JP2011230955A - GaN SUBSTRATE AND LIGHT-EMITTING DEVICE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a GaN substrate having a low absorption coefficient for light having a wavelength within a light emission wavelength region of a light-emitting device and specific resistance not higher than a prescribed value and being suitable for the light-emitting device.SOLUTION: The GaN substrate 10 has an absorption coefficient not lower than 7 cmfor light having a wavelength of 380 nm and light having a wavelength of 1,500 nm, an absorption coefficient lower than 7 cmfor at least light having a wavelength not shorter than 500 nm and not longer than 780 nm, and specific resistance not higher than 0.02 Ω×cm. Here, the absorption coefficient for light having a wavelength not shorter than 500 nm and not longer than 780 nm can be lower than 7 cm.

Description

  The present invention relates to a GaN substrate with high light transmittance in the red light region or visible light region from blue to red and high conductivity, and a light emitting device including such a GaN substrate.

As a substrate used for a light emitting device, a substrate having high light transmittance and high conductivity is required. For example, Japanese Patent Laying-Open No. 2005-213075 (Patent Document 1) discloses a GaN substrate having an absorption coefficient of 7 cm ^{−1 to} 68 nm ⁻¹ for light having a wavelength of 375 nm to 500 nm. Japanese Patent Laid-Open No. 2007-126320 (Patent Document 2) forms a TiN thin film having a large number of micropores on a substrate and grows a GaN crystal on the TiN thin film while suppressing the introduction of impurities other than Si. Thus, it is disclosed to obtain a GaN substrate having an absorption coefficient of less than 7 cm ⁻¹ for light having a wavelength of 380 nm or more.

JP-A-2005-213075 JP 2007-126320 A

  However, there is a trade-off between light transmittance and conductivity. If the impurities in the substrate are reduced in order to increase the light transmittance, the conductivity decreases, and the impurities in the substrate are increased in order to increase the conductivity. Increasing the light decreases the light transmittance.

For example, Japanese Patent Laying-Open No. 2005-213075 (Patent Document 1) can only reduce the absorption coefficient of light having a wavelength of 375 nm to 500 nm to about 7 cm ⁻¹ in order to maintain predetermined conductivity. It was.

On the other hand, Japanese Patent Application Laid-Open No. 2007-126320 (Patent Document 2) discloses a GaN substrate that maintains predetermined conductivity and has an absorption coefficient of less than 7 cm ⁻¹ for light having a wavelength of 380 nm or more. A special method (called VAS (Void-Assisted Separation) method) in which a TiN thin film having a large number of fine holes is formed on a substrate and a GaN crystal is grown on the TiN thin film while suppressing the incorporation of impurities other than Si. ), The cost is very high.

  In addition, the substrate for the light emitting device only needs to have a low absorption coefficient with respect to light having a wavelength within the light emission wavelength region, and needs to have a low absorption coefficient even with respect to light with a wavelength outside the light emission wavelength region. There is no.

  Therefore, from the above viewpoint, the present invention has a low absorption coefficient with respect to light having a wavelength within the emission wavelength region of the light emitting device, and has a specific resistance equal to or lower than a predetermined value, and is suitable for the light emitting device It is another object of the present invention to provide a light emitting device including the GaN substrate.

The present invention, wavelength is at an absorption coefficient relates to 380nm light and the wavelength of 1500nm light 7 cm ^-1 or more, at least wavelength absorption coefficient for 780nm light below or 500nm than 7 cm ^-1, specific resistance 0 A GaN substrate of 0.02 Ωcm or less.

In the GaN substrate according to the present invention, the absorption coefficient relating to light having a wavelength of 440 nm or more and 780 nm or less can be made less than 7 cm ⁻¹ .

Further, the present invention has a wavelength is in the absorption coefficient for 380nm light and the wavelength of 1500nm light 7 cm ^-1 or more, at least wavelength absorption coefficient for 780nm light below or 500nm is less than 7 cm ^-1, resistivity Is a light emitting device including the above GaN substrate having a light emission peak wavelength of 500 nm or more and 780 nm or less. The present invention also includes the above GaN substrate having an absorption coefficient of 7 cm ⁻¹ or more and a specific resistance of 0.02 Ωcm or less for light having a wavelength of 380 nm and light having a wavelength of 1500 nm, and has a peak emission wavelength of 440 m. The light-emitting device has a thickness of 780 nm or less.

  According to the present invention, a GaN substrate having a low absorption coefficient with respect to light having a wavelength within the emission wavelength region of the light-emitting device and having a specific resistance equal to or lower than a predetermined value, and the GaN substrate suitable for the light-emitting device Can be provided.

It is a schematic sectional drawing which shows an example of the method of manufacturing the GaN board | substrate which is one embodiment of this invention. Here, (A) shows a step of preparing a base substrate and a step of growing a GaN crystal doped with impurities on the base substrate, and (B) shows a step of processing the GaN crystal to form a GaN substrate. . It is the schematic which shows the HVPE apparatus used for the growth of a GaN crystal. It is a schematic sectional drawing which shows an example of the light-emitting device which is other embodiment of this invention.

