UV semiconductor light-emitting element

Abstract

To provide an ultraviolet semiconductor light-emitting element that allows a user to easily check whether it is driven and emitting deep ultraviolet light.SOLUTION: A ultraviolet semiconductor light-emitting element according to the present invention includes a single crystal AlN substrate, an n-type AlGaN layer formed on the single crystal AlN substrate, an active layer formed on the n-type AlGaN layer and having an emission peak wavelength of 250 nm or more and 280 nm or less, and a p-type AlGaN layer formed on the active layer, and the C concentration in the single crystal AlN substrate is 3×1017 atoms / cm3 or more.SELECTED DRAWING: Figure 1

Description

[Technical Field] 【0001】 The present invention relates to a semiconductor light-emitting element, and more particularly to an ultraviolet semiconductor light-emitting element capable of emitting ultraviolet light. [Background technology] 【0002】 In recent years, semiconductor light-emitting devices with emission peak wavelengths in the deep ultraviolet region have attracted attention as light sources that have a sterilizing effect on air and water. 【0003】 For example, Patent Document 1 discloses a deep ultraviolet optical semiconductor device in which an AlGaN-based semiconductor layer is formed on an AlN substrate. [Prior art documents] [Patent Documents] 【0004】 [Patent Document 1] Japanese Patent Publication No. 2019-110168 [Non-patent literature] 【0005】 [Non-Patent Document 1] Applied Physics Letters 104, 202106 (2014) [Non-Patent Document 2] Semiconductor Science and Technology 35 (2020) 125006 [Non-Patent Document 3] Applied Physics Letters 100, 191914 (2012) [Non-Patent Document 4] Applied Physics Express 5 (2012) 125501 [Overview of the project] [Problems that the invention aims to solve] 【0006】 When using equipment employing the aforementioned optical semiconductor elements, the deep ultraviolet light emitted from these elements can affect the human body. Therefore, it is necessary to urge equipment operators to avoid exposure to the human body while the optical semiconductor elements are operating. Ideally, the operation of the optical semiconductor elements, when they are operating and emitting deep ultraviolet light, should be immediately recognizable. 【0007】 However, since deep ultraviolet light is invisible to the naked eye, it was difficult to visually inspect the optical semiconductor element to determine whether it was operating or not, that is, whether it was emitting deep ultraviolet light. 【0008】 This invention has been made in view of the above-mentioned points, and aims to provide an ultraviolet semiconductor light-emitting element that allows the user to easily confirm whether or not it is being driven and emitting deep ultraviolet light. [Means for solving the problem] 【0009】 The ultraviolet semiconductor light-emitting device according to the present invention comprises a single-crystal AlN substrate, an n-type AlGaN layer formed on the single-crystal AlN substrate, an active layer formed on the n-type AlGaN layer having an emission peak wavelength of 250 nm to 280 nm, and a p-type AlGaN layer formed on the active layer, wherein the carbon concentration in the single-crystal AlN substrate is 3 × 10⁻¹⁶. 17 atoms / cm 3 That's all. 【0010】 Furthermore, the ultraviolet semiconductor light-emitting device according to the present invention comprises a single-crystal AlN substrate, an n-type AlGaN layer formed on the single-crystal AlN substrate, an active layer formed on the n-type AlGaN layer having an emission peak wavelength of 250 nm to 280 nm, and a p-type AlGaN layer formed on the active layer, wherein the emission peak in the wavelength range of 450 nm to 800 nm is in the range of 590 nm to 610 nm. [Brief explanation of the drawing] 【0011】 [Figure 1] This is a top view of the light-emitting device according to Example 1. [Figure 2] Figure 1 is a cross-sectional view of the light-emitting device. [Figure 3] This figure shows the optical output of the light-emitting device according to Example 1 at a wavelength of 265 nm. [Figure 4] This figure shows the light output of the light-emitting device according to Example 1 at a wavelength of 600 nm. [Figure 5] This figure shows the emission spectra for each drive current of the light-emitting device according to Example 1. [Figure 6] This figure shows the emission spectra for each drive current of the light-emitting device according to Example 1. [Figure 7] This is a top view of the light-emitting device according to Example 2. [Figure 8] This is a cross-sectional view of the light-emitting device according to Example 2. [Figure 9] This is a top view of the light-emitting device according to Example 3. [Figure 10] This is a top view of a modified light-emitting device according to Example 3. [Modes for carrying out the invention] 【0012】 Preferred embodiments of the present invention will be described below, but these may be modified and combined as appropriate. In the following description and accompanying drawings, substantially identical or equivalent parts will be denoted by the same reference numerals. [Examples] 【0013】 The configuration of the light-emitting device 10 according to Embodiment 1 of the present invention will be described with reference to the attached drawings. 