JP2016051824A - Epitaxial growth method and growth device, and method of producing quantum well structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an epitaxial growth method and growth device capable of achieving ultra-migration at a low temperature by utilizing the Leidenfrost phenomenon and of producing a high-quality thin film, to provide a quantum well structure consisting of an oxide semiconductor with a high-potential corundum structure, and to provide a semiconductor device including the quantum well structure.SOLUTION: Provided is an epitaxial growth method for forming an epitaxial layer on a base substance by utilizing the Leidenfrost phenomenon. A mist or droplets generated by atomizing raw material solution or by forming droplets of raw material solution is made thermally react to form the epitaxial layer on the base substance.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an epitaxial growth method and growth apparatus, and a method for manufacturing a quantum well structure.

The development of optical / electronic devices using quantum wells (QW) is very active, and various studies have been made on quantum well structures.
Patent Document 1 describes an oxide artificial superlattice thin film obtained by epitaxially growing an oxide in atomic layer units on a substrate crystal plane.
Patent Document 2 describes a quantum well structure of a non-doped ZnO layer and a p-type doped ZnTe layer.
Patent Document 3 describes a structure using a zinc oxide or zinc oxide mixed crystal thin film as a quantum well.
Patent Document 4 describes a quantum well structure of GaN and InGaN formed on a β-Ga ₂ O ₃ substrate via an AlN buffer layer.
Patent Document 5 describes a semiconductor laser including a quantum well composed of an InGaAsP well layer and an InGaPSb barrier layer.

  However, when fabricating quantum wells, it is necessary to control the film formation at the atomic layer level, and migration of the deposited atoms is very important, so the substrate temperature has to be increased to a high temperature (> 500 ° C.). . On the other hand, in order to produce QW on general-purpose equipment such as glass, it is necessary to try film formation at a lower temperature. Thus, attempts have been made to lower the production temperature (about 400 ° C.) by using a surfactant such as bismuth (surfactant effect), but this has not been satisfactory.

By the way, a semiconductor device using gallium oxide (Ga ₂ O ₃ ) having a large band gap is attracting attention as a next-generation switching element capable of realizing high breakdown voltage, low loss, and high heat resistance, and a power semiconductor device such as an inverter. Application to is expected. According to Non-Patent Document 1, the gallium oxide can control the band gap by using mixed crystals of indium and aluminum, respectively. In particular, In _{X ′} Al _{Y ′} Ga _Z An InAlGaO-based semiconductor represented by _' O ₃ (0 ≦ X ′ ≦ 2, 0 ≦ Y ′ ≦ 2, 0 ≦ Z ′ ≦ 2, X ′ + Y ′ + Z ′ = 1.5 to 2.5) is extremely It is an attractive material.
However, it has been difficult to produce an InAlGaO-based quantum well structure having a high-potential corundum structure so far, and the establishment of its production method has been awaited.

JP 2000-154100 A JP 2000-332296 A International Publication No. WO2002 / 056392 International Publication No. WO2012 / 137781 JP 2012-212748 A

Kentaro Kaneko, “Growth and Physical Properties of Corundum Structure Gallium Oxide Mixed Crystal Thin Films”, Kyoto University Doctoral Dissertation, March 2013 Sawada, H .: Mater. Res. Bull. 29 (1994) 127 – 133 W.H.Zachariasen, Skr. Nor. Vidensk.-Akad., Kl. 1: Mat.-Naturvidensk. Kl., 4 (1928) 6-166.

  The present invention provides an epitaxial growth method and growth apparatus capable of producing a high-quality thin film by making use of the Leidenfrost phenomenon and capable of supermigration at a low temperature, and a quantum well structure comprising an oxide semiconductor having a high-potential corundum structure. An object is to provide a manufacturing method.

As a result of intensive studies to achieve the above object, the present inventors have found that, by using the mist CVD method, it is possible to produce a high-quality thin film by using the Leidenfrost phenomenon and enabling supermigration at a low temperature. As a result, they have found that the conventional problems described above can be solved at once.
Moreover, after obtaining the said knowledge, the present inventors repeated investigation further, and came to complete this invention.

