JP2009013028A - Aluminum oxide-gallium oxide solid solution and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid solution containing a gallium oxide in which optical absorption in short wavelength is improved, and to provide a method for producing the same. <P>SOLUTION: The aluminum oxide-gallium oxide solid solution has an optical absorption edge wavelength of not less than 230 nm and less than 255 nm. The method for producing the solid solution comprises a step of obtaining an aluminum oxide-gallium oxide solid solution by a floating zone melting method in which a sintered compact using a gallium oxide powder and an aluminum oxide powder as raw materials is used and a gallium oxide single crystal is used as a seed crystal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an aluminum oxide-gallium oxide solid solution and a method for producing the same, and more specifically, semiconductor light emission such as a light emitting diode (LED) and a laser diode (LD) used in various fields such as display, communication, and recording equipment. The present invention relates to an aluminum oxide-gallium oxide solid solution useful as an element substrate and a method for producing the same.

Group III nitride AlGaInN-based mixed crystals can emit blue and ultraviolet light, and can emit light in the entire visible range by using phosphors. However, light emission in the deep ultraviolet region is still difficult. The causes include difficulty in manufacturing a single crystal substrate, thermal strain due to high temperature growth, deep acceptor levels, impurity oxygen, and the like.
In addition, LEDs using AlN as an active layer have been manufactured so far, and current injection light emission from a wavelength of 210 nm has been realized, but the light emission efficiency is less than 1% (Non-patent Document 1).

  In contrast to this group III nitride, research aimed at deep ultraviolet light emission using a ZnMgO mixed crystal system which is diamond or an oxide semiconductor has been made. Diamond has a characteristic that it can emit deep ultraviolet light with a band gap of ~ 5.5 eV, but there are problems in practical use in terms of production cost such as use of a diamond substrate. On the other hand, ZnMgO mixed crystal has advantages such that, unlike nitride, highly reactive oxygen does not become an impurity, and since it is an oxide, many growth methods can be selected. However, the crystal structures of ZnO and MgO are different from each other, and phase separation occurs at a high Mg composition. Therefore, the band gap can be expanded only up to 4.5 eV (up to 280 nm) (Non-patent Documents 2 and 3).

On the other hand, gallium oxide single crystal is colorless and transparent and has a large band gap of 4.8 eV, so optical materials in the ultraviolet region, substrates for nitride semiconductors such as LEDs and LDs, transparent oxide conductors, high-temperature oxygen gas sensor materials, and field effects Device applications such as type transistor (FET) materials and deep ultraviolet light receiving elements are being studied. In addition, the band gap of gallium oxide single crystal 4.8eV (~ 260nm) corresponds to the emission line of mercury (254nm), so in the lighting industry, which is the largest market for light emitting devices, an alternative to the current fluorescent lamp Application as an excitation light source is also conceivable. In an optical device, it is necessary to be transparent in the ultraviolet region, and it is required to shorten the wavelength of light absorption.
Y. Taniyasu et al., Nature 441 (2006) 325. Koizumi et al., Science 292 (2001) 1899. T. Takagi et al., Jpn. J. Appl. Phys. 42 (2003) L401.

An object of the present invention is to provide a solid solution containing gallium oxide having improved light absorption at a short wavelength.
Another object of the present invention is to provide a method for producing a solid solution containing the gallium oxide.
Still another object of the present invention is to provide a method for adjusting the light absorption edge wavelength of the solid solution containing gallium oxide.
Still another object of the present invention is to provide a substrate for growing a nitride semiconductor film or an oxide semiconductor film using the solid solution containing gallium oxide.

  In order to solve the above-mentioned problems, the present inventor has made extensive studies on the feasibility of deep ultraviolet light emission using gallium oxide, taking advantage of oxides and focusing on gallium oxide having a large band gap. . As a result, by adding aluminum oxide to gallium oxide, a single crystal in which aluminum oxide is uniformly dissolved in gallium oxide single crystal can be obtained, and the light absorption edge wavelength of the obtained single crystal is gallium oxide. The inventors have found that the wavelength can be made shorter than that of a single crystal, and have reached the present invention.

