Scintillator

Abstract

A scintillator is provided with a support substrate and a light-emitting layer that is formed of 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

TECHNICAL FIELD

[0001] The present disclosure relates to a scintillator. BACKGROUND

[0002] In Patent Literature 1, a scintillator provided with a luminescent layer composed of ZnO and generating scintillation light according to the incidence of a radiation is described. In the scintillator described in Patent Literature 1, since the luminescent layer is composed of ZnO, the luminescent lifetime (luminescent time) of the scintillation light is short, and high-speed responsiveness is achieved.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT LITERATURE

[0005] Patent Literature 1: Japanese Patent No. 6676372 SUMMARY

[0006] PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] The scintillator described above can be used for converting electrons into light, for example, in a light detector used in a scanning electron microscope (SEM), a time-of-flight mass spectrometer (TOF-MS), or the like. In such a scintillator, in addition to shortening the luminescent time (high-speeding), it is also required to improve the brightness of light (high-brightening). On the other hand, in the case where the luminescent time is short, the signal amount of light decreases, and the brightness of light can decrease.

[0008] Therefore, an object of one aspect of the present disclosure is to provide a scintillator capable of achieving high-speeding and high-brightening in balance.

[0009] MEANS FOR SOLVING THE PROBLEMS

[0010] The scintillator according to one aspect of the present disclosure is: [1] “a scintillator, wherein a support substrate and a luminescent layer formed of ZnO and disposed on the support substrate to emit light according to the incidence of a charged particle or a photon are provided, the luminescent layer has a plurality of first layers having a first impurity concentration, and a plurality of second layers are alternately stacked with the plurality of first layers and have a second impurity concentration lower than the first impurity concentration”.

[0011] In this scintillator, since the light-emitting layer is formed of ZnO, the emission time of the scintillating light can be shortened, enabling high-speed operation. Furthermore, the light-emitting layer has a structure in which multiple first layers and multiple second layers are alternately stacked, wherein the multiple first layers have a first impurity concentration, and the multiple second layers have a second impurity concentration lower than the first impurity concentration. This allows for maintaining high speed while achieving high brightness. Thus, according to this scintillator, both high speed and high brightness can be achieved.

[0012] The scintillator involved in one aspect of this disclosure may also 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 it may be: [3] "the scintillator according to [1] or [2], wherein the concentration of the first impurity is 4 × 10 20 atoms / cm 3 (atoms / cm) 3 "Below." In these cases, it can appropriately achieve the aforementioned effects of simultaneously realizing high speed and high brightness.

[0013] The scintillator involved in one aspect of this disclosure can also be: [4] "the scintillator according to any one of [1] to [3], wherein the thickness of each of the plurality of first layers is less than 20 nm". In this case, the brightness of the light can be increased more effectively.

[0014] The scintillator involved in one aspect of this disclosure can also be: [5] "the scintillator according to any one of [1] to [4], wherein the supporting substrate is formed of sapphire, quartz, glass, ScMgAlO4 or GaN"; or it can be: [6] "the scintillator according to any one of [1] to [5], wherein the supporting substrate is a sapphire substrate having an a-side as the main surface, and the light-emitting layer is disposed on the main surface." In these cases, the aforementioned effects of achieving both high speed and high brightness can be appropriately achieved.

[0015] The scintillator involved in one aspect of this disclosure may also be: [7] "the scintillator according to any one of [1] to [6], wherein it further comprises: 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 to the support substrate side through the metal layer, thereby improving the light utilization efficiency.

[0016] One aspect of this disclosure relates to a scintillator that can be: [8] "the scintillator according to [7], wherein the metal layer is formed of Al or Ti." In this case, the light utilization efficiency can be effectively improved.

