aluminum carbide layer is brought into contact with the aluminum gallium nitride semiconductor layer, and a carbon from the aluminum diffuses into the aluminum gallium nitride semiconductor layer of the substrate, thereby forming the aluminum gallium nitride semiconductor comprising carbon.
  • the aluminum gallium nitride semiconductor comprising carbon may be grown by using metal organic chemical vapor deposition.
  • the gas containing aluminum may be trimethyl aluminum
  • the gas containing gallium may be trimethyl gallium
  • the gas containing nitrogen may be ammonia
  • the first face of the substrate may be formed of aluminum gallium nitride.
  • the first face of the substrate may be formed of sapphire.
  • a method for fabricating a p-type aluminum gallium nitride semiconductor and a light emitting diode including the same using a new source material According to the present invention, a p-type aluminum gallium nitride semiconductor and a light emitting diode including the same can be fabricated using a new source material which is safer and cheaper than CBr 4 .
  • Fig. 1 is a schematic view illustrating a method for fabricating a p-type AlGaN semiconductor according to an embodiment of the present invention.
  • Fig. 2 is a sectional view of the p-type AlGaN semiconductor taken along A-A' of Fig. 1, wherein Figs. 2 (a) and (b) illustrate sectional views of a substrate before and after an AlGaN semiconductor layer was formed thereon, respectively, when using a sapphire substrate as a substrate 101.
  • Fig. 3 (a) is a view of a substrate on which a carbon-doped AlGaN semiconductor layer is formed according to an embodiment of the present invention
  • Fig. 3 (b) is a sectional view of the semiconductor taken along A-A' of Fig. 3 (a).
  • Fig. 4 is a graph illustrating SIMS measurement results of the carbon-doped AlGaN semiconductor layer according to an embodiment of the present invention.
  • Fig. 5 is a sectional view of a lower half of the substrate of Fig 3, wherein Figs. 5 (a) and (b) illustrate sectional views of the substrate before and after the AlGaN semiconductor layer was formed thereon, respectively, when using a substrate with an AlGaN layer 103 formed on a first face thereof as a substrate 101
  • Fig. 6 is a graph illustrating SIMS measurement results of the carbon-doped AlGaN semiconductor layer according to an embodiment of the present invention.
  • Fig. 7 is a schematic view illustrating a method for fabricating a p-type AlGaN semiconductor according to an embodiment of the present invention.
  • Fig. 8 is a schematic view showing a method for fabricating a p-type AlGaN semiconductor according to an example of the present invention.
  • the present inventors have disclosed a technology of growing a crystalline aluminum carbide (AlC) thin film in a C-face of a sapphire substrate.
  • AlC crystalline aluminum carbide
  • the present inventors have found that an AlGaN semiconductor layer could be doped with carbon using AlC as a source material. They have also found that a p-type AlGaN semiconductor layer was formed by using a fabrication method according to the present invention.
  • the aforementioned AlC thin film disclosed in Korean Patent Application No. 2011-30875 may be used in a method for fabricating a p-type AlGaN semiconductor according to the present invention.
  • the AlC thin film may be formed by metal organic chemical vapor deposition (hereinafter referred to as "MOCVD") using a surface of a sapphire substrate, on which an AlC thin film is formed, as a C-face of the substrate.
  • MOCVD metal organic chemical vapor deposition
  • the gas containing carbon and the gas containing aluminum are each used in a source material for forming the AlC thin film.
  • Methane (CH 4 ) may be used as the gas containing carbon
  • trimethyl aluminum ((CH 3 ) 3 Al; hereinafter referred to as "TMA" may be used as the gas containing aluminum.
  • hydrogen (H 2 ), nitrogen (N 2 ), or a gas mixture of hydrogen (H 2 ) and nitrogen (N 2 ) may be used as a carrier gas.
  • Commercially available source materials used in the field of semiconductor, particularly LED, may be used as each source material.
  • the AlC crystal may be preferably grown at a temperature of 700 °C or higher, more preferably at a temperature of 1100 °C or higher. Needed time to grow the AlC crystal depends on the flow rate of source material or the thickness of the AlC thin film formed, and is from approximately 60 minutes to 120 minutes, for example. It is preferable to perform annealing by supplying hydrogen gas before growing the AlC crystal. Annealing is preferably carried out at 1150 °C.
  • annealing may be performed for 10 minutes when the flow rate of hydrogen gas is maintained to 10 slm (standard liter per minute).
  • the AlC thin film so obtained is used as a material piece having aluminum carbide (hereinafter referred to as "AlC material piece") in a method for fabricating a p-type AlGaN semiconductor according to an embodiment of the present invention.
  • Fig. 1 is a schematic view illustrating a method for fabricating a p-type AlGaN semiconductor according to this embodiment of the present invention.
  • Fig. 2 shows a sectional view of the p-type AlGaN semiconductor taken along A-A' of Fig. 1.
  • an AlC material piece 110 is disposed on a first face (top face) of a substrate 101 such that a p-type AlGaN semiconductor layer 130 is formed on the substrate 101 by MOCVD.
  • the p-type AlGaN semiconductor layer 130 is formed on the substrate 101 by supplying a gas containing aluminum, a gas containing gallium, and a gas containing nitrogen from a first direction perpendicular to the first face of the substrate 101 within a MOCVD apparatus.
  • the AlC material piece 110 is, for instance, a piece in which an AlC layer 113 is formed on a sapphire substrate 111.
  • the AlC material piece 110 is disposed such that the sapphire substrate 111 is brought into contact with the substrate 101.
  • TMA trimethyl aluminum
  • TMGa trimethyl gallium
  • NH 3 ammonia
  • Fig. 3 shows a view illustrating a carbon-doped AlGaN semiconductor layer according to an embodiment of the present invention.
  • Fig. 3 Growth of the AlGaN semiconductor layer by MOCVD, which is illustrated as an example, was performed in the arrangement such as shown in Fig. 3.
  • This furnace is for one sheet of a two-inch substrate, and an upper half of Fig. 3 is for performing growth of the semiconductor layer.
  • the AlC material piece 110 in which the AlC layer 113 was formed on the sapphire substrate 111 was disposed such that the AlC layer 113 was faced upward.
