Light-emitting body

Abstract

A light-emitting body according to the present invention converts an incident electron beam into fluorescence. The light-emitting body comprises a substrate that transmits fluorescence and a quantum well structure part that is formed on one surface of the substrate and emits fluorescence when struck by an electron beam. The quantum well structure part has a first wavelength layer that emits fluorescence of a first wavelength in response to being struck by an electron beam and a second wavelength layer that is layered on the first wavelength layer and emits fluorescence of a second wavelength that is shorter than the first wavelength in response to being struck by an electron beam.

Description

Luminous body

[0001] This disclosure relates to a light-emitting device.

[0002] Light-emitting materials that convert incident electron beams into fluorescence are known. As an example of this type of technology, Patent Document 1 describes a scintillator light-emitting part formed by creating a quantum well structure on a sapphire substrate.

[0003] Patent No. 6666626

[0004] In recent years, for example, in order to separate electron beams of different energies incident on a light-emitting material, there is a need for a light-emitting material that emits multiple colors corresponding to the energy of the incident electron beam. Therefore, the object of this disclosure is to provide a light-emitting material that can emit multiple colors corresponding to the energy of the incident electron beam.

[0005] The light-emitting material according to the present disclosure is [1] "a light-emitting material that converts an incident electron beam into fluorescence, comprising: a substrate transparent to fluorescence; and a quantum well structure formed on one surface of the substrate, which emits fluorescence upon incidence of the electron beam, wherein the multiple quantum well structure comprises: a first wavelength layer which emits fluorescence of a first wavelength in response to incidence of the electron beam; and a second wavelength layer laminated on the first wavelength layer which emits fluorescence of a second wavelength shorter than the first wavelength in response to incidence of the electron beam."

[0006] In this light-emitting material, when an electron beam is incident on it, fluorescence is emitted in the wavelength layer on the electron beam incident side of the first and second wavelength layers (hereinafter also referred to as the "incident wavelength layer"). At this time, for example, if the energy of the electron beam is low, the electron beam will not reach the wavelength layer on the opposite side of the electron beam incident side of the first and second wavelength layers (hereinafter also referred to as the "opposite wavelength layer"), and the opposite wavelength layer will not emit fluorescence. On the other hand, for example, if the energy of the electron beam is high, the electron beam is more likely to reach the opposite wavelength layer, and as a result, in addition to emitting fluorescence in the incident wavelength layer, fluorescence of a different wavelength from that fluorescence will be emitted in the opposite wavelength layer. In other words, the light-emitting material according to this disclosure makes it possible to emit light in multiple colors depending on the energy of the incident electron beam.

[0007] The light-emitting material according to this disclosure may also be [2] "the light-emitting material according to [1], wherein the quantum well structure is configured such that one of the first wavelength layer and the second wavelength layer, opposite to the electron beam incident surface of the quantum well structure, is sensitive to the electron beam having an energy of a predetermined value or higher." In this case, the light-emitting material can emit light in multiple colors depending on whether the energy of the incident electron beam is above a predetermined value or higher.

[0008] The light-emitting material according to this disclosure may also be [3] "the light-emitting material according to [2], wherein the quantum well structure is such that the thickness of the other of the first and second wavelength layers is set such that one of the first and second wavelength layers, on the side opposite to the electron beam incident surface, is sensitive to electron beams with energy equal to or greater than the predetermined value." In this case, it becomes possible to set the emission of multiple colors depending on whether the energy of the incident electron beam is equal to or greater than the predetermined value by setting the thickness of the incident-side wavelength layer.

[0009] The light-emitting material according to this disclosure may be [4] "the light-emitting material according to any one of [1] to [3], wherein the first wavelength layer and the second wavelength layer each include a plurality of light-emitting layers made of a nitride semiconductor containing Ga and In, and the proportion of In in the composition of the plurality of light-emitting layers included in the first wavelength layer is greater than the proportion of In in the composition of the plurality of light-emitting layers included in the second wavelength layer." In this case, the first wavelength layer and the second wavelength layer can be specifically configured.