[0017] One aspect of this disclosure relates to a scintillator that can also be: [9] "the scintillator according to [7] or [8], wherein it further comprises: a protective layer having a band gap larger than ZnO and disposed between the light-emitting layer and the metal layer." In this case, it is possible to suppress the outflow of electrons or holes generated in the light-emitting layer to the metal layer, thereby improving the luminous efficiency of the light-emitting layer.

[0018] One aspect of this disclosure relates to a scintillator that can be:

[10] "a scintillator according to any one of [1] to [9], wherein it further comprises: 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.

[0019] The scintillator involved in one aspect of this disclosure may also be:

[11] "the 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." In this case, the brightness of the light can be further improved more effectively.

[0020] The scintillator involved in one aspect of this disclosure may also 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, high speed can be achieved more effectively.

[0021] The effects of the invention

[0022] According to one aspect of this disclosure, a scintillator capable of achieving both high speed and high brightness can be provided. Attached Figure Description

[0023] Figure 1 This is a cross-sectional view of the scintillator involved in the implementation method.

[0024] Figure 2 This is a graph showing the comparison results of CL spectra.

[0025] Figure 3 This is a graph showing the comparison results of the voltage dependence of cathodoluminescence.

[0026] Figure 4 This is a table showing the comparison results of afterglow characteristics.

[0027] Figure 5 This is a graph showing an example of the distribution of Ga concentration in the emitting layer.

[0028] Figure 6 It is a graph showing the comparison results of spectra.

[0029] Figure 7 It is a diagram used to illustrate how a multi-layered structure can enhance light emission.

[0030] Figure 8 This is a cross-sectional view of the scintillator involved in the modified example.

[0031] Figure 9 This is a graph showing the comparison results of the voltage dependence of cathodic emission.

[0032] Figure 10 This is a table showing the comparison results of the afterglow characteristics of cathodic emission.

[0033] Figure 11 This is a chart showing the comparison results of photoluminescence intensity.

[0034] Figure 12 This is a table showing the comparison results of the afterglow characteristics of photoluminescence.

[0035] Symbol Explanation

[0036] 1... scintillator, 2... support substrate, 3... light-emitting layer, 4... metal layer, 31... first layer, 32... second layer. Detailed Implementation

[0037] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, the same or equivalent elements are referred to by the same reference numerals, and repeated descriptions are omitted.

[0038] like Figure 1 As shown, the scintillator 1 includes a support substrate 2, a light-emitting layer 3, and a metal layer 4. The light-emitting layer 3 is disposed on the main surface 2a of the support substrate 2, and the metal layer 4 is disposed on the surface 3a opposite to the support substrate 2 of the light-emitting layer 3. In the scintillator 1, scintillation light (fluorescence) is generated in the light-emitting layer 3 based on the incident light of charged particles (e.g., electrons), and the light-emitting layer 3 emits light. The scintillator 1 can be used, for example, in photodetectors used in scanning electron microscopes, time-of-flight mass spectrometry analysis devices, etc., to convert electrons into light.

[0039] The support substrate 2 is a sapphire substrate (a-side sapphire substrate) having an a-side (crystal plane) as its main surface 2a. The support substrate 2 is transmissive to the scintillating light generated in the light-emitting layer 3. In the scintillator 1, the scintillating light generated in the light-emitting layer 3 passes through the support substrate 2 and is emitted to the outside.

[0040] The light-emitting layer 3 is formed by alternately stacking multiple first layers 31 and multiple second layers 32. In this example, the second layers 32 are disposed at 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 on the second layers 32.

[0041] The light-emitting layer 3 (first layer 31 and second layer 32) is formed 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 such 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, the second impurity concentration of the second layer 32 is lower than the first impurity concentration of the first layer 31).