  • the AlC material piece 110 was disposed to form a GaN buffer layer (not shown) to a thickness of 20 nm at 500 °C, and a gas containing aluminum, gallium and nitrogen was allowed to flow along the GaN buffer layer at 1000 °C for 40 minutes to form a film.
  • the grown film had a thickness of 1.2 to 2.5 ⁇ m and an Al composition of 25%.
  • the AlGaN semiconductor was n-type or p-type on measuring points P1 to P4 thereof after conducting MOCVD.
  • the film would be an n-type AlGaN semiconductor or insulator since the film has an Al composition of more than 20%.
  • the measuring points P1 and P4 exhibited n-type semiconductor characteristics and the measuring point P3 exhibited p-type semiconductor characteristics. If the p-type AlGaN semiconductor layer could be formed simply by supplying the gas containing carbon, the measuring points of P1 and P4 would have also exhibited the p-type semiconductor characteristics.
  • the AlC material piece 110 disposed at the inlet side of the source material gas functions as a source material such that AlC (or carbon contained in AlC) becomes a source material gas, and the source material gas is supplied onto the substrate 101 together with the other source material gases such that a p-type AlGaN semiconductor layer is formed only in a region (a region surrounded by broken lines) on the substrate 101 onto which the source material gas derived from AlC has been supplied.
  • Fig. 2 (a) shows a sectional view of a substrate before an AlGaN semiconductor layer is formed thereon, when using a sapphire substrate as a substrate 101.
  • Fig. 2 (b) shows a sectional view of the substrate after the AlGaN semiconductor layer is formed thereon.
  • Source material gases supplied from the inlet flow through the AlC material piece 110 disposed on the substrate 101.
  • an AlC-derived source material gas derived from the AlC material piece 110 as well as various source material gases are supplied onto the substrate 101 such that a carbon doped p-type AlGaN semiconductor layer 130 is grown on the substrate 101.
  • an n-type AlGaN semiconductor layer 135 is grown since the AlC-derived source material gas is not sufficiently supplied onto a region nearer to the inlet side (upstream of the gas flow) than the AlC material piece 110 or a region adjacent to the AlC material piece 110 downstream of the gas flow.
  • a secondary ion mass spectrometer (SIMS) measurement was performed to illustrate the measurement result in Fig. 4.
  • Measurements of samples and a single crystal SiC were performed at the same time to calculate a concentration of carbon (atomic number: 12) from the atomic density.
  • the concentration of carbon in AlGaN was calculated based on the measurement result of the single crystal SiC.
  • the x-axis is a time axis at the general measurement of SIMS, whereas the depth values, which were obtained by measuring the depths of holes formed by the measurement after the measurement and converting the measured hole depths into the depths at the measurement points, were indicated on the x-axis in this embodiment.
  • n-type characteristics are shown at this measuring point since a V/III ratio (a ratio of ammonia to gallium plus aluminum) was considerably increased (there is a report that the n-type characteristics are shown in GaN when the V/III ratio is high). Therefore, it can be predicted that the n-type characteristics were shown at the measuring point P1 whereas the p-type characteristics were shown at the measuring point P3.
  • V/III ratio a ratio of ammonia to gallium plus aluminum
  • the carbon concentration indicated herein became remarkably high as compared to C ⁇ 10 19 cm -3 disclosed in Non-patent document 4.
  • a method for fabricating a p-type AlGaN semiconductor is a method for disposing an AlC material piece on a substrate to form an AlGaN semiconductor layer wherein the p-type AlGaN semiconductor layer can be formed at a region downstream of the AlC material piece along the gas flow.
  • safety during the fabrication can be improved and fabrication cost can also be reduced, because the AlC material piece is used as a carbon source instead of conventional CBr 4 .
  • Fig. 5 shows a sectional view different from that of Fig. 1.
  • a substrate in which a first face of the substrate 101 is formed with the AlGaN layer 103 is used (Fig. 5 (a)).
  • the AlC material piece 110 is disposed on the AlGaN layer 103 of the substrate 101 in such a manner that the AlGaN layer 103 is brought into contact with the AlC layer 113, and an AlGaN semiconductor layer is then formed by MOCVD.
  • a p-type AlGaN semiconductor layer 130 is formed on a region of the AlGaN semiconductor layer 103 beneath the AlC material piece 110 (a region where the AlGaN layer 103 is brought into contact with the AlC layer 113). It can be assumed that AlC (or carbon contained in AlC) derived from the AlC material piece 110 diffuses into the AlGaN semiconductor layer 103 beneath the AlC material piece 110 to form the p-type AlGaN semiconductor layer 130.
  • carbon can diffuse into the AlGaN semiconductor layer 103 by subjecting the AlGaN semiconductor layer 103 to heat treatment at high temperature and flowing a gas, which protects the AlGaN semiconductor layer 103 from being damaged, through the AlGaN semiconductor layer 103 while bringing the AlC layer 113 into contact with the AlGaN semiconductor layer 103 on which nothing has been doped.
  • a test was conducted using a lower half of the substrate shown in Fig. 3.
  • a GaN buffer layer (not shown) was formed to 20 nm at 500 °C on a sapphire substrate 101, which has been made by rotating the substrate 101, and Al 0.25 Ga 0.75 N was grown to 2.7 ⁇ m.
  • the AlC material piece 110 in which the AlC layer 113 was formed on a sapphire substrate 111 was disposed on the surface of AlGaN layer 103 in such a manner that the AlC layer 113 was brought into contact with the AlGaN layer 103, and the AlC material piece 110 was heated at 1000 °C for 40 minutes. Accordingly, the lower half of the substrate shown in Fig. 3 is shaded in black.
  • Fig. 3 (b) is a sectional view illustrating the structure of the lower half of the substrate.
  • FIG. 6 an SIMS result of carbon is illustrated in Fig. 6.
  • P8 was used as a measuring point.
  • the x-axis indicates a depth from the surface (at the measuring point P3) of the AlGaN layer after removing the AlC material piece 110, in the same manner as in Fig. 4.
  • the measurement result of holes at the measuring point P8 was a p-type.
  • the carbon concentration varies with a thickness of a P-type layer, wherein the concentration P was 3 x 10 18 cm -3 when the thickness of the P-type layer was 200 nm.
  • FIG. 7 is a schematic view illustrating a method for fabricating a p-type AlGaN semiconductor according to this embodiment of the present invention.