[0010] The light-emitting material according to this disclosure may be [5] "the light-emitting material according to any one of [1] to [4], wherein the first wavelength layer includes a plurality of barrier layers, and the plurality of barrier layers included in the first wavelength layer include a first barrier layer and a second barrier layer located on the electron beam incident surface side of the quantum well structure relative to the first barrier layer, and the first barrier layer is thicker than the second barrier layer." In this case, it is possible to improve the luminescence efficiency of the light-emitting material and increase the luminescence intensity.

[0011] The light-emitting material according to this disclosure may be [6] "the light-emitting material according to any one of [1] to [5] wherein the second wavelength layer includes a plurality of barrier layers, and the plurality of barrier layers included in the second wavelength layer have the same thickness as each other." In this case, it is possible to improve the luminescence efficiency of the light-emitting material and increase the luminescence intensity.

[0012] The light-emitting material according to this disclosure may be [7] "the light-emitting material according to any one of [1] to [6] wherein the first wavelength layer and the second wavelength layer each include a plurality of barrier layers, and the average thickness of the plurality of barrier layers included in the first wavelength layer is greater than the average thickness of the plurality of barrier layers included in the second wavelength layer." In this case, it is possible to improve the luminescence efficiency of the light-emitting material and increase the luminescence intensity.

[0013] The light-emitting material according to this disclosure may be [8] "the light-emitting material according to any one of [1] to [7] wherein the first wavelength layer is laminated on the electron beam incident surface side of the quantum well structure on the second wavelength layer." In this case, it is possible to suppress the excitation of the first wavelength layer by short-wavelength fluorescence emitted in the second wavelength layer.

[0014] According to one aspect of the present invention, it is possible to provide a light-emitting body that can emit light in multiple colors depending on the energy of the incident electron beam.

[0015] Figure 1 is a cross-sectional view showing the configuration of the light-emitting element according to the embodiment. Figure 2(a) is a cross-sectional view showing the configuration of the long-wavelength layer of the light-emitting element in Figure 1. Figure 2(b) is a cross-sectional view showing the configuration of the short-wavelength layer of the light-emitting element in Figure 1. Figure 3 is a graph illustrating the fluorescence emitted from the multiple quantum well structure in Figure 1. Figure 4 is a graph showing the relationship between the energy of the electron beam incident on the light-emitting element in Figure 1 and the relative integrated intensity of each fluorescence. Figure 5 is a table showing the results of evaluating the fluorescence brightness in various examples where the configuration of the multiple quantum well structure in Figure 1 is changed.

[0016] The embodiments will be described in detail below with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions are omitted.

[0017] Figure 1 is a cross-sectional view showing the configuration of the light-emitting body 1 according to the embodiment. Figure 1 shows a cross-section along the thickness direction of the light-emitting body 1 (the same applies to Figures 2(a) and 2(b) below). As shown in Figure 1, the light-emitting body 1 converts an incident electron beam E into fluorescence. The light-emitting body 1 comprises a substrate 10, a multiple quantum well structure (quantum well structure) 20 formed on a main surface 12a which is one surface of the substrate 10, and a conductive layer 30 provided on the multiple quantum well structure 20.

[0018] The substrate 10 is a plate-shaped member that is transparent (in other words, light-transmitting) to the wavelength of fluorescence emitted from the multiple quantum well structure 20. The constituent material of the substrate 10 is not particularly limited as long as it transmits the light emitted from the multiple quantum well structure 20 and allows for the epitaxial growth of the multiple quantum well structure 20. In one example, the substrate 10 is a sapphire substrate. In another example, the substrate 10 transmits light with a wavelength of 170 nm or more. The substrate 10 has a main surface (one surface) 10a as the surface facing the conductive layer 30.

