Group iii nitride crystal, group iii nitride substrate, and method for producing group iii nitride crystal

Abstract

The present application provides a Group III nitride crystal, a Group III nitride substrate, and a method for producing a Group III nitride crystal. A Group III nitride crystal having excellent electrical conductivity and a low light absorption coefficient is provided. The Group III nitride crystal is doped with an N-type dopant and a germanium element, and the concentration of the N-type dopant is 1 x 10 19 cm ‑3 The concentration of the germanium element is 9 times or more the concentration of the N-type dopant.

Description

Technical Field

[0001] This invention relates to group III nitride crystals, group III nitride substrates, and apparatus for manufacturing group III nitride crystals. Background Technology

[0002] Semiconductors with group III nitride substrates are used in optical devices such as semiconductor lasers and light-emitting diodes, as well as in high-frequency or high-power electronic devices. Compared to silicon-based devices, such semiconductors offer the potential for reduced switching losses during power conversion, and have therefore attracted significant attention in recent years. To fabricate high-frequency or high-power electronic devices, devices need to be fabricated on high-quality group III nitride substrates capable of suppressing crystal defects generated in the device layers. Such group III nitride substrates are sometimes manufactured by dicing multiple pieces from a group III nitride crystal.

[0003] Methods for manufacturing group III nitride crystals include, for example, hydride vapor phase growth (hereinafter also known as HVPE), ammonothermal method, sodium flux method, and oxide vapor phase growth (hereinafter also known as OVPE).

[0004] In the HVPE method, hydrogen halide gas is introduced into a group III raw material to generate a halide gas, which is then used as the raw material gas for crystal growth. For example, in the case of gallium nitride crystal growth, gallium chloride (e.g., GaCl) gas is generated by introducing HCl gas into Ga metal, and the gallium chloride-containing gas is used as a group III source, thereby achieving high-speed growth of 1 mm / h or higher (see, for example, Non-Patent Document 1). In the HVPE method, it is known that group III nitride crystals with N-type conductivity can be obtained mainly by adding silicon, germanium, oxygen, etc., to the group III nitride crystal. For example, by adding oxygen to the crystal using the HVPE method, gallium nitride crystals with N-type conductivity are produced (see, for example, Patent Document 1). Furthermore, in the HVPE method, by reducing the impurity concentration added to the gallium nitride crystal, an absorption coefficient of 1 cm⁻¹ relative to light with energy lower than 3.39 eV, which is the band gap of gallium nitride, is obtained. -1 The following are examples of transparent crystals (see, for example, Non-Patent Document 2).

[0005] In the ammonothermal process, to manufacture gallium nitride crystals, single-crystal gallium nitride is produced from polycrystalline gallium nitride in supercritical ammonia (see, for example, Patent Document 2). In this method, impurities can be added to the manufactured crystal at a high concentration, but sometimes the crystal is colored yellow, brown, or black (see, for example, Non-Patent Document 3).

[0006] In the OVPE process, oxygen is added at a high concentration to group III nitride crystals using an oxide feedstock gas to produce crystals (see, for example, Patent Document 3). In this method, group III oxide gas is reacted with a nitrogen-containing gas to produce group III nitride crystals.

[0007] By processing the group III nitride crystal manufactured using the method described above, a group III nitride substrate can be obtained. From a manufacturing cost perspective, it is desirable to cut multiple wafers from the group III nitride crystal to manufacture the substrate, thereby reducing material loss during processing. As processing methods for group III nitride substrates, non-contact processing methods using lasers, such as laser slicing and stealth cutting, are sometimes employed. In such non-contact processing methods, material loss during substrate manufacturing can be significantly reduced compared to mechanical processing methods such as wire slicing.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2000-44400

[0011] Patent Document 2: Japanese Patent Application Publication No. 2003-277182

[0012] Patent Document 3: WO2015 / 053341A1

[0013] Non-patent literature

[0014] Non-patent literature 1: Yoshida et al., Physics Status Solidi C No.8, No.7-8, 2110-2112 (2011)

[0015] Non-patent literature 2: S. Pimputkar et al., J. Cryst. Growth 432 (2015) 49-53

[0016] Non-patent literature 3: R. Kucharski et al., Crystals 2017, 7, 187 Summary of the Invention

[0017] The problem that the invention aims to solve

[0018] However, in any of the HVPE, ammonothermal, sodium flux, and OVPE methods, if an N-type dopant is added to the group III nitride crystal to increase the carrier concentration and improve the conductivity of the group III nitride crystal, the crystal will be colored and the light absorption coefficient will increase.

[0019] Therefore, when manufacturing group III nitride substrates by cutting from group III nitride crystals with high concentrations of N-type dopant to improve conductivity, light is absorbed at or near the surface of the crystal during photoprocessing, making it difficult to process the interior. To prevent crystal discoloration, the concentration of N-type dopant has been adjusted to maintain a low absorption coefficient over a wide wavelength range.

[0020] However, in this case, it is difficult to sufficiently improve conductivity. That is, it is not easy to obtain a group III nitride crystal that combines low absorption coefficient and high conductivity.

[0021] The present invention was made in view of the above circumstances, and its object is to provide a group III nitride crystal with excellent conductivity and low light absorption coefficient.

