JP2009038179A - Element substrate and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such problems: that crystal growth including consideration of the direction of spontaneous polarization derived from the crystal structure of zinc oxide and zinc oxide solid solution is obtained in manufacturing an electronic element and an optical element each comprising zinc oxide and zinc oxide solid solution; that in order to actualize the crystal growth, the following must be studied, such as selection of a substrate material quality in crystal growth and conditions in crystal growth or preprocessing after crystal growth, and a technique for growing crystals for a desired spontaneous direction must be obtained, i.e. a desired crystal growth direction; and that when economic aspects such as a manufacturing cost is taken into consideration, zinc oxide enabling the use of substrate material which is more fluently circulated in the market and having a controlled spontaneous polarization direction, i.e. a crystal growth direction is required. <P>SOLUTION: This element substrate has a buffer layer of a spinnel structure between a substrate and a zinc oxide thin film, and the zinc oxide thin film has a Wultzite crystal structure and its surface as a zinc (0001) face. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an element substrate having a substrate useful in the fields of optics and electric / electronic industry, zinc oxide and / or a zinc oxide thin film that is a solid solution thereof, and a method for manufacturing the same.

  For optical / electronic devices having various functions, Si, GaAs, GaN and the like have been used. On the other hand, focusing on oxides, zinc oxide has been used for varistors, gas sensors, sunscreens, etc. Recently, optical elements, electronic elements, piezoelectric elements and transparent electrodes have been used due to their optical characteristics, electronic element characteristics and piezoelectric characteristics. It has been attracting attention because of its application to substrates on which such elements are formed. Oxides are stable in the atmosphere, and zinc oxide has relatively high electron mobility and excellent light-emitting properties, so that it is being applied as an element substrate for electronic elements or optical elements. .

  For example, (Patent Document 1) discloses a technique related to the formation of a high mobility zinc oxide transistor, and (Patent Document 2) discloses a technique related to the formation of a zinc oxide light emitting diode.

In the Zn _1-x Mg _x O solid solution, it has been shown that a band gap wider than that of zinc oxide can be obtained by adjusting the composition x. (Non-patent Document 1) When considering application to a light-emitting diode In order to increase luminous efficiency, it is generally necessary to adopt a double heterostructure. By adopting the above structure, the efficiency of confining carriers and light is improved, and the light emission efficiency is improved. In order to form the above structure, it is necessary to realize a structure in which a light emitting layer having a relatively narrow band gap is sandwiched between an n layer and a p layer having a relatively wide band gap, and both the band gap and the conductivity are controlled. Crystal growth technology is required.

  Control of n-type and p-type conductivity is indispensable for forming an electronic device using zinc oxide and a zinc oxide solid solution. On the other hand, since zinc oxide has a wurtzite type crystal structure, it has spontaneous polarization, and it is known that this strongly influences impurity uptake during crystal growth. In order to obtain zinc oxide that exhibits p-type conduction, which is relatively difficult to synthesize compared to n-type, or a solid solution thereof, means for efficiently introducing impurities for forming an acceptor level is required. At this time, from the spontaneous polarization characteristics, it is considered effective to grow zinc oxide while supplying an impurity serving as an acceptor using a crystal plane having a zinc surface, that is, a (0001) plane as a growth plane. In order to incorporate nitrogen more efficiently when introducing nitrogen as an acceptor, it is incorporated from a (0001) plane having a zinc surface instead of a (000-1) plane which is a crystal plane having an oxygen surface. Has already been disclosed to be effective. (Non-Patent Document 4)

In order to improve electronic element characteristics and optical element characteristics in zinc oxide and its solid solution, or a laminate composed thereof, high crystallinity is required. As means for obtaining highly crystalline zinc oxide and zinc oxide solid solution crystals, in particular, vapor phase growth method using high-quality zinc oxide crystals as a substrate (Non-patent Document 2), or ScAlMgO ₄ crystals as a substrate Vapor phase epitaxy (Non-patent Document 3) used as a substrate is disclosed, however, the circulation amount of these substrates is smaller than that of crystals such as sapphire, and it is more economical for further development of zinc oxide related industries. A technique for growing higher crystalline zinc oxide and its solid solution crystal using a typical substrate material is required.