That is, the present invention is as follows.
1. An aluminum oxide-gallium oxide solid solution having a light absorption edge wavelength of 230 nm or more and less than 255 nm.
2. 2. The aluminum oxide-gallium oxide solid solution as described in 1 above, wherein a ratio of aluminum oxide in the aluminum oxide-gallium oxide solid solution is 40 mol% or less with respect to gallium oxide.
3. 3. The aluminum oxide-gallium oxide solid solution according to 1 or 2 above, wherein the cathodoluminescence emission of the aluminum oxide-gallium oxide solid solution is light emission on a shorter wavelength side than the gallium oxide single crystal.
4). Any of the above 1 to 3 having a step of obtaining an aluminum oxide-gallium oxide solid solution by a floating zone melting method using a gallium oxide powder and an aluminum oxide powder as a raw material and using a gallium oxide single crystal as a seed crystal A method for producing the described aluminum oxide-gallium oxide solid solution.
5). 5. The production method according to 4 above, wherein an oxygen-nitrogen mixed gas or dry air is used as the atmospheric gas in the floating zone melting method.
6). The method to adjust the light absorption edge wavelength of the said solid solution by adjusting the said aluminum oxide amount in the aluminum oxide-gallium oxide solid solution in any one of said 1-3.
7). A substrate for growing a nitride semiconductor film using the aluminum oxide-gallium oxide solid solution according to any one of 1 to 3 above.
8). A substrate for growing an oxide semiconductor film using the aluminum oxide-gallium oxide solid solution according to any one of 1 to 3 above.

According to the present invention, it is possible to provide an aluminum oxide-gallium oxide solid solution with improved light absorption at a short wavelength and a method for producing the same.
Moreover, according to this invention, the method of adjusting the light absorption edge wavelength of a gallium oxide solid solution by the simple method of adjusting the addition amount of aluminum oxide can be provided.
Furthermore, according to the present invention, a substrate for growing a nitride semiconductor film or an oxide semiconductor film using the aluminum oxide-gallium oxide solid solution can be provided.

Hereinafter, the present invention will be described in more detail.
(Aluminum oxide-gallium oxide solid solution)
The aluminum oxide-gallium oxide solid solution of the present invention is characterized by having a light absorption edge wavelength of 230 nm or more and less than 255 nm. The solid solution of the present invention can be obtained by growing a single crystal of a solid solution by a floating zone melting method using a gallium oxide powder and a sintered body made of aluminum oxide powder as a raw material and using a gallium oxide single crystal as a seed crystal. it can.

  Since the floating zone melting method (floating zone method; FZ method) does not use a container when forming the melting zone, the solid solution obtained by growing does not have to worry about contamination originating from the container, and obtains a high-quality solid solution. be able to. The apparatus used in the FZ method is not particularly limited. For example, as a heating means, if necessary, electromagnetic induction heating or electric resistance heating using a susceptor together, electric resistance heating, infrared heating, electron beam, arc, or condensing heating using a lamp Alternatively, heating by a laser or a flame can be used, but it is preferable to perform condensing heating using a lamp that can ensure stable heating conditions and does not cause the introduction of impurities during heating.