[0022] Methods for solving problems

[0023] The group III nitride crystal of the present invention is doped with an N-type dopant and germanium, wherein the concentration of the N-type dopant is 1 × 10⁻⁶. 19 cm -3 The concentration of germanium is more than nine times that of the N-type dopant.

[0024] The group III nitride substrate of the present invention comprises the above-described group III nitride crystal.

[0025] The method for manufacturing group III nitride crystals of the present invention includes:

[0026] The process of introducing gases containing Group III elements, nitrogen, N-type dopants, and germanium; and

[0027] The process of reacting the introduced gas containing group III elements, the gas containing nitrogen, the gas containing N-type dopant, and the gas containing germanium to generate group III nitride crystals on a seed substrate.

[0028] The effects of the invention

[0029] According to the present invention, it is possible to obtain group III nitride crystals with excellent electrical conductivity and low light absorption coefficient. Attached Figure Description

[0030] Figure 1 This is a cross-sectional view schematically illustrating an example of the apparatus used in the method for manufacturing group III nitride crystals according to Embodiment 1.

[0031] Figure 2 This is a graph showing the absorption coefficients of the group III nitride crystals manufactured in the examples and comparative examples.

[0032] Explanation of reference numerals in the attached figures

[0033] 101: Reaction Vessel

[0034] 102: Germanium-containing gas inlet tube

[0035] 103: Gas introduction tube containing N-type dopant

[0036] 104: Nitrogen-containing gas inlet tube

[0037] 105: Gas inlet tube containing Group III elements

[0038] 106: Gas generation section containing Group III elements

[0039] 107: Materials containing Group III elements

[0040] 108: Gas inlet pipe for generating gas containing Group III elements

[0041] 109: Gas exhaust pipe

[0042] 111: Reactor Heater

[0043] 112: Germanium-containing gas inlet pipe heater

[0044] 113: Gas inlet tube heater containing N-type dopant

[0045] 114: Nitrogen-containing gas inlet pipe heater

[0046] 115: Heater for generating gases containing Group III elements

[0047] 201: Seed substrate

[0048] 202: Substrate tray Detailed Implementation

[0049] The first scheme uses a group III nitride crystal doped with an N-type dopant and germanium.

[0050] The concentration of the above-mentioned N-type dopant is 1×10⁻⁶. 19 cm -3 above,

[0051] The concentration of germanium is more than nine times that of the N-type dopant.

[0052] Regarding the second scheme of group III nitride crystals, based on the first scheme described above, the concentration of the N-type dopant can be 1×10⁻⁶. 19 cm -3 Above and 5×10 21 cm -3 the following.

[0053] Regarding the group III nitride crystal of the third scheme, based on the first or second scheme described above, the N-type dopant may contain at least one of silicon and oxygen.

[0054] Regarding the fourth scheme of group III nitride crystals, based on the third scheme mentioned above, the N-type dopant can contain oxygen.

[0055] Regarding the fifth scheme of group III nitride crystals, based on any of the first to fourth schemes mentioned above, the absorption coefficient of the aforementioned group III nitride crystals becomes 60 cm⁻¹. -1 Light with the following energies can exist in the range of band gap energies lower than those of the aforementioned Group III nitride crystals.

[0056] Regarding the group III nitride crystal of the sixth scheme, based on any of the first to fourth schemes mentioned above, the absorption coefficient of the group III nitride crystal becomes 60 cm⁻¹. -1 Light with the following energies can exist in the range below 3.39 eV.

[0057] Regarding the group III nitride crystal of the seventh scheme, based on any of the first to sixth schemes mentioned above, the resistivity can be below 1 mΩ·cm.

[0058] The group III nitride substrate of the eighth embodiment has a group III nitride crystal of any one of the first to seventh embodiments described above.

[0059] Regarding the group III nitride substrate of the ninth scheme, based on the eighth scheme mentioned above, the thickness can be 100 μm or more.

[0060] The method for manufacturing group III nitride crystals according to scheme 10 includes:

[0061] The process of introducing gases containing Group III elements, nitrogen, N-type dopants, and germanium; and

[0062] The process of generating and growing a group III nitride crystal on a seed substrate by reacting the introduced gas containing group III elements, the gas containing nitrogen, the gas containing N-type dopant, and the gas containing germanium.

[0063] Regarding the method for manufacturing group III nitride crystals in the eleventh scheme, based on the tenth scheme mentioned above, the N-type dopant gas may include at least one of silicon-containing gas and oxygen-containing gas.

[0064] Regarding the manufacturing method of the group III nitride crystal in the twelfth scheme, based on the eleventh scheme, the gas containing the N-type dopant may include the gas containing the oxygen element.

[0065] Regarding the method for manufacturing group III nitride crystals in scheme thirteen, based on any of schemes ten to twelfth mentioned above, the germanium-containing gas may contain at least one selected from germanium gas, GeO gas, GeH4 gas, GeH3Cl gas, and GeH2Cl2 gas.

[0066] Regarding the method for manufacturing group III nitride crystals in scheme fourteen, based on any of schemes ten to thirteen above, the nitrogen-containing gas may include at least one selected from ammonia, hydrazine, and dimethylhydrazine.