  In addition to growing high crystallinity, growing a zinc oxide crystal with high surface flatness is also an important technical issue. For example, an electroluminescent device using an organic semiconductor and a transparent electrode used in manufacturing a liquid crystal panel using liquid crystal are required to have a very flat surface. Since zinc oxide is a polar crystal, at the time of crystal growth, it is easy to obtain a pencil shape like a crystal of a self-shaped crystal, that is, a hexagonal columnar crystal with one end sharp and one end flat. In order to obtain a flatter crystal, it is necessary to consider this crystal habit and to select a growth direction in which a sharp shape on the surface is difficult to develop and to grow the crystal. For example, zinc oxide formed by pulsed laser deposition on the (000-1) plane of zinc oxide single crystal has a concavo-convex structure such that the tip side of the pencil as shown in FIG. On the other hand, zinc oxide formed by the same means on the (0001) plane of zinc oxide single crystal grows as a flat crystal as shown in FIG.

As described above, since zinc oxide and its solid solution are crystals having spontaneous polarization, a doping technique or crystal growth technique considering the polarity of spontaneous polarization is required. However, in crystal growth using a sapphire substrate or the like, which is an oxide wafer generally distributed as a substrate for growing a semiconductor, zinc oxide having an oxygen plane, that is, a (000-1) plane, grows. This resulted in a crystal structure in which needle-shaped crystals with a pointed tip were arranged, and a structure that was not necessarily advantageous for introducing an acceptor. That is, in order to construct a higher performance zinc oxide electronic device, it is indispensable to provide a zinc oxide crystal in consideration of the spontaneous polarization and its flatness and ease of doping.
JP-A-2005-72067 JP 2003-046081 A A. Ohtomo et. al, Applied Physics Letters, Vol. 72, no. 19, 11 May 1998, 2466-2468 H. Matui et al, Journal of Vacuum Science and Technology B, Vol. 22, no. 5, Sep / Oct 2004, 2454-2461 A. Ohtomo et. al, Applied Physics Letters, Vol. 75, no. 17, 25 October 1999, 2635-2637 Maki et al. Jpn. J. et al. Appl. Phys. 42 (2003) 75-77 H. L. Mosbacker, Y.M. M.M. Strzhemechny, B.M. D. White, E.E. Smith, D.D. C. Look, D.D. C. Reynolds, C.I. W. Litton, and L.L. J. et al. Brillson, Appl. Phys. Lett. 87, 0210102 (2005) K. Nakahara, T .; Tanabbe, H.M. Takasu, P.A. Fons, K.C. Iwata, A.I. Yamada, K .; Matsubara, R.A. Hunger, and S.H. Niki, Jpn. J. et al. Appl. Phys. 40, 250 (2001). )

  As described above, in the production of electronic devices and optical devices made of zinc oxide and zinc oxide solid solution, crystal growth considering the direction of spontaneous polarization derived from the crystal structure of zinc oxide and zinc oxide solid solution is required. It is done. In order to realize these, the selection of the substrate material during crystal growth, the growth conditions during crystal growth, or post-treatment after crystal growth, etc. are studied, and the desired spontaneous polarization direction, that is, the desired crystal growth. Techniques must be obtained for growing crystals in the direction. In addition, in consideration of economics such as manufacturing cost, to provide a zinc oxide with a controlled spontaneous polarization direction, that is, a crystal growth direction, which can use a substrate material with a larger distribution amount and a stable supply. Is required.

The above problems can be solved by the following present invention.
The element substrate of the invention 1 has a buffer layer having a spinel structure between the substrate and the zinc oxide thin film, and the zinc oxide thin film has a wurtzite crystal structure, and the surface thereof is a zinc (0001) surface. It is characterized by being.

  Invention 2 is characterized in that in the element substrate of Invention 1, a buffer layer is provided on the (11-20) plane of the substrate.

  Invention 3 is a method for manufacturing an element substrate according to Invention 1 or 2, wherein when a crystal of zinc oxide or / and a solid solution thereof is vapor-phase grown on a substrate, a hardly solid-soluble metal is added to the zinc component. The buffer layer is formed by vapor deposition on the heated substrate, and the zinc oxide thin film is grown on the surface of the buffer layer.

