JP5026271B2 - Method for producing hexagonal nitride single crystal, method for producing hexagonal nitride semiconductor crystal and hexagonal nitride single crystal wafer - Google Patents

Description

  The present invention relates to a method for producing a hexagonal nitride single crystal, a hexagonal nitride semiconductor crystal, and a method for producing a hexagonal nitride single crystal wafer. Specifically, a method for producing a hexagonal nitride single crystal, a hexagonal nitride single crystal, a hexagonal nitride semiconductor crystal obtained thereby, and a method for producing the same, and a hexagonal nitride single crystal wafer The present invention relates to a method and a hexagonal nitride single crystal wafer obtained thereby.

  A hexagonal nitride single crystal such as gallium nitride (GaN) is attracting attention as a material for semiconductor elements that emit blue or ultraviolet light. Blue laser diodes (LD) are applied to high-density optical discs and displays, and blue light-emitting diodes (LEDs) are applied to displays and illumination. In addition, ultraviolet LD is expected to be applied to biotechnology and the like, and ultraviolet LED is expected as an ultraviolet source of fluorescent lamps.

  Therefore, efforts to produce larger and higher quality hexagonal nitride single crystals are widely performed. One example is crystal growth in a liquid phase. The liquid phase growth method originally required ultra-high pressure and ultra-high temperature, but a method for growing crystals in Na flux was developed. As a result, the pressure and temperature conditions were about 50 ° C. at about 750 ° C. (5. It was possible to reduce the pressure to about 07 MPa). Recently, a mixture of Ga and Na was melted at 800 ° C. and 50 atm (5.07 MPa) in a nitrogen gas atmosphere containing ammonia, and the maximum crystal size was 1. with a growth time of 96 hours using this melt. A single crystal of about 2 mm is obtained (for example, see Patent Document 1).

In addition, after a GaN crystal layer is formed on a sapphire substrate by a metal organic chemical vapor deposition (MOCVD) method, a single crystal is grown by a liquid phase epitaxy (LPE) method, A method of growing a GaN single crystal by an HVPE method (hydride vapor phase epitaxy) using a substrate as a seed crystal has been performed (see, for example, Patent Document 2). In the HVPE method, GaN crystals can be grown on a sapphire substrate or GaAs substrate by reacting Ga and HCl gas to synthesize GaCl, and then reacting GaCl and NH ₃ to synthesize GaN. However, the obtained GaN substrate has a dislocation density exceeding 1 × 10 ⁷ / cm ² (see, for example, Patent Document 3).

  On the other hand, for semiconductor devices such as light emitting diodes and semiconductor lasers, methods for forming devices on surfaces other than the C surface have been proposed for the purpose of improving light emission efficiency. For example, when a device is formed on the (0001) plane (C plane) of an n-type GaN substrate, GaN has polarization in the C-axis direction. When AlGaN is formed on GaN, since lattice constants are different between GaN and AlGaN, distortion occurs at the interface. This strain causes the band structure to bend due to the generation of electric charges due to piezo polarization, so that the recombination efficiency of electrons and holes is lowered, and as a result, the light emission efficiency of the semiconductor laser or the light emitting diode is lowered (piezo effect). This piezo effect is particularly noticeable when a nitride light emitting device having a long wavelength (for example, blue-green or green wavelength) is produced. Therefore, it is important to reduce the piezo effect in a device that emits blue or green light. It becomes.

As a method of reducing the piezo effect, a method of forming a device on an inclined crystal plane inclined with respect to the main surface of the substrate has been proposed (for example, see Patent Document 4). In this method, an n-GaN layer is grown on a sapphire substrate, a growth mask film having an opening is formed thereon, an n-GaN crystal is grown from the opening, and an inclined crystal plane (1-101) The active layer and the p-GaN layer are grown on the substrate. According to this, from the viewpoint that threading dislocations from the substrate can be suppressed, the light emission efficiency can be improved by improving the crystallinity.
JP 2002-293696 A JP 2000-22212 A JP 2002-29897 A JP 2002-100805 A (Pamphlet of International Publication No. 02/07231)

  In order to reduce the piezo effect, it is conceivable to use a substrate whose principal surface is a surface other than the C surface. However, for example, when crystal growth is performed in the A-plane direction by liquid phase growth, high-quality crystals with high growth surface flatness due to unevenness on the crystal growth surface or coloring due to the incorporation of impurities from the inclined surface, etc. The present inventors have found a problem that it is difficult to obtain.

  As another method for reducing the piezo effect, a hexagonal nitride single crystal wafer having a surface other than the C-plane is manufactured by slicing a hexagonal nitride single crystal in parallel with the C-axis direction using the HVPE method. How to do is being studied. However, in order to realize the method for manufacturing the wafer, a hexagonal nitride single crystal having a larger thickness than the conventional one is required, but with the growth rate of the hexagonal nitride single crystal in the current method, This is insufficient from the viewpoint of practical use, and further improvement of the growth rate is required.