[0067] Regarding the method for manufacturing group III nitride crystals in scheme 15, based on any of schemes 10 to 14 above, the group III element-containing gas may contain at least one of group III element oxides and group III element halides.

[0068] Regarding the method for manufacturing group III nitride crystals in scheme sixteen, based on any of schemes ten to fifteen above, the aforementioned group III element-containing gas may include at least one of Ga2O and GaCl.

[0069] <The Process of Completing This Invention>

[0070] First, the inventors will explain the process of completing the present invention.

[0071] The inventors discovered that in group III nitride crystals with the same concentration of N-type dopant and the same carrier concentration, the absorption coefficients sometimes differ significantly. They believed that the direct cause of the decrease in absorption coefficient was not the N-type dopant and explored the underlying principle.

[0072] The inventors analyzed the light energy dependence of the absorption coefficient of a group III nitride crystal containing a high concentration of N-type dopant. The results showed that the absorption coefficient tails exponentially from the band edge of the group III nitride crystal towards the lower energy side. Therefore, the increase in the absorption coefficient over a wide wavelength region when a high concentration of N-type dopant is added to a group III nitride crystal may be caused by a phenomenon known as the Urbach tail.

[0073] The phenomenon known as the Urbach band tail is also visible in GaAs, a compound semiconductor. In GaAs, the more the concentration of p-type dopant is added, the stronger the Urbach band tail is observed, thereby increasing the absorption coefficient in a wide wavelength region.

[0074] Next, the inventors discovered that the Urbach belt tail is proportional to the square of the ion valence of the point defects (including substitution by impurities) in the crystal that contribute to this phenomenon, as well as the density of the point defects.

[0075] However, it is known that vacancy defects in group III elements function as trivalent p-type dopants in group III nitride crystals. In contrast, silicon and oxygen, which are typically N-type dopants, function as monovalent N-type dopants in group III nitride crystals. Since p-type and N-type dopants differ, a simple comparison is not possible. However, based on ion valence, it is inferred that vacancy defects in group III elements significantly improve the absorption coefficient compared to N-type dopants.

[0076] Furthermore, the inventors focused on the fact that a high concentration of N-type dopant can increase the density of vacancy defects in group III elements within group III nitride crystals. They then established the hypothesis that the N-type dopant is not the direct cause of the increased absorption coefficient, but rather that the increased density of vacancy defects in group III elements resulting from adding a high concentration of N-type dopant to group III nitride crystals is the reason for the increased absorption coefficient.

[0077] Next, the inventors believe that if other elements can be used to fill the vacancies in group III elements, the Urbach tail phenomenon may be reduced. It is inferred that candidate elements should possess the following characteristics: elements with atomic radii close to those of group III elements. Furthermore, in order not to hinder the effect of N-type dopants, it is important that the other elements used to fill the vacancies exhibit N-type characteristics when added. Moreover, it is believed that in group III nitride crystals containing high concentrations of N-type dopants, using elements different from the constituent elements of group III nitrides and the N-type dopants (mainly silicon and oxygen) as other elements can increase entropy. It is speculated that by increasing entropy, other elements stably enter the crystal and effectively function to fill the vacancies in group III elements. The inventors have found that germanium is particularly preferred as an other element satisfying the above characteristics.

[0078] Furthermore, since germanium is used to directly fill vacancy defects, it can be inferred that the higher the density of vacancy defects, the higher the concentration of germanium needs to be. That is, it was considered whether, in the case of a high concentration of N-type dopant in a group III nitride crystal, a certain concentration of germanium could be added based on the concentration of the N-type dopant, thereby achieving both low light absorption and high conductivity.

[0079] It should be noted that the determination of point defects of group III elements in group III nitride crystals can be carried out by the positron pair annihilation method. However, in this method, since positrons generated by radioactive isotopes are used for determination, there is a danger, and it is difficult to easily carry out the determination. In addition, in order to quantify the defect density, it is necessary to compare with group III nitride crystals with a very low defect density. However, since it is difficult to obtain crystals with a very low defect density, it is difficult to carry out the determination of point defects of group III elements. Based on these circumstances, it is difficult to determine the mechanism by which the addition of germanium element as described above reduces the absorption coefficient of group III nitride crystals. Ultimately, it is the speculation of the inventors.

[0080] Hereinafter, the group III nitride crystals, the manufacturing method of group III nitride crystals, and the manufacturing apparatus of group III nitride crystals in the embodiments of the present invention will be described in detail.

[0081] (Embodiment 1)

[0082] <Group III nitride crystal>

[0083] The group III nitride crystal of Embodiment 1 (hereinafter, sometimes referred to as crystal X.) is doped with an N-type dopant and germanium element. The concentration of the N-type dopant in crystal X is 1×10 19 cm -3 or more. In addition, the concentration of germanium element in crystal X is 9 times or more the concentration of the N-type dopant.

