JP6034252B2 - Method for forming Er-doped ZnO phosphor film - Google Patents

Description

  The present invention relates to an Er-doped ZnO phosphor film forming method for forming a phosphor film made of ZnO doped with Er on the C-plane or A-plane of a sapphire substrate.

Conventionally, light emission associated with electronic transition between 4f levels of rare earth trivalent ions doped in a base material such as a semiconductor or an insulator is not so dependent on the base material, and the half width is narrow and sharp. It has the characteristics. In particular, the central wavelength of the emission of Er ³⁺ ions exists in the vicinity of 1540 nm, and overlaps with the wavelength band used in optical communication. For this reason, an optical fiber doped with a small amount of Er ³⁺ ions has been put into practical use as an optical fiber amplifier and has become a very important device in the optical communication field.

A. K. Pradhan et al., "Pulsed-laser deposited Er: ZnO films for 1.54 m emission", APPLIED PHYSICS LETTERS, vol.90, 072108, 2007. S. Komuro et al., "Highly erbium-doped zinc.oxide thin film prepared by laser ablation and its 1.54 mm emission dynamics", JOURNAL OF APPLIED PHYSICS, vol. 88, no. 12, pp.7129-7136, 2000. Y. Liu et al., "Spectroscopic evidence of the multiplesite structure of Eu3 + ions incorporated in ZnO nanocrystals", OPTICS LETTERS, vol. 32, no. 5, pp.566-568, 2007.

The optical fiber amplifier amplifies signal light by using light emission from Er ³⁺ ions that are slightly doped in a certain length of optical fiber. On the other hand, in an optical circuit in which minute optical components are integrated on a substrate, a section of an optical waveguide having an optical amplification function corresponds to an optical fiber amplifier. However, in order to perform optical amplification in an optical waveguide shorter than the optical fiber amplifier, it is necessary to minimize the influence of optical attenuation in the optical amplification section. Further, in order to realize a strong light emission intensity, it is necessary to select a high Er concentration, but in this case, the problem of concentration quenching cannot be avoided. Note that temperature quenching can be mitigated by selecting a wide band gap material for the host crystal.

In particular, ZnO having a wide band gap of 3.37 eV is suitable for a host that accepts Er ³⁺ ions. However, there have been few reports on ZnO: Er thin films, and no ZnO: Er fluorescent films that emit strong light have been reported (see Non-Patent Documents 1 and 2). This is the valence of the valence and Er ³⁺ ions Zn ²⁺ ions occupying the ZnO cation sites is different, and Zn ²⁺ ions and Er ³⁺ for the radius of the ions is quite different, the Er ³⁺ ions This is because it is difficult to replace the Zn ²⁺ ion site in the bulk crystal.

As a solution to this problem, for example, in the case of ZnO: Eu, the surface area is increased by making ZnO into nanocrystals, and Eu ³⁺ ions are coordinated at the interface of the crystal grains, and the emission intensity from Eu ³⁺ ions Has been reported (see Non-Patent Document 3). However, no matter how much nanocrystals are collected, these are just nanocrystal powders. In order to finally use for a solid-state device that emits light by current injection, it is necessary to obtain strong light emission in at least a two-dimensionally continuous ZnO: Er fluorescent film, but this is not easy.

  The present invention has been made to solve the above-described problems, and an object thereof is to form a two-dimensionally continuous Er-doped ZnO phosphor film capable of obtaining strong light emission.

  An Er-doped ZnO phosphor film forming method according to the present invention includes a heating step of heating a sapphire substrate whose main surface is a C-plane or an A-plane to any temperature between 550 ° C. and 900 ° C., and a heated sapphire substrate A phosphor film forming step of forming a phosphor film made of ZnO doped with Er on the main surface of the phosphor by sputtering, and in the phosphor film forming step, the total number of Er and Zn atoms in the phosphor film The ratio of the number of Er atoms is 0.6 at. % Or more 3 at. % Or less.

In the Er-doped ZnO phosphor film formation method, a phosphor film forming process, more electron cyclotron resonance sputtering method using a target made of ZnO containing Er, form a phosphor film.

  As described above, according to the present invention, it is possible to obtain an excellent effect that a two-dimensionally continuous Er-doped ZnO phosphor film capable of obtaining strong light emission can be formed.

