JP2017088454A - Substrate, luminous element, and method of producing substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate capable of achieving a luminous element having high characteristic and reliability, or another semiconductor element.SOLUTION: A substrate includes a sapphire substrate 1, a buffer layer 2 formed on the sapphire substrate 1, and comprising an oxide having a rhombohedral structure containing at least one of gallium, iron, chromium, aluminum and indium, and a conductor layer 3 formed on the buffer layer 2, and comprising indium tin oxide (ITO) having a rhombohedral structure. In the sapphire substrate 1, a crystal orientation is some one between a c surface, an r surface, an a surface and an m surface.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a substrate, a light emitting element, and a method for manufacturing the substrate.

  An LED having a so-called lateral structure in which n-type GaN (gallium nitride), MQW (multiple quantum well), p-type AlGaN (aluminum gallium nitride), and p-type GaN are formed on a sapphire substrate and MQW is used as a light emitting layer ( Light Emitting Diode) has been proposed. In the LED of this horizontal structure, one electrode is arranged in a state shifted from the other electrode in a direction orthogonal to the thickness direction of the light emitting layer. Therefore, the current flowing through the light emitting layer and the n-type GaN becomes non-uniform, and there is a problem that the current concentrated portion of the light emitting layer and the n-type GaN is likely to deteriorate. In this regard, in an LED having a vertical structure, since one electrode and the other electrode are arranged at substantially the same position in the direction orthogonal to the thickness direction of the light emitting layer, the current flowing through the light emitting layer and GaN is not uniform. It has the characteristics that the efficiency is suppressed and the efficiency and reliability are high.

  For example, in Patent Document 1, after forming GaN on a sapphire substrate, GaN is lifted off from the sapphire substrate using a laser, and after forming an MQW layer and p-GaN, a conductive support substrate is formed on the GaN lift-off side. It is practiced to avoid current concentration by forming an electrode and further attaching an electrode. However, since Patent Document 1 employs a manufacturing method called lift-off, it is necessary to introduce an excimer laser, and there is a problem in that process costs and manufacturing equipment costs are required. In addition, since a thin structure of about several μm must be handled, there is a problem that further devices and devices are required to increase the yield.

  For this reason, a conductor layer lattice-matched with GaN is formed on a sapphire substrate having high mechanical strength, and an n-type GaN layer, a light-emitting layer, and a p-type GaN layer are sequentially grown on this conductor layer. There is a demand for realizing an LED having a vertical structure. In such a vertical LED, when improving light extraction efficiency or extracting light to the substrate side, the conductor layer is required to be a material transparent to blue light emitted from the light emitting layer. However, it is generally difficult to grow GaN with good crystallinity on the conductive layer.

  In response to this requirement, in Patent Document 2, a zinc oxide film (ZnO) often used as a transparent conductive film is formed on a sapphire substrate. Here, it is known that ZnO can impart high conductivity. However, when GaN is formed on a ZnO film, since the lattice mismatch between ZnO and GaN is as large as 2%, the crystallinity of GaN is lowered and the characteristics of semiconductor elements such as LEDs are greatly deteriorated. There are some disadvantages.

ITO (indium tin oxide film, a compound obtained by adding several percent of tin oxide (SnO ₂ ) to indium oxide (In ₂ O ₃ )) is widely used as a transparent conductive film. As a preparation method, an amorphous film (amorphous film) is formed by sputtering or vapor deposition of ITO, and crystallization is performed by heat treatment. ITO has a stable phase cubic crystal (bixbyite structure, hereinafter referred to as bcc-ITO) and a metastable phase rhombohedral crystal (hereinafter referred to as rhomboITR), and usually facilitates film formation. bcc-ITO is used. Since meta-stable phase rh-ITO requires special conditions such as high pressure and high temperature for film formation, although there are examples of formation of fine particles, there are few examples of formation as a thin film. Therefore, generally used ITO is almost cubic (bcc-ITO) or amorphous, and rhombohedral rh-ITO is hardly used.

Non-Patent Document 1 discloses an example (an example of use as a semiconductor) in which α-Fe ₂ O ₃ is formed as a buffer layer on a sapphire substrate and rhombohedral α-In ₂ O ₃ is formed thereon. Have been described. However, there is no description about forming rh-ITO as a transparent electrode by adding tin to α-In ₂ O ₃ to make crystal growth more difficult. Furthermore, it is described that even if α-Ga ₂ O ₃ described in Non-Patent Document 1 is used as a buffer material, even high-quality α-In ₂ O ₃ could not be formed. This shows how difficult it is to form rh-ITO.

