JP6064695B2 - Gallium nitride crystal and method for producing gallium nitride crystal - Google Patents

Description

  The present invention relates to a gallium nitride crystal and a method for producing a gallium nitride crystal.

  Periodic table Group 13 metal nitride crystals typified by gallium nitride have a large band gap, and the transition between bands is a direct transition type. It has been put to practical use as a light emitting element on the short wavelength side. In addition, with the recent development of crystal growth technology, the manufacture of gallium nitride substrates used in these devices has also been realized.

  Periodic table Group 13 metal nitride crystals for use as light-emitting elements are required to emit light efficiently when used in devices, and there are few defects in the crystals in order to improve luminous efficiency. It is necessary to produce crystals.

  The hexagonal periodic table group 13 metal nitride crystal has a problem of a decrease in internal quantum efficiency due to a problem of spontaneous polarization and piezoelectric polarization. If a crystal can be formed on the nonpolar surface of the Group 13 metal nitride crystal of the periodic table, problems such as a decrease in internal quantum efficiency can be solved, but the dislocation density and stacking fault density are low on the nonpolar surface. At present, it is very difficult to epitaxially grow GaN crystals. For example, for this problem, it has been proposed to form an intermediate layer containing carbon and aluminum on a substrate (see Patent Document 1).

  On the other hand, by using a semipolar plane as a main surface of the seed and growing a Group 13 metal nitride crystal on the seed in a solution containing a nitrogen element and a Group 13 metal element in the molten salt, surface irregularities can be obtained. A method for producing a small number of Group 13 metal nitride crystals has been proposed (see Patent Document 2).

JP 2010-30877 A JP 2011-178594 A

As described in Patent Document 1, when homoepitaxial growth is performed on a nonpolar surface of a periodic table group 13 metal nitride substrate, stacking faults are likely to occur. It is difficult to epitaxially grow a low density GaN crystal. Further, as a result of investigations by the present inventors, when a crystal was grown on a seed substrate in which a stacking fault exists, the stacking fault propagated to the crystal growth layer, and the stacking fault increased as compared with the seed substrate.
An object of the present invention is to provide a gallium nitride crystal in which the generation of stacking faults, which are considered to have a great influence on the quality of the crystal, is reduced as much as possible.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have focused on a peak existing in a specific photon energy value in a spectrum obtained when a grown crystal is observed at low temperature PL. . Then, a low-temperature PL measurement is performed on the crystal growth layer, and the ratio of the emission intensity (BSF peak) at 3.41 eV to the band edge emission (NBE peak) of gallium nitride (BSF peak / NBE peak) is 0.1. The present inventors have found that the following crystal is a crystal in which the occurrence of stacking faults is suppressed, thereby completing the present invention.

The present invention is as follows.
(1) A gallium nitride crystal having a gallium nitride crystal growth layer on a seed substrate made of gallium nitride having a nonpolar plane or a semipolar plane as a main surface, the gallium nitride crystal measured by low-temperature PL measurement A gallium nitride crystal having a ratio (BSF peak / NBE peak) of emission intensity (BSF peak) of emission at 3.41 eV to band edge emission (NBE peak) of the growth layer of 0.1 or less.
(2) The ratio (BSF peak / NBE peak) of the emission intensity (BSF peak) at 3.41 eV to the band edge emission (NBE peak) of the seed substrate made of gallium nitride measured by low-temperature PL measurement is 0 The gallium nitride crystal according to (1), which is 1 or more.
(3) The gallium nitride crystal according to (1) or (2), wherein the growth thickness of the gallium nitride crystal growth layer is 10 μm or more.
(4) The gallium nitride crystal according to any one of (1) to (3), wherein a main surface of the seed substrate made of gallium nitride is a nonpolar surface.
(5) the Si concentration of the gallium nitride crystal growth layer is rather higher than O concentration, and has a dislocation extending in the vertical direction of the non-polar surface or a semipolar plane, according to any one of (1) (4) Gallium nitride crystal.
(6) the dislocation density before Symbol dislocation is 1.0 × 10 ⁸ cm ^-2 or less, the gallium nitride crystal according to (5).
( 7 ) The gallium nitride crystal according to (5) or ( 6), wherein the Si concentration is 1 × 10 ¹³ cm ⁻³ or more.
( 8 ) The gallium nitride crystal according to any one of (5) to ( 7 ), wherein the O concentration is 3 × 10 ¹⁸ cm ⁻³ or less.
( 9 ) The gallium nitride crystal according to any one of (1) to ( 8 ), wherein the Na concentration in the gallium nitride crystal growth layer is 1 × 10 ¹⁷ cm ⁻³ or less.

Moreover, another aspect of the present invention is as follows.
( 10 ) A method for producing a gallium nitride crystal, comprising: a crystal growth step of growing a gallium nitride crystal growth layer on a seed substrate made of gallium nitride having a nonpolar plane or a semipolar plane as a principal plane, the low temperature PL The ratio of the emission intensity (BSF peak / NBE peak) of the emission (BSF peak) at 3.41 eV to the band edge emission (NBE peak) of the gallium nitride crystal growth layer obtained by the crystal growth step measured by the measurement is The manufacturing method of the gallium nitride crystal | crystallization which is 0.1 or less.
( 11 ) The ratio (BSF peak / NBE peak) of the emission intensity (BSF peak) at 3.41 eV to the band edge emission (NBE peak) of the seed substrate made of gallium nitride measured by low-temperature PL measurement is 0. The manufacturing method of the gallium nitride crystal as described in ( 10 ) which is .1 or more.
( 12 ) The method for producing a gallium nitride crystal according to ( 10 ) or ( 11 ), wherein a main surface of the seed substrate made of gallium nitride is a nonpolar surface.
( 13 ) The method for producing a gallium nitride crystal according to any one of ( 10 ) to ( 12 ), wherein the crystal growth step is performed so that the growth surface is a flat surface.
( 14 ) The method for producing a gallium nitride crystal according to any one of ( 10 ) to ( 13 ), wherein the crystal growth step is performed by a liquid phase method.

  According to the present invention, it is possible to provide a gallium nitride (GaN) crystal in which the occurrence of stacking faults is suppressed.

It is a conceptual diagram of the apparatus used for the crystal growth which performed the Example of this invention. It is the seed substrate used for the Example of this invention (drawing substitute photograph). It is a graph which shows the result of the low-temperature PL measurement with respect to the seed substrate used for the Example of this invention. It is the figure which observed the surface of the GaN crystal growth layer grown in Example 1 with the optical microscope (drawing substitute photograph). 3 is a graph showing the results of low-temperature PL measurement for a GaN crystal growth layer grown in Example 1. FIG. 6 is a graph showing the results of low-temperature PL measurement for a GaN crystal growth layer grown in Example 2. 6 is a graph showing the results of low-temperature PL measurement for a GaN crystal growth layer grown in Example 3. It is a conceptual diagram showing the direction where a dislocation extends. It is a conceptual diagram showing the direction of the dislocation of the sliced crystal.

The gallium nitride crystal and the method for producing the gallium nitride crystal of the present invention will be described in detail below, but the present invention is not limited to these contents unless it is contrary to the spirit of the present invention.
In the present specification, a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

The present invention is invention relates to a gallium nitride crystal, the polar surface of the gallium nitride crystal having a hexagonal crystal structure (wurtzite crystal structure), for example (0001) plane and (000-1) plane and the like, non Examples of the polar plane include the (10-10) plane, the (11-20) plane, and planes equivalent to these planes in terms of crystal geometry, and the semipolar plane includes the (20-21) plane and (20-2). -1) plane, (10-11) plane, (10-1-1) plane, (10-12) plane, (10-1-2) plane, (11-21) plane, (11-2-1) ) Plane, (11-2-2) plane, (11-2-2) plane, (22-41) plane, (22-4-1 plane), plane equivalent to these planes, etc. Is mentioned.

