JP2001072498A - Oxide single crystal thin film and its processing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To progress the two-dimensional growth of ZnO thin film, to grow the single crystal thin film having good crystallinity with little defects, and to maximumly draw out the exciton-localizing function of the ZnO thin film by using an oxide polar crystal LiGaO2 lattice-matching to the ZnO as a substrate, and further to provide an optical device by using the thin film. SOLUTION: A (001) substrate of LiGaO2 single crystal lattice-matching to ZnO and localizing the polarity to a single domain is used instead of a sapphire c-face substrate Al2O3 (0001)) providing extremely large lattice mismatch with the ZnO (0001). Zn1-xLixO (0<=x<=0.3) single crystal thin film is epitaxially grown on an oxygen surface on the (001) substrate of the LiGaO2 single crystal to provide the objective thin film. A wave guide having a transmission loss smaller than that of the wave guide of the ZnO single crystal thin film formed on the sapphire c-face substrate of a conventional substrate is produced by using the LiGaO2 (001) substrate crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an oxide obtained by epitaxially growing Zn _{1 -X} Li _X O (0 ≦ X <0.3) on a lithium gallate (LiGaO ₂ ) substrate having a wurtzite crystal structure. Regarding the single crystal thin film, LiG
On the aO ₂ substrate, Zn _1-x Li _x O (0 ≦
X <0.3) A method for processing an oxide single crystal thin film using a good quality single crystal film.

[0002]

2. Description of the Related Art Recently, when a ZnO thin film having a c-axis orientation is grown on a sapphire c-plane, a thin film having a cluster of about 50 nm shows not only photoluminescence at a low temperature but higher intensity than a bulk single crystal, but also at room temperature. It was found to emit light. When the pump light is further increased, laser oscillation occurs at 390 nm at room temperature. The mechanism of this light emission is not based on the normal transition between bands, but involves excitons having a small Bohr radius, and is laser oscillation by so-called exciton confinement. That is, it is considered that room-temperature-excited laser oscillation occurs at a low threshold value due to carrier confinement due to the grain boundary of the ZnO thin film and light confinement due to a change in the refractive index. However, in order to improve the oscillation efficiency of such a laser, it is desired to improve the crystallinity of the single crystal thin film.

Further, zinc oxide ZnO has a piezoelectric property of I.
It is a group I-IV semiconductor and has been applied to functional devices such as ultrasonic transducers and surface acoustic wave filters due to its large piezoelectric constant. Recently, it has been found that when part of Zn in ZnO is replaced with Li, ferroelectricity is exhibited at room temperature (Onodera, Journal of the Physical Society of Japan 53 (1998) p282). At this time, when ZnO, which is usually a semiconductor, is doped with Li, the electrical resistance is about 10 ¹⁰ Ωcm.
It becomes insulating. Although the mechanism of this ferroelectricity is unknown, large displacements of atoms and changes in crystal symmetry such as those found in perovskite ferroelectrics represented by BaTiO ₃ have not been found. It is speculated to be the main cause. In order to obtain a good quality single crystal thin film, it is desirable to epitaxially grow on a substrate crystal with good lattice matching.

[0004] ZnO is an important material for a waveguide functional device utilizing these effects because ZnO exhibits excellent piezoelectricity, has a large electro-optic effect and a large nonlinear optical effect, and is relatively easy to be made thin. The c-axis oriented film of ZnO is made of a polycrystalline ZnO film in which the c-axis is oriented almost vertically in the plane by performing sputtering under appropriate conditions using an amorphous material such as glass, fused quartz, SiO ₂ / Si as a substrate. It is possible to deposit. The single crystal film is formed on a (0001) sapphire (Al2O3) substrate by epitaxial growth by sputtering or chemical vapor deposition (CVD).

[0005]

However, the conventional sapphire c-plane substrates {Al ₂ O ₃ (0001)} and Z
Since the lattice mismatch with nO (0001) is as large as about 18%, a ZnO thin film grows, but there is a problem that luminous efficiency is low due to many defects in the film. In addition, there is a problem that a film having good crystallinity cannot be obtained due to many defects in the film. This is because the film grows three-dimensionally on the substrate due to large lattice mismatch. In addition, since conventional sapphire has no polarity, there is a disadvantage that the polarities of the grown ferroelectric thin films cannot be made uniform.