Non-Patent Document 2 discloses an example in which α-Ga ₂ O ₃ is formed as a buffer layer on a sapphire substrate and an α- (In _x Ga _1-x ) ₂ O ₃ thin film is formed thereon (used as a semiconductor). ) Is described. However, there is no description about formation of a rh-ITO thin film similarly.

Special table 2007-526618 JP 2013-204074 A

N. Suzuki, K .; Kaneko, S .; Fujita, J .; Cryst. Growth, 364 (2013) 30-33. N. Suzuki, K .; Kaneko, S .; Fujita, J .; Cryst. Growth, 401 (2014) 670-672.

  As described above, in a manufacturing method employing a general vapor deposition method or sputtering method, a thin film containing rh-ITO having a crystal structure (for example, rhombohedral structure) lattice-matched with a GaN crystal on a sapphire substrate is used. It is difficult to get. When a GaN layer is stacked on an ITO thin film produced by a conventional manufacturing method, the crystallinity of the GaN layer deteriorates. Therefore, a light-emitting element or other semiconductor element having such a GaN layer has its characteristics. In addition, there is a problem that reliability is lowered.

  The present invention has been made in view of the above-described reasons, and an object of the present invention is to provide a substrate capable of realizing a light-emitting element or other semiconductor element with high characteristics and reliability.

The substrate according to the present invention comprises:
A sapphire substrate,
A buffer layer formed on the sapphire substrate and made of an oxide having a rhombohedral structure including at least one of gallium, iron, chromium, indium, and aluminum;
And a conductive layer made of ITO (Indium Tin Oxide) having a rhombohedral crystal structure formed on the buffer layer.

The light emitting device according to the present invention is
The substrate;
A first cladding layer formed on the substrate and containing GaN;
A light emitting layer formed on the first cladding layer;
A second cladding layer formed on the light emitting layer;
A first electrode formed on the second cladding layer,
The conductor layer of the base is a second electrode.

The method for producing a substrate according to the present invention includes:
Preparing a sapphire substrate;
Forming a buffer layer made of an oxide having a rhombohedral structure containing at least one of gallium, iron, chromium, aluminum, and indium on the sapphire substrate by mist CVD;
Forming a conductor layer made of ITO (Indium Tin Oxide) having a rhombohedral crystal structure on the buffer layer by a mist CVD method.

  According to the present invention, the base is a buffer layer made of an oxide having a rhombohedral structure containing at least one of gallium, iron, chromium, indium and aluminum, and a rhombohedral crystal formed on the buffer layer. And a conductive layer made of ITO (Indium Tin Oxide) (rh-ITO) having a structure. As a result, a GaN layer with good crystallinity can be formed on the conductor layer side of the substrate. For example, when a light emitting device or other semiconductor device having a GaN layer laminated on the conductor layer side of this substrate is produced. The characteristics and reliability of this light emitting element or other semiconductor element can be improved. That is, a light-emitting element or other semiconductor element with favorable characteristics and high reliability can be realized.

2 is a cross-sectional view of a base according to Embodiment 1. FIG. 1 is a schematic configuration diagram of a mist CVD apparatus according to Embodiment 1. FIG. 6 is a cross-sectional view of a light emitting device according to Embodiment 2. FIG. (A) is a figure which shows the result of XRD about Example 1, (B) is a figure which shows the result of XRD about Comparative Example 1. (A) is a SEM photograph of the surface on the conductor layer side of the substrate according to Example 1, and (B) is a SEM photograph of the surface on the conductor layer side of the substrate according to Comparative Example 1. (A) is a figure which shows the result of XRD about Example 2, (B) is a figure which shows the result of XRD about Comparative Example 2. 6 is a diagram showing a transmitted light spectrum for Example 2. FIG. (A) is a figure which shows the result of XRD about Example 3, (B) is a figure which shows the result of XRD about Comparative Example 3.

(Embodiment 1)
Hereinafter, the substrate according to Embodiment 1 of the present invention will be described with reference to the drawings. As shown in FIG. 1, the base 10 according to the present embodiment includes a sapphire substrate 1, a buffer layer 2 formed on the sapphire substrate 1, and a conductor layer 3 formed on the buffer layer 2. . The sapphire substrate 1 has a flat surface on at least the side on which the buffer layer 2 is formed, and the surface is any one of c-plane, r-plane, a-plane, and m-plane. Further, the sapphire substrate 1 is PSS (Patterned Sapphire Substrate, hereinafter referred to as “PSS substrate”), that is, a fine unevenness in which at least the surface on which the buffer layer 2 is formed is c-plane and regularly aligned on the surface. May be formed.

