JP5042636B2 - Functional element - Google Patents

Description

The present invention relates to a functional element using an oxide material for a transparent electrode .

  In recent years, there has been an increasing need for larger display panels and smaller portable displays. In order to realize this, it is necessary to reduce the power consumption of the display element, and it is indispensable to apply a transparent electrode having a high visible light transmittance and a low resistance value.

  Therefore, in order to further reduce the resistance value of the transparent conductive thin film, an indium tin oxide film (hereinafter referred to as ITO film) made of indium oxide doped with several percent of tin is provided on the surface of a transparent substrate such as a glass plate. Have been proposed (see, for example, Patent Document 1).

  However, although this ITO film has excellent transparency and high electrical conductivity, the crustal content of In is as low as 50 ppb, and has the disadvantage that the cost of raw materials increases with the depletion of resources.

  Particularly in recent years, zinc oxide-based materials have been proposed as inexpensive materials having high plasma resistance.

  However, zinc oxide-based materials are vulnerable to acids and alkalis, and are gradually eroded even in a carbon dioxide atmosphere. In addition, it is conceivable to deal with such a chemical resistance by coating the surface of zinc oxide. However, it is necessary to increase the coating process by one, resulting in an increase in manufacturing cost. is there.

  In other words, in order to expand the application range of the transparent conductor, it is necessary to configure it with a material that can be stably supplied and to configure it with a material that also has chemical resistance and durability.

Therefore, titanium dioxide (TiO ₂ ) having both chemical resistance and durability has attracted attention (for example, see Non-Patent Document 1), and a TiO ₂ film is epitaxially grown on a sapphire substrate or the like (for example, (See Non-Patent Documents 2, 3, and 4).

  However, when a sapphire substrate is used, the function of joining different materials between the substrate material and the thin film material (heterojunction) cannot be used, and it is difficult to make the sapphire substrate function as more than just a structural material.

JP 2004-95240 A Applied Physics Vol.73, No.5 (2004), paragraphs 587-592 Jpn. J. Appl. Phys. Vol. 40 (2001) pp. L 1204 ~ L 1206 Nature Materials 3, 221-224 (2004) APPLIED PHYSICS LETTERS VOLUME 78, NUMBER 18, 2664-2666 (2001)

  Therefore, the present invention has been devised in view of the above-described situation, and an object thereof is to provide a functional element having a new characteristic and an oxide material forming method.

  According to this invention, in order to achieve the above-mentioned object, the configuration as described in the claims is adopted. Hereinafter, the present invention will be described in detail.

The present invention is formed of a semiconductor layer made of Al _x Ga _y In _z N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1) and on the semiconductor layer in contact with the semiconductor layer. A transparent electrode made of a metal oxide oxide material film , wherein the metal oxide is Ti _1-p Nb _p O ₂ (where 0.01 ≦ p ≦ 0.2), and the wavelength is 400 nm. As described above, the functional element is characterized in that the transmittance for light in the range of 800 nm or less is 80% or more and the resistivity at room temperature is in the order of 10 ⁻⁴ Ωcm.

According to this configuration, a TiO ₂ film that has both chemical resistance and durability is formed integrally on a Group III nitride that has excellent physical and chemical properties, with low reflection at the interface. A functional element is obtained.

In the present specification and claims, Al _x Ga _y In _z N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1) is expressed as x + y + z = 1. This includes the case where nothing is doped, the case where a transition metal, Si, Mg, Zn or the like is doped, the case where a p-type semiconductor or an n-type semiconductor is used.

  According to the present invention, a functional element formed by integrally forming a film having low chemical reflection and low chemical resistance and durability on a group III nitride having excellent physical and chemical properties. Is obtained.

  Other objects, features, or advantages of the present invention will become apparent from a more detailed description based on embodiments of the present invention described later and the accompanying drawings.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  As shown in FIG. 1, the oxide material film 12 is formed on the substrate 11.

  The substrate 11 is made of, for example, a GaN template (Si-doped n-type GaN manufactured by Technologies and Devices International, Inc.) whose substrate surface 11a is a (0001) plane.

The substrate 11 may be made of Al _x Ga _y In _z N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1).

The oxide material film 12 formed on the substrate 11 is made of a metal oxide TiO ₂ .

TiO ₂ is not only doped with nothing, but M: TiO ₂ (M is Nb, Ta, Mo, As, Sb, Al, W, Co, Fe, Cr, Sn, Ni, Mn or Any one of V or a combination thereof). As will be described later, if the doped M is Nb, Ta, Mo, As, Sb, Al, or W, an improvement in electrical conductivity can be expected while maintaining transparency. On the other hand, if the doped M is Co, Fe, Cr, Sn, Ni, Mn or V, a magneto-optical effect can be expected.

  Next, a method for manufacturing the oxide material film 12 will be described.