  • an AlC-derived source material gas is supplied from the AlC material piece 110 to a region downstream of a source material gas inlet of the MOCVD apparatus. Therefore, when the AlGaN semiconductor layer is formed on the substrate 101 while rotating the substrate, carbon is doped over the entire AlGaN semiconductor layer such that the entire AlGaN semiconductor layer has p-type semiconductor characteristics. Even in such a case, however, an n-type AlGaN semiconductor layer was formed in a region adjacent to the AlC material piece 110. Nevertheless, since the substrate is rotated, the region adjacent to the material piece will be moved to a position where carbon is supplied, so that a p-type AlGaN semiconductor layer is formed on the region.
  • a method for fabricating a p-type AlGaN semiconductor according to this embodiment is a method for forming an AlGaN semiconductor layer while rotating the substrate 101, wherein carbon is doped over the entire AlGaN semiconductor layer such that p-type semiconductor characteristics can be given to the entire AlGaN semiconductor layer.
  • the AlC material piece 110 was disposed directly on the substrate 101 to form an AlGaN semiconductor layer.
  • a p-type AlGaN semiconductor layer is formed at a region downstream of the AlC material piece 110 along the gas flow of the source material gases. Therefore, the AlC material piece 110 may be spaced apart from the substrate 101, so long as the AlC material piece 110 is located at a supply side of the source material gases in the MOCVD apparatus even though the AlC material piece 110 is not disposed on the substrate 101.
  • a method for fabricating a p-type AlGaN semiconductor according to this present embodiment is a method for allowing the AlC material piece to be spaced apart from the substrate, wherein a p-type AlGaN semiconductor layer can be formed over the entire substrate.
  • Example 1 TMA was used as the gas containing aluminum, TMGa was used as the gas containing gallium, and NH 3 was used as the gas containing nitrogen.
  • An AlC material piece 110 was disposed directly on a two-inch sapphire substrate 101 on which an AlGaN layer 103 was formed, and carbon was diffused onto the AlGaN layer 103 to form a p-type AlGaN semiconductor layer 130.
  • AlGaN was grown by heating the inside of an MOCVD apparatus and simultaneously further lighting the lamps disposed in the MOCVD apparatus to heat the AlGaN to a temperature range of 1000 to 1200 °C in an atmosphere of ammonia gas. Thereafter, four electrodes on each of which Au/Ni was formed to 10 ⁇ m were disposed to measure halls in the magnetic field. As carbon diffused into the AlGaN layer at 1000 °C, the surface of the AlGaN layer became a p-type. The concentration of a P-type layer could not be determined since the diffusion depth was unclear.
  • Example 2 an AlC material piece 110 was spaced apart from a substrate 101 to form a p-type AlGaN semiconductor layer 130.
  • a buffer layer of GaN was formed to 20 nm at 500 °C and GaN was formed to 2 ⁇ m at 1050 °C.
  • AlC heated to 1000 °C was disposed on a carbon supporter 1600, which was spaced 5 cm apart from the substrate 101 toward the inlet side of source material gases, and the AlC was mixed with the source material gases. Heating was performed by means of a heater 1100.
  • FIG 8 is a schematic view illustrating a method for fabricating a p-type AlGaN semiconductor according to this Example.
  • the AlC material piece 110 was heated by collecting light emitted from a lamp 1200 using a lens 1300.
  • the temperature of the AlC material piece 110 could be raised up to 1200 °C.
  • AlC did not contribute to the gas flow rate at all when the lens 1300 was covered by a cover 1400. It can be confirmed from the fact that the hall coefficient and the mobility are not changed when growing the GaN after covering the lens in a state where the lamp 1200 was attached.
  • AlC is not vaporized if light from the lamp 1200 is not irradiated onto the AlC material piece 110, and the type of an AlGaN semiconductor layer so formed is an insulator or an n-type.
  • the AlGaN semiconductor layer is formed into a p-type AlGaN semiconductor layer when the light from the lamp 1200 is irradiated onto the AlC material piece 110 and carbon is maintained at a temperature of 700 °C or higher.
  • AlC is vaporized at 1000 °C, and a depletion time of AlC is shortened at 1100 °C.
  • AlC with a thickness of 1 ⁇ m is retained at 1000 °C for one hour, whereas AlC is depleted in 10 minutes at 1100 °C. Therefore, a layer structure of n-AlGaN/P-AlGaN/n-AlGaN may also be fabricated by turning on or off the lamp 1200 during the formation of the semiconductor layer.
  • N 1 x 10 17 cm -3 for GaN
  • P 5 x 10 18 cm -3 for Al 0.3 Ga 0.7 N.
  • the profile measured by SIMS indicated the maximum value on the surface.
  • An LED was fabricated using the p-type AlGaN fabricated in Example 2.
  • An n-type GaN with a thickness of 3 ⁇ m, an n-type Al 0.3 Ga 0.7 N with a thickness of 0.1 ⁇ m, an Al 0.15 Ga 0.85 N with a thickness of 10 nm, an Al 0.25 Ga 0.75 N with a thickness of 0.1 ⁇ m, and an Mg doped p-type GaN with a thickness of 10 nm were stacked onto a sapphire substrate.
  • SiH 3 and CP 2 Mg were used as impurities of the n-type and p-type semiconductor layers, respectively.
  • the sapphire substrate with the AlC layer formed thereon was disposed on and overlapped with the LED structure in such a manner that the AlC layer faced downward.
  • the structure was subjected to diffuse at 1050 °C for 10 minutes in an atmosphere of ammonia in an annealing furnace.
  • Al/Ti (n-type) and Au/Ni (p-type) electrodes were prepared and annealed. After connecting wires to the electrodes, current-voltage characteristics of the electrodes were measured. A current started to flow at a voltage of about 4 V, and a current of 20 mA flowed at a voltage of 4.5 V. A current of greater than 1 mA did not flow up to 10 V in a reverse direction. Light emission was observed when a current of 20 mA flowed. An emission wavelength was 330 nm, and a full width at half maximum was 15 nm.
  • An LED was fabricated using the p-type AlGaN fabricated in Example 2.