The buffer layer 2 is formed of an oxide having a rhombohedral structure including at least one of gallium, iron, chromium, aluminum, and indium, and the a-axis length is between 0.4754 nm and 0.5487 nm. It is in the range. The buffer layer 2 is made of, for example, α-Fe ₂ O ₃ , α-Cr ₂ O ₃ , α-Al ₂ O ₃ , α-In ₂ O ₃ or α-Ga ₂ O ₃ .

  The conductor layer 3 is made of ITO (Indium Tin Oxide, rh-ITO) having a rhombohedral crystal structure. The conductor layer 3 may be formed of indium oxide containing at least one of titanium, zirconium, fluorine, and chlorine as impurities in addition to ITO.

  The substrate according to the present embodiment includes a step of laminating the buffer layer 2 on the sapphire substrate 1 and a step of laminating the conductor layer 3 on the buffer layer 2 using a mist CVD (Chemical Vapor Deposition) method. Manufactured in order. In the manufacture of a substrate using the mist CVD method, a mist CVD apparatus as shown in FIG. 2 is used. The mist CVD apparatus includes a gas supply source 21, a flow meter 23, a raw material supply container 31, a water storage container 33, an ultrasonic vibrator 35, a reaction container 41, a heater 42, and a susceptor 43. The gas supply source 21 and the raw material supply container 31 are connected via a first gas supply pipe P1. The raw material supply container 31 and the reaction container 41 are connected via a second gas supply pipe P2. The reaction vessel 41 is connected to an exhaust pipe P3 for discharging excess gas in the reaction vessel 41. The raw material supply container 31 stores a raw material solution 32 formed by dissolving an oxide precursor raw material for forming the buffer layer 2 or an ITO precursor raw material for forming the conductor layer 3 in a solvent (for example, water or hydrochloric acid). Has been. In FIG. 2, only one raw material supply container 31 is shown, and the buffer layer 2 and the conductor layer 3 can be formed sequentially, but two raw material supply containers for the buffer layer 2 and the conductor layer 3 are formed. 31 can be formed continuously by switching between the formation of the buffer layer 2 and the formation of the conductor layer 3.

  Examples of the precursor material for the oxide forming the buffer layer 2 include compounds of one or more selected from β-diketone compounds, alcohol compounds, and the like, and metals such as gallium, iron, chromium, indium, and aluminum. It is done. The precursor material for the oxide forming the conductor layer 3 includes one or more compounds selected from β-diketone compounds, alcohol compounds, etc., and a compound of indium or tin, titanium, zirconium. And chlorine compounds.

  The gas supply source 21 supplies a carrier gas such as air, nitrogen, or oxygen for feeding the atomized raw material solution into the reaction vessel 41 to the raw material supply container 31. Ultrasound matching water 34 is stored in the water storage container 33, and the raw material supply container 31 is disposed inside the water storage container 33 with a part of the raw material supply container 31 immersed in the water 34 stored in the water storage container 33. Has been. An ultrasonic transducer 35 is fixed to the water storage container 33. The ultrasonic waves generated by the ultrasonic vibrator 35 are transmitted to the raw material solution 32 stored in the raw material supply container 31 through the matching water 34 stored in the water storage container 33.

  Next, the operation of the mist CVD apparatus will be described. First, when the ultrasonic vibrator 35 vibrates, vibration energy is transmitted to the raw material solution 32 via the matching water 34, and the raw material solution 32 becomes mist (mist) by the vibration energy. Then, the atomized raw material solution is sent into the reaction vessel 41 through the second gas supply pipe P2 by the carrier gas supplied from the gas supply source 21 into the raw material supply vessel 31. At this time, the amount of the raw material solution fed into the reaction vessel 41 is adjusted by adjusting the flow rate of the carrier gas flowing through the first gas supply pipe P <b> 1 while checking the flow meter 23. The atomized raw material solution fed into the reaction vessel 41 is supplied to the surface of the sapphire substrate 1 supported by the susceptor 43 in the reaction vessel 41. When the mist-like raw material solution supplied to the surface of the sapphire substrate 1 is heated by the heater 42, the metal compound in the raw material solution and water chemically react, and a metal oxide grows on the surface of the sapphire substrate 1. To do.

