Laminated body having a single crystal substrate of a group 13 element nitride

Abstract

[Problem] To provide a laminate having a buffer layer on a group 13 element nitride single crystal, a channel layer having a thickness of 700 nm or less on the buffer layer, and a barrier layer on the channel layer, wherein decreases in sheet carrier density and carrier mobility are suppressed. [Solution] This laminate 1 comprises: a group 13 element nitride single crystal substrate 2 composed of a group 13 element nitride single crystal and having a first main surface 2a and a second main surface 2b; a buffer layer 3 provided on the first main surface 2a of the group 13 element nitride single crystal substrate 2; a channel layer 4 provided on the buffer layer 3; and a barrier layer 5 provided on the channel layer 4. The thickness of the channel layer 4 is 700 nm or less, and the off angle of the first main surface 2a of the group 13 element nitride single crystal substrate 2 is 0.4° to 1.0°, inclusive.

Description

[Technical Field]

[0001] The present invention relates to a laminate having a single crystal substrate of a nitride of a group 13 element. [Background technology]

[0002] Nitride semiconductor devices are widely used not only in optical devices but also in electronic devices such as high-electron mobility transistors (HEMTs). For example, an epitaxial substrate is known in which a buffer layer, a channel layer, and a barrier layer are formed on a freestanding substrate made of semi-insulating zinc-doped gallium nitride single crystal.

[0003] For example, Patent Document 1 discloses that in a HEMT structure on a silicon carbide substrate, the thickness of the channel layer is set to less than 500 nm in order to suppress both leakage current and current collapse.

[0004] Furthermore, heteroepitaxial growth of gallium nitride films on heterogeneous substrates can lead to the generation of numerous defects due to differences in lattice constant and thermal expansion coefficient between the gallium nitride and the heterogeneous substrate. For this reason, homoepitaxial growth of gallium nitride films on gallium nitride substrates has also been investigated.

[0005] When using a gallium nitride substrate, it is desirable to use a semi-insulating gallium nitride substrate to prevent leakage current between the source and drain electrodes when the HEMT device is driven at high voltage, and it is known that doping elements that form deep acceptor levels, such as transition metal elements, into the gallium nitride single crystal is effective in achieving this. Patent documents 2, 3, and 4 describe the use of zinc, manganese, and iron as doping elements.

[0006] Patent Documents 5 and 6 disclose the use of a zinc-doped semi-insulating free-standing gallium nitride substrate as an epitaxial substrate for a HEMT device. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2021-2616 [Patent Document 2] Patent 5039813 [Patent Document 3] Patent Publication No. 2006-24597 [Patent Document 4] Special Table 2007-534580 [Patent Document 5] Patent 6730302 [Patent Document 6] Patent 6705831 Summary of the Invention [Problem to be solved by the invention]

[0008] Patent Document 1 discloses that in a HEMT structure on a silicon carbide substrate, the thickness of the channel layer is set to less than 500 nm in order to suppress both leakage current and current collapse. Even when the HEMT element is operated in a high frequency band of, for example, several tens of GHz or more, it is considered effective to make the film thickness of the channel layer thin in order to prevent deterioration of characteristics due to the parasitic capacitance of the channel layer.

[0009] Therefore, in order to improve the characteristics of HEMT devices, the inventors fabricated and evaluated an epitaxial substrate including a thin-film channel layer on a single crystal substrate of a group 13 element nitride, but encountered problems of a decrease in the sheet carrier density and carrier mobility, which are performance indicators.

[0010] An object of the present invention is to suppress a decrease in sheet carrier density and carrier mobility in a stack having a buffer layer provided on a first main surface of a group 13 element nitride single crystal substrate, a channel layer having a thickness of 700 nm or less provided on the buffer layer, and a barrier layer provided on the channel layer. [Means for solving the problem]

[0011] The present invention provides a Group 13 element nitride single crystal substrate comprising a Group 13 element nitride single crystal and having a first main surface and a second main surface; a buffer layer provided on the first main surface of the Group 13 element nitride single crystal substrate; a channel layer disposed on the buffer layer; and a barrier layer provided on the channel layer; A laminate having The channel layer has a thickness of 700 nm or less, and the off-angle of the first main surface of the Group 13 element nitride single crystal substrate is 0.4° to 1.0°. [Effects of the Invention]

