Scintillator

Abstract

This scintillator comprises: a support substrate; and a light-emitting layer that is formed from ZnO, is disposed on the support substrate, and emits light in response to the incidence of charged particles or photons. The light-emitting layer has a plurality of first layers having a first impurity concentration, and a plurality of second layers alternately laminated with the plurality of first layers and having a second impurity concentration lower than the first impurity concentration.

Description

Scintillator

[0001] The present disclosure relates to scintillators.

[0002] Patent Document 1 describes a scintillator that includes a light-emitting layer made of ZnO and generates scintillation light in response to incident radiation. In the scintillator described in Patent Document 1, the light-emitting layer is made of ZnO, so the light-emitting lifetime (light-emitting time) of the scintillation light is short, and high-speed response is achieved.

[0003] Patent No. 6676372

[0004] The scintillators described above can be used to convert electrons into light in photodetectors used in, for example, scanning electron microscopes (SEMs) and time-of-flight mass spectrometers (TOF-MSs). Such scintillators are required to not only shorten the light emission time (high speed), but also increase the brightness of the light (high brightness). On the other hand, if the light emission time is short, the amount of light signal decreases, and the brightness of the light may decrease.

[0005] Therefore, an object of one aspect of the present disclosure is to provide a scintillator that can achieve both high speed and high brightness.

[0006] A scintillator according to one aspect of the disclosure is [1] "a scintillator comprising: a support substrate; and a light-emitting layer formed of ZnO and disposed on the support substrate, the light-emitting layer emitting light in response to incidence of charged particles or photons, the light-emitting layer having a plurality of first layers having a first impurity concentration, and a plurality of second layers alternately stacked with the plurality of first layers and having a second impurity concentration lower than the first impurity concentration."

[0007] In this scintillator, the light-emitting layer is formed of ZnO, which shortens the emission time of scintillation light and enables high-speed operation. Furthermore, the light-emitting layer has a structure in which a plurality of first layers having a first impurity concentration and a plurality of second layers having a second impurity concentration lower than the first impurity concentration are alternately stacked. This allows high brightness to be achieved while maintaining high speed. Thus, this scintillator allows both high speed and high brightness to be achieved.

[0008] A scintillator according to one aspect of the present disclosure may be [2] "the scintillator according to [1], wherein the impurities contained in the plurality of first layers are Ga, Al, In, Sb, F, Cl, or I," or [3] "the first impurity concentration is 4×10 ２０ atoms / cm ３ The scintillator may be the scintillator according to [1] or [2] below. In these cases, the above-mentioned advantageous effect of achieving both high speed and high brightness is preferably achieved.

[0009] A scintillator according to one aspect of the present disclosure may be [4] "the scintillator according to any one of [1] to [3], wherein each of the plurality of first layers has a thickness of less than 20 nm." In this case, the luminance of light can be further increased effectively.

[0010] A scintillator according to one aspect of the present disclosure includes: [5] "the support substrate is made of sapphire, quartz, glass, ScMgAlO ４ Alternatively, the scintillator may be a scintillator according to any one of [1] to [4], which is formed of GaN or GaN, or may be a scintillator according to [6], which is a scintillator according to any one of [1] to [5], in which the support substrate is a sapphire substrate having an a-plane as a main surface, and the light-emitting layer is disposed on the main surface. In these cases, the above-mentioned advantageous effect of achieving both high speed and high brightness is preferably achieved.

[0011] A scintillator according to one aspect of the present disclosure may be [7] "the scintillator according to any one of [1] to [6], further comprising a metal layer formed on the light-emitting layer on the side opposite to the support substrate." In this case, light from the light-emitting layer can be reflected by the metal layer toward the support substrate, thereby improving light utilization efficiency.

[0012] A scintillator according to one aspect of the present disclosure may be [8] "the scintillator according to [7], in which the metal layer is formed of Al or Ti." In this case, light utilization efficiency can be effectively improved.

[0013] A scintillator according to one aspect of the present disclosure may be [9] "the scintillator according to [7] or [8], further comprising a protective layer having a band gap larger than that of ZnO and disposed between the light-emitting layer and the metal layer." In this case, electrons and holes generated in the light-emitting layer can be prevented from flowing out to the metal layer, and the luminous efficiency of the light-emitting layer can be increased.