  In the step of laminating the buffer layer 2 on the sapphire substrate 1, a raw material solution obtained by dissolving a precursor raw material containing at least one of gallium, iron, and chromium in a solvent is used. The sapphire substrate 1 is heated to a temperature between 300 ° C. and 1000 ° C. In this step, the buffer is made of an oxide containing at least one of gallium, iron, and chromium, having a rhombohedral structure, and having an a-axis length between 0.4952 nm and 0.5053 nm. Layer 2 is formed.

  In the step of laminating the buffer layer 2 on the sapphire substrate 1, a precursor material containing at least one of indium and aluminum in addition to gallium, iron, and chromium may be used as a raw material solution. In this case, the buffer layer 2 made of an oxide having a rhombohedral structure and an a-axis length between 0.4754 nm and 0.5487 nm is formed.

  In the step of laminating the conductor layer 3 on the buffer layer 2, a raw material solution in which a precursor raw material of indium containing tin is dissolved in a solvent is used. The sapphire substrate 1 on which the buffer layer 2 is laminated is heated to a temperature between 300 ° C. and 1000 ° C. In this step, the conductor layer 3 made of ITO having a rhombohedral structure (rh-ITO) is formed.

  In the step of laminating the conductor layer 3 on the buffer layer 2, a raw material solution in which an indium precursor raw material containing at least one of titanium, zirconium, fluorine, and chlorine is dissolved in a solvent is used. May be. In this case, the conductor layer 3 having a rhombohedral structure and made of indium oxide doped with at least one of titanium, zirconium, fluorine, and chlorine as an impurity is formed. Such indium oxide doped with impurities such as ITO has a higher carrier density and lower resistance than indium oxide not doped with impurities. Among various indium oxides doped with the impurities, ITO has the lowest resistance. Further, as a raw material solution, an indium precursor raw material containing at least one of gallium, aluminum, iron, and chromium in addition to at least one of tin, titanium, zirconium, fluorine, and chlorine was dissolved in a solvent. Things may be used. In this case, not only GaN, but also a conductor layer that can combine Al with GaN and lattice match well with AlGaN (aluminum gallium nitride), AlN (aluminum nitride), and AnGaInN (aluminum indium gallium nitride). 3 is formed.

  As described above, the base body 10 according to the present embodiment has the conductor layer 3 containing ITO (rh-ITO) having a rhombohedral structure lattice-matched with GaN via the buffer layer 2 on the surface of the sapphire substrate 1. Is provided. Thereby, a GaN layer with good crystallinity can be formed on the conductor layer 3 side of the base body 10, so that, for example, a light-emitting element or other semiconductor element having a GaN layer stacked on the conductor layer 3 side of the base body 10 When the is manufactured, the characteristics and reliability of the light-emitting element or other semiconductor elements can be improved. That is, a light-emitting element and other semiconductor elements with favorable characteristics and high reliability can be realized. In addition, the substrate 10 according to the present embodiment is substantially transparent to blue light, and has a transmittance of 80% or more in the blue wavelength band (415 nm to 500 nm). Thereby, for example, when a light emitting element that emits blue light is formed on the side of the conductor layer 3 in the substrate 10, the light extraction efficiency can be improved. It is also possible to extract light from the base 10 side of the light emitting element to the outside.

  In addition, since the mist CVD method employed in the method for manufacturing the substrate 10 according to the present embodiment is a technique comprising a non-vacuum process, a configuration for realizing a vacuum atmosphere is not required, so that the apparatus can be simplified. Can do. In addition, according to the mist CVD method, a thin film with less distortion and damage can be generally produced as compared with a sputtering method or other CVD methods.

  Note that the method used to manufacture the buffer layer 2 and the conductor layer 3 is not limited to the mist CVD method, and a sputtering method, other CVD methods, or the like may be employed. Further, as a method for generating a mist-like raw material solution in the mist CVD method, for example, a method using a two-fluid spray nozzle may be employed.

(Embodiment 2)
The light emitting device 100 according to the present embodiment is a vertical LED (Light Emitting Diode), and as shown in FIG. 3, a sapphire substrate (PSS) having a crystal orientation of c-plane and a fine uneven shape formed on the surface. The substrate 10 is provided with a base 10 on which a buffer layer 2 and a conductor layer 3 are sequentially laminated. Here, since the conductor layer 3 of the base 10 has a sufficiently low resistance, it functions as an electrode (second electrode). The light emitting device 100 includes a first cladding layer 104, a light emitting layer 105, a second cladding layer 106, and an electrode layer 107 (first electrode). The first cladding layer 104 is formed on the side of the conductor layer 3 of the base 10 and is made of n-type GaN. The light emitting layer 105 has, for example, an MQW (Multi Quantum Well) structure, and is formed on the first cladding layer 104. The second cladding layer 106 is formed on the light emitting layer 105 and is made of p-type GaN. The electrode layer 107 is made of a conductive material such as ITO. The electrode layer 107 is formed on the second cladding layer 106.