[0012] The present inventors have discovered that a stack having a buffer layer provided on a first main surface of a Group 13 element nitride single crystal substrate, a channel layer having a thickness of 700 nm or less provided on the buffer layer, and a barrier layer provided on the channel layer can suppress decreases in sheet carrier density and carrier mobility, and have arrived at the present invention. Although the reason for this effect is not clear, it is believed that by setting the off-angle of the first main surface of the Group 13 element nitride single crystal substrate to 0.4° to 1.0°, the surface flatness of the thinned channel layer was improved, which contributed to the improvements in sheet carrier density and carrier mobility. [Brief explanation of the drawings]

[0013] [Figure 1] 1(a) is a schematic diagram showing a laminate 1 according to an embodiment of the present invention, and FIG. 1(b) is a schematic diagram showing a composite substrate 8 for forming an epitaxially grown layer. [Figure 2] FIG. 1(a) is a schematic perspective view of a representative group 13 element nitride single crystal substrate 100 according to a preferred embodiment, and FIG. 1(b) is a schematic explanatory view illustrating the plane orientations and crystal planes in the crystal structure of the group 13 element nitride single crystal substrate according to a preferred embodiment. [Figure 3]1 is a graph showing the dependency of the sheet carrier density of the channel layer on the off-angle of a zinc-doped group 13 element nitride single crystal substrate. [Figure 4] 1 is a graph showing the dependence of carrier mobility in a channel layer on the off-angle of a zinc-doped group 13 element nitride single crystal substrate. [Figure 5] 1 is a photograph showing the surface morphology of a channel layer when the off-angle of the first main surface of a zinc-doped Group 13 element nitride single crystal substrate is 0.66°. [Figure 6] 1 is a photograph showing the surface morphology of a channel layer when the off-angle of the first main surface of a zinc-doped Group 13 element nitride single crystal substrate is 0.09°. [Figure 7] 1 is a photograph showing the surface morphology of a channel layer when the off-angle of the first main surface of a zinc-doped Group 13 element nitride single crystal substrate is 1.15°. [Figure 8] 1 is a graph showing an example of the relationship between the off-angle of the first main surface of a zinc-doped Group 13 element nitride single crystal substrate and the carbon concentration in the channel layer. DETAILED DESCRIPTION OF THE INVENTION

[0014] FIG. 1(a) is a schematic diagram of a laminate 1 according to one embodiment of the present invention. The group 13 element nitride single crystal substrate 2 has a first main surface 2a and a second main surface 2b. The first main surface 2a of the group 13 element nitride single crystal substrate 2 is selected as a film formation surface, and an epitaxially grown layer is formed on the first main surface 2a. Specifically, in this example, a buffer layer 3 is formed on the first main surface 2a of the group 13 element nitride single crystal substrate 2, a channel layer 4 is formed on the main surface 3a of the buffer layer 3, and a barrier layer 5 is formed on the main surface 4a of the channel layer 4. A predetermined electrode or the like can be provided on the main surface 5a of the barrier layer 5.

[0015] The group 13 element nitride single crystal substrate 2 is made of a group 13 element nitride single crystal, and has a first main surface 2a and a second main surface 2b. The group 13 element is a group 13 element defined by IUPAC, and is particularly preferably gallium, aluminum, and / or indium. Furthermore, the group 13 element nitride single crystal is preferably a group 13 element nitride single crystal selected from gallium nitride, aluminum nitride, indium nitride, or a mixed crystal thereof. More specifically, GaN, AlN, InN, Ga x Al 1-x N(1>x>0), Ga x In 1-x N(1>x>0), Al x In 1-x N(1>x>0), Ga x Al y In z N(1>x>0, 1>y>0, x+y+z=1).

[0016] The definition of a single crystal is as follows. It includes, but is not limited to, a textbook single crystal in which atoms are regularly arranged throughout the crystal. It also refers to a single crystal that is commonly distributed industrially. In other words, the crystal may contain some defects, have inherent distortion, or contain impurities.

[0017] The Group 13 element nitride single crystal substrate may be a free-standing substrate. A "free-standing substrate" refers to a substrate that can be handled as a solid object without being deformed or broken by its own weight when handled. The free-standing substrate of the present invention can be used as a substrate for various semiconductor devices such as light-emitting elements. In a preferred embodiment, the thickness of the free-standing substrate after polishing is preferably 300 μm or more and 1000 μm or less. The size of the freestanding substrate is not particularly limited, but is preferably 2 inches, 4 inches, or 6 inches, and may be 8 inches or larger.

[0018] 1(b), a composite substrate 8 for forming an epitaxially grown layer can be obtained by directly bonding a base substrate 7 made of a material with a higher thermal conductivity than the group 13 element nitride single crystal to the second main surface 2b side of the group 13 element nitride single crystal substrate 2. SiC, AlN, and diamond are preferred materials for such a base substrate. The thermal conductivity of the base substrate is preferably 200 W / m K or higher, and more preferably 500 W / m K or higher.