In this specification, the (10-10) plane and a plane geometrically equivalent to this plane may be abbreviated as “M plane”.
In addition, in this specification, when referring to a specific index plane, it includes a plane within a range having an off angle within 10 ° from each crystal axis measured with an accuracy within ± 0.01 °. The off angle is preferably within 5 °, more preferably within 3 °.
In the present invention, the “main surface” means a surface on which a device is to be formed or a surface having the largest area in the crystal.

<Gallium nitride crystal of the present invention>
The gallium nitride crystal of the present invention is a gallium nitride crystal having a gallium nitride crystal growth layer on a seed substrate made of gallium nitride whose main surface is a nonpolar plane or a semipolar plane.
When a gallium nitride crystal is grown by homoepitaxial growth on a gallium nitride substrate having a nonpolar or semipolar surface as a main surface, many stacking faults are generated in the crystal growth layer. The present invention is a gallium nitride crystal in which the occurrence of stacking faults in such a crystal growth layer is suppressed.
The gallium nitride crystal growth layer grown on the “seed substrate” made of gallium nitride means a crystal growth layer grown on the seed substrate. In particular, the gallium nitride crystal growth layer is formed directly on the seed substrate. A grown layer is preferable. The growth layer grown directly on the seed substrate is a crystal growth layer grown in a direction normal to the seed substrate main surface, and is a crystal growth layer grown in a direction parallel to the seed substrate main surface (so-called lateral growth). Are removed from the range of the gallium nitride crystal growth layer grown on the “seed substrate”.

  The gallium nitride (GaN) crystal of the present invention does not contain GaN having a cubic structure and has a hexagonal structure. The gallium nitride crystal of the present invention includes a GaN crystal containing an impurity as a dopant, and the impurity contains an element such as H, O, C, Si, Cl, Li, Na, Ti, Mg. Also good.

In the gallium nitride crystal of the present invention, the ratio of the emission intensity of light emission (BSF peak) at 3.41 eV to the band edge emission (NBE peak) of gallium nitride measured by low-temperature PL measurement in the growth layer grown on the seed substrate. (BSF peak / NBE peak) is 0.1 or less.
By measuring the crystal by low-temperature PL measurement, the degree of impurities and defects present in the crystal can be measured. The present inventors examined the result of low-temperature PL measurement on the crystal, and emitted light at 3.41 eV, which is considered to originate from stacking faults, with respect to the emission intensity ratio of band edge emission (NBE peak) of gallium nitride ( It was conceived that when the ratio of emission intensity (BSF peak) (BSF peak / NBE peak) was 0.1 or less, it was a crystal in which the occurrence of stacking faults was suppressed. This will be described below with reference to the drawings.

FIG. 2 shows a GaN seed substrate used in the example of the present invention. The GaN seed substrate was subjected to low-temperature PL measurement at four locations (Point 1 to Point 4) shown in FIG. And the graph which plotted the spectrum obtained by the low-temperature PL measurement of Point1 thru | or Point4 in FIG. 3 is shown.
From FIG. 3, the spectrum at each point has a sharp peak near 3.47 eV, and this peak is the band edge emission (NBE peak) of gallium nitride. And it has a gentle peak in the vicinity of 3.41 eV, and this peak is a BSF peak considered to be derived from stacking faults present in the crystal. The gallium nitride crystal of the present invention is a crystal in which the ratio of the emission intensity (BSF peak) at 3.41 eV to the band edge emission (NBE peak) (BSF peak / NBE peak) is 0.1 or less. A crystal that satisfies such requirements is a crystal in which the occurrence of stacking faults is suppressed.

In the present invention, the low temperature PL measurement is performed using a He—Cd laser having a central wavelength of 325 nm as an excitation light source. The measurement temperature is not strictly limited, but it is preferable to perform the measurement at 20K or less. As an apparatus capable of performing PL measurement under such conditions, for example, a combination of an Omnichrome series 74 He-Cd laser, an Acton SpectraPro 2300 i spectrometer, and a Princeton Instruments PI-MAX1024HQ-Blu CCD detector can be cited.
In the case of low-temperature PL measurement, there is a case where a crystal having a high carrier concentration in the crystal cannot obtain a sufficient PL spectrum intensity and cannot be evaluated. In such a case, measurement is performed after reducing the influence of carriers during low-temperature PL measurement by stacking undoped GaN (i-GaN) using the MOCVD method or the like on the crystal surface to be measured. The thickness of the i-GaN layer to be laminated is usually 0.01 μm or more, more preferably 0.1 μm or more, further preferably 0.5 μm or more, and usually 100 μm or less, more preferably It is 10 μm or less, more preferably 5 μm or less. If the thickness of the i-GaN layer to be stacked is too thin, the influence of carriers cannot be sufficiently reduced, and if it is too thick, the effect of defects generated in the stacked i-GaN layer is detected.

The ratio (BSF peak / NBE peak) of the emission intensity (BSF peak) at 3.41 eV to the band edge emission (NBE peak) of gallium nitride measured by low-temperature PL measurement of the crystal growth layer is 0.1. Or less, more preferably 0.05 or less, and still more preferably 0.01 or less.
Note that in a gallium nitride crystal, the degree of stacking fault may vary depending on the position in the crystal. In the present invention, the ratio of the emission intensity (BSF peak / NBE peak) of the emission (BSF peak) at 3.41 eV to the band edge emission (NBE peak) measured by the low-temperature PL measurement in at least a part of the crystal. However, it is preferable that the portions satisfying the ratio of the emission intensity are continuously present in a range of 10 mm ² or more, and more preferably in a range of 100 mm ² or more.

In a preferred embodiment of the present invention, the ratio (BSF peak / NBE peak) of the emission intensity (BSF peak) at 3.41 eV to the band edge emission (NBE peak) of the seed substrate made of gallium nitride, measured by low temperature PL measurement. ) Is 0.1 or more.
When the seed substrate has a stacking fault, conventionally, when a crystal is grown on the seed substrate, the stacking fault propagates to the grown crystal layer. More than stacking faults. The gallium nitride crystal of the present invention does not propagate the stacking faults present in the seed substrate, the amount of stacking faults is maintained or reduced, and a crystal growth layer with few stacking faults can be obtained in the first place. That is, it is preferable that the ratio of the emission intensity in the crystal growth layer is 0.1 or less even when the ratio of the emission intensity measured by low-temperature PL measurement with respect to the seed substrate is 0.1 or more.
The ratio of the emission intensity by the low temperature PL measurement on the seed substrate may be larger than 0.1, or may be 0.5 or more.

In the present invention, the thickness of the crystal growth layer of gallium nitride crystal is preferably 10 μm or more. When the thickness of the crystal growth layer is 10 μm or more, the crystal growth layer can be used as a substrate for manufacturing a light emitting element or a substrate for manufacturing a semiconductor device. The thickness of the growth layer is more preferably 50 μm or more, and further preferably 100 μm or more.
The main surface of the seed substrate of the present invention is a nonpolar surface or a semipolar surface, but is preferably a nonpolar surface, and particularly preferably an M surface.