[GaN substrate]
GaN substrate is an embodiment of the present invention, the wavelength is at an absorption coefficient relates to 380nm light and the wavelength of 1500nm light 7 cm ^-1 or more, at least wavelength absorption coefficient for 780nm light below or 500 nm 7 cm ^-1 The specific resistance is 0.02 Ωcm or less. Here, the light absorption coefficient is calculated by measuring the transmittance and reflectance of light of a target wavelength using a spectrophotometer. The specific resistance is measured by a four-probe method using a specific resistance meter.

  Such a GaN substrate is suitably used as a GaN substrate for a light-emitting device having a peak emission wavelength of at least 500 nm to 780 nm. Hereinafter, more specific embodiments will be described.

(Embodiment 1)
The GaN substrate of the present embodiment has an absorption coefficient of 7 cm ⁻¹ or more for light having a wavelength of 380 nm and light having a wavelength of 1500 nm, an absorption coefficient for light having a wavelength of 500 nm or more and 780 nm or less, and less than 7 cm ^−1. The resistance is 0.02 Ωcm or less. The GaN substrate of the present embodiment is suitably used as a substrate of a light emitting device that has a red light region having a light emission peak wavelength of 500 nm to 780 nm. From this viewpoint, it is preferable that the absorption coefficient regarding light having a wavelength of 500 nm or more and 780 nm or less is 5 cm ⁻¹ or less. The specific resistance is preferably 0.015 Ωcm or less.

(Embodiment 2)
The GaN substrate of the present embodiment has an absorption coefficient of 7 cm ⁻¹ or more for light having a wavelength of 380 nm and light having a wavelength of 1500 nm, an absorption coefficient for light having a wavelength of 440 nm or more and 780 nm or less, and less than 7 cm ^−1. The resistance is 0.02 Ωcm or less. The GaN substrate of this embodiment is suitably used as a substrate for a light emitting device having a light emission peak wavelength in a visible light region from a blue light region to a red light region of 440 nm to 780 nm. From this viewpoint, it is preferable that the absorption coefficient regarding light having a wavelength of 440 nm or more and 780 nm or less is 5 cm ⁻¹ or less. The specific resistance is preferably 0.015 Ωcm or less.

The GaN substrate of any of the above embodiments preferably has a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ or more and 2 × 10 ¹⁸ cm ⁻³ or less. If the carrier concentration is too low, the specific resistance becomes too high, and if the carrier concentration is too high, the light absorption coefficient becomes too high. From this viewpoint, the carrier concentration is more preferably 7 × 10 ¹⁷ cm ⁻³ or more and 1.1 × 10 ¹⁸ cm ⁻³ or less. Here, the carrier concentration is measured using a CV characteristic measurement method.

The GaN substrate of any of the above embodiments preferably has an average density of dislocations penetrating through its main surface (hereinafter referred to as the average dislocation density) of 3 × 10 ⁶ cm ⁻² or less. The lower the average density of such dislocations, the higher the reliability of the light emitting device. From this viewpoint, the average density of dislocations penetrating the main surface (average dislocation density) is more preferably 1 × 10 ⁶ cm ⁻² or less. Also, from the viewpoint of current substrate manufacturing technology, the average density of dislocations penetrating the main surface (average dislocation density) is currently difficult to be smaller than 10 cm ⁻² , and is therefore about 10 cm ^−2. That's it. The average density of dislocations penetrating the main surface of the GaN substrate is calculated from the measurement of dark spot density by CL (cathode luminescence).

  The GaN substrate of any of the above embodiments preferably has a flat main surface and a radius of curvature of a crystal plane closest to the main surface is 10 m or more. As the radius of curvature of the crystal plane increases, a light emitting device having a uniform emission wavelength within the substrate plane can be obtained. From this point of view, the radius of curvature of the crystal plane closest to the main surface is more preferably 20 m or more. Also, from the viewpoint of the current substrate manufacturing technology, the average density of dislocations penetrating the main surface is currently difficult to be larger than 100 m, and is therefore about 100 m or less. The radius of curvature of the crystal plane is measured by X-ray diffraction with respect to the target crystal plane.

  The crystal plane closest to the main surface of the GaN substrate is not particularly limited, but from the viewpoint of epitaxially growing a highly crystalline semiconductor layer on the main surface, the {0001} plane, the {10-10} plane, the {11- 20} plane, {10-11} plane, {11-22} plane, {20-21} plane, {22-44} plane, etc. are preferable. From the viewpoint of epitaxially growing a highly crystalline semiconductor layer on the main surface of the GaN substrate, the main surface of the GaN substrate preferably has an absolute value of an off angle of 5 ° or less with respect to the crystal plane. Here, the plane orientation of the crystal plane closest to the GaN substrate and the off-angle between the main surface and the crystal plane are measured by X-ray diffraction.

[Method of manufacturing GaN substrate]
FIG. 1 is a schematic cross-sectional view showing an example of a method for manufacturing the GaN substrate of the present embodiment. The method of manufacturing the GaN substrate of the present embodiment is not particularly limited, but referring to FIG. 1, a step of preparing the base substrate 11, a step of growing the GaN crystal 12 doped with impurities on the base substrate 11, A step of forming the GaN substrate 10 by processing the GaN crystal 12. In this manufacturing method, the GaN substrate 10 of the present embodiment can be obtained at low cost by adjusting the concentration of impurities (referred to as dopant hereinafter) added to the GaN crystal 12.