  Accordingly, the present invention provides a method for producing a hexagonal nitride single crystal capable of improving a growth rate and growing a large crystal of high quality in a short time, a high quality hexagonal nitride semiconductor crystal, and a high quality hexagonal crystal. An object of the present invention is to provide a method for producing a hexagonal nitride single crystal wafer from which a nitride single crystal wafer is obtained.

  The method for producing a hexagonal nitride single crystal of the present invention includes a step of simultaneously growing hexagonal nitride single crystals on both surfaces of a planar seed crystal substrate by liquid phase growth.

  The hexagonal nitride semiconductor crystal of the present invention is a hexagonal nitride semiconductor crystal whose outer shape is a hexagonal frustum.

  In the method for producing a hexagonal nitride single crystal wafer of the present invention, a hexagonal nitride single crystal grown in the C-axis or M-axis direction by liquid phase growth is obtained by combining an A plane, a (1-101) plane, and ( 11-22) Cut out by one surface selected from the group consisting of surfaces.

  In the method for producing a hexagonal nitride single crystal according to the present invention, since the hexagonal nitride single crystal is simultaneously grown on both surfaces of the planar seed crystal substrate, the growth rate is improved and a larger hexagonal nitride is obtained. A single crystal is obtained. Further, by simultaneously growing crystals on both surfaces of the seed crystal substrate, a high-quality hexagonal nitride single crystal in which the generation of strain inside the hexagonal nitride single crystal is reduced can be obtained.

  The hexagonal nitride semiconductor crystal of the present invention whose outer shape is a hexagonal frustum is of high quality.

  In the method for producing a hexagonal nitride single crystal wafer according to the present invention, a hexagonal nitride single crystal grown in the C-axis or M-axis direction is formed from an A plane, a (1-101) plane, and a (11-22) plane. Therefore, a high-quality hexagonal nitride single crystal wafer having an A-plane, a (1-101) plane, or a (11-22) plane is obtained. By using this hexagonal nitride single crystal wafer, the piezo effect is further reduced, and a semiconductor device having a further excellent luminous efficiency can be manufactured.

  Hereinafter, the present invention will be described in detail.

(Method for producing hexagonal nitride single crystal)
As described above, the method for producing a hexagonal nitride single crystal of the present invention includes a step of simultaneously growing a hexagonal nitride single crystal on both surfaces of a planar seed crystal substrate by liquid phase growth. To do.

  The hexagonal nitride single crystal is preferably a group III nitride single crystal, and examples of the group III nitride single crystal include a GaN single crystal and an AlN single crystal.

  The crystal growth includes at least one group III element selected from the group consisting of gallium, aluminum, and indium, a flux of at least one of an alkali metal and an alkaline earth metal, and nitrogen in the presence of a nitrogen-containing gas. It is preferable to carry out in the melt. Among them, it is more preferable to produce a GaN crystal using Ga as the group III element.

  The alkali metal is lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and francium (Fr), and the alkaline earth metal is calcium (Ca), magnesium. (Mg), strontium (Sr), barium (Ba) and radium (Ra). These may be used alone or in combination of two or more. For example, when growing a GaN single crystal, sodium (Na) is preferable, and a mixed flux obtained by adding lithium (Li), calcium (Ca), or the like to these may be used. In the case of growing an AlN single crystal, for example, calcium (Ca) and magnesium (Mg) are preferable, and bismuth (Bi), tin (Sn), lithium (Li), sodium (Na), etc. and calcium ( It is a mixed flux with Ca) and magnesium (Mg).

The nitrogen-containing gas is not particularly limited, and examples thereof include nitrogen (N ₂ ) gas, ammonia (NH ₃ ) gas, and a mixed gas of the two gases. Further, the seed crystal substrate may be dissolved by the melt before the nitrogen concentration in the melt increases. In order to prevent this, it is preferable that nitride is present in the melt at least at the initial stage of the reaction. Examples of the nitride include Ca ₃ N ₂ , Li ₃ N, NaN ₃ , BN, Si ₃ N ₄ and InN. These may be used alone or in combination of two or more. Good.

  The arrangement of the seed crystal substrate in the melt is not particularly limited as long as a hexagonal nitride single crystal can be grown on both surfaces of the seed crystal substrate, and both surfaces of the seed crystal substrate are in contact with the melt. What is necessary is just to arrange | position in the said melt in the state which contacted, For example, the method etc. which arrange | position the said seed crystal substrate in the state stood substantially perpendicularly in the said melt etc. are mentioned. As a specific example of the method of arranging the seed crystal substrate in a state of standing substantially vertically in the melt, a method of arranging the seed crystal substrate in a state of standing substantially perpendicular to the bottom surface of the crucible can be cited.