[0084] Crystal X has excellent conductivity by doping an N-type dopant at a concentration of 1×10 19 cm -3 or more. Therefore, the group III nitride substrate formed using crystal X is useful for high-frequency or high-output power electronic devices and the like. In crystal X, in addition to the N-type dopant, germanium element is doped at a concentration of 9 times or more the concentration of the N-type dopant. Thus, although crystal X contains an N-type dopant at a concentration of 1×10 19 cm -3 or more, it can have a low absorption coefficient. That is, although crystal X contains an N-type dopant at a concentration of 1×10 19 cm -3 or more, it is not easily colored. In the processing method using a laser, it is necessary to allow light to sufficiently enter the processing portion of the workpiece. Therefore, in the light wavelength region used for processing, it is necessary to make the absorption coefficient of the processing portion of the workpiece sufficiently low. For example, in the case of manufacturing a group III nitride substrate from crystal X by laser processing, since crystal X has a low absorption coefficient, the laser is not easily absorbed by crystal X, and crystal X can be processed well.

[0085] The N-type dopant preferably contains at least one of silicon and oxygen. In this case, the conductivity of crystal X can be significantly improved.

[0086] N-type dopants preferably contain oxygen. In this case, especially when crystal X is fabricated by the OVPE method, oxygen can be well added to crystal X.

[0087] The preferred concentration of the N-type dopant is 1 × 10⁻⁶. 19 cm -3 Above and 5×10 21 cm -3 In this case, the conductivity of crystal X can be further improved.

[0088] The concentration of germanium is more than nine times that of the N-type dopant. Furthermore, there is no specific upper limit to the concentration of germanium; for example, it can be 2 × 10⁻⁶. 22 cm -3 In this case, crystal X has superior conductivity and a lower absorption coefficient, which further prevents coloration of crystal X.

[0089] The absorption coefficient of crystal X is 60 cm⁻¹. -1 Light with the following energy is preferably located in the range below the bandgap energy value of crystal X. When processing semiconductor materials, light with energy above the bandgap energy value of the semiconductor material is easily absorbed near the surface of the semiconductor material. Therefore, when processing crystal X, it is preferable to use a laser that outputs light with energy below the bandgap energy value of crystal X. Furthermore, particularly by using an absorption coefficient of 60 cm⁻¹ -1 The light used for processing is light with the following energy, making it less susceptible to absorption by crystal X. Therefore, crystal X can be processed particularly well, reducing material loss during the fabrication of group III nitride substrates from crystal X. Furthermore, by using an absorption coefficient of 60 cm⁻¹... -1 Processing is performed using light of the following energy, so that even when a group III nitride substrate with a thickness of 100 μm or more is manufactured from crystal X, the light used for processing can easily reach deep into the substrate from the surface of crystal X. Therefore, processing can be performed well.

[0090] It should be noted that the value of the bandgap energy varies depending on the composition of crystal X. For example, in the processing of gallium nitride, if a laser that emits light with an energy lower than the bandgap of 3.39 eV is used, the processing can be carried out well. In addition, in the processing of aluminum nitride, if a laser that emits light with an energy lower than the bandgap of 6.2 eV is used, the processing can be carried out well. The lower limit of the energy value of the light used in the processing is not particularly limited, and for example, it can be 1 eV. By using light with an energy of 1 eV or more for processing, the laser is not easily absorbed by the high-concentration free carriers present in crystal X with a high concentration of N-type dopants, and it is easy for the laser to enter the interior of the crystal. In this case, the absorption coefficient of crystal X becomes 60 cm -1 It is sufficient that light with an energy below this exists within the range of 1 eV or more and lower than the bandgap energy value of crystal X.

[0091] The absorption coefficient of crystal X becomes 60 cm -1 It is preferred that light with an energy below this exists within the range lower than 3.39 eV. In the case where crystal X is gallium nitride, by using light with an energy within the range of 1 eV or more and lower than 3.39 eV and having an absorption coefficient of 60 cm -1 below, the processing of crystal X can be carried out particularly well. The absorption coefficient of crystal X becomes 60 cm -1 It is preferred that light with an energy below this exists within the range of 1 eV or more and lower than 3.39 eV.

[0092] The resistivity of crystal X is preferably 1 mΩ·cm or less. In this case, the group III nitride substrate made of crystal X can have excellent conductivity. The resistivity of crystal X is more preferably 0.7 mΩ·cm or less.

[0093] By processing crystal X, a group III nitride substrate can be obtained. That is, the group III nitride substrate of the present invention contains crystal X. The thickness of the group III nitride substrate is preferably 100 μm or more. In this case, the group III nitride substrate has higher strength.

[0094] <Manufacturing method of group III nitride crystal>

[0095] Next, refer to Figure 1 The manufacturing method of crystal X (group III nitride crystal) will be described. In the following description, examples of manufacturing using gases will be described, but even in the case of manufacturing in a solution or melt, the crystal X of the present invention can be obtained.

[0096] The method for manufacturing crystal X includes a step of introducing a raw material gas and a step of generating and growing crystal X. In the step of introducing the raw material gas, a gas containing a group III element, a gas containing nitrogen, a gas containing an N-type dopant, and a gas containing germanium are introduced. In the step of generating and growing crystal X, the introduced gas containing a group III element, a gas containing nitrogen, a gas containing an N-type dopant, and a gas containing germanium react to generate and grow crystal X on a seed substrate 201 disposed on a substrate tray 202.