In the present invention, the Si concentration in the crystal growth layer is preferably higher than the O concentration. The gallium nitride crystal growth layer formed by the vapor phase growth method is prone to oxygen doping due to impurity oxygen contained in the growth atmosphere or raw material during crystal growth, and tends to be a crystal layer with a relatively large amount of oxygen doping as a result. It is in. Oxygen doping increases the extinction coefficient of the crystal, so when a device is formed using a crystal with a large amount of oxygen doping as the substrate, part of the light emitted from the device is absorbed by the substrate and the amount of light emission decreases. There is a problem of end up. In addition, in oxygen doping caused by impurity oxygen, it is difficult to precisely control the dopant concentration in the crystal.
In epitaxial growth with the C plane as the growth plane, oxygen tends to be difficult to be taken in, and the above problem can be inevitably solved. However, as in the present invention, gallium nitride having a nonpolar plane or a semipolar plane as the main plane is used. In the case of a gallium nitride crystal growth layer obtained by epitaxial growth on a seed substrate made of the above, the above problem becomes important in terms of quality. Therefore, a gallium nitride crystal having a gallium nitride crystal growth layer that suppresses oxygen doping caused by impurity oxygen and has a Si concentration higher than the O concentration is preferable. Note that by suppressing oxygen doping caused by impurity oxygen, it is possible to precisely control the dopant concentration by silicon, and a higher quality gallium nitride crystal can be obtained.

In the present invention, the dopant concentration in the crystal growth layer is not particularly limited, but is usually 1 × 10 ¹³ cm ⁻³ or more, preferably 1 × 10 ¹⁴ cm ⁻³ or more, more preferably 1 × 10 ¹⁷ cm ⁻³ or more. In general, it is 1 × 10 ²¹ cm ⁻³ or less, preferably 1 × 10 ²⁰ cm ⁻³ or less, more preferably 5 × 10 ¹⁹ cm ⁻³ or less. If the dopant concentration is too high, the properties as a semiconductor may be impaired. If the dopant concentration is too low, the conductivity is low and the substrate having a high conductivity is preferably not suitable.

In the present invention, the carrier concentration in the crystal growth layer is not particularly limited, but is 1 × 10 ¹³ cm ⁻³ or more, preferably 1 × 10 ¹⁴ cm ⁻³ or more, more preferably 1 × 10 ¹⁷ cm ⁻³ or more. Usually, it is 1 × 10 ²¹ cm ⁻³ or less, preferably 1 × 10 ²⁰ cm ⁻³ or less, more preferably 5 × 10 ¹⁹ cm ⁻³ or less. When the carrier concentration is too high, the properties as a semiconductor may be impaired. When the carrier concentration is too low, the conductivity becomes low and the substrate having a high conductivity is preferably not suitable.

In the present invention, specific values of the O concentration and the Si concentration in the crystal growth layer are not particularly limited, but the O concentration is usually 1 × 10 ¹³ cm ⁻³ or more, preferably 1 × 10 ¹⁴ cm ⁻³ or more. Yes, usually 3 × 10 ¹⁸ cm ⁻³ or less, preferably 5 × 10 ¹⁷ cm ⁻³ or less, more preferably 5 × 10 ¹⁶ cm ⁻³ or less. If the O concentration is too large, the light absorption coefficient increases and the properties as a semiconductor may be impaired. If it is too small, the conductivity is preferably low and the conductivity is preferably high. It is not suitable for.
The Si concentration is usually 1 × 10 ¹³ cm ⁻³ or more, preferably 1 × 10 ¹⁷ cm ⁻³ or more, usually 1 × 10 ²¹ cm ⁻³ or less, preferably 1 × 10 ²⁰ cm ⁻³ or less, more preferably Is 1 × 10 ¹⁹ cm ⁻³ or less. When the Si concentration is too high, the properties as a semiconductor may be impaired. When the Si concentration is too low, the conductivity becomes low and the substrate having a high conductivity is preferably not suitable.

In the present invention, the concentration of other elements in the crystal growth layer is not particularly limited. For example, the Na concentration is usually 1 × 10 ¹⁷ cm ⁻³ or less, preferably 1 × 10 ¹⁶ cm ⁻³ or less, more preferably 1 ×. 10 ¹⁵ cm ⁻³ or less. If the Na concentration is too high, the properties as a semiconductor may be impaired.

  It is known that gallium nitride crystals obtained by epitaxial growth have dislocations extending parallel to the growth direction (see Japanese Patent Application Laid-Open No. 2007-84435). Strictly speaking, there are many dislocations whose main direction is not parallel to the growth direction but whose main direction is parallel to the growth direction. “Main direction” means the direction of the largest component when the direction in which dislocations extend is divided into a growth direction component and a component perpendicular to the growth direction. Referring to FIG. 8, when the direction in which the dislocation 5 extends is divided into a growth direction component 6 and a growth direction component 7 perpendicular to the growth direction, the growth direction component 6 is larger, so the main direction is The dislocation 5 is a dislocation whose main direction is parallel to the growth direction. For the sake of convenience, the description of the dislocation extending direction in the specification, claims, drawings, and abstract of the present application intends the “main direction” of dislocation, and the dislocation parallel to the growth direction is shown in FIG. In FIG. 2, not only dislocation 4 but also dislocation 5 is included.

The direction of dislocations in the crystal obtained by epitaxial growth is an index for determining which crystal plane of the base substrate is epitaxially grown as the main surface. This point will be described with reference to FIG. For example, a crystal epitaxially grown in the m-axis direction on the main surface of the base substrate whose main surface is a non-polar M-plane has threading dislocations parallel to the m-axis, so that the upper side of FIG. As shown in FIG. 2, dislocations perpendicular to the M plane exist in the substrate having the M plane obtained by slicing parallel to the M plane. On the other hand, the M plane obtained by slicing a crystal epitaxially grown in the c-axis direction on the base substrate having the C plane as the main plane in parallel with the M plane as shown in the lower side of FIG. In the substrate, dislocations extend in the c-axis direction, and dislocations perpendicular to the m-axis exist in the crystal, which is different from the crystal described above.
When obtaining an M-plane substrate having the M plane as the principal plane from a crystal epitaxially grown in the m-axis direction on the principal plane of the base substrate having the M plane as the principal plane, the size of the underlying substrate and the size of the obtained substrate Since the size is close, it is easy to obtain a large M-plane substrate.
On the other hand, when an M-plane substrate is obtained from a crystal epitaxially grown in the c-axis direction on a base substrate having a C-plane as a main surface, for example, in order to obtain a 2-inch or 4-inch M-plane substrate, the c-axis direction is used. Each of them needs to be grown to a thickness of 2 inches or 4 inches or more, and there is a problem that it is difficult to obtain a large substrate.
For the same reason, when a substrate having a semipolar surface as a main surface is obtained, a semipolar surface or a nonpolar surface is used as a main surface, rather than epitaxial growth on a main surface of an underlying substrate having a C surface as a main surface. It is easier to obtain a large semipolar surface substrate by epitaxial growth on the main surface of the base substrate.

In the present invention, the direction of dislocation and the dislocation density in the crystal growth layer are not particularly limited, but a gallium nitride crystal obtained by epitaxial growth on a seed substrate made of gallium nitride whose main surface is a nonpolar or semipolar surface. Therefore, there is a tendency for dislocations extending in a direction perpendicular to the main surface of the seed substrate (including dislocations whose main direction is parallel to the growth direction). The dislocation density of threading dislocations extending in the direction perpendicular to the nonpolar plane or semipolar plane (dislocation density when measured from the nonpolar plane side or the semipolar plane side) is usually 1 × 10 ⁸ cm ⁻² or less, preferably Is 1 × 10 ⁷ cm ⁻² or less, more preferably 1 × 10 ⁶ cm ⁻² or less.