  The seed crystal substrate preferably has a + C plane and a -C plane. By using a seed crystal substrate having these planes, it is possible to obtain a hexagonal nitride single crystal having a higher crystal flatness, a lower dislocation density, and a higher quality. Further, in crystal growth on the −C plane, that is, crystal growth in the −C axis direction, polarity inversion occurs at the growth interface, and as a result, growth occurs in the + C axis direction. Therefore, when a GaN free-standing substrate is used as a seed crystal substrate and grown in a liquid phase, a high-quality crystal can be grown in the −C axis direction as in the + C axis direction by the polarity inversion, and a larger hexagonal system A nitride single crystal can be easily produced. By growing crystals on both sides of the seed crystal substrate in this way, the growth rate can be substantially doubled.

The seed crystal substrate, that the composition formula _{Al s Ga t In 1-st} N ( However, 0 ≦ s ≦ 1,0 ≦ t ≦ 1, s + t ≦ 1) is a hexagonal nitride semiconductor represented by preferable. Also, if the expansion coefficient of the seed crystal substrate is different from that of the single crystal grown on the seed crystal substrate, cracks are likely to occur during cooling after crystal growth. More preferably, the hexagonal nitride single crystal for crystal growth has the same composition. The seed crystal substrate can be formed on a heterogeneous substrate by, for example, metal organic chemical vapor deposition (MOCVD), halide vapor deposition (HVPE), molecular beam epitaxy (MBE), sublimation, or the like. When formed on a heterogeneous substrate, the heterogeneous substrate is preferably removed, and the seed crystal substrate is preferably only a hexagonal nitride single crystal.

The shape of the seed crystal substrate is not particularly limited, and examples thereof include a circle, a square, and a rectangle. The size of the seed crystal substrate is not particularly limited, and may be determined according to, for example, the size of a wafer to be cut out. The thickness of the seed crystal substrate is not particularly limited, and is preferably in the range of 0.1 mm to 1 mm, for example. Further, the dislocation density of the seed crystal substrate is not particularly limited, but is preferably a degree required for a semiconductor device, for example, 1 × 10 ⁷ / cm ² or less, more preferably 1 × 10 ⁵ / cm ² or less. It is.

Next, the hexagonal nitride single crystal of the present invention is a hexagonal nitride single crystal obtained by the method for producing a hexagonal nitride single crystal of the present invention. The hexagonal nitride single crystal of the present invention is a hexagonal nitride single crystal in which a hexagonal nitride single crystal having a growth surface of the + C plane is formed on both surfaces of a seed crystal substrate having a + C plane and a −C plane. It may be a single crystal or a hexagonal nitride single crystal obtained by cutting out the seed crystal substrate. The hexagonal nitride single crystal of the present invention is preferably an AlN single crystal and a GaN single crystal, and the dislocation density of threading dislocations in the growth direction is preferably 1 × 10 ⁵ / cm ² or less, for example.

(Hexagonal nitride semiconductor crystal and manufacturing method thereof)
The outer shape of the hexagonal nitride semiconductor crystal of the present invention is a hexagonal frustum. The hexagonal nitride semiconductor crystal is a crystal grown in the + C-axis direction, and the side surface of the crystal is preferably a (1-101) plane. The hexagonal nitride semiconductor crystal is preferably, for example, an AlN single crystal or a GaN single crystal. In the present invention, the hexagonal nitride semiconductor crystal and the hexagonal nitride single crystal are synonymous.

  The method for producing a hexagonal nitride semiconductor crystal of the present invention includes a step of growing a hexagonal nitride semiconductor crystal by liquid phase growth on a planar seed crystal substrate having a + C plane and a −C plane.

  The hexagonal nitride semiconductor crystal is a group III element nitride single crystal, and the crystal growth is at least one group III element selected from the group consisting of gallium, aluminum, and indium in the presence of a nitrogen-containing gas. And in a melt containing nitrogen and at least one flux of alkali metal and alkaline earth metal. The alkali metal and alkaline earth metal are as described above.

The seed crystal substrate can be the same as the method for producing a hexagonal nitride single crystal of the present invention. As will be described later, for example, when a hexagonal nitride single crystal is grown in the + C-axis direction from the + C plane of the seed crystal substrate, the obtained crystal has an inclination angle of 62 degrees with respect to the + C plane. Since it is a hexagonal frustum having side surfaces, the diameter (φ2 (mm)) of the seed crystal substrate is preferably determined so as to satisfy the relationship of the following formula.
(Φ2)> φ1 + {2T / tan (62 °)}
In the above formula, T (mm) is the thickness of the crystal grown on the + C plane of the seed crystal substrate, and φ1 (mm) indicates the diameter of the wafer cut out from the hexagonal nitride single crystal. The diameter is a line connecting a point on the outer periphery of the wafer surface and other points and is the length of the longest line.

  Since hexagonal nitride semiconductor crystals grow in the shape of a hexagonal frustum, in order to produce a single crystal of the same size, after crystal growth, the seed crystal substrate is cut out, and the cut out seed crystal substrate is It is preferably used again as a seed crystal substrate for crystal growth. Thus, by reusing the seed crystal substrate, not only the size but also the quality of the obtained crystal can be maintained more stably, so the practical effect is extremely large.