That is, the present invention relates to the following inventions.
[1] An epitaxial growth method in which an epitaxial layer is formed on a substrate using the Leidenfrost phenomenon, wherein a mist or droplets generated by atomizing or dropletizing a raw material solution is reacted with heat on the substrate. An epitaxial growth method comprising forming an epitaxial layer.
[2] The epitaxial growth method according to [1], wherein the thermal reaction is performed at a temperature equal to or higher than the evaporation temperature of the raw material solution.
[3] The epitaxial growth method according to [1] or [2], wherein a quantum well structure is formed by alternately forming different epitaxial layers.
[4] An epitaxial growth apparatus that forms an epitaxial layer on a substrate using the Leidenfrost phenomenon, and includes means for thermally reacting mist or droplets generated by atomizing or dropletizing a raw material solution. An epitaxial growth apparatus characterized by the above.
[5] In a method of fabricating a quantum well structure by alternately stacking different layers on a substrate by epitaxial growth, supplying the mist generated by atomizing a raw material solution to the substrate by a carrier gas, A method of manufacturing a quantum well structure, which is performed by a mist CVD method in which a film is formed on the substrate by a thermal reaction.
[6] The method according to [5], wherein the thermal reaction is performed under a temperature condition of 500 ° C. or lower.
[7] The method according to [5] or [6], wherein the thermal reaction is performed in an oxygen atmosphere.
[8] A first raw material solution containing one or more metals selected from gallium, iron, indium and aluminum, gallium, iron, indium, aluminum, vanadium, titanium, chromium, rhodium, The method according to any one of the above [5] to [7], which has at least two types of the second raw material solution containing one or more metals selected from nickel and cobalt.
[9] The method according to any one of [5] to [8], wherein the substrate is a base substrate whose main component is a substrate material having a corundum structure.
[10] The method according to any one of [5] to [9], wherein at least two different layers are alternately stacked.
[11] A quantum well structure manufactured by the method according to any one of [5] to [10].
[12] A semiconductor device including the quantum well structure according to [11].

  According to the present invention, an epitaxial growth method and a growth apparatus capable of producing a high-quality thin film by making use of the Leidenfrost phenomenon and enabling supermigration at a low temperature, and a quantum well comprising an oxide semiconductor having a corundum structure with high potential The structure can be made industrially advantageous.

It is a block diagram of the mist CVD apparatus used in the Example. It is a figure which shows the film-forming time in an Example. It is a figure which shows the measurement result of the scanning transmission electron microscope (STEM) in an Example. It is a figure which shows the measurement result of the energy dispersive X-ray spectrometer and the measurement result of a STEM image in an Example. It is a figure which shows the X-ray-diffraction image in an Example. It is a figure which shows the X-ray-diffraction pattern in an Example. It is a figure which shows the result of the reciprocal lattice mapping of the (0006) plane by the X-ray diffraction in an Example. It is a figure explaining the (0006) plane in FIG. 7 using an atomic structure model. It is a figure which shows the result of the reciprocal lattice mapping of the (10-1, 10) plane by the X-ray diffraction in an Example. It is a figure explaining the (10-1, 10) plane in FIG. 9 using an atomic structure model. It is a figure which shows the result of the reciprocal lattice mapping of (11-2,9) plane by the X-ray diffraction in an Example. It is a figure explaining the (11-2, 9) plane in FIG. 11 using an atomic structure model. A comparison of the satellite peaks of FIGS. 7, 9 and 11 is shown.

  The epitaxial growth method of the present invention is an epitaxial growth method in which an epitaxial layer is formed on a substrate by utilizing the Leidenfrost phenomenon, and a mist or droplet generated by atomizing or dropletizing a raw material solution is reacted with heat. And forming an epitaxial layer on the substrate. The means for atomizing or dropping the raw material solution is not particularly limited as long as the object of the present invention is not impaired, and may be a known means. In the present invention, the thermal reaction is preferably performed at a temperature equal to or higher than the evaporation temperature of the raw material solution. According to the epitaxial growth method, a high quality epitaxial layer can be formed. In the present invention, the quantum well structure may be formed by alternately forming different epitaxial layers.

  In addition, the manufacturing method of the present invention is a method of manufacturing a quantum well structure by alternately stacking different layers on a substrate by epitaxial growth. In the manufacturing method of the present invention, mist generated by atomizing a raw material solution is generated by a carrier gas. The method is characterized in that it is carried out by a mist CVD method in which the film is supplied to the substrate and formed on the substrate by a thermal reaction. The production method of the present invention will be described below.