Further, it is desired to improve the crystallinity of the single crystal thin film in order to improve the waveguide propagation loss. Conventionally used sapphire c-plane substrate {Al ₂ O ₃ (0001)} and Zn
Since the lattice mismatch with O (0001) is as large as 18%, a ZnO thin film grows, but a high quality single crystal film cannot be obtained. Therefore, the waveguide propagation loss is about 0.3 dB.
/ Cm.

The present invention has been made in view of the above points, and has been made of an oxide polar crystal LiG lattice-matched to ZnO.
By using aO ₂ as a substrate, the two-dimensional growth of a ZnO thin film is promoted, a single crystal thin film having few defects and good crystallinity is grown, and the exciton confinement function of the ZnO thin film is maximized. Providing a device, and using an oxide polar crystal LiGaO ₂ lattice-matched to ZnO as a substrate.
Providing an optoelectronic device using this thin film by growing a high-quality single-crystal thin film with few defects in the n _1-x Li _x O thin film and aligning the polarization direction to maximize the characteristics of the ferroelectric thin film The purpose is to be able to.

Still another object of the present invention is to provide ZnO ( _ne
= 2.015, n _o =1.999@λ=633nm) oxide crystal LiGaO ₂ lattice-matched to (n _x = 1.76
2, n _y = 1.731, n _z =1.759＠λ=633
nm) as a substrate to grow a single crystal thin film having high quality crystallinity, maximize the function of the ZnO thin film as a waveguide layer, and provide a waveguide optical device using this thin film. It is to be.

[0009]

In order to achieve the above object, the present invention provides an oxide substrate crystal Li that is lattice-matched to ZnO.
It is characterized in that a ZnO single crystal thin film is epitaxially grown by using GaO ₂ as a substrate and further using a substrate in which the outermost surface element is specified.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In order to solve the above problems, an oxide single crystal thin film of the present invention is formed on a single crystal substrate having a wurtzite type crystal structure by using Zn _1-X Li _X O (0 ≦ X <0). (3) The feature is that a single crystal thin film is epitaxially grown.

Further, the oxide single crystal thin film of the present invention is characterized in that the single crystal substrate having a wurtzite type crystal structure is a LiGaO ₂ single crystal (001) substrate.

Further, the oxide single crystal thin film of the present invention
The (001) substrate of iGaO ₂ single crystal is characterized in that the polarity is single-domain.

Further, the oxide single crystal thin film of the present invention has a
_{The surface on which a 1-X} Li _X O (0 ≦ X <0.3) single crystal thin film is epitaxially grown has a single-domain L
It is characterized in that it is the oxygen plane of the (001) substrate of iGaO ₂ single crystal.

The method for processing an oxide single crystal thin film of the present invention comprises:
The present invention is characterized in that a zinc oxide (ZnO) single crystal thin film is used as a waveguide layer on a (001) substrate surface cut out from a wurtzite-type oxide single crystal having a single domain with respect to polarity.

Further, in the method for processing an oxide single crystal thin film according to the present invention, the substrate surface of the oxide single crystal having a wurtzite crystal structure is an oxygen surface of the LiGaO ₂ single crystal (001) substrate. It has features.

Further, the method of processing an oxide single crystal thin film of the present invention is characterized in that a groove of a waveguide layer is formed by performing chemical etching using an acidic aqueous solution.

In the method for processing an oxide single crystal thin film according to the present invention, the substrate surface of the oxide single crystal having a wurtzite type crystal structure is a metal surface of a LiGaO ₂ single crystal (001) substrate. It has features.