【0014】 Figure 1 is a top view of the light-emitting device 10. The light-emitting device 10 is composed of an ultraviolet semiconductor light-emitting element 11 which includes a submount substrate 15 with a rectangular top surface and a substrate 13 with a rectangular top surface disposed on the submount substrate 15. In the light-emitting device 10, the rectangular top surface 13S of the substrate 13 is the light-emitting surface. 【0015】 Figure 2 is a cross-sectional view of the light-emitting device 10 cut along the line 2-2 in Figure 1. The submount substrate 15 is a flat substrate with a rectangular top surface, as described above. The submount substrate 15 is an insulating substrate such as an AlN ceramic substrate. The submount substrate 15 may be a substrate made of another material, such as an alumina substrate. 【0016】 On the upper surface of the submount substrate 15, spaced apart metal electrodes, p-wiring electrodes 16 and n-wiring electrodes 17, are formed. On the lower surface of the submount substrate 15, spaced apart metal electrodes, p-backside electrodes 18 and n-backside electrodes 19, are formed. The p-backside electrodes 18 and n-backside electrodes 19 are electrically connected to the p-wiring electrodes 16 and n-wiring electrodes 17, respectively, for example, via through-vias. 【0017】 The ultraviolet semiconductor light-emitting element 11 is composed of a substrate 13 and a semiconductor laminate 20 consisting of a plurality of nitride-based semiconductor layers, including an active layer formed on the lower surface of the substrate 13. The emission peak wavelength of the active layer is light in the deep ultraviolet region, specifically light with a wavelength of 250 nm to 280 nm. 【0018】 The substrate 13 is a flat plate-shaped substrate having a rectangular top surface as described above. The substrate 13 is a single-crystal AlN substrate containing C (carbon), Si (silicon), and O (oxygen) as impurities. As described above, the top surface 13S of the substrate 13 is the light-emitting surface of the light-emitting device 10. Furthermore, the substrate 13 has optical properties such as absorbing a portion of ultraviolet light with a wavelength of 250 nm to 280 nm when incident on it, and emitting visible light in accordance with that absorption. 【0019】 The semiconductor laminate 20 is a laminated structure that includes a plurality of semiconductor layers formed to cover the lower surface of the substrate 13. The semiconductor laminate 20 includes an n-type cladding layer 21, an active layer 23, and a p-type semiconductor layer 25 that are epitaxially grown on the substrate 13 in order by metal-organic chemical vapor deposition (MOCVD). 【0020】 The n-type cladding layer 21 is formed to cover the lower surface of the substrate 13 and is an AlGaN layer doped with n-type impurities to be conductive. For example, Si is doped into the n-type cladding layer 21. 【0021】 The n-type cladding layer 21 has a mesa shape. Specifically, the n-type cladding layer 21 has a depression along the outer edge of its lower surface (the right-hand portion in the figure), and the areas other than this depression form a plateau. 【0022】 Alternatively, an AlN buffer layer lattice-matched with the substrate 13 may be provided between the substrate 13 and the n-type cladding layer 21. 【0023】 The active layer 23 is formed on the mesa-shaped plateau portion beneath the n-type cladding layer 21. The active layer 23 has a quantum well structure composed of a barrier layer and a well layer, both of which are AlGaN layers with different composition ratios. The emission peak wavelength of the active layer 23 is in the range of 250 to 280 nm. 【0024】 The structure of the active layer 23 is not particularly limited as long as it is configured so that the emission peak wavelength is 250-280 nm. For example, the emission peak wavelength can be set to 250-280 nm by appropriately setting the Al composition and film thickness of the well layer, the Al composition of the barrier layer, etc. The well layer and barrier layer may be Si-doped n-type layers. 