[0042] In this example, the first layer 31 is a layer with added impurities (doped layer), and the second layer 32 is a layer without added impurities (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 × 10⁻⁶. 20 atoms / cm 3 The degree of impurity concentration in the second layer 32 (second impurity concentration) is, for example, 1 × 10⁻⁶. 18 atoms / cm 3 The degree of doping. In this case, an undoped layer differs from a doped layer, where impurities are intentionally added during formation. It refers to a layer where, by intentionally not adding impurities during formation, the impurity concentration is more than two orders of magnitude lower than that of a doped layer (becoming less than 1 / 100). In this example, the thickness of the light-emitting layer 3 is 1 μm, and the thicknesses of each first layer 31 and each second layer 32 are 10 nm.

[0043] The metal layer 4 is formed, for example, of Al (aluminum). The metal layer 4 reflects the scintillation light from the light-emitting layer 3 to the support substrate 2. That is, a portion of the scintillation light generated in the light-emitting layer 3 is reflected in the metal layer 4 and then emitted outward through the support substrate 2. In addition, the metal layer 4 can also be used as an electrode for voltage application when a voltage is applied to the light-emitting layer 3.

[0044] The following is for reference Figures 2-4 The results confirming the characteristics of the flasher 1 are explained. Figure 2 This is a graph showing the comparison results of the CL (cathodoluminescence) spectra of Example 1 and Comparative Example 1. The CL spectrum refers to the spectrum of light produced when accelerated electrons are irradiated onto an object. Example 1 corresponds to the scintillator 1 described above. Comparative Example 1 corresponds to the scintillator 1 in which the light-emitting layer 3 does not have multiple layers but consists of a 7×10 19 atoms / cm 3 The case involves a single layer with a thickness of 1 μm and a high impurity concentration. The accelerating voltage of the electron beam incident on the scintillator is set to 10 kV.

[0045] like Figure 2As shown, the CL spectra of Example 1 and Comparative Example 1 are similar in shape. In Example 1, where the emitting layer is a multilayer structure (superlattice structure), similarly to Comparative Example 1 where the emitting layer is a single layer structure, no emission originating from defects was generated. Furthermore, due to... Figure 2 It can be seen that in Example 1, the same level of high speed (short light emission time) as in Comparative Example 1 was maintained. Furthermore, from Figure 2 It can be seen that in Example 1, not only are there no defects, but the emission wavelength also exhibits a blue shift (shift towards the shorter wavelength side) compared to Comparative Example 1. This indicates that due to the higher emission in the undoped layer with lower carrier density, the emission caused by inter-impurity transitions with longer emission lifetimes and longer wavelengths is reduced, and the proportion of exciton emission increases.

[0046] Figure 3 This is a graph showing the voltage dependence of cathodic emission for Examples 2-1, 2-2, 2-3 and Comparative Examples 1 and 2. Figure 3 The graph shows the relationship between the accelerating voltage (horizontal axis) of the electron beam incident on the scintillator and the intensity of the scintillating light (vertical axis). Examples 2-1 to 2-3 correspond to cases where the thickness of the light-emitting layer 3 in the scintillator 1 is 1 μm, 2 μm, and 3 μm, respectively. Comparative Example 2 corresponds to the case where the impurity concentration of the light-emitting layer in Comparative Example 1 is 2 × 10⁻⁶. 20 atoms / cm 3 In this case, the impurity concentration of the light-emitting layer in Comparative Example 2 was higher than that in 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 flowing through the light-emitting layer 3 was set to 0.8 μA / cm. 2 .

[0047] Depend on Figure 3 It can be seen that in Examples 2-1 to 2-3, compared with Comparative Examples 1 and 2, the luminous intensity of the flickering light is greater, indicating high brightness. Furthermore, based on the high acceleration region ( Figure 3 As can be seen from the comparison of the luminescence intensity of Examples 2-1 to 2-3 in the right area of ​​the chart, the thicker the luminescent layer 3, the greater the brightness of the flicker light in the high acceleration region.