  • GaN with a thickness of 3 ⁇ m, an n-type Al 0.3 Ga 0.7 N with a thickness of 0.1 ⁇ m, an Al 0.15 Ga 0.85 N with a thickness of 10 nm, an AlC doped p-type Al 0.25 Ga 0.75 N with a thickness of 0.1 ⁇ m, and an Mg doped p-type GaN with a thickness of 10 nm were stacked onto a sapphire substrate.
  • a heating temperature of AlC at that time was 1000 °C.
  • a lamp was covered by a cover, except when growing the p-type AlGaN. The subsequent processes are the same as described in Example 3.

Abstract

Provided is a method for fabricating a p-type aluminum gallium nitride semiconductor using a new material. The present invention provides a method for fabricating a p-type aluminum gallium nitride semiconductor, which comprises the steps of: disposing a material piece having aluminum carbide on a first face of a substrate; and supplying a gas containing aluminum, a gas containing gallium, and a gas containing nitrogen from a first direction perpendicular to the first face of the substrate, thereby forming an aluminum gallium nitride semiconductor including carbon on the first face of the substrate.

Description

METHOD FOR FABRICATING P-TYPE ALUMINUM GALLIUM NITRIDE SEMICONDUCTOR
The present invention relates to a method for fabricating a p-type aluminum gallium nitride semiconductor. More particularly, the present invention relates to a method for fabricating a carbon-doped p-type aluminum gallium nitride semiconductor.
A light emitting diode (hereinafter referred to as "LED") using gallium nitride (GaN) based semiconductor is applied to various devices such as signals or backlights for liquid crystal panels. An AlxGa1-xN (hereinafter referred to as "AlGaN") based LED that is applicable to a wavelength range shorter than 360 nm has long been developed since it can be expected that they are used as a medical purpose (e.g., sterilization) or an industrial purpose (e.g., ultraviolet curing of resins). However, even the AlGaN based LED has only 8% of external light extraction efficiency in a wavelength range of 300 to 350 nm and also has no practical use since it has only less than 1% of external light extraction efficiency in a wavelength range of 280 nm or less (See Non-patent document 1).
Activation energy of a donor and an acceptor in an AlGaN semiconductor layer is dependent on the mole fraction of AlN in AlGaN. In an n-type AlGaN semiconductor layer, a high free electron concentration can be maintained to a high AlN mole fraction. On the other hand, in a p-type AlGaN semiconductor layer, the mole fraction of AlN in AlGaN was hard to exceed 0.2 in a case where previously used magnesium (Mg) was used as p-type impurities. Accordingly, it was difficult to improve external light extraction efficiency in a wavelength range of less than 330 nm. Furthermore, an LED using conventional p-type AlGaN semiconductor layers doped with Mg and the like requires a high resistance and a high voltage of 20 V or higher since an energy level is too deep (See Non-patent document 2).
In a conventional AlGaN based LED, a p-type AlxGa1-xN (x<0.2) or Schottky barrier was used to obtain light in a wavelength range of less than 330 nm. However, both of the p-type AlxGa1-xN (x<0.2) and Schottky barrier allow AlGaN not to exhibit its light-emitting capability and cause the efficiency to drop in a high current region, and thus, it is expected to develop a new p-type AlGaN semiconductor layer even in view of energy efficiency.
Recently, results of studies on a carbon (C) doped AlGaN semiconductor layer have been presented (See Non-patent documents 3 and 4). It is described in these documents to form a p-type AlGaN semiconductor layer of high AlN mole fraction using carbon tetrabromide (CBr4) as impurities.
(Prior Technical Non-patent Documents)
1. Amano Hiroshi, Applied Physics, 74, 1433-1436 (2005).
2. Y. Taniyasu et al., Nature, 441, 325-328 (2006).
3. Maeda Noritoshi, Hirayama Hideki, Preview of 59th United Lectures for Applied Physics, 16a-DP1-31 (Spring 2012).
4. H. Kawanishi et al., phys. Stat. sol, 249, 459-463 (2012).
In a method of forming a carbon doped p-type AlGaN semiconductor layer as described above, the semiconductor layer is grown by metal organic chemical vapor deposition (MOCVD) while supplying CBr4. However, CBr4 is a toxic chemical compound, and thus, if CBr4 can be replaced by more inexpensive source materials, it is expected that an LED using a carbon doped p-type AlGaN semiconductor layer can be put in practical use.
The present invention aims to provide a method for fabricating a p-type aluminum gallium nitride semiconductor using new source materials.
In accordance with an embodiment of the present invention, there is provided a method for fabricating a p-type aluminum gallium nitride semiconductor, which comprises disposing a material piece having aluminum carbide on a first face of a substrate, supplying a gas containing aluminum, a gas containing gallium, and a gas containing nitrogen from a first direction perpendicular to the first face of the substrate, and forming an aluminum gallium nitride semiconductor comprising carbon on the first face of the substrate.
The material piece having aluminum carbide may comprise a sapphire substrate and an aluminum carbide layer disposed on the sapphire substrate.
An aluminum gallium nitride semiconductor layer is formed on the first face of the substrate, the material piece having aluminum carbide may be disposed on the aluminum gallium nitride semiconductor layer such that the aluminum carbide layer is brought into contact with the aluminum gallium nitride semiconductor layer, and a carbon from the aluminum diffuses into the aluminum gallium nitride semiconductor layer of the substrate, thereby forming the aluminum gallium nitride semiconductor comprising carbon.
The aluminum gallium nitride semiconductor comprising carbon may be grown by using metal organic chemical vapor deposition.
The gas containing aluminum may be trimethyl aluminum, the gas containing gallium may be trimethyl gallium, and the gas containing nitrogen may be ammonia.
The first face of the substrate may be formed of aluminum gallium nitride.
The first face of the substrate may be formed of sapphire.
According to the present invention, there is provided a method for fabricating a p-type aluminum gallium nitride semiconductor and a light emitting diode including the same using a new source material. According to the present invention, a p-type aluminum gallium nitride semiconductor and a light emitting diode including the same can be fabricated using a new source material which is safer and cheaper than CBr4.
Fig. 1 is a schematic view illustrating a method for fabricating a p-type AlGaN semiconductor according to an embodiment of the present invention.
Fig. 2 is a sectional view of the p-type AlGaN semiconductor taken along A-A' of Fig. 1, wherein Figs. 2 (a) and (b) illustrate sectional views of a substrate before and after an AlGaN semiconductor layer was formed thereon, respectively, when using a sapphire substrate as a substrate 101.
