JP2014205618A - β-Ga2O3-BASED SINGLE CRYSTAL AND SUBSTRATE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-quality β-GaO-based single crystal and a substrate by suppressing variation of a crystal structure in the vertical direction to a b-axis.SOLUTION: A β-GaO-based single crystal in which a crystal growth direction is a b-axis direction, and the addition concentration of Sn is 0.005 mol%-1.0 mol% is grown by using an EFG(Edge-defined Film-fed Growth) method. In the obtained single crystal, each substrate whose position from a seed crystal is 40 mm and 90 mm is cut out respectively, and a difference between a peak position of an X-ray diffraction profile of each substrate and the rotation angle of an approximate curve is determined, and the mean value α thereof is determined. The α becomes smaller in proportion to the smallness of variation of the peak position of the X-ray diffraction profile in the vertical direction to the b-axis. The variation of a crystal structure in the vertical direction to the b-axis is more similar to that of the seed crystal in proportion to the smallness of the α ratio which is a ratio of α in each crystal to α of the seed crystal, thereby a high-quality crystal obtained.

Description

The present invention relates to a β-Ga ₂ O ₃ single crystal and a substrate.

Conventionally, a growth method of a tabular Ga ₂ O ₃ single crystal using an EFG (Edge-defined Film-fed Growth) method is known (for example, see Patent Document 1).

According to Patent Document 1, Si is added to a Ga ₂ O ₃ single crystal using SiO ₂ as a dopant raw material. SiO ₂ has a small difference in melting points of _{Ga 2 O 3, Ga 2 O} 3 has a low vapor pressure at the growth temperature of the single crystal _(Ga 2 _{O 3} melting point of the single crystal raw material), _Ga 2 _{O 3} single crystal It is easy to control the amount of dopant therein.

Conventionally, a columnar β-Ga ₂ O ₃ single crystal growth method using an FZ (Floating Zone) method is known (see, for example, Patent Document 2).

According to Patent Document 2, Si, Sn, Zr, Hf, Ge, or the like is added to the β-Ga ₂ O ₃ single crystal as an additive for adjusting thermal melting. By adding the additive for adjusting the heat melting property, the infrared absorption characteristic of the β-Ga ₂ O ₃ single crystal is increased, and the infrared light from the light source of the FZ apparatus is efficiently used by the β-Ga ₂ O ₃ single crystal. To absorb. For this reason, even if the outer diameter of the β-Ga ₂ O ₃ -based single crystal is large, the temperature difference between the central portion and the outside becomes small, and the central portion becomes difficult to solidify.

JP 2011-190127 A JP 2006-273684 A

One of the objects of the present invention is to provide a high-quality β-Ga ₂ O ₃ -based single crystal and a substrate while suppressing variations in crystal structure in the direction perpendicular to the b-axis.

One aspect of the present invention, in order to achieve the above object, the addition concentration of Sn is 0.005mol% ~1.0mol% of _β-Ga 2 _{O 3} single crystal, and the _β-Ga 2 _{O 3} system single A substrate made of a crystal is provided.

According to the present invention, it is possible to provide a high-quality β-Ga ₂ O ₃ single crystal and a substrate while suppressing variations in crystal structure in the direction perpendicular to the b-axis.

FIG. 1 is a vertical sectional view of a part of an EFG crystal manufacturing apparatus according to an embodiment. FIG. 2 is a perspective view illustrating a state during the growth of the β-Ga ₂ O ₃ single crystal. FIG. 3A is a plan view showing a substrate cut out from a β-Ga ₂ O ₃ -based single crystal and measurement positions of X-ray diffraction. FIG. 3B is an image diagram in which X-ray diffraction profiles obtained at each measurement point are arranged along a direction perpendicular to the b-axis. FIG. 4 is a diagram showing the distribution of X-ray diffraction intensity for each measurement point. FIG. 5 is a graph showing a curve representing the relationship between the substrate position and the peak position of the X-ray diffraction profile and its approximate straight line. 6A and 6B show the distribution of X-ray diffraction intensity for each measurement point on a substrate centered on a point 40 mm from the seed crystal, cut out from crystals A and B, respectively. FIGS. 7A and 7B show the distribution of X-ray diffraction intensity for each measurement point of the substrate centered on a point 40 mm from the seed crystal, cut out from the crystals C and D, respectively. FIG. 8 is a diagram showing variations in crystal structures in the direction perpendicular to the b-axis of crystals A and B to which Sn is added, crystals C and D to which Si is added, and crystal EF to which no additive is added.