[0048] Figure 4 This is a table showing the comparison results of the afterglow characteristics of Examples 3-1, 3-2, 3-3, 3-4 and Comparative Examples 1 and 2. Figure 4 The "90%→10% afterglow characteristic" shown in the table refers to the time it takes for the brightness of the scintillating light generated by cathode luminescence to decrease from 90% to 10% of the emission time. Examples 3-1 to 3-4 correspond to cases where the thickness of the light-emitting layer 3 in the above-described scintillator 1 is 1 μm, 2 μm, 3 μm, and 3 μm, respectively. Figure 4It can be seen that the afterglow characteristics of Examples 3-1 to 3-4 are the same as those of Comparative Examples 1 and 2, and Examples 3-1 to 3-4 have the same high speed as Comparative Examples 1 and 2.

[0049] Figure 5 This 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 thickness of the first layer 31 and the second layer 32 constituting the light-emitting layer 3. Figure 5 In the graph, the horizontal axis represents the depth of the luminescent layer 3 from the surface 3a of the metal layer 4, 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). Figure 5 As can be seen from the Ga concentration distribution in the graph, in the light-emitting layer 3 of the scintillator 1, the first layer 31 with high impurity concentration and the second layer 32 with low impurity concentration are alternately stacked with a thickness of 4-5 nm. Furthermore, in Figure 5 In the graph, due to the decreased resolution in the depth direction, the Ga concentration becomes smaller than the actual value at deeper locations. Furthermore, the distribution of Zn secondary ion intensity indicates that both the first layer 31 and the second layer 32 are primarily composed of ZnO, and Zn is uniformly distributed throughout the luminescent layer 3.

[0050] Figure 6 This is a chart showing the comparison results of the CL spectra of 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 the cases where the thicknesses of the first layer 31 and the second layer 32 in the above-described scintillator 1 are 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, layers having one layer each of the first layer 31 and the second layer 32 are considered as a pair, and the number of pairs of the first layer 31 and the second layer 32 is set such that the thickness of the light-emitting layer 3 is 1 μm. Specifically, the number of pairs of the first layer 31 and the second layer 32 is set to 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 accelerating voltage of the electron beam incident on the scintillator was set to 8 kV. The current flowing through the light-emitting layer 3 was set to 0.8 μA / cm. 2 The exposure time is set to 200ms.

[0051] Depend on Figure 6It can be seen that, when comparing the luminescence intensity at the peak wavelength, the luminescence intensity of Examples 6-1 and 6-2 is higher than that of Examples 5-1 and 5-2, and the luminescence intensity of Examples 5-1 and 5-2 is higher than that of Examples 7-1 and 7-2. Therefore, it can be seen that by making the thickness of the first layer 31 and the second layer 32 less than 20 nm (set to be less than 20 nm), high brightness can be achieved. Furthermore, in the case where the luminescent layer has a single-layer structure and the thickness of the luminescent layer is 1 μm, as in Comparative Example 1 described above, the luminescence intensity is smaller than that of Examples 5-1 and 5-2 and larger than that of Examples 7-1 and 7-2.

[0052] Reference Figure 7 The enhancement of light emission produced by setting the light-emitting layer 3 as a multilayer structure will be explained. Figure 7 Only three layers, namely the first layer 31 and the second layer 32, constituting the luminescent layer 3 are shown. First, in the case of a monolayer structure of the luminescent layer as described in Comparative Example 1, increasing the free electron concentration by doping with Ga increases the luminescence intensity. However, compared to free exciton luminescence with its short fluorescence lifetime, luminescence caused by impurity transitions with slow fluorescence speeds (donor-acceptor pair luminescence) increases, impairing high-speed performance. Furthermore, the absorption of transition energy caused by free electrons leads to an increase in non-luminescent recombination (Auger effect), causing slow luminescence (luminescence with long luminescence times) to extinct. Therefore, while high speed can be achieved, it is difficult to increase brightness. Thus, the thickness of the luminescent layer is determined based on factors such as electron penetration length and fluorescence self-absorption. Additionally, even if one wants to increase the amount of luminescence by increasing the absorption of the incident electron beam through thickening the luminescent layer, it is difficult to enhance luminescence due to fluorescence self-absorption.