  The invention 4 is characterized in that, in the production method of the invention 3, when the film forming component is deposited, the substrate is heated to a predetermined temperature to form a buffer layer.

  According to the present invention, it is possible to realize crystal growth with a zinc surface as a growth surface, and this makes it possible to provide a flat material at an atomic level, and therefore, electric field concentration caused by unevenness when forming an element. In addition, it is possible to avoid problems such as p-type zinc oxide, and the ease of introduction of impurities as acceptors is also increased with respect to p-type zinc oxide, which remains a problem in the manufacturing method thereof, so that zinc oxide and zinc oxide solid solution This makes it possible to manufacture electronic devices and optical devices using the above, and to realize higher performance device characteristics.

  In the present invention, when zinc oxide or a zinc oxide solid solution is grown on a substrate by vapor phase growth, the zinc oxide having a zinc surface has a flat surface (zinc (0001) surface) as shown in FIG. Therefore, step-flow type crystal growth is possible on this zinc surface when growing zinc oxide with n-type or p-type conductivity control or introducing a light emission center with high quality. Therefore, a zinc oxide having a zinc surface grown or a zinc oxide solid solution, having a surface structure as shown in FIG. 2 and having a large particle diameter, is a highly flat zinc oxide. Thin film crystals are the most desirable embodiment.

Here, the structure using the (11-20) plane of sapphire as a substrate will be described in more detail as an example. The (11-20) plane of sapphire has a surface atomic arrangement in which oxygen sublattices on the surface are present at the corners of the rectangle, and is generally used for epitaxial growth of hexagonal zinc oxide (0001). The surface is advantageous from the viewpoint of lattice matching as compared with a sapphire substrate having a surface. On the planarized surface of ZnO, a step structure having one unit of ZnO crystal lattice as a unit is formed. The lower the frequency of occurrence of this step, the higher the planarity of the ZnO film. Therefore, it is desirable to use the (11-20) substrate surface of this sapphire as a means for lengthening the expression cycle of the step structure.
In addition, if it has not only sapphire but the crystal structure similar to this, it is estimated that the same effect is exhibited.
Further, the above description does not deny the use of a general (0001) plane. Depending on the material and the required flatness, it can be expected that it can be used effectively.

  An effective embodiment of the present invention is a zinc oxide having a wurtzite type crystal structure formed on a substrate, and a single crystal thin film that is a solid solution thereof, the surface of which is a (0001) plane, that is, a zinc plane It is most important that In this element substrate, a transistor element and a diode element can be obtained by depositing n-type or p-type zinc oxide and its solid solution.

  For example, on a zinc oxide thin film crystal having a step and terrace structure as shown in FIG. 3, it has a composition of (Mg, Zn) O and a wurtzite type crystal structure, and has a wider band gap than zinc oxide. Forming an n-type solid solution layer having an additive-free ZnO layer having a low defect concentration, and then having a composition of (Mg, Zn) O and a wurtzite type crystal structure, By forming an n-type solid solution layer having a wider band gap than zinc oxide, a pin type double heterostructure based on zinc oxide can be obtained. Here, as means for obtaining n-type (Mg, Zn) O and p-type (Mg, Zn) O, substitution of zinc with group III elements such as aluminum and gallium, and nitrogen, respectively, There is oxygen substitution by. A Schottky diode is formed by forming a Schottky electrode made of a metal such as gold on an n-type zinc oxide thin film crystal having a zinc surface. In this case, in order to suppress electric field concentration and to obtain stable device characteristics, zinc oxide without unevenness is necessary, and the substrate provided by the present invention has a zinc surface and is flat at the atomic level. The use of zinc oxide or a zinc oxide solid solution is a very effective technique.

  The second of the embodiments of the present invention is that a zinc oxide thin film crystal is grown after the buffer layer is formed on the substrate.

Zinc is known for its high vapor pressure. When zinc oxide is grown by vapor phase growth in which the wafer is kept at a high temperature and the raw material is supplied from the vapor phase, all the zinc components that have reached the wafer surface are all present. It does not crystallize as zinc oxide and part is re-evaporated.
For example, when growing zinc oxide on the sapphire (11-20) plane, it is considered that the effect of re-evaporation is larger than growing zinc oxide on the sapphire (0001) plane. In growing zinc oxide on the sapphire (11-20) surface, it is known that zinc oxide does not grow unless initial growth is performed at a low temperature at which re-evaporation does not easily occur. (Non-patent document 6)
In the zinc oxide crystal growth method according to the present invention, on the contrary, zinc oxide having the zinc surface as a surface was obtained by utilizing the effect of this re-evaporation.

