JP6339972B2 - Zinc oxide compound light-emitting film and method for producing the same - Google Patents

Description

  The present invention relates to a zinc oxide compound light-emitting film.

Eu ³⁺ ions, which are trivalent ions of the rare earth element europium (Eu), are most widely used as emission centers in phosphors. As a red light emitting device utilizing light emission from Eu ³⁺ ions, application to LED is conceivable. The phosphor is powdery and emits light by light having a wavelength shorter than the emission wavelength or electronic excitation. It is used in many fields including fluorescent lamps and fluorescent paints.

  On the other hand, a phosphor thin film formed on a substrate by a technique such as sputtering has become the center of recent light emitting devices, as represented by inorganic EL and LEDs. In particular, wide band gap semiconductors doped with rare earth ions are less prone to temperature quenching and are considered promising. Zinc oxide ZnO, gallium nitride GaN, and the like are known as typical host materials.

H. Akazawa and H. Shinojima, “Concentration effect of H / OH and Eu3 + species on activating photoluminescence from ZnO: Eu3 + thin films” J. Appl. Phys. 114 (2013) 153502. H. Dixit, N. Tandon, S. Cottenier, R. Saniz, D. Lamoen, B. Partoens, V. Van Speybroeck, M. Waroquier, “Electronic structure and band gap of zinc spinel oxides beyond LDA: ZnAl2O4, ZnGa2O4 and ZnIn2O4 ”New J. Phys. 13 (2011) 063002.

Even if Eu ³⁺ ions are doped with ZnO as a host, it is not easy for Eu ³⁺ to substitute the Zn ²⁺ site at the lattice point due to the difference in valence between Zn ²⁺ and Eu ³⁺ . In addition, the fact that Eu ³⁺ has a larger ionic radius than Zn ²⁺ is considered to be a cause of difficulty in substitution. Therefore, in order to realize a ZnO film doped with Eu ³⁺ ions capable of emitting light, it is necessary to co-add Li ⁺ ions or introduce Eu ³⁺ in the form of EuF ₃ or (La, Eu) OF. is necessary. As a method for avoiding such impurities, it has been reported that Eu ³⁺ ions in an optically active state can be introduced by adding H ₂ O gas during sputtering (Non-patent Document 1). However, the process conditions are narrow. In the phosphor powder having a large surface area compared to the volume, most of the rare earth ions are bonded to the surface of the host crystallite. This is because the problem of difference in valence can be absorbed by defects on the surface and interface. However, in the case of a thin film, the surface in contact with the outside world is only a part of the whole, and most Eu ³⁺ ions are confined inside the film. For this reason, it is difficult to replace the active sites as described above, leading to a film that does not emit light. In the case of GaN, since Ga ³⁺ is a trivalent ion, Eu ³⁺ ion can easily replace the Ga ³⁺ site.

The present invention has been made in view of the above-described conventional problems. An object of the present invention is to provide a zinc oxide compound light-emitting film in which Eu ³⁺ ions are stably doped in a zinc oxide-based material and a method for manufacturing the same. It is to provide.

In order to solve the above-described problem, the invention described in an embodiment includes Eu ³⁺ ions in a crystal using any one of a ZnGa ₂ O ₄ crystal, a ZnAl ₂ O ₄ crystal, and a ZnIn ₂ O ₄ crystal as a host. A zinc oxide compound light-emitting film that is doped.

An invention according to another embodiment, a step of forming a Eu ³⁺ doped ZnGa ₂ O ₄ crystal film, to have a concentration gradient composition formed on the substrate by deposition location, Eu ^{3 A} step of simultaneously performing sputtering of a sputtering source including a ZnO target containing ions and a sputtering source including a Ga ₂ O ₃ target from different positions, and a composition formed according to a position on the substrate on which the sputtered atoms are deposited Determining a Zn / Ga composition ratio that emits the strongest light using a concentration gradient of the substrate and determining a post-annealing temperature condition using a region having the same Zn / Ga composition ratio on the substrate, and the determined data And a step of post-annealing at an optimal temperature for an optimal Zn / Ga composition region, It is a manufacturing method.

An invention according to another embodiment, a step of forming a Eu ³⁺ doped ZnAl ₂ O ₄ crystal film, to have a concentration gradient composition formed on the substrate by deposition location, Eu ^{3 A} step of simultaneously performing sputtering of a sputtering source including a ZnO target containing ions and a sputtering source including an Al ₂ O ₃ target from different positions, and a composition formed according to a position on the substrate on which the sputtered atoms are deposited Determining a Zn / Al composition ratio that emits the strongest light using a concentration gradient of the substrate and determining a post-annealing temperature condition using a region having the same Zn / Al composition ratio on the substrate, and the determined data And a step of post-annealing at an optimal temperature for an optimal Zn / Al composition region based on It is a manufacturing method.