  First, the GaN substrate is processed. The procedure of this process is as follows, for example. The substrate is washed with acetone, ethanol or the like. Next, the substrate is immersed in high-purity hydrochloric acid (EL grade, concentration 36%, manufactured by Kanto Chemical) for 2 minutes. Next, the substrate is moved into pure water and rinsed with hydrochloric acid or the like. Next, the substrate is moved into fresh pure water, and ultrasonic cleaning is performed for 5 minutes. Next, the substrate is taken out from the pure water, and nitrogen gas is blown onto the substrate surface to remove moisture from the substrate surface. These treatments are performed at room temperature, for example.

  By these treatments, oxides, organic substances and the like are removed from the surface of the substrate, and it is considered that the Ga terminal is exposed on the substrate surface instead of the N terminal. Here, although the example using hydrochloric acid was demonstrated, you may use acids, such as aqua regia and hydrofluoric acid. The treatment may be performed at room temperature or a heated acid may be used.

  After these treatments, the substrate was introduced into the chamber 31 described below, and the condition of the sample surface was evaluated by reflection electron beam diffraction (RHEED) and heated to 400 ° C. did. For comparison, FIG. 2 shows the RHEED pattern of the substrate before processing and the RHEED pattern of the substrate after processing. It can be seen that a flat substrate surface is obtained from the streak pattern of the RHEED image of the processed substrate.

Next, for example, Ta: TiO ₂ is deposited on the (0001) plane of the substrate 11 based on the physical vapor deposition (PVD) method. In the following embodiment, a case where such vapor deposition is performed based on a pulsed laser deposition (PLD method) will be described.

  In this PLD method, for example, the oxide material film 12 is deposited on the substrate 11 using a PLD apparatus 30 as shown in FIG. The PLD apparatus 30 is configured by disposing a substrate 11 and a target 39 in a chamber 31, and an optical oscillator 32 disposed on the side facing the surface of the target 39 outside the chamber 31, A gas supply for injecting oxygen gas into the chamber 31, and a reflecting mirror 33 for adjusting the position of the pulsed laser light oscillated by the oscillator 32 and a lens 34 for controlling the spot diameter of the laser light. And a portion 44.

The chamber 31 is provided for producing a high-quality thin film by maintaining an appropriate degree of vacuum and preventing external contamination with impurities. An infrared lamp 36 for heating the substrate is installed in the chamber 31. The substrate temperature is monitored by a radiation thermometer 37 installed outside the chamber 31 through the window 31b, and is controlled so as to be always a constant temperature. The chamber is also provided with a valve 45 for adjusting the flow rate of oxygen gas. In order to realize film formation under reduced pressure, a turbo molecular pump 42 and a pressure valve 43 are connected to the chamber 31. The pressure in the chamber 31 is controlled to be 1 × 10 ⁻⁷ torr to 1 × 10 ⁻⁴ torr, for example, in an oxygen atmosphere using the oxygen gas flow rate adjusting valve 45 and the pressure valve 43. The turbo molecular pump 42 is connected to an oil rotary pump 40 and a backflow prevention valve 41, and the pressure on the exhaust side of the turbo molecular pump 42 is always kept at 1 × 10 ⁻³ torr or less.

  The chamber 31 is further provided with a window 31a on the surface facing the target 39, and the pulse laser beam from the optical oscillator 32 is incident through the window 31a. The optical oscillator 32 oscillates, for example, a KrF excimer laser having a pulse frequency of 1 to 10 Hz, a laser power of 100 mJ / pulse, and a wavelength of 248 nm as the pulse laser light. The oscillated pulse laser beam is spot-adjusted by the reflecting mirror 33 and the lens 34 so that the focal position is in the vicinity of the target 39, and is applied to the surface of the target 39 disposed in the chamber 31 through the window 31a. Incident at an angle of about 45 °.

The target 39 is made of, for example, a Ta: TiO ₂ sintered body. Here, Ta is taken as an example of the metal to be substituted, but any of Nb, Mo, As, Sb, and W may be used, or a plurality of types of metals may be used in combination. This Ta: TiO ₂ sintered body is produced by mixing each powder of TiO ₂ and Ta ₂ O ₅ weighed so as to have a desired atomic ratio, and further heat-molding the mixed powder. . The target 39 is disposed so as to be substantially parallel to the (0001) plane of the substrate 11.

Incidentally, the target 39 Nb: if composed of TiO ₂ sintered body, Nb: TiO ₂ sintered body, each of TiO ₂ and Nb ₂ O ₅ which are weighed to have a desired atomic ratio It is produced by mixing powder and further heat-molding the mixed powder. Target 39 Co, Nb: if composed of TiO ₂ sintered body, Co, Nb: TiO ₂ sintered body, the TiO ₂ and Nb ₂ O ₅ which are weighed to have a desired atomic ratio It is produced by mixing each powder with CoO, and further heat-molding the mixed powder.

  The film forming process based on the PLD method is as follows.

  First, the pretreated substrate 11 is set in the chamber 31.

