KR100938000B1 - MANUFACTURE METHOD FOR ZnO BASED COMPOUND SEMICONDUCTOR CRYSTAL AND ZnO BASED COMPOUND SEMICONDUCTOR SUBSTRATE - Google Patents

Abstract

The present invention provides a method for producing a ZnO-based compound semiconductor crystal from which a good ZnO-based compound semiconductor crystal can be obtained.

According to the present invention, a plurality of terraces constituted by (0001) planes have a main surface extending in a step shape in the m-axis direction, and an inclination angle based on the (0001) planes of the stairs defined by the plurality of terraces is 2 °. The following ZnO substrates are prepared, and ZnO-based compound semiconductor crystals are grown on the main surface.

Semiconductor Crystal, ZnO, Terrace, Stair, Surface Slope

Description

Method for producing a compound based on a semiconductor compound semiconductor crystal, and a compound based on a nano compound semiconductor substrate {MANUFACTURE METHOD FOR ZnO BASED COMPOUND SEMICONDUCTOR CRYSTAL AND ZnO BASED COMPOUND SEMICONDUCTOR SUBSTRATE}

1 is a schematic partially broken perspective view showing a substrate for crystal growth of ZnO based compound semiconductor crystals according to an embodiment.

2 is a schematic partially broken perspective view illustrating a ZnO-based compound semiconductor substrate according to an embodiment.

3A to 3J are AFM images of the surface of a ZnO single crystal layer grown on a ZnO (0001) substrate having various surface inclination angles in the m-axis or a-axis direction by an atomic force microscope (AFM). It is an image.

4 is a graph showing the surface tilt angle dependence of the surface roughness (root-mean-square, RMS) of the ZnO single crystal layer.

 5 is a measurement result showing the surface tilt angle dependence of the electron mobility of the ZnO single crystal layer.

<Description of Symbols in Drawings>

5: substrate for crystal growth

5a: first terrace

15: ZnO-based compound semiconductor crystal layer

15a: 2nd Terrace

20: ZnO-based compound semiconductor substrate

The present invention relates to a method for producing a zinc oxide (ZnO) compound semiconductor crystal, and a ZnO compound semiconductor substrate. ZnO-based compound semiconductors such as ZnO are one of the wide gap semiconductors, and their exciton bonding energy is as large as 60 meV. By constructing a light emitting device using the ZnO compound semiconductor as an active layer material, it is theoretically possible to obtain a device having a higher luminous efficiency than a light emitting device using a gallium nitride based compound semiconductor as an active layer material.

For this reason, ZnO-based compound semiconductors are expected to be used as materials for active layers in blue light emitting devices or ultraviolet light emitting devices.

In order to use a ZnO-based compound semiconductor as an active layer material of a light emitting element, first, it is necessary to obtain a single crystal layer of the compound semiconductor.

The single crystal layer of ZnO-based compound semiconductor is directly or templated on a surface sapphire substrate or c surface sapphire substrate, for example, by molecular beam epitaxy (MBE) or laser ablation deposition. It is formed through a layer.

The crystal structure of the ZnO-based compound semiconductor is a wurtzite structure, which is one of hexagonal crystals. Crystal growth on the a-plane sapphire substrate or the c-plane sapphire substrate is usually caused in the -c axis (oxygen (O) plane) direction. For example, when a gallium (Ga) plane GaN film is used as the template layer, it is also possible to crystal-grow the ZnO-based compound semiconductor in the + c-axis (zn plane) direction. Also in the Zn plane ZnO substrate, crystal growth can be performed in the + c axis direction.

In order to use a ZnO compound semiconductor, for example as an activation layer of a light emitting element, it is preferable to obtain a single crystal layer with few crystal defects. However, crystal defects tend to occur in the single crystal of the ZnO compound semiconductor.

The inventors have invented a crystal growth substrate and the like which are suitable for growing a ZnO compound semiconductor having a hexagonal crystal structure. See, for example, Japanese Patent Laid-Open No. 2003-282602 and its corresponding US Pat. No. 6,673,478. The sapphire substrate is used as the crystal growth substrate, but the sapphire substrate is not conductive and electrodes cannot be provided on the back surface of the substrate.

An object of the present invention is to provide a method for producing a ZnO compound semiconductor crystal capable of obtaining a high quality ZnO compound semiconductor crystal.

It is also an object of the present invention to provide a high quality ZnO based compound semiconductor substrate.