  3A to 3C show an example of a process for reusing the seed crystal substrate. First, a GaN free-standing substrate is prepared, and its surface is processed to form a seed crystal substrate 301 (FIG. 3A, surface processing step). The accuracy (Ra) of the processed surface is preferably 100 nm or less, more preferably 10 nm or less. Further, the work-affected layer contains, for example, crystal distortion and dislocations, which may affect the dislocation density and the like of the growing hexagonal nitride single crystal. For this reason, the thickness of the work-affected layer is preferably as small as possible, for example, 500 nm or less, preferably 100 nm or less, and more preferably 10 nm or less. The accuracy of the processed surface can be measured by, for example, AFM (Atomic Force Microscope), and the processed deteriorated layer means, for example, a portion where dislocations, defects, etc. are generated by processing.

  Next, for example, a hexagonal nitride semiconductor crystal 302 is grown on the seed crystal substrate using the apparatus 400 shown in FIG. 4 (FIG. 3B). Thereafter, the seed crystal substrate 301 and the hexagonal nitride semiconductor crystal 302 are separated by, for example, a wire saw (FIG. 3C). At this time, it is preferable to cut the seed crystal substrate and the single crystal above the seed crystal substrate and in the vicinity of the growth interface of the single crystal. In addition, the growth interface at the initial stage of growth contains a large amount of impurities. For this reason, by removing a semiconductor crystal portion (for example, a part of 302) grown on the seed crystal substrate 301 by processing such as polishing or grinding, the work-affected layer on the surface of the seed crystal substrate is removed. A seed crystal substrate 301 is obtained. In this way, it can be used again as a seed crystal substrate.

(Method for producing hexagonal nitride single crystal wafer)
In the method for producing a hexagonal nitride single crystal wafer of the present invention, a hexagonal nitride single crystal grown in the C-axis or M-axis direction by liquid phase growth is obtained by combining an A plane, a (1-101) plane, and ( 11-22) Cut out by one surface selected from the group consisting of surfaces.

  The hexagonal nitride single crystal is preferably a single crystal grown in the C-axis direction. By cutting a wafer from a hexagonal nitride single crystal grown in the C-axis direction at a plane other than the C plane, a high-quality wafer having an A plane, a (1-101) plane, or a (11-22) plane is obtained. can get. By using the hexagonal nitride single crystal wafer obtained by the manufacturing method of the present invention, the piezo effect can be further reduced, and a semiconductor device having further excellent luminous efficiency can be manufactured. The cut-out surface may be a surface having an angle of, for example, 0 degree to 5 degrees from the surface orientation.

  The hexagonal nitride single crystal includes, in the presence of a nitrogen-containing gas, at least one group III element selected from the group consisting of gallium, aluminum, and indium, and a flux of at least one of an alkali metal and an alkaline earth metal. A group III nitride single crystal grown on a seed crystal substrate in a melt containing nitrogen is preferable. Further, the hexagonal nitride single crystal of the present invention or the hexagonal nitride semiconductor crystal of the present invention may be used. The alkali metal, alkaline earth metal, and seed crystal substrate are as described above. The shape of the seed crystal substrate is not particularly limited, and examples thereof include a circle, a square, and a rectangle. Among these, a rectangle is preferable. By using a hexagonal seed crystal substrate grown in the + C-axis or + M-axis direction using a rectangular seed crystal substrate, for example, the A plane, M plane, (1-101) plane, and (11-22) More wafers having a surface such as a surface can be cut out. The growth surface of the seed crystal substrate is preferably processed flat.

  The cutting out of the wafer is not particularly limited, and can be performed by, for example, a wire saw. Moreover, when cutting out on a plane perpendicular to the A-axis of the single crystal ingot, for example, a cleavage plane may be used.

  The thickness of the wafer is not particularly limited, and is, for example, 0.4 to 0.5 mm. It is preferable that at least one surface of the wafer is mirror-finished and a peripheral portion thereof is chamfered.

  The thickness of the hexagonal nitride single crystal is not particularly limited, but the larger the thickness of the single crystal to be used, the larger the size of the wafer to be obtained. The thickness is, for example, 10 mm or more, preferably 25 mm or more, and more preferably 50 mm or more. For example, when the thickness in the + C-axis direction is 50 mm or more, a wafer having a diameter of 50 mm (2 inches) whose surface is the A surface is obtained.

  Next, the hexagonal nitride single crystal wafer of the present invention is a hexagonal nitride single crystal wafer obtained by the method for producing a hexagonal nitride single crystal wafer of the present invention. The surface of the hexagonal nitride single crystal wafer is preferably any one of the A plane, the (1-101) plane, and the (11-22) plane, and the shape is not particularly limited. , Round, rectangular and trapezoidal.

(Semiconductor device)
The semiconductor device of the present invention is a semiconductor device using a nitride semiconductor, and the nitride semiconductor includes the hexagonal nitride single crystal of the present invention.