Embodiment
In this embodiment, a tabular β-Ga ₂ O ₃ single crystal to which Sn is added is grown in the b-axis direction using a seed crystal. Thereby, a β-Ga ₂ O ₃ -based single crystal with small variations in crystal quality in the direction perpendicular to the b-axis direction can be obtained.

Conventionally, in many cases, Si is used as a conductive impurity added to the Ga ₂ O ₃ crystal. Si has a relatively low vapor pressure at the growth temperature of the Ga ₂ O ₃ single crystal among the conductivity type impurities added to the Ga ₂ O ₃ crystal, and the amount of evaporation during crystal growth is small. Control of the conductivity of the Ga ₂ O ₃ crystal is relatively easy.

On the other hand, Sn has a higher vapor pressure at the growth temperature of the Ga ₂ O ₃ single crystal than Si, and the amount of evaporation during crystal growth is large. Therefore, it is a little difficult to treat as a conductive impurity added to the Ga ₂ O ₃ crystal.

However, the inventors of the present application added the Si under a specific condition of growing a flat β-Ga ₂ O ₃ single crystal in the b-axis direction, so that the crystal structure in the b-axis direction is constant. However, it has been found that there is a large variation in the crystal structure in the direction perpendicular to the b-axis. The inventors of the present application have found that the problem can be solved by adding Sn instead of Si.

(Growth of β-Ga ₂ O ₃ single crystal)
Hereinafter, as an example of a method for growing a flat β-Ga ₂ O ₃ single crystal, a method using an EFG (Edge-defined film-fed growth) method will be described. Note that the growth method of the flat β-Ga ₂ O ₃ single crystal of the present embodiment is not limited to the EFG method, and other growth methods such as a pulling-down method such as a micro PD (pulling-down) method are used. May be. Further, a die having a slit like a die of the EFG method may be applied to the Bridgman method to grow a plate-like β-Ga ₂ O ₃ single crystal.

FIG. 1 is a vertical sectional view of a part of the EFG crystal manufacturing apparatus according to the present embodiment. The EFG crystal manufacturing apparatus 10 includes a crucible 13 for receiving a Ga ₂ O ₃ melt 12, a die 14 having a slit 14 a installed in the crucible 13, and a die 14 including an opening 14 b of the slit 14 a. A lid 15 that closes the upper surface of the crucible 13 so as to expose the upper part, a seed crystal holder 21 that holds a β-Ga ₂ O ₃ -based seed crystal (hereinafter referred to as “seed crystal”) 20, and a seed crystal holder And a shaft 22 that supports 21 so as to be movable up and down.

The crucible 13 contains a Ga ₂ O ₃ melt 12 obtained by dissolving Ga ₂ O ₃ powder. The crucible 13 is made of a material such as iridium having heat resistance that can accommodate the Ga ₂ O ₃ melt 12.

The die 14 has a slit 14a for raising the Ga ₂ O ₃ melt 12 by capillary action.

The lid 15 prevents the high-temperature Ga ₂ O ₃ melt 12 from evaporating from the crucible 13 and further prevents the vapor of the Ga ₂ O ₃ melt 12 from adhering to a portion other than the upper surface of the slit 14a. .

Lowers the seed crystal 20 is contacted from the opening 14b of the slit 14a in the _Ga 2 _{O 3} KeiTorueki 12 spread on the top surface of the die 14, pulling the seed crystal 20 in contact with the _Ga 2 _{O 3} KeiTorueki 12 As a result, a flat β-Ga ₂ O ₃ single crystal 25 is grown. crystal orientation of the _β-Ga 2 _{O 3} single crystal 25 is equal to the crystal orientation of the seed crystal 20, in order to control the crystal orientation of the _β-Ga 2 _{O 3} single crystal 25 is, for example, the bottom surface of the seed crystal 20 Adjust the plane orientation and angle in the horizontal plane.