  In the light emitting element 100, when a current is injected into the light emitting layer 105 by applying a voltage between the conductor layer 3 and the electrode layer 107, the light emitting layer 105 emits light. A part of the light emitted from the light emitting layer 105 passes through the first cladding layer 104 and reaches the fine irregularities formed on the surface of the sapphire substrate 1 of the base 10. Then, a part of the light reaching the fine unevenness formed on the surface of the sapphire substrate 1 is scattered by the unevenness, so that the light is efficiently extracted outside (for example, above) the light emitting element 100. Accordingly, light generated in the light emitting layer 105 is extracted with high efficiency to the outside of the light emitting element 100. In addition, the conductor layer 3 and the electrode layer 107 of the substrate 10 are arranged so as to face each other with the light emitting layer 105 in the thickness direction of the light emitting layer 105. Thereby, current is injected into the light emitting layer 105 substantially uniformly, so that the LED 100 has high light emission efficiency and high reliability. A voltage is applied to the conductor layer 3 through, for example, an electrode body (not shown) made of a metal in contact with a part of the conductor layer 3.

  Note that the sapphire substrate 1 is not limited to a PSS substrate, and may be a substrate whose crystal orientation is c-plane, r-plane, a-plane or m-plane and whose surface is flat, for example.

  Moreover, the light emitting element 100 is not limited to LED. For example, a surface emitting laser diode that emits laser light along the thickness direction of the light emitting layer 105 by providing a reflective layer (not shown) on the sapphire substrate 1 side and the electrode layer 107 side of the light emitting element 100 described above. It may be. Alternatively, the light emitting element 100 may be a laser diode provided with reflection portions on both sides in a direction orthogonal to the thickness direction of the light emitting layer 105.

  Furthermore, the present invention is not limited to the light emitting element 100, and may be a semiconductor element in which a switching element such as a HEMT is formed on the substrate 10 described in the first embodiment. Alternatively, another switching element such as an IGBT (Insulated Gate Bipolar Transistor) or a thyristor including the base body 10 described in the first embodiment or a diode (rectifier element) may be used.

  The substrate according to the present invention will be described based on examples and comparative examples. The substrate according to the comparative example is obtained by forming only the conductor layer 3 on the sapphire substrate 1. As described in the first embodiment, the method of manufacturing the substrate 10 according to each example includes the step of stacking the buffer layer 2 on the sapphire substrate 1, the step of stacking the conductor layer 3 on the buffer layer 2, and Consists of. On the other hand, the substrate manufacturing method according to the comparative example includes only a step of laminating the conductor layer 3 on the sapphire substrate 1. The mist CVD method is also employed in the substrate manufacturing method according to the comparative example.

(Substrate manufacturing conditions, etc.)
An ultrasonic vibrator (HM-2412, manufactured by Honda Electronics Co., Ltd.) that vibrates at a frequency of 2.4 MHz is used as the ultrasonic vibrator of the mist CVD apparatus used for manufacturing the base body 10 according to each example and the base body according to the comparative example. Adopted. Moreover, nitrogen was adopted as a carrier gas used in this mist CVD apparatus.

  In the step of laminating the buffer layers 2 according to all the examples, the sapphire substrate 1 was placed on the susceptor 43 in the reaction vessel 41 and then heated to 450 ° C. by the heater 42. The film formation time in the step of laminating the buffer layer 2 was set to 1 min.

  In the step of laminating the conductor layers 3 according to all the examples, the conductor layer 3 is laminated on the buffer layer 2 of the sapphire substrate 1 on which the buffer layer 2 is laminated, whereas all the comparative examples are concerned. In the step of laminating the conductor layer 3, the conductor layer 3 is directly laminated on the sapphire substrate 1. In any of the steps of laminating the conductor layers 3 according to all the examples and comparative examples, the sapphire substrate 1 was placed on the susceptor 43 in the reaction vessel 41 and then heated to 500 ° C. by the heater 42. It was in a state. In this step, a raw material solution in which indium acetylacetonate and tin (II) chloride were dissolved in water and hydrochloric acid was used. The film formation time in the step of laminating the conductor layer 3 was set to 30 minutes.