[0014] A scintillator according to one aspect of the present disclosure may be

[10] "the scintillator according to any one of [1] to [9], further comprising a buffer layer formed of ZnO and disposed between the support substrate and the light-emitting layer." In this case, the light-emitting layer can be suitably formed on the support substrate.

[0015] A scintillator according to one aspect of the present disclosure may be

[11] "the scintillator according to any one of [1] to

[10] , wherein each of the plurality of first layers has a thickness of 2.5 nm or more and 15 nm or less." In this case, the brightness of the light can be increased even more effectively.

[0016] A scintillator according to one aspect of the present disclosure may be

[12] "the scintillator according to any one of [1] to

[11] , wherein the thickness of each of the plurality of first layers is equal to the thickness of each of the plurality of second layers." In this case, it is possible to more effectively increase the speed.

[0017] According to one aspect of the present disclosure, it is possible to provide a scintillator that can achieve both high speed and high brightness.

[0018] 1 is a cross-sectional view of a scintillator according to an embodiment; FIG. 2 is a graph showing the results of a comparison of CL spectra; FIG. 3 is a graph showing the results of a comparison of voltage dependence of cathode luminescence; and FIG. 4 is a table showing the results of a comparison of afterglow characteristics. FIG. 5 is a graph showing an example of the distribution of Ga concentration in a light-emitting layer; FIG. 6 is a graph showing the results of a comparison of spectra; and FIG. 7 is a diagram for explaining that light emission is enhanced by a multilayer structure. 1 is a cross-sectional view of a scintillator according to a modified example; FIG. 7 is a graph showing the results of a comparison of voltage dependence of cathode luminescence; and FIG. 8 is a table showing the results of a comparison of afterglow characteristics of cathode luminescence. and FIG. 9 is a graph showing the results of a comparison of photoluminescence intensity. and FIG. 10 is a table showing the results of a comparison of afterglow characteristics of photoluminescence.

[0019] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the following description, the same or equivalent elements will be designated by the same reference numerals, and redundant description will be omitted.

[0020] 1 , scintillator 1 includes a support substrate 2, a light-emitting layer 3, and a metal layer 4. Light-emitting layer 3 is disposed on a main surface 2 a of support substrate 2, and metal layer 4 is disposed on a surface 3 a of light-emitting layer 3 opposite to support substrate 2. In scintillator 1, scintillation light (fluorescence) is generated in light-emitting layer 3 in response to incident charged particles (e.g., electrons), causing light to be emitted by light-emitting layer 3. Scintillator 1 can be used to convert electrons into light in a photodetector used in, for example, a scanning electron microscope or a time-of-flight mass spectrometer.

[0021] The support substrate 2 is a sapphire substrate (a-plane sapphire substrate) having an a-plane (crystal plane) as its main surface 2a. The support substrate 2 is transparent to the scintillation light generated in the light-emitting layer 3. In the scintillator 1, the scintillation light generated in the light-emitting layer 3 passes through the support substrate 2 and is emitted to the outside.

[0022] The light-emitting layer 3 is configured by alternately stacking a plurality of first layers 31 and a plurality of second layers 32. In this example, the second layers 32 are disposed on both ends of the light-emitting layer 3 in the stacking direction, and the light-emitting layer 3 contacts the support substrate 2 and the metal layer 4 at the second layers 32.

[0023] The light-emitting layer 3 (first layer 31 and second layer 32) is made of ZnO (zinc oxide). In the light-emitting layer 3, the impurity concentrations of the first layer 31 and the second layer 32 are set so that the first impurity concentration of the first layer 31 is higher than the second impurity concentration of the second layer 32 (in other words, so that the second impurity concentration of the second layer 32 is lower than the first impurity concentration of the first layer 31).

[0024] In this example, the first layer 31 is a layer to which an impurity is added (a doped layer), and the second layer 32 is a layer to which an impurity is not added (an undoped layer). The impurity added to the first layer 31 is Ga (gallium), and the impurity concentration of the first layer 31 (first impurity concentration) is, for example, 1×10 ２０ atoms / cm ３ The impurity concentration (second impurity concentration) of the second layer 32 is, for example, 1×10 １８ atoms / cm ３ In this way, unlike a doped layer in which impurities are intentionally added during formation, an undoped layer refers to a layer in which impurities are not intentionally added during formation, and as a result, the impurity concentration is two orders of magnitude lower (1 / 100 or less) than that of a doped layer. In this example, the thickness of the light-emitting layer 3 is 1 μm, and the thickness of each of the first layers 31 and each of the second layers 32 is 10 nm.