In the present invention, the other physical properties in the crystal growth layer are not particularly limited, but the half width of the rocking curve of the (100) diffraction peak of X-ray diffraction is usually 500 arcsec or less, preferably 200 arcsec or less, more preferably 100 arcsec or less, Preferably it is 50 arcsec or less.
Further, the full width at half maximum of the rocking curve of the (300) diffraction peak of X-ray diffraction is usually 500 arcsec or less, preferably 200 arcsec or less, more preferably 100 arcsec or less, and even more preferably 50 arcsec or less.
The full width at half maximum of the rocking curve of the (102) diffraction peak of X-ray diffraction is usually 500 arcsec or less, preferably 200 arcsec or less, more preferably 100 arcsec or less. More preferably, it is 50 arcsec or less.
When the full width at half maximum of the rocking curve of the diffraction peak of X-ray diffraction is too large, impurities such as oxygen enter crystal defects and the O concentration tends to be too high due to poor crystallinity.

  In the present invention, a method for growing a crystal in which the emission intensity ratio measured by low-temperature PL measurement of the crystal growth layer is within the above range will be described below. That is, another aspect of the present invention provides a method for producing a gallium nitride crystal having a crystal growth step of growing a gallium nitride crystal growth layer on a seed substrate made of gallium nitride whose main surface is a nonpolar plane or a semipolar plane. A ratio of emission intensity of emission (BSF peak) at 3.41 eV to band edge emission (NBE peak) of the gallium nitride crystal growth layer obtained by the crystal growth step, measured by low temperature PL measurement ( This is a method for producing a gallium nitride crystal having a BSF peak / NBE peak) of 0.1 or less.

In the present invention, examples of a method for growing a crystal whose emission intensity ratio measured by low-temperature PL measurement of the crystal growth layer is in the above range include a method in which crystal growth is performed while the crystal growth surface is flat in the crystal growth step.
As a growth method for controlling the crystal growth surface to a flat surface, it is preferable to perform crystal growth in a liquid phase. As a method for performing crystal growth in the liquid phase, a solution or melt containing an alkali metal as a main component can be mentioned. “Containing as a main component” means containing 10% or more by weight% concentration.
Examples of the alkali metal include Li, Na, K, and Cs. The solution or melt used in the crystal growth step preferably contains these alkali metal components, but does not inhibit the epitaxial growth on the seed. There are no particular restrictions on the type of the product.

Among these, it is preferable to perform crystal growth in a liquid phase using hydrogen molecules and / or hydrides. Specifically, (1) a step of producing a solution or melt containing a raw material and a solvent (2) a liquid phase in the presence of a liquid phase that is a solution or a melt and a gas phase having hydrogen molecules and / or hydrides. Among them, a method including a growth step of epitaxially growing a gallium nitride crystal is preferable.
The “gas phase having hydrogen molecules and / or hydrides” means hydrogen molecules (H ₂ ), ammonia (NH ₃ ), methane (CH ₄ ), ethane (C ₂ H ₆ ), etc. in the gas phase. This means that at least a hydrogen molecule such as a nitrogen molecule (N ₂ ) or a component other than a hydride may be contained. Among these, ammonia or a combination of hydrogen (molecule) and nitrogen (molecule) is more preferable,
(1 ′) Step of producing a solution or melt containing a raw material and a solvent (2 ′) Nitriding in the liquid phase in the presence of a liquid phase that is a solution or a melt and a gas phase containing hydrogen and nitrogen or ammonia A method including a growth step of epitaxially growing a gallium crystal is particularly preferable.
In the present invention, the crystal surface is flat. When the crystal surface is observed with a microscope with a magnification of 100 times, if an acute angle protrusion (spin) can be confirmed, it is determined that the crystal surface is not flat. If not, it is judged flat. Even if there is a gentle slope, it will be flat if there are no sharp projections.

  The above (1) and (1 ') mean a step of preparing a liquid phase solution or melt used for epitaxial growth as a pre-stage of the crystal growth step. For example, an operation of dissolving the raw material in a solvent or an operation of adjusting the melt by heating or the like when the compound serving as the solvent is solid at room temperature is also included in the step of preparing the solution or the melt. However, the solution or melt containing the raw material and the solvent does not need to be completely dissolved in the solvent, and may be a heterogeneous system in which the solid raw material is dispersed or present in the solution as a solid.

  The above (2) and (2 ′) are growth steps using a liquid phase growth method in which a gallium nitride crystal is epitaxially grown in a region surrounded by the liquid phase. Further, hydrogen molecules and / or hydrides are introduced into the reaction system. It is a growth process that has a gas phase and uses hydrogen molecules and / or hydrides for reactions in epitaxial growth. Here, the “liquid phase that is a solution or a melt” in the growth step is not necessarily intended to be the same as the “solution or melt” in the step of preparing the solution or the melt described above. The “solution or melt” in the process of preparing the solution or melt is prepared for use in the growth process, but the “solution or melt” in the growth process includes a by-product generated by the reaction of epitaxial growth. This is because H, N, or the like supplied from the gas phase may be included and is not always the same as the initial composition (before the start of epitaxial growth).

With reference to a conceptual diagram (FIG. 1) of an apparatus used for crystal growth in a liquid phase using hydrogen molecules and / or hydrides, a manufacturing example of gallium nitride will be described in detail below. 1, 104 represents a reaction vessel, 108 represents LiCl as a molten salt serving as a solvent, 106 represents Li ₃ GaN ₂ (solid) as a composite nitride serving as a raw material, and 105 represents a gallium nitride crystal serving as a seed substrate. Yes. The growth process according to the present invention is characterized in that 109 gas phases containing hydrogen molecules and / or hydrides and 108 liquid phases comprising a solution or a melt exist.
Li ₃ GaN ₂ (Li ₃ GaN ₂ is considered to form a complex salt with Li ₃ N and dissolve) in the “liquid phase that is a solution or melt” reaches the seed substrate surface that is also present in the liquid phase. Crystal growth proceeds by an equilibrium reaction represented by the following formula (2).

Further, hydrogen molecules and / or hydrides in the “gas phase having hydrogen molecules and / or hydrides” are dissolved directly or in the liquid phase to hydrogenate Li ₃ N produced by the above formula (2). And / or nitriding to produce lithium hydride, lithium imide, or lithium amide.
For example, lithium amide (LiNH ₂ ) is produced by the reaction represented by the following formula (3) and / or (4). An increase in the Li ₃ N concentration in the vicinity of the gallium nitride crystal causes a decrease in the growth rate, and an abrupt decrease in the Li ₃ N concentration also leads to rapid GaN formation, leading to the generation of miscellaneous crystals and a decrease in crystallinity. Hydrogen molecules and / or hydrides serve to moderately regulate the growth rate. Incidentally, lithium hydride, lithium imide, the reaction of lithium amide is produced is both equilibrium reaction, it is possible to adjust the Li 3 _N concentration by the concentration of hydrogen molecules and / or hydride.