FIG. 2 is a perspective view illustrating a state during the growth of the β-Ga ₂ O ₃ single crystal. A surface 26 in FIG. 2 is a main surface of the β-Ga ₂ O ₃ single crystal 25 parallel to the slit direction of the slit 14a. If cut out _β-Ga 2 _{O 3} single crystal 25 is grown to form a _β-Ga 2 _{O 3} system board, the plane orientation of the desired major surface of the _β-Ga 2 _{O 3} based substrate beta-Ga The plane orientation of the face 26 of the ₂ O ₃ system single crystal 25 is matched. For example, when a β-Ga ₂ O ₃ -based substrate having a (−201) plane as a main surface is formed, the plane orientation of the plane 26 is set to (−201). The grown β-Ga ₂ O ₃ single crystal 25 can be used as a seed crystal for growing a new β-Ga ₂ O ₃ single crystal. The crystal growth direction shown in FIGS. 1 and 2 is a direction (b-axis direction) parallel to the b-axis of the β-Ga ₂ O ₃ -based single crystal 25.

The β-Ga ₂ O ₃ single crystal 25 and the seed crystal 20 are a β-Ga ₂ O ₃ single crystal or a Ga ₂ O ₃ single crystal to which an element such as Al or In is added. For example, Al and In are _β-Ga 2 _{O 3} single crystal is added _{(Ga x Al y In (1-} x - y)) 2 O 3 (0 <x ≦ 1,0 ≦ y ≦ 1,0 <X + y ≦ 1) A single crystal may be used. When Al is added, the band gap is widened, and when In is added, the band gap is narrowed.

An amount of Sn raw material is added to the β-Ga ₂ O ₃ type raw material such that Sn having a desired concentration is added. For example, when the β-Ga ₂ O ₃ single crystal 25 for cutting out an LED substrate is grown, SnO ₂ is added in such an amount that Sn having a concentration of 0.005 mol% or more and 1.0 mol% or less is added. Add to _β-Ga 2 _{O 3} system material. When the concentration is less than 0.005 mol%, sufficient characteristics as a conductive substrate cannot be obtained. Moreover, when it exceeds 1.0 mol%, problems such as a decrease in doping efficiency, an increase in absorption coefficient, and a decrease in yield are likely to occur.

Below, an example of the growth conditions of the β-Ga ₂ O ₃ based single crystal 25 of the present embodiment will be described.

For example, the β-Ga ₂ O ₃ single crystal 25 is grown in a nitrogen atmosphere.

In the example shown in FIGS. 1 and 2, a seed crystal 20 having a horizontal cross section substantially the same size as the Ga ₂ O ₃ single crystal 25 is used. In this case, since the shoulder widening process for expanding the width of the Ga ₂ O ₃ single crystal 25 is not performed, twinning that is likely to occur in the shoulder widening process can be suppressed.

In this case, since the seed crystal 20 is larger than the seed crystal used for normal crystal growth and is weak against thermal shock, the seed crystal 20 from the die 14 before contacting with the Ga ₂ O ₃ melt 12 is high. The thickness is preferably low to some extent, for example, 10 mm. The descending speed of the seed crystal 20 until it contacts with the Ga ₂ O ₃ melt 12 is preferably low to some extent, for example, 1 mm / min.

The waiting time until the seed crystal 20 is pulled up after being brought into contact with the Ga ₂ O ₃ melt 12 is preferably long to some extent in order to stabilize the temperature and prevent thermal shock, for example, 10 minutes.

  The rate of temperature rise when melting the raw material in the crucible 13 is preferably low to some extent in order to prevent the temperature around the crucible 13 from rising rapidly and causing thermal shock to the seed crystal 20. Melt.