Table 1 below summarizes the types of sapphire substrates, presence / absence of the step of forming the buffer layer 2, and types of the buffer layer 2 in each example and each comparative example.
In Table 1, “c-plane PSS substrate” refers to a sapphire substrate in which the crystal orientation is c-plane and a fine uneven shape is formed on the surface. The “c-plane flat substrate” refers to a substrate having a c-plane crystal orientation and a flat surface. Here, the “flat substrate” means that the roughness (RMS value) of the substrate surface is in the range of 0.1 nm to 2 nm. The “r-plane flat substrate” refers to a substrate having a crystal orientation of r-plane and a flat surface.

In Table 1, when the type of the buffer layer 2 is gallium oxide “Ga ₂ O ₃ ”, a solution in which gallium acetylacetonate is dissolved in water and hydrochloric acid is used as a raw material solution used in the step of laminating the buffer layer 2. .

(About the evaluation results of the substrate)
By carrying out the confirmation of the crystal structure, the specific resistance value of the conductor layer 3, the SEM observation of the surface on the conductor layer 3 side, and the transmitted light spectrum measurement for the substrates according to the examples and comparative examples shown in Table 1. Each substrate was evaluated.

  The crystal structures of the buffer layer 2 and the conductor layer 3 of the substrate according to each example and each comparative example are the positions of diffraction peaks measured using an X-ray diffraction (XRD) measuring apparatus (manufactured by BRUKER, D8 DISCOVER). Confirmed by

  The specific resistance of the conductor layer 3 according to each example and each comparative example was measured by using a sheet resistance measuring instrument (manufactured by Mitsubishi Chemical Analytech Co., Ltd., Loresta GP MCP-T610 type) employing a 4-probe method.

  Observation of the surface on the conductor layer 3 side of the substrate according to each example and each comparative example was performed using an electron microscope (SEM) (manufactured by JEOL Ltd., JSM7400).

  The transmitted light spectrum of the substrate was measured using a transmittance meter (manufactured by Hitachi High-Tech Science Co., Ltd., UV-VIS U-4100).

Hereinafter, the results of evaluation performed on the base 10 according to each example and the base according to each comparative example will be described in detail.
Example 1
According to XRD, as shown in FIG. 4A, a diffraction peak of (0006) corresponding to ITO having a rhombohedral structure (rh-ITO) was confirmed. That is, it was found that the conductor layer 3 made of ITO having a rhombohedral crystal structure was formed. Further, a diffraction peak (α-Al ₂ O ₃ (0006)) corresponding to the c-plane sapphire substrate 1 and a peak (α-Ga ₂ O ₃ (0006)) corresponding to gallium oxide having a rhombohedral crystal structure, Was confirmed. From this, it was found that the buffer layer 2 was gallium oxide having a rhombohedral crystal structure. That is, it was found that the conductor layer 3 made of ITO having a rhombohedral crystal structure lattice-matched with GaN was formed on the α-Ga ₂ O ₃ layer as the buffer layer 2. The specific resistance calculated from the sheet resistance of the conductor layer 3 was 4.0 × 10 ⁻⁴ Ω · cm. As shown in FIG. 5A, it was found that the conductor layer 3 was continuously connected on the surface of the base on the conductor layer 3 side. Thus, it was thought that the specific resistance of the conductor layer 3 was lowered by the continuous connection of the conductor layer 3. In order to cause the conductor layer 3 to function as an electrode, it is generally preferable that the specific resistance of the conductor layer 3 is 1.0 × 10 ⁻³ Ω · cm or less. On the other hand, it can be said that the conductor layer 3 of Example 1 satisfies the condition because the conductor layer 3 functions as an electrode.

(Comparative Example 1)
According to XRD, as shown in FIG. 4B, no peak corresponding to ITO having a rhombohedral structure was confirmed. The sheet resistance of the conductor layer 3 showed a higher resistance value that exceeded the measurement limit of the sheet resistor. On the surface of the substrate on the conductor layer side, as shown in FIG. 5 (B), a conductor layer is formed only on the concave and convex portions (mountain portions) and conductive on the concave and convex portions (valley portions). It was found that no body layer was formed. Thus, since the conductor layer 3 was not formed in the concave portion and the conductor layers formed in the adjacent convex portions were electrically insulated from each other, it was considered that the sheet resistance of the conductor layer was increased. .