That is, when a raw material containing a metal (for example, aluminum) that is hardly soluble in zinc is supplied to a high-temperature substrate, the adhesion rate of the zinc component that easily re-evaporates in the raw material is low, and conversely A component having a high rate becomes highly concentrated on the substrate surface. For this reason, increasing the concentration of the hardly soluble metal (M) induces nucleation of M _x ZnO ₄ (Al ₂ ZnO ₄ ), not zinc oxide, and a spinel structure (completely formed on the substrate). In addition to a spinel structure, a thin film having a structure in which a large amount of defects are introduced, or a similar structure such as a structure distorted due to lattice mismatch with the substrate is formed. When this (111) -oriented thin film is generated, a situation in which zinc oxide nucleation is likely to occur occurs. In particular, even if the growth conditions such as the raw material supply and the wafer temperature are not changed, the zinc surface is spontaneously formed. Nucleation of zinc oxide occurs. This is shown in FIG. Typical synthesis conditions include, for example, a vapor deposition method in which a raw material to which aluminum (a hardly soluble metal) having a concentration of about 1% is added to zinc is supplied, and the substrate is kept at 6 × 10 ² ° C. (111) -oriented layer having a spinel structure is nucleated, and when the substrate is covered with a thin film having a spinel structure, nucleation of zinc oxide occurs and aluminum is added. The growth of zinc oxide having the zinc surface as the surface is started.

  As can be seen from Example 1 and Comparative Example 1 compared thereto, when aluminum is added to the raw material, a buffer layer (interface layer) having a spinel structure is spontaneously formed by the supplied aluminum and zinc. A zinc oxide thin film formed and having a zinc surface as a surface is obtained. On the other hand, as shown in Comparative Example 1, when grown with only zinc oxide raw material to which aluminum (hardly soluble metal) was not added, a zinc oxide thin film having an oxygen surface as a surface was obtained. This is due to the fact that, under the crystal growth conditions of Comparative Example 1, zinc oxide was nucleated without forming a spinel layer on the sapphire substrate, and a spinel-like buffer layer using a raw material to which aluminum was added. This is a typical example showing that a zinc oxide thin film crystal having a zinc surface can be obtained by forming.

  In the third embodiment of the present invention, first, a zinc oxide layer is formed and subjected to heat treatment to induce a solid-state reaction between the hardly soluble metal (aluminum) of the substrate (sapphire) and zinc oxide. To form a (111) -oriented buffer layer having a spinel structure, which is a complex oxide of a hardly soluble metal (aluminum) and zinc, on the substrate (sapphire), and a structure called spinel structure / substrate (sapphire) is formed. Then, zinc oxide or a solid solution thereof is grown on the buffer layer. The outline is shown in FIG. A crystalline buffer layer with a (111) -oriented spinel structure can be formed on the surface of the substrate (sapphire) by reacting zinc oxide and the hardly soluble metal (aluminum) of the substrate (sapphire) at a high temperature. is there.

The zinc oxide layer formed first can be vapor-grown at a relatively low temperature, and a zinc oxide layer having a thickness of about several tens of nanometers may be formed. Further, as seen in FIG. 5, the ZnO layer formed first may be zinc oxide having needle-like irregularities as shown in FIG. Since the heat treatment for forming the spinel layer needs to induce solid phase diffusion, it is desirable that the temperature be at least 8 × 10 ² ° C. or higher in consideration of the diffusion coefficient in the oxide. In the method of forming the spinel structure layer that becomes the buffer layer while continuously growing as described in the previous section, the spinel structure layer is formed while supplying the zinc raw material, but in the method of this section, the buffer layer is formed without supplying zinc. In particular, when heat treatment is performed at a high temperature, the formation of a spinel structure crystal phase and the disappearance of zinc due to evaporation are in competition. It must be at the temperature at which the layer is formed.