FIG. 1 is an explanatory view for explaining an Er-doped ZnO phosphor film forming method according to an embodiment of the present invention. FIG. 2 is a configuration diagram illustrating a configuration example of an ECR sputtering apparatus. FIG. 3 is a configuration diagram showing a configuration example of a film forming apparatus that realizes film formation by two sputtering methods. FIG. 4 shows an Er concentration of 3.9 at. % ZnO: Er film (a), Er concentration 4.2 at. % ZnO: Er film (b), Er concentration 1.5 at. % ZnO: Er film (c), Er concentration 1.7 at. It is a characteristic view which shows the light emission (PL spectrum) from Er <^3+> ion about% ZnO: Er film | membrane (d). FIG. 5 shows an Er concentration of 0.6 at. FIG. 6 is a characteristic diagram showing a relationship between a change in substrate temperature condition when a ZnO: Er film of% is formed and a change in emission spectrum. FIG. 6 is a characteristic diagram showing a PL spectrum of a series of ZnO: Er film samples with different concentrations of incorporated Er at a substrate temperature of 550 ° C., after heating at 700 ° C. in vacuum after film formation. FIG. 7 is a characteristic diagram showing a PL spectrum of a series of ZnO: Er film samples with different concentrations of incorporated Er at a substrate temperature of 550 ° C., after heating at 700 ° C. in oxygen after film formation. FIG. 8 shows that the Er concentration is 1.5 at. It is a characteristic view which shows the change of the emission spectrum when the temperature of the post-deposition heating in vacuum is changed about the sample of the ZnO: Er film | membrane made into%. FIG. 9 shows an Er concentration of 2.0 at. It is a characteristic view which shows the change of the emission spectrum when changing the heating temperature after film-forming in oxygen about the sample of the ZnO: Er film made into%. FIG. 10 is a characteristic diagram showing an X-ray diffraction pattern of a ZnO: Er film in an example formed by the Er-doped ZnO phosphor film forming method according to the embodiment of the present invention. FIG. 11 is a characteristic diagram showing a result of plotting 2θ diffraction angles of ZnO (002) peaks in samples of ZnO: Er films having different Er concentrations. FIG. 12 is a characteristic diagram showing a measurement result of an emission spectrum from a ZnO: Er film sample according to the present invention with a ZnO buffer layer.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory view for explaining an Er-doped ZnO phosphor film forming method according to an embodiment of the present invention. In this forming method, in the first step S101, the substrate 101 made of sapphire (corundum) whose main surface is the C-plane or A-plane is heated to any temperature between 550 ° C. and 900 ° C. (heating step).

  Next, in the second step S102, the phosphor film 102 made of ZnO doped with Er is formed on the main surface of the heated substrate 101 by a sputtering method (phosphor film forming process). Here, in the formation of the phosphor film 102 by sputtering, the ratio of the number of Er atoms to the total number of Er and Zn atoms in the phosphor film 102 is 0.6 at. % Or more 3 at. %.

For example, the ratio (Er concentration) of the number of Er atoms to the total number of Er and Zn atoms in the target to be used may be in the above-described range. Further, for example, by using both sputtering using ZnO as a target and sputtering using Er ₂ O ₃ as a target, the ratio of the number of Er atoms to the total number of Er and Zn atoms in the phosphor film 102 formed. However, 0.6 at. % Or more 3 at. % Or less.

  The manufacturing method described above makes it possible to form a two-dimensionally continuous Er-doped ZnO phosphor film capable of obtaining strong light emission. As will be described later, the phosphor film 102 is formed in contact with the main surface of the substrate 101 without using a buffer layer or the like.

  Here, the phosphor film 102 made of ZnO doped with Er may be formed by, for example, electron cyclotron resonance (ECR) sputtering using a target made of ZnO containing Er. For this, a well-known ECR sputtering apparatus may be used.

  As shown in FIG. 2, the ECR sputtering apparatus includes a film formation chamber 201 and a plasma generation chamber 203 that communicates with the film formation chamber 201. For example, 2.45 GHz microwaves can be supplied to the plasma generation chamber 203 by a microwave supply source 204. Further, around the plasma generation chamber 203, for example, a magnetic coil 205 that generates a magnetic field of 0.0875 T (Tesla) in the plasma generation chamber 203 is provided.