(Process for preparing the base substrate)
Referring to FIG. 1A, the base substrate 11 prepared in the step of preparing the base substrate 11 is not particularly limited as long as it is a substrate on which the GaN crystal 12 can be epitaxially grown. From the viewpoint of high consistency, a silicon (Si) base substrate, a sapphire (Al ₂ O ₃ ) base substrate, a GaAs base substrate, and a group III nitride base substrate such as a GaN base substrate and an AlN base substrate are preferably used. Among these, a GaN base substrate is particularly preferably used. The use of a GaN base substrate is preferable because it can suppress contamination of impurities from the base substrate. From this point of view, the cleanliness of the surface of the base substrate is important. In particular, the back surface of the base substrate (the surface of the base substrate in contact with the inner wall of the growth furnace; the same applies hereinafter) cannot be etched in the growth furnace before crystal growth. It is necessary to raise. For this reason, it is preferable to etch the back surface of the substrate and then put it into the growth furnace. Etching methods include etching with an alkaline solvent and etching with a halogen-based gas.

(Step of growing GaN crystal with added impurities)
Referring to FIG. 1A, the method for growing the GaN crystal 12 doped with impurities on the base substrate 11 is not particularly limited as long as it is a method capable of epitaxial growth, but GaN having high crystallinity. From the viewpoint of growing the crystal 12, vapor phase methods such as HVPE (hydride vapor phase epitaxy) method, MOCVD (metal organic chemical vapor deposition) method, MBE (molecular beam growth) method are preferable, and the crystal growth rate is particularly high. To HVPE is particularly preferred.

Here, in the HVPE method, the growth is usually performed in the quartz reaction tube, so that the crystal in the quartz reaction tube is heated, so that the quartz reaction tube is also heated together with the crystal. Therefore, the decomposition gas from the quartz reaction tube heated to a high temperature is taken into the crystal as an impurity. Therefore, it is preferable to cover the inside of the quartz reaction tube with a liner tube formed of a material that is stable at the growth temperature (for example, pBN). Further, it is preferable to flow a purge gas (for example, H ₂ , N ₂ , and / or Ar) for purging the gap between the quartz reaction tube and the liner tube so that impurities do not stay. In addition, since the susceptor on which the base substrate is disposed also becomes high temperature, it is preferable to form such a susceptor with pBN or coat it with a high-purity and stable material such as pBN, AlN, Al ₂ O ₃ , or SiC. .

The impurity (dopant) added to the GaN crystal 12 is not particularly limited, but Si is preferable from the viewpoint of reducing the light absorption coefficient and reducing the specific resistance. The method for adding Si to the GaN crystal 12 is not particularly limited, but a gas containing Si as a doping gas, for example, SiF ₄ (silicon tetrafluoride) gas, SiH ₄ (silane) gas, Si ₂ H ₆ (disilane) gas, SiH ₃ Cl (silane monochloride) gas, SiH ₂ Cl ₂ (silane dichloride) gas, SiHCl ₃ (silane trichloride) gas, SiCl ₄ (silicon tetrachloride) gas, etc. are preferably used Among these, SiF ₄ gas is particularly preferably used. SiF ₄ gas is less likely to be decomposed even at a high temperature of 900 ° C. or higher and 1300 ° C. or lower as compared with other Si-containing gases, and therefore can be efficiently added to the GaN crystal 12.

  For example, a method for growing the GaN crystal 12 doped with Si as a dopant by the HVPE method will be described below. FIG. 2 is a schematic view showing an HVPE apparatus used for growing the GaN crystal 12. Referring to FIG. 2, the HVPE apparatus 100 includes a first source gas cylinder 101, a doping gas cylinder 102, a second source gas cylinder 103, a first gas introduction pipe 104, a doping gas introduction pipe 105, and a second gas introduction. A pipe 106, a source boat 107, a susceptor 108, a heater 109, a reaction pipe 110, an exhaust pipe 111, and an exhaust gas treatment device are provided. The HVPE apparatus 100 is, for example, a horizontal reaction tube. The HVPE apparatus 100 may be a vertical reaction tube.

The reaction tube 110 is a container for holding the base substrate 11 inside and growing the GaN crystal 12 on the base substrate 11. As the reaction tube 110, for example, a quartz reaction tube can be used. In addition, a liner tube 120 made of pBN is disposed inside the reaction tube 110. The first source gas cylinder 101, the second source gas cylinder 103, and the source boat 107 are each supplied with a source containing an element constituting a GaN crystal to be grown. The doping gas cylinder 102 is filled with, for example, SiF ₄ gas as a gas containing Si as a dopant. The first gas introduction pipe 104, the doping gas introduction pipe 105, and the second gas introduction pipe 106 are used to introduce each of the first source gas G1, the doping gas G2, and the second source gas G3 from the outside to the inside of the reaction tube 110. Are provided in the reaction tube 110. The source boat 107 accommodates and holds, for example, metal Ga as a metal raw material of the GaN crystal, and is disposed in the second gas introduction pipe 106.