[0019] The multiple quantum well structure 20 is a portion that emits fluorescence upon incidence of an electron beam E, and is formed on the main surface 10a of the substrate 10. Emitting fluorescence means emitting light with a emission intensity above a certain level, or in other words, emitting light with an emission intensity above a certain level. The multiple quantum well structure 20 is a layer epitaxially grown on the main surface 10a of the substrate 10. The surface of the multiple quantum well structure 20 on the conductive layer 30 side constitutes the electron beam incidence surface S of the multiple quantum well structure 20. The multiple quantum well structure 20 has a long-wavelength layer (first wavelength layer) 20A and a short-wavelength layer (second wavelength layer) 20B laminated on the substrate 10 side of the long-wavelength layer 20A.

[0020] The long-wavelength layer 20A is a wavelength layer that emits fluorescence SA (see Figure 3) at a first wavelength in response to the electron beam E. The long-wavelength layer 20A is laminated on the side of the electron beam incident surface S on the short-wavelength layer 20B. The short-wavelength layer 20B is a wavelength layer that emits fluorescence SB (see Figure 3) at a second wavelength shorter than the first wavelength in response to the electron beam E. The short-wavelength layer 20B is laminated on the substrate 10 side of the long-wavelength layer 20A (i.e., the side opposite to the electron beam incident surface S).

[0021] Figure 2(a) is a cross-sectional view showing the configuration of the long-wavelength layer 20A of the light-emitting body 1 in Figure 1. As shown in Figure 2(a), the long-wavelength layer 20A includes a plurality of light-emitting layers 21A and a plurality of barrier layers 22A. The light-emitting layer 21A is a layer composed of a material that emits fluorescence when exposed to an electron beam E. The light-emitting layer 21A is composed of a nitride semiconductor containing, for example, Ga and In, and specifically In x Ga 1-x It is composed of a nitride semiconductor mainly containing N (0 < x < 1) crystals. In one example, the light-emitting layer 21A is made of Si-doped In x Ga 1-x It is composed of N crystals. The composition of the multiple light-emitting layers 21A constituting the long-wavelength layer 20A is the same as that of the others. The thickness of the multiple light-emitting layers 21A constituting the long-wavelength layer 20A is equal to that of the others.

[0022] The barrier layer 22A has a band gap energy greater than that of the light-emitting layer 21A. By sandwiching the light-emitting layer 21A between the barrier layers 22A, electrons can be efficiently collected in the light-emitting layer 21A and converted into fluorescence. The barrier layer 22A is a nitride semiconductor layer mainly containing GaN crystals. In one example, the barrier layer 22A consists of Si-doped GaN crystals. The barrier layer 22A may also contain other group III atoms (e.g., In) besides Ga. The compositions of the multiple barrier layers 22A constituting the long-wavelength layer 20A may be equal to each other. The long-wavelength layer 20A is configured such that the thickness of the multiple barrier layers 22A becomes thinner as it approaches the electron beam incident surface S. In other words, in the long-wavelength layer 20A, the multiple barrier layers 22A have a gradient structure.

[0023] Figure 2(b) is a cross-sectional view showing the configuration of the short-wavelength layer 20B of the light-emitting body 1 in Figure 1. As shown in Figure 2(b), the short-wavelength layer 20B includes a plurality of light-emitting layers 21B and a plurality of barrier layers 22B. The light-emitting layer 21B is a layer composed of a material that emits light when it receives an electron beam E. The light-emitting layer 21B is composed of a nitride semiconductor containing, for example, Ga and In, and specifically In ｙ Ga 1-ｙ It is composed of a nitride semiconductor mainly containing N (0 < y < 1) crystals. In one example, the light-emitting layer 21B is made of Si-doped In ｙ Ga1-ｙ It is made of N crystals. The composition of the multiple light-emitting layers 21B that make up the short-wavelength layer 20B is the same as that of the other. The thickness of the multiple light-emitting layers 21B that make up the short-wavelength layer 20B is equal to that of the other.