[0097] It should be noted that the feed gas can be four different types of gases, or three or fewer types of gases. That is, the gases containing Group III elements, nitrogen, N-type dopants, and germanium can be different from each other or the same. For example, the same gas can be used as the nitrogen-containing gas and the germanium-containing gas. Similarly, the same gas can be used as the Group III-containing gas and the N-type dopant gas.

[0098] In the method for manufacturing a group III nitride crystal according to Embodiment 1, the group III element-containing gas preferably includes at least one of group III element oxides and group III element halides. In this case, a high concentration of the group III element-containing gas can be maintained. Furthermore, the growth rate of crystal X can be accelerated. In the case of manufacturing gallium nitride, the group III element-containing gas particularly preferably includes at least one of Ga₂O or GaCl.

[0099] In the manufacturing method of this embodiment, when using Group III element oxide gas or Group III element halide gas as the Group III element-containing gas, it is preferable to further include a step of reacting a Group III element-containing material with the gas to generate the Group III element-containing gas. In this case, it is easier to prevent the gas from becoming unstable in environments other than high temperatures, causing solid precipitation, and making it difficult to control the gas supply. The step of generating the Group III element-containing gas preferably includes at least one of the steps of reacting a Group III element-containing material with an oxidizing gas or a halide gas and a step of reducing a Group III element oxide solid with hydrogen to generate a Group III element oxide gas.

[0100] The oxidizing gas preferably includes at least one of water vapor and oxygen. Additionally, the halide gas preferably includes HCl.

[0101] Examples of reactions between materials containing Group III elements and oxidizing gases include:

[0102]

[0103] Examples of reactions between materials containing Group III elements and halide gases include:

[0104]

[0105] Examples of reactions between solid oxides of Group III elements and hydrogen include, for example:

[0106]

[0107] <Nitrogen-containing gases>

[0108] In the method for manufacturing Group III nitride crystals according to this embodiment, the nitrogen-containing gas preferably includes at least one selected from ammonia, hydrazine, and dimethylhydrazine. Ammonia, hydrazine, and dimethylhydrazine have boiling points below 200°C, and therefore can be more easily supplied to the reaction vessel in a gaseous state, resulting in higher reactivity. Therefore, crystal X can be grown more effectively.

[0109] <Gas containing N-type dopants>

[0110] In the method for manufacturing a Group III nitride crystal according to this embodiment, the N-type dopant gas preferably includes at least one of a silicon-containing gas and an oxygen-containing gas. In this case, it can be easily supplied to the reaction vessel in a gaseous state at room temperature, and furthermore, it exhibits excellent reactivity, thus enabling the crystal X to grow well. The N-type dopant gas more preferably includes an oxygen-containing gas.

[0111] <Silicon-containing gas>

[0112] The silicon-containing gas preferably comprises at least one selected from SiH4, SiH3Cl, and SiH2Cl2. In this case, the silicon-containing gas, which is in a gaseous state at room temperature, can be easily supplied into the reaction vessel, and it has high reactivity, thus enabling crystal X to grow well.

[0113] <Oxygen-containing gases>

[0114] The oxygen-containing gas preferably comprises at least one selected from water vapor, oxygen, N2O gas, NO gas, NO2 gas, CO gas, and CO2 gas. In this case, the oxygen-containing gas, which is in a gaseous state at room temperature, can be easily supplied into the reaction vessel, and it has high reactivity, thus enabling crystal X to grow well.

[0115] The N-type dopant gas particularly preferably comprises at least one selected from GeO gas, Ga2O gas, and In2O gas. In this case, the N-type dopant gas can be readily generated at a temperature close to the manufacturing temperature of crystal X, and it has high reactivity, thus enabling crystal X to grow particularly well.

[0116] <Germanium-containing gas>

[0117] The germanium-containing element gas preferably contains at least one selected from GeH4, GeH3Cl, and GeH2Cl2. In this case, it is possible to easily supply the germanium-containing element gas in a gaseous state at room temperature into the reaction vessel, and since the reactivity is high, crystal X can grow well.

[0118] It should be noted that in the method for manufacturing a group III nitride crystal of the present embodiment, as the group III element-containing gas, nitrogen element-containing gas, N-type dopant-containing gas, germanium-containing element gas, and carrier gas, different gases may be used respectively, or the same gas may be used. For example, Ga2O gas may be used as the group III element-containing gas, and Ga2O may also be used as the N-type dopant-containing gas. Thus, in the case of using the same gas, sometimes the gas introduction paths can be aggregated, and the manufacturing equipment can be simplified.

[0119] In the method for manufacturing a group III nitride crystal of the present embodiment, in the growth process of growing crystal X, from the viewpoint of the reactivity of the gases used in the manufacturing, the temperature at which the group III element-containing gas reacts with the nitrogen element-containing gas is preferably 700 °C or higher and 1500 °C or lower. From the viewpoint of ensuring the crystal growth rate and improving the crystal quality, it is more preferably 1000 °C or higher and 1400 °C or lower.