  In the film forming chamber 201, a ring-shaped target 202 surrounding the vicinity of the outlet of the plasma generation chamber 203 is disposed. A predetermined target bias (high frequency power) can be applied to the target 202.

After the substrate W is placed about 20 cm apart from the target 202 in the film forming chamber 201 of the ECR sputtering apparatus configured as described above, the film forming chamber is formed by a well-known exhaust mechanism (not shown). The inside of 201 is evacuated to a predetermined pressure. For example, the inside of the film forming chamber 201 is depressurized to a high vacuum state pressure of 10 ⁻⁴ to 10 ⁻⁵ Pa.

Next, an inert gas such as argon and O ₂ gas are introduced into the plasma generation chamber 203 of the ECR sputtering apparatus to obtain a predetermined degree of vacuum (pressure). In this state, a 2.45 GHz microwave is generated by the magnetic coil 205. ECR plasma is formed in the plasma generation chamber 203 by supplying an electron cyclotron resonance condition by supplying a magnetic field of about 500 W and about 0.0875 T.

  The ECR plasma generated as described above is emitted from the plasma generation chamber 203 to the film formation chamber 201 communicating with the ECR plasma by the divergent magnetic field of the magnetic coil 205. In this state, for example, high frequency power (target bias) of 13.56 MHz · 500 W is supplied (applied) to the target 202 disposed at the outlet of the plasma generation chamber 203. As a result, the particles generated by the generated ECR plasma collide with the target 202 to cause a sputtering phenomenon, and the particles constituting the target 202 jump out.

By generating ECR plasma in the sputter state as described above, particles (Zn atoms, O atoms, Er atoms) sputtered from the target 202 are deposited on the substrate W, A phosphor film made of ZnO doped with Er is formed. By controlling the ratio of the number of Er atoms to the total number of Er and Zn atoms in the target 202 and appropriately setting the ratio, the ratio of the number of Er atoms to the total number of Er and Zn atoms in the phosphor film is 0.6 at. % Or more 3 at. % Or less. In addition, since O ₂ gas is added, oxygen atoms taken into the formed phosphor film can be compensated.

For example, the phosphor film made of ZnO doped with Er may be formed by an ECR sputtering method using a target made of ZnO and a magnetron sputtering method using a target made of Er ₂ O ₃ .

  A film forming apparatus that realizes film formation by the two sputtering methods described above will be described with reference to FIG. This film forming apparatus includes a vacuum processing chamber 301 communicated with a vacuum exhaust device such as a turbo molecular pump (not shown), an ECR plasma source 302 provided in the vacuum processing chamber 301, and an ECR generated from the ECR plasma source 302. And a target 303 made of ZnO for sputtering by plasma. The ECR plasma source 302 and the target 303 constitute an ECR sputtering source that realizes the ECR sputtering method. The ECR plasma source 302 is operated, ECR plasma is generated using argon gas, and RF is applied to the cylindrical target 303 to sputter Zn atoms and O atoms, and the surface of the substrate W located downstream thereof Adhere to. The substrate W is placed on the substrate table 310.

In addition, the film forming apparatus includes an RF magnetron plasma generation unit 304 and a target 305 made of Er ₂ O ₃ for performing sputtering with plasma generated by the RF magnetron plasma generation unit 304, and these include an introduction unit It is connected to the vacuum processing chamber 301 by 306. The RF magnetron plasma generation unit 304 and the target 305 constitute an RF magnetron sputtering source that realizes a magnetron sputtering method.

  The RF magnetron plasma generation unit 304 generates argon gas plasma and applies RF to the disk-shaped target 305, whereby the Er atoms and O atoms of the target 305 are sputtered (RF magnetron sputtering), and these are downstream. It adheres to the surface of the substrate W located.

With these configurations, particles sputtered and sputtered from the target 303 and particles sputtered and sputtered from the target 305 are deposited on the film formation surface of the substrate W to be processed disposed inside the vacuum processing chamber 301. It becomes possible. Further, the vacuum processing chamber 301 is provided with a gas inlet 307 for introducing O ₂ gas. In FIG. 3, the introduction of a sputtering gas such as argon is omitted. By using the target 305 made of Er ₂ O ₃ , a ZnO: Er film can be formed.