[0024] The barrier layer 22B has a band gap energy greater than that of the light-emitting layer 21B. By sandwiching the light-emitting layer 21B between the barrier layers 22B, electrons can be efficiently collected in the light-emitting layer 21B and converted into fluorescence. The barrier layer 22B is a nitride semiconductor layer mainly containing GaN crystals. In one example, the barrier layer 22B consists of Si-doped GaN crystals. The barrier layer 22B may also contain other Group III atoms (e.g., In) besides Ga. The compositions of the multiple barrier layers 22B constituting the short-wavelength layer 20B may be equal to each other. The multiple barrier layers 22B are configured such that the thicknesses of the multiple barrier layers 22B are the same. In other words, in the short-wavelength layer 20B, the multiple barrier layers 22B have a constant-thickness layer structure. In this embodiment, the statement that the thickness of one layer is equal to the thickness of the other layer means that the difference in thickness between one layer and the other layer is ±10% or less of the thickness of the other layer.

[0025] In this embodiment, the long-wavelength layer 20A includes six light-emitting layers 21A and six barrier layers 22A. The thickness of each of the multiple light-emitting layers 21A is the same at 1.5 nm. The thicknesses of the multiple barrier layers 22A, in order from the electron beam incident surface S, are 10 nm, 20 nm, 150 nm, 200 nm, 240 nm, and 260 nm. The short-wavelength layer 20B includes ten light-emitting layers 21B and eleven barrier layers 22B. The thickness of each of the multiple light-emitting layers 21B is the same at 1.5 nm. The thickness of each of the multiple barrier layers 22B is the same at 100 nm.

[0026] The proportion of In in the composition of the multiple light-emitting layers 21A contained in the long-wavelength layer 20A is greater than the proportion of In in the composition of the multiple light-emitting layers 21B contained in the short-wavelength layer 20B. In the composition formulas of the light-emitting layers 21A and 21B described above, y < x < 1 and 0 < y < x < 1. In the light-emitting layers 21A and 21B, the wavelength of the emitted fluorescence becomes longer as the In composition increases (and shorter as the In composition decreases). The average thickness of the multiple barrier layers 22A contained in the long-wavelength layer 20A is greater than the average thickness of the multiple barrier layers 22B contained in the short-wavelength layer 20B. In other words, the average thickness of the multiple barrier layers 22B is less than or equal to the average thickness of the multiple barrier layers 22A.

[0027] Figure 3 is a graph illustrating the fluorescence SA and SB emitted from the multiple quantum well structure 20. In Figure 3, the horizontal axis represents wavelength, and the vertical axis represents relative emission intensity. As shown in Figure 3, for example, the first wavelength fluorescence SA emitted from the long-wavelength layer 20A has a peak wavelength of 440 nm. For example, the second wavelength fluorescence SB emitted from the short-wavelength layer 20B has a peak wavelength of 390 nm. The first wavelength of fluorescence SA and the second wavelength of fluorescence SB correspond to their respective peak wavelengths. The difference ΔP between the first and second wavelengths is, for example, 50 nm. Note that the first wavelength of fluorescence SA and the second wavelength of fluorescence SB are not limited to peak wavelengths, but may be, for example, the average value of the emission peak wavelength range.

[0028] Figure 4 is a graph showing the relationship between the energy of the electron beam E incident on the light emitter 1 and the relative integrated intensity of each fluorescence SA and SB. In Figure 4, the horizontal axis represents the acceleration voltage of the electron beam E, which corresponds to the energy of the electron beam E incident on the light emitter 1. The vertical axis represents the relative integrated intensity, which is, for example, the relative value of the intensity at the peak wavelength. As shown in Figure 4, when the energy of the electron beam E incident on the light emitter 1 is above the lower limit threshold α and below a predetermined value β, fluorescence SA is emitted in the long-wavelength layer 20A, but fluorescence SB is not emitted in the short-wavelength layer 20B.