According to the consistency point of this invention, the several terraces comprised by (A) (0001) surface have the main surface arrange | positioned continuously in the step shape in the m-axis direction, and the stairs which a plurality of terraces decide Preparation of a ZnO-based compound semiconductor crystal having a step of preparing a ZnO substrate having an inclination angle of 2 ° or less with respect to the (0001) plane, and (B) growing a ZnO-based compound semiconductor bottom on the electrical main surface A method is provided.

According to another aspect of the present invention, a plurality of terraces constituted by the (0001) plane have a main surface continuously arranged in a step shape in the m-axis direction, and (0001) of the stairs defined by the plurality of terraces. ZnO compound semiconductor substrate having an epitaxial growth layer consisting of a ZnO single crystal base substrate having an inclination angle of 2 ° or less from a plane and a ZnO compound semiconductor formed on the main surface of the electric base substrate This is provided.

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

 A method of manufacturing a ZnO-based compound semiconductor crystal according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2.

1 is a schematic partially broken perspective view showing a substrate for crystal growth of ZnO-based compound semiconductor crystals according to an embodiment.

The crystal growth substrate 5 is formed of a ZnO single crystal having a hexagonal wurtzite crystal structure. For the following description, the coordinate system C1 which shows the direction of the crystal axis (a-axis, c-axis, and m-axis) in the crystal growth substrate 5 is shown. In the coordinate system C1, the c axis represented by the mirror index (MIRROR INDEX) [0001], the m axis represented by the mirror index [1-100], and the a axis represented by the mirror index [11-20] are orthogonal to each other. In addition, in the case of a Miller index, the "bar" above the number for the negative value is the original notation, but in the present specification, the claims, and in the drawings, the minus sign "- Is added to indicate that the value on the right is denied.

The main surface of the crystal growth substrate 5 is formed between the first terraces 5a having a plurality of (0001) planes successively stepped in the m-axis direction of the ZnO single crystal, and the first terraces 5a adjacent to each other. It is comprised by the step of connecting. In addition, the first terrace 5a is a ZnO plane. Here, the "main surface" means the front surface of the wafer on which semiconductor crystals grow.

The angle of inclination (the angle of inclination of the main surface and the total angle of inclination relative to the (0001) plane) from the lower first terrace 5a to the upper first terrace 5a is 2 ° or less, preferably 0.1 ° or more. It is selected to be less than 1 °.

The height of one step is, for example, the thickness of the two-molecule layer (approximately 0.52 nm).

The crystalline substrate (ZnO substrate) 5 having the first terrace 5a is made by, for example, treating a ZnO substrate having a flat (0001) surface with a gradient polishing and annealing in an oxygen atmosphere. Can be.

In the case where a plurality of first terraces are formed on the crystal growth substrate (ZnO substrate) 5 by annealing in an oxygen atmosphere, the annealing conditions are, for example, 1000 ° C for 1 hour.

The crystal structure of the crystal growth substrate (ZnO substrate) 5 and the inclination angle of the main surface with respect to the (0001) plane can be confirmed using, for example, an X-ray diffraction apparatus.

Hereinafter, the manufacturing method of a ZnO type compound semiconductor crystal is demonstrated, for example, when forming a zinc oxide (ZnO) single crystal layer by MBE method. And before performing MBE method, it is common to perform thermal cleaning (heat processing). Thermal cleaning is performed for about 30 minutes at 600-1000 degreeC, for example.

The crystal growth substrate 5 is mounted on the substrate holder in the growth chamber of the MBE apparatus, the substrate temperature is 300 to 500 ° C (for example 350 ° C), and the zinc (Zn) beam is placed on the crystal growth substrate 5. (Zinc molecular beams) and oxygen (O) radical beams (oxygen radical molecular beams) are irradiated to form a zinc oxide (ZnO) buffer layer having a film thickness of 30 to 100 nm.

The irradiation of the Zn beam and the O radical beam is once stopped and the flatness of the ZnO buffer layer surface is improved. This flatness improvement can be performed by, for example, performing a heat treatment (high temperature cleaning) for 10 to 30 minutes at a substrate temperature of 700 to 1000 ° C.

The substrate temperature is a growth temperature of ZnO crystals, for example, 650 to 700 ° C., and then the ZnO buffer layer is irradiated with Zn beams and O radical beams simultaneously, and the ZnO crystals are formed on the ZnO buffer layer by the + c plane (zn plane). In the direction of 1).