  Next, an example of the method for producing a hexagonal nitride single crystal of the present invention will be specifically described.

The method for producing a hexagonal nitride single crystal of the present invention is carried out, for example, using an apparatus 400 shown in FIG. As shown in the figure, this apparatus has a flow rate regulator 409, a growth furnace 401 having a crucible fixing base 404, and a crucible 406 arranged on the crucible fixing base 404. A pipe is connected to the flow rate regulator 409, and a gas cylinder (not shown) is connected to one end of the pipe. The other end enters into the growth furnace 401 and is disposed on the crucible 406. A thermocouple 403 is attached to the growth furnace 401, and a heater 402 is disposed on the side wall of the crucible fixing base 404 in the growth furnace 401. A swinging mechanism (not shown) capable of rotating the crucible fixing base 404 around the rotation shaft 405 is attached to the crucible fixing base 404, whereby a crucible 406 disposed in the crucible fixing base 404 is attached. Can be swung. In the crucible 406, a crystal growth material, a seed crystal substrate 501 and the like can be arranged. Examples of the material of the crucible 406 include alumina (Al ₂ O ₃ ), boron nitride (BN), tungsten (W), tantalum (Ta), yttria (Y ₂ O ₃ ), and the like. The crucible may be a crucible whose surface is coated with these materials.

  A method for producing a hexagonal nitride single crystal using this apparatus will be described by taking production of a GaN single crystal as an example. First, Ga and flux, which are crystal materials, are charged into the crucible 406. Next, as shown in FIG. 4, the seed crystal substrate is placed in a state of being substantially perpendicular to the bottom surface of the crucible 406. These materials may be added simultaneously or separately. The crucible 406 is disposed in the growth furnace 401. In this state, the nitrogen-containing gas is sent into the growth furnace 401 through the pipe and heated. Then, by pressurizing and heating for a certain time, the material is melted to produce a melt 407, and Ga and nitrogen are reacted in the melt 407 to generate and grow a GaN crystal 502. After completion of the growth, the obtained crystal is taken out from the crucible 406. In order to produce a higher quality GaN single crystal with few dislocations, it is preferable to melt back the processed surface of the seed crystal substrate and further remove the work-affected layer before growing the crystal on the substrate.

  The reaction conditions are not particularly limited, but the temperature is, for example, in the range of 700 ° C. to 1100 ° C., preferably in the range of 800 ° C. to 900 ° C., and the pressure is, for example, in the range of 0.1 MPa to 20 MPa. Yes, preferably in the range of 1 MPa to 5 MPa.

  In the present invention, the swinging of the crucible is not particularly limited. For example, after the crucible is tilted in a certain direction, the crucible is tilted in a direction opposite to the direction to swing the crucible in a certain direction. Etc. Further, the rocking may be regular rocking or intermittent and irregular rocking. Moreover, you may use rotary motion together with rocking | fluctuation. The inclination of the crucible during rocking is not particularly limited.

  Before starting the growth of the crystal, the crucible is tilted in one direction and the melt is stored on one side (tilted side) of the crucible so that the melt does not contact the substrate surface. preferable. In this way, after confirming that the temperature of the melt has become sufficiently high, the melt can be supplied onto the substrate by swinging the crucible. And the like, and higher quality crystals can be obtained.

  In addition, after the growth of the single crystal, the crucible is tilted in one direction and the melt is stored on one side (tilted side) of the crucible bottom, thereby forming a hexagonal nitride formed on the substrate. It is preferable that the surface is removed from the single crystal surface. In this way, when the temperature in the crucible drops after the end of crystal growth, the hexagonal nitride single crystal from which the melt is obtained does not come into contact. As a result, it is possible to prevent a low-quality crystal from growing on the obtained crystal.

  Hereinafter, the present invention will be described in more detail with reference to examples.

  First, a seed crystal substrate was produced. A substrate having a diameter of 3 inches (75 mm) in which a GaN thin film having a thickness of 10 μm was formed on a sapphire substrate by MOCVD was prepared. Next, a GaN crystal having a thickness of 500 μm is grown on the substrate on which the GaN thin film has been formed by growing it at 850 ° C., 25 atm (2.59 MPa) for 96 hours in a melt of Na and Ga under a pressurized nitrogen atmosphere. Grew. A GaN substrate and a sapphire substrate were separated using a laser lift-off method. Specifically, since the sapphire substrate can transmit light up to 143 nm and the GaN crystal can transmit light near 370 nm, the third harmonic of the Nd: YAG laser (pulse width 5 nsec, repetition 10 Hz), By irradiating through the sapphire substrate and condensing the light at the interface between the sapphire substrate and the GaN crystal, the GaN crystal is decomposed to generate metal Ga and nitrogen gas to form voids. Separated. Using the separated GaN crystal as a seed crystal substrate, the growth surface (+ C plane and −C plane) was processed. Thereby, even if a thick single crystal is produced, a GaN free-standing substrate that can prevent the occurrence of cracks can be prepared as a seed crystal substrate.