An invention according to another embodiment, a step of forming a Eu ³⁺ doped ZnIn ₂ O ₄ crystal film, to have a concentration gradient composition formed on the substrate by deposition location, Eu ^{3 A} step of simultaneously performing sputtering of a sputtering source including a ZnO target containing ions and a sputtering source including an In ₂ O ₃ target from different positions, and a composition formed according to a position on the substrate on which the sputtered atoms are deposited Determining a Zn / In composition ratio that emits the strongest light using a concentration gradient of the substrate and determining a post-annealing temperature condition using a region having the same Zn / In composition ratio on the substrate, and the determined data And a step of post-annealing at an optimal temperature for an optimal Zn / In composition region based on It is a manufacturing method.

It is a figure which shows the structural example of a light emitting film formation apparatus. It is a figure which shows the observation method of the sample produced on the board | substrate of a light emitting film forming apparatus. It is a figure which shows the Ga / Zn composition ratio in the A, B, C, D, E, and F row | line | column of FIG. Corresponding to the B column in FIG. 2, to the film of the composition ZnGa _1.3 O _2.9, it is a graph showing an emission spectrum after having been subjected to the post-annealing for 1 hour in a vacuum. Corresponding to column D of Figure 2, to the film of the composition ZnGa _2.8 O _5.1, it is a graph showing an emission spectrum after having been subjected to the post-annealing for 1 hour in a vacuum. It is a figure which shows the emission spectrum after performing post-annealing for 1 hour at 700C in a vacuum with respect to the film | membrane with which a composition of 5 lines of FIG. 2 differs. It is a figure which shows the X-ray-diffraction pattern of 4 samples of FIG. It is a figure which shows the emission spectrum with respect to the film | membrane of a different composition of 3 rows of FIG. 2 about the sample sputter-deposited by oxygen gas addition with the substrate temperature of 500C.

  Hereinafter, embodiments of the present invention will be described in detail.

The zinc oxide compound light-emitting film according to the present invention has a configuration in which Eu ³⁺ ions are doped inside a crystal using any one of a ZnGa ₂ O ₄ crystal, a ZnAl ₂ O ₄ crystal, and a ZnIn ₂ O ₄ crystal as a host. Such a zinc oxide compound light-emitting film employs ZnGa ₂ O ₄ , ZnAl ₂ O ₄ , and ZnIn ₂ O ₄ , which are wide band gap crystals, as a ZnO-based host. These compounds have a spinel structure, the band gap of ZnGa ₂ O ₄ is 4.4-5.0 eV, and the band gap of ZnAl ₂ O ₄ is 3.8-3.9 eV (see Non-Patent Document 2).

Compared with Zn ²⁺ , Ga ³⁺ , Al ³⁺ , In ³⁺ ions are stoichiometrically contained twice in the crystal unit, so Eu ³⁺ ions steadily move these trivalent cation sites. Can be replaced. This leads to a process advantage that the film formation environment, that is, the substrate temperature at the time of film formation, the oxygen gas flow rate, or the Ga / Zn composition ratio is not so severe in realizing good light emission characteristics. .

  FIG. 1 is a diagram illustrating a configuration example of a light emitting film forming apparatus. In the light emitting film forming apparatus for forming a zinc oxide compound light emitting film according to the present invention, as shown in FIG. 1, the light emitting film forming apparatus 10 can be constituted by a so-called combinatorial sputtering apparatus using two sputtering sources.

  In the light emitting film forming apparatus 10, ECR sputtering of, for example, Zn, Eu, O, or the like is performed on the substrate 15 with a cylindrical target 11, an electromagnet 12, and an ECR (Electron Cyclotron Resonance) plasma 13. An RF (Radio Frequency: high frequency) magnetron gun 14 can perform RF sputtering of, for example, Ga and O. The ECR sputtering apparatus and the RF magnetron gun 14 are arranged so that the compound concentration by ECR sputtering is high at one end of the substrate 15 and the compound concentration by RF sputtering is high at the other end of the substrate 15. For example, as shown in FIG. 1, an ECR plasma sputter source is inclined 30 degrees with respect to the vertical of the substrate 15 and shifted in the Y direction with respect to a substrate 15 having a horizontal XY axis, and an RF magnetron sputter source is disposed. Are inclined by 45 degrees with respect to the vertical of the substrate 15 and shifted in the X direction. With this configuration, a complex oxide film having a concentration gradient corresponding to the position of the substrate can be formed.