(Raw material solution)
The raw material solution is not particularly limited as long as it contains a material capable of forming each layer of the quantum well structure, but in the present invention, the first solution containing one or more metals selected from gallium, iron, indium, and aluminum is used. 1 raw material solution and at least two of a second raw material solution containing one or more metals selected from gallium, iron, indium, aluminum, vanadium, titanium, chromium, rhodium, nickel and cobalt Is preferred.

  The raw material solution is not particularly limited as long as it can atomize the metal, but as the raw material solution, a solution obtained by dissolving or dispersing the metal in an organic solvent or water in the form of a complex or a salt is preferably used. Can do. Examples of complex forms include acetylacetonate complexes, carbonyl complexes, ammine complexes, hydride complexes, and the like. Examples of the salt form include metal chloride salts, metal bromide salts, metal iodide salts, and the like.

Moreover, you may mix additives, such as a hydrohalic acid and an oxidizing agent, with the said raw material solution. Examples of the hydrohalic acid include hydrobromic acid, hydrochloric acid, hydroiodic acid, etc. Among them, hydrobromic acid or hydroiodic acid is preferable. Examples of the oxidizing agent include hydrogen peroxide (H ₂ O ₂ ), sodium peroxide (Na ₂ O ₂ ), barium peroxide (BaO ₂ ), and benzoyl peroxide (C ₆ H ₅ CO) ₂ O _2. Peroxides, hypochlorous acid (HClO), perchloric acid, nitric acid, ozone water, organic peroxides such as peracetic acid and nitrobenzene.

The raw material solution may contain a dopant. The dopant is not particularly limited as long as the object of the present invention is not impaired. Examples of the dopant include n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium or niobium, or p-type dopants. The concentration of the dopant may usually be about 1 × 10 ¹⁶ / cm ³ to 1 × 10 ²² / cm ³ , and the concentration of the dopant is set to a low concentration of about 1 × 10 ¹⁷ / cm ³ or less, for example. May be. Furthermore, according to the present invention, the dopant may be contained at a high concentration of about 1 × 10 ²⁰ / cm ³ or more.

(Substrate)
The substrate is not particularly limited as long as it can support a quantum well structure. The material of the substrate is not particularly limited as long as the object of the present invention is not impaired, and may be a known substrate, an organic compound, or an inorganic compound. Examples of the shape of the substrate include plate shapes such as flat plates and disks, fiber shapes, rod shapes, columnar shapes, prismatic shapes, cylindrical shapes, spiral shapes, spherical shapes, ring shapes, and the like. A substrate is preferred. Although the thickness of a board | substrate is not specifically limited in this invention, Preferably, it is 10-2000 micrometers, More preferably, it is 50-800 micrometers.

  The substrate is not particularly limited as long as it has a plate shape and serves as a support for a quantum well structure. The substrate may be an insulator substrate, a semiconductor substrate, or a conductive substrate, but the substrate is preferably an insulator substrate, and has a metal film on the surface. A substrate is also preferred. Examples of the substrate include a base substrate containing a substrate material having a corundum structure as a main component, a base substrate containing a substrate material having a β-gallia structure as a main component, and a substrate material having a hexagonal crystal structure as a main component. Examples thereof include a base substrate. Here, the “main component” means that the substrate material having the specific crystal structure is preferably 50% or more, more preferably 70% or more, and still more preferably 90% by atomic ratio with respect to all components of the substrate material. % Or more, meaning that it may be 100%.

The substrate material is not particularly limited as long as the object of the present invention is not impaired, and may be a known material. Examples of the substrate material having the corundum structure include the same materials as those exemplified as the material having the corundum structure. In the present invention, α-Al ₂ O ₃ or α-Ga ₂ O is used. ₃ is preferred. As a base substrate mainly composed of a substrate material having a corundum structure, a sapphire substrate (preferably a c-plane sapphire substrate), an α-type gallium oxide substrate, or the like is given as a suitable example. As a base substrate mainly composed of a substrate material having a β-gallia structure, for example, a β-Ga ₂ O ₃ substrate, or a Ga ₂ O ₃ and Al ₂ O ₃ containing Al ₂ O ₃ content of more than 0 wt% Examples thereof include a mixed crystal substrate of 60 wt% or less. In addition, examples of the base substrate whose main component is a substrate material having a hexagonal crystal structure include a SiC substrate, a ZnO substrate, and a GaN substrate. Note that each layer may be stacked directly or via another layer (for example, a buffer layer) on a base substrate whose main component is a substrate material having a hexagonal crystal structure.
In the present invention, the base is preferably a base substrate mainly composed of a substrate material having a corundum structure, more preferably a sapphire substrate or an α-type gallium oxide substrate, and a c-plane sapphire substrate. Is most preferred.