  The susceptor 108 is coated with a pBN film and holds the base substrate 11. The susceptor 108 is arranged so that the surface of the reaction tube 110 on which the base substrate 11 is held by the susceptor 108 is positioned below the first gas introduction tube 104, the doping gas introduction tube 105, and the second gas introduction tube 106. ing. The susceptor 108 is disposed horizontally in the reaction tube 110. The susceptor 108 may be configured such that the base substrate 11 is arranged vertically. The HVPE apparatus 100 may further include a local heating mechanism for heating such as a resistance heater of the base substrate 11.

  The heater 109 is disposed outside the reaction tube 110 and has the ability to heat the interior of the reaction tube 110 to, for example, 700 ° C. or more and 1500 ° C. or less. The exhaust pipe 111 is provided in the reaction tube 110 in order to discharge the reacted gas to the outside of the reaction tube 110. The exhaust gas treatment device is configured to remove the gas after reaction discharged from the exhaust pipe 111 so as to reduce the load on the environment.

  As shown in FIG. 2, first, the prepared base substrate 11 is held on the susceptor 108. At this time, a plurality of base substrates 11 may be held by the susceptor 108.

Next, a first source gas cylinder 101 and a second source gas cylinder 103 filled with NH ₃ (ammonia) gas as the first source gas and HCl (hydrogen chloride) gas as the second source gas are prepared. Further, metal Ga is supplied to the source boat 107. Further, a doping gas cylinder 102 filled with SiF ₄ gas is prepared.

Thereafter, the source boat 107 is heated. Then, the HCl gas (second source gas G3) supplied from the second gas introduction pipe 106 and the metal Ga of the source boat 107 are reacted to generate GaCl gas (gallium chloride) gas (reaction gas G7). The NH ₃ gas (first source gas G1), the doping gas G2, and the reaction gas G7 supplied from the first gas introduction pipe 104 are caused to flow (supplied) to react with the surface of the base substrate 11 to be reacted. At this time, a carrier gas for transporting these gases to the base substrate 11 may be used. As the carrier gas, for example, an inert gas such as N ₂ (nitrogen) gas, H ₂ (hydrogen) gas, and Ar (argon) gas can be used.

  In the HVPE method, the heater 109 is used to heat the inside of the reaction tube 110 to a temperature at which the GaN crystal 12 grows at an appropriate rate. The temperature at which the GaN crystal 12 is grown is preferably 900 ° C. or higher and 1300 ° C. or lower, and more preferably 1050 ° C. or higher and 1200 ° C. or lower. When the GaN crystal 12 is grown at 900 ° C. or more, generation of defects in the GaN crystal 12 can be prevented, and generation of a plane orientation different from the plane orientation to be grown (for example, pits in the case of the c plane) can be suppressed. . That is, the GaN crystal 12 having stable and good crystallinity can be grown with respect to the plane orientation to be grown. When the GaN crystal 12 is grown at 1050 ° C. or higher, the crystallinity can be improved. On the other hand, when the GaN crystal 12 is grown at 1300 ° C. or lower, it is possible to suppress decomposition of the GaN crystal 12 to be grown, so that deterioration of the crystallinity can be suppressed. When the GaN crystal 12 is grown at 1200 ° C. or lower, the crystallinity deterioration can be further suppressed.

  Here, the crystal growth surface of the GaN crystal to be grown preferably has an inclination angle from the (0001) plane of less than 1 °. In a GaN crystal, by making the inclination angle of the crystal growth surface from the (0001) plane less than 1 °, the incorporation of impurities other than the doping gas on the crystal growth surface can be suppressed. In order to set the inclination angle of the crystal growth surface of the GaN crystal from the (0001) plane to less than 1 °, the crystal growth temperature is preferably set to 1100 ° C. or higher. In addition, by optimizing the flow and flow rate of the source gas, carrier gas, and doping gas, the tilt angle from the (0001) plane is set to 1 over almost the entire crystal growth surface (from 80% to 100%). It can be less than °.

The partial pressure of the gas containing Si (SiF ₄ gas) during the growth of the GaN crystal 12 is preferably 2.0 × 10 ⁻⁷ atm or more and 1.0 × 10 ⁻⁵ atm or less. When the partial pressure of the gas containing Si (SiF ₄ gas) is 2.0 × 10 ⁻⁷ atm or more, Si as an n-type dopant is sufficiently taken into the GaN crystal 12. On the other hand, when the partial pressure of the SiF ₄ gas is 1.0 × 10 ⁻⁵ atm or less, the generation of Si _x N _y (silicon nitride) compounds can be further suppressed, so that the controllability for doping Si is better. it can. In consideration of the concentration of Si doped into the GaN crystal 12, the partial pressure of the gas containing Si (SiF ₄ gas) is 1.0 × 10 ⁻⁵ atm or less. The total (total) partial pressure of each of the gases contained in the reaction tube 110 such as the source gas, the carrier gas, and the doping gas is 1 atm. The concentration of the gas containing Si (SiF ₄ gas) is proportional to the partial pressure.