  By sputtering using two sputtering sources, it is possible to obtain films having a concentration gradient of these complex oxides at once, and to evaluate the characteristics combinatorially. This makes it possible to easily determine the optimum process conditions during film formation, so that a film that emits light well can be obtained using a film in a region that satisfies the conditions on the substrate.

  FIG. 2 shows an observation method of a sample manufactured on the substrate of the light emitting film forming apparatus. Specifically, as shown in FIG. 2, the sample prepared on the substrate 15 is divided into a plurality of sections (AF) on the XY axis of the substrate having a concentration gradient, and the emission spectrum in each of the sections is obtained. By observing, the Zn / Ga composition ratio that emits the strongest light is determined. Further, a predetermined region of the Zn / Ga composition ratio is further divided into a plurality of sections (1-6) along an axis perpendicular to the XY axis, and the emission spectrum is observed by changing the post-annealing temperature conditions in each of the sections. By doing so, it is possible to determine the conditions for the optimum post-annealing temperature for the optimum Zn / Ga composition region.

In order to demonstrate the effectiveness of the present invention, a ZnGa ₂ O ₄ : Eu film was formed. In the light emitting film forming apparatus 10 shown in FIG. % ECR plasma sputtering from a cylindrical ZnO target and RF magnetron sputtering from a 2-inch disk type Ga ₂ O ₃ target were simultaneously performed.

Ions generated in the ECR plasma are transported toward the substrate by sputtering the inner surface of the cylindrical target. A 4-inch silicon substrate was used as the substrate. Zn, O, and Eu atoms supplied from the ECR plasma sputtering source come from a direction of 30 degrees with respect to the vertical of the substrate. On the other hand, Ga and O ions supplied from the RF magnetron sputter source fly from a direction of 45 degrees with respect to the vertical of the substrate. At the point where both intersect, a ZnGa _x O _{1 + 1.5x} film is formed.

The plasma was generated by argon gas, and O ₂ or H ₂ O gas was added as an oxygen source. The PL (photoluminescence) spectrum was measured by He-Cd laser excitation with a wavelength of 325 nm. The band gap of the ZnGa _x O _{1 + 1.5x} film is larger than the photon energy 3.8 eV corresponding to this excitation wavelength, but the band edge tail has absorption.

As shown in FIG. 1, the ECR sputtering source is disposed on the Y side at the right end of the substrate 15. Since the sputtered atoms diverge, the flux is inversely proportional to the square of the distance. Therefore, the closer to the Y side, the larger the Zn composition in the ZnGa _x O _{1 + 1.5x} film. On the other hand, the RF magnetron sputter source is disposed on the X side at the left end of the substrate 15, and the Y side at the right end is far. Therefore, the Ga composition in the ZnGa _x O _{1 + 1.5x} film increases as the position becomes the X side. When the above principles are combined, the Zn / Ga ratio increases toward the Y side.

FIG. 2 is a view of a sample in which a ZnGa _x O _{1 + 1.5x} film is formed on a 4-inch substrate, as viewed from above on the substrate 15 of FIG. FIG. 2 shows a cutting line for obtaining a measurement sample by dicing. 4, 5 and 6 show the emission spectra at each position of the sample. In FIG. 2, sputtered atoms from the Ga ₂ O ₃ target come mainly from the left (X) direction of the substrate, and sputtered atoms from the ZnO target come mainly from the right (Y) direction. Black circles indicate measurement points in FIGS. 4, 5, and 6. Samples divided into 66 sections were cut out, and sample positions were represented by combinations of rows A, B, C, D, E, and F, and 1, 2, 3, 4, 5, and 6 rows. X and Y correspond to the position of the substrate shown in FIG. The closer the sample row is to F, the higher the Ga content. Within each row, the Ga content is generally uniform. The content of Eu is 1 at. %.

FIG. 3 is a diagram plotting the compositions in rows A, B, C, D, E, and F. The film formation conditions at this time were a microwave input of 400 W for generating ECR plasma, an RF output of 400 W to the ZnO: Eu target, and an RF magnetron output of 60 W of the Ga ₂ O ₃ target. It can be seen that the composition can be continuously changed from ZnGa _0.9 O _2.3 to ZnGa _6.3 O _10..5 from left to right of the wafer. A composition almost equal to the stoichiometric composition of ZnGa ₂ O ₄ is obtained at point C. If you go to the left from there, Ga will be excessive, and if you go to the right, Ga will be insufficient.