[0053] In contrast, in the light-emitting layer 3 of the aforementioned scintillator 1, by having a multi-layered structure, free electrons from the first layer 31 can diffuse to the second layer 32, increasing the contribution of light emission in the second layer 32, which has a lower impurity concentration than the first layer. As a result, it is believed that light emission can be enhanced. That is, as... Figure 7 As shown, it is believed that because the thickness of the first layer 31 is close to the wavelength of electrons, free electrons A, which are confined in the first layer 31, can easily diffuse into the environment of the second layer 32. The free electrons A2 supplied to the second layer contribute to the luminescence in the second layer. As a result, the electron concentration of the heavily doped first layer decreases, thus reducing the extinction caused by the Auger effect and increasing the luminescence intensity of the first layer. That is, it is believed that the function of separating the generation of charge carriers in the first layer 31 from the luminescence in the second layer 32 can be achieved.

[0054] [Functions and Effects]

[0055] As described above, in the scintillator 1, since the light-emitting layer 3 is formed of ZnO, the emission time of the scintillating light can be shortened, and high speed can be achieved. Furthermore, the light-emitting layer 3 has a structure in which multiple first layers 31 and multiple second layers 32 are alternately stacked (multilayer structure), wherein the multiple first layers 31 have a first impurity concentration, and the multiple second layers 32 have a second impurity concentration lower than the first impurity concentration. Therefore, high speed can be maintained and high brightness can be achieved. In this way, the scintillator 1 can achieve both high speed and high brightness. In addition, since the light-emitting layer 3 is formed of ZnO in the scintillator 1, the light-emitting layer 3 can be uniformly formed even when it is necessary to thicken the light-emitting layer 3 or to repeatedly produce the light-emitting layer 3.

[0056] The first layer 31 contains Ga as an impurity. Furthermore, the concentration of the first impurity in the first layer 31 is 4 × 10⁻⁶. 20 atoms / cm 3 Therefore, it can appropriately achieve the aforementioned effects of simultaneously realizing high speed and high brightness.

[0057] The thickness of the first layer 31 is less than 20 nm. This allows for a more effective increase in the brightness of the flickering light. Furthermore, by setting the thickness of the first layer 31 to less than 10 nm, the quantum effect is more strongly manifested, thus further enhancing the brightness of the light.

[0058] The support substrate 2 is a sapphire substrate with surface a as the main surface 2a, and the light-emitting layer 3 is disposed on the main surface 2a. Therefore, it can appropriately achieve the aforementioned effects of simultaneously realizing high speed and high brightness.

[0059] A metal layer 4 is formed on the light-emitting layer 3 on the opposite side of the support substrate 2. As a result, the flashing light from the light-emitting layer 3 can be reflected back to the support substrate 2 through the metal layer 4, thereby improving the light utilization efficiency.

[0060] Metal layer 4 is formed of Al. This allows for a more effective increase in the utilization efficiency of the scintillation light.

[0061] [Variation Example]

[0062] like Figure 8 As with the scintillator 1A in the modified example shown, a protective layer 5 having a band gap larger than that of ZnO can be provided between the light-emitting layer 3 and the metal layer 4. In this case, the outflow of electrons and holes generated in the light-emitting layer 3 to the metal layer 4 can be suppressed, and the luminous efficiency in the light-emitting layer 3 can be improved. Alternatively, a buffer layer 6 formed of ZnO can be provided between the support substrate 2 and the light-emitting layer 3. In this case, the light-emitting layer 3 can be appropriately formed on the support substrate 2.