[0025] The metal layer 4 is made of, for example, Al (aluminum). The metal layer 4 reflects the scintillation light from the light-emitting layer 3 toward the support substrate 2. That is, a portion of the scintillation light generated in the light-emitting layer 3 is reflected by the metal layer 4 and then transmitted through the support substrate 2 to be emitted to the outside. Furthermore, when a voltage is applied to the light-emitting layer 3, the metal layer 4 can also be used as an electrode for applying a voltage.

[0026] The results of confirming the characteristics of scintillator 1 will be described below with reference to Figs. 2 to 4. Fig. 2 is a graph showing the comparison results of CL (cathodoluminescence) spectra for Example 1 and Comparative Example 1. The CL spectrum is the spectrum of light generated when accelerated electrons are irradiated onto a target. Example 1 corresponds to the scintillator 1. Comparative Example 1 is a scintillator 1 in which the light-emitting layer 3 does not have multiple layers, and the luminescent layer 3 is 7 x 10 １９ atoms / cm ３ The acceleration voltage of the electron beam incident on the scintillator was set to 10 kV.

[0027] As shown in FIG. 2, the shapes of the CL spectra of Example 1 and Comparative Example 1 are similar, and even in Example 1, in which the light-emitting layer has a multilayer structure (superlattice structure), no defect-derived light emission occurred, as in Comparative Example 1, in which the light-emitting layer has a single-layer structure. Furthermore, from FIG. 2, it can be seen that Example 1 also maintained the same high speed (short light-emitting time) as Comparative Example 1. Furthermore, from FIG. 2, it can be seen that in Example 1, not only is there no defect, but the light emission wavelength is blue-shifted (transitioned to the shorter wavelength side) compared to Comparative Example 1. This indicates that, because there is a lot of light emission in the undoped layer with a low carrier density, light emission due to impurity transitions with long wavelengths and long light-emitting lifetimes is reduced, and the proportion of exciton light emission is increased.

[0028] 3 is a graph showing the voltage dependence of cathodoluminescence for Examples 2-1, 2-2, and 2-3 and Comparative Examples 1 and 2. The graph in FIG. 3 shows the relationship between the acceleration voltage (horizontal axis) of the electron beam incident on the scintillator and the intensity of the scintillation light (vertical axis). Examples 2-1 to 2-3 correspond to the above scintillator 1 in which the thicknesses of the light-emitting layer 3 are 1 μm, 2 μm, and 3 μm, respectively. Comparative Example 2 corresponds to the same example as Comparative Example 1 in which the impurity concentration of the light-emitting layer is 2×10 ２０ atoms / cm ３That is, the impurity concentration of the light-emitting layer of Comparative Example 2 is higher than that of Comparative Example 1. In Examples 2-1 to 2-3 and Comparative Examples 1 and 2, the metal layer 4 was not provided. The current value flowing through the light-emitting layer 3 was 0.8 μA / cm ２ It was decided.

[0029] 3 shows that Examples 2-1 to 2-3 had higher luminous intensity and brightness of the scintillation light than Comparative Examples 1 and 2. Furthermore, a comparison of the luminous intensity of Examples 2-1 to 2-3 in the high acceleration region (the region on the right side in the graph in FIG. 3) shows that the luminance of the scintillation light in the high acceleration region increased significantly as the thickness of light-emitting layer 3 increased.

[0030] FIG. 4 is a table showing the comparison results of the afterglow characteristics for Examples 3-1, 3-2, 3-3, and 3-4 and Comparative Examples 1 and 2. The "90% to 10% afterglow characteristics" shown in the table of FIG. 4 is the time it takes for the brightness of scintillation light generated by cathode luminescence to decrease from 90% at the time of light emission to 10%. Examples 3-1 to 3-4 correspond to the cases where the thicknesses of the light-emitting layer 3 in the scintillator 1 are 1 μm, 2 μm, 3 μm, and 3 μm, respectively. It can be seen from FIG. 4 that the afterglow characteristics of Examples 3-1 to 3-4 were comparable to those of Comparative Examples 1 and 2, and that Examples 3-1 to 3-4 had similar high-speed characteristics to those of Comparative Examples 1 and 2.