Further, the method of processing an oxide single crystal thin film of the present invention is characterized in that a groove is formed in a waveguide layer by performing chemical etching using a basic aqueous solution.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The operation of the present invention will be described below together with the knowledge obtained when the present invention is carried out. In order to improve the crystallinity of the single crystal thin film, it is effective to use a lattice matching substrate. Since the method for growing bulk ZnO single crystals is limited to the hydrothermal method or the flux method, it is very difficult to grow high quality and large single crystals. Thus, the present inventors searched for a wurtzite-type oxide material and noticed that LiGaO ₂ has a crystal structure similar to that of ZnO.

FIG. 1 shows the crystal structure of LiGaO ₂ , FIG. 2 shows the crystal structure of ZnO, and FIG. 3 shows the crystal structure of Zn _{1 -x} Li _x O. From this figure, it can be seen that when Zn is replaced by Li and Ga by 50%, LiGaO ₂ is derived from ZnO. Further, the lattice mismatch rate estimated from the lattice constant was 2.8%, which was much smaller than that of sapphire, and was considered to be a lattice-matched substrate. Therefore, the present inventor has proposed this LiGaO ₂
In order to obtain a large single crystal, growth was attempted by the rotation pulling method. When cutting the c-plane substrate of a single crystal was pulled on the results c-axis direction, the crystal c than space group Pna2 ₁
It has been found that having a polar axis on the axis (z-axis) causes polarity reversal and forms a multidomain structure with respect to polarity. Therefore, a method for avoiding this polarity reversal is studied, and a single crystal having a single domain with respect to polarity can be grown by pulling up in the a-axis (x-axis) or b-axis (y-axis) direction perpendicular to the polarity axis. (Japanese Patent Application No. 9-332)
62).

The thus grown LiGaO ₂ (0
01) In the substrate, the etching experiment with a nitric acid aqueous solution and the identification of the terminal surface element by coaxial direct impact ion scattering spectroscopy (CAICISS) revealed that the easily etched surface was an oxygen surface and the hardly etched surface was a metal surface. (Fig. 4) (Ishii et al., Applied Physics European Journal, Volume 37 (19
98) p672). In this case, the etching rates on both sides of the substrate differ about 10 times.

When an acidic etching solution such as the above-mentioned nitric acid aqueous solution is used, the easily-etched surface is an oxygen surface and the hardly-etched surface is a metal surface. The easily etched surface is a metal surface, and the hardly etched surface is an oxygen surface.

In growing a ZnO single crystal thin film using a lattice-matched substrate crystal whose characteristics of the substrate surface are apparent in advance, the present inventors considered the following. That is, ZnO grows on both surfaces of LiGaO ₂ (001), but when ZnO grows on the oxygen surface, it grows as Zn—O—Zn—O, but when ZnO grows on the metal surface, two types of terminal metals are formed. And therefore its chemical bonding state is complicated, so that Li on the top surface of the metal is ZnO
It is expected to spread to. Therefore, when a ZnO film not containing Li is formed, it is effective to grow it on an oxygen surface. That is, it is important to use a substrate having an oxygen surface.

In order to maximize the characteristics of the ferroelectric, it is very important to make the polar directions uniform. In the present invention, since the crystal structures of the substrate and the film are similar and the polarity of the substrate is made into a single domain, the polarity of the film can be made uniform. ZnO is grown on both surfaces (metal surface and oxygen surface) of LiGaO ₂ (001), but the polarity direction is reversed between the case where ZnO is grown on the metal surface and the case where ZnO is grown on the oxygen surface. In other words, by defining the polarity of the substrate based on the difference in the outermost surface, the polarity of the grown film can be defined. Further, since the polarities are uniform, a large dielectric constant is developed. This is because sapphire, which is a conventional substrate, is not a polar crystal, so that the polarity of the film cannot be controlled, and thus the dielectric constant does not increase.

Based on such a prediction, the present inventor has proposed that Li
In order to grow a ZnO single crystal thin film on a GaO ₂ (001) substrate, LiGa was used in a process of repeating many experiments.
In the case of the O ₂ (001) substrate, it has been found that a high-quality ZnO single crystal thin film grows on the oxygen surface of a single-domain substrate. In addition, in the process of repeating a number of experiments, a LiGaO ₂ (001) substrate was formed on a single-domain substrate with Zn _{1 -X} L of good quality and uniform polarity.
i _X O single crystal thin film was completed the present invention found that growth.