In the step of growing the GaN crystal to which the impurity is added, the carrier concentration in the GaN crystal 12 is preferably 5 × 10 ¹⁷ cm ⁻³ or more and 1.5 × 10 ¹⁸ cm ⁻³ or less (the corresponding Si concentration is 5 × 10 ¹⁷ cm ⁻³ or more and 1.6 × 10 ¹⁸ cm ⁻³ or less, more preferably 6.6 × 10 ¹⁷ cm ⁻³ or more and 1.1 × 10 ¹⁸ cm ⁻³ or less (corresponding Si concentration is 6.9). The doping gas is supplied to the base substrate 11 so as to be in the range of × 10 ¹⁷ cm ^{−3 to} 1.1 × 10 ¹⁸ cm ⁻³ . When the carrier concentration is 5 × 10 ¹⁷ cm ⁻³ or more, the specific resistance of the GaN crystal 12 can be reduced to ensure sufficient conductivity. In the case where the carrier concentration is 6.6 × 10 ¹⁷ cm ⁻³ or more, the specific resistance of the GaN crystal 12 can be further reduced to ensure sufficient conductivity. On the other hand, when the carrier concentration is 1.5 × 10 ¹⁸ cm ⁻³ or less, the light absorption coefficient of the GaN crystal can be reduced to ensure sufficient light transmission. When the carrier concentration is 1.1 × 10 ¹⁸ cm ⁻³ or less, the light absorption coefficient of the GaN crystal can be made smaller, and the light transmission can be sufficiently secured. Further, the doping amount of impurities other than Si (oxygen, carbon, etc.) is preferably 1/5 or less, more preferably 1/10 or less, and even more preferably 1/20 or less of the Si doping amount.

  In the step of growing the GaN crystal 12 to which impurities are added, the GaN crystal 12 is grown so that the specific resistance of the GaN crystal 12 is 0.02 Ωcm or less, preferably 0.015 Ωcm or less. When the specific resistance is 0.02 Ωcm or less, it is possible to grow the GaN crystal 12 having conductivity that is suitably used for the substrate of the light emitting device. When the specific resistance of the GaN crystal is 0.015 Ωcm or less, it is preferably used for the substrate of the light emitting device.

In the step of growing the GaN crystal 12 to which the impurity is added, the GaN crystal is grown so that the absorption coefficient for light having a wavelength of 500 nm or more and 780 nm or less is less than 7 cm ⁻¹ , preferably 5 cm ⁻¹ or less. Grow. The GaN crystal 12 is a substrate of a light emitting device having a light emission peak wavelength of 500 nm or more and 780 nm or less when the light absorption coefficient for light having a wavelength of 500 nm or more and 780 nm or less is less than 7 cm ⁻¹ , preferably 5 cm ⁻¹ or less. Is preferably used.

In the step of growing the GaN crystal 12 to which the impurity is added, the GaN crystal is grown so that the absorption coefficient for light having a wavelength of 440 nm or more and 780 nm or less is less than 7 cm ⁻¹ , preferably 5 cm ⁻¹ or less. Grow. The GaN crystal 12 is a substrate of a light emitting device having a light emission peak wavelength of 440 nm or more and 780 nm or less when the light absorption coefficient relating to light having a wavelength of 440 nm or more and 780 nm or less is less than 7 cm ⁻¹ , preferably 5 cm ⁻¹ or less. Is preferably used.

In the step of growing the GaN crystal to which the impurity is added, the average density of dislocations in the GaN crystal 12 is preferably 3 × 10 ⁶ cm ⁻² or less, more preferably 1 × 10 ⁶ cm ⁻² or less. The GaN crystal 12 is grown so that By processing such a GaN crystal, a GaN substrate having an average density of dislocations penetrating the main surface 12m is preferably 3 × 10 ⁶ cm ⁻² or less, more preferably 1 × 10 ⁶ cm ⁻² or less. Easy to obtain. Here, the average density of dislocations in the GaN crystal 12 and the average density of dislocations penetrating the main surface 12m of the GaN substrate (average dislocation density) are calculated from the measurement of dark spot density by CL (cathode luminescence).

  Referring to FIG. 1A, in the step of growing GaN crystal 12 to which impurities are added, main surface 11m is {0001} plane, {10-10} plane, {11-20} plane, {10 Group III nitride substrate (underlying substrate) having an absolute value of an off angle of 5 ° or less from any of the −11}, {11-22}, {20-21}, and {22-44} planes 11), the main surface 12m of crystal growth is {0001} plane, {10-10} plane, {11-20} plane, {10-11} plane, {11-22} plane, {20-21 } It is preferable to grow the GaN crystal 12 having an absolute value of an off angle of 5 ° or less from any one of the {} -plane and the {22-44} plane. From such GaN crystal, the main surface 10m is {0001} plane, {10-10} plane, {11-20} plane, {10-11} plane, {11-22} plane, {20-21} plane, and {20-21} plane. The GaN substrate 10 having an absolute off angle of 5 ° or less from any one of the 22-44} planes can be easily obtained.