[0120] The method for manufacturing a group III nitride crystal of the present embodiment can be implemented, for example, by using Figure 1 the manufacturing apparatus for a group III nitride crystal shown. It should be noted that Figure 1 the manufacturing apparatus for a group III nitride crystal shown is merely an example, and as long as it is an apparatus capable of manufacturing crystal X of the present invention, it is not limited to Figure 1 the manufacturing apparatus. In this figure, for easy understanding, there are cases where the sizes and ratios of each part are different from the actual ones. In addition, sometimes the materials that need to be pre-arranged in the manufacturing apparatus when manufacturing crystal X are shown.

[0121] <Manufacturing Apparatus for Group III Nitride Crystal>

[0122] In this manufacturing apparatus for a group III nitride crystal, a germanium-containing element gas introduction pipe 102, an N-type dopant-containing gas introduction pipe 103, a nitrogen element-containing gas introduction pipe 104, a group III element-containing gas introduction pipe 105, and a gas exhaust pipe 109 are connected to a reaction vessel 101. Inside the reaction vessel 101, a substrate tray 202 provided with a seed substrate 201 is arranged. It should be noted that the arrangements of the germanium-containing element gas introduction pipe 102, the N-type dopant-containing gas introduction pipe 103, the nitrogen element-containing gas introduction pipe 104, and the group III element-containing gas introduction pipe 105 are not limited to Figure 1 the arrangements shown.

[0123] As mentioned above, four different types of gases can be used as the feedstock gas, or three or fewer types of gases can be used. Therefore, in Figure 1 The manufacturing apparatus shown is provided with four inlet tubes: a germanium-containing gas inlet tube 102, an N-type dopant-containing gas inlet tube 103, a nitrogen-containing gas inlet tube 104, and a group III element-containing gas inlet tube 105. However, the apparatus may have three or fewer inlet tubes.

[0124] A gas containing Group III elements reacts with a gas containing nitrogen elements, and crystal X grows on a seed substrate 201. Unreacted gases and byproduct gases are discharged from the gas exhaust pipe 109.

[0125] The group III element-containing gas is generated by reacting the group III element-containing material 107 with the group III element-containing gas introduced from the group III element-containing gas inlet pipe 108 in the group III element-containing gas generating section 106.

[0126] Furthermore, in each gas inlet pipe or reaction section, heating can be applied by each heater to adjust the gas reaction state or crystal X growth conditions to achieve the desired conditions. For example, as... Figure 1 As shown, at least one of the following can be provided: a reaction vessel heater 111 adjacent to the reaction vessel 101, a germanium-containing gas inlet pipe heater 112 adjacent to the germanium-containing gas inlet pipe 102, an N-type dopant-containing gas inlet pipe heater 113 adjacent to the N-type dopant-containing gas inlet pipe 103, a nitrogen-containing gas inlet pipe heater 114 adjacent to the nitrogen-containing gas inlet pipe 104, and a group III-containing gas generating section heater 115 adjacent to the group III-containing gas generating section 106.

[0127] Materials containing Group III elements

[0128] The material 107 containing a group III element is a material containing at least one selected from aluminum (Al), gallium (Ga), indium (In), and thallium (Tl). Furthermore, from an operational viewpoint, the material 107 containing a group III element is preferably a material that is solid or liquid at room temperature. Examples of group III element materials 107 that are solid at room temperature include Al₂O₃, Ga₂O₃, In₂O₃, Tl₂O₃, Al, In, and Tl. Examples of group III element materials 107 that are liquid at room temperature include Ga.

[0129] Examples of gases introduced into the Group III element gas generating section 106 for generating Group III element gases include hydrogen, water vapor, and hydrogen chloride. Furthermore, from the viewpoint of reaction control, the gas introduced into the Group III element gas generating section 106 is preferably mixed with a carrier gas before introduction.

[0130] <Carrier Gas>

[0131] There are no particular limitations on the carrier gas; examples include nitrogen, hydrogen, argon, and helium. A mixture of these gases can also be used as a carrier gas.

[0132] <Substrate>

[0133] The material of the seed substrate 201 is not particularly limited and can be appropriately selected according to the characteristics of the crystal X to be manufactured. For example, the seed substrate 201 is preferably a single crystal substrate having the same elemental composition ratio as the crystal X to be manufactured. Examples of materials for the seed substrate 201 include sapphire, ScAlMgO4, group III nitrides, LiAlO2, and ZnO.

[0134] It should be noted that the present invention is not limited to the embodiments described above. For example, the above-described constituent elements can be combined arbitrarily, or other embodiments implemented by removing some of the above-described constituent elements can be used as embodiments of the present invention.

[0135] (Example)

[0136] The methods for manufacturing group III nitride crystals of Examples 1-2 and Comparative Examples 1-2 will be described.

[0137] In this embodiment, a gas is used to manufacture a gallium nitride crystal, which is a group III nitride crystal. Ga₂O gas is used as the group III element-containing gas and the N-type dopant-containing gas; ammonia gas is used as the nitrogen-containing gas; and GeO gas is used as the germanium-containing gas. Ga is used as the group III element-containing material, and oxygen is used as the gas for generating the group III element-containing gas. A gallium nitride crystal is used as the seed substrate 201.