Next, for example, the pulse frequency is set to 2 Hz, the laser power is set to 100 mJ / pulse, the oxygen partial pressure is set to 1 × 10 ⁻⁵ torr, the substrate temperature is set to 400 ° C., and the substrate is rotated by the motor 35 for 40 minutes. I do. Further, by intermittently irradiating the pulsed laser light while rotating the target 39 via the rotating shaft 38, the temperature of the surface of the target 39 is rapidly increased to generate ablation plasma. Ti, Ta, and O atoms contained in the ablation plasma move to the substrate 11 while gradually changing the state while repeating a collision reaction with the oxygen gas in the chamber 31 and the like. Then, the particles containing Ti, Ta, and O atoms that have reached the substrate 11 are diffused as they are to the (0001) plane on the substrate 11 and are thinned in the most stable state of lattice matching. Thereafter, the substrate is rapidly cooled to room temperature under an oxygen partial pressure of 1 × 10 ⁻⁵ torr. As a result, the oxide material film 12 is produced.

In general, in heteroepitaxial growth, it is known that lattice mismatch between a thin film and a substrate greatly affects the generation of crystal defects in the thin film. The lattice mismatch is
Lattice mismatch = (afilm-asub) / asub
(Afilm: lattice constant of thin film, asub: lattice constant of substrate crystal)
It is expressed. The larger this value, the larger the lattice mismatch and the more difficult the heteroepitaxial growth. Further, as shown in Table 1 and FIG. 4, the crystal structure of GaN and the crystal structure of TiO ₂ are completely different.

(About * Non-Patent Document 5)
(About ** Non-Patent Documents 6, 7 and 8)
The Blue Laser Diode, S. Nakamura et al., Springer Nagaguchi: Titanium oxide and glaze / ceramics titanium No.44 P.11-13 (1956) Shozo Kataoka: Titanium Zirconium Industrial Titanium Zirconium vol.12 No.12 P.8,9 (1964) Shinkosha homepage

Therefore, it was expected that it was difficult to form a TiO ₂ film on the GaN substrate. However, as a result of trying to grow a TiO ₂ film on a GaN substrate this time, it was found that the TiO ₂ film was epitaxially grown on GaN, contrary to expectations.

  As described above, it has been found that the oxide material film 12 can be formed by the PLD method. However, it is not limited to the PLD method described above, and other physical vapor deposition (PVD) methods such as molecular beam epitaxy (MBE) method and sputtering method, or methods other than PLD method such as MOCVD method are used. The oxide material film 12 may be formed based on the chemical vapor deposition (CVD) method.

  As shown in FIG. 5 (A) to FIG. 5 (D), in general, when a film is formed by the crystal growth technique, there are four levels depending on the quality of the crystal ((A) Level1: multiphase polycrystalline film, (B ) Level 2: single phase polycrystalline film, (C) Level 3: single phase oriented epitaxial film, and (D) Leve 4: single crystal epitaxial film). In the present specification and claims, the single-phase film indicates Level 2 or higher, and the epitaxial film indicates Level 3 or higher.

  For example, other than physical vapor deposition (PVD), such as molecular beam epitaxy (MBE) or sputtering, or methods other than PLD, such as chemical vapor deposition (CVD) using MOCVD, a film of Level 2 or higher Is thought to be formed.

Here, FIG. 6 shows an electron diffraction pattern (RHEED pattern) of the TiO ₂ surface formed by the PVD method on the GaN substrate subjected to the hydrochloric acid treatment and the GaN substrate surface before the film formation. FIG. 7 shows an electron diffraction pattern (RHEED pattern) of the TiO ₂ surface formed by the PVD method on the GaN substrate not subjected to hydrochloric acid treatment and the GaN substrate surface before the film formation.

A clear streak pattern is observed on the TiO ₂ surface, indicating that it is epitaxially grown. By using this result together with X-ray diffraction (XRD), it was confirmed that a film of Level 3 or higher was formed according to the PLD method.

In addition, when the GaN substrate is processed, it can be seen from the streak pattern of the RHEED image that a flat and good TiO ₂ film is obtained.

Further, FIG. 8 shows an atomic force microscope (AFM) image of the TiO ₂ surface formed by the PVD method on the GaN substrate treated with hydrochloric acid. The average surface roughness was 0.2 nm. From these, it can be seen that a TiO ₂ film having extremely high flatness was obtained.

In any of the cases shown in FIGS. 6, 7, and 8, the substrate temperature during film formation is 400 ° C., and the TiO ₂ film is doped with 1% Ta. The same clear streak pattern is observed even when the TiO ₂ film is not doped with other elements.

Next, characteristics of M: TiO ₂ prepared by the above method will be described.

Table 2 shows the characteristics of Ta: TiO ₂ produced on the GaN substrate.

  A tester was used for measuring the resistance value at this time.

  As can be seen from this table, in order to reduce the resistance value, the substrate temperature during film formation is preferably set to 320 ° C. or higher and 550 ° C. or lower. In order to further reduce the resistance value, the substrate temperature during film formation is preferably set to 320 ° C. or higher and 450 ° C. or lower. The range of 320 ° C to 550 ° C is the general growth temperature (700) required for metalorganic vapor phase epitaxy (MOCVD) or molecular beam epitaxy (MBE), which is currently the mainstream for nitride crystal growth. ℃ or higher). Therefore, it is preferable that the substrate temperature is 320 ° C. or higher and 550 ° C. or lower also in that the influence on the substrate is small. Moreover, the problem of thermal distortion in the sample cooling process can be prevented by forming the film at a low temperature. Furthermore, low temperature growth with low reactivity is desired even in consideration of combinations with other materials. Therefore, from these viewpoints, the substrate temperature during film formation is more preferably 320 ° C. or more and 400 ° C. or less. It is highly possible that a film can be formed between room temperature and 320 degrees.