The method of crystal growth in the liquid phase using hydrogen molecules and / or hydrides is very effective for obtaining a gallium nitride crystal growth layer having a Si concentration higher than the O concentration. The hydrogen or hydride in the “gas phase having hydrogen molecules and / or hydride” is oxygen (O ₂ ) and / or oxygen-containing compounds (for example, H ₂ O, SiO ₂ ) present as impurities in the atmosphere in which epitaxial growth is performed. Removes and / or collects. Further, as described above, the hydrogen molecules and / or hydrides function to moderately adjust the growth rate, and can form gallium nitride crystals with few crystal defects such as dislocations, voids, and stacking faults. A crystal defect has a characteristic that it easily takes in a dopant such as oxygen, and a crystal with many defects inevitably tends to have a high O concentration. Therefore, by adopting such a growth method, it is possible to easily form a crystal having a Si concentration higher than the O concentration. In addition, the molten salt in which Li ₃ N is dissolved is a solution or melt in which the Si-containing component is easily dissolved, and also plays a role of increasing the Si concentration of the gallium nitride crystal growth layer.

The raw material for crystal growth in the liquid phase using hydrogen and nitrogen or ammonia can be set as appropriate. For example, like Li ₃ GaN ₂ described above, gallium (Ga) and the period can be set. A composite nitride containing a Group 1 metal and / or a Group 2 metal of the periodic table can be exemplified as a preferable example. Examples of the Group 1 metal and / or Group 2 metal include Na, Ca, Sr, Ba, Mg and the like in addition to Li. As a composite nitride containing Ga and a Group 1 metal and / or Group 2 metal, in addition to Li ₃ GaN ₂ , Ca ₃ Ga ₂ N ₄ , Ba ₃ Ga ₂ N ₄ , Mg ₃ GaN ₃ , Ba ₃ Ga ₂ N ₄ and the like. The composite nitride containing Ga and Group 1 metal and / or Group 2 metal is, for example, gallium nitride powder and Group 1 metal and / or Group 2 metal nitride powder (for example, Li ₃ N, Ca ₃ N ₂ ) and then a solid phase reaction by raising the temperature; a method of producing an alloy containing Ga and a Group 1 metal and / or a Group 2 metal and heating in a nitrogen atmosphere; etc. Can be prepared. For example, Li ₃ GaN ₂ can be manufactured by heat-treating a Ga—Li alloy at 600 to 800 ° C. in a nitrogen atmosphere.

  As a raw material other than the composite nitride containing Ga and Group 1 metal and / or Group 2 metal, for example, a target made of an alloy of Ga and Group 1 metal and / or Group 2 metal is used and reacted. Examples thereof include mixed nitride films synthesized by reacting with nitrogen plasma by a reactive sputtering method. The mixed nitride film is suitable when a nitride that is difficult to synthesize chemically is used.

  When the raw material is a solid in the above (2), the solid raw material does not need to be completely dissolved in the solvent. Even when a part is not dissolved but is present in the reaction vessel, the amount consumed by crystal growth is supplied to the solvent as needed. Further, the amount of the raw material with respect to the solvent is not particularly limited and can be appropriately set according to the purpose. These are usually 50% by mass or less, preferably 30% by mass or less, and more preferably 20% by mass or less. Within the above range, the efficiency for continuous production can be increased, and a space in the reaction vessel can be secured.

The specific kind of hydride in the “gas phase having hydrogen molecules and / or hydrides”, the concentration of hydrogen molecules and / or hydrides in the gas phase, and the like are not particularly limited. Examples of the hydride include ammonia (NH ₃ ), methane (CH ₄ ), ethane (C ₂ H ₆ ) and the like, and ammonia (NH ₃ ) is particularly preferable. Further, as described above, the gas phase may contain components other than hydrogen molecules and hydrides, for example, nitrogen molecules (N ₂ ) and the like. Hereinafter, conditions such as concentration when hydrogen molecules (H ₂ ) are included, when ammonia (NH ₃ ) is included, and when nitrogen (N ₂ ) is included will be described in detail.
When hydrogen molecules (H ₂ ) are included, the H ₂ concentration in the gas phase is usually 0.001 mol% or more, preferably 0.1 mol% or more, more preferably 1 mol% or more, usually 99.9 mol% or less, Preferably it is 99 mol% or less, More preferably, it is 90 mol% or less.
When ammonia (NH ₃ ) is contained, the NH ₃ concentration in the gas phase is usually 0.001 mol% or more, preferably 0.01 mol% or more, more preferably 0.1 mol% or more, and usually 99.9 mol% or less. , Preferably 99 mol% or less, more preferably 90 mol% or less.
When nitrogen molecules (N ₂ ) are contained, the N ₂ concentration in the gas phase is usually 0.1 mol% or more, preferably 1 mol% or more, more preferably 10 mol% or more, and usually 100 mol% or less, preferably 99.9 mol. % Or less, more preferably 99 mol% or less.
Furthermore, these components may be supplied in advance during the crystal growth, in addition to being previously contained in the gas phase.
When hydrogen gas (H ₂ ) is sequentially supplied, the supply flow rate is an amount converted to normal temperature and normal pressure, and is usually 0.0001 L / min or more, preferably 0.001 L / min or more, more preferably 0.01 L / min or more. It is usually 10 L / min or less, preferably 5 L / min or less, more preferably 1 L / min or less.
When ammonia gas (NH ₃ ) is sequentially supplied, it is usually 0.0001 L / min or more, preferably 0.001 L / min or more, more preferably 0.01 L / min or more, and usually 10 L / min or less, preferably 5 L. / Min or less, more preferably 1 L / min or less.
When nitrogen molecules (N ₂ ) are sequentially supplied, the supply flow rate is an amount converted to normal temperature and normal pressure, and is usually 0.001 L / min or more, preferably 0.01 L / min or more, more preferably 0.1 L / min or more. Usually, it is 100 L / min or less, preferably 50 L / min or less, more preferably 10 L / min or less.
In the case of sequentially supplying a mixed gas of hydrogen gas (H ₂ ) and nitrogen gas (N ₂ ) (when H _{2 is} 10 vol%), usually 0.001 L / min or more, preferably 0.01 L / min or more, more preferably Is 0.1 L / min or more, usually 100 L / min or less, preferably 50 L / min or less, more preferably 10 L / min or less.
When sequentially supplying a mixed gas of ammonia gas (NH ₃ ) and nitrogen gas (N ₂ ) (in the case of NH ₃ : 2.7 vol%), usually 0.001 L / min or more, preferably 0.01 L / min or more, More preferably, it is 0.1 L / min or more, usually 100 L / min or less, preferably 50 L / min or less, more preferably 10 L / min or less.
Within the above range, the gallium nitride crystal of the present invention can be produced efficiently.

  Although the solvent to be used is not specifically limited, the solvent which has a metal salt as a main component is preferable. The content of the metal salt is preferably 50% by weight or more, more preferably 70% by weight or more, and still more preferably 90% by weight or more. In particular, a molten salt obtained by melting a metal salt is preferably used as a solvent.

The type of the metal salt is not particularly limited as long as it does not inhibit the crystal growth. Alkali metal salts such as Li, Na and K and / or halides and carbonates of alkaline earth metal salts such as Mg, Ca and Sr Examples thereof include salts, nitrates, and sulfides. _{Specifically, LiCl, KCl, NaCl, CaCl} 2, BaCl 2, CsCl, LiBr, KBr, CsBr, LiF, KF, NaF, LiI, NaI, metal halides such as CaI 2, BaI ₂ preferably, LiCl, KCl, NaCl, CsCl, CaCl ₂ and BaCl ₂ are more preferable. The type of metal salt is not limited to one type, and a plurality of types of metal salts may be used in appropriate combination. Among these, it is more preferable to use lithium halide and a metal salt other than this together. The content of lithium halide is preferably 30% or more, more preferably 80% or more, based on the total amount of the metal salt.