[0138] First, Ga is placed in the group III element gas generation section 106, and Ga₂O is generated using oxygen. The generated Ga₂O is supplied to the reaction vessel 101 from the group III element gas inlet pipe 105. Furthermore, ammonia gas, as a nitrogen-containing gas, is introduced into the reaction vessel 101 from the nitrogen-containing gas inlet pipe 104. Additionally, GeO gas, as a germanium-containing gas, is introduced into the reaction vessel 101 from the germanium-containing gas inlet pipe 102, thereby manufacturing group III nitride crystals.

[0139] The manufacturing conditions for group III nitride crystals are described in detail. First, each heater (111, 112, 113, 114, 115) is heated. After the temperature of the group III element gas generation section 106 reaches 1100°C and the temperature of the reaction vessel reaches 1200°C, oxygen is introduced into the group III element gas generation section 106 at a flow rate of 9 sccm, and a mixture of nitrogen and hydrogen is introduced as a carrier gas at a flow rate of 300 sccm. This mixture reacts on Ga placed in the group III element gas generation section 106 to generate Ga₂O gas. The resulting Ga₂O gas is then introduced into the reaction vessel 101 as a group III element gas and an N-type dopant gas. Furthermore, the flow rate of ammonia gas (as a nitrogen-containing gas) is set to 200 sccm, and the flow rate of GeO gas (as a germanium-containing gas) is set to 5 sccm. A mixture of nitrogen and hydrogen gas, serving as their carrier gases, is introduced into the reaction vessel 101 at a flow rate of 4 slm. Inside reaction vessel 101, Ga₂O gas reacts with ammonia gas to generate gallium nitride crystals on seed substrate 201. The gallium nitride crystal generation reaction is carried out for 5 hours. In this way, a gallium nitride crystal with a thickness of 300 μm is fabricated as an epitaxial layer on a GaN substrate.

[0140] For the gallium nitride crystal of Comparative Example 1, the flow rate of GeO gas, which is a germanium-containing gas, was set to 1 sccm, and otherwise it was manufactured in the same manner as in Example 1 above.

[0141] For the gallium nitride crystal of Comparative Example 2, germanium-containing gas was not used, but the manufacturing process was carried out in the same manner as in Example 1 above.

[0142] The crystals manufactured in Examples and Comparative Examples 1-2 were ground to a thickness of 150 μm to manufacture a self-supporting gallium nitride substrate consisting only of a crystal layer.

[0143] The properties shown in Table 1 were evaluated using the substrates of the examples and Comparative Examples 1-2 obtained in this way. It should be noted that, regarding the absorption coefficient, the minimum value of the absorption coefficient was measured among the absorption coefficients of light with energies in the range of energy below 3.39 eV for the bandgap energy of gallium nitride.

[0144] Table 1

[0145] Example Comparative Example 1 Comparative Example 2 <![CDATA[Hydrogen concentration (atoms / cm 3 )]]> <![CDATA[1.1×10 19 ]]> <![CDATA[2.1×10 20 ]]> <![CDATA[3.0×10 20 ]]> <![CDATA[Germanium concentration (atoms / cm 3 )]]> <![CDATA[1.0×10 20 ]]> <![CDATA[9.5×10 19 ]]> <![CDATA[<8.0×10 16 ]]> <![CDATA[Minimum value of absorption coefficient (cm -1 )]]> 52 75 93 Resistivity (Ω·cm) <![CDATA[5.84×10 -4 ]]> <![CDATA[1.07×10 -3 ]]> <![CDATA[1.11×10 -3 ]]>

[0146] The concentration of impurities in the gallium nitride crystals fabricated in the examples was analyzed using SIMS, and the oxygen concentration was found to be 1.1 × 10⁻⁶. 19 atoms / cm 3 The concentration of germanium is 1.0 × 10⁻⁶. 20 atoms / cm 3The concentration of germanium is higher than that of oxygen in N-type dopant, exceeding nine times the concentration of N-type dopant. Additionally, the resistivity is 5.84 × 10⁻⁶. -4 The minimum absorption coefficient is 52 cm⁻¹ relative to light with an energy of 1.48 eV. -1 The absorption coefficient is [not specified]. In the embodiments, the high concentrations of oxygen and germanium elements result in low resistivity and thus a smaller absorption coefficient.

[0147] The concentration of impurities in the gallium nitride crystal fabricated in Comparative Example 1 was analyzed using SIMS, and the oxygen concentration was found to be 2.1 × 10⁻⁶. 20 atoms / cm 3 The concentration of germanium is 9.5 × 10⁻⁶. 19 atoms / cm 3 The concentration of germanium is lower than that of oxygen in N-type dopant. Additionally, the resistivity is 1.07 × 10⁻⁶. -3 The minimum absorption coefficient is 75 cm⁻¹ relative to light with an energy of 1.23 eV. -1 The absorption coefficient.

[0148] The impurity concentration of the gallium nitride crystal fabricated in Comparative Example 2 was analyzed by SIMS, and the result showed that the oxygen content was 3.0 × 10⁻⁶. 20 atoms / cm 3 Germanium levels were below the detection limit of 8.0 × 10⁻⁶. 16 atoms / cm 3 Additionally, the resistivity is 1.11 × 10⁻⁶. -3 Ω·cm, the minimum absorption coefficient is 93 cm⁻¹ relative to light with an energy of 1.23 eV. -1 The absorption coefficient.