  After the (111) oriented buffer layer is formed, a zinc oxide thin film having a zinc surface as a surface can be obtained by growing a zinc oxide thin film crystal or a zinc oxide solid solution thin film crystal by vapor phase growth. it can. Moreover, when manufacturing the zinc oxide which has a zinc surface on the surface using this method, or a zinc oxide solid solution, a substrate uses either a (0001) surface or a (11-20) surface. In the heat treatment for forming the buffer layer of the spinel structure, for example, the structure in which zinc oxide is deposited on the substrate is polished to prevent evaporation of zinc oxide and promote the formation of the spinel structure. It is also effective to heat-treat with a cover having a flat surface such as zirconium oxide single crystal.

  In the fourth embodiment of the present invention, by subjecting the substrate (sapphire) to heat treatment, a solid-state reaction between the hardly soluble metal (aluminum) of the substrate and zinc oxide and recrystallization of zinc oxide are induced. This is a growth method for obtaining a structure of zinc oxide / spinel structure / substrate in which a (111) -oriented buffer layer having a spinel structure is formed on the substrate at the interface. The outline is shown in FIG.

This means is characterized as a method for realizing the formation of the buffer layer and the formation of the zinc oxide film by one-step heat treatment. Note that the zinc oxide film formed first does not necessarily have a flat structure, and may be a concavo-convex zinc oxide film made of needle-like crystals as shown in FIG. A cover for preventing excessive evaporation of zinc oxide is put on the structure in which zinc oxide is formed on the substrate, and this is heat-treated at a temperature at which mild sublimation of zinc oxide occurs. The cover is preferably a cover having a flat surface, such as a well-polished zirconium oxide single crystal. Also, the heat treatment temperature is 10 × 10 ² ° C. or more to 15 × 10 5 to ensure the solid phase diffusion rate at which the formation of the buffer layer having the spinel structure occurs and to promote the recrystallization of zinc oxide. High temperatures below ² ° C are desirable. By this heat treatment, a spinel layer is formed at the interface between the substrate and zinc oxide, and the zinc oxide is recrystallized on the crystalline phase of the spinel structure in the formation process, so that a single surface with the zinc surface as the surface is formed. Crystalline zinc oxide thin film crystals are obtained.

  However, since the zinc oxide thin film crystal obtained by this method is a thing obtained in the process of solid-phase reaction with the substrate, it is likely to be zinc oxide into which the hardly soluble metal (aluminum) impurities of the substrate (sapphire) have invaded This is mainly an effective method for forming an n-type electrode layer when forming a zinc oxide electronic device.

In the present invention, zinc oxide having a zinc surface or zinc oxide solid solution is formed on a substrate (sapphire) by crystal growth functioning as a buffer layer (Al ₂ ZnO ₄ layer). The method of using a crystal having a spinel structure as a substrate is a method suitable for manufacturing zinc oxide or a zinc oxide solid solution having a flat surface that can be applied to the formation of electronic elements, not necessarily the zinc surface. It can't be. That is, as shown in Comparative Example 2, a material in which zinc oxide is grown on Al ₂ MgO ₄ , which is a representative example of an oxide having a spinel structure, is obtained from the viewpoint of obtaining a single crystal thin film. It cannot be the most appropriate method from the viewpoint of stability.

That is, when crystal growth is performed using Al ₂ MgO ₄ having a (111) plane as a substrate, it is certainly possible to obtain (0001) -oriented zinc oxide. However, when heat treatment for increasing the surface flatness of zinc oxide grown using Al ₂ MgO ₄ having a (111) plane as a substrate is performed, magnesium in Al ₂ MgO ₄ diffuses into the zinc oxide thin film, zinc oxide becomes a (Zn, Mg) results with O film _varies, magnesium of the Al 2 MgO ₄ surplus aluminum component is present as a result of the diffused into the zinc oxide thin film, ZnO / Al ₂ A plurality of crystal phases such as (Zn, Mg) O, alumina, and Al ₂ (Zn, Mg) O ₄ solid solution are formed at the MgO ₄ interface, and they have a function of impairing the flatness of the interface. As a result, the unevenness on the surface of the zinc oxide thin film becomes remarkable, or the crystal orientation of the zinc oxide thin film is disturbed.