Al _x Ga _y In _z N light-emitting diodes, optical semiconductor such as a semiconductor laser, a power device, are often used as a semiconductor material for electronic devices such as a light emitting element. In order to improve the luminous efficiency without changing these internal structures, it is conceivable to apply the oxide material film 12 of the present invention as a transparent electrode. Here, the refractive indexes of GaN, TiO ₂ and ZnO are about 2.5, about 2.5 and about 2.0, respectively, and the combination of GaN and transparent electrode TiO ₂ is more at the interface than the combination of GaN and transparent electrode ZnO. Less reflection. Therefore, it can be seen that it is advantageous to use a transparent electrode made of TiO ₂ in order to increase the luminous efficiency. In order to reduce the difference in refractive index, it is possible to adjust the doping amount of other elements to TiO ₂ .

  It is also conceivable to apply the oxide material film 12 of the present invention as a transparent electrode of a surface emitting laser. In this case, since the transparent electrode can be disposed even in the light emitting region, the area of the electrode can be increased, and there is an advantage from the viewpoint of efficient injection of current into the active layer.

  In a light emitting device or the like, it is generally considered that a transparent electrode is provided on a p-type semiconductor layer, but the transparent electrode may be in contact with the n-type semiconductor layer as necessary.

Next, an internal transmittance of Nb: TiO ₂ (chemical formula Ti _1-x Nb _x O ₂ ) will be described.

Nb: TiO ₂ (chemical formula Ti _1-x Nb _x O ₂ ) Nb substitution amount x is x = 0, 0.01, 0.02, 0.03, 0.06, 0.1, 0.15, 0.2 Rate (Transmittance in the original sense means that the amount of reflection must be regarded as a defect, and therefore the transmittance that becomes 100% when the amount of reflection in the oxide material film 12 is subtracted is hereinafter referred to as internal transmittance. ) Is measured, it can be seen that a good result of 80% or more is obtained in the visible light region (wavelength 400 to 800 nm) as shown in FIG. In particular, it has been shown that an internal transmittance of 95% or more can be realized in the visible light region in a sample having an Nb substitution amount of x ≦ 0.06. The causes of internal transmittance decreases as increasing the amount of substitution Nb, the amount of Ti ³⁺ increases with Nb substitution amount, the transition probabilities between t _{2 g} -e _g band having an absorption edge in the visible light region increases It is thought that it was because of. The Nb: TiO ₂ is formed on a strontium titanate (SrTiO ₃ ) substrate finished so that the surface becomes a (100) plane, but Ti ₁ is also formed on other substrates such as a GaN substrate. _-xy Co _x Nb _y O ₂ is considered to exhibit the same basic physical properties (resistivity, etc.).

  However, when applied to an actual device, the thickness of the oxide material film 12 is often set to 100 nm or more. In particular, the specifications required for the current ITO have an internal transmittance of 80 nm for a thickness of 100 nm or more. % Or more. In order to satisfy this specification, an internal transmittance of 95% or more is required for a film thickness of 50 nm. As shown in FIG. 9, since the above specifications can be satisfied by limiting the Nb substitution amount to x ≦ 0.06, it is also possible to produce a transparent conductor thin film exceeding the internal transmittance of the conventional ITO thin film.

FIG. 10 shows the temperature dependence of the resistivity of the oxide material film 12 manufactured with the Nb substitution amount described above. As shown in FIG. 10, the oxide material film 12 in which the substitution amount x of Nb is 0.01 ≦ x ≦ 0.2 is as good as 10 ⁻⁴ Ωcm level at room temperature compared with the case where Nb is not substituted. It can be seen that the conduction characteristics are obtained. This Nb: TiO ₂ is also prepared on a strontium titanate (SrTiO ₃ ) substrate finished so that the surface becomes a (100) plane, but Ti ₁ is also formed on other substrates such as a GaN substrate. _-xy Co _x Nb _y O ₂ is considered to exhibit the same basic physical properties (resistivity, etc.).

Not only when the substitution amount x of Nb in the oxide material film 12 is 0.01 ≦ x ≦ 0.2, but also when the substitution amount x of Nb is 0.001 ≦ x ≦ 0.2, the resistivity is in the order of 10 ⁻⁴ Ωcm. Can be obtained.

  Further, when the substitution amount x of Nb in this oxide material film 12 is 0.01 ≦ x ≦ 0.06, the internal transmittance is 95% to 98% at a film thickness of 50 nm (80% or more even at a film thickness of several hundred nm). It becomes possible to improve even to.