FIG. 4 shows an emission spectrum after subjecting a film having a composition of ZnGa _1.3 O _2.9 as a sample along the row B in FIG. 2 to post-annealing in vacuum for 1 hour. The annealing temperatures are 300C for (B, 1), 400C for (B, 2), 500C for (B, 3), 600C for (B, 4), 700C for (B, 5), and (B, 6). It was 800C.

In the 300C annealing, a sufficient number of Eu ³⁺ ions do not enter the active site, or excess oxygen remains in the film as a result of low-temperature annealing, and thus no light emission is observed. However, when annealed at 400 C, light emission corresponding to the transition of ⁵ D ₀ ⁷ F ₂ appears at 615 nm. This emission wavelength is shifted to the longer wavelength side by 3 nm compared to 612 nm of the Eu ³⁺ doped ZnO film, suggesting that the environment of the crystal field where Eu ³⁺ ions are present is different. The peaks corresponding to other emission transitions are ⁵ D ₀ ⁷ F ₀ (575 nm), ⁵ D ₀ ⁷ F ₁ (595 nm), ⁵ D ₀ ⁷ F ₃ (650 nm), and ⁵ D ₀ ⁷ F ₄ (705 nm). is there.

In 600-800C, the intensity of this emission peak is almost constant. In contrast to the case of ZnO: Eu, the emission does not decay even when annealed at a high temperature of 800C. In ZnO: Eu, when it exceeds 500 C, it does not emit light rapidly. This is escape from almost completely film Annealing is hydrogen 800C, in a system where Eu ³⁺ ions are stabilized by H or OH, because Eu ³⁺ ions can not stay in the light-emitting site When annealed at 800 C, a light emission peak is also observed at 360-400 nm, which is emission at the band edge from the ZnGa _1.3 O _2.9 host crystal.

FIG. 5 shows an emission spectrum of the film having the composition ZnGa ₂₈ O ₅₁ along post-annealing for 1 hour in a vacuum along the column D in FIG. The annealing temperatures are 300C for (D, 1), 400C for (D, 2), 500C for (D, 3), 600C for (D, 4), 700C for (D, 5), and (D, 6). It was 800C. It can be seen that the activation of Eu ³⁺ ions is insufficient at an annealing temperature of 300 C as in the composition ZnGa _1.3 O _2.9 of FIG. In the range of 500-700C, the same emission intensity is obtained. However, unlike FIG. 4, the 800C annealing is completely quenched. This result shows that an annealing temperature of 500-700 C is optimal for this composition.

FIG. 6 shows the change in the emission spectrum with respect to the change in the composition of the sample along line 5 in FIG. The sample was post-annealed at 700C. Taking the state of the stoichiometric composition of ZnGa ₂ O ₄ , ZnGa _1.3 O _2.9 is Ga-deficient, ZnGa _1.8 O _3.8 is close to the stoichiometric ratio, ZnGa _2.8 O _5.1 is Ga excess, ZnGa _4.1 O _7.1 is significantly Ga Excessive. From the result of FIG. 6, it can be seen that Eu ³⁺ ions emit light strongly in a fairly wide range of 1.3 <x <2.8.

The ZnO—Ga ₂ O ₃ complex oxide forms a homologous series superlattice in epitaxial growth. That is, it takes a crystal structure in which a ZnO layer and a Ga ₂ O ₃ layer are stacked in the vertical direction at a ratio according to the composition. When the Ga content is low, the ZnO layer is large and the characteristics closer to the ZnO host crystal are exhibited. When the Ga content is high, the Ga ₂ O ₃ layer is large and the characteristics closer to the Ga ₂ O ₃ host crystal are exhibited.

FIG. 7 is a diagram in which the structure of the four samples in FIG. 6 is evaluated by X-ray diffraction. For all samples, many peaks are attributed to ZnGa ₂ O ₄ . There is no diffraction peak attributed to ZnO crystal or Ga ₂ O ₃ crystal. This indicates that crystals having a composition of ZnGa ₂ O ₄ are likely to be formed even if there is a slight compositional shift.

As described above, when the ZnGa _x O _{1 + 0.5x} film is formed by sputtering at room temperature under H ₂ O gas flow, the composition is as wide as 1.3 <x <2.8 from FIG. With respect to the range and the post-annealing temperature, it was found that strong light emission from Eu ³⁺ ions was obtained in the range of 600 to 700C from FIGS. Therefore, if only the region from the B row to the D row obtained by film formation from the two sputtering sources is cut out and annealed in the range of 600 to 700 C, a light emitting film having uniform light emission characteristics is generated.