[0063] This disclosure is not limited to the embodiments and modifications described above. The materials and shapes of each structure are not limited to those described above, and a wide variety of materials and shapes can be used. For example, the impurities added to the first layer 31 are not limited to Ga, but can also be Al (aluminum), In (indium), Sb (antimony), F (fluorine), Cl (chlorine), or I (iodine). The metal layer 4 can also be formed of Ti (titanium). The support substrate 2 may not be a sapphire substrate with surface a as the main surface; for example, it can be a sapphire substrate with surface c as the main surface. The support substrate 2 may not be formed of sapphire; for example, it can be formed of quartz, glass, ScMgAlO4 (magnesium scandium aluminate), or GaN (gallium nitride). The light-emitting layer 3 can also replace the first layer 31 and contact the support substrate 2 and the metal layer 4 in the second layer 32.

[0064] In the above embodiment, the second layer 32 is an undoped layer, but the second layer 32 can also be a doped layer with added impurities, just like the first layer 31, 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 the case where impurities are added to the ZnO constituting the light-emitting layer 3. In the above example, the first layer 31 is a doped layer with added impurities in ZnO, and the second layer 32 is an undoped layer with no added impurities in ZnO, or a doped layer with added impurities in ZnO. "The light-emitting layer 3 is formed of ZnO" does not include, for example, the case where the light-emitting layer 3 is composed mainly of GaN, MgZnO, etc. In the above embodiment, it is described that the light-emitting layer 3 emits light according to the incident light of charged particles, but the light-emitting layer 3 can also emit light according to the incident light of photons (e.g., ultraviolet light). In this case, scintillation light is generated in the light-emitting layer 3 by photoluminescence (PL). According to scintillator 1, it is also possible to achieve both high speed and high brightness for the emission corresponding to the incident photon.

[0065] Figures 9-12 This represents the experimental results for Examples 8-1, 8-2, 8-3, and 8-4. Example 8-4 was not included in... Figure 9 , Figure 11 , Figure 12 As shown in the figure, only Figure 10 As shown in the image.

[0066] Examples 8-1 to 8-3 are equivalent to the cases in the above-described scintillator 1 where the thickness of the undoped second layer 32 is consistently set to 10 nm, while the thickness of the doped first layer 31 is set to different thicknesses. Specifically, the thickness of the first layer 31 is 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, structures having one first layer 31 and one second layer 32 are considered as a pair, and the number of pairs of the first layer 31 and the second layer 32 is set such that the thickness of the light-emitting layer 3 is approximately 1 μm. Specifically, the number of pairs of the first layer 31 and the second layer 32 is: 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 are 1038 nm, 1045 nm, and 1048 nm, respectively. The concentration of the first impurity in the first layer 31 of Examples 8-1 to 8-3 is 7.96 × 10⁻⁶. 19 atoms / cm 3 In Examples 8-1 to 8-3, the metal layer 4 was not provided.

[0067] Example 8-4 corresponds to the case in the scintillator 1 described above, where the thickness of the first layer 31 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 are set to be the same. The number of pairs of the first layer 31 and the second layer 32 is set to 50, with the thickness of the light-emitting layer 3 being 0.4 μm. In Example 8-4, the metal layer 4 is not provided.

[0068] Figure 9 This is a graph showing the voltage dependence of cathodic emission in Examples 8-1 to 8-3. Figure 9 The graph shows the relationship between the accelerating voltage of the electron beam incident on the scintillator (horizontal axis) and the intensity of the scintillating light (vertical axis). The current flowing through the luminescent layer 3 is set to 0.8 μA / cm. 2 .

[0069] according to Figure 9 It can be seen that in Example 8-2, where the thickness of the first layer 31 is 5.0 nm, the luminous intensity of the flashing light is greater and exhibits high brightness compared to Examples 8-1, where the thickness of the first layer 31 is 2.5 nm, and Examples 8-3, where the thickness of the first layer 31 is 15 nm. Therefore, it is considered that if the thickness of the first layer 31 is increased from 2.5 nm to 15 nm, the luminous intensity of the flashing light increases to a predetermined thickness (e.g., 5.0 nm) and then decreases. Therefore, it is considered that by setting the thickness of the first layer 31 to be 2.5 nm or more and 15 nm or less, high brightness can be achieved.