[0029] On the other hand, if the energy of the electron beam E incident on the light-emitting body 1 is greater than or equal to a predetermined value β, fluorescence SA is emitted in the long-wavelength layer 20A, and fluorescence SB is emitted in the short-wavelength layer 20B. In other words, the multiple quantum well structure 20 is configured such that the short-wavelength layer 20B is sensitive to electron beams E incident on the light-emitting body 1 whose energy is greater than or equal to a predetermined value. The predetermined value is not specifically defined, but for example, it is 15 kV.

[0030] Specifically, in the multiple quantum well structure 20, the thickness of the long-wavelength layer 20A is set such that the short-wavelength layer 20B is sensitive to electron beams E whose energy is greater than or equal to a predetermined value β when incident on the light-emitting body 1. More specifically, it is set as follows: That is, for example, if the long-wavelength layer 20A is thicker, the energy required to pass through the long-wavelength layer 20A increases accordingly. For example, if an electron beam E with high energy is incident on the electron beam incident surface S, the electron beam E will reach the short-wavelength layer 20B on the substrate 10 side, but if an electron beam with low energy is incident on the electron beam incident surface S, the electron beam E will not reach the short-wavelength layer 20B. In other words, if an electron beam E with high energy is incident on the electron beam incident surface S, the short-wavelength layer 20B will emit fluorescence SB, but if an electron beam E with low energy is incident on the electron beam incident surface S, the short-wavelength layer 20B will not emit fluorescence SB.

[0031] On the other hand, if the long-wavelength layer 20A is thin, the energy required for the electron beam E to pass through the long-wavelength layer 20A is reduced accordingly. Therefore, even if an electron beam E with low energy is incident on the electron beam incident surface S, the electron beam E will reach the short-wavelength layer 20B. In other words, even if an electron beam E with low energy is incident on the electron beam incident surface S, the short-wavelength layer 20B will emit fluorescence SB. Based on this understanding, in the multiple quantum well structure 20, the thickness of the long-wavelength layer 20A is set such that when an electron beam E with an energy of a predetermined value β or more is incident on the long-wavelength layer 20A from the electron beam incident surface S, it will pass through the long-wavelength layer 20A while emitting fluorescence SA, reach the short-wavelength layer 20B, and emit fluorescence SB there.

[0032] The conductive layer 30 is used as one electrode for guiding electrons to the light emitter 1. The conductive layer 30 mainly contains, for example, a metal, and mainly contains aluminum (Al) in one embodiment. The thickness of the conductive layer 30 is, for example, 10 nm or more and 1000 nm or less, and is approximately 300 nm in one embodiment. When the conductive layer 30 mainly contains a metal, the conductive layer 30 also functions as a light reflection film. That is, part of the fluorescence generated in the multiple quantum well structure portion 20 directly reaches the substrate 10 from the multiple quantum well structure portion 20, transmits through the substrate 10, and is emitted to the outside of the light emitter 1, while the remaining part of the fluorescence generated in the multiple quantum well structure portion 20 reaches the conductive layer 30 from the multiple quantum well structure portion 20, is reflected by the conductive layer 30, then transmits through the substrate 10, and is emitted to the outside of the light emitter 1.

[0033] An example of a method for producing the light emitter 1 will be described. First, the substrate 10 is introduced into a growth chamber of a Metal-Organic Vapor Phase Epitaxy (MOVPE) apparatus, and heat treatment is performed at 1100°C for 10 minutes in a hydrogen atmosphere to clean the main surface 12a. Then, the temperature of the substrate 10 is lowered to 500°C to 800°C, and In x Ga 1-x N / GaN multiple quantum well structure portion 20 is formed. Then, the substrate 10 is transferred into a vapor deposition apparatus, and the conductive layer 30 is formed into a film on the multiple quantum well structure portion 20, whereby the production of the light emitter 1 is completed.