  Therefore, the effect obtained by simply using a crystal phase having a spinel structure and a (111) surface as a substrate is limited, and as a result of considering this, the present invention uses sapphire as a substrate material. The present inventors have found that the problem can be avoided by using a layer having a structure similar to the (111) -oriented spinel structure formed by the reaction of this and the zinc component as a buffer layer.

A zinc oxide thin film is formed on a sapphire (11-20) substrate by pulsed laser deposition. The substrate temperature during growth is 7 × 10 ² ° C., and a zinc oxide sintered body to which 1% of aluminum is added is used as a target. In particular, a zinc oxide thin film having a thickness of about 400 nm is synthesized without changing the growth conditions during growth. By doing so, a conductive zinc oxide thin film can be obtained. Further, if the crystal polarity of the zinc oxide thin film thus obtained is analyzed by ion scattering spectroscopy, it can be confirmed that the thin film obtained as shown in FIG. 7 is a zinc oxide thin film having a zinc surface.

  In the thin film structure thus obtained, a zinc oxide thin film having a zinc surface is obtained by a crystal phase similar to a spinel structure serving as a spontaneously formed buffer layer. Zinc oxide having an additive-free native n-type conductivity is further deposited on the zinc oxide crystal having the zinc surface, and a Schottky electrode is disclosed in Example 1 of Japanese Patent Application Laid-Open No. 2004-183038. Thus, an indium ohmic electrode is formed by a forming method mainly comprising heating and evaporating indium metal in a state where DC plasma is generated in a vacuum chamber to form a low contact resistance electrode on the n-type conductive zinc oxide. Form. Then, a Schottky diode using the transparent electrode layer as the lower electrode as shown in FIG. 8 is obtained. Here, an example in which the present invention is implemented by performing crystal growth using pulsed laser deposition has been shown, but this crystal growth means and the examples shown in the present example are only examples, and It is not a thing that limits the scope of application.

Comparative Example 1

A zinc oxide thin film is formed on a sapphire (11-20) substrate by pulsed laser deposition. The substrate temperature during growth is 7 × 10 ² ° C., and a pure zinc oxide sintered body to which aluminum is not added is used as a target. In particular, a zinc oxide thin film having a thickness of about 400 nm is synthesized without changing the growth conditions during growth. Then, a conductive zinc oxide thin film is obtained. However, when the thus obtained ZnO is analyzed by ion scattering spectroscopy, it can be confirmed that the obtained thin film is a zinc oxide thin film having an oxygen surface as shown in FIG. That is, in the situation where no positive supply of aluminum is made, the formation of a crystal phase similar to the spinel structure does not occur spontaneously, and a zinc oxide thin film having an oxygen surface is obtained. Zinc cannot be obtained.

  A zinc oxide thin film is formed on a sapphire substrate. The thickness of the thin film is 20 nm. By heat-treating this at 1100 ° C., a solid phase reaction between aluminum and zinc oxide in sapphire is induced, and as a result, a (111) -oriented spinel structure thin film is obtained. When a thin film is formed on a sapphire substrate on which a buffer layer having a spinel structure is formed at a substrate temperature of 600 ° C. by using a target to which 5% of magnesium is added by a pulse laser deposition method, the zinc surface becomes the surface. A zinc oxide thin film is formed. By subjecting this to a heat treatment at 1100 ° C., a ZnO solid solution thin film having a flat surface can be obtained. This ZnO solid solution thin film is used as a substrate material having a flat surface having a zinc surface, which can be used for manufacturing a zinc oxide diode or a zinc oxide transistor. Here, an example in which the present invention is implemented by performing crystal growth using pulsed laser deposition has been shown, but this crystal growth means and the examples shown in the present example are only examples, and The scope of application is not limited.

Comparative Example 2

A zinc oxide thin film is grown using a wafer having an Al ₂ MgO ₄ single crystal having the same spinel type crystal structure as Al ₂ ZnO ₄ and having a flat (111) surface as a substrate. In this case, the growth of the thin film is performed by pulsed laser deposition using undoped zinc oxide as a target. Thereby, a relatively flat zinc oxide thin film with c-axis orientation is formed on the Al ₂ MgO ₄ single crystal. In order to improve the crystallinity and surface flatness of the zinc oxide thin film, it is generally assumed that heat treatment is performed. Therefore, when this thin film is subjected to heat treatment at 1100 ° C., the zinc oxide thin film does not flatten, but on the contrary, it changes to a thin film with low orientation, in which hexagonal columnar crystal grains are aggregated. On the other hand, from the viewpoint of an epitaxial structure, it becomes a thin film crystal in a deteriorated state. This is because the reaction occurring at the interface is a reaction that promotes the decomposition of Al ₂ MgO ₄ , and the reaction tends to impair the flatness of the interface between the thin film and the substrate.