FIG. 5 is an explanatory view showing the steps of a method for processing an oxide single crystal thin film according to an embodiment of the present invention. When an acidic etching solution such as an aqueous nitric acid solution is used, L
Since there is a large difference in the etching rate between the two surfaces of the iGaO ₂ substrate 1, it is necessary to pattern the layer to be processed using the resist 2 in advance to provide the opening 3 and form the groove 4 for filling by chemical etching. it can. Next, ZnO5, that is, a single-crystal ZnO thin film is deposited by an appropriate crystal growth method. At this time, the polarity of the epitaxially grown ZnO film inherits the polarity of the underlying substrate. Therefore, if mechano-chemical polishing (MCP) is performed using an appropriate etchant, the etching speed is high on the substrate surface side, so that polishing is easy and a smooth waveguide 6 surface can be formed.

If an acidic aqueous solution and a basic aqueous solution are properly used as an etching solution, a buried waveguide can be formed regardless of whether the substrate end surface is an oxygen surface or a metal surface.
Based on such a prediction, the present inventor considered that LiGaO ₂ (0
01) In order to form a ZnO single crystal thin film waveguide on a substrate, LiGaO
_The present inventors have found that a high-quality ZnO single-crystal waveguide can be formed on a ₂ (001) substrate on a single-domain substrate, and have accomplished the present invention.

Example 1 A ZnO thin film was formed by an ArF excimer laser deposition method. The target used was a sintered ZnO pellet (30 mmφ, 5 mmt). The frequency of the laser pulse was 1 Hz. Substrate temperature is 720
° C, an oxygen partial pressure of 10 ^-4 torr, and a film thickness of about 100
nm deposited. As an evaluation of crystallinity, an X-ray rocking curve of ZnO (0002) was measured by an X-ray two-crystal method. The substrate crystal used was LiGaO ₂ (0
01) The oxygen surface and the metal surface were used. As a comparative example, a film was grown also on the sapphire c-plane of a conventional substrate having a large lattice mismatch. The flatness was evaluated by an atomic force microscope (A
FM).

Table 1 shows the half width of the rocking curve (FWH).
M) and the average roughness Rms obtained from the AFM. Table 1 Substrate FWHM Rms Oxygen surface of LiGaO ₂ (001) 80 arcsec. Metal surface of 0.6 nm LiGaO ₂ (001) 120 arcsec. 1.8 nm Al ₂ O ₃ (0001) 430 arcsec. LiGaO ₂ (001) with single domain from the results of 5.0 nm or more
It was clarified that the ZnO single crystal thin film grown on the oxygen plane had good crystallinity and improved flatness as compared with conventional sapphire. Therefore, compared with sapphire which is a conventional substrate crystal, LiGaO
_{2 The} (001) substrate was found to be effective as a lattice-matched substrate for ZnO.

(Example 2) A ZnO thin film was formed by a molecular beam epitaxy method. Zn was dissolved and evaporated by K-cell. Further, ozone was used as an oxygen source. The oxygen partial pressure was set to 10 ^-5 torr, and the film was deposited to a thickness of about 100 nm. As an evaluation of the crystallinity, ZnO (0
002) was measured. The substrate crystal used was a single domain LiGaO ₂ (001) oxygen plane and metal plane. As a comparative example, a film was grown also on the sapphire c-plane of a conventional substrate having a large lattice mismatch. The flatness was evaluated by AFM.

Table 2 shows the half width (FWH) of the rocking curve.
M) and the average roughness Rms obtained from the AFM. Table 2 Substrate FWHM Rms Oxygen surface of LiGaO ₂ (001) 74 arcsec. Metal surface of 0.5 nm LiGaO ₂ (001) 110 arcsec. 1.6 nm Al ₂ O ₃ (0001) 430 arcsec. LiGaO ₂ (001) with single domain from results of 4.6 nm or more
It has been found that the ZnO single crystal thin film grown on the oxygen surface of Example 1 has good crystallinity and has improved flatness as compared with conventional sapphire. Therefore, compared with sapphire which is a conventional substrate crystal, LiGaO ₂ (0
01) The substrate was found to be effective as a lattice-matched substrate for ZnO.