[0019] In a preferred embodiment, the Group 13 element nitride single crystal contains one or more elements selected from the group consisting of zinc, manganese, and iron as dopant components. From the viewpoint of the present invention, the total content of one or more elements selected from the group consisting of zinc, manganese, and iron in the Group 13 element nitride single crystal substrate is 1×10 18 atoms / cm 3 ~1×10 21 atoms / cm 3 Preferably, it is 1×10 19 atoms / cm 3 ~1×10 21 atoms / cm 3 It is more preferable that the content of the above elements in the group 13 element nitride single crystal substrate is measured by SIMS (secondary ion mass spectrometry).

[0020] Furthermore, the single crystal of a nitride of a Group 13 element may contain elements other than the dopant, such as hydrogen (H), oxygen (O), and silicon (Si).

[0021] The off-angle of the first main surface of the Group 13 element nitride single crystal substrate is set to 0.4° or more and 1.0° or less, where the reference axis of the off-angle may be the a-axis, c-axis, or m-axis of wurtzite.

[0022] 2(a) is a schematic perspective view of a group 13 element nitride single crystal substrate 100 according to a preferred embodiment. As shown in FIG. 2(a), the group 13 element nitride single crystal substrate 100 according to this embodiment has a plane orientation of 1 / 2 with respect to a normal vector A of its first surface. <0001> That is, the group 13 element nitride single crystal substrate 100 according to this embodiment has a plane orientation (c-axis) that is tilted. <0001> The substrate is an off-angle substrate having an off-angle tilted from the substrate.

[0023] 2(b) is a schematic diagram illustrating the crystal orientation and crystal planes in the crystal structure of the Group 13 element nitride single crystal substrate according to a preferred embodiment. In the crystal structure shown in FIG. 2(b), <0001> The c-axis direction is the <1-100> direction, the m-axis direction is the <11-20> direction, and the a-axis direction is the <11-20> direction. The top surface of the hexagonal crystal, which can be considered as a regular hexagonal prism, is the c-plane, and the side wall surface of the regular hexagonal prism is the m-plane.

[0024] In the group 13 element nitride single crystal substrate according to this embodiment, the c-plane is inclined with respect to the orientation of the first surface. In other words, in the group 13 element nitride single crystal substrate according to this embodiment, the c-plane is inclined with respect to the normal vector of the first surface (normal vector A in FIG. 2(a)). <0001> The direction of the tilt (c-axis direction) may be the a-axis or the m-axis.

[0025] By setting the off-angle to 0.4° or more, degradation of the channel layer's properties can be prevented even when the channel layer is thinned, and in particular, degradation of the sheet carrier density and carrier mobility of the two-dimensional electron gas can be suppressed. From this perspective, it is more preferable to set the off-angle to 0.5° or more. Furthermore, when the off-angle exceeds 1.0°, step bunching occurs in a small region on the channel layer surface, changing the strain at the interface of the channel layer, for example, the interface between the barrier layer and the channel layer, resulting in degradation of properties, particularly a decrease in sheet carrier density. From this perspective, the off-angle is set to 1.0° or less, but 0.9° or less is more preferable, and 0.7° or less is even more preferable from the viewpoint of achieving both sheet carrier concentration and carrier mobility.

[0026] In a preferred embodiment, the resistivity of the group 13 element nitride single crystal substrate at room temperature is 1×10 7 Ωcm or more. In other words, the present group 13 element nitride single crystal substrate is semi-insulating, which is effective in preventing leakage current between the source and drain electrodes in semiconductor devices, such as HEMT devices. From this perspective, the resistivity of the group 13 element nitride single crystal substrate at room temperature is 1×10 9 It is more preferable that the resistivity of the single crystal substrate of a group 13 element nitride is 1×10 13 It is often less than Ω·cm.

[0027] (Production of single crystals of nitrides of group 13 elements) Examples of methods for producing the Group 13 element nitride single crystal include gas phase methods such as metal organic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE), pulsed photoexcited deposition (PXD), MBE, and sublimation, and liquid phase methods such as ammonothermal and flux methods. Particularly preferred are those produced by the flux method.

[0028] In the case of the flux method, it is preferable to provide a seed crystal film on the surface of a support substrate such as sapphire or a single crystal of a nitride of a group 13 element, and grow the single crystal of a nitride of a group 13 element on the seed crystal film by the flux method.