[0070] Figure 10 This is a table showing the comparison results of the afterglow characteristics of Examples 8-1 to 8-4. Figure 10 The “90%→10% afterglow characteristic (CL)” shown in the table refers to the time it takes for the brightness of the scintillation light generated by cathode emission to decrease from 90% to 10% of the emission time.

[0071] Depend on Figure 10 It can be seen that, compared with Examples 8-1 to 8-3, Example 8-4 exhibits higher speed performance. Therefore, it can be concluded 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 thicknesses of the first layer 31 and the second layer 32 are different. Furthermore, from... Figure 10 It can be seen that the afterglow characteristics of Examples 8-1 to 8-3 are of the same degree, and Examples 8-1 to 8-3 are independent of the thickness of the first layer 31 and have the same degree of high speed.

[0072] Figure 11 This is a graph showing the comparison results of the photoluminescence (PL) intensity of Examples 8-1 to 8-3. According to... Figure 11 It can be seen that, when comparing the luminescence intensity at the peak wavelength, the luminescence intensity of Example 8-2, where the thickness of the first layer 31 is 5.0 nm, is greater than that of Example 8-1, where the thickness of the first layer 31 is 2.5 nm, and the luminescence intensity of Example 8-3, where the thickness of the first layer 31 is 15 nm. Therefore, it is considered that if the thickness of the first layer 31 is increased from 2.5 nm to 15 nm, the luminescence intensity increases to a predetermined thickness (e.g., 5.0 nm) and then decreases. Therefore, it is believed that by setting the thickness of the first layer 31 to be 2.5 nm or more and 15 nm or less, high brightness can be achieved.

[0073] The above is from Figure 9 and Figure 11 They believe that even in the case of cathodic emission and photoluminescence, high brightness can be achieved by setting the thickness of the first layer 31 to be above 2.5 nm and below 15 nm.

[0074] Figure 12 This is a table showing the comparison results of the afterglow characteristics of Examples 8-1 to 8-3. Figure 12 The "90%→10% afterglow characteristic (PL)" shown in the table refers to the time it takes for the brightness of the flickering light generated by photoluminescence to decrease from 90% to 10% of its initial value. Figure 12 It can be seen that the afterglow characteristics of Examples 8-1 to 8-3 are of the same degree. In Examples 8-1 to 8-3, regardless of the thickness of the first layer 31, they have the same degree of high speed.

Claims

1. A scintillator, wherein a support substrate, and a light emitting layer formed of ZnO and disposed on the support substrate to emit light in accordance with incidence of a charged particle or a photon, the light emitting layer has a plurality of first layers having a first impurity concentration, and a plurality of second layers stacked alternately 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 impurity included in the plurality of first layers is Ga, Al, In, Sb, F, Cl, or I.

3. The scintillator according to claim 1 or 2, wherein The first impurity concentration is 4 x 10 20 atoms / cm 3 The following.

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

5. The scintillator according to any one of claims 1 to 4, wherein the support substrate is formed of sapphire, quartz, glass, ScMgAlO4, or GaN.

6. The scintillator according to any one of claims 1 to 5, wherein the support substrate is a sapphire substrate having an a-plane as a main surface, the light emitting layer is disposed on the main surface.

7. The scintillator according to any one of claims 1 to 6, wherein a metal layer is further provided on the light emitting layer on the opposite side from the support substrate.

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

9. The scintillator according to claim 7 or 8, wherein a protective layer having a larger band gap than ZnO is further provided between the light emitting layer and the metal layer.

10. The scintillator according to any one of claims 1 to 9, wherein a buffer layer formed of ZnO is further provided between the support substrate and the light emitting layer.

11. The 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. The 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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