The raw material rod in the FZ method is a sintered body using gallium oxide powder and aluminum oxide powder as raw materials. The gallium oxide powder and the aluminum oxide powder preferably have a purity of 99.99% (4N) or higher. The gallium oxide powder is preferably β-Ga ₂ O ₃ powder because it is thermally most stable.
The sintered body is formed by sealing a gallium oxide powder and an aluminum oxide powder in a rubber tube or the like, rubber-pressing at a hydrostatic pressure of 50 to 600 MPa, preferably 100 to 500 MPa for about 5 minutes, and forming into a cylindrical shape, and then 1500 to 1700 ° C. The sintering is preferably performed at a sintering temperature of 1550 to 1650 ° C. for 10 to 20 hours, preferably 12 to 15 hours. When this sintering temperature is lower than 1500 ° C., when aluminum oxide having a melting point higher than that of gallium oxide is mixed and sintered, it becomes difficult to obtain a sintered body with sufficient bulk density due to insufficient sintering. A temperature higher than 1700 ° C. is not preferable because it approaches the melting point (˜1740 ° C.) of gallium oxide. On the other hand, if the sintering time is shorter than 10 hours, the sintering may not be sufficiently performed. Conversely, if the sintering time exceeds 20 hours, the effect is saturated. On the other hand, the sintering atmosphere is not particularly limited and may be performed in the air. The gallium oxide-aluminum oxide sintered body thus obtained has a cylindrical shape.

  Subsequently, the sintered body obtained above was installed as the raw material rod on the upper axis of the heating furnace used in the FZ method, and the lower axis was attached with a gallium oxide single crystal as a seed crystal, and the solid solution single crystal in the present invention was Develop. In this case, the seed crystal is preferably a gallium oxide single crystal produced by a FZ method using a gallium oxide sintered body obtained by firing gallium oxide powder in advance as a raw material. Moreover, about the rotational speed of a raw material stick | rod and a seed crystal, it is 10-30 rpm, respectively, Preferably it may be 15-20 rpm, and it is preferable to make it rotate mutually reverse. The heating temperature for melting the gallium oxide-aluminum oxide sintered body is preferably 1740 ° C. or higher, which is the melting point of gallium oxide, and since the melting point of the added aluminum oxide is ˜2050 ° C., 1740 ° C. The temperature is preferably 2100 ° C.

As for the growth atmosphere of the solid solution single crystal, a flow rate of oxygen with respect to the total amount of the inert gas (O ₂ / inert) using a mixed gas of one or more inert gases such as nitrogen, argon, and helium and oxygen. It is good to supply to a heating furnace so that gas total amount may be 1-20 vol%, Preferably it is 2-5 vol%. If the flow rate ratio of oxygen to the total amount of the inert gas is less than 1 vol%, the oxygen ratio is too small, and evaporation from the raw material rod becomes remarkable, so that a solid solution single crystal does not grow sufficiently. On the other hand, when the flow rate ratio is larger than 20 vol%, there is a possibility that it will be confined in the single crystal obtained by bubbling in the melt and cause cracking. Moreover, it is good to supply the mixed gas of oxygen and an inert gas at 200-600 ml / min in the quartz tube of a heating furnace so that it may become said suitable growth atmosphere. A preferable growth atmosphere in the present invention is dry air from which oxygen-nitrogen mixed gas and moisture are removed to 0.1% or less.

  The crystal growth rate of the solid solution single crystal is 2.5 to 20 mm / h, preferably 5 to 15 mm / h. In the FZ method, it is generally considered that a crystal having a relatively slow growth rate has a good crystal quality. However, in the present invention, a solid crystal having excellent quality can be obtained even if the crystal growth rate is increased as compared with the conventional method. Moreover, about the pressure in the case of crystal growth, atmospheric pressure may be sufficient and you may carry out in the pressurized state. As an effect of pressurization, it is possible to suppress evaporation from the raw material rod during single crystal growth, to suppress the clouding of the inner wall of the transparent quartz tube through which atmospheric gas flows, and to reduce the efficiency of heating from the outside of the quartz tube It is possible to operate without any problems.