A zinc oxide thin film is formed on a sapphire substrate. The thickness of the thin film is 200 nm. At this time, the obtained ZnO is a zinc oxide thin film having an oxygen surface as a surface, and a zirconium oxide single-layer having a (111) surface polished flat as a cover for avoiding excessive evaporation of zinc. A heat treatment is performed at 1200 ° C. with the crystals placed. Then, an Al ₂ ZnO ₄ layer having a spinel structure is formed at the interface between sapphire and zinc oxide, and crystallization of zinc oxide occurs via the gas phase, and the zinc oxide / spinel structure Al ₂ ZnO ₄ / sapphire is formed. A structure consisting of At this time, the surface of zinc oxide is a zinc surface, and a step terrace structure is formed on the surface. The obtained ZnO is an n-type conductor having an electron concentration of 10 ¹⁹ cm ⁻³ at room temperature.

  According to the present invention, it is possible to provide a zinc oxide thin film or a zinc oxide thin film that is a solid solution thereof that can be easily introduced into a smooth and acceptor impurity on an inexpensive substrate having a large amount of circulation. Light emitting elements such as light emitting diodes and lasers can be realized. Zinc oxide has a band gap of about 3.4 eV and an exciton energy of about 60 meV at room temperature, so that a high-efficiency light-emitting element in the ultraviolet region can be realized. These include optical displays, data storage devices, communication devices, lighting devices, Applications in a wide range of fields such as medical equipment are expected.

Schematic diagram of zinc oxide grown with oxygen-terminated surface Schematic diagram of zinc oxide grown with a zinc terminated surface Atomic force microscope image of ZnO surface with step terrace structure By re-evaporation of zinc, Al ₂ ZnO ₄ is first nucleated from the supplied components of aluminum, zinc and oxygen, and the presence of this Al ₂ ZnO ₄ increases the zinc adhesion rate and suppresses re-evaporation. Thus, ZnO is formed on the spontaneously formed Al ₂ ZnO ₄ buffer layer. When the ZnO layer on the sapphire is reacted with sapphire, Al ₂ ZnO ₄ is nucleated to form the Al ₂ ZnO ₄ layer, and when growth is resumed, ZnO is formed on the Al ₂ ZnO ₄ buffer layer. Outline of the process that promotes recrystallization of zinc oxide while applying heat treatment to zinc oxide grown on sapphire to form an Al ₂ ZnO ₄ buffer layer at the interface 4 is an ion scattering spectral waveform of the zinc oxide thin film manufactured in Example 1. FIG. Comparison with zinc oxide single crystal standard sample with zinc surface Schematic of the zinc oxide Schottky diode manufactured in Example 1 The ion scattering spectroscopy waveform of the zinc oxide thin film manufactured by the comparative example 1. Comparison with zinc oxide single crystal standard sample with oxygen surface

Claims (4)

  An element substrate having a zinc oxide thin film that is a substrate and zinc oxide or / and a solid solution thereof, and has a buffer layer having a spinel structure between the substrate and the zinc oxide thin film. An element substrate having an ore-type crystal structure, the surface of which is a zinc (0001) plane.   2. The element substrate according to claim 1, further comprising a buffer layer on a (11-20) plane of the substrate.   3. The method of manufacturing an element substrate according to claim 1 or 2, wherein when a zinc oxide or / and a solid solution crystal thereof is vapor-phase grown on the substrate, a hardly soluble metal is added to the zinc component and heated. The buffer layer is formed by vapor deposition on the substrate, and the zinc oxide thin film is grown on the surface of the buffer layer.   4. The manufacturing method according to claim 3, wherein the buffer layer is formed by heating the substrate to a predetermined temperature when depositing the film forming component.