2 is a schematic partially cut perspective view illustrating a ZnO based compound semiconductor substrate according to an embodiment of the present invention. Through the process described with reference to FIG. 1, the ZnO compound semiconductor substrate 20 shown in this figure is manufactured.

The ZnO compound semiconductor substrate 20 has a crystal growth substrate (base substrate) 5 and a ZnO compound semiconductor crystal layer 15 formed on the crystal growth substrate 5. If necessary, a buffer layer having a film thickness of 30 to 100 nm formed of a ZnO-based compound semiconductor can be provided between them.

1, the coordinate system C2 which shows the direction of the crystal axis (a-axis, c-axis, and m-axis) in the ZnO type compound semiconductor crystal layer 15 shown in FIG. In this figure, the c-axis shown by the Miller index [0001], the m-axis shown by the Miller index [1-100], and the a-axis shown by the Miller index [11-20] are orthogonal to each other. The a-axis, m-axis, and c-axis in the ZnO-based compound semiconductor crystal layer 15 are parallel to the a-axis, m-axis, and c-axis in the crystal growth substrate (ZnO) 5, respectively.

The ZnO-based compound semiconductor crystal layer 15 is grown on the crystal growth substrate (ZnO) 5 in the + c plane (Zn plane) and in a plurality of (0001) planes extending stepwise in the m-axis direction. And a step of connecting the second terrace 15a and the second terrace 15a adjacent to each other.

Since the ZnO-based compound semiconductor crystal layer 15 is formed by epitaxial growth, the inclination angle from the second terrace 15a at the lower end to the second terrace 15a at the upper end is used for crystal growth. By selecting the inclination angle in the substrate (substrate substrate) 5, the angle is adjustable and is 2 ° or less, preferably 0.1 ° or more and 1 ° or less.

The height of one step is, for example, the thickness of the two-molecule layer (approximately 0.52 nm).

The crystal structure of the ZnO-based compound semiconductor crystal layer 15 and the inclination angle can be confirmed using, for example, an X-ray diffraction apparatus.

The present inventors crystal-grow the ZnO-based compound semiconductor crystal layer 15 on the crystal growth substrate 5 having the surface inclination angle in the m-axis direction as described above, thereby providing a high-quality ZnO-based compound semiconductor crystal layer 15 Checked out).

3A to 3J illustrate the surface of a ZnO single crystal layer in which the inventors have grown a surface inclination angle on a ZnO (0001) substrate (a substrate on which a terrace exposed by the (0001) surface constitutes a main surface) in the m-axis or a-axis direction. , AFM image taken using an atomic force microscope (AFM).

For FIGS. 3A, 3C, 3E, 3G, and 3i, the image portion shows a size of 5 mu m x 5 mu m on the surface of the ZnO single crystal layer. 3B, 3D, 3F, 3H, and 3J, the image portion shows an area of 1 mu m x 1 mu m on the ZnO single crystal surface.

See FIGS. 3A and 3B. These two photographs are AFM images of the surface of a ZnO single crystal layer grown on a ZnO substrate having a 0.2 ° surface tilt angle in the m-axis direction.

The surface roughness RMS in the region of 5 mu m x 5 mu m size shown in Fig. 3a was 0.4 nm. And RMS in the 1 micrometer x 1 micrometer size area | region shown in FIG. 3B was 0.3 nm. As described above, the surface of the ZnO single crystal layer grown on the ZnO substrate having a 0.2 ° surface tilt angle in the m-axis direction is flat and exhibits excellent surface shape.

See FIGS. 3C and 3D. These two photographs are AFM images of the surface of a ZnO single crystal layer grown on a ZnO substrate having a 2 ° surface tilt angle in the m-axis direction.

The surface roughness RMS in the region of 5 μm × 5 μm shown in FIG. 3C was 1.3 nm, and the RMS in the region of 1 μm × 1 μm shown in FIG. 3D was 1.0 nm. The surface of the ZnO single crystal layer grown on the ZnO substrate having a 0.2 ° surface inclination angle in the m-axis direction is not flat but exhibits a flat and excellent surface property.

See FIGS. 3E and 3F. These two photographs are AFM images of the surface of a ZnO single crystal layer grown on a ZnO substrate having a 4 ° surface tilt angle in the m-axis direction.