In order to increase the solubility of the composite nitride containing Ga and the Group 1 metal and / or the Group 2 metal, for example, Li ₃ N, Ca ₃ N ₂ , Mg ₃ N ₂ , Sr ₃ N ₂ , It is preferable that a group 1 metal such as Ba ₃ N ₂ or a nitride of a group 2 metal is included in the solvent.

  Metal salts generally have a high hygroscopic property and therefore contain a large amount of moisture. In order to produce a gallium nitride crystal, it is necessary to remove impurities that can be an oxygen source such as moisture as much as possible, that is, it is preferable to purify the solvent in advance. Although the purification method is not particularly limited, for example, a method in which a reactive gas is blown into a solvent using an apparatus described in JP-A-2007-084422 can be mentioned. For example, when a metal salt that is solid at room temperature is used as a solvent, it is melted by heating to hydrogen chloride, hydrogen iodide, hydrogen bromide, ammonium chloride, ammonium bromide, ammonium iodide, chlorine, bromine, or iodine. Impurities such as moisture can be removed by bubbling with a reactive gas such as. It is particularly preferable to use hydrogen chloride for the molten salt of chloride.

In order to grow the crystal growth surface as a flat surface, it is preferable that the impurities in the liquid phase are small. Impurities in the liquid phase refer to elemental species dissolved in the liquid phase, chemical species dispersed in the liquid phase, chemical species attached to the substrate surface, and the like. When these impurities adhere to the crystal surface, it becomes difficult to grow the crystal growth surface as a flat surface, and stacking faults tend to occur in the crystal growth layer.
These impurities are preferably 100 ppm or less in the liquid phase, more preferably 10 ppm or less, and still more preferably 1 ppm or less.

  The form of the reaction vessel used for maintaining the liquid phase is not particularly limited, and can be appropriately set depending on the purpose. In addition, the material of the reaction vessel is not particularly limited as long as it does not inhibit the reaction in the production method of the present invention, but the main component is a thermally and chemically stable metal, oxide, nitride, or carbide. Is preferred. A metal containing a Group 4 element (Ti, Zr, Hf) of the periodic table is suitable, and Ti is preferably used.

The material of the reaction vessel is preferably a material rich in processability and mechanical durability.
It is more preferable to use a metal whose weight% is the Group 4 element. More preferably, 99% by weight or more of a metal that is the Group 4 element is used. Further, the surfaces of these reaction vessels are preferably made of nitrides of Group 4 elements of the periodic table, and it is preferable to form nitrides beforehand by a nitriding method as described later.

In addition, members to be used, such as a stirring blade, a seed crystal holding rod, a seed crystal holding table, a baffle, a gas introduction pipe, a valve, etc., are subjected to nitriding treatment as described below, on the surface in contact with the solution or melt. It is preferable to form a strong and stable nitride. In order to maintain workability and mechanical durability, the nitride may be formed in the form of a nitride film.
The nitriding treatment method is not particularly limited as long as the nitride formed on the surface is stable. For example, the member of the reaction vessel is heated and held in a nitrogen atmosphere at 700 ° C. or higher, so that stable nitriding is performed on the surface of the member. A film can be formed.
Furthermore, the surface of the member can be nitrided using an alkali metal nitride or alkaline earth metal nitride as a nitriding agent at a high temperature, preferably an alkali metal halide or an alkaline earth metal halide. A stable nitride film can be formed by holding it in a mixed melt with the alkali metal nitride or alkaline earth metal nitride. In addition, the nitriding treatment can be easily performed by holding the member under the same conditions as the actual crystal growth conditions.

  The growth temperature when growing the gallium nitride crystal in the reaction vessel is usually 200 ° C. or higher, preferably 400 ° C. or higher, more preferably 600 ° C. or higher, and usually 1000 ° C. or lower, preferably 850 ° C. or lower. More preferably, it is 800 degrees C or less. The pressure in the reaction vessel is usually 10 MPa or less, preferably 3 MPa or less, more preferably 0.3 MPa or less, more preferably 0.11 MPa or less, and usually 0.01 MPa or more, preferably 0.09 MPa. That's it.

  In order to uniformly distribute hydrogen or ammonia dissolved from the gas phase to the liquid phase in the solution or melt, it is desirable to stir the solution or melt. The stirring method is not particularly limited, but a method of stirring by rotating a substrate, a method of stirring by inserting a stirring blade, a method of creating and stirring a flow with a liquid feed pump, or rotating or swinging a reaction vessel Examples include a stirring method.

  The growth rate of crystal growth can be adjusted by the temperature, pressure, and the like. In particular, in order to grow the crystal growth surface as a flat surface, the growth rate may be 50 μm / day to 1 cm / day. Preferably, it is 100 μm / day to 0.5 cm / day.

  In crystal growth in the liquid phase, the seed substrate is usually held in the liquid phase by a fixing substrate holder. When crystal growth is performed, for example, a seed substrate fixed to a substrate holder is rotated in order to maintain uniformity in the liquid phase. By rotating the seed substrate, two surfaces are generated on the surface of the seed substrate: a surface that faces the liquid by the rotation and a surface that moves away from the liquid. In FIG. 1, the surface of the seed substrate 105 is a surface on the left half of the rotation axis that rotates toward the near side of the drawing and toward the liquid by the rotation. On the other hand, the right half of the rotating shaft rotates toward the back side in the figure, and becomes a surface away from the liquid by the rotation. The growth layer grown on the seed substrate surface toward the liquid, that is, on the left side in FIG. 1, is easy to grow with the growth surface as a flat surface. On the other hand, the growth layer grown on the side away from the liquid on the surface of the seed substrate, that is, on the right side portion in FIG. This is because a flow occurs in the liquid phase due to the rotation of the substrate, and the flow away from the surface of the seed substrate surface is disturbed. Therefore, it is difficult to grow the growth surface as a flat surface. This is also the case with stirring methods other than rotating the seed substrate, and even when using a stirring blade or a liquid feed pump, or when rotating or swinging the reaction vessel, In a place where the flow of the liquid is not easily disturbed, the growth surface is easy to grow as a flat surface.

Thus, in the crystal growth step, when crystal growth is performed while the crystal growth surface is flat, it is difficult to incorporate impurities into the crystal. Therefore, the impurity concentration other than the gallium nitride in the crystal growth layer is usually 10 ¹⁸ atoms / cm ³ or less, preferably 10 ¹⁷ atoms / cm ³ or less, more preferably 10 ¹⁶ atoms / cm ³ or less. Examples of impurities include H, O, C, Si, Cl, Li, Na, Ti, and Mg. However, when manufacturing an impurity semiconductor crystal as a crystal growth layer, the impurity element (O, Si, Mg, etc.) that can be a dopant is not limited to this, and a necessary amount can be controlled and incorporated.

  The gallium nitride crystal according to the present invention can be used for various applications. In particular, as a substrate for manufacturing a light emitting element on a relatively short wavelength side such as an ultraviolet to blue light emitting diode or a semiconductor laser, and a light emitting element on a relatively long wavelength side of green to red, further a semiconductor device such as an electronic device is used. It is also useful as a substrate.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, it is not limitedly interpreted only to the specific form shown in the following Examples.

<Evaluation of seed substrate>
A GaN crystal grown by the HVPE method was prepared, and this was used as a seed substrate as a GaN substrate (thickness 300 μm, size 5 × 20 mm) having a (10-10) plane as a main surface.
With respect to this seed substrate, low-temperature PL measurement was performed at four points (Point 1 to Point 4) shown in FIG. The result is shown in FIG. The low temperature PL measurement was performed at a measurement temperature of 4K using a He—Cd laser having a central wavelength of 325 nm as an excitation light source. The seed substrate used has a PL intensity ratio (BSF peak / NBE peak) near 0.14 to 0.87 due to stacking faults in the vicinity of 3.41 eV with respect to the band edge PL intensity of GaN, and contains a large amount of stacking faults. Met.