【0025】 Furthermore, the number of quantum well layers is not particularly limited; it may be a multi-quantum well (MQW) structure with multiple well layers, or a single quantum well (SQW). For example, the number of well layers is preferably determined appropriately within the range of 1 to 5. 【0026】 The p-type semiconductor layer 25 is constructed by stacking an electron blocking layer 27, a p-type cladding layer 29, and a contact layer 31 on the active layer 23 in that order. 【0027】 The electron blocking layer 27 is formed on the active layer 23 and is an AlN layer containing Mg (magnesium) as a p-type dopant. The electron blocking layer 27 functions as an electron blocking layer (EBL) to suppress the overflow of electrons injected into the active layer 23 to the p-type cladding layer 29. 【0028】 The electron blocking layer 27 may be configured to not contain a p-type dopant. Alternatively, the ultraviolet semiconductor light-emitting element 11 may be configured without an electron blocking layer 27. 【0029】 The p-type cladding layer 29 is an AlGaN layer formed on the electron blocking layer 27 and doped with Mg as a p-type dopant. 【0030】 The contact layer 31 is a GaN layer formed on the p-type cladding layer 29 and doped with Mg as a p-type dopant. The contact layer 31 is provided to reduce the contact resistance with the electrode provided on the contact layer 31. 【0031】 In addition to Mg, other materials such as Zn (zinc), Be (beryllium), and C (carbon) can be used as the p-type dopant material for the electron blocking layer 27, the p-type cladding layer 29, and the contact layer 31. 【0032】 The n-electrode 33 is a metal electrode provided on the exposed surface 21E of the n-type cladding layer 21. The n-electrode 33 is electrically connected to the n-type cladding layer 21. The n-electrode 33 is also electrically connected to the n-wiring electrode 17 on the submount substrate 15 via a conductive bonding member 35. 【0033】 The p electrode 37 is a metal electrode provided on the contact layer 31. The p electrode 37 is electrically connected to the contact layer 31. The p electrode 37 is also electrically connected to the p wiring electrode 16 on the submount substrate 15 via a conductive bonding member 39. 【0034】 As described above, the ultraviolet semiconductor light-emitting element 11 is flip-chip mounted on the submount substrate 15. Although the description above has shown the ultraviolet semiconductor light-emitting element 11 having a mesa shape, it is not limited to this, and the n-type cladding layer 21 and the n-type wiring electrodes 17 may be electrically connected via through holes provided in the semiconductor laminate 20 that reach the n-type cladding layer 21. 【0035】 With the above configuration, when current is injected into the light-emitting device 10 via the p back electrode 18 and the n back electrode 19, deep ultraviolet light with an emission peak wavelength of 250 nm to 280 nm is emitted from the active layer 23 of the ultraviolet semiconductor light-emitting element 11. In addition, visible light generated by the absorption of the deep ultraviolet light by the substrate 13 is emitted from the upper surface 13S of the substrate 13 along with the deep ultraviolet light. 【0036】 [Preferred optical properties of substrate 13] Next, the optical properties of the substrate 13 and the configuration of the substrate 13 that provide favorable optical properties for the light-emitting device 10 will be described in detail. As described above, the substrate 13 has the optical property of absorbing a portion of the light emitted from the active layer 23 and emitting light with a longer wavelength than the emitted light. 【0037】 Specifically, the substrate 13 absorbs a portion of the light emitted from the active layer 23 with a peak wavelength of approximately 265 nm and a wavelength between 250 nm and 280 nm (hereinafter also simply referred to as deep ultraviolet light), and through an absorption-emitting process by impurities contained in the substrate 13, emits light with a peak wavelength of approximately 600 nm and a wavelength between 590 nm and 610 nm (hereinafter also simply referred to as red light). 【0038】 In the light-emitting device 10, it is preferable that visible light that appears orange to red and is visible is emitted from the light-emitting surface 13S so that the user can easily see that the ultraviolet semiconductor light-emitting element 11 is emitting light during operation. Orange to red is a preferred color for the emission of ultraviolet semiconductor light-emitting element 11 because, in addition to being easily visible, it often has the meaning of a warning or prohibition, and can draw the user's attention to the fact that the ultraviolet semiconductor light-emitting element 11 is emitting light. 