In the present invention, the proportion of aluminum oxide in the aluminum oxide-gallium oxide solid solution is preferably 40 mol% or less with respect to gallium oxide. The lower limit of the added amount of aluminum oxide is, for example, 5 mol%, although it depends on the target light absorption edge wavelength. Depending on the amount of aluminum oxide added, an aluminum oxide-gallium oxide solid solution having a light absorption edge wavelength of 230 nm or more and less than 255 nm can be obtained. According to the present invention, the light absorption edge wavelength of the solid solution can be adjusted by appropriately adjusting the amount of aluminum oxide in the aluminum oxide-gallium oxide solid solution.
For example, in order to obtain a solid solution having a light absorption edge wavelength of 230 nm, aluminum oxide may be added at about 40 mol% with respect to gallium oxide.
For example, in order to obtain a solid solution having a light absorption edge wavelength of 240 nm, aluminum oxide may be added at about 25 mol% with respect to gallium oxide.
For example, in order to obtain a solid solution having a light absorption edge wavelength of 250 nm, aluminum oxide may be added at about 5 mol% with respect to gallium oxide.
When increasing the amount of aluminum oxide added, it is preferable to set the crystal growth rate faster (for example, when adding about 40 mol% of aluminum oxide to gallium oxide, the crystal growth rate is 12%. It is preferable to speed up to 5 mm / h.)

  The thus obtained aluminum oxide-gallium oxide solid solution of the present invention is shaped by cutting or the like, and is polished and flattened on the main surface, thereby forming a substrate for growing a nitride semiconductor film or an oxide semiconductor film. Useful as. A method for growing a nitride semiconductor film or an oxide semiconductor film using the substrate of the present invention is not particularly limited, and a known growth method can be applied. For example, it is preferable to use MOCVD method, HVPE method, MBE method (molecular beam epitaxy method), PLD method (pulse laser deposition method) and the like.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, this invention is not restrict | limited to the following example.

Example 1 (Preparation example of aluminum oxide-gallium oxide solid solution)
As starting materials, β-Ga ₂ O ₃ powder (purity 4N) and α-Al ₂ O ₃ powder (purity 4N) were mixed. In addition, the mixing ratio of β-Ga ₂ O ₃ powder and α-Al ₂ O ₃ powder is 10 mol% of α-Al ₂ O ₃ with respect to β-Ga ₂ O ₃ . After the mixed powder was sealed in a rubber tube, it was press-molded under hydrostatic pressure to produce a rod-shaped molded body having a diameter of about 10 mmφ and a length of about 8 cm. The molded body thus mixed was heated and sintered in the air and in an electric furnace to produce a sintered body. The sintering conditions are a temperature of 1600 ° C. and a sintering time of 10 hours. Using this sintered body as a raw material rod, a β-Ga ₂ O ₃ single crystal (seed crystal) prepared in advance by the FZ method was used as a seed crystal to prepare an aluminum oxide-gallium oxide solid solution by the FZ method. The FZ method conditions are as follows. As a device, a commercially available optical FZ device (trade name iAce manufactured by Canon Machinery Co., Ltd.) is used. In a nitrogen-oxygen mixed gas atmosphere containing 20 vol% of oxygen, the pressure is 1 atm, and the rotation speed of the seed crystal and the raw material rod is 20 rpm. A single crystal of a solid solution was grown. The growth rate of the single crystal was 7.5 mm / h.
FIG. 1 is a diagram showing the results of analyzing a solid solution single crystal obtained in the above preparation example by powder X-ray diffraction. From the diffraction pattern of the single crystal of the solid solution in FIG. 1, it can be seen that the peak is slightly shifted to the high angle side under the influence of α-Al ₂ O ₃ addition, but it was identified as β-Ga ₂ O ₃ . . GaAlO ₃ considered as a reaction product with Ga ₂ O ₃ by addition of α-Al ₂ O ₃ was not detected.