[0149] As shown in Table 1, the oxygen concentration of any group III nitride crystals produced in Examples 1 and 2 is 1 × 10⁻⁶. 19 atoms / cm 3 The high concentration results in a low resistivity of approximately 1 mΩ·cm. Furthermore, the concentration of germanium is 1 × 10⁻⁶. 20 atoms / cm 3 The crystals in the above embodiments have an absorption coefficient of 60 cm⁻¹ in the range below the band gap energy value. -1 Light with the following energy. On the other hand, in Comparative Examples 1 and 2, the minimum absorption coefficient was 75 cm⁻¹ in the range below the band gap energy value. -1 and 93cm -1 Therefore, it can be seen that the absorption coefficient of the crystal in the examples is smaller compared to the crystals in Comparative Examples 1-2.

[0150] The absorption coefficients of the group III nitride crystals manufactured in Examples and Comparative Examples 1-2 are shown in the figure. Figure 2 In the chart. Figure 2 This indicates the relationship between the energy value of light and the absorption coefficient for that light. For example... Figure 2 As shown, compared to Comparative Examples 1-2, in the embodiment where the concentration of germanium in the group III nitride crystal is more than 9 times that of the N-type dopant, the absorption coefficient is low over a wide range in the energy region smaller than the bandgap energy of 3.39 eV, and it exists as 60 cm⁻¹. -1 The following energy of light.

[0151] Based on the above results, in the group III nitride crystal of the present invention, even when the concentration of the N-type dopant in the crystal is increased to reduce resistivity, the absorption coefficient over a wide energy region can be reduced by containing germanium at a specific concentration or higher in the crystal. Therefore, laser-based internal processing of the crystal becomes possible.

[0152] It should be noted that, in this invention, there is a possibility of appropriately combining any of the above-described various implementation methods and / or embodiments, which can achieve the effects of each implementation method and / or embodiment.

[0153] Industrial availability

[0154] As described above, the group III nitride crystal, the method for manufacturing group III nitride crystal, and the apparatus for manufacturing group III nitride crystal according to the present invention can process group III element nitride crystals with high conductivity in a manner with low material loss, and fabricate group III nitride semiconductor substrates, which can be expected to improve the performance and reduce the cost of high-frequency or high-output power electronic devices.

Claims

1. A group III nitride crystal, wherein, N-type dopants other than germanium and germanium itself, The N-type dopant other than germanium includes at least one of silicon and oxygen. The concentration of the N-type dopant other than germanium is 1×10⁻⁶. 19 cm -3 above, The concentration of germanium is more than nine times the concentration of N-type dopants other than germanium.

2. The group III nitride crystal according to claim 1, wherein, The concentration of the N-type dopant other than germanium is 1×10⁻⁶. 19 cm -3 Above and 5×10 21 cm -3 the following.

3. The group III nitride crystal according to claim 1 or 2, wherein, The N-type dopant, other than germanium, includes oxygen.

4. The group III nitride crystal according to claim 1 or 2, wherein, The absorption coefficient of the group III nitride crystal is 60 cm⁻¹. -1 Light with the following energies exists in the range below the band gap energy value of the group III nitride crystal.

5. The group III nitride crystal according to claim 1 or 2, wherein, The absorption coefficient of the group III nitride crystal is 60 cm⁻¹. -1 Light with the following energies exists in the range below 3.39 eV.

6. The group III nitride crystal according to claim 1 or 2, wherein, The resistivity is below 1 mΩ•cm.

7. A group III nitride substrate comprising any one of the group III nitride crystals according to claims 1 to 6.

8. The group III nitride substrate according to claim 7, wherein, The thickness is 100μm or more.

9. A method for manufacturing the group III nitride crystal according to claim 1, comprising: The process of introducing gases containing group III elements, gases containing nitrogen, N-type dopants other than germanium, and gases containing germanium. The process of reacting the introduced gas containing group III elements, the gas containing nitrogen, the N-type dopant gas other than germanium, and the gas containing germanium to generate and grow group III nitride crystals on a seed substrate. The N-type dopant gas other than germanium contains at least one of silicon-containing gas and oxygen-containing gas.

10. The method for manufacturing group III nitride crystals according to claim 9, wherein, The N-type dopant gas, other than that containing germanium, includes the oxygen-containing gas.

11. The method for manufacturing group III nitride crystals according to claim 9 or 10, wherein, The germanium-containing gas contains at least one selected from germanium gas, GeO gas, GeH4 gas, GeH3Cl gas, and GeH2Cl2 gas.

12. The method for manufacturing group III nitride crystals according to claim 9 or 10, wherein, The nitrogen-containing gas includes at least one selected from ammonia, hydrazine, and dimethylhydrazine.

13. The method for manufacturing group III nitride crystals according to claim 9 or 10, wherein, The group III-containing gas includes at least one of group III oxides and group III halides.

14. The method for manufacturing group III nitride crystals according to claim 9 or 10, wherein, The gas containing group III elements includes at least one of Ga2O and GaCl.

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