(Process of forming GaN substrate by processing GaN crystal)
Referring to FIG. 1B, the process of forming the GaN substrate 10 by processing the obtained GaN crystal 12 doped with impurities is not particularly limited, and includes a sub-process of removing the base substrate 11. Can do. The method for removing the base substrate 11 is not particularly limited, and there are a method of cutting with an outer peripheral blade, an inner peripheral blade, a wire saw, a laser, or the like, and a method of grinding with a diamond grindstone. Thus, the GaN crystal 12 having the main surfaces 12m and 12n is obtained.

  The step of processing the GaN crystal 12 to form the GaN substrate 10 can also include a sub-step of slicing the GaN crystal 12. The method for slicing the GaN crystal 12 is not particularly limited, and includes a method of cutting with an outer peripheral blade, an inner peripheral blade, a wire saw, a laser, or the like. Further, a sub-process of polishing and / or surface-treating the main surface of the sliced GaN crystal 12 can be included. Examples of a method for polishing the main surface of the GaN crystal 12 include mechanical polishing and chemical mechanical polishing. Examples of the method for treating the main surface of the GaN crystal 12 include dry etching and wet etching.

  The step of processing the GaN crystal 12 to form the GaN substrate 10 can also include a sub-step of removing the outer periphery of the GaN crystal 12. The method for removing the outer peripheral portion of the GaN crystal 12 is not particularly limited, and there is a method of grinding with a diamond grindstone or the like.

The GaN substrate 10 is obtained from the GaN crystal 12 by one or more of the sub-processes described above.
In the GaN substrate 10 of the present embodiment obtained by the above GaN substrate manufacturing method, the average density of dislocations penetrating the main surface (average dislocation density) is preferably 3 × 10 ⁶ cm ⁻² or less, and 1 × 10 ⁶ cm ⁻² or less is more preferable. The lower the average density of such dislocations, the higher the reliability of the light emitting device. Also, from the viewpoint of the current substrate manufacturing technology, the average density of dislocations penetrating the main surface is currently difficult to be smaller than 1 × 10 ⁴ cm ⁻² , and therefore, 1 × 10 ⁴ cm. ^-2 or more.

  In addition, the GaN substrate of the present embodiment obtained by the above-described method for manufacturing a GaN substrate is preferably such that the main surface is flat and the radius of curvature of the crystal plane closest to the main surface is 10 m or more, More preferably, it is 20 m or more. As the radius of curvature of the crystal plane is larger, a light emitting device having higher in-plane uniformity of emission wavelength can be obtained. Also, from the viewpoint of the current substrate manufacturing technology, the average density of dislocations penetrating the main surface is currently difficult to be larger than 100 m, and is therefore about 100 m or less.

[Light emitting device]
FIG. 3 is a schematic cross-sectional view showing an example of a light emitting device according to another embodiment of the present invention. Referring to FIG. 3, the light emitting device of the present embodiment includes the GaN substrate 10 of the first embodiment or the second embodiment, and has an emission peak wavelength of 500 nm or more and 780 nm or less or 440 nm or more and 780 nm or less. The light emitting device of this embodiment has a low light absorption coefficient and high light emission efficiency for light in the wavelength region of 500 nm to 780 nm or less or 440 nm to 780 nm.

  Referring to FIG. 3, the light emitting device of the present embodiment is more specifically formed on the GaN substrate 10 of the first embodiment or the second embodiment and one main surface 10 m of the GaN substrate 10. It includes at least one semiconductor layer 20, a first electrode 30 formed on the outermost layer of the semiconductor layer 20, and a second electrode 40 formed on the other main surface 10n of the GaN substrate 10. Such a light-emitting device includes a light-emitting layer in the semiconductor layer 20 and emits light from the GaN substrate 10 side. Hereinafter, more specific embodiments will be described.

(Embodiment 3)
Referring to FIG. 3, the light emitting device of the present embodiment has an absorption coefficient of 7 cm ⁻¹ or more for light having a wavelength of 380 nm and light having a wavelength of 1500 nm, and an absorption coefficient of 7 cm ⁻¹ for light having a wavelength of 500 nm or more and 780 nm or less. ^-1 and a specific resistance of 0.02 Ωcm or less, at least one semiconductor layer 20 formed on one main surface 10m of the GaN substrate 10, and an outermost layer of the semiconductor layer 20 And the second electrode 40 formed on the other main surface 10n of the GaN substrate 10, and the peak wavelength of light emission is 500 nm or more and 780 nm or less.

(Embodiment 4)
Referring to FIG. 3, the light emitting device of this embodiment has an absorption coefficient of 7 cm ⁻¹ or more for light having a wavelength of 380 nm and light having a wavelength of 1500 nm, and an absorption coefficient of 7 cm ⁻¹ for light having a wavelength of 440 nm or more and 780 nm or less. ^-1 and a specific resistance of 0.02 Ωcm or less, at least one semiconductor layer 20 formed on one main surface 10m of the GaN substrate 10, and an outermost layer of the semiconductor layer 20 And the second electrode 40 formed on the other main surface 10n of the GaN substrate 10, and the peak wavelength of light emission is not less than 440 nm and not more than 780 nm.