Fig. 3 (a) is a view of a substrate on which a carbon-doped AlGaN semiconductor layer is formed according to an embodiment of the present invention, and Fig. 3 (b) is a sectional view of the semiconductor taken along A-A' of Fig. 3 (a).
Fig. 4 is a graph illustrating SIMS measurement results of the carbon-doped AlGaN semiconductor layer according to an embodiment of the present invention.
Fig. 5 is a sectional view of a lower half of the substrate of Fig 3, wherein Figs. 5 (a) and (b) illustrate sectional views of the substrate before and after the AlGaN semiconductor layer was formed thereon, respectively, when using a substrate with an AlGaN layer 103 formed on a first face thereof as a substrate 101
Fig. 6 is a graph illustrating SIMS measurement results of the carbon-doped AlGaN semiconductor layer according to an embodiment of the present invention.
Fig. 7 is a schematic view illustrating a method for fabricating a p-type AlGaN semiconductor according to an embodiment of the present invention.
Fig. 8 is a schematic view showing a method for fabricating a p-type AlGaN semiconductor according to an example of the present invention.
Hereinafter, a method for fabricating a p-type aluminum gallium nitride semiconductor of the present invention will be described in detail with reference to the accompanying drawings. A method for fabricating a p-type aluminum gallium nitride semiconductor of the present invention should not be construed as being limited to the descriptions of the embodiments and examples set forth below. Furthermore, like or similar reference numerals indicate like or similar elements in the drawings used to illustrate the embodiments and examples, and repeated descriptions are omitted.
In Japanese Patent Application No. 2011-30875, the present inventors have disclosed a technology of growing a crystalline aluminum carbide (AlC) thin film in a C-face of a sapphire substrate. The present inventors have found that an AlGaN semiconductor layer could be doped with carbon using AlC as a source material. They have also found that a p-type AlGaN semiconductor layer was formed by using a fabrication method according to the present invention.
(Method of Preparing Aluminum Carbide Thin Film)
For example, the aforementioned AlC thin film disclosed in Korean Patent Application No. 2011-30875 may be used in a method for fabricating a p-type AlGaN semiconductor according to the present invention. For example, the AlC thin film may be formed by metal organic chemical vapor deposition (hereinafter referred to as "MOCVD") using a surface of a sapphire substrate, on which an AlC thin film is formed, as a C-face of the substrate.
The gas containing carbon and the gas containing aluminum are each used in a source material for forming the AlC thin film. Methane (CH4) may be used as the gas containing carbon, and trimethyl aluminum ((CH3)3Al; hereinafter referred to as "TMA" may be used as the gas containing aluminum. Further, hydrogen (H2), nitrogen (N2), or a gas mixture of hydrogen (H2) and nitrogen (N2) may be used as a carrier gas. Commercially available source materials used in the field of semiconductor, particularly LED, may be used as each source material.
It is preferable to supply TMA in a flow rate of 33 μmol/min to 66 μmol/min and to supply methane in a flow rate of 13 mmol/min to 27 mmol/min as a condition for growing an AlC crystal. Further, the AlC crystal may be preferably grown at a temperature of 700 ℃ or higher, more preferably at a temperature of 1100 ℃ or higher. Needed time to grow the AlC crystal depends on the flow rate of source material or the thickness of the AlC thin film formed, and is from approximately 60 minutes to 120 minutes, for example. It is preferable to perform annealing by supplying hydrogen gas before growing the AlC crystal. Annealing is preferably carried out at 1150 ℃. For example, annealing may be performed for 10 minutes when the flow rate of hydrogen gas is maintained to 10 slm (standard liter per minute). The AlC thin film so obtained is used as a material piece having aluminum carbide (hereinafter referred to as "AlC material piece") in a method for fabricating a p-type AlGaN semiconductor according to an embodiment of the present invention.
(Embodiment 1)
Fig. 1 is a schematic view illustrating a method for fabricating a p-type AlGaN semiconductor according to this embodiment of the present invention. Fig. 2 shows a sectional view of the p-type AlGaN semiconductor taken along A-A' of Fig. 1. In the present embodiment, an AlC material piece 110 is disposed on a first face (top face) of a substrate 101 such that a p-type AlGaN semiconductor layer 130 is formed on the substrate 101 by MOCVD. Specifically, the p-type AlGaN semiconductor layer 130 is formed on the substrate 101 by supplying a gas containing aluminum, a gas containing gallium, and a gas containing nitrogen from a first direction perpendicular to the first face of the substrate 101 within a MOCVD apparatus. Herein, the AlC material piece 110 is, for instance, a piece in which an AlC layer 113 is formed on a sapphire substrate 111. The AlC material piece 110 is disposed such that the sapphire substrate 111 is brought into contact with the substrate 101.
Although the aforementioned various source material gases are not limited to the following gases, it is very suitable to use trimethyl aluminum (hereinafter referred to as "TMA") as a gas containing aluminum, trimethyl gallium (hereinafter referred to as "TMGa") as a gas containing gallium, and ammonia (NH3) as a gas containing nitrogen.
Here, a question arises whether a carbon doped p-type AlGaN semiconductor layer can be formed simply by performing MOCVD while the gas containing carbon is supplied. However, it is necessary to dispose the AlC material piece on the substrate in order to form the p-type AlGaN semiconductor layer. It will be described as follows. Fig. 3 shows a view illustrating a carbon-doped AlGaN semiconductor layer according to an embodiment of the present invention.
Growth of the AlGaN semiconductor layer by MOCVD, which is illustrated as an example, was performed in the arrangement such as shown in Fig. 3. This furnace is for one sheet of a two-inch substrate, and an upper half of Fig. 3 is for performing growth of the semiconductor layer. At the inlet side of source material gas, the AlC material piece 110 in which the AlC layer 113 was formed on the sapphire substrate 111 was disposed such that the AlC layer 113 was faced upward. After the sapphire substrate 111 was annealed beforehand at 1150 ℃ for 10 minutes and then cooled to a room temperature, the AlC material piece 110 was disposed to form a GaN buffer layer (not shown) to a thickness of 20 nm at 500 ℃, and a gas containing aluminum, gallium and nitrogen was allowed to flow along the GaN buffer layer at 1000 ℃ for 40 minutes to form a film. The grown film had a thickness of 1.2 to 2.5 ㎛ and an Al composition of 25%.