[0031] FIG. 5 is a graph showing an example of the distribution of Ga concentration and Zn secondary ion intensity in the light-emitting layer 3 of Example 4. Example 4 differs from the scintillator 1 described above only in the thicknesses of the first layer 31 and the second layer 32 constituting the light-emitting layer 3. In the graph of FIG. 5, the horizontal axis represents the depth from the surface 3a of the light-emitting layer 3 on the metal layer 4 side, the left vertical axis represents the Ga concentration, and the right vertical axis represents the intensity of Zn secondary ions. Measurements were performed using SIMS (Secondary Ion Mass Spectrometry). The distribution of Ga concentration in the graph of FIG. 5 reveals that the light-emitting layer 3 of the scintillator 1 was formed by alternatingly stacking first layers 31 with high impurity concentrations and second layers 32 with low impurity concentrations, each with a thickness of 4 to 5 nm. Note that in the graph of FIG. 5, due to degradation of resolution in the depth direction, the Ga concentration appears smaller than the actual value at deeper positions. Furthermore, from the distribution of Zn secondary ion intensity, it is found that both the first layer 31 and the second layer 32 are layers containing ZnO as a main component, and that Zn is distributed uniformly throughout the light-emitting layer 3 .

[0032] 6 is a graph showing the comparison results of the CL spectra for Examples 5-1, 5-2, 6-1, 6-2, 7-1, and 7-2 (5-1 to 7-2). Examples 5-1 to 7-2 correspond to cases where the thickness of each of the first layer 31 and the second layer 32 in the scintillator 1 was 4 nm in Examples 5-1 and 5-2, 10 nm in Examples 6-1 and 6-2, and 20 nm in Examples 7-1 and 7-2. In Examples 5-1 to 7-2, one pair included one first layer 31 and one second layer 32, and the number of pairs of the first layer 31 and the second layer 32 was set so that the thickness of the light-emitting layer 3 was 1 μm. Specifically, the number of pairs of the first layer 31 and the second layer 32 was 125 pairs in Examples 5-1 and 5-2, 50 pairs in Examples 6-1 and 6-2, and 25 pairs in Examples 7-1 and 7-2. In Examples 5-1 to 7-2, the metal layer 4 was not provided. The acceleration voltage of the electron beam incident on the scintillator was 8 kV. The current value flowing through the light-emitting layer 3 was 0.8 μA / cm ２ The exposure time was 200 ms.

[0033] 6, comparing the emission intensities at the peak wavelengths, it can be seen that the emission intensities of Examples 6-1 and 6-2 were higher than those of Examples 5-1 and 5-2, and that the emission intensities of Examples 5-1 and 5-2 were higher than those of Examples 7-1 and 7-2. This shows that high brightness can be achieved by making the thicknesses of the first layer 31 and the second layer 32 less than 20 nm (20 nm or less). Note that when the light-emitting layer has a single-layer structure and is 1 μm thick, as in Comparative Example 1 described above, the emission intensity is lower than that of Examples 5-1 and 5-2 and higher than that of Examples 7-1 and 7-2.

[0034] With reference to FIG. 7 , the enhancement of luminescence by forming the light-emitting layer 3 into a multilayer structure will be described. FIG. 7 shows only three layers of the first layer 31 and the second layer 32 constituting the light-emitting layer 3. First, when the light-emitting layer has a single-layer structure as in Comparative Example 1 described above, increasing the free electron concentration by Ga doping increases the luminescence intensity, but impairs high-speed performance by increasing the luminescence due to impurity transitions (donor-acceptor luminescence), which has a slow fluorescence velocity, compared to free exciton luminescence, which has a short fluorescence lifetime. Furthermore, absorption of transition energy by free electrons increases non-radiative recombination (Auger effect), quenching slow luminescence (luminescence with a long emission time). This allows for high-speed operation, but makes it difficult to increase brightness. Therefore, the thickness of the light-emitting layer is determined by factors such as electron penetration depth and fluorescence self-absorption. Furthermore, even if an attempt is made to increase the luminescence intensity by increasing the thickness of the light-emitting layer to increase the absorption of incident electron beams, it is difficult to enhance luminescence due to fluorescence self-absorption.