[0034] In the above example, trimethylgallium (Ga(CH3)3:TMGa) can be used as the Ga source, trimethylindium (In(CH3)3:TMIn) as the In source, ammonia (NH3) as the N source, hydrogen gas (H2) or nitrogen gas (N2) as the carrier gas, and monosilane (SiH4) as the Si source. Alternatively, other organometallic raw materials (e.g., triethylgallium (Ga(C2H5)3:TEGa), triethylindium (In(C2H5)3:TEIn), etc.) and other hydrides (e.g., disilane (Si2H4), etc.) may be used. Furthermore, although a MOVPE apparatus is used in the above example, a hydride vapor phase epitaxy (HVPE) apparatus or a molecular beam epitaxy (MBE) apparatus may also be used. The growth temperatures are not limited to those described above.

[0035] In the light-emitting device 1 configured as described above, when an electron beam E is incident on it, fluorescence SA is emitted in the long-wavelength layer 20A. At this time, if the energy of the electron beam E is low, the electron beam E does not reach the short-wavelength layer 20B, and the short-wavelength layer 20B does not emit fluorescence SB. On the other hand, if the energy of the electron beam E is high, the electron beam E is more likely to reach the short-wavelength layer 20B, and as a result, in addition to emitting fluorescence SA in the long-wavelength layer 20A, fluorescence SB is also emitted in the short-wavelength layer 20B. In other words, the light-emitting device 1 makes it possible to emit light in multiple colors depending on the energy of the incident electron beam E. For example, the light-emitting device 1 makes it possible to separate multiple electron beams E with different energies that are incident simultaneously.

[0036] In the light-emitting body 1, the multiple quantum well structure 20 is configured such that the short-wavelength layer 20B is sensitive to electron beams E with an energy of a predetermined value β or higher. In this case, the light-emitting body 1 can emit light in multiple colors depending on whether the energy of the incident electron beam E is above the predetermined value β or higher.

[0037] In the light emitter 1, the thickness of the long-wavelength layer 20A is set such that the short-wavelength layer 20B is sensitive to an electron beam E having an energy of a predetermined value β or higher in the multiple quantum well structure section 20. In this case, multicolor light emission depending on whether the energy of an incident electron beam E is equal to or higher than a predetermined value can be set by adjusting the thickness of the long-wavelength layer 20A.

[0038] In the light emitter 1, the long-wavelength layer 20A and the short-wavelength layer 20B each include a plurality of light-emitting layers 21A and 21B formed of a nitride semiconductor containing Ga and In, respectively. The proportion of In in the composition of the plurality of light-emitting layers 21A included in the long-wavelength layer 20A is higher than the proportion of In in the composition of the plurality of light-emitting layers 21B included in the short-wavelength layer 20B. In this case, the long-wavelength layer 20A and the short-wavelength layer 20B can be specifically configured.

[0039] In the light emitter 1, the plurality of barrier layers 22A included in the long-wavelength layer 20A are configured such that their thickness becomes thinner as they approach the electron beam incident surface S. That is, the plurality of barrier layers 22A include a first barrier layer and a second barrier layer located on the electron beam incident surface S side relative to the first barrier layer, and the first barrier layer is thicker than the second barrier layer. In this case, it is possible to improve the luminous efficiency of the light emitter 1 and increase the luminous intensity.

[0040] In the light emitter 1, the plurality of barrier layers 22B included in the short-wavelength layer 20B have the same thickness as each other. In this case, it is possible to improve the luminous efficiency of the light emitter 1 and increase the luminous intensity.

[0041] In the light emitter 1, the average thickness of the plurality of barrier layers 22A included in the long-wavelength layer 20A is larger than the average thickness of the plurality of barrier layers 22B included in the short-wavelength layer 20B. In this case, it is possible to improve the luminous efficiency of the light emitter 1 and increase the luminous intensity.