  In the present invention, a quantum well structure is formed by laminating at least one first layer and second layer on a substrate using a mist CVD method. In the mist CVD method, the raw material solution is atomized (atomization step), the generated mist is supplied to the substrate by a carrier gas (mist supply step), and a film is formed on the substrate by a thermal reaction (a formation process). Membrane process).

  In the atomization step, the raw material solution is adjusted, and the raw material solution is atomized to generate mist. The blending ratio of the metal is not particularly limited, but is preferably 0.01 to 70% by mass, and more preferably 0.1 to 50% by mass with respect to the entire raw material solution.

  In this step, the raw material solution is atomized to generate mist. The atomizing means is not particularly limited as long as it can atomize the raw material solution, and may be a known atomizing means, but in the present invention, it is preferably an atomizing means using ultrasonic waves.

  In the carrier gas supply step, a carrier gas is supplied to the mist. The type of the carrier gas is not particularly limited as long as the object of the present invention is not impaired. For example, an inert gas such as oxygen, ozone, nitrogen or argon, or a reducing gas such as hydrogen gas or forming gas is preferable. As mentioned. Further, the type of carrier gas may be one type, but may be two or more types, and a diluent gas (for example, a 10-fold diluted gas) whose carrier gas concentration is changed is used as the second carrier gas. Further, it may be used. Further, the supply location of the carrier gas is not limited to one location but may be two or more locations.

  In the mist supply step, the mist is supplied to the substrate by the carrier gas. The flow rate of the carrier gas is not particularly limited. For example, in the case of forming a film on a 30 mm square substrate, it is preferably 0.01 to 20 L / min, and more preferably 1 to 10 L / min.

  In the film forming step, the mist is reacted by heat to form a film on part or all of the substrate surface. The thermal reaction may be performed as long as the mist reacts with heat, and the reaction conditions are not particularly limited as long as the object of the present invention is not impaired. In this step, the thermal reaction is preferably performed at a temperature of 600 ° C. or less, more preferably at a temperature of 500 ° C. or less, and most preferably at 450 ° C. or less. Further, the thermal reaction may be performed in any atmosphere of a vacuum, a non-oxygen atmosphere, a reducing gas atmosphere, and an oxygen atmosphere as long as the object of the present invention is not impaired. Although it may be carried out under any conditions of reduced pressure and reduced pressure, it is preferably carried out under atmospheric pressure in the present invention. The film thickness can be set by adjusting the film formation time. In the present invention, the thicknesses of the first layer and the second layer, which are constituent units of the quantum well structure, are preferably 50 nm or less, more preferably 25 nm or less, and each 10 nm or less. Is most preferred.

  In the present invention, the first layer and the second layer may be laminated directly on the substrate, or may be laminated on the substrate via another layer such as a buffer layer. Other layers, such as the said buffer layer, are not specifically limited unless the objective of this invention is inhibited, You may be a well-known layer.

  The quantum well structure of the present invention is not particularly limited as long as the first layer and the second layer whose main component is a material different from the first layer are alternately stacked one by one. In the present invention, the first layer and the second layer are preferably laminated at least 2 layers, more preferably 3 layers, and most preferably 5 layers. preferable.

  Since the quantum well structure of the present invention includes an oxide semiconductor having a corundum structure, the quantum well structure is useful for a semiconductor device. When the quantum well structure is used in a semiconductor device, the quantum well structure may be used as it is in a semiconductor device, or may be used after post-processing the quantum well structure.

  In the present invention, when an insulator substrate such as a sapphire substrate is used as the substrate, for example, after bonding other layers such as a p-type semiconductor layer, the quantum well structure is peeled from the substrate to form a semiconductor device. It is preferable to use it. The peeling means is not particularly limited as long as the object of the present invention is not impaired, and may be a known means. Examples of the peeling means include a means for peeling by applying a mechanical impact, a means for peeling by applying heat and applying thermal stress, a means for peeling by applying vibration such as ultrasonic waves, a means for peeling by etching, etc. Is mentioned.