[0029] The material of the seed crystal film is Al x Ga 1-x N(0≦x≦1) and In x Ga 1-x N (0≦x≦1) is a suitable example, and gallium nitride is particularly preferred. The seed crystal film is preferably formed by vapor phase growth, but examples include metal organic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE), pulsed photoemission deposition (PXD), MBE, and sublimation. Metal organic chemical vapor deposition is particularly preferred. The growth temperature is preferably 950 to 1200°C.

[0030] When growing a single crystal of a Group 13 element nitride by the flux method, the type of flux is not particularly limited as long as it is capable of producing the single crystal. In a preferred embodiment, the flux is a flux containing at least one of an alkali metal and an alkaline earth metal, and a flux containing sodium metal is particularly preferred. The flux is used by mixing a metal raw material. The metal raw material may be a simple metal, an alloy, or a metal compound, but a simple metal is preferable from the viewpoint of handling.

[0031] The growth temperature and holding time for growing a Group 13 element nitride single crystal in the flux method are not particularly limited and are changed as appropriate depending on the composition of the flux. For example, when growing a gallium nitride crystal using a sodium- or lithium-containing flux, the growth temperature is preferably 800 to 950°C, and more preferably 850 to 900°C.

[0032] In the flux method, a single crystal of a nitride of a Group 13 element is grown in an atmosphere containing a gas containing nitrogen atoms. This gas is preferably nitrogen gas, but ammonia may also be used. The pressure of the atmosphere is not particularly limited, but from the viewpoint of preventing evaporation of the flux, a pressure of 10 atmospheres or more is preferable, and 30 atmospheres or more is more preferable. However, since a high pressure requires a large-scale apparatus, the total pressure of the atmosphere is preferably 2000 atmospheres or less, and more preferably 500 atmospheres or less. The gas other than the gas containing nitrogen atoms in the atmosphere is not limited, but an inert gas is preferable, and argon, helium, and neon are particularly preferable.

[0033] In a particularly preferred embodiment, an MOCVD-GaN template is placed in a crucible, which is then filled with 10 to 60 parts by mass of metallic Ga, 15 to 90 parts by mass of metallic Na, and a total of 0.1 to 5 parts by mass of one or more metals selected from the group consisting of metallic zinc, metallic manganese, and metallic iron, and 10 to 500 mg of C. The crucible is placed in a heating furnace, and heated at a furnace temperature of 800°C to 950°C and a furnace pressure of 3 MPa to 5 MPa for approximately 20 to 400 hours, after which it is cooled to room temperature. After cooling is complete, the crucible is removed from the furnace. The gallium nitride single crystal thus obtained is polished with diamond abrasive grains to flatten its surface, resulting in the formation of a gallium nitride single crystal on the MOCVD-GaN template.

[0034] (Formation of each epitaxial growth layer) In the present invention, as shown in FIG. 1(a), for example, a buffer layer 3, a channel layer 4, and a barrier layer 5 are epitaxially grown on a first main surface 2a of a group 13 element nitride single crystal substrate 2. Examples of epitaxial growth layers grown on a single crystal substrate of a nitride of a group 13 element include gallium nitride, aluminum nitride, indium nitride, and mixed crystals thereof. Specifically, gallium nitride (GaN), aluminum nitride (AlN), indium nitride (InN), aluminum gallium nitride (Ga x Al 1-x N(1>x>0)), indium gallium nitride (Ga x In 1-x N(1>x>0)), aluminum indium nitride (Al x In 1-x N(1>x>0)), aluminum indium gallium nitride (Ga x Al y In z N(1>x>0, 1>y>0, x+y+z=1) can be listed.

[0035] The buffer layer 3, channel layer 4, and barrier layer 5 can be formed by, for example, metalorganic chemical vapor deposition (MOCVD). Layer formation by MOCVD involves supplying metalorganic precursor gases (such as TMG (trimethylgallium), TMA (trimethylaluminum), or TMI (trimethylindium)) according to the target composition, ammonia gas, hydrogen gas, and nitrogen gas into the reactor of an MOCVD furnace, and heating a Group 13 element nitride single crystal substrate placed in the reactor to a predetermined temperature, while sequentially generating nitride crystals through a gas-phase reaction between the metalorganic precursor gases corresponding to each layer and ammonia gas.

[0036] The buffer layer can prevent the metal element doped in the single crystal nitride of a group 13 element from diffusing into the channel layer. In a preferred embodiment, the buffer layer is made of aluminum nitride or aluminum gallium nitride. By using such a composition with a high aluminum concentration for the buffer layer, the diffusion of metal elements into the channel layer can be further suppressed. Furthermore, by setting the thickness of the buffer layer to 1 nm or more and 20 nm or less, the buffer layer can function as a back barrier that confines electrons in the channel layer, thereby increasing the sheet carrier density and carrier mobility.