(Quality evaluation method of β-Ga ₂ O ₃ single crystal)
A substrate is cut out from a seed crystal of β-Ga ₂ O ₃ single crystal grown using the above method and the like, mirror-polished, and then evaluated for crystal quality by X-ray diffraction measurement. This crystal quality is evaluated by evaluating the variation in crystal structure in the direction perpendicular to the b-axis of the substrate.

FIG. 3A is a plan view showing a substrate cut out from a β-Ga ₂ O ₃ -based single crystal and measurement positions of X-ray diffraction. At the measurement points arranged along the direction perpendicular to the b-axis of the β-Ga ₂ O ₃ single crystal indicated by “x” in FIG. 3A, the b-axis direction of the β-Ga ₂ O ₃ single crystal is expressed as follows. The X-ray diffraction intensity is measured while rotating the substrate as an axis to obtain an X-ray diffraction profile. Here, the rotation angle about the b-axis direction of the substrate is ω [deg].

  FIG. 3B is an image diagram in which X-ray diffraction profiles obtained at each measurement point are arranged along a direction perpendicular to the b-axis.

  FIG. 4 is a view of FIG. 3B as viewed from above, and represents the distribution of X-ray diffraction intensity at each measurement point. The horizontal axis in FIG. 4 represents the position [mm] on the substrate in the direction perpendicular to the b-axis, and the vertical axis represents the rotation angle ω [deg] of the substrate. The region where the dot density is high is a region where the X-ray diffraction intensity is high, and the curve connects the peak positions of the X-ray diffraction profile at each measurement point. Note that the position on the substrate on the horizontal axis is the origin of the center of the substrate.

  FIG. 5 is a graph showing a curve representing the relationship between the substrate position and the peak position of the X-ray diffraction profile and an approximate straight line obtained from the linear approximation by the least square method. The horizontal axis in FIG. 5 represents the position [mm] on the substrate in the direction perpendicular to the b-axis, and the vertical axis represents the rotation angle ω [deg] of the substrate.

  From FIG. 5, the difference between the peak position of the X-ray diffraction profile at each substrate position and the rotation angle ω of the approximate line is obtained, and the average value α is obtained. The smaller the variation in the peak position of the X-ray diffraction profile in the direction perpendicular to the b-axis, the smaller this α, which means that the variation in crystal structure in the direction perpendicular to the b-axis of the substrate is smaller.

(Quality evaluation result of β-Ga ₂ O ₃ based single crystal)
As an example of the present embodiment, Sn having a concentration of 0.05 mol% is added to grow two flat β-Ga ₂ O ₃ single crystals having a (−201) principal surface (crystals A and B). From the crystals A and B, a substrate centered at a point 40 mm from the seed crystal and a substrate centered at a point 90 mm from the seed crystal were cut out one by one. The diameter of each substrate was 50 mm.

Similarly, as a comparative example, Si having a concentration of 0.05 mol% was added to grow two flat β-Ga ₂ O ₃ single crystals having a (−201) principal surface (crystals C and D). The substrate centering on the point where the position from the seed crystal is 40 mm was cut out from these crystals C and D. The diameter of each substrate was 50 mm.

Further, as another comparative example, _two flat β-Ga ₂ O ₃ single crystals having a (−201) plane principal surface without adding a dopant were grown (referred to as crystals E and F). From the crystals E and F, a substrate centered around a point 40 mm from the seed crystal and a substrate centered at a point 90 mm from the seed crystal were cut out one by one. The diameter of each substrate was 50 mm.

  The width of the flat crystals A to F (width perpendicular to the crystal growth direction) was set to 52 mm in order to cut out a substrate having a diameter of 50 mm.

Four Sn-added β-Ga ₂ O ₃ single crystal substrates, four Si-added β-Ga ₂ O ₃ single crystal substrates, and four undoped β-Ga ₂ O ₃ single crystal substrates On the other hand, the crystal structure variation in the direction perpendicular to the b-axis of the substrate was evaluated by the above evaluation method.

  6A and 6B show the distribution of X-ray diffraction intensity for each measurement point on a substrate centered on a point 40 mm from the seed crystal, cut out from crystals A and B, respectively. FIGS. 7A and 7B show the distribution of X-ray diffraction intensity for each measurement point on a substrate centered on a point 40 mm from the seed crystal, cut out from crystals C and D, respectively. Represent. FIGS. 6A and 6B and FIGS. 7A and 7B correspond to FIG.