Further, when the substitution amount x of Nb in the oxide material film 12 is 0.02 ≦ x ≦ 0.06, the internal transmittance is further improved, and the resistivity is further 5 × 10 ⁻⁴ at room temperature (280 K to 300 K). It can be reduced to about Ωcm and to 1 × 10 ⁻⁴ Ωcm at extremely low temperature (5K to 20K).

In other words, Nb: TiO ₂ obtained as a result of replacing the Ti site of anatase (TiO ₂ ) with Nb is used as the oxide material film 12, so that the transparency can be improved and the low resistance comparable to that of ITO. Ratio (conductivity on the order of 10 ⁻⁴ Ωcm) can be obtained.

Further, Nb is set so that the resistivity of the oxide material film 12 is 2 × 10 ^{−4 to} 5 × 10 ⁻⁴ Ωcm at room temperature, or 8 × 10 ⁻⁵ to 2 × 10 ⁻⁴ Ωcm at an extremely low temperature. By replacing it, it becomes possible to dramatically expand the applicability to various devices including display panels.

In addition, the oxide material film 12 can be increased in area and mass-produced by utilizing a TiO ₂ film-forming technique that has already been used in a photocatalyst or the like. By applying this low-resistivity oxide material film 12 to a display panel, it becomes possible to reduce the power consumption of these display elements, and in turn, promote the enlargement and miniaturization of the display panel. Is possible. In addition, for the reasons described above, the oxide material film 12 can facilitate the procurement of raw materials, reduce costs associated with simplification of the manufacturing process, and greatly reduce the labor involved in manufacturing. Become.

That is, by applying the oxide material film 12 to which the present invention is applied as an electrode, a transparent electrode having the conventional performance can be produced at a lower cost, and the application range can be expanded. Further, when M: TiO ₂ that is less susceptible to acid and alkali is used as the oxide material film 12, the applicable range can be expanded without being controlled by the surrounding environment. .

  Furthermore, the transparent metal 1 to which the present invention is applied is not limited to the use as an electrode, and may be applied to other parts such as parts, thin films, and devices that are required to be transparent and have high conductivity. Of course.

Next, description will be given of a magnetic-optical properties of the _{Ti 1-xy Co x Nb y} O 2 which were prepared by the procedure as described above.

FIG. 11 is a diagram showing the applied magnetic field dependence of the Faraday rotation coefficient of Ti _1-xy Co _x Nb _y O ₂ (thin film thickness: 50 nm) at room temperature. The horizontal axis represents the applied magnetic field, and the vertical axis represents the Faraday rotation coefficient. This Ti _1-xy Co _x Nb _y O ₂ was made on a (La _x Sr _1-x ) (Al _x Ta _1-x ) O ₃ (LSAT) substrate (substrate thickness: 0.5 mm). However, Ti _1-xy Co _x Nb _y O ₂ is considered to exhibit equivalent characteristics on other substrates such as a GaN substrate.

For TiO ₂ thin film of Co was added to 5% and Nb 20% both in the case of TiO ₂ thin films 5% and Nb and Co was added 10% co, and, in the case of the TiO ₂ thin film prepared by adding Co 5% is Satisfies a value of 0.1 × 10 ⁴ degree / cm or more, which is considered a practical level.

The Faraday rotation coefficient is shown near 400 nm under no magnetic field. Further, in the case of the TiO ₂ thin film in which Co is added at 5% and Nb is added at 10%, the Faraday rotation coefficient is about 0.45 × 10 ⁴ degree / cm. Compared with the Nb-free thin film, the Faraday rotation coefficient near 400 nm is improved about twice in the case of the TiO ₂ thin film in which Co is added at 5% and Nb is added at 10%.

FIG. 12 is a diagram showing the wavelength dependence of the Faraday rotation coefficient of Ti _1-xy Co _x Nb _y O ₂ (thin film thickness: 50 nm) at room temperature. The horizontal axis indicates the wavelength, and the vertical axis indicates the Faraday rotation coefficient. This Ti _1-xy Co _x Nb _y O ₂ is also produced on an LSAT substrate (substrate thickness: 0.5 mm), but Ti _1-xy Co _x is also produced on other substrates such as a GaN substrate. Nb _y O ₂ is considered to exhibit equivalent characteristics.

For TiO ₂ thin film of Co was added to 5% and Nb 20% both in the case of TiO ₂ thin films 5% and Nb and Co was added 10% co, and, in the case of the TiO ₂ thin film prepared by adding Co 5% is The Faraday rotation coefficient satisfying a value of 0.1 × 10 ⁴ degree / cm or more, which is considered to be a sufficiently practical level at 600 nm or less, was shown. Furthermore, in the case of a TiO ₂ thin film in which Co is added at 5% and Nb is added at 10%, it can be seen that the Faraday rotation coefficient is particularly improved at 600 nm or less.

FIG. 13 is a diagram showing the external transmittance at room temperature of a TiO ₂ thin film co-doped with Co 5% and Nb 10%. The horizontal axis indicates the wavelength, and the vertical axis indicates the transmittance.