FIG. 8 is a diagram showing the Ga / Zn ratio dependence of the emission spectrum obtained along the third row of FIG. 2 for the sample sputtered by addition of oxygen gas at a substrate temperature of 500C. At a high Ga / Zn composition ratio corresponding to the E column or the F column, no light emission from Eu ³⁺ ions is observed. In this case as well, the emission intensity is maximum at x = 1.8 or x = 2.8, as in FIG. In the case of film formation with oxygen gas, for the sample post-annealed after film formation at room temperature, the defect emission of the host crystal is prevalent, and the emission from Eu ³⁺ ions was buried in the defect emission and was not clearly observed. . Therefore, it became clear that strong light emission can be obtained by forming a film at room temperature using H ₂ O and activating it by post-annealing.

In this example, only the results of study on the ZnGa ₂ O ₄ host crystal are shown, but also for ZnAl ₂ O ₄ and ZnIn ₂ O ₄ composed of Al and In belonging to the same column on the periodic table. Since Eu ³⁺ ions are substituted into Al ³⁺ and In ³⁺ sites, similar emission spectra can be obtained, and optimum process conditions can be determined by the same approach as in this example. .

To maximize the function of the composite oxide thin film, many parameters such as composition and process conditions must be optimized. When a ZnO crystal film is used as a host, in order to obtain strong red light emission from doped Eu ³⁺ ions, it is necessary to use H ₂ O as an oxygen source or to co-dope with different atoms. Furthermore, the optimum post-annealing temperature is also low, and the emission intensity greatly depends on the oxidation degree of ZnO, so the range of conditions for obtaining sufficient emission intensity is extremely narrow. Not only does it take time to adjust the conditions, but there is also a problem that the process stability is low. This is mainly based on the physical restriction that Eu ³⁺ ions are difficult to replace Zn ²⁺ sites having different valences. By adopting a host crystal such as ZnGa ₂ O ₄ which is a wide band gap semiconductor and whose trivalent cation is a main constituent atom, it is possible to ensure a relatively wide process window with respect to composition and post-annealing temperature. did it. This is important for manufacturing purposes.

  Usually, in order to obtain optimum conditions, it is necessary to produce a large number of samples by trial and error and evaluate their physical property values. However, according to the method of the present invention, if it is limited only to the composition and the post-annealing temperature, it can be achieved only by film formation on one substrate.

DESCRIPTION OF SYMBOLS 10 Light emitting film forming apparatus 11 Cylindrical target 12 Electromagnet 13 ECR plasma 14 RF magnetron gun 15 Substrate

Claims (4)

A step of forming a Eu ³⁺ doped ZnGa ₂ O ₄ crystal film, comprising a ZnO target containing Eu ³⁺ ions so that the composition formed on the substrate has a concentration gradient depending on the deposition position And simultaneously performing sputtering with a sputtering source comprising a Ga ₂ O ₃ target from different positions;
A Zn / Ga composition ratio that emits the strongest light is determined using a concentration gradient of the composition formed according to the position on the substrate on which the sputtered atoms are deposited, and the Zn / Ga composition ratio on the substrate is the same. Determining the post-annealing temperature condition using
And a post-annealing step at an optimal temperature for an optimal Zn / Ga composition region based on the determined data. A step of forming a Eu ³⁺ doped ZnAl ₂ O ₄ crystal film, comprising a ZnO target containing Eu ³⁺ ions so that the composition formed on the substrate has a concentration gradient depending on the deposition position And simultaneously performing sputtering with a sputtering source comprising an Al ₂ O ₃ target from different positions;
A region in which the Zn / Al composition ratio on the substrate is the same is determined by using the concentration gradient of the composition formed according to the position on the substrate on which the sputtered atoms are deposited to determine the Zn / Al composition ratio that emits the strongest light. Determining the post-annealing temperature condition using
And a step of post-annealing at an optimum temperature with respect to an optimum Zn / Al composition region based on the determined data, a method for producing a zinc oxide compound light-emitting film. A step of forming a Eu ³⁺ doped ZnIn ₂ O ₄ crystal film, comprising a ZnO target containing Eu ³⁺ ions so that the composition formed on the substrate has a concentration gradient depending on the deposition position And simultaneously performing sputtering with a sputtering source comprising an In ₂ O ₃ target from different positions;
A Zn / In composition ratio that emits the strongest light is determined using a concentration gradient of a composition that is formed according to the position on the substrate on which the sputtered atoms are deposited, and the Zn / In composition ratio on the substrate is the same. Determining the post-annealing temperature condition using
And a step of post-annealing at an optimum temperature with respect to an optimum Zn / In composition region based on the determined data. During sputtering, a method for manufacturing a zinc oxide compound emission film according to any one of claims 1 to 3, characterized in that the addition of H ₂ O vapor gas.