It was determined whether the AlGaN semiconductor was n-type or p-type on measuring points P1 to P4 thereof after conducting MOCVD. At a normal growth, it is apparent that the film would be an n-type AlGaN semiconductor or insulator since the film has an Al composition of more than 20%. In this case, however, the measuring points P1 and P4 exhibited n-type semiconductor characteristics and the measuring point P3 exhibited p-type semiconductor characteristics. If the p-type AlGaN semiconductor layer could be formed simply by supplying the gas containing carbon, the measuring points of P1 and P4 would have also exhibited the p-type semiconductor characteristics. From these results, it can be predicted that the AlC material piece 110 disposed at the inlet side of the source material gas functions as a source material such that AlC (or carbon contained in AlC) becomes a source material gas, and the source material gas is supplied onto the substrate 101 together with the other source material gases such that a p-type AlGaN semiconductor layer is formed only in a region (a region surrounded by broken lines) on the substrate 101 onto which the source material gas derived from AlC has been supplied.
Fig. 2 (a) shows a sectional view of a substrate before an AlGaN semiconductor layer is formed thereon, when using a sapphire substrate as a substrate 101. Fig. 2 (b) shows a sectional view of the substrate after the AlGaN semiconductor layer is formed thereon. In the present embodiment, it can be predicted that the same formation result can be obtained if at least a first face of the substrate 101 is made of sapphire. Source material gases supplied from the inlet flow through the AlC material piece 110 disposed on the substrate 101. At this time, an AlC-derived source material gas derived from the AlC material piece 110 as well as various source material gases are supplied onto the substrate 101 such that a carbon doped p-type AlGaN semiconductor layer 130 is grown on the substrate 101. On the other hand, an n-type AlGaN semiconductor layer 135 is grown since the AlC-derived source material gas is not sufficiently supplied onto a region nearer to the inlet side (upstream of the gas flow) than the AlC material piece 110 or a region adjacent to the AlC material piece 110 downstream of the gas flow. In the method for fabricating a p-type AlGaN semiconductor according to an embodiment of the present invention, it may be predicted that n-type semiconductor characteristics were detected at the measuring point P1 by the formation mechanism of an AlGaN semiconductor layer.
In order to find out such a mechanism, a secondary ion mass spectrometer (SIMS) measurement was performed to illustrate the measurement result in Fig. 4. Measurements of samples and a single crystal SiC were performed at the same time to calculate a concentration of carbon (atomic number: 12) from the atomic density. The concentration of carbon in AlGaN was calculated based on the measurement result of the single crystal SiC. Further, the x-axis is a time axis at the general measurement of SIMS, whereas the depth values, which were obtained by measuring the depths of holes formed by the measurement after the measurement and converting the measured hole depths into the depths at the measurement points, were indicated on the x-axis in this embodiment.
Although at least 1020 carbon atoms/cm3 was detected at both measuring points P1 and P3, it was confirmed that the carbon atom density was higher at the measuring point P3 than at the measuring point P1. It is assumed that since the growth was performed without rotating the substrate, uniform growth could not be achieved across the entire substrate 101 due to non-uniform compositions of Al, Ga and nitrogen. In particular, the film had a thin thickness of 1.2 ㎛ at the measuring point P1. This indicates that a supplied amount of Ga + Al was considerably reduced. On the other hand, ammonia gas flowed as much as about 4,000 times more than gallium gas. Thus, it is believed that the n-type characteristics are shown at this measuring point since a V/III ratio (a ratio of ammonia to gallium plus aluminum) was considerably increased (there is a report that the n-type characteristics are shown in GaN when the V/III ratio is high). Therefore, it can be predicted that the n-type characteristics were shown at the measuring point P1 whereas the p-type characteristics were shown at the measuring point P3.
The concentration of electron-hole varies with the thicknesses of an n-type layer and a p-type layer. It is assumed that at the measuring point P1, the conductive type becomes an n-type, N = 1018 cm-3 when the thickness is 100 nm, and N = 8 x 1016 cm-3 when the thickness is 1.5 ㎛. In comparison, it is assumed that at the measuring point P3, the conductive type becomes a p-type, P = 6 x 1019 cm-3 when the thickness is 100 nm, and P = 4 x 1018 cm-3 when the thickness is 1.5 ㎛. The carbon concentration indicated herein became remarkably high as compared to C < 1019 cm-3 disclosed in Non-patent document 4.
As described above, a method for fabricating a p-type AlGaN semiconductor according to an embodiment of the present invention is a method for disposing an AlC material piece on a substrate to form an AlGaN semiconductor layer wherein the p-type AlGaN semiconductor layer can be formed at a region downstream of the AlC material piece along the gas flow. In this embodiment, safety during the fabrication can be improved and fabrication cost can also be reduced, because the AlC material piece is used as a carbon source instead of conventional CBr4.
(Embodiment 2)
Fig. 5 shows a sectional view different from that of Fig. 1. In a method for fabricating a p-type AlGaN semiconductor according to Embodiment 2 of the present invention, a substrate in which a first face of the substrate 101 is formed with the AlGaN layer 103 is used (Fig. 5 (a)). The AlC material piece 110 is disposed on the AlGaN layer 103 of the substrate 101 in such a manner that the AlGaN layer 103 is brought into contact with the AlC layer 113, and an AlGaN semiconductor layer is then formed by MOCVD.
In a fabrication method according to this embodiment, a p-type AlGaN semiconductor layer 130 is formed on a region of the AlGaN semiconductor layer 103 beneath the AlC material piece 110 (a region where the AlGaN layer 103 is brought into contact with the AlC layer 113). It can be assumed that AlC (or carbon contained in AlC) derived from the AlC material piece 110 diffuses into the AlGaN semiconductor layer 103 beneath the AlC material piece 110 to form the p-type AlGaN semiconductor layer 130. In this embodiment, carbon can diffuse into the AlGaN semiconductor layer 103 by subjecting the AlGaN semiconductor layer 103 to heat treatment at high temperature and flowing a gas, which protects the AlGaN semiconductor layer 103 from being damaged, through the AlGaN semiconductor layer 103 while bringing the AlC layer 113 into contact with the AlGaN semiconductor layer 103 on which nothing has been doped.