  According to this, it can be seen that light having a wavelength of 260 nm or more can be transmitted through this thin film. It can also be seen that a transmittance of 70% or more can be obtained with light of 350 nm or more, and a transmittance of 80% or more can be obtained with light of 500 nm or more. That is, it can be seen that this thin film can secure a transmittance of about 70 to 80% in the visible light region.

  As described above, according to the oxide material shown in the present embodiment, a magneto-optical material useful in a short wavelength region can be obtained.

  In addition, the Faraday rotation angle can be controlled by changing the amount of Nb added.

Note that _{x in} Ti _1-xy Co _x Nb _y O ₂ is preferably 0 <x. This is because in the case of 0, there is a possibility that ferromagnetism does not appear. In order to obtain a larger spontaneous magnetization, x is more preferably 0.03 ≦ x.

_{Y in} Ti _1-xy Co _x Nb _y O ₂ is preferably 0.1 ≦ y ≦ 0.2. This is because the Faraday rotation coefficient may be reduced when the value is 0.1, and the Faraday rotation coefficient may be reduced again when the value is greater than 0.2.

_{Y of} Ti _1-xy Co _x Nb _y O ₂ (x = 0.05) is preferably 0 <y ≦ 0.2. This is because when Nb is not included, there is a disadvantage that the Faraday rotation coefficient is smaller than that when Nb is added, and when it is larger than 0.2, there is a disadvantage that the Faraday rotation coefficient may be reduced again. In order to obtain a large Faraday rotation coefficient, y is more preferably 0.1 ≦ y ≦ 0.2.

Next, various physical properties when a Ti _1-x Nb _x O ₂ film is formed on an i-GaN substrate or a p-GaN substrate will be described.

Fig. 14 (A) shows the composition dependency of resistivity when TiO ₂ film is formed on the i-GaN substrate and Fig. 14 (B) is changed on the p-GaN substrate while changing the Nb doping amount. It is. The oxygen partial pressure when forming the TiO ₂ film was 1 × 10 ⁻⁶ Torr for any substrate.

  From these figures, from the viewpoint of reducing the resistivity, the Nb doping amount is 1% or more and 15% or less, preferably Nb doping amount is 3% or more and 15% or less, more preferably, in any substrate. It can be understood that the Nb doping amount is preferably 6% or more and 15% or less, and more preferably the Nb doping amount is 6% or more and 10% or less.

Fig. 15 (A) shows the formation of a TiO ₂ film on the i-GaN substrate, and Fig. 15 (B) shows the formation of a TiO ₂ film with an Nb doping amount of 6% while changing the substrate temperature during film formation. It is a figure which shows the substrate temperature dependence of the resistivity at the time of doing. The oxygen partial pressure when forming the TiO ₂ film was 1 × 10 ⁻⁷ Torr for any substrate. The temperature when the resistance measurement was performed was 300K.

  From these figures, from the viewpoint of reducing the resistivity, the substrate temperature at the time of film formation is 350 ° C. or more and 500 ° C. or less, preferably 400 ° C. or more and 500 ° C. or less, regardless of the substrate. Further, it can be understood that the substrate temperature is more preferably 450 ° C. or higher and 500 ° C. or lower.

It should be noted that, when the substrate temperature is 350 ° C. or more and 500 ° C. or less, the oxygen partial pressure is 1 × 10 ⁻⁶ Torr and 1 × 10 ⁻⁷ Torr, regardless of the substrate. The resistivity was lower when the oxygen partial pressure was 1 × 10 ⁻⁷ Torr. In addition, when the substrate temperature is 450 ° C., the oxygen partial pressure is 1 × 10 ⁻⁷ Torr, and the TiO ₂ film having an Nb doping amount of 6% is formed on the i-GaN substrate, the sheet resistance is 234Ω / □. there were.

Fig. 16 (A) shows the wavelength dependence of the transmittance when a TiO ₂ film with an Nb doping amount of 6% is formed on the i-GaN substrate and Fig. 16 (B) on the p-GaN substrate. FIG. The oxygen partial pressure when forming the TiO ₂ film was 1 × 10 ⁻⁶ Torr for any substrate.

From these figures, it can be seen that the transmittance hardly depends on the film forming temperature and the type of the substrate, and that a transmittance of 90% or more can be secured over a wide wavelength range.
Figure 17 (A) shows the substrate temperature dependence of the transmittance when a TiO ₂ film with an Nb doping amount of 6% is formed on the i-GaN substrate and Figure 17 (B) shows the p-GaN substrate. It is a figure which shows oxygen partial pressure dependence. Oxygen partial pressure for forming the TiO ₂ film, in either case the substrate was set to 1 × 10 ^-6 Torr or 1 × 10- ⁷ Torr.

From these figures, regardless of the substrate, when the oxygen partial pressure is 1 × 10 ⁻⁶ Torr, a transmittance of 93% or more is secured, and when the oxygen partial pressure is 1 × 10 ⁻⁷ Torr, the transmittance is It can be seen that 75% to 80% can be secured.

  Next, the measurement by the film formation temperature gradient film will be described.