Example 3 A ZnO thin film was formed by ECR sputtering. The target used was Zn. Microwave power and RF sputter power are 6
00W and 500W. The substrate temperature was 500 ° C., the oxygen partial pressure was 5 × 10 ⁻⁴ torr, and the film thickness was about 100
nm deposited. As an evaluation of crystallinity, an X-ray rocking curve of ZnO (0002) was measured by an X-ray two-crystal method. The substrate crystal used was LiGaO ₂ (0
01) The oxygen surface and the metal surface were used. As a comparative example, a film was grown also on the sapphire c-plane of a conventional substrate having a large lattice mismatch. The flatness was evaluated by AFM.

Table 3 shows the half width (FWH) of the rocking curve.
M) and the average roughness Rms obtained from the AFM. Table 3 Substrate FWHM Rms Oxygen surface of LiGaO ₂ (001) 98 arcsec. Metal surface of 1.0 nm LiGaO ₂ (001) 160 arcsec. 2.5 nm Al ₂ O ₃ (0001) 580 arcsec. A single domain LiGaO ₂ (001) based on the result of 8.0 nm or more
It has been found that the ZnO single crystal thin film grown on the oxygen surface of Example 1 has good crystallinity and has improved flatness as compared with conventional sapphire. Therefore, compared with sapphire which is a conventional substrate crystal, LiGaO ₂ (0
01) The substrate was found to be effective as a lattice-matched substrate for ZnO.

(Example 4) A Zn _1-x Li _x O thin film was coated with Ar
It was prepared by an F excimer laser evaporation method. The target was a sintered Zn _0.8 Li _0.2 O pellet (30 mmφ,
5 mmt). The frequency of the laser pulse was 1 Hz. The substrate temperature is 720 ° C., and the oxygen partial pressure is 10 ⁻⁴ to
rr and a film thickness of about 100 nm was deposited. As an evaluation of crystallinity, an X-ray rocking curve of ZnO (0002) was measured by an X-ray two-crystal method. The substrate crystal used was a single domain LiGaO ₂ (001) oxygen plane and metal plane. As a comparative example, a film was grown also on the sapphire c-plane of a conventional substrate having a large lattice mismatch. The domain structure of the film was examined by etching using a nitric acid aqueous solution.

Table 4 shows the half width (FWH) of the rocking curve.
M) and the domain structure. Table 4 Substrate FWHM domain structure Oxygen surface of LiGaO ₂ (001) 250 arcsec. Metal surface of single domain LiGaO ₂ (001) 260 arcsec. Single domain Al ₂ O ₃ (0001) 1680 arcsec. Multi-domain LiGaO ₂ (001) made into a single domain from the above results
It was found that the Zn _1-X Li _X O single crystal thin film grown on the oxygen surface of Example ₁ had good crystallinity, and that the domain structure was single-domain compared to conventional sapphire. Was. Therefore, it was found that the LiGaO ₂ (001) substrate was more effective as a lattice matching substrate for Zn _{1 -x} Li _x O than sapphire, which is a conventional substrate crystal.

Example 5 A Zn _0.8 Li _0.2 O thin film was formed by a molecular beam epitaxy method. Zn and Li are K-
Dissolved and evaporated by cell. Further, oxygen radicals generated by a radical beam source were used as an oxygen source. The oxygen partial pressure was 10 ⁻⁵ torr, and the film thickness was about 100 nm. As an evaluation of crystallinity, ZnO (000
The X-ray rocking curve of 2) was measured. The substrate crystal used was a single domain LiGaO ₂ (001) oxygen plane and metal plane. As a comparative example, a film was grown also on the sapphire c-plane of a conventional substrate having a large lattice mismatch. The domain structure of the film was examined by etching using a nitric acid aqueous solution.