In this embodiment, the GaN thin film formed by the MOCVD method is used as the seed crystal substrate, but it may be formed by using, for example, the HVPE method. That is, first, a GaN thin film is formed on a sapphire substrate by MOCVD. A Ti metal film is formed on the GaN thin film, and then a TiN film with voids is formed by performing a heat treatment of NH _{3 on} the Ti film. Then, for example, a GaN crystal having a thickness of 1000 μm is formed on the TiN film by HVPE. Specifically, hydrogen and hydrogen chloride gas are sprayed onto a Ga port containing Ga melt, GaCl is generated, and hydrogen and NH ₃ gas are sprayed near the susceptor on which the substrate on which the TiN film is formed is disposed. A GaN crystal grows. Then, a GaN free-standing substrate is obtained by peeling off the GaN crystal.

Using the apparatus shown in FIG. 4, a gallium nitride single crystal was grown simultaneously on both the + C plane and the −C plane of the seed crystal substrate as described above. Specifically, in a nitrogen (N ₂ ) gas atmosphere, Ga and flux Na were heated and pressurized under the following conditions, and then the seed crystal substrate was placed substantially vertically on the bottom of the crucible. Arranged and grown gallium nitride single crystal. The obtained gallium nitride single crystal is shown in the optical micrograph of FIG. 1A, and FIG. 1B shows a schematic diagram of its shape. As shown in the optical micrograph of FIG. 1A, a gallium nitride single crystal having a thickness of 1000 μm was grown on the + C plane, and a 580 μm thick gallium nitride single crystal was grown on the −C plane. In addition, the gallium nitride single crystal grown on the −C plane was inverted in polarity at the growth interface, and was grown in the + C axis direction. That is, the polarity was reversed with respect to the seed crystal substrate, and the gallium nitride single crystal was grown with the + C plane as the growth plane. Similarly to the + C plane, crystal growth is also possible on the −C plane, so that the growth rate can be substantially doubled by simultaneously growing crystals on both sides of the seed crystal substrate. Furthermore, since the growth on the + C plane and the growth on the −C plane are isotropic growth, distortion inside the crystal can be reduced, and a high quality single crystal was obtained. From the GaN single crystal thus obtained, a substrate having a C-plane main surface can be sliced and a large number of substrates can be cut out. Further, by cutting out the GaN single crystal grown on both surfaces of the seed crystal substrate in a direction perpendicular to the surface direction of the seed crystal substrate, a larger substrate whose main surface is the A plane and the M plane is taken out. You can also.

(Production conditions)
Growth temperature: 850 ° C
Growth pressure: 30 atm (3.04 MPa)
Growth time: 144 hours Used crucible: Alumina crucible used gas: N ₂ gas

A gallium nitride single crystal was grown only on one side (+ C plane) of the seed crystal substrate under the same manufacturing conditions as in Example 1. Specifically, Ga and Na as a flux were heated and pressurized under a nitrogen (N ₂ ) gas atmosphere under the following conditions to be melted. Subsequently, the seed crystal substrate was placed in a state in which it was laid down in the melt to grow a gallium nitride single crystal, and a gallium nitride single crystal having a thickness of 3 mm was obtained. 2A shows the obtained gallium nitride single crystal, FIG. 2B shows a schematic diagram thereof, and FIG. 2C shows a plan view from the direction of the arrow in FIG. As shown in the photograph of FIG. 2A, when the obtained crystal was observed from the + C plane, the side surface of the obtained crystal had an inclined surface. More specifically, the bottom surface of the obtained crystal was a hexagon surrounded by an M plane, and the side surface was a (1-101) plane having an inclination angle of 62 degrees with the + C plane. The mechanism having such a shape is assumed as follows. That is, when a crystal is grown by liquid phase growth, the crystal grows in a region where the supersaturation in the melt is small, so that the driving force for growth is small and the natural surface of the crystal is likely to be formed. Therefore, when a seed crystal substrate having a + C plane is used, it grows on a flat surface in the C-axis direction, but the side surface is assumed to be a (1-101) plane, that is, an inclined plane.

(Production conditions)
Growth temperature: 850 ° C
Growth pressure: 30 atm (3.04 MPa)
Growth time: 144 hours Used crucible: Alumina crucible used gas: N ₂ gas

  In the HVPE method, the same examination was performed using a planar seed crystal substrate having a + C plane. As a result, as in the case of the liquid phase growth, the gallium nitride single crystal grows in the + C-axis direction, and when viewed from the + C plane, is a hexagon surrounded by the M plane, and its side surface is 62 degrees from the + C plane. (1-101) plane having an inclination angle of.