  A film-forming temperature gradient film is formed on a single substrate with a temperature gradient. For example, it is possible to simultaneously realize film formation on the substrate at a low temperature at one end of the substrate while film formation on the substrate is performed at a high temperature at the other end of the substrate while being on one substrate. This time, the film formation temperature gradient film was used to investigate the optimum film formation temperature in detail.

  FIG. 18 is a diagram showing various measurement results using the film formation temperature gradient film.

  FIG. 18A is a diagram showing the relationship between the substrate position and the temperature distribution. As shown in FIG. 18A, the deposition temperature is changed along the longitudinal direction of the substrate. Thereby, the position in the longitudinal direction of the substrate and the film formation temperature are associated with each other on a one-to-one basis.

  FIG. 18B is a diagram showing the relationship between the substrate position and the diffraction intensity distribution by X-ray diffraction (XRD). This XRD mapping measurement shows the relationship between the substrate position and the 2θ relationship. According to FIGS. 18A and 18B, the film formation temperature is around 450 ° C. at a position where the diffraction intensity is high. That is, it is understood that the crystallinity is the best when the film forming temperature is around 450 ° C.

  FIG. 18C is a diagram showing the relationship between the substrate position and the resistance value distribution. According to FIGS. 18A and 18C, the resistance value is minimized when the substrate temperature is 450 ° C. In particular, if the film is formed at 450 ° C. compared to 500 ° C., the resistance value may be reduced by 25%. In this measurement, resistance measurement by a two-terminal method was performed.

Next, the SnO ₂ film formed by the PLD method will be described.

FIG. 19 is a diagram showing the results of X-ray diffraction (XRD) measurement of the SnO ₂ film formed on the p-GaN substrate by the PLD method. According to this XRD spectrum, it can be confirmed that SnO ₂ is stably generated on the p-GaN substrate.

FIG. 20 is a diagram showing an electron beam diffraction image (RHEED pattern) of the SnO ₂ film formed on the p-GaN substrate by the PLD method. A clear streak pattern is observed on the SnO ₂ surface, indicating that it is epitaxially grown. It can also be seen from the streak pattern of the RHEED image that a SnO ₂ film with good crystallinity is obtained.

When these SnO ₂ films were formed, the oxygen partial pressure was 1 × 10 ⁻⁵ Torr, the film thickness was 50 nm, and the resistivity was 5 × 10 ⁻² Ωcm ⁻¹ .

Note that SnO ₂ is not only doped with nothing, but M: SnO ₂ (M is P, As, Sb, S, Se, Te, Al, Ga, In, Co, Fe, Cr, Mn, Any one of V and Ni or a combination thereof may be used. If the doped M is P, As, Sb, S, Se, Te, Al, Ga, or In, improvement in electrical conductivity can be expected while maintaining transparency. On the other hand, if the doped M is Co, Fe, Cr, Mn, V, or Ni, a magneto-optical effect can be expected.

  In the near future, the wavelength of light expected to be used in optical communications is expected to shift to short wavelength bands such as blue and ultraviolet light. Under such circumstances, this oxide material can also be used as a magneto-optical device exhibiting a large Faraday rotation coefficient in the vicinity of a wavelength of 400 nm. In particular, the fact that a Faraday rotation coefficient as large as a magnetic garnet film currently in practical use can be obtained makes it possible to fabricate an optical isolator suitable for next-generation short-waveband communication. Is shown.

  Applications of the oxide material shown in the present embodiment are not limited to use as an optical isolator, but include magneto-optical devices such as optical circulators, variable optical attenuators, and optical communication devices, magneto-optical devices, optical circuits, non-optical devices, and the like. It can also be used for reciprocal optical components, nonreciprocal optical elements, semiconductor lasers equipped with isolators, current magnetic field sensors, magnetic domain observation, magneto-optical measurement, and the like.

  The optical isolator includes, for example, a module in which an LD and an isolator are integrated, an optical isolator for fiber insertion, an optical isolator for an optical amplifier, a deflection-dependent optical isolator, a deflection-independent optical isolator, and a waveguide-type optical isolator. An isolator is mentioned. Examples of the waveguide type optical isolator include those using a Mach-Zehnder type branching waveguide and those using a rib type waveguide.

  The optical circulator may be a deflection-dependent optical circulator or a deflection-independent circulator.

If TiO ₂ doped with Co or the like is applied to a light emitting device composed of a GaN-based compound semiconductor, an optical isolator corresponding to a short wavelength band such as blue or ultraviolet light can be realized. If realized by growing further epitaxial an optical isolator on the TiO ₂ film, not only the TiO ₂ film functions as a buffer for the crystal growth, it is possible to obtain a functional element monolithically. That is, it is possible to develop not only a high-efficiency light-emitting element and an inexpensive and large-area display, but also a monolithic functional element. For example, fusion of a transparent electrode and an optical device, and fusion of a light-emitting device and a magneto-optical device can be realized. Further, the oxide material shown in this embodiment may be used for a light receiving element, a high frequency device such as a HEMT (High Electron Mobility Transistor), and an electronic device.