[0035] In contrast, the luminescent layer 3 of the scintillator 1 has a multilayer structure, which allows free electrons from the first layer 31 to diffuse into the second layer 32, thereby increasing the contribution of luminescence in the second layer 32, which has a lower impurity concentration than the first layer. As a result, it is believed that luminescence can be enhanced. That is, as shown in FIG. 7 , the thickness of the first layer 31 is close to the wavelength of electrons, creating an environment in which free electrons A confined in the first layer 31 can easily seep into the second layer 32, and the free electrons A2 supplied to the second layer are believed to contribute to luminescence in the second layer. This reduces the electron concentration in the heavily doped first layer, thereby reducing quenching due to the Auger effect and increasing the luminescence intensity of the first layer. That is, it is believed that functional separation can be achieved, separating carrier generation in the first layer 31 from luminescence in the second layer 32. [Actions and Effects]

[0036] As described above, in the scintillator 1, the light-emitting layer 3 is formed of ZnO, which shortens the emission time of scintillation light and enables higher speeds. Furthermore, the light-emitting layer 3 has a structure (multilayer structure) in which a plurality of first layers 31 having a first impurity concentration and a plurality of second layers 32 having a second impurity concentration lower than the first impurity concentration are alternately stacked. This allows for higher brightness while maintaining high speeds. Thus, the scintillator 1 achieves both higher speeds and higher brightness. Furthermore, in the scintillator 1, the light-emitting layer 3 is formed of ZnO, which allows for uniform formation of the light-emitting layer 3 even when it is necessary to thicken the light-emitting layer 3 or when the light-emitting layer 3 is repeatedly produced.

[0037] The first layer 31 contains Ga as an impurity. The first impurity concentration of the first layer 31 is 4×10 ２０ atoms / cm ３ This advantageously achieves both high speed and high brightness.

[0038] The thickness of the first layer 31 is smaller than 20 nm (20 nm or less). This makes it possible to effectively increase the brightness of the scintillation light. Furthermore, by making the thickness of the first layer 31 10 nm or less, the quantum effect is more strongly exerted, making it possible to more effectively increase the brightness of the light.

[0039] The support substrate 2 is a sapphire substrate having an a-plane as the principal surface 2a, and the light-emitting layer 3 is disposed on the principal surface 2a, thereby suitably achieving the above-mentioned effect of achieving both high speed and high brightness.

[0040] A metal layer 4 is formed on the light-emitting layer 3 on the side opposite to the support substrate 2. This allows the scintillation light from the light-emitting layer 3 to be reflected by the metal layer 4 toward the support substrate 2, thereby improving the light utilization efficiency.

[0041] The metal layer 4 is made of Al, which effectively improves the utilization efficiency of scintillation light.

[0042] As in the modified scintillator 1A shown in Fig. 8 , a protective layer 5 having a band gap larger than that of ZnO may be provided between the light-emitting layer 3 and the metal layer 4. In this case, it is possible to prevent electrons and holes generated in the light-emitting layer 3 from flowing out to the metal layer 4, thereby improving the luminous efficiency of the light-emitting layer 3. In addition, a buffer layer 6 made of ZnO may be provided between the support substrate 2 and the light-emitting layer 3. In this case, the light-emitting layer 3 can be suitably formed on the support substrate 2.

[0043] The present disclosure is not limited to the above-described embodiments and modifications. The materials and shapes of each component are not limited to those described above, and various materials and shapes can be adopted. For example, the impurity added to the first layer 31 is not limited to Ga, but may be Al (aluminum), In (indium), Sb (antimony), F (fluorine), Cl (chlorine), or I (iodine). The metal layer 4 may be made of Ti (titanium). The support substrate 2 does not have to be a sapphire substrate having an a-plane as its main surface, and may be, for example, a sapphire substrate having a c-plane as its main surface. The support substrate 2 does not have to be made of sapphire, and may be made of, for example, quartz, glass, or ScMgAlO ４ The light emitting layer 3 may be formed of scandium magnesium aluminate (ScA) or GaN (Gallium Nitride). The light emitting layer 3 may be in contact with the support substrate 2 and the metal layer 4 at the second layer 32 instead of the first layer 31.