  In the film forming apparatus described above, the angle formed between the normal line of the surface of the target 305 (the surface to be sputtered) and the normal line of the surface of the substrate W (the surface to be formed) is 60 ° or more and less than 90 °. Yes. In FIG. 3, the angle θ is set to 60 ° or more and less than 90 °. The direction in which the plasma from the ECR plasma source 302 flows is the normal direction of the substrate W, and the angle between the normal line on the surface of the target 305 and the direction in which the plasma from the ECR plasma source 302 flows is θ, which is 60 More than 90 ° and less than 90 °. In this example, a cylindrical target 303 is used, and a line passing through the center of the hollow portion of the target 303 is a direction in which plasma from the ECR plasma source 302 flows.

  When the angle is within the above-described range, the Er deposition rate is not excessively increased, and the amount of Er introduced can be controlled within a desired range. On the other hand, when the angle exceeds 90 °, the target 305 cannot be expected from the film forming surface of the substrate W, and particles from the target 305 hardly reach. For this reason, the said angle shall be less than 90 degrees. Actually, if the angle exceeds 80 °, the region (width) of the surface of the substrate W that can be expected from the target 305 becomes too narrow. Therefore, the angle formed between the normal line of the surface of the target 305 and the normal line of the surface of the substrate W is preferably in the range of 60 ° to 80 °.

  In the plane direction parallel to the surface of the substrate W, the substrate W is disposed at a position that falls within a region (range) where the sputtered particles from the target 305 reach. Further, the substrate stage 310 is provided with a substrate rotation function for rotating the substrate W about the normal line passing through the central portion, and by rotating the substrate W by this function, the film thickness and each composition in the plane of the substrate W Can be ensured.

  The direction in which the plasma from the ECR plasma source 302 flows is the normal direction of the substrate W, and this state maximizes the deposition rate of the ZnO film by the ECR sputtering source. As the normal direction of the substrate W is shifted with respect to the direction in which the plasma from the ECR plasma source 302 flows, the density per unit area of the ECR plasma flow (sputtered particles) decreases and the deposition rate (film formation rate) decreases. . If the normal direction of the substrate W is shifted too much with respect to the direction in which the plasma from the ECR plasma source 302 flows, the deposition rate of the ZnO film decreases too much, and the amount of Er doping increases relatively, and the desired Er doping is achieved. The amount may not be obtained. Therefore, the angle of the normal direction of the substrate W with respect to the direction in which the plasma from the ECR plasma source 302 flows should not be so large.

By using the film forming apparatus described above, a phosphor film made of ZnO doped with Er can be formed on the substrate W made of sapphire. For example, by controlling the sputtering power in the RF magnetron plasma generation unit 304, the ratio of the number of Er atoms to the total number of Er and Zn atoms in the phosphor film formed on the substrate W is 0.6 at. % Or more 3 at. % Or less. In addition, if sputtering film formation is performed by introducing O ₂ gas, oxygen atoms taken into the formed phosphor film can be supplemented. In the sputter film formation described above, the substrate is not heated, but the substrate temperature rises to about 70 ° C. during the film formation process.

  Hereinafter, the Er-doped ZnO phosphor film formed by the sputtering method in the embodiment will be described in more detail using examples. In the present invention, as described above, the ratio of the number of Er atoms on the main surface of the heated sapphire substrate in a state where the main surface is heated to 550 ° C. or more and 900 ° C. or less with the C-plane or A-plane being the main surface. However, 0.6 at. % Or more 3 at. It is characterized in that a phosphor film (ZnO: Er film) made of ZnO doped with Er is formed by sputtering under the condition of% or less.

Since the ZnO: Er film and the sapphire substrate are lattice-matched, the ZnO crystal grows epitaxially at the initial stage of growth. For example, when a ZnO: Er film is sputter-deposited on a sapphire substrate at a high temperature, there are many defects such as dislocations in the ZnO crystal from the middle due to lattice distortion caused by the difference in lattice constant between the ZnO crystal at the initial growth stage and the sapphire substrate. be introduced. In addition, since the thermal expansion coefficients of the ZnO crystal and the sapphire substrate are quite different, the crystal is divided into small grains due to strain, thereby attempting to relieve the lattice strain. Such increased grain boundaries increase the substantial surface area of the ZnO crystal and provide a crystal surface / interface that contains a large number of Er ³⁺ ions. Such a state enables strong light emission from Er ³⁺ ions.