For the above items, an SnO ₂ film doped with Al, Sb or the like may be used.

So far, oxide materials such as various TiO ₂ films and various SnO ₂ films have been described, but these may be rutile type or anatase type. The anatase type is preferable from the viewpoint of reducing the resistivity, and the rutile type is preferable from the viewpoint of ease of production. These may be amorphous.

  The present invention has been described above with reference to specific embodiments. However, it is obvious that those skilled in the art can make modifications or substitutions of the embodiment without departing from the gist of the present invention. That is, the present invention has been disclosed in the form of exemplification, and the contents described in the present specification should not be interpreted in a limited manner. In order to determine the gist of the present invention, the claims section described at the beginning should be considered.

  It will also be appreciated that illustrative embodiments of the invention achieve the above objects, but that many modifications and other examples can be made by those skilled in the art. The elements or components of each embodiment described in the claims, specification, drawings, and description may be employed in combination with one or more other elements. The claims are intended to cover such modifications and other embodiments, which are within the spirit and scope of the present invention.

  By forming a metal oxide having excellent characteristics, it can be applied to various functional elements.

It is a figure which shows the oxide material film | membrane formed on the board | substrate. It is a figure which shows the RHEED pattern of the board | substrate before pre-processing, and the RHEED pattern of the board | substrate after pre-processing. It is a figure for demonstrating per structure of a PLD apparatus. Is a diagram showing the crystal structure of GaN (wurtzite _{(wurtzite) Al x Ga y In z N} ). Four levels depending on crystal quality ((A) Level1: Polyphase polycrystalline film, (B) Level2: Single phase polycrystalline film, (C) Level3: Single phase oriented epitaxial film, and (D) Leve4: Single crystal It is a figure which shows an epitaxial film. It shows an electron beam diffraction image of the formed TiO ₂ surface and the film-formation of the GaN substrate surface by a PVD method described above on a GaN substrate which has been subjected to hydrochloric acid treatment to (RHEED pattern). It shows an electron beam diffraction image of the formed TiO ₂ surface and the film-formation of the GaN substrate surface by a PVD method on a GaN substrate not subjected to hydrochloric acid treatment to (RHEED pattern). Is a diagram showing an atomic force microscope (AFM) images of the formed TiO ₂ surface by a PVD method on a GaN substrate which has been subjected to hydrochloric acid treatment. It is a figure which shows the result of having measured the internal transmittance of the metal oxide layer. It is a figure which shows the temperature dependence in the resistivity of a metal oxide layer. Is a diagram showing an applied magnetic field dependence of the Faraday rotation coefficient at room temperature of _{Ti 1-xy Co x Nb y} O 2. It is a figure which shows the wavelength dependence of the Faraday rotation coefficient of Ti _1-xy Co _x Nb _y O ₂ at room temperature. The Co5% and NB 10% is a diagram showing an external transmittance at room temperature of the TiO ₂ thin films codoped. While changing the Nb doping amount is a diagram showing the composition dependency of the resistivity in the case of forming the TiO ₂ film. It is a diagram showing a substrate temperature dependence of the resistivity in the case of forming the TiO ₂ film to 6% Nb doping amount while changing the substrate temperature during deposition. It is a graph showing the wavelength dependence of transmittance in the case of forming the TiO ₂ film to the Nb doping amount 6%. The Nb doping amount in the case of forming the TiO ₂ film to 6%, which is a diagram showing a substrate temperature dependence and the oxygen partial pressure dependence of the transmittance. It is a figure which shows the various measurement results using a film-forming temperature gradient film. It is a diagram showing the results of X-ray diffraction (XRD) measurement of the SnO ₂ film deposited by a PLD method. It shows an electron beam diffraction image of the SnO ₂ film was formed (RHEED pattern) by the PLD method.

Explanation of symbols

11 Substrate, 12 Oxide material film, 30 PLD device, 31 Chamber, 32 Optical oscillator, 33 Reflector, 34 Lens, 36 Infrared lamp, 39 Target, 40 Oil rotary pump, 41 Backflow prevention valve, 42 Turbo molecular pump, 43 Pressure valve, 45 oxygen gas flow control valve

Claims (6)

A semiconductor layer made of Al _x Ga _y In _z N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1),
A transparent electrode comprising an oxide material film of a metal oxide formed on the semiconductor layer in contact with the semiconductor layer;
Have
The metal oxide is Ti _1-p Nb _p O ₂ (0.01 ≦ p ≦ 0.2) and has a transmittance of 80% or more for light having a wavelength in the range of 400 nm or more and 800 nm or less. A functional element having a resistivity at room temperature in the order of 10 ⁻⁴ Ωcm. 2. The functional device according to claim 1, wherein a composition ratio p of Nb in the metal oxide is 0.01 ≦ p ≦ 0.06 , and the transmittance is 95% or more.   The functional element according to claim 1, wherein the metal oxide is anatase. The functional element according to claim 1, wherein the oxide material film is a single-phase film. The functional element according to claim 1, wherein the oxide material film is an epitaxial film.   The functional element according to claim 1, wherein the functional element is a light emitting element.