  In the light-emitting devices of Embodiment 3 and Embodiment 4 described above, the wavelength region and peak wavelength of the light emission can be changed by changing the chemical composition and / or configuration of the semiconductor layer 20.

[Method for manufacturing light-emitting device]
The method for manufacturing the light emitting device of the present embodiment is not particularly limited. For example, referring to FIG. 3, the step of preparing the GaN substrate 10 of Embodiment 1 or 2 and one of the GaN substrates 10 are prepared. A step of forming at least one semiconductor layer 20 on the main surface, a step of forming a first electrode 30 formed on the outermost layer of the semiconductor layer 20, and a second step on the other main surface 10 n of the GaN substrate 10. Forming two electrodes 40. Here, the order of the step of forming the first electrode 30 and the step of forming the second electrode 40 may be reversed.

(Process for preparing GaN substrate)
The method of preparing the GaN substrate of Embodiment 1 or Embodiment 2 is as described in the above GaN substrate manufacturing method.

(Step of forming at least one semiconductor layer on the GaN substrate)
The method for forming at least one semiconductor layer 20 on one main surface 10m of the GaN substrate 10 is not particularly limited, but from the viewpoint of epitaxially growing the semiconductor layer 20 having good crystallinity on the GaN substrate, MOCVD, MBE The gas phase method such as the HVPE method is preferable. Further, by changing the chemical composition and / or configuration of the semiconductor layer 20, the wavelength region and peak wavelength of light emission can be changed.

(Step of forming the first electrode and the second electrode)
A method for forming the first electrode and the second electrode is not particularly limited, but from the viewpoint of increasing productivity and reducing production cost, a sputtering method, a vapor deposition method, or the like is preferable.

[Example]
In this example, a plurality of GaN substrates having different carrier concentrations, specific resistances, and light absorption coefficients were obtained by changing the partial pressure of the doping gas containing Si in the HVPE method by the following method.

1. First, a GaN base substrate 11 having a diameter of 60 mm and a thickness of 400 μm was prepared with reference to FIG. The main surface 11m of the base substrate 11 was flat, and the crystal plane closest to the main surface 11m was the (0001) plane. The radius of curvature of the (0001) plane was 20 m as measured by X-ray diffraction. The average density of dislocations penetrating the main surface 11m of the base substrate 11 (hereinafter referred to as the average dislocation density) is calculated from the measurement of dark spot density by CL (cathode luminescence), and is 5 × 10 ⁵ cm ⁻³ . there were.

2. Growth of GaN crystal Next, referring to FIG. 1 (A), the by HVPE, on underlying substrate 11, the Si concentration by using SiF ₄ gas as the doping gas is grown seven different GaN crystal 12 (Experiment No. 1-7).

The HVPE apparatus shown in FIG. 2 was used for the growth of these GaN crystals. NH ₃ gas was prepared as the first source gas G1, HCl gas was used as the second source gas G3, SiF ₄ gas was used as the doping gas G2, and H ₂ gas having a purity of 99.999% or more was prepared as the carrier gas. A carrier gas was introduced into the reaction tube 110 from each of the first gas introduction tube 104, the second gas introduction tube 106, and the doping gas introduction tube 105, and the temperature of the heater 109 was raised to 1100 ° C. Thereafter, metal Ga was supplied to the source boat 107 to heat the source boat 107.

By reacting HCl gas supplied from the second gas introduction pipe 106 and Ga in the source boat 107 as Ga + HCl → GaCl + 1 / 2H ₂ , GaCl gas was generated as the reaction gas G7.

Next, NH ₃ gas as a first source gas G 1 supplied from the first gas introduction pipe 104 and GaCl gas are flowed together with the carrier gas so as to hit the main surface on which the GaN crystal of the base substrate 11 is grown. above, it was reacted as _{GaCl + NH 3 → GaN + HCl} + H 2.

  As a condition for growing seven GaN crystals 12 (Experiment Nos. 1 to 7) having different Si concentrations, the supply partial pressure of the doping gas was adjusted to the values shown in Table 1. As a result, seven GaN crystals having a diameter of 60 mm and a thickness of 5 mm with different Si concentrations were grown at a crystal growth temperature of 1100 ° C. and a crystal growth time of 16.67 hours. The growth rate of these GaN crystals was 300 μm / hr.

3. Formation of GaN Substrate Next, referring to FIG. 1 (B), each GaN crystal 12 obtained was sliced in the thickness direction using a slicer. Next, the outer peripheral portion of the sliced GaN crystal 12 was removed. Next, CMP (chemical mechanical polishing) was performed on the GaN crystal that had been sliced to remove the outer peripheral portion, and the work-affected layer was removed. Thus, five GaN substrates 10 having a diameter of 2 inches (50.8 mm) and a thickness of 400 μm were obtained from each GaN crystal.