The surface roughness RMS in the region of 5 μm × 5 μm shown in FIG. 3E was 4.0 nm, and the RMS in the region of 1 μm × 1 μm shown in FIG. 3F was 2.2 m. Compared with a ZnO single crystal layer grown on a ZnO substrate having a 2 ° surface inclination angle in the m-axis direction, it is difficult to show excellent surface properties.

See FIGS. 3G and 3H. These two photographs are AFM images of the surface of a ZnO single crystal layer grown on a ZnO substrate having a 2 ° surface tilt angle in the a-axis direction.

The surface roughness RMS in the region of 5 μm × 5 μm shown in FIG. 3G was 2.9 nm, and the RMS in the region of 1 μm × 1 μm shown in FIG. 3H was 1.9 m. Compared with a ZnO single crystal layer grown on a ZnO substrate having a surface inclination angle equal to the same angle (2 °) in the m-axis direction, the surface properties are not good. It can be seen that the surface inclination angle is effective to take the m-axis direction rather than the a-axis direction.

See FIGS. 3I and 3J. These two photographs are AFM images of the surface of the ZnO single crystal layer grown on a ZnO substrate having a 4 ° surface tilt angle in the a-axis direction.

The surface roughness RMS in the region of 5 μm × 5 μm shown in FIG. 3I was 4.1 nm, and the RMS in the region of 1 μm × 1 μm shown in FIG. 3J was 3.2 m. The surface properties are worse than when the surface inclination angle is 2 ° in the a-axis direction and when the surface inclination angle is 4 ° in the m-axis direction.

The present inventors took a surface inclination angle in the m-axis or a-axis directions, respectively, and grew a ZnO single crystal layer on a ZnO (0001) substrate to measure surface roughness (RMS).

4 is a graph showing the surface tilt angle dependence of the surface roughness (RMS) of the ZnO single crystal layer.

The horizontal axis represents the surface tilt angle in units of degrees. In the horizontal axis right direction, the surface inclination angle is provided in the a-axis direction, and in the left direction, the surface inclination angle is provided in the m axis direction. The vertical axis represents the surface roughness in RMS in units of "nm" in the region of 1 占 퐉 x 1 占 퐉. From the inclination of the graph, it can be seen that the surface inclination angle is easy to obtain the flatness of the surface by taking in the m-axis direction rather than the a-axis direction.

When the surface inclination angle is 0.4 ° in the m-axis direction, the ZnO single crystal layer having the most flat and excellent surface property is obtained. It is judged that the range of the surface inclination-angle which makes RMS 1 nm or less is 2 degrees or less with respect to the m-axis direction, and 0.8 degrees or less with respect to the a-axis direction. The range of the surface inclination angle which makes RMS 0.5 nm or less is judged to be 1 degrees or less.

When the surface inclination angle taken in the m-axis direction was 1 ° or less, the terrace and the step (0.52 nm) were clearly observed on the surface of the ZnO single crystal layer, and it was confirmed that step bunching did not occur. It was also confirmed that step bunching occurred when the surface inclination angle taken in the m-axis direction was 4 °.

Further, while repeating the experiment under various conditions, the present inventors found that the growth rate in the a-axis direction is faster than the growth rate in the m-axis direction for the growth in the transverse direction of the ZnO single crystal layer. Therefore, it is thought that the surface inclination angle is preferably taken in the m axis direction.

Next, the present inventors measured the electron mobility of the ZnO single crystal layer grown on the Zn0 (0001) substrate by taking the surface inclination angle in the m-axis or a-axis direction in various ways, and examined the crystallinity good and bad.

5 is a measurement result showing the surface tilt angle dependence of the electron mobility of the ZnO single crystal layer. In the horizontal axis, the surface inclination angle is expressed in units of degrees. In the horizontal axis right direction, the surface inclination angle was taken in the a-axis direction. The vertical axis represents electron mobility in units "cm 2 / Vs". The ZnO single crystal layer was not doped with impurities.

It can be seen that the case where the surface inclination angle is taken in the m-axis direction is higher than the case in which the angle of inclination is taken in the a-axis direction and a ZnO single crystal layer having good crystallinity is formed.

When the surface gradient is 0.4 ° in the m-axis direction, the ZnO single crystal layer having the highest electron mobility and the best crystallinity is formed. And when the surface inclination of 2 degrees or less in the m-axis direction is taken, it can be seen that the electron mobility of the ZnO single crystal layer exceeds 100 cm 2 / Vs. In addition, when the surface gradient is less than 1 °, the electron mobility is judged to be 130 cm 2 / Vs or more.