[0044] In the above embodiment, the second layer 32 is an undoped layer. However, like the first layer 31, the second layer 32 may also be a doped layer to which an impurity is added, as long as the first impurity concentration of the first layer 31 is higher than the second impurity concentration of the second layer 32. In this specification, "the light-emitting layer 3 is formed of ZnO" means that the light-emitting layer 3 is composed mainly of ZnO. "The light-emitting layer 3 is formed of ZnO" includes cases where the ZnO constituting the light-emitting layer 3 is doped with an impurity. In the above example, the first layer 31 is a doped layer in which an impurity is added to ZnO, and the second layer 32 is an undoped layer in which an impurity is not added to ZnO, or a doped layer in which an impurity is added to ZnO. "The light-emitting layer 3 is formed of ZnO" does not include cases where the light-emitting layer 3 is composed mainly of GaN, MgZnO, or the like. In the above embodiment, the light-emitting layer 3 is described as emitting light in response to incident charged particles, but the light-emitting layer 3 can also emit light in response to incident photons (e.g., ultraviolet rays). In this case, scintillation light is generated by photoluminescence (PL) in the light-emitting layer 3. The scintillator 1 can achieve both high speed and high brightness in light emission in response to incident photons.

[0045] 9 to 12 show the experimental results for Examples 8-1, 8-2, 8-3, and 8-4. Example 8-4 is not shown in Figures 9, 11, and 12, but is shown only in Figure 10.

[0046] Examples 8-1 to 8-3 correspond to cases in which, in the scintillator 1, the thickness of the undoped second layer 32 was uniformly set to 10 nm, and the thickness of the doped first layer 31 was set to different thicknesses. Specifically, the thickness of the first layer 31 was set to 2.5 nm in Example 8-1, 5.0 nm in Example 8-2, and 10 nm in Example 8-3. In Examples 8-1 to 8-3, one pair included one first layer 31 and one second layer 32, and the number of pairs of first layers 31 and second layers 32 was set so that the thickness of the light-emitting layer 3 was approximately 1 μm. Specifically, the number of pairs of first layers 31 and second layers 32 was 80 pairs in Example 8-1, 66 pairs in Example 8-2, and 40 pairs in Example 8-3. The thicknesses of the light-emitting layer 3 in Examples 8-1 to 8-3 were 1038 nm, 1045 nm, and 1048 nm, respectively. The first impurity concentration of the first layer 31 in Examples 8-1 to 8-3 was 7.96×10 １９ atoms / cm ３ In Examples 8-1 to 8-3, the metal layer 4 was not provided.

[0047] Example 8-4 corresponds to a case where the thickness of the first layer 31 in the scintillator 1 is 4.0 nm and the thickness of the second layer 32 is 4.0 nm. That is, in Example 8-4, unlike Examples 8-1 to 8-3, the thickness of the first layer 31 and the thickness of the second layer 32 were set to be the same. The number of pairs of the first layer 31 and the second layer 32 was set to 50 pairs so that the thickness of the light-emitting layer 3 was 0.4 μm. In Example 8-4, the metal layer 4 was not provided.

[0048] 9 is a graph showing the voltage dependence of cathodoluminescence for Examples 8-1 to 8-3. The graph in Fig. 9 shows the relationship between the acceleration voltage (horizontal axis) of the electron beam incident on the scintillator and the intensity of the scintillation light (vertical axis). The current value flowing through the light-emitting layer 3 was 0.8 μA / cm ２ It was decided.

[0049] 9 shows that Example 8-2, in which the thickness of the first layer 31 was 5.0 nm, had a higher luminance and intensity of scintillation light than Example 8-1, in which the thickness of the first layer 31 was 2.5 nm, and Example 8-3, in which the thickness of the first layer 31 was 15 nm. This suggests that increasing the thickness of the first layer 31 from 2.5 nm to 15 nm increases the luminance of scintillation light up to a predetermined thickness (e.g., 5.0 nm) and then decreases. Therefore, it is believed that increasing the luminance can be achieved by setting the thickness of the first layer 31 to be 2.5 nm or more and 15 nm or less.

[0050] Fig. 10 is a table showing the comparison results of the afterglow characteristics for Examples 8-1 to 8-4. The "90% to 10% afterglow characteristics (CL)" shown in the table of Fig. 10 is the time it takes for the brightness of scintillation light generated by cathode luminescence to decrease from 90% at the time of light emission to 10%.