In order to demonstrate this, a test was conducted using a lower half of the substrate shown in Fig. 3. A GaN buffer layer (not shown) was formed to 20 nm at 500 ℃ on a sapphire substrate 101, which has been made by rotating the substrate 101, and Al0.25Ga0.75N was grown to 2.7 ㎛. The AlC material piece 110 in which the AlC layer 113 was formed on a sapphire substrate 111 was disposed on the surface of AlGaN layer 103 in such a manner that the AlC layer 113 was brought into contact with the AlGaN layer 103, and the AlC material piece 110 was heated at 1000 ℃ for 40 minutes. Accordingly, the lower half of the substrate shown in Fig. 3 is shaded in black. Fig. 3 (b) is a sectional view illustrating the structure of the lower half of the substrate.
As an example, an SIMS result of carbon is illustrated in Fig. 6. After removing the AlC material piece 110 in the lower half of Fig. 3, P8 was used as a measuring point. In Fig. 6, the x-axis indicates a depth from the surface (at the measuring point P3) of the AlGaN layer after removing the AlC material piece 110, in the same manner as in Fig. 4. In this example, it is apparent that at least 1018 carbon atoms/cm3 diffused into AlGaN layer and present in the AlGaN layer. The measurement result of holes at the measuring point P8 was a p-type. The carbon concentration varies with a thickness of a P-type layer, wherein the concentration P was 3 x 1018 cm-3 when the thickness of the P-type layer was 200 nm.
(Embodiment 3)
In the embodiments described above, an AlGaN semiconductor layer was formed in a state where the substrate 101 was fixed. In this embodiment, an example in which an AlGaN semiconductor layer is formed while rotating the substrate 101 will be explained. Fig. 7 is a schematic view illustrating a method for fabricating a p-type AlGaN semiconductor according to this embodiment of the present invention.
As shown in Fig. 7, an AlC-derived source material gas is supplied from the AlC material piece 110 to a region downstream of a source material gas inlet of the MOCVD apparatus. Therefore, when the AlGaN semiconductor layer is formed on the substrate 101 while rotating the substrate, carbon is doped over the entire AlGaN semiconductor layer such that the entire AlGaN semiconductor layer has p-type semiconductor characteristics. Even in such a case, however, an n-type AlGaN semiconductor layer was formed in a region adjacent to the AlC material piece 110. Nevertheless, since the substrate is rotated, the region adjacent to the material piece will be moved to a position where carbon is supplied, so that a p-type AlGaN semiconductor layer is formed on the region.
In addition, as described in Embodiment 2, when using a substrate in which the first face of the substrate 101 is formed with the AlGaN layer 103, carbon diffuses even into the AlGaN semiconductor layer beneath the AlC material piece 110 such that the p-type AlGaN semiconductor layer can be formed even on a region of the AlGaN semiconductor layer beneath the AlC material piece 110.
As described above, a method for fabricating a p-type AlGaN semiconductor according to this embodiment is a method for forming an AlGaN semiconductor layer while rotating the substrate 101, wherein carbon is doped over the entire AlGaN semiconductor layer such that p-type semiconductor characteristics can be given to the entire AlGaN semiconductor layer.
(Embodiment 4)
In the aforementioned embodiments, the AlC material piece 110 was disposed directly on the substrate 101 to form an AlGaN semiconductor layer. As found in the aforementioned embodiments, a p-type AlGaN semiconductor layer is formed at a region downstream of the AlC material piece 110 along the gas flow of the source material gases. Therefore, the AlC material piece 110 may be spaced apart from the substrate 101, so long as the AlC material piece 110 is located at a supply side of the source material gases in the MOCVD apparatus even though the AlC material piece 110 is not disposed on the substrate 101.
A method for fabricating a p-type AlGaN semiconductor according to this present embodiment is a method for allowing the AlC material piece to be spaced apart from the substrate, wherein a p-type AlGaN semiconductor layer can be formed over the entire substrate.
[Examples]
Hereinafter, specific examples will be described further in detail with respect to a method for fabricating a p-type AlGaN semiconductor according to the above embodiments of the present invention.
(Example 1)
In Example 1, TMA was used as the gas containing aluminum, TMGa was used as the gas containing gallium, and NH3 was used as the gas containing nitrogen. An AlC material piece 110 was disposed directly on a two-inch sapphire substrate 101 on which an AlGaN layer 103 was formed, and carbon was diffused onto the AlGaN layer 103 to form a p-type AlGaN semiconductor layer 130.
AlGaN was grown by heating the inside of an MOCVD apparatus and simultaneously further lighting the lamps disposed in the MOCVD apparatus to heat the AlGaN to a temperature range of 1000 to 1200 ℃ in an atmosphere of ammonia gas. Thereafter, four electrodes on each of which Au/Ni was formed to 10 ㎛ were disposed to measure halls in the magnetic field. As carbon diffused into the AlGaN layer at 1000 ℃, the surface of the AlGaN layer became a p-type. The concentration of a P-type layer could not be determined since the diffusion depth was unclear. Although the concentration of the P layer was increased according to the increase in the fabrication temperature, AlGaN was etched such that irregularities were formed on the surface of a p-type AlGaN semiconductor layer 130. It was confirmed that carbon diffused to a depth of about 0.05 ㎛ into a layer when measuring the diffusion depth in layer that includes sapphire, GaN (2 ㎛) and Al0.3Ga0.7N (0.1 ㎛) at 1050 ℃ for 10 minutes using SIMS. This layer has a P-type layer concentration of about 1 1017 cm-3. However, a profile of carbon measured by SIMS was a complementary error function from the diffusion, and a value corresponding to one fifth of the surface concentration was used as a thickness of the P layer. Furthermore, a hall coefficient was derived using a value of the N layer since sapphire was an insulator and GaN was n-type in this layer.