In the same manner as in Example 1, a rectangular seed crystal substrate (width 30 mm, length 100 mm, thickness 1 mm) was prepared, and a gallium nitride single crystal was formed on the + C plane of the seed crystal substrate using the apparatus shown in FIG. Grew. Specifically, a predetermined amount of Ga and Na was heated and pressurized and melted under the following conditions in a nitrogen (N ₂ ) gas atmosphere. Subsequently, the seed crystal substrate was placed in a state of being laid in the melt, and a gallium nitride single crystal was grown. During crystal growth, the crucible was swung at a speed of one cycle per minute with the seed crystal substrate being present in the melt. As a result, a rectangular parallelepiped GaN single crystal having a thickness of 30 mm was obtained at a growth rate of about 60 μm / h. In this way, by using a rectangular seed crystal substrate and growing a rectangular parallelepiped GaN single crystal, for example, a substrate whose A-plane, (1-101) plane, (11-22) plane, etc. are main planes. Is obtained.

(Production conditions)
Growth temperature: 800 ° C
Growth pressure: 50 atm (5.07 MPa)
Growth time: 480 hours Used crucible: Alumina crucible used gas: N ₂ gas

  Using a rectangular GaN single crystal having a thickness of 30 mm obtained by the method of Example 3, a circular GaN single crystal wafer having a substrate surface A-plane was manufactured by steps 1 to 3 shown in FIG. That is, first, a GaN single crystal ingot is cylindrically processed by grinding, an orientation flat is formed in the periphery (step 1), the ingot is sliced with a wire saw at a pitch of 700 μm, and a circular substrate having a thickness of 500 μm is formed. Obtained (step 2). Then, lapping and surface polishing were performed on the surface of the circular substrate (Step 3) to manufacture a circular GaN single crystal wafer having a diameter of 25 mm (1 inch) and a thickness of 350 μm.

  A rectangular GaN seed crystal substrate (width 30 mm, length 100 mm, thickness 1 mm) having a + C plane and having the longitudinal direction of the A axis was used, and a GaN single crystal was grown thereon (thickness 30 mm). A schematic diagram of the GaN single crystal ingot is shown in FIG. 6A. Next, the ingot was sliced along a plane perpendicular to the + A axis (FIG. 6A) to produce a trapezoidal wafer having an A plane surrounded by a C plane and a (1-101) plane (FIG. 6B). By cutting out from a hexagonal nitride single crystal grown in the C-plane direction, a hexagonal nitride single crystal wafer having a higher quality A-plane could be produced.

  A wafer was fabricated using the same GaN single crystal ingot as in Example 5. That is, a GaN single crystal having a thickness of 30 mm on a rectangular GaN seed crystal substrate (width 30 mm, length 100 mm, thickness 1 mm) having a + C plane and a longitudinal direction of the A axis is 58.4 degrees with respect to the + C plane. By slicing on a plane having an angle (FIG. 7A), a trapezoidal wafer having a (11-22) plane was produced (FIG. 7B). By cutting out from a hexagonal nitride single crystal grown in the C-plane direction, a hexagonal nitride single crystal wafer having an A plane having a higher quality (11-22) plane could be produced.

  A rectangular GaN seed crystal substrate (width 30 mm, length 100 mm, thickness 1 mm) having a + C plane and the longitudinal direction of the M axis was used, and a GaN single crystal was grown thereon (thickness 30 mm). A schematic diagram of the GaN single crystal ingot is shown in FIG. 8A. Next, as shown in FIG. 8A, the ingot is sliced by a plane inclined from the M plane, that is, a plane having an angle of 62 degrees with the + C plane, thereby forming a trapezoidal wafer having a (1-101) plane. Was produced (FIG. 8B). By cutting out from a hexagonal nitride single crystal grown in the C-plane direction, a hexagonal nitride single crystal wafer having an A-plane having a higher quality (1-101) plane could be produced.

A semiconductor laser shown in FIG. 9 was fabricated on the A-plane GaN substrate obtained by the manufacturing method of Example 2. That is, on the A-plane GaN substrate A01, a contact layer A02, an n-type cladding layer A03 made of n-type Al _0.05 Ga _0.95 N (thickness 1.2 μm), and an optical guide layer A04 made of n-type GaN (thickness 0.05 μm) , A quantum well active layer A05 having a multiple quantum well structure containing InGaN (well layer 7 nm, barrier layer 10 nm and two well layers (total thickness 37 nm)), undoped GaN cap layer (not shown, thickness 0) .01 μm), p-type GaN light guide layer A06 (thickness 0.05 μm), p-type AlGaN p-type cladding layer A07 (thickness 0.5 μm), p-type GaN contact layer A08 (thickness 0.15 μm) ) Were sequentially laminated by crystal growth, and an insulating layer A09 (thickness 0.1 μm) made of SiO ₂ was further laminated thereon. The insulating layer A09 is provided with a stripe-shaped opening extending in the direction of the resonator in order to form a current confinement structure, and the p-type GaN contact layer A08 is exposed from the opening. A p-electrode A10 (material Pd / Ti / Pt / Au, thickness 0.3 μm) is formed on the exposed upper surfaces of the p-type GaN contact layer A08 and the insulating layer A09, whereby carriers (holes) are formed in the current confinement structure. Can be injected. On the back surface of the n-type GaN substrate A01, an n-electrode A11 (material Mo / Ti / Au, thickness 0.3 μm) was formed. The length, width and thickness of the laser resonator were 600 μm, 300 μm and 80 μm, respectively, and the width of the current confinement structure 115 was about 2 μm.