Table 5 shows the half width (FWH) of the rocking curve.
M) and the domain structure. Table 5 Substrate FWHM domain structure Oxygen surface of LiGaO ₂ (001) 220 arcsec. Metal surface of single domain LiGaO ₂ (001) 200 arcsec. Single domain Al ₂ O ₃ (0001) 1530 arcsec. Multi-domain LiGaO ₂ (001) made into a single domain from the above results
It was found that the Zn _1-X Li _X O single crystal thin film grown on the oxygen surface of Example ₁ had good crystallinity, and that the domain structure was single-domain compared to conventional sapphire. Was. Therefore, it was found that the LiGaO ₂ (001) substrate was more effective as a lattice matching substrate for Zn _{1 -x} Li _x O than sapphire, which is a conventional substrate crystal.

Example 6 A Zn _1-x Li _x O thin film was subjected to EC
It was prepared by the R sputtering method. Target is Zn _0.7
Li _0.3 O was used. Microwave power and RF sputter power were 600 W and 500 W, respectively. The substrate temperature is 500 ° C., the partial pressure of argon and oxygen is 5
The deposition was set to × 10 ^-4 torr and the film thickness was about 100 nm. As an evaluation of crystallinity, ZnO (000
The X-ray rocking curve of 2) was measured. The substrate crystal used was a single domain LiGaO ₂ (001) oxygen plane and metal plane. As a comparative example, a film was grown also on the sapphire c-plane of a conventional substrate having a large lattice mismatch. The domain structure of the film was examined by etching using a nitric acid aqueous solution.

Table 6 shows the half width of the rocking curve (FWH).
M) and the domain structure. Table 6 Substrate FWHM domain structure Oxygen surface of LiGaO ₂ (001) 280 arcsec. Metal surface of single domain LiGaO ₂ (001) 250 arcsec. Single domain Al ₂ O ₃ (0001) 2850 arcsec. Multi-domain LiGaO ₂ (001) made into a single domain from the above results
It was found that the Zn _1-X Li _X O single crystal thin film grown on the oxygen surface of Example ₁ had good crystallinity, and that the domain structure was single-domain compared to conventional sapphire. Was. Therefore, it was found that the LiGaO ₂ (001) substrate was more effective as a lattice matching substrate for Zn _{1 -x} Li _x O than sapphire, which is a conventional substrate crystal.

(Example 7) A LiGaO ₂ single crystal (001) substrate cut from a single-domain crystal was patterned with an organic resist on the oxygen side,
The substrate was immersed in a 90 ° C. nitric acid aqueous solution and etched to a predetermined depth. Then, the groove of the waveguide was formed in the substrate by dissolving the resist. Next, a ZnO thin film was formed by ArF excimer laser evaporation. The target is sintered Zn
O pellets (30 mmφ, 5 mmt) were used. The frequency of the laser pulse was 1 Hz. The substrate temperature was set to 720 ° C., the oxygen partial pressure was set to 10 ⁻⁴ torr, and a predetermined film thickness was deposited. After that, MCP is performed, and Z
Except for the nO film, a smooth waveguide surface was formed. Waveguide propagation loss (dB / cm) was measured as waveguide characteristics. As a comparative example, a waveguide was prepared by growing a film on the sapphire c-plane of a conventional substrate having a large lattice mismatch, and evaluated.

Table 7 shows the waveguide propagation loss. Table 7 Substrate Waveguide propagation loss (dB / cm) Oxygen surface of LiGaO ₂ (001) 0.12 Al ₂ O ₃ (0001) 0.38 Based on the above results, LiGaO ₂ (001) which is made into a single domain
It was found that good propagation loss was obtained in the ZnO single crystal thin film waveguide grown on the oxygen plane, and that the waveguide was improved as compared with the conventional sapphire. Therefore, compared to the conventional substrate crystal, sapphire, LiGaO
_{2 The} (001) substrate was found to be effective as a lattice-matched substrate for ZnO.