(Example 2)
In Example 2, an AlC material piece 110 was spaced apart from a substrate 101 to form a p-type AlGaN semiconductor layer 130. On the sapphire substrate 101, a buffer layer of GaN was formed to 20 nm at 500 ℃ and GaN was formed to 2 ㎛ at 1050 ℃. Thereafter, when growing Al0.3Ga0.7N to a thickness of 0.1 ㎛ at 1100 ℃, AlC heated to 1000 ℃ was disposed on a carbon supporter 1600, which was spaced 5 cm apart from the substrate 101 toward the inlet side of source material gases, and the AlC was mixed with the source material gases. Heating was performed by means of a heater 1100. Fig. 8 is a schematic view illustrating a method for fabricating a p-type AlGaN semiconductor according to this Example. The AlC material piece 110 was heated by collecting light emitted from a lamp 1200 using a lens 1300. The temperature of the AlC material piece 110 could be raised up to 1200 ℃. Here, AlC did not contribute to the gas flow rate at all when the lens 1300 was covered by a cover 1400. It can be confirmed from the fact that the hall coefficient and the mobility are not changed when growing the GaN after covering the lens in a state where the lamp 1200 was attached.
AlC is not vaporized if light from the lamp 1200 is not irradiated onto the AlC material piece 110, and the type of an AlGaN semiconductor layer so formed is an insulator or an n-type. The AlGaN semiconductor layer is formed into a p-type AlGaN semiconductor layer when the light from the lamp 1200 is irradiated onto the AlC material piece 110 and carbon is maintained at a temperature of 700 ℃ or higher. AlC is vaporized at 1000 ℃, and a depletion time of AlC is shortened at 1100 ℃. AlC with a thickness of 1 ㎛ is retained at 1000 ℃ for one hour, whereas AlC is depleted in 10 minutes at 1100 ℃. Therefore, a layer structure of n-AlGaN/P-AlGaN/n-AlGaN may also be fabricated by turning on or off the lamp 1200 during the formation of the semiconductor layer.
As the result of measuring holes in a p-type AlGaN semiconductor layer formed by this Example, N = 1 x 1017 cm-3 for GaN, and P = 5 x 1018 cm-3 for Al0.3Ga0.7N. In this case, the profile measured by SIMS indicated the maximum value on the surface.
(Example 3)
An LED was fabricated using the p-type AlGaN fabricated in Example 2. An n-type GaN with a thickness of 3 ㎛, an n-type Al0.3Ga0.7N with a thickness of 0.1 ㎛, an Al0.15Ga0.85N with a thickness of 10 nm, an Al0.25Ga0.75N with a thickness of 0.1 ㎛, and an Mg doped p-type GaN with a thickness of 10 nm were stacked onto a sapphire substrate. In addition, SiH3 and CP2Mg were used as impurities of the n-type and p-type semiconductor layers, respectively. The sapphire substrate with the AlC layer formed thereon was disposed on and overlapped with the LED structure in such a manner that the AlC layer faced downward. The structure was subjected to diffuse at 1050 ℃ for 10 minutes in an atmosphere of ammonia in an annealing furnace.
Al/Ti (n-type) and Au/Ni (p-type) electrodes were prepared and annealed. After connecting wires to the electrodes, current-voltage characteristics of the electrodes were measured. A current started to flow at a voltage of about 4 V, and a current of 20 mA flowed at a voltage of 4.5 V. A current of greater than 1 mA did not flow up to 10 V in a reverse direction. Light emission was observed when a current of 20 mA flowed. An emission wavelength was 330 nm, and a full width at half maximum was 15 nm.
(Example 4)
An LED was fabricated using the p-type AlGaN fabricated in Example 2. GaN with a thickness of 3 ㎛, an n-type Al0.3Ga0.7N with a thickness of 0.1 ㎛, an Al0.15Ga0.85N with a thickness of 10 nm, an AlC doped p-type Al0.25Ga0.75N with a thickness of 0.1 ㎛, and an Mg doped p-type GaN with a thickness of 10 nm were stacked onto a sapphire substrate. A heating temperature of AlC at that time was 1000 ℃. A lamp was covered by a cover, except when growing the p-type AlGaN. The subsequent processes are the same as described in Example 3.
According to the current-voltage characteristics, a current shot up at a voltage of 3.8 V and a current of 20 mA flowed at a voltage of 4.3 V. In a reverse direction, a current of greater than 1 mA did not flow up to 10 V. Light emission was observed at a voltage of 4.3 V. An emission wavelength was 330 nm, and a full width at half maximum was 15 nm.
Although the present invention has been described with reference to the examples and preferred embodiments, it is not limited thereto. It should be understood that changes and modifications may be made by those skilled in the art without departing from the spirit and scope of the present disclosure, which fall within the scope and spirit of the principles of the disclosures.
(Explanation of Reference Numerals)
101: Substrate
103: AlGaN layer
110: AlC material piece
111: Sapphire substrate
113: AlC layer
130: p-type AlGaN semiconductor layer
135: n-type AlGaN semiconductor layer
1100: Heater
1200: Lamp
1300: Lens
140: Quartz Cover
1500: Stainless Steel Cover
1600: Carbon supporter

Claims (7)

  1. A method for fabricating a p-type aluminum gallium nitride semiconductor comprising:
    disposing a material piece having aluminum carbide on a first face of a substrate, and
    supplying a gas containing aluminum, a gas containing gallium, and a gas containing nitrogen from a first direction perpendicular to the first face of the substrate, thereby forming an aluminum gallium nitride semiconductor comprising carbon on the first face of the substrate.
  2. The method of claim 1, wherein the material piece having aluminum carbide comprise a sapphire substrate and an aluminum carbide layer disposed on the sapphire substrate.
  3. The method of claim 2, wherein an aluminum gallium nitride semiconductor layer is formed on the first face of the substrate, the material piece having aluminum carbide is disposed on the aluminum gallium nitride semiconductor layer such that the aluminum carbide layer is brought into contact with the aluminum gallium nitride semiconductor layer, and a carbon from the aluminum carbide layer diffuses into the aluminum gallium nitride semiconductor layer of the substrate, thereby forming the aluminum gallium nitride semiconductor comprising carbon.
  4. The method of any one of claims 1 to 3, wherein the aluminum gallium nitride semiconductor comprising carbon is grown by using metal organic chemical vapor deposition.
  5. The method of any one of claims 1 to 3, wherein the gas containing aluminum is trimethyl aluminum, the gas containing gallium is trimethyl gallium, and the gas containing nitrogen is ammonia.
  6. The method of any one of claims 1 to 3, wherein the first face of the substrate is formed of aluminum gallium nitride.
  7. The method of any one of claims 1 to 3, wherein the first face of the substrate is formed of sapphire.
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