  6 (a), 6 (b), 7 (a) and 7 (b) show that the substrate cut from the crystals A and B to which Sn is added is cut from the crystals C and D to which Si is added. This shows that the variation in the peak position of the X-ray diffraction profile in the direction perpendicular to the b-axis is smaller than that of the substrate, and the variation in the crystal structure in the direction perpendicular to the b-axis is small.

  FIG. 8 is a diagram showing variations in crystal structures in the direction perpendicular to the b-axis of crystals A and B to which Sn is added, crystals C and D to which Si is added, and crystal EF to which no additive is added. The vertical axis in FIG. 8 represents the ratio of α to α of the seed crystal in each crystal. As the α ratio is smaller, the crystal structure variation in the direction perpendicular to the b-axis is closer to that of the seed crystal, indicating that a high-quality crystal is obtained.

  The upper part of the character column aligned along the horizontal axis at the bottom of FIG. 8 represents the type of crystal (crystals A to F) obtained by cutting the substrate, and the middle part represents the type of added dopant (Si, Sn, none). The lower row represents the distance (40 mm, 90 mm) from the seed crystal at the center of the substrate before being cut out from the crystal.

FIG. 8 shows that the α ratio of the crystals A and B to which Sn is added is smaller than the α ratio of the crystals C and D to which Si is added, and the crystal structure variation in the direction perpendicular to the b-axis of the crystals A and B Is small. The α ratio of the crystals A and B to which Sn is added is close to the α ratio of the crystals E and F to which no additive is added, and is in a direction perpendicular to the b-axis of the β-Ga ₂ O ₃ single crystal to which Sn is added. It shows that the variation in crystal structure is close to that of an additive-free β-Ga ₂ O ₃ single crystal.

Further, in general, in a grown crystal, the crystal quality is lower in a region farther from the seed crystal, but b in a region where the distance from the seed crystal of the crystals A and B to which Sn is added is 90 mm. The variation in the crystal structure in the direction perpendicular to the axis is smaller than that in the region where the distance from the seed crystal of crystals C and D to which Si is added is 40 mm. This indicates that by adding Sn instead of Si, variation in the crystal structure in the direction perpendicular to the b-axis of the β-Ga ₂ O ₃ single crystal can be greatly reduced.

Incidentally, the same evaluation methods, were evaluated variation of b-axis direction of the crystal structure was added Sn β-Ga ₂ O ₃ system single crystal, the β-Ga ₂ O ₃ system single crystal both added with Si, There was almost no variation in the crystal structure in the b-axis direction.

(Effect of embodiment)
According to the present embodiment, by using Sn as a dopant that imparts conductivity to the β-Ga ₂ O ₃ single crystal, a high-quality β-Ga ₂ O ₃ single crystal having a small variation in crystal structure is converted to b. It can be grown in the axial direction.

As an example, by adding Sn and growing a plate-like β-Ga ₂ O ₃ single crystal having a length of 65 mm and a width of 52 mm or more, from a region centered on a point whose distance from the seed crystal is 40 mm A conductive substrate having a diameter of 50 mm and excellent crystal quality can be obtained.

Note that the effect of this embodiment does not depend on the Sn addition concentration, and the variation in the crystal structure in the direction perpendicular to the b-axis of the β-Ga ₂ O ₃ single crystal is almost unchanged up to at least 1.0 mol%. It has been confirmed.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the invention.

  The embodiments described above do not limit the invention according to the claims. In addition, it should be noted that not all the combinations of features described in the embodiments are essential to the means for solving the problems of the invention.

10 ... EFG crystal manufacturing apparatus, 20 ... seed _{crystal, 25 ... β-Ga 2 O} 3 single crystal

Claims (2)

A β-Ga ₂ O ₃ single crystal in which the concentration of Sn added is 0.005 mol% to 1.0 mol%. A substrate comprising the β-Ga ₂ O ₃ -based single crystal according to claim 1.

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