4). Measurement of physical properties of GaN substrate Of the obtained five GaN substrates 10a, 10b, 10c, 10d, and 10e, at five measurement points on the third GaN substrate 10c from the base substrate 11 side, the Si concentration, the carrier concentration, The specific resistance and the absorption coefficient for light having wavelengths of 380 nm, 500 nm to 780 nm, 440 nm to 780 nm and 1500 nm were measured, and their minimum and maximum values were calculated. Here, the five measurement points are a center point on the main surface, a point 2 cm away from the center point in the direction [11-20], a point 2 cm away from the center point, and a point 10 [10] from the center point. −10] The total number of points was −2 cm apart and +2 cm apart. Here, the Si concentration was measured by SIMS (secondary ion mass spectrometry). The carrier concentration was measured by a CV characteristic measurement method. The specific resistance was measured by a four-probe method using a specific resistance meter. The light absorption coefficient was calculated by measuring transmittance and reflectance using a spectrophotometer. Here, assuming that the absorption coefficient in the GaN substrate is constant regardless of the depth, multiple reflection was also considered. The results are summarized in Table 1.

  Here, the variation of the carrier concentration in the main surface of the GaN substrate was within ± 5% from the average value, and the variation of the carrier concentration in the thickness direction was also within ± 5% from the average value.

Further, the average density of dislocations (average dislocation density) penetrating the main surface at the above five measurement points of the third GaN substrate 10c of each GaN crystal 12 is 5 × 10 ⁵ cm ^−2. The density was as low as that of the substrate 11. In addition, the radius of curvature of the (0001) plane at the above five measurement points of the third GaN substrate 10c of each GaN crystal 12 was 20 m as measured by X-ray diffraction, and was as large as the underlying substrate. . Moreover, no crack was generated in any of the obtained GaN substrates.

Referring to Table 1, in the HVPE method, the crystal growth temperature is 1000 ° C. or more and 1200 ° C. or less, and the partial pressure of the doping gas containing Si is 0.6 × 10 ⁻⁶ atm or more and 1.0 × 10 ⁻⁶ atm or less. By adjusting the carrier concentration to 0.66 × 10 ¹⁸ cm ⁻³ or more and 1.1 × 10 ¹⁸ cm ⁻³ or less, the specific resistance is 0.02 Ωcm or less and the absorption coefficient for light having a wavelength of 380 nm is 7 cm. ^A GaN substrate having an absorption coefficient of less than 7 cm ⁻¹ for light having a wavelength of 500 nm to 780 nm and an absorption coefficient of 7 cm ⁻¹ or more for light having a wavelength of 1500 nm was obtained. In addition, the crystal growth temperature is adjusted to 1000 ° C. or more and 1200 ° C. or less, the partial pressure of the doping gas containing Si is adjusted to 0.6 × 10 ⁻⁶ atm or more and 0.8 × 10 ⁻⁶ atm or less, and the carrier concentration is set to 0. By setting it to 66 × 10 ¹⁸ cm ⁻³ or more and 0.82 × 10 ¹⁸ cm ⁻³ or less, the specific resistance is 0.02 Ωcm or less, the absorption coefficient for light having a wavelength of 380 nm is 7 cm ⁻¹ or more, and the wavelength is 440 nm to 780 nm. A GaN substrate having an absorption coefficient for light of less than 7 cm ^{−1, a} wavelength of 1500 nm and an absorption coefficient for light of 7 cm ⁻¹ or more was obtained. The impurity concentration of elements other than Si in all the grown crystals was measured by SIMS. O (oxygen) was 5 × 10 ¹⁶ cm ⁻³ or less and C (carbon) was 5 × 10 ^16. cm ^-3 or less, it was also more than 1 × 10 ¹⁶ cm ^-3 other elements.

  The above example is a case where a GaN substrate in which the crystal plane closest to the main surface is the (0001) plane is produced. The crystal plane closest to the main surface is the (10-10) plane and the (11-20) plane. Similar results were obtained when a GaN substrate having a (10-11), (11-22), (20-21), or (22-44) plane was produced.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  10, 10a, 10b, 10c, 10d, 10e GaN substrate, 10m, 10n, 11m, 12m, 12n Main surface, 11 Substrate, 12 GaN crystal, 20 Semiconductor layer, 30 First electrode, 40 Second electrode, 100 HVPE Equipment: 101 First source gas cylinder, 102 Doping gas cylinder, 103 Second source gas cylinder, 104 First gas introduction pipe, 105 Doping gas introduction pipe, 106 Second gas introduction pipe, 107 Source boat, 108 Susceptor, 109 Heater, 110 Reaction Pipe, 111 exhaust pipe, 120 liner pipe, G1 first source gas, G2 doping gas, G3 second source gas, G7 reaction gas.

Claims (4)

The absorption coefficient for light having a wavelength of 380 nm and light having a wavelength of 1500 nm is 7 cm ⁻¹ or more, the absorption coefficient for light having a wavelength of 500 nm to 780 nm is less than 7 cm ⁻¹ , and the specific resistance is 0.02 Ωcm or less. A GaN substrate. The GaN substrate according to claim 1, wherein an absorption coefficient for light having a wavelength of 440 nm or more and 780 nm or less is less than 7 cm- ¹ .   A light emitting device comprising the GaN substrate according to claim 1 and having a peak wavelength of light emission of 500 nm or more and 780 nm or less.   A light emitting device comprising the GaN substrate according to claim 2 and having a light emission peak wavelength of 440 m or more and 780 nm or less.

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