[0037] The preferred growth conditions for the buffer layer by MOCVD are as follows: Growth temperature=700℃~1200℃ Reactor pressure = 5kPa to 30kPa Carrier gas = hydrogen Nitrogen gas / Group 13 element gas ratio = 5000 to 20000 Aluminum source gas / Group 13 source gas ratio = 0.7 to 1.0

[0038] The thickness of the channel layer is set to 700 nm or less. This prevents degradation of characteristics due to parasitic capacitance of the channel layer. From this viewpoint, the thickness of the channel layer is preferably set to 500 nm or less, and more preferably to 300 nm. Furthermore, the thickness of the channel layer is preferably set to 50 nm or more.

[0039] In a preferred embodiment, the channel layer is made of gallium nitride. In a preferred embodiment, the epitaxially grown layer preferably contains less carbon. In this case, the carbon content in the epitaxially grown layer is preferably 5×10 16 atom / cm 3 Preferably, it is 2 x 10 or less. 16 atom / cm 3 It is more preferable that the carbon content in the epitaxially grown layer is measured by SIMS (Secondary Ion Mass Spectroscopy).

[0040] In a preferred embodiment, when a channel layer is grown by MOCVD on a Group 13 element nitride single crystal substrate having one main surface with an off-angle of 0.4 to 1.0°, the growth temperature is set to 1000°C or less and the growth rate is set to 1 μm / hour or less. By setting the growth temperature to 1000°C or less, diffusion of metal elements doped into the Group 13 element nitride single crystal substrate into the channel layer is suppressed, and a decrease in sheet carrier density and carrier mobility when the channel layer is thinned is suppressed.

[0041] That is, in thinning the channel layer, we investigated methods for preventing the increase in resistance of the channel layer and the deterioration of crystallinity due to the diffusion and incorporation of doping elements, particularly Zn, Fe, and Mn, into the channel layer of the Group 13 element nitride single crystal substrate. As a result, we found that by setting the growth temperature of the channel layer to 1000°C or less and the growth rate to 1 μm / hour or less, high crystallinity can be obtained while suppressing the diffusion of doping elements into the channel layer. Growing the channel layer at 1000°C or less raises concerns about the deterioration of surface flatness and the increase in carbon concentration in the channel layer. However, by setting the growth rate to 1 μm / hour or less and further setting the off-angle of the first main surface of the Group 13 element nitride single crystal substrate to a range of 0.4° or more, high surface flatness can be obtained. In a preferred embodiment, the carbon concentration is 2×10 16 / cm 3 It became possible to do the following:

[0042] From this perspective, the growth temperature of the channel layer is preferably 990°C or lower. Furthermore, the growth temperature of the channel layer is preferably 950°C or higher. If the growth temperature is 950°C or lower, pits are likely to occur on the surface of the epitaxially grown layer. The growth temperature is more preferably 960°C or higher.

[0043] From the above viewpoint, the growth rate of the channel layer is more preferably 0.8 μm / hour or less. Also, the growth rate of the channel layer is preferably 0.3 μm / hour or more, and more preferably 0.5 μm / hour or more. If the growth rate is 0.3 μm / hour or less, the surface flatness of the channel layer tends to deteriorate.

[0044] The preferred manufacturing conditions for the channel layer are as follows. Growth temperature = above Reactor pressure = 30kPa to 105kPa Carrier gas = hydrogen Nitrogen gas / Group 13 element gas ratio = 1000 to 10000

[0045] In a preferred embodiment, the barrier layer is made of indium aluminum gallium nitride, indium aluminum nitride, or aluminum gallium nitride.

[0046] When the barrier layer is formed by MOCVD using aluminum gallium nitride, the following manufacturing conditions are preferred. Growth temperature=1000℃~1200℃ Reactor pressure = 1kPa to 30kPa Nitrogen gas / Group 13 element source gas ratio = 5000 to 20000 Carrier gas = hydrogen Aluminum source gas / Group 13 element source gas ratio = 0.1 to 0.4

[0047] When the barrier layer is formed by MOCVD using aluminum indium nitride, the following manufacturing conditions are preferred. Growth temperature=700℃~900℃ Reactor pressure = 1kPa to 30kPa Nitrogen gas / Group 13 element source gas ratio = 2000 to 20000 Carrier gas = nitrogen Indium source gas / Group 13 element source gas ratio = 0.1 to 0.9