As will be described later, it was experimentally confirmed that the lower limit of the substrate temperature for realizing the above-described state was 550 ° C. Further, when the substrate temperature exceeds 900 ° C., oxygen easily escapes from the ZnO crystal. Therefore, the upper limit of the substrate temperature is desirably 900 ° C. If a film is formed at a substrate temperature of 550 ° C. or higher, Er ³⁺ ions emit light in a state (as-depo) in which no other treatment such as heat treatment is performed after the film formation.

Next, with regard to the Er concentration, 2 at. From the balance between the number of Er ³⁺ ions contributing to light emission and concentration quenching. % Or more, 4 at. It has been experimentally shown that the emission intensity becomes the highest at% or less as described later.

By the way, the amount of oxygen in the ZnO film varies depending on the amount of oxygen gas that flows when the ZnO: Er film is formed. If the formed film is not in the optimum oxidation state where Er ³⁺ ions emit the strongest light, the amount of oxygen contained is adjusted by heat treatment after film formation (heating after film formation). it can. For example, if the film is excessively oxidized, excess oxygen atoms can be removed by heating in vacuum after film formation. On the other hand, if the ZnO crystal is in a reducing state, it is possible to promote oxidation by performing heating after deposition in oxygen to achieve stronger light emission.

[Example]
Examples will be described below. In order to demonstrate the effectiveness of the present invention described above, a ZnO: Er film was formed on a sapphire C-plane substrate, and the emission characteristics of the formed ZnO: Er film were examined. Even when an A-plane substrate is used, a similar result is obtained because the ZnO crystal film grows with the C-plane terminated.

First, a ZnO: Er film to be a sample is formed by the above-described ECR sputtering method using a target made of ZnO and magnetron sputtering method using a target made of Er ₂ O ₃ . The film formation apparatus described with reference to FIG. 3 may be used. In the ECR sputtering unit, a ZnO target is used, and an argon gas added with an oxygen gas is used as a plasma gas. The addition of oxygen gas is performed to supplement oxygen atoms taken into the film. The oxygen flow rate was set so that the pressure in the film forming chamber was between 5 × 10 ⁻³ Pa and 3 × 10 ⁻² Pa.

While forming a ZnO host crystal by ECR sputtering equipped with a ZnO target, sputtering from an RF magnetron sputtering gun equipped with an Er ₂ O ₃ target was also used to incorporate Er into ZnO. Further, the microwave power for ZnO film formation by ECR sputtering was 500 W, and the RF power applied to the ZnO target was 500 W. The Er content in the deposited ZnO: Er thin film is changed by RF magnetron sputtering power using an Er ₂ O ₃ target. The RF magnetron sputtering power was adjusted by changing it to 10, 15, 20, 30, 50, and 70 W.

As the substrate, a sapphire C-plane substrate having a diameter of 2 inches was used. The sapphire substrate was divided into 9 × 3 × 3, and the emission intensity from Er ³⁺ ions in each region and the Er concentration dependency of the X-ray diffraction pattern were obtained. Further, luminescence from Er ³⁺ ions excited solid laser 532nm, ⁴ I _13/2 - ⁴ were measured PL spectrum of 1.54μm wavelength band based on the transition of I _15/2.

4 shows an Er concentration of 3.9 at. % ZnO: Er film (a), Er concentration 4.2 at. % ZnO: Er film (b), Er concentration 1.5 at. % ZnO: Er film (c), Er concentration 1.7 at. It is a characteristic view which shows the light emission (PL spectrum) from Er <^3+> ion about% ZnO: Er film | membrane (d). Here, the Er concentration is 4.2 at. % ZnO: Er film (b) and Er concentration 1.7 at. % ZnO: Er film (d) is subjected to substrate temperature conditions at the time of film formation at room temperature (about 20 to 25 ° C.) and is not subjected to heat treatment thereafter. On the other hand, the Er concentration is 3.9 at. % ZnO: Er film (a) and Er concentration of 1.5 at. % Of the ZnO: Er film (c) is subjected to heat treatment under conditions of 700 ° C. and 1 hour after film formation at a substrate temperature condition of the film formation.