<Example 1>
(1) Put 4.5 g of solid Li ₃ GaN ₂ into a reaction vessel made of titanium (Ti) having an outer diameter of 34 mm, an inner diameter of 30 mm, and a height of 200 mm, and then pulverize 45 g of LiCl as a solvent in a tungsten carbide mortar. Into the reaction vessel. Solid Li ₃ GaN ₂ having a particle size of 710 μm or more and 2 mm or less was selected and used using a sieve. Next, a tungsten seed holding rod to which a reaction vessel and a GaN seed substrate were attached was set in a quartz reaction tube, and the gas inlet and the gas exhaust port of the reaction tube were closed. All these operations were performed in an Ar box.
(2) The reaction tube was taken out from the Ar box and set in an electric furnace. After connecting the gas introduction pipe to the reaction pipe and reducing the pressure inside the introduction pipe, the gas introduction port of the reaction pipe is further opened to reduce the pressure inside the reaction pipe, and then the pressure is restored to atmospheric pressure with a hydrogen-nitrogen mixed gas (hydrogen 10 vol%). The reaction tube was filled with hydrogen / nitrogen atmosphere. Thereafter, the gas exhaust port of the reaction tube was opened, and a hydrogen nitrogen mixed gas (hydrogen 10 vol%) was allowed to flow at a flow meter set value of 100 cm ³ / min (converted value with respect to 20 ° C. and 1 atm).
(3) Heating of the electric furnace was started, the temperature was raised in one hour until the inside of the reaction vessel reached room temperature to 750 ° C., and a molten salt obtained by melting LiCl as a salt was used as a solvent.
(4) After holding at 750 ° C. for 2 hours, the seed substrate attached to the tip of the seed holding rod was put into the solution (melt) in the reaction vessel to start crystal growth. (10-10 for seed substrate)
) Substrate was used as the main surface (thickness 300 μm, size 5 × 10 mm plate, same as the left half of FIG. 2 of the substrate used in the evaluation of the seed substrate).
(5) After growing at 750 ° C. for 89.5 hours, the seed substrate was lifted from the solution, and then the heating of the furnace was stopped and the quartz reaction tube was cooled. After cooling, the seed substrate was taken out from the reaction tube, and the salt adhering to the seed substrate was dissolved with water. A GaN crystal growth layer made of GaN crystals was formed on the main surface of the seed substrate, and the thickness was 23 μm. As a result of visual observation, the obtained GaN growth layer is colorless and transparent, and the O concentration in the GaN growth layer is sufficiently low, and the Si concentration is considered to be higher than the O concentration.

(6) PL measurement was performed using a He—Cd laser having a central wavelength of 325 nm as an excitation light source at a measurement temperature of 4K. Low-temperature PL measurement is performed on Point 5 and Point 6 shown in FIG. 4, and the results are shown in FIG. Among the generated GaN crystal growth layers, for Point 5, the PL intensity ratio (BSF peak / NBE peak) due to stacking faults near 3.41 eV with respect to the band edge PL intensity is 0.005, and the stacking faults are greatly reduced. Was confirmed to exist. As a result of observation with an optical microscope, the growth surface of the region where stacking faults were reduced was smooth, and the area of the flat portion in the crystal growth layer was 13 mm ^{2 as a} whole, and was continuously 10 mm ² .
On the other hand, for Point 6, the PL intensity ratio (BSF peak / NBE peak) due to stacking faults near 3.41 eV with respect to the band edge PL intensity was 0.18.

<Example 2>
(1) 2.16 g of solid Li ₃ GaN _{2 is} placed in a titanium (Ti) reaction vessel having an outer diameter of 34 mm, an inner diameter of 30 mm, and a height of 200 mm, and then 28.8 g of LiCl as a solvent is pulverized in a tungsten carbide mortar. Then, it was put in a reaction container. Solid Li ₃ GaN ₂ having a particle size of 710 μm or more and 2 mm or less was selected and used using a sieve. Next, a tungsten seed holding rod to which a reaction vessel and a GaN seed substrate were attached was set in a quartz reaction tube, and the gas inlet and the gas exhaust port of the reaction tube were closed. All these operations were performed in an Ar box.
(2) The reaction tube was taken out from the Ar box and set in an electric furnace. After connecting the gas introduction pipe to the reaction pipe and reducing the pressure inside the introduction pipe, the gas introduction port of the reaction pipe is further opened to reduce the pressure inside the reaction pipe, and then the pressure is restored to atmospheric pressure with a hydrogen-nitrogen mixed gas (hydrogen 5 vol%). The reaction tube was filled with hydrogen / nitrogen atmosphere. Thereafter, the gas exhaust port of the reaction tube was opened, and a hydrogen nitrogen mixed gas (hydrogen 5 vol%) was allowed to flow at a flow meter set value of 300 cm ³ / min (converted value for 20 ° C., 1 atm).
(3) Heating of the electric furnace was started, the temperature inside the reaction vessel was raised from room temperature to 745 ° C. over 1 hour, and a molten salt obtained by melting LiCl as a salt was used as a solvent.
(4) After holding at 745 ° C. for 7 hours, the seed substrate attached to the tip of the seed holding rod was put into the solution (melt) in the reaction vessel to start crystal growth. As the seed substrate, a GaN substrate (plate shape having a thickness of 800 μm and a size of 5 × 10 mm) having a (10-10) plane as a main surface was used. The GaN substrate is obtained by the same manufacturing method as the substrate used in the evaluation of the seed substrate, and is caused by a stacking fault near 3.41 eV with respect to the band edge PL intensity equivalent to the substrate used in the evaluation of the seed substrate. The PL intensity ratio (BSF peak / NBE peak) is shown.
(5) After growing at 745 ° C. for 40 hours, the seed substrate was lifted from the solution, and then the heating of the furnace was stopped, and the quartz reaction tube was cooled. After cooling, the seed was taken out from the reaction tube, and the salt adhering to the seed substrate was dissolved with water. A GaN growth layer made of GaN crystal was formed on the main surface of the seed substrate, and the thickness was 19 μm. As a result of visual observation, the obtained GaN growth layer was colorless and transparent.

(6) When SIMS measurement of the obtained growth layer was performed, the Si concentration was 1.8 × 10 ¹⁸ cm ⁻³ and the O concentration was below the detection lower limit (actual measurement value: 2.5 × 10 ¹⁶ cm ⁻³ , lower limit). Value: 3 × 10 ¹⁶ cm ^-3
), And the Na concentration was 3.2 × 10 ¹⁵ cm ⁻³ .
(7) The full width at half maximum of the rocking curve of the (100) diffraction peak of the X-ray diffraction of the obtained growth layer is 22 arcsec when the X-ray is incident in the direction parallel to the c-axis, and the X-ray is perpendicular to the c-axis. The incident light was 29 arcsec. The half-width of the rocking curve of the (300) diffraction peak measured by incidence of X-rays perpendicular to the c-axis was 70 arcsec, and measured by incidence of X-rays perpendicular to the c-axis (102) rocking of diffraction peaks. The half width of the curve was 32 arcsec, and all the results showed that the crystallinity of the obtained growth layer was extremely good. Further, 97% of the obtained growth surface was a nonpolar surface or a semipolar surface.