  From the evaluation results of Example 1 and Comparative Example 1, due to the presence of the buffer layer 2, lattice matching with GaN is achieved above the sapphire substrate 1 having a crystal orientation of c-plane and a fine irregular shape formed on the surface. It can be said that the conductor layer 3 made of ITO having a rhombohedral crystal structure is formed. In addition, since the buffer layer 2 is present, the conductor layer 3 is continuously connected to each other at both the ridge and valley portions of the concavo-convex shape on the surface of the sapphire substrate 1. 3 sheet resistance becomes low. Thus, in the PSS substrate, the formation of the rh-ITO conductor layer 3 that is difficult to form a thin film with good crystallinity by forming the buffer layer 2 is a great effect on the characteristics of the device substrate.

(Example 2)
According to XRD, as shown in FIG. 6A, the diffraction peak of (0006) corresponding to ITO having rhombohedral structure (rh-ITO), the diffraction peak corresponding to c-plane sapphire substrate 1 (α -Al ₂ O ₃ (0006)), a peak corresponding to gallium oxide having a rhombohedral structure corresponding to the buffer layer 2 (α-Ga ₂ O ₃ (0006)) was confirmed. From this, it was found that the buffer layer 2 made of gallium oxide having a rhombohedral structure and the conductor layer 3 made of ITO having a rhombohedral structure lattice-matched with GaN were formed. The transmitted light spectrum was as shown in FIG. From FIG. 7, it was found that the transmittance of the substrate 10 in the blue wavelength band (415 to 500 nm) was 80% or more. The specific resistance calculated from the sheet resistance of the conductor layer 3 was 2.4 × 10 ⁻⁴ Ω · cm. Therefore, it can be said that the conductor layer 3 of Example 2 satisfies the conditions for allowing the above-described conductor layer 3 to function as an electrode.

(Comparative Example 2)
According to XRD, as shown in FIG. 6B, diffraction peaks corresponding to (222) and (400) corresponding to ITO having a bcc structure (bcc-ITO), and diffraction peaks corresponding to sapphire substrate 1 on the c-plane. Only (α-Al ₂ O ₃ (0006)) could be confirmed. However, a diffraction peak corresponding to ITO having a rhombohedral crystal structure (rh-ITO) could not be confirmed.

  From the evaluation results of Example 2 and Comparative Example 2, when the buffer layer 2 is present, a conductor layer 3 containing ITO having a rhombohedral structure lattice-matched with GaN is present above the c-plane sapphire substrate 1. It can be said that it is formed.

(Example 3)
According to XRD, as shown in FIG. 8A, a diffraction peak corresponding to (10-12) corresponding to ITO having a rhombohedral structure (rh-ITO), and a diffraction peak corresponding to the r-plane sapphire substrate 1 A peak (α-Ga ₂ O ₃ (10-12)) corresponding to (α-Al ₂ O ₃ (10-12)) and gallium oxide having a rhombohedral structure corresponding to the buffer layer 2 was confirmed. From this, it was found that the buffer layer 2 made of gallium oxide having a rhombohedral structure and the conductor layer 3 made of ITO having a rhombohedral structure lattice-matched with GaN were formed. The specific resistance calculated from the sheet resistance of the conductor layer 3 was 3.0 × 10 ⁻⁴ Ω · cm. Therefore, it can be said that the conductor layer 3 of Example 3 satisfies the conditions because the conductor layer 3 described above functions as an electrode.

(Comparative Example 3)
According to XRD, as shown in FIG. 8B, a diffraction peak of (400) corresponding to ITO having a bcc structure (bcc-ITO), a diffraction peak corresponding to r-plane sapphire substrate 1 (α-Al Only ₂ O ₃ (10-12)) could be confirmed. However, a diffraction peak corresponding to ITO having a rhombohedral crystal structure (rh-ITO) could not be confirmed. That is, it was found that when the buffer layer 2 does not exist, the conductor layer 3 containing ITO having a rhombohedral structure lattice-matched with GaN is not formed.

  From the evaluation results of Example 3 and Comparative Example 3, when the buffer layer 2 is present, the conductor layer 3 made of ITO having a rhombohedral structure lattice-matched with GaN is formed above the r-plane sapphire substrate 1. It can be said that it is formed.