[0048] When the barrier layer is formed by MOCVD using aluminum indium gallium nitride, the following manufacturing conditions are preferred. Growth temperature=700℃~1000℃ Reactor pressure = 1kPa to 30kPa Nitrogen gas / Group 13 element source gas ratio = 2000 to 20000 Carrier gas = nitrogen Aluminum source gas / Group 13 element source gas ratio = 0.1 to 0.9 Indium source gas / Group 13 element source gas ratio = 0.1 to 0.9 [Example]

[0049] (Experiment A) (Fabrication of zinc-doped gallium nitride single crystal substrates) GaN template fabrication A 2-μm-thick gallium nitride seed crystal film was deposited on a 2-inch diameter c-plane sapphire substrate by MOCVD to obtain an MOCVD-GaN template that can be used as a seed substrate. The off-angle of the c-plane sapphire substrate was adjusted appropriately so that the off-angle of the deposition surface of the MOCVD-GaN template was between 0 and 1.2°, and multiple GaN templates with different off-angles of the deposition surface were fabricated.

[0050] Growth of zinc-doped gallium nitride single crystals by flux method Using the resulting multiple MOCVD-GaN templates as seed substrates, zinc-doped gallium nitride single crystals were grown using the Na flux method. Specifically, metallic gallium, metallic sodium, and granular zinc as doping materials were filled into an alumina crucible, which was then covered with an alumina lid. The ratio of metallic gallium to metallic sodium was adjusted to Ga / (Ga + Na) (mol%) = 15 mol%. The crucible was placed in a heating furnace, heated to a furnace temperature of 850°C and a furnace pressure of 4.5 MPa, and heated for 100 hours, then cooled to room temperature. After cooling, the alumina crucible was removed from the furnace, and a gallium nitride single crystal was deposited on the surface of the seed substrate to a thickness of approximately 1000 μm.

[0051] ·Surface flattening The gallium nitride single crystal thus obtained was polished using diamond abrasive grains to flatten its surface and to make the total thickness of the gallium nitride single crystal formed on the c-plane sapphire substrate 700 μm. This resulted in the formation of a GaN single crystal on the MOCVD-GaN template. Visual inspection of the resulting substrate and gallium nitride single crystal revealed no cracks.

[0052] ·Seed substrate separation The seed substrate was separated from the gallium nitride single crystal by laser lift-off to obtain a gallium nitride single crystal substrate.

[0053] Wafer processing The first and second main surfaces of the gallium nitride single crystal substrate were subjected to polishing treatment to obtain a zinc-doped gallium nitride single crystal substrate having a thickness of 400 μm.

[0054] ·Resistivity measurement The resistivity of the zinc-doped gallium nitride single crystal substrate was measured by the capacitance method and found to be 5×10 7 ~2×10 11 Ω·cm was obtained.

[0055] Epitaxial growth layer formation A buffer layer 3, a channel layer 4, and a barrier layer 5 were grown by MOCVD on the first principal surface 2a of a zinc-doped gallium nitride single crystal substrate 2 to produce a laminate 1. When the buffer layer is made of aluminum nitride or aluminum gallium nitride, the channel layer is made of gallium nitride, and the barrier layer is made of aluminum gallium nitride, MOCVD furnaces configured to supply gallium and aluminum metal-organic (MO) precursor gases (trimethylgallium (TMG) and trimethylaluminum (TMA)), ammonia gas, hydrogen gas, and nitrogen gas into the reactor are used. While the zinc-doped gallium nitride single crystal substrate placed in the reactor is heated to a predetermined temperature, gallium nitride crystals or aluminum gallium nitride crystals are sequentially deposited on the freestanding substrate by vapor-phase reactions of the metal-organic precursor gases corresponding to each layer with ammonia gas. When the barrier layer is made of aluminum indium nitride or aluminum indium gallium nitride, a metal-organic precursor gas containing indium (trimethylindium) is also used.

[0056] More specifically, the manufacturing conditions were as follows: (Buffer layer: AlN) Growth temperature=980℃ Reactor pressure = 5kPa 15 group / 13 group gas ratio = 15,000 Al source gas / Group 13 source gas ratio=1.0 Thickness = 20 nm (Channel layer: GaN) Growth temperature=980℃ Reactor pressure = 100 kPa 15 group / 13 group gas ratio = 6800 Growth rate=0.7μm / hour Thickness = 200 nm (Barrier layer: AlGaN) Growth temperature=1050℃ Reactor pressure = 5kPa 15 group / 13 group gas ratio = 12000 Al source gas / Group 13 source gas ratio=0.25 Thickness=25 nm