(8) Low temperature PL measurement was performed using a He-Cd laser having a central wavelength of 325 nm as an excitation light source at a measurement temperature of 13K. The result is shown in FIG. The generated GaN crystal growth layer had a PL intensity ratio (BSF peak / NBE peak) due to stacking faults in the vicinity of 3.41 eV with respect to the band edge PL intensity of 0.008. As a result of observation with an optical microscope, the surface of the GaN crystal growth layer was smooth, the area of the flat portion in the crystal growth layer was 45 mm ^{2 as a} whole, and the range of the continuous flat portion was 45 mm ² .

<Example 3>
(1) Put 1.5 g of solid Li ₃ GaN ₂ into a reaction vessel made of titanium (Ti) having an outer diameter of 34 mm, an inner diameter of 30 mm, and a height of 200 mm, and then pulverize 15 g of LiCl as a solvent in a tungsten carbide mortar. Into the reaction vessel. Solid Li ₃ GaN ₂ having a particle size of 710 μm or more and 2 mm or less was selected and used using a sieve. Next, a tungsten seed holding rod fitted with a reaction vessel and a GaN seed was set in a quartz reaction tube, and the gas inlet and the gas exhaust port of the reaction tube were closed. All these operations were performed in an Ar box.
(2) The reaction tube was taken out from the Ar box and set in an electric furnace. After connecting the gas introduction tube to the reaction tube and reducing the pressure in the introduction tube, the gas introduction port of the reaction tube is further opened to reduce the pressure in the reaction tube, and then the atmospheric pressure is applied with an ammonia-nitrogen mixed gas (ammonia 2.7 vol%). The pressure in the reaction tube was changed to an ammonia-nitrogen mixed atmosphere. Then, the gas exhaust port of the reaction tube was opened, and ammonia nitrogen mixed gas (ammonia 2.7 vol%) was circulated at a flow meter set value of 100 cm ³ / min (converted value for 20 ° C. and 1 atm).
(3) Heating of the electric furnace was started, the temperature was raised in one hour until the inside of the reaction vessel reached room temperature to 750 ° C., and a molten salt obtained by melting LiCl as a salt was used as a solvent.
(4) After holding at 745 ° C. for 2 hours, the seed substrate attached to the tip of the seed holding rod was put into the solution (melt) in the reaction vessel to start crystal growth. As the seed substrate, a GaN substrate (a plate shape having a thickness of 330 μm and a size of 5 × 10 mm) having a (20-21) plane as a main surface was used. The GaN substrate is obtained by the same manufacturing method as the substrate used in the evaluation of the seed substrate, and is caused by a stacking fault near 3.41 eV with respect to the band edge PL intensity equivalent to the substrate used in the evaluation of the seed substrate. The PL intensity ratio (BSF peak / NBE peak) is shown.
(5) After growing at 750 ° C. for 20 hours, the seed was lifted from the solution and then the furnace was turned off and the quartz reaction tube was cooled. After cooling, the seed substrate was taken out from the reaction tube, and the salt adhering to the seed substrate was dissolved with water. A GaN crystal growth layer made of GaN crystals was formed on the main surface of the seed substrate. As a result of visual observation, the obtained GaN growth layer was colorless and transparent.

(6) When SIMS analysis of the obtained GaN growth layer was performed, the Si concentration was 5.0 × 10 ¹⁷ cm ⁻³ , and the O concentration was below the detection lower limit (actual value: 2.0 × 10 ¹⁶ cm ⁻³ , Lower limit: 5 × 10 ¹⁶ cm ⁻³ ) and Na concentration was 1.6 × 10 ¹⁴ cm ⁻³ .
(7) The full width at half maximum of the rocking curve of the (201) diffraction peak of X-ray diffraction of the obtained GaN growth layer is 47 arcsec, indicating that the obtained GaN growth layer has good crystallinity. Further, 97% of the obtained growth surface was a nonpolar surface or a semipolar surface.

(8) Low temperature PL measurement was performed using a He-Cd laser with a central wavelength of 325 nm as the excitation light source at a measurement temperature of 4K. The result is shown in FIG. The produced GaN growth layer had a PL intensity ratio (BSF peak / NBE peak) due to stacking faults in the vicinity of 3.41 eV with respect to the band edge PL intensity of 0.003. As a result of observation with an optical microscope, the surface of the GaN growth layer was smooth, the area of the flat portion in the crystal growth layer was 60 mm ^{2 as a} whole, and the range of the continuous flat portion was also 60 mm ² .

DESCRIPTION OF SYMBOLS 100 Gas introduction port 101 Gas exhaust port 102 Electric furnace 103 Reaction tube 104 made of quartz Reaction vessel 105 Seed (underlying substrate)
106 Raw material 107 Seed holding rod 108 Solution or melt (liquid phase)
109 Gas phase with hydrogen and nitrogen or ammonia

Claims (12)

A gallium nitride crystal having a gallium nitride crystal growth layer on a seed substrate made of gallium nitride whose main surface is a nonpolar plane or a semipolar plane,
The ratio (BSF peak / NBE peak) of the emission intensity (BSF peak) at 3.41 eV to the band edge emission (NBE peak) of the gallium nitride crystal growth layer measured by low-temperature PL measurement is 0.1 or less. Oh it is,
A gallium nitride crystal in which the Si concentration in the gallium nitride crystal growth layer is higher than the O concentration .   Ratio of emission intensity (BSF peak / NBE peak) of emission (BSF peak) at 3.41 eV to band edge emission (NBE peak) of the seed substrate made of gallium nitride measured by low temperature PL measurement is 0.1 or more The gallium nitride crystal according to claim 1, wherein   The gallium nitride crystal according to claim 1 or 2, wherein a growth thickness of the gallium nitride crystal growth layer is 10 µm or more.   The gallium nitride crystal according to claim 1, wherein a main surface of the seed substrate made of gallium nitride is a nonpolar surface. 5. The nitriding according to claim 1 , having dislocations extending in a direction perpendicular to a nonpolar plane or a semipolar plane, and a dislocation density of the dislocations of 1.0 × 10 ⁸ cm ⁻² or less. Gallium crystal. The gallium nitride crystal according to claim 1, wherein the Si concentration is 1 × 10 ¹³ cm ⁻³ or more. The gallium nitride crystal according to claim 1, wherein the O concentration is 3 × 10 ¹⁸ cm ⁻³ or less. The Na concentration of the gallium nitride crystal growth layer is 1 × ¹⁰ 17 ^{cm -3} or less, the gallium nitride crystal according to any one of claims 1 7. A method for producing a gallium nitride crystal, comprising: a crystal growth step of growing a gallium nitride crystal growth layer on a seed substrate made of gallium nitride having a nonpolar plane or a semipolar plane as a main surface by a liquid phase method ,
Ratio of emission intensity (BSF peak / NBE peak) of emission (BSF peak) at 3.41 eV to band edge emission (NBE peak) of the gallium nitride crystal growth layer obtained by the crystal growth step, measured by low temperature PL measurement ) Is 0.1 or less, the manufacturing method of the gallium nitride crystal. Ratio of emission intensity (BSF peak / NBE peak) of emission (BSF peak) at 3.41 eV to band edge emission (NBE peak) of the seed substrate made of gallium nitride measured by low temperature PL measurement is 0.1 or more The method for producing a gallium nitride crystal according to claim 9 . The method for producing a gallium nitride crystal according to claim 9 or 10 , wherein a main surface of the seed substrate made of gallium nitride is a nonpolar surface. The method for producing a gallium nitride crystal according to claim 9 , wherein the crystal growth step is performed such that the growth surface is a flat surface.