  Although the emission intensity is increased by heating, the noise is conspicuous, and it can be seen that the emission is not so strong. At all post-deposition heating temperatures of 900 ° C. or lower, the emission intensity was about 10,000 to 20,000 counts.

Let us consider these results. When the film is formed at room temperature (about 20 to 25 ° C.), the ZnO film grows two-dimensionally and Er ³⁺ ions are confined in the ZnO crystal. Even if this is heated, the shape of the ZnO crystal does not change, so even if some of the Er ₃₊ ions can replace the cation site, it is presumed that most of the remainder does not contribute to light emission. When the film is formed at room temperature, only the peak at 1538 nm is strong and the surrounding sub-peak is weak, so that the emission spectrum has a substantially small half width.

  FIG. 5 shows an Er concentration of 0.6 at. It shows how the emission spectrum changes when the substrate temperature when the ZnO: Er film of% is changed. At 500 ° C. or less, it is at most 10,000 counts, but at 600 ° C., it increases to 40000 counts. Together with other experimental results, it was confirmed that when the substrate temperature exceeded 550 ° C., the emission intensity increased at a stretch.

FIG. 6 shows a series of ZnO: Er film samples in which the Er concentration is changed by changing the sputtering power in RF sputtering using an Er ₂ O ₃ target at a substrate temperature of 550 ° C. in vacuum after film formation. It is a characteristic view which shows PL spectrum after heating at 700 degreeC. Er concentration 0.1 at. As the Er concentration is increased from%, the emission intensity gradually increases, but 3.9 at. %, The light is emitted very strongly. When the Er concentration is further increased, light emission stops due to concentration quenching.

FIG. 7 shows a series of ZnO: Er film samples in which the concentration of Er incorporated by changing the sputtering power in RF sputtering using an Er ₂ O ₃ target at a substrate temperature of 550 ° C. is changed in oxygen after film formation. It is a characteristic view which shows PL spectrum after heating at 700 degreeC. Thus, when heating is performed after film formation in oxygen, 2.0 at. %, Remarkably strong light emission is obtained.

When the sputtering power input to the Er ₂ O ₃ target is increased, a large amount of oxygen is taken into the ZnO: Er film simultaneously with Er ³⁺ ions. In the case of heating in oxygen, the ZnO: Er film has a still low degree of oxidation with an Er concentration of 2.0 at. % Shows the strongest light emission, whereas in the vacuum heating, oxygen is partially lost and becomes reductive, so that the Er concentration of 3.9 at. % Is the optimal condition. As described above, the Er concentration that gives the maximum light emission intensity slightly changes depending on the heating atmosphere. % Or more, 4 at. It has been found that the strongest luminescence can be obtained at an Er concentration of not more than%.

  FIG. 8 shows that the Er concentration is 1.5 at. It is a characteristic view which shows the change of the emission spectrum when the temperature of the post-deposition heating in a vacuum is changed about the sample made into%. The emission intensity becomes maximum when heating at 600 ° C., and the emission intensity decreases at 700 ° C. or higher. This is considered to be because the amount of oxygen at the time of film formation was slightly insufficient, and when heated at a high temperature, it became more reductive and deviated from the optimum conditions.

  9 shows an Er concentration of 2.0 at. For a ZnO: Er film on the same substrate for which the results of FIG. It is a characteristic view showing the change of the emission spectrum when the% region is cut out as a sample and the heating temperature after film formation in oxygen is changed. In this case, the emission intensity is maximum at 700 ° C., but there is no significant difference in the range from 600 ° C. to 900 ° C. This is probably because the original sample was slightly reductive, so that an appropriate degree of oxidation was obtained by heating in oxygen.

  From the above results, the Er concentration is 2 to 4 at. % ZnO: Er film is formed, the heating intensity in vacuum or oxygen is selected according to the oxidation-reduction state, and the film is heated in the range of 600 ° C to 900 ° C. It became clear that

Next, FIG. 10 shows the X-ray diffraction pattern obtained for evaluating the ZnO: Er film that emits strong light as described above. All samples were deposited at a substrate temperature of 550 ° C. or higher. As shown in FIG. 10, the Er concentration was 0.1 at. % To 22 at. Even if it is increased to%, a strong diffraction pattern of only ZnO (002) is obtained. This indicates that the ZnO crystal has a stable c-axis orientation structure regardless of the Er concentration. The ZnO (002) peak intensity was measured at an Er concentration of 5 at. %, But the Er concentration is 5 at. %, It gradually decreases and exceeds 22 at. %, 0.1 at. Compared to the% pattern, it is about 3 digits lower. This indicates that the presence of Er ³⁺ ions incorporated in a large amount in the ZnO film prevents the formation of a large ZnO crystal domain.