(Embodiment 8) A LiGaO ₂ single crystal (001) substrate cut from a single-domain crystal was patterned with an organic resist on the oxygen side,
The substrate was immersed in a 95 ° C. nitric acid aqueous solution and etched to a predetermined depth. After that, the resist was melted to form a substrate to form a groove of the waveguide. Next, a ZnO thin film was formed by a molecular beam epitaxy method. Using Zn as an electron gun (E-gu
Dissolution evaporation according to n). Further, radical oxygen was used as an oxygen source. The substrate temperature was set to 670 ° C., the oxygen partial pressure was set to 10 ⁻⁵ torr, and a predetermined film thickness was deposited. After that, MCP was performed to remove the ZnO film deposited in the portions other than the grooves and to form a smooth waveguide surface. Waveguide propagation loss (dB / cm) was measured as waveguide characteristics. As a comparative example, a waveguide was prepared by growing a film on the sapphire c-plane of a conventional substrate having a large lattice mismatch, and evaluated.

Table 8 shows the waveguide propagation loss. Table 8 Substrate Waveguide propagation loss (dB / cm) Oxygen surface of LiGaO ₂ (001) 0.09 Al ₂ O ₃ (0001) 0.40 Based on the above results, LiGaO ₂ (001) with a single domain
It was found that good propagation loss was obtained in the ZnO single crystal thin film waveguide grown on the oxygen plane, and that the waveguide was improved as compared with the conventional sapphire. Therefore, compared to the conventional substrate crystal, sapphire, LiGaO
_{2 The} (001) substrate was found to be effective as a lattice-matched substrate for ZnO.

(Example 9) A LiGaO ₂ single crystal (001) substrate cut from a single-domain crystal was patterned with an organic resist on the oxygen side,
The substrate was immersed in a 95 ° C. nitric acid aqueous solution and etched to a predetermined depth. After that, the resist was melted to form a substrate to form a groove of the waveguide. Next, a ZnO thin film was formed by an ECR sputtering method. The target used was Zn.
Microwave power and RF sputter power were 600 W and 500 W, respectively. Substrate temperature is 500 ℃
The oxygen partial pressure was set to 5 × 10 ⁻⁴ torr, and a predetermined film thickness was deposited. After that, CP was performed to remove the ZnO film deposited in the portions other than the grooves and to form a smooth waveguide surface.
Waveguide propagation loss (dB / cm) was measured as waveguide characteristics. As a comparative example, a waveguide was prepared by growing a film on the sapphire c-plane of a conventional substrate having a large lattice mismatch, and evaluated.

Table 9 shows the waveguide propagation loss. Table 9 Substrate Waveguide propagation loss (dB / cm) Oxygen surface of LiGaO ₂ (001) 0.13 Al ₂ O ₃ (0001) 0.39 Based on the above results, LiGaO ₂ (001) with a single domain
It was found that good propagation loss was obtained in the ZnO single crystal thin film waveguide grown on the oxygen plane, and that the waveguide was improved as compared with the conventional sapphire. Therefore, compared to the conventional substrate crystal, sapphire, LiGaO
_{2 The} (001) substrate was found to be effective as a lattice-matched substrate for ZnO.

In the above embodiment of the method for processing an oxide single crystal thin film, an acidic aqueous solution of nitric acid is used as an etching solution. However, an acidic aqueous solution and a basic aqueous solution can be selectively used. Although a ZnO single crystal thin film was used, ZnO
_It can be applied to a _1-x Li _x O (0 ≦ X <0.3) single crystal thin film.

The above embodiment is one example, and it goes without saying that various changes or improvements can be made without departing from the technical idea of the present invention. For example, the present invention enables the formation of a BeO single crystal thin film, although the application field is different.