  The p-type semiconductor layer is not particularly limited as long as it does not hinder the object of the present invention, but is preferably a p-type semiconductor layer containing a metal oxide having a hexagonal crystal structure as a main component. Preferred examples of the metal oxide include Delafossite, rhodium oxide, and oxychalcogenide.

  The semiconductor device can be classified into a horizontal element (horizontal device) in which electrodes are formed on one side of a semiconductor layer and a vertical element (vertical device) having electrodes on both sides of the semiconductor layer. However, the quantum well structure of the present invention can be suitably used for both horizontal and vertical devices.

  Examples of the semiconductor device include a semiconductor laser, a diode, or a transistor, and more specifically, a distributed feedback (DFB) laser, a distributed reflection (DBR) laser, an external resonator laser, and a Schottky barrier. Diode (SBD), metal semiconductor field effect transistor (MESFET), high electron mobility transistor (HEMT), metal oxide semiconductor field effect transistor (MOSFET), electrostatic induction transistor (SIT), junction field effect transistor (JFET), Examples thereof include an insulated gate bipolar transistor (IGBT) or a light emitting diode.

  Needless to say, the semiconductor device may include other layers (for example, an insulator layer, a semi-insulator layer, a conductor layer, a semiconductor layer, a buffer layer, or other intermediate layers). Good.

  The mist CVD apparatus used in this example will be described with reference to FIG. The mist CVD apparatus of FIG. 1 includes a supply unit 10 and a reaction unit 11 having a fine channel structure. The supply unit 10 includes a carrier gas supplied from the ultrasonic vibrator 1, the container 2, and a carrier gas supply unit. 3 is provided, and a flow rate adjusting valve 4a for adjusting the flow rate of the dilution gas 4 supplied from the dilution gas supply means is provided. The reaction unit 11 includes a flow rate adjusting valve 5a for adjusting the flow rate of ozone 5 supplied from the ozone supply means, a mist mixing unit 6 for mixing mist supplied from the supply unit 10, a heater 7 and a substrate 8. It has been.

  The raw material solution 9 a is atomized by using the ultrasonic vibrator 1 to be a mist 9 b, and the mist 9 b is sent to the reaction unit 11 by the carrier gas 3. Dilution gas is supplied to the mist 9b on the way to the reaction section 11, and ozone 5 is further supplied to the mist mixing section 6. In the mist mixing unit 6, the mist 9b is mixed, and the mixed mist 9b is sent out to the reaction space having a height of 1 mm. A substrate 8 is provided in the reaction space, and the heater 7 causes the mist 9b to undergo a thermal reaction so that the Leidenfrost effect is developed and a film can be formed on the substrate 8.

Using the CVD apparatus, α-Ga ₂ O ₃ films and α-Fe ₂ O ₃ films were alternately stacked on the substrate to produce a quantum well structure. The film forming conditions are shown in Table 1 and FIG.

  The obtained quantum well structure was measured using a scanning transmission electron microscope (STEM). The measurement results are shown in FIG. FIG. 3 shows that a quantum well structure is formed on the substrate. In addition, using an energy dispersive X-ray spectrometer, the Fe source and Ga source of the produced quantum well structure were measured and compared with STEM images. The results are shown in FIG. It can be seen from FIG. 4 that the quantum well is formed by alternating layers including Fe and Ga.

About the obtained quantum well structure, each phase was identified using the X-ray-diffraction apparatus. The measurement was performed by performing 2θ / ω scan using CuKα rays. An X-ray diffraction image is shown in FIG. 5, and an X-ray diffraction pattern is shown in FIG. From the X-ray diffraction image of FIG. 5, it can be seen that a lattice image is seen and a quantum well structure is formed. Further, from FIG. 6, _α-Fe 2 _{O 3} phase and _α-Ga 2 _{O 3} phase can be confirmed, on c-plane sapphire _(α-Al 2 _{O 3)} substrate, _α-Fe 2 _{O 3} It can be seen that the quantum well structure of / α-Ga ₂ O ₃ is well formed.