The formed film consists of only the domain of the c-axis orientation is not Er ³⁺ ions occupy lattice points of the crystal, present on the surface and interface of crystallite, ZnO crystallites themselves, Er ³ It means being placed in the same environment as a ZnO crystal containing no ⁺ ion.

  For the purpose of confirming the above, the 2θ diffraction angle of the ZnO (002) peak in each ZnO: Er film sample having different Er concentrations described with reference to FIG. 7 was plotted. The result is shown by white circles in FIG. The result shown by the white circle in FIG. 11 shows the same value as the undoped ZnO crystal. Therefore, it can be said that the crystal distortion of the ZnO: Er crystal formed by the method of the embodiment is completely relaxed.

In order to show that the state of the ZnO host crystal affects the light emission from the doped Er ³⁺ ions, the temperature condition is set to room temperature, an undoped ZnO buffer layer is deposited on the sapphire substrate to a thickness of 300 nm, and then the substrate temperature Was raised to 550 ° C. to prepare a sample in which a ZnO: Er film was formed. The lower temperature buffer layer has an effect of stepwise relieving lattice distortion directly generated between the sapphire substrate and the upper ZnO: Er film. In fact, the surface of the ZnO: Er film was a very smooth mirror surface. When the X-ray diffraction pattern of the sample in which such a buffer layer was formed was measured, it was confirmed that the ZnO (002) peak was the main c-axis alignment film, similar to the result shown in FIG. .

  Here, the black circles in FIG. 11 show the result of plotting the 2θ diffraction angle of the sample on which the buffer layer is formed. As is clear from comparison between the black circle and the white circle in FIG. 11, the 2θ angle is smaller than that without the buffer layer, indicating that the c-axis length is longer than that of the undoped ZnO crystal. Thus, it is shown that the stress caused by the lattice mismatch with the sapphire substrate remains in the ZnO buffer layer and the ZnO: Er film.

The measurement result of the emission spectrum from the ZnO: Er film | membrane sample with a ZnO buffer layer is shown in FIG. Although the ZnO: Er film itself was formed at 550 ° C., the emission intensity was remarkably reduced to 1/10 or less as compared with the results described with reference to FIGS. As a result, as shown in FIG. 11, the fact that the lattice relaxation of the ZnO: Er film is insufficient affects the number of Er ³⁺ ions present at the sites capable of emitting light. Conceivable. As can be seen from this result, it is understood that it is better not to use the buffer layer.

  As described above, according to the present invention, a sapphire substrate whose main surface is C-plane or A-plane is heated to any temperature of 550 ° C. or more and 900 ° C. or less, and the main surface of the heated sapphire substrate is applied. A phosphor film made of ZnO doped with Er is used with an Er concentration of 0.6 at. % Or more 3 at. %, The two-dimensional continuous Er-doped ZnO phosphor film capable of obtaining strong light emission (infrared light emission) can be formed.

  As described above, according to the present invention, by using a sapphire single crystal substrate and setting process conditions appropriately, it is possible to realize strong infrared emission that cannot be obtained with other general Si substrates. Is possible. By using the Er-doped ZnO phosphor film according to the present invention, application to an LED (Light-Emitting Diode) or the like is possible.

  The present invention is not limited to the embodiment described above, and many modifications and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious.

  101 ... substrate, 102 ... phosphor film.

Claims (1)

A heating step of heating the sapphire substrate whose main surface is the C-plane or A-plane to any temperature of 550 ° C. or more and 900 ° C. or less;
A phosphor film forming step of forming a phosphor film made of ZnO doped with Er on the main surface of the heated sapphire substrate by an electron cyclotron resonance sputtering method using a target made of ZnO containing Er. ,
In the phosphor film forming step,
The ratio of the number of Er atoms to the total number of Er and Zn atoms in the phosphor film is 0.6 at. % Or more 3 at. % Or less, an Er-doped ZnO phosphor film forming method.