[0048]

As described above, LiGaO ₂ (00)
1) By using a substrate crystal, a film having better crystallinity than a ZnO single crystal thin film grown on a conventional sapphire c-plane substrate could be grown. Therefore, the present invention has an effect of greatly contributing to improvement of the oscillation efficiency of the exciton confined laser by ZnO. In addition, LiGaO ₂
By using the (001) substrate crystal, a film having better crystallinity could be grown than a Zn _1-x Li _x O single crystal thin film grown on a sapphire c-plane substrate, which is a conventional substrate. Furthermore, the polarity of the ferroelectric film could be made uniform by using a single-domain substrate. Therefore, the present invention has the effect of improving the quality of the Li-doped ZnO ferroelectric thin film and, further, since the substrate is transparent, greatly contributing to an optoelectronic device using the thin film crystal. Further, as described above, by using the LiGaO ₂ (001) substrate crystal, a waveguide having a smaller propagation loss than a ZnO single crystal thin film waveguide formed on a conventional sapphire c-plane substrate can be formed. Therefore, the present invention
This has the effect of greatly contributing to the improvement of the performance of the O single crystal thin film waveguide.

[Brief description of the drawings]

FIG. 1 shows LiGaO in an oxide single crystal thin film of the present invention.
FIG. ₂ is a view showing a crystal structure of No. ₂ .

FIG. 2 is a view showing a crystal structure of ZnO in an oxide single crystal thin film of the present invention.

FIG. 3 shows Zn _1- XL in the oxide single crystal thin film of the present invention.
is a diagram showing the crystal structure of i _X O.

FIG. 4 is a diagram showing an oxygen surface and a metal surface of LiGaO _{2 in} an example of the present invention.

FIG. 5 is an explanatory view showing steps of a method for processing an oxide single crystal thin film in an example of the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 LiGaO ₂ substrate 2 resist 3 opening 4 groove 5 ZnO 6 waveguide

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G02F 1/03 501 G02F 1/355 501 5F043 1/035 1/365 5F103 1/355 501 H01L 21/363 1/365 G02B 6/12 N H01L 21/306 M 21/363 H01L 21/306 B F term (reference) 2H047 NA02 NA08 PA03 PA04 PA24 QA02 2H079 AA02 AA12 BA01 BA03 CA05 DA03 DA22 EA02 2K002 CA02 CA22 DA06 FA02 HA02 HA13 4G077 AA03 BB07 BC02 DA05 DA12 ED05 ED06 HA01 SC01 4K029 AA04 AA24 BA49 BA50 BB09 BC07 BD00 CA01 CA05 DB05 DB08 DB20 DC03 DC35 5F043 AA40 BB30 FF01 GG10 5F103 AA01 AA04 AA08 DD30 GG01

Claims (9)

[Claims] 1. A single crystal group having a wurtzite type crystal structure
Zn on plate_1-XLi _XO (0 ≦ X <0.3) single crystal thin film
Oxides characterized by epitaxially growing
Crystal thin film. 2. A single bond having the wurtzite-type crystal structure
Substrate is LiGaO _TwoIt must be a single crystal (001) substrate
The oxide single crystal thin film according to claim 1, wherein: 3. The oxide single crystal thin film according to claim 2, wherein the (001) substrate of the LiGaO ₂ single crystal has a single domain. 4. A surface on which a Zn _1-X Li _X O (0 ≦ X <0.3) single crystal thin film is epitaxially grown is formed on a (001) substrate of a single-domain LiGaO ₂ crystal having a single polarity. 4. The oxide single crystal thin film according to claim 3, wherein the oxide single crystal thin film is a plane. 5. An oxide characterized in that a zinc oxide (ZnO) single crystal thin film is used as a waveguide layer on a (001) substrate surface cut out from a wurtzite-type oxide single crystal having a single domain with respect to polarity. Processing method of single crystal thin film. 6. The oxide single crystal according to claim 5, wherein the substrate surface of the oxide single crystal having a wurtzite crystal structure is an oxygen surface of a (001) substrate of LiGaO ₂ single crystal. Processing method of thin film. 7. The method for processing an oxide single crystal thin film according to claim 6, wherein a groove of the waveguide layer is formed by performing chemical etching using an acidic aqueous solution. 8. The oxide single crystal according to claim 5, wherein the substrate surface of the oxide single crystal having a wurtzite type crystal structure is a metal surface of a LiGaO ₂ single crystal (001) substrate. Processing method of thin film. 9. The groove of the waveguide layer is formed by performing chemical etching using a basic aqueous solution.
The method for processing an oxide single crystal thin film according to the above.