FIG. 7 shows the result of reciprocal lattice mapping of the (0006) plane by X-ray diffraction. For reference, FIG. 8 shows the (0006) plane in FIG. 7 using an atomic structure model. Relates reciprocal lattice mapping of Fig. 7, derive an assumed value of (0006) plane of the axis q _Z from the non-Patent Document 2 and Non-Patent Document 3, as shown in Table 2, were compared with measured values. As a result, it can be seen that Al ₂ O ₃ and Ga ₂ O ₃ match the assumed values and the actual measurement values and are not subjected to compressive stress. On the other hand, it can be seen that Fe ₂ O ₃ has no peak and receives compressive stress from Ga ₂ O ₃ .

  FIG. 9 shows the result of reciprocal lattice mapping of the (10-1, 10) plane by X-ray diffraction, and FIG. 11 shows the result of reciprocal lattice mapping of the (11-2, 9) plane. For reference, FIG. 10 shows the (10-1, 10) plane in FIG. 9 and FIG. 12 shows the (11-2, 9) plane in FIG. 11 using an atomic structure model. From these results, the normal direction of the (10-10) plane is taken as the x-axis, and measurement is performed on the x-direction plane and the y-direction plane. Since qz is horizontal in the z-direction, the interface is It turns out that it is parallel to it.

FIG. 13 shows a comparison diagram of the satellite peaks of FIGS. 7, 9 and 11. From the satellite peak, it can be seen that the quantum well structure of Ga ₂ O ₃ / Fe ₂ O ₃ is well formed.
The distance between the quantum well was measured using an X-ray diffractometer _(length per unit of the repeating units of the _{Ga 2 O 3 / Fe 2 O} 3) was about 20.5 nm.

  The epitaxial growth method and growth apparatus and quantum well structure of the present invention can be used in all fields such as semiconductors (for example, compound semiconductor electronic devices), electronic parts / electric equipment parts, optical / electrophotographic related apparatuses, industrial members, In particular, it is useful in the semiconductor field.

DESCRIPTION OF SYMBOLS 1 Ultrasonic vibrator 2 Container 3 Carrier gas 3a Flow control valve 4 Dilution gas 4a Flow control valve 5 Ozone 5a Flow control valve 6 Mist mixing part 7 Heater 8 Substrate 9a Raw material solution 9b Mist 10 Supply part 11 Reaction part

Claims (12)

  An epitaxial growth method in which an epitaxial layer is formed on a substrate by utilizing the Leidenfrost phenomenon, and an epitaxial layer is formed on a substrate by thermally reacting mist or droplets generated by atomizing or dropletizing a raw material solution. An epitaxial growth method comprising forming the epitaxial growth method.   The epitaxial growth method according to claim 1, wherein the thermal reaction is performed at a temperature equal to or higher than an evaporation temperature of the raw material solution.   3. The epitaxial growth method according to claim 1, wherein the quantum well structure is formed by alternately forming different epitaxial layers.   An epitaxial growth apparatus for forming an epitaxial layer on a substrate using the Leidenfrost phenomenon, characterized by comprising means for thermally reacting mist or droplets generated by atomizing or dropletizing a raw material solution Epitaxial growth equipment.   In a method for producing a quantum well structure by alternately stacking different layers on a substrate by epitaxial growth, the epitaxial growth is performed by supplying a mist generated by atomizing a raw material solution to the substrate by a carrier gas, and by thermal reaction. A method for producing a quantum well structure, which is performed by a mist CVD method for forming a film on the substrate.   The method according to claim 5, wherein the thermal reaction is performed under a temperature condition of 500 ° C. or less.   The method according to claim 5 or 6, wherein the thermal reaction is carried out in an oxygen atmosphere.   A first raw material solution containing one or more metals selected from gallium, iron, indium and aluminum; and gallium, iron, indium, aluminum, vanadium, titanium, chromium, rhodium, nickel and cobalt The method in any one of Claims 5-7 which has at least 2 sort (s) with the 2nd raw material solution containing 1 type, or 2 or more types of metals chosen from these.   The method according to any one of claims 5 to 8, wherein the substrate is a base substrate whose main component is a substrate material having a corundum structure.   The method according to claim 5, wherein at least two alternately different layers are laminated.   The quantum well structure produced by the method in any one of Claims 5-10. A semiconductor device comprising the quantum well structure according to claim 11.