In the above preparation example, the amount of aluminum oxide added to 0 mol% (nonDope), 1 mol% (Al 1%), 5 mol% (Al 5%) with respect to gallium oxide The change of lattice constant of single crystal was measured by X-ray diffraction. The result is shown in FIG. FIG. 2 also shows the case of the above preparation example (amount of aluminum oxide added = 10 mol% (Al 10%)). 2A to 2B, the vertical axis represents the length (Å) of the a-axis, b-axis, or c-axis, and the horizontal axis represents the amount of aluminum oxide added. In FIG. 2C, the vertical axis represents unit cell deposition (Å ³ ), and the horizontal axis represents the amount of aluminum oxide added. From FIG. 2, it can be seen that as the amount of added Sanka aluminum increases, the lengths of the axes a, b, and c become shorter, and thus the unit cell volume also decreases. This is thought to be because Al was substituted at the Ga site because the ion radius of Al was as small as 0.54 mm while the ion radius of Ga was 0.62 mm. From this change in the lattice constant, it is suggested that the added Al was replaced with Ga sites to form a solid solution (mixed crystal).
In order to confirm this, the solid solution state in the single crystal of the solid solution was further analyzed using an electron probe microscope (EPMA). FIG. 3 is a diagram showing results of elemental mapping analysis of Ga, O, and Al by EPMA. Looking at the Al element (lower right in the figure), you can see that it is distributed almost uniformly.
Furthermore, the state analysis of Al dissolved in this gallium oxide was performed by EPMA. The result is shown in FIG. In general, it is known that the state of Al and Al compounds can be identified from the shape and intensity ratio of the spectrum peak of AlKα, and the spectrum shapes of Al and Al ₂ O ₃ are different (see FIG. 5). When the spectrum shape by the EPMA state analysis shown in FIG. 4 is seen, it is closer to the shape showing Al ₂ O ₃ than Al. This shows that Al in gallium oxide is dissolved as Al ₂ O ₃ . That is, it is considered that an aluminum oxide-gallium oxide solid solution was obtained.

Example 2
As starting materials, β-Ga ₂ O ₃ powder (purity 4N) and α-Al ₂ O ₃ powder (purity 4N) were mixed in a mortar. Incidentally, beta-Ga ₂ O ₃ powder and the mixing ratio of α-Al ₂ O ₃ powder, beta-Ga ₂ O ₃ to α-Al ₂ O ₃ is 0 mol%, and 5 mol% or 10 mol% did. This mixed powder was sealed in a rubber tube, press-molded with hydrostatic pressure, and sintered in the atmosphere at 1600 ° C. for 10 hours. Using this sintered body as a raw material rod, a β-Ga ₂ O ₃ single crystal (seed crystal) prepared in advance by the FZ method was used as a seed crystal to prepare an aluminum oxide-gallium oxide solid solution by the FZ method. The FZ method conditions are as follows. As a device, a commercially available optical FZ device (trade name iAce, manufactured by Canon Machinery Co., Ltd.) was used. In a dry air atmosphere with a moisture content of 0.1% or less, the pressure was 1 atm, and the rotation speed of the seed crystal and the raw material rod was 20 rpm. Single crystals of solid solution were grown. The growth rate of the single crystal was 7.5 mm / h. The obtained solid solution single crystal was cut and processed into a wafer having a thickness of 0.4 mm by CMP (chemical mechanical) polishing. The crystal orientation in this case is the (100) plane.
FIG. 6 shows the result of measuring the transmittance using this as a sample. The broken line (3) is an additive-free gallium oxide single crystal that does not contain aluminum oxide, and its light absorption edge wavelength is 255 nm. In the solid solution single crystal to which 5 mol% of aluminum oxide is added as indicated by the solid line (2), The light absorption edge wavelength of the solid solution single crystal added with 10 mol% of the aluminum oxide indicated by the solid line (1) is 250 nm, and the light absorption edge wavelength is shorter as the added amount of aluminum oxide is increased. It can be seen that there is a shift to the wavelength side. This result shows that the light absorption edge wavelength can be adjusted to the short wavelength side by adding aluminum oxide.

Example 3
Cathodoluminescence (CL) measurement of a single crystal of a solid solution having an aluminum oxide addition amount of 5 mol% (5 mol Al2O3) and 10 mol% (10 mol Al2O3) prepared in Example 2 was performed to evaluate the light emission characteristics. FIG. 7 is a diagram showing a CL spectrum result measured at room temperature with respect to the (100) plane. In FIG. 7, the solid line (4) is the CL measurement result when the amount of aluminum oxide added is 5 mol% (5 mol Al2O3), the solid line (5) is the CL measurement result of 10 mol% (10 mol Al2O3), and the solid line (6) is the oxidation. It is a CL measurement result of an additive-free gallium oxide single crystal (non-doped) that does not contain aluminum. It can be seen that as the amount of aluminum oxide added increases, the emission wavelength shifts to the lower energy side. This shows the result corresponding to the shortening of the light absorption edge wavelength in Example 2.