[0057] - Fabrication of Hall effect measurement element The resulting epitaxial substrate for semiconductor devices was used to fabricate devices for measuring sheet carrier density and carrier mobility. For the measurement devices, multiple 6 mm square chips were cut from the epitaxial substrate for semiconductor devices, and ohmic electrodes were formed near the four corners of the chips. The electrodes were formed as 1 mm square patterns of Ti / Al / Ni / Au using vacuum deposition and photolithography processes to form Hall measurement devices. The thicknesses of the Ti / Al / Ni / Au metal layers are preferably in the ranges of 5 nm to 50 nm, 40 nm to 400 nm, 4 nm to 40 nm, and 20 nm to 200 nm, respectively. Subsequently, to improve the ohmic properties of the source and drain electrodes, heat treatment is preferably performed for 10 to 1000 seconds in a nitrogen gas atmosphere at 600°C to 1000°C.

[0058] · Sheet carrier density · Carrier mobility measurement The fabricated Hall measurement device was used to measure the sheet carrier density and carrier mobility of the epitaxially grown layer at room temperature using the Hall effect measurement (van der Pauw method). A Hall effect measurement system (ResiTest8300, manufactured by Toyo Corporation) was used for the Hall effect measurement. The measurement results are shown in Table 1. Figure 3 shows the relationship between the off-axis angle and the sheet carrier density, and Figure 4 shows the relationship between the off-axis angle and the carrier mobility. From the Al composition and film thickness of the barrier layer considered in this embodiment, the sheet carrier density is 8.5 × 10 12 / cm 3 The electron mobility is 1400 cm 2 If it is / Vs or higher, it can be said to be good.

[0059] Offset angle measurement To investigate the relationship between the sheet carrier density and carrier mobility and the off-angle, the off-angle of the first principal surface of the zinc-doped gallium nitride single crystal substrate was measured using an X-ray diffraction method with a Hall measurement element. A multipurpose X-ray diffractometer (D8 DISCOVER manufactured by Bruker AXS) was used for the X-ray diffraction measurement. The measurement results for each example are shown in Table 1. FIG. 3 shows the relationship between the off-angle and the sheet carrier density, and FIG. 4 shows the relationship between the off-angle and the carrier mobility.

[0060] [Table 1]

[0061] As can be seen from Table 1, when the off-angle of the first main surface (epitaxial growth surface) of the zinc-doped gallium nitride single crystal substrate was within the range of 0.4 to 1.0°, the sheet carrier density and carrier mobility were high. In contrast, when the off-angle of the first main surface of the zinc-doped gallium nitride single crystal substrate was less than 0.4° or more than 1.0°, a decrease in the sheet carrier density and carrier mobility was observed.

[0062] Surface morphology evaluation The surface morphology of the epitaxially grown layer was evaluated using a differential interference optical microscope (Leica DM8000M). The observation magnification was 100x. As a result, in Examples in which the off-angle of the first main surface 2a of the zinc-doped gallium nitride single crystal substrate 2 was 0.4° to 1.0°, a good surface morphology with little unevenness was confirmed on the surface of the channel layer. For example, Figure 5 shows the surface morphology of the channel layer when the off-angle of the first main surface of the zinc-doped Group 13 element nitride single crystal substrate was 0.66°, and a smooth surface morphology with little unevenness can be observed.

[0063] On the other hand, in the comparative example where the off angle was outside the above range, the surface unevenness of the channel layer was large. That is, when the off angle was less than 0.4°, the surface of the channel layer had a morphology in which many fine island-shaped protrusions were dispersed. For example, Figure 6 shows the surface morphology of the channel layer when the off angle was 0.09°.

[0064] Furthermore, step bunching occurred in the range of the large off-angle. For example, Figure 7 shows the surface morphology of the channel layer when the off-angle is 1.15°, and it can be seen that many fine, elongated steps are formed.

[0065] Carbon concentration evaluation in the channel layer The carbon concentration in the channel layer was measured by SIMS. The results are shown in Figure 8. In samples with an off-angle of more than 0.4°, the carbon concentration in the channel layer was 1×10 16 / cm 3 On the other hand, in samples with an off angle of less than 0.4°, an increase in carbon concentration was observed in the channel layer.

[0066] (Experiment B) In Experiment A, the off angle was set to 0.6°, but the thickness of the channel layer was changed to 1000 nm, 700 nm, 500 nm, 200 nm, 100 nm, 50 nm, and 30 nm by adjusting the growth time. The sheet carrier density and carrier mobility of the channel layer at room temperature were measured using the Hall effect (van der Pauw method). The parasitic capacitance of the channel layer was also measured using the CV method. However, when performing the CV method, a Schottky electrode with a diameter of 1 cm was formed, and the measurement frequency was 100 kHz. The parasitic capacitance was measured when a voltage of -3 V was applied, and the results are shown in Table 2.