[0042] In the luminous body 1, the long-wavelength layer 20A is laminated on the short-wavelength layer 20B on the electron beam incident surface S side. In this case, excitation of the long-wavelength layer 20A by the short-wavelength fluorescence SB emitted from the short-wavelength layer 20B can be suppressed. That is, since the fluorescence SB passes through the long-wavelength layer 20A when traveling toward the substrate 10, it is possible to suppress the occurrence of fluorescence SA in the long-wavelength layer 20A caused by incidence of the fluorescence SB instead of being caused by incidence of the electron beam E. In addition, since absorption of the short-wavelength fluorescence SB emitted from the short-wavelength layer 20B by the long-wavelength layer 20A can be suppressed, the emission efficiency of the fluorescence SB in the luminous body 1 can be improved.

[0043] It should be noted that the multiple quantum well structure 20 may include one or more intermediate layers (buffer layers) having light transmittance for the wavelength of fluorescence emitted from the multiple quantum well structure 20 between the substrate 10 and the short-wavelength layer 20B, and between the long-wavelength layer 20A and the short-wavelength layer 20B. In the above description, the nitride semiconductor refers to a compound containing at least one of Ga, In and Al as a group III element and containing N as a main group V element. The phrase "having light transmittance" refers to, for example, the property of transmitting 50% or more of target light.

[0044] FIG. 5 is a table showing results of evaluating the luminance of fluorescence SA of the long-wavelength layer 20A and the luminance of fluorescence SB of the short-wavelength layer 20B in each example in which the configuration of the multiple quantum well structure 20 is changed. The presence / absence of the intermediate layer in the figure indicates the presence / absence of the aforementioned intermediate layer between the long-wavelength layer 20A and the short-wavelength layer 20B. The total thickness of the long-wavelength layer 20A refers to the thickness of the entire long-wavelength layer 20A, and the total thickness of the short-wavelength layer 20B refers to the thickness of the entire short-wavelength layer 20B. "△", "〇" and "◎" for the fluorescence SA and SB of the long-wavelength layer 20A and the short-wavelength layer 20B indicate that the luminance increases in this order.

[0045] In the evaluation results illustrated in Figure 5, the highest fluorescence SA and SB values ​​were obtained when the configuration of the multiple quantum well structure 20 was in the fifth example. That is, as shown in the fifth example, it was confirmed that the multiple quantum well structure 20 contributes to increased fluorescence SA and SB values ​​when it has at least one of the following configurations: (a) the barrier layer 22A of the long-wavelength layer 20A has a gradient structure, (b) the barrier layer 22B of the short-wavelength layer 20B has a constant-thickness layer structure, (c) the average thickness of the barrier layer 22A of the long-wavelength layer 20A > the average thickness of the barrier layer 22B of the short-wavelength layer 20B, (d) the number of light-emitting layers 21A of the long-wavelength layer 20A < the number of light-emitting layers 21B of the short-wavelength layer 20B, (e) the total thickness of the long-wavelength layer 20A < the total thickness of the short-wavelength layer 20B, and (f) there is no intermediate layer.

[0046] One aspect of the present invention is not limited to the above embodiment, and various other modifications are possible.

[0047] In the above embodiment, the long-wavelength layer 20A is laminated on the electron beam incident surface S side on the short-wavelength layer 20B, but the lamination order may be reversed (i.e., the short-wavelength layer 20B is on top of the long-wavelength layer 20A). In the above embodiment, the multiple quantum well structure 20 may further have a third-wavelength layer laminated on the long-wavelength layer 20A and the short-wavelength layer 20B, which emits fluorescence at a third wavelength different from the first and second wavelengths in response to the incidence of the electron beam E.

[0048] In the above embodiment, the composition of the light-emitting layers 21A, 21B and barrier layers 22A, 22B constituting the multiple quantum well structure 20 is not limited to the example described above. In the above embodiment, an example was shown in which the light-emitting layers 21A, 21B and barrier layers 22A, 22B of the multiple quantum well structure 20 are doped with Si, but the embodiment is not limited to this, and other impurities may be doped. Alternatively, the light-emitting layers 21A, 21B and barrier layers 22A, 22B may be composed of semiconductors other than nitride semiconductors.