  As can be seen from the above examples, the light absorption edge wavelength and the CL emission wavelength position can be adjusted by adjusting the amount of aluminum oxide in the aluminum oxide-gallium oxide solid solution single crystal. Specifically, as the added amount of aluminum oxide increases, the light absorption edge wavelength is shortened, and the CL emission wavelength position is also shifted to the lower energy side, and the single crystal can be shortened. The solid solution of the present invention is useful as a material corresponding to future shortening of the wavelength of optical devices.

  According to the present invention, an aluminum oxide-gallium oxide solid solution useful as a substrate for a semiconductor light emitting element such as a light emitting diode (LED) or a laser diode (LD) used in various fields such as display, communication, and recording equipment, and a method for producing the same. Can provide.

It is a figure which shows the result of having analyzed the single crystal of the solid solution obtained by the preparation example by powder X-ray diffraction. It is a figure which shows the change of the lattice constant of the single crystal of the solid solution obtained by the preparation example measured by X-ray diffraction. It is a figure which shows each element mapping analysis result of Ga, O, and Al by EPMA. It is a figure which shows the result of the state analysis of Al solid-solved in the gallium oxide by EPMA. It is a diagram for explaining the differences in the spectral shape of AlKα of Al and Al ₂ O _3. 4 is a graph showing the transmittance of a single crystal sample of a solid solution prepared in Example 2. FIG. The solid line (1) is a solid solution single crystal added with 10 mol% of aluminum oxide, the solid line (2) is a solid solution single crystal added with 5 mol% of aluminum oxide, and the broken line (3) is an additive-free oxide containing no aluminum oxide. It is an example of a gallium single crystal. FIG. 4 is a diagram showing a CL spectrum result of a single crystal sample of a solid solution prepared in Example 3. Solid line (4) shows the CL measurement result when the amount of aluminum oxide added is 5 mol% (5 mol Al2O3), solid line (5) shows the CL measurement result of 10 mol% (10 mol Al2O3), and solid line (6) does not contain aluminum oxide. It is a CL measurement result of an additive-free gallium oxide single crystal.

Claims (8)

  An aluminum oxide-gallium oxide solid solution having a light absorption edge wavelength of 230 nm or more and less than 255 nm.   The aluminum oxide-gallium oxide solid solution according to claim 1, wherein a ratio of aluminum oxide in the aluminum oxide-gallium oxide solid solution is 40 mol% or less with respect to gallium oxide.   3. The aluminum oxide-gallium oxide solid solution according to claim 1, wherein cathodoluminescence emission of the aluminum oxide-gallium oxide solid solution is emission on a shorter wavelength side than the gallium oxide single crystal.   4. The method according to claim 1, further comprising a step of obtaining an aluminum oxide-gallium oxide solid solution by a floating zone melting method using a gallium oxide powder and a sintered body made of aluminum oxide powder as a raw material and using a gallium oxide single crystal as a seed crystal. A method for producing the aluminum oxide-gallium oxide solid solution described in 1.   The manufacturing method according to claim 4, wherein an oxygen-nitrogen mixed gas or dry air is used as an atmospheric gas in the floating zone melting method.   The method to adjust the light absorption edge wavelength of the said solid solution by adjusting the said aluminum oxide amount in the aluminum oxide-gallium oxide solid solution in any one of Claims 1-3.   A substrate for growing a nitride semiconductor film using the aluminum oxide-gallium oxide solid solution according to claim 1.   A substrate for growing an oxide semiconductor film using the aluminum oxide-gallium oxide solid solution according to claim 1.

Images