[0051] 10 shows that Example 8-4 had higher speed performance than Examples 8-1 to 8-3. This shows that when the thickness of the first layer 31 and the thickness of the second layer 32 are the same, the speed performance is improved compared to when the thickness of the first layer 31 and the thickness of the second layer 32 are different. Furthermore, FIG. 10 shows that the afterglow characteristics of Examples 8-1 to 8-3 were comparable, and that Examples 8-1 to 8-3 had similar speed performance regardless of the thickness of the first layer 31.

[0052] FIG. 11 is a graph showing the comparison results of the photoluminescence (PL) intensity for Examples 8-1 to 8-3. Comparing the emission intensities at the peak wavelengths, it can be seen from FIG. 11 that the emission intensity of Example 8-2, in which the first layer 31 had a thickness of 5.0 nm, was greater than the emission intensity of Example 8-1, in which the first layer 31 had a thickness of 2.5 nm, and the emission intensity of Example 8-3, in which the first layer 31 had a thickness of 15 nm. This suggests that increasing the thickness of the first layer 31 from 2.5 nm to 15 nm increases the emission intensity up to a predetermined thickness (e.g., 5.0 nm) and then decreases. Therefore, it is believed that increasing the brightness can be achieved by setting the thickness of the first layer 31 to be 2.5 nm or more and 15 nm or less.

[0053] From the above, it can be seen from Figures 9 and 11 that, regardless of whether the light emission is cathode luminescence or photoluminescence, high brightness can be achieved by setting the thickness of the first layer 31 to be 2.5 nm or more and 15 nm or less.

[0054] Fig. 12 is a table showing the comparison results of the persistence characteristics of Examples 8-1 to 8-3. The "90% to 10% persistence characteristics (PL)" shown in the table of Fig. 12 is the time it takes for the brightness of the scintillation light generated by photoluminescence to decrease from 90% at the time of light emission to 10%. Fig. 12 shows that the persistence characteristics of Examples 8-1 to 8-3 were comparable to each other, and that Examples 8-1 to 8-3 had comparable high-speed performance regardless of the thickness of the first layer 31.

[0055] 1...scintillator, 2...support substrate, 3...luminescent layer, 4...metal layer, 31...first layer, 32...second layer.

Claims

1. A scintillator comprising: a support substrate; and a light-emitting layer formed of ZnO and disposed on the support substrate, the light-emitting layer emitting light in response to the incidence of charged particles or photons, the light-emitting layer having a plurality of first layers having a first impurity concentration, and a plurality of second layers alternately stacked with the plurality of first layers and having a second impurity concentration lower than the first impurity concentration.

2. The scintillator according to claim 1, wherein the impurities contained in the plurality of first layers are Ga, Al, In, Sb, F, Cl or I.

3. The first impurity concentration is 4×10 ２０ atoms / cm ３ 3. The scintillator according to claim 1, wherein:

4. A scintillator according to any one of claims 1 to 3, wherein each of the plurality of first layers has a thickness of 20 nm or less.

5. The support substrate is made of sapphire, quartz, glass, ScMgAlO ４ 5. The scintillator according to claim 1, wherein the scintillator is made of GaN or GaN.

6. A scintillator according to any one of claims 1 to 5, wherein the supporting substrate is a sapphire substrate having an a-plane as its principal surface, and the light-emitting layer is disposed on the principal surface.

7. The scintillator according to any one of claims 1 to 6, further comprising a metal layer formed on said light-emitting layer on the side opposite said supporting substrate.

8. The scintillator according to claim 7, wherein the metal layer is formed of Al or Ti.

9. The scintillator of claim 7 or 8, further comprising a protective layer having a band gap larger than that of ZnO and disposed between the luminescent layer and the metal layer.

10. A scintillator according to any one of claims 1 to 9, further comprising a buffer layer formed of ZnO and disposed between the supporting substrate and the light-emitting layer.

11. A scintillator according to any one of claims 1 to 10, wherein the thickness of each of the plurality of first layers is 2.5 nm or more and 15 nm or less.

12. A scintillator according to any one of claims 1 to 11, wherein the thickness of each of the plurality of first layers is equal to the thickness of each of the plurality of second layers.

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