[0067] [Table 2]

[0068] As a result, it was found that the parasitic capacitance was kept low when the channel layer thickness was in the range of 50nm to 700nm. At the same time, the sheet carrier density and carrier mobility were good when the channel layer thickness was in the range of 50nm to 700nm, but a decrease in the sheet carrier density was observed when the channel layer thickness was 30nm. This is thought to be due to the inhibition of carrier generation in the 2DEG layer.

[0069] (Experiment C: Mn doped) Mn-doped gallium nitride single crystal substrates were grown under the same conditions as in Experiment A. However, the doping material added to the flux was changed to granular manganese. As a result, several Mn-doped gallium nitride single crystal substrates with different off-angles were obtained. The resistivity of the Mn-doped gallium nitride single crystal substrates at room temperature was measured using the capacitance method, and it was found to be 8×10 7 ~3×10 11 Ω·cm was obtained.

[0070] Next, a buffer layer, a channel layer, and a barrier layer were formed on the first main surface of the Mn-doped gallium nitride single crystal substrate under the same conditions as in Experiment A. The sheet carrier density and carrier mobility of the channel layer were measured at room temperature using Hall effect measurement (van der Pauw method). The measurement results are shown in Table 3. As a result, good results were obtained in terms of sheet carrier density and carrier mobility when the off angle was in the range of 0.4 to 1.0°.

[0071] [Table 3]

[0072] (Experiment D: Fe doping) Fe-doped gallium nitride single crystal substrates were grown under the same conditions as in Experiment A. However, the doping material added to the flux was changed to granular iron. As a result, several Fe-doped gallium nitride single crystal substrates with different off-angles were obtained. The resistivity of the Fe-doped gallium nitride single crystal substrates at room temperature was measured using the capacitance method, and it was found to be 1×10 7 ~2×10 9 Ω·cm was obtained.

[0073] Next, under the same conditions as in Experiment A, Fe A buffer layer, a channel layer, and a barrier layer were formed on the first principal surface of the doped gallium nitride single crystal substrate. The sheet carrier density and carrier mobility of the epitaxially grown layer were measured at room temperature using Hall effect measurement (van der Pauw method). The measurement results are shown in Table 4. As a result, good results were obtained in terms of sheet carrier density and carrier mobility when the off angle was in the range of 0.4 to 1.0°.

[0074] [Table 4]

Claims

1. a single crystal substrate of a nitride of a group 13 element, the single crystal substrate being made of a nitride of a group 13 element and having a first main surface and a second main surface; a buffer layer provided on the first main surface of the Group 13 element nitride single crystal substrate; a channel layer disposed on the buffer layer; and a barrier layer provided on the channel layer; A laminate having The group 13 element nitride single crystal is made of a gallium nitride single crystal containing one or more elements selected from the group consisting of zinc, manganese, and iron as a dopant, the thickness of the channel layer is 700 nm or less, and the carrier mobility of the channel layer is 1400 cm 2 / Vs or more, and the off-angle of the first main surface of the Group 13 element nitride single crystal substrate is 0.4° or more and 1.0° or less.

2. The resistivity of the group 13 element nitride single crystal substrate at room temperature is 1×10 ７ The laminate according to claim 1, characterized in that it has a resistivity of Ω·cm or more.

3. 3. The laminate according to claim 1, wherein the buffer layer is made of aluminum nitride or aluminum gallium nitride.

4. 3. The laminate according to claim 1, wherein the buffer layer has a thickness of 1 nm or more and 20 nm or less, and the buffer layer is made of aluminum nitride or aluminum gallium nitride.

5. The carbon concentration of the channel layer is 2×10 １６ / cm ３ 3. The laminate according to claim 1, wherein:

6. 3. The laminate according to claim 1, wherein the barrier layer is made of indium aluminum gallium nitride, indium aluminum nitride, or aluminum gallium nitride.

7. 3. The laminate according to claim 1, wherein the channel layer is made of gallium nitride.

8. 3. The laminate according to claim 1, wherein the off angle of the first main surface is 0.5° or more and 0.7° or less.

9. 3. The laminate according to claim 1, wherein the single crystal of the nitride of a Group 13 element is produced by a flux method.

10. A laminate according to claim 1 or 2, characterized in that it comprises a base substrate bonded to the second main surface side of the Group 13 element nitride single crystal substrate, the base substrate being made of a material having a higher thermal conductivity than the Group 13 element nitride single crystal.

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