[0049] In the above embodiment, the number of light-emitting layers 21A, 21B and barrier layers 22A, 22B is not particularly limited, and the number of light-emitting layers 21A, 21B and barrier layers 22A, 22B can be any number of two or more. In the above embodiment, the barrier layer 22A of the long-wavelength layer 20A has a gradient structure, but it may also have a constant-thickness layer structure. In the above embodiment, the barrier layer 22B of the short-wavelength layer 20B has a constant-thickness layer structure, but it may also have a gradient structure. In the above embodiment, some of the multiple barrier layers 22A included in the long-wavelength layer 20A may have a gradient structure, while the other parts may have a constant-thickness layer structure.

[0050] The configurations in the above embodiments and modifications are not limited to the materials and shapes described above, and various materials and shapes can be applied. The configurations in the above embodiments and modifications can be arbitrarily applied to the configurations in other embodiments or modifications. The numerical values ​​above may include errors in measurement, manufacturing, and design. The terms "equal" and "same" above include not only cases where they are exactly equal and exactly the same, but also cases where they are approximately equal and approximately the same.

[0051] 1...light-emitting element, 10...substrate, 10a...main surface (one side), 20...multiple quantum well structure (quantum well structure), 20A...long-wavelength layer (first wavelength layer), 20B...short-wavelength layer (second wavelength layer), 21A, 21B...light-emitting layer, 22A, 22B...barrier layer, E...electron beam, S...electron beam incident surface, SA, SB...fluorescence.

Claims

1. A light-emitting body that converts an incident electron beam into fluorescence, comprising: a substrate transparent to fluorescence; and a quantum well structure formed on one surface of the substrate and emitting fluorescence upon incidence of the electron beam, wherein the quantum well structure comprises: a first wavelength layer that emits fluorescence of a first wavelength in response to incidence of the electron beam; and a second wavelength layer laminated on the first wavelength layer and emitting fluorescence of a second wavelength shorter than the first wavelength in response to incidence of the electron beam.

2. The light-emitting body according to claim 1, wherein the quantum well structure is configured such that one of the first wavelength layer and the second wavelength layer, on the side opposite to the electron beam incident surface of the quantum well structure, is sensitive to the electron beam having an energy of a predetermined value or higher.

3. The light-emitting body according to claim 2, wherein the quantum well structure is configured such that the thickness of the other of the first and second wavelength layers is set such that the side of the first and second wavelength layers opposite to the electron beam incident surface is sensitive to the electron beam having an energy of or greater than the predetermined value.

4. The light-emitting body according to any one of claims 1 to 3, wherein the first wavelength layer and the second wavelength layer each include a plurality of light-emitting layers made of a nitride semiconductor containing Ga and In, and the proportion of In in the composition of the plurality of light-emitting layers included in the first wavelength layer is greater than the proportion of In in the composition of the plurality of light-emitting layers included in the second wavelength layer.

5. The light-emitting body according to any one of claims 1 to 4, wherein the first wavelength layer includes a plurality of barrier layers, each of which comprises a first barrier layer and a second barrier layer located on the electron beam incident surface side of the quantum well structure relative to the first barrier layer, and the first barrier layer is thicker than the second barrier layer.

6. The light-emitting body according to any one of claims 1 to 5, wherein the second wavelength layer includes a plurality of barrier layers, and the plurality of barrier layers included in the second wavelength layer have the same thickness as each other.

7. The light-emitting body according to any one of claims 1 to 6, wherein the first wavelength layer and the second wavelength layer each include a plurality of barrier layers, and the average thickness of the plurality of barrier layers included in the first wavelength layer is greater than the average thickness of the plurality of barrier layers included in the second wavelength layer.

8. The light-emitting body according to any one of claims 1 to 7, wherein the first wavelength layer is laminated on the electron beam incident surface side of the quantum well structure on the second wavelength layer.

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