When the surface gradient was 4 ° in the m-axis direction, the electron mobility became about 60 cm 2 / Vs, and it was confirmed by AFM that the crystallinity was not good.

When surface inclination degree was taken in the a-axis direction, even if it is 0.7 degrees, electron mobility became 100 cm <2> / Vs or less, and it turned out that favorable crystallinity cannot be obtained.

From the measurement results of FIGS. 4 and 5, it is considered that the surface inclination angle in the m-axis direction may be 2 ° or less, more preferably 0.1 ° or more and 1 ° or less. Here, "0.1 degrees or more" is because when it is less than 0.1 degrees, it becomes difficult to form ZnO single crystal with good crystallinity on the first terrace.

If the inclination angle exceeds 2 °, the surface morphology of the ZnO single crystal substrate is deteriorated by thermal cleaning (heat treatment) which is generally performed prior to the growth of the ZnO single crystal. It may be difficult to grow them.

As mentioned above, although this invention was demonstrated according to the Example, this invention is not limited to these. For example, in the embodiment, the substrate of the Zn plane (+ c plane) is used, but the substrate of the O plane (-c plane) may be used. Even in that case, the same effect can be obtained by taking the surface inclination angle in the m-axis direction. It is apparent to those skilled in the art that various modifications, improvements, combinations, and the like are possible.

The present invention can be used for the production of ZnO-based compound semiconductor crystals.

The ZnO-based compound semiconductor substrate can be used for various semiconductor devices such as light emitting devices such as light emitting diodes and laser oscillators, circuit devices such as field effect transistors and bipolar transistors, or light receiving devices.

According to the present invention, from the viewpoint of improving the crystallinity of the ZnO-based compound semiconductor crystal, it is preferable to grow the ZnO-based compound semiconductor in the + c-axis (Zn plane).

By using the above-described method for producing a ZnO-based compound semiconductor crystal, the ZnO-based compound semiconductor can be grown in the + c-axis (Zn plane) direction and a high-quality ZnO-based compound semiconductor crystal can be obtained.

Claims (18)

(A) The plurality of terraces constituted by the (0001) plane have a main surface extending in the m-axis direction, and the inclination angle based on the (0001) plane of the stairs defined by the plurality of terraces is 0.1 ° or more. Preparing a ZnO substrate of 1 ° or less, (B) A method for producing a ZnO-based compound semiconductor crystal, comprising the step of growing a ZnO-based compound semiconductor crystal on the electrical main surface. delete The method for producing a ZnO-based compound semiconductor crystal according to claim 1, comprising the step of forming a buffer layer containing ZnO on the main surface of the ZnO substrate before the step (B). The ZnO-based compound semiconductor crystal according to claim 1, wherein the step (A) comprises a step of gradient polishing a flat (0001) surface of the ZnO substrate and annealing the polished ZnO substrate in an oxygen atmosphere. Manufacturing method. delete The method for producing a ZnO compound semiconductor crystal according to claim 1, wherein the step (B) grows the ZnO compound semiconductor crystal to have an RMS surface roughness of greater than 0 and 1 nm or less. The method for producing a ZnO-based compound semiconductor crystal according to claim 1, wherein in the step (B), a ZnO-based compound semiconductor crystal is grown on the main surface using a molecular beam epitaxy. The method of manufacturing a ZnO-based compound semiconductor crystal according to claim 1, wherein the height of the step of connecting adjacent terraces of the (0001) plane corresponds to the thickness of the two-molecule layer. The plurality of terraces constituted by (0001) planes have a main surface extending in the m-axis direction, and the inclination angle with respect to the (0001) planes of the stairs defined by the plurality of terraces is 0.1 ° or more and 1 °. A base substrate of ZnO single crystals, A ZnO compound semiconductor substrate having an epitaxial growth layer of a ZnO compound semiconductor formed on a main surface of an electric substrate. delete 10. The ZnO compound semiconductor substrate according to claim 9, wherein a buffer layer containing ZnO is formed on the main surface of the substrate and under the epitaxial growth layer. delete 10. The ZnO-based compound semiconductor substrate of claim 9, wherein the epitaxial growth layer has an RMS surface roughness of greater than 0 and less than 1 nm. 10. The ZnO-based compound semiconductor substrate according to claim 9, wherein the height of the step of connecting adjacent terraces of the (0001) plane of the main surface of the base substrate corresponds to the thickness of the two-molecule layer. delete delete delete delete

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