  The laser resonator is formed by cleavage, and a dielectric multilayer film is formed on the front end face and the rear end face of the cavity end face so that the reflectivity of the front end face is 10% and the reflectivity of the rear end face is 90%. I made it.

  Since the semiconductor laser manufactured as described above has a light emitting region formed on the A-plane capable of suppressing piezo polarization, it is possible to suppress a decrease in light emission recombination probability due to piezo polarization seen in conventional semiconductor lasers. A blue / green semiconductor laser with a low threshold current can be realized.

  As described above, according to the manufacturing method of the present invention, the planar seed crystal substrate is used, and the hexagonal nitride single crystal is simultaneously grown on both surfaces thereof, so that the growth rate can be further improved. . Furthermore, since the crystal growth on both sides of the seed crystal substrate is isotropic, distortion inside the crystal can be reduced, the resulting crystal is of high quality, and its practical effect is great. The hexagonal nitride single crystal obtained according to the present invention can be used as, for example, a semiconductor, and can be particularly suitably used as a substrate of a light emitting device, and can be used for other purposes.

FIG. 1A is an optical micrograph of the gallium nitride crystal obtained in Example 1 of the present invention, and FIG. 1B is a schematic diagram showing its shape. 2A is an optical micrograph of the gallium nitride single crystal obtained in Example 2 of the present invention, FIG. 2B is a schematic diagram showing the shape, and FIG. 2C is a view from the direction of the arrow in FIG. 2B. It is a top view of a crystal. FIG. 3 is a process diagram showing an example of a method for producing a hexagonal nitride single crystal of the present invention. FIG. 4 is a structural sectional view showing an example of the structure of a production apparatus used in the method for producing a hexagonal nitride single crystal of the present invention. FIG. 5 is a scheme showing an example of a method for producing a hexagonal nitride single crystal wafer of the present invention. FIG. 6A is a schematic view showing another example of the method for producing a hexagonal single crystal wafer of the present invention, and FIG. 6B is a schematic view of a hexagonal nitride single crystal wafer obtained thereby. FIG. 7A is a schematic view showing still another example of the method for producing a hexagonal single crystal wafer of the present invention, and FIG. 7B is a schematic view of a hexagonal nitride single crystal wafer obtained thereby. FIG. 8A is a schematic view showing still another example of the method for producing a hexagonal single crystal wafer of the present invention, and FIG. 8B is a schematic view of a hexagonal nitride single crystal wafer obtained thereby. . FIG. 9 is a sectional view showing the configuration of the semiconductor laser manufactured in Example 8 of the present invention.

Explanation of symbols

101, 201, 301, 501 Seed crystal substrate 102, 202, 502 Hexagonal nitride single crystal 302 Hexagonal nitride semiconductor crystal 400 Manufacturing apparatus 401 Growth furnace 402 Heater 403 Thermocouple 404 Crucible fixing base 405 Rotating shaft 406 Crucible 407 Melt 409 Flow controller A01 Substrate A02, A08 Contact layer A03, A07 Clad layer A04, A06 Light guide layer A05 Active layer A09 Insulating layer A10, A11 Electrode

Claims (5)

A method for producing a group III element nitride single crystal,
Preparing a seed crystal substrate having a + C plane and a -C plane and having the same composition as the group III element nitride single crystal for crystal growth;
A melt containing at least one group III element selected from the group consisting of gallium, aluminum and indium, at least one flux of alkali metal and alkaline earth metal, nitrogen, and the + C plane and − of the seed crystal substrate Arranging the seed crystal substrate so that the C-plane is in contact;
A method for producing a group III element nitride single crystal, comprising simultaneously growing a group III element nitride single crystal from both the + C plane and the −C plane of the seed crystal substrate in the presence of a nitrogen-containing gas. The method for producing a group III element nitride single crystal according to claim 1, wherein the seed crystal substrate is arranged in a state of being substantially vertical in the melt. The seed crystal substrate, the composition formula _{Al s Ga t In 1-st} N ( However, 0 ≦ s ≦ 1,0 ≦ t ≦ 1, s + t ≦ 1) is a group III element nitride single crystal represented claimed Item 3. A process for producing a Group III element nitride single crystal according to Item 1. 2. The group III element nitride according to claim 1, wherein the group III element nitride single crystal grown from the −C plane of the seed crystal substrate has a polarity reversed with respect to the seed crystal substrate and grows using the + C plane as a growth plane. A method for producing a single crystal. A method for producing a group III element nitride single crystal wafer,
A group III element nitride single crystal obtained by the manufacturing method according to claim 1 is cut out by one plane selected from the group consisting of an A plane, a (1-101) plane, and a (11-22) plane. A method for producing a group III element nitride single crystal wafer.

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