  In Examples 1 to 3, the example of the base body 10 having the c-plane and r-plane sapphire substrate 1 has been described. However, even if the a-plane and m-plane sapphire substrate 1 is used, the ITO has a rhombohedral crystal structure. It is considered that the base 10 having the conductor layer 3 can be obtained. For example, when the lattice matching degree is calculated in the c-plane and the r-plane, the a-axis length of the sapphire substrate 1 is 0.4754 nm, and the a-axis length of ITO having a rhombohedral crystal structure is 0.5487 nm. The degree of lattice mismatch between the surface of the sapphire substrate 1 and the ITO having a rhombohedral crystal structure is 15.4%. On the other hand, when the lattice matching degree is calculated in the a-plane and the m-plane, the c-axis length of the sapphire substrate 1 is 1.2982 nm, and the c-axis length of ITO having a rhombohedral crystal structure is 1.4510 nm. The degree of lattice mismatch between the surface of the a-plane and m-plane sapphire substrate 1 and ITO having a rhombohedral crystal structure is 11.8%. That is, the degree of lattice mismatch between the surface of the a-plane and m-plane sapphire substrate 1 and the ITO having a rhombohedral crystal structure is as follows. It is smaller than the degree of lattice mismatch between. Accordingly, it is considered that ITO having a rhombohedral crystal structure can be formed more easily on the a-plane and m-plane sapphire substrate 1 than on the c-plane and r-plane sapphire substrate 1. Therefore, even if the a-plane and m-plane sapphire substrate 1 is used, the base body 10 having the conductor layer 3 made of ITO having a rhombohedral crystal structure can be obtained.

Further, α-Ga ₂ O ₃ is used as the oxide buffer layer 2, but α-Al ₂ O ₃ , α-Fe ₂ O ₃ , α-Cr ₂ O ₃ , and α-In ₂ O ₃ are used. You can also.

  Further, in the step of laminating the buffer layer 2 according to the embodiment, the sapphire substrate 1 is placed on the susceptor 43 in the reaction vessel 41 and then heated to 450 ° C. by the heater 42, and the conductor layer 3 is formed. In any of the laminating steps, the sapphire substrate 1 is placed on the susceptor 43 in the reaction vessel 41 and then heated to 500 ° C. by the heater 42, but both are between 300 ° C. and 1000 ° C. Can be set. Preferably, the buffer layer 2 forming step can be set to be heated to 350 ° C. to 700 ° C., and the conductor layer 3 forming step can be set to be heated to 400 ° C. to 800 ° C.

  The substrate according to the present invention is suitable for light-emitting elements, solar cells, high-frequency devices, power devices, and the like.

1: sapphire substrate, 2: buffer layer, 3: conductor layer, 10: substrate, 21: gas supply source, 23: flow meter, 31: raw material supply container, 33: water storage container, 35: ultrasonic transducer, 41 : Reaction vessel, 42: heater, 43: susceptor, 100: light emitting element, 104: first cladding layer, 105: light emitting layer, 106: second cladding layer, 107: electrode layer, P1: first gas supply pipe, P2 : Second gas supply pipe, P3: Exhaust pipe

Claims (6)

A sapphire substrate,
A buffer layer formed on the sapphire substrate and made of an oxide having a rhombohedral structure including at least one of gallium, iron, chromium, aluminum, and indium;
A conductive layer made of ITO (Indium Tin Oxide) formed on the buffer layer and having a rhombohedral structure;
Substrate. In the sapphire substrate, the crystal orientation is any one of c-plane, r-plane, a-plane and m-plane, and the surface on the buffer layer side in the thickness direction is flat.
The substrate according to claim 1. The sapphire substrate has a c-plane crystal orientation and a concavo-convex shape formed on the surface on the buffer layer side in the thickness direction.
The substrate according to claim 1. The buffer layer includes at least one of α-Fe ₂ O ₃ , α-Al ₂ O ₃ , α-Ga ₂ O ₃ , α-Cr ₂ O ₃ , α-In ₂ O ₃ ,
The substrate according to any one of claims 1 to 3. A substrate according to any one of claims 1 to 4,
A first cladding layer formed on the substrate and containing GaN;
A light emitting layer formed on the first cladding layer;
A second cladding layer formed on the light emitting layer;
A first electrode formed on the second cladding layer,
The conductor layer of the substrate is a second electrode;
Light emitting element. Preparing a sapphire substrate;
Forming a buffer layer made of an oxide having a rhombohedral structure containing at least one of gallium, iron, chromium, aluminum, and indium on the sapphire substrate by mist CVD;
Forming a conductor layer made of ITO (Indium Tin Oxide) having a rhombohedral structure on the buffer layer by a mist CVD method,
A method for manufacturing a substrate.