【0039】 To achieve the emission of red light that appears as an orange to red color, it is preferable that the emission spectrum of the light emitted from the light-emitting surface 13S of the light-emitting device 10 has a peak in the range of 590 nm to 610 nm within the visible light wavelength range of 450-800 nm. Furthermore, in order to make the emitted red light visible, it is preferable that the red light has a light output of a predetermined level or higher (for example, 0.15 μW or more). 【0040】 In order for the light-emitting device to emit visible red light as described above, while obtaining sufficient deep ultraviolet light emission intensity to achieve its primary purpose of sterilization using deep ultraviolet light, the substrate 13 needs to absorb deep ultraviolet light to an extent that sufficient red light emission can be obtained, while minimizing the absorption of deep ultraviolet light. The mechanism by which visible light is emitted from the substrate 13 in the light-emitting device 10 and a preferred configuration of the substrate 13 based on this mechanism will be described below. 【0041】 [About the mechanism by which visible light is emitted] As described above, in substrate 13, absorption of ultraviolet light originating from impurities and subsequent emission of visible light occur. We will investigate the mechanism of ultraviolet light absorption by impurities in substrate 13 and the emission of visible light, including light with a wavelength of approximately 600 nm. 【0042】 It is known that single-crystalline AlN can exhibit various light absorption and emission patterns depending on the impurity species and impurity concentrations contained in the crystal. Table 1 shows examples of the absorption energy (eV) and emission energy (eV) of defect structures and substitution structures that absorb light in the vicinity of 250 to 280 nm, which is the emission wavelength of the ultraviolet semiconductor light-emitting device 11 in this embodiment, and cause emission. 【0043】 【Table 1】 In Table 1, "C N " indicates a point defect where the nitrogen site of the AlN crystal is substituted by C. Also, "Si Al " in Table 1 indicates Si substitution at the Al site of the AlN crystal, and "O N " indicates O substitution at the nitrogen site. "V N " indicates a nitrogen defect where nitrogen has desorbed from the nitrogen site of the AlN crystal. 【0044】 For "C N " where the nitrogen site is substituted by C, it has been reported to show absorption of light at 4.7 eV corresponding to a wavelength of about 265 nm and emissions at 3.9 eV (≈320 nm) and 2.8 eV (≈440 nm) (Non-Patent Document 1). 【0045】 "C N " and "Si Al " complex (complex) "C N -Si Al " shows absorption of light at 5.5 eV and emission at 4.3 eV. This "C N -Si Al " is formed when the Si concentration in the AlN crystal is greater than the C concentration (Non-Patent Document 1). 【0046】 Also, it has been reported that donor-acceptor transition between the donor-type defect "O N " and the adjacent acceptor "C N " causes absorption at 4.7 eV (≈265 nm) and emission at 2.19 eV (≈570 nm) (Non-Patent Document 2). 【0047】 Furthermore, there is a donor defect called "V N " and the adjacent acceptor "C N It has been reported that a donor-acceptor transition between these two components results in an absorption of 4.7 eV (≒265 nm) and an emission of 1.9 eV (≒650 nm) (Non-Patent Literature 2). 【0048】 From the above, the absorption at a wavelength of 265 nm (4.7 eV) in the present invention is due to "C" in the substrate 13. N It is presumed that this is the main cause. In addition, the red emission at 600 nm (=2.07 eV) in this invention is due to "O N "V N " and other defects in donor suitability and "C" as an acceptor N This is presumed to be due to the donor-acceptor transition between the two. 【0049】 [Preferred configuration of substrate 13] Based on the mechanism described above, a preferred configuration of the substrate 13 will be explained below. 【0050】 [absorption coefficient] The substrate 13 has an absorption coefficient of 15 cm² for deep ultraviolet light at the emission peak wavelength of the active layer 23. -1 The above is preferable. The absorption of deep ultraviolet light is C as described above. N This is considered to be the main cause. 【0051】 Absorption coefficient of 15cm -1 If the following conditions are met, for example, even if the thickness of substrate 13 is increased, it will be difficult to obtain sufficient red light emission to be visually recognizable. This is because of the C in substrate 13. N Due to the low concentration, the adjacent "C" mentioned above N " and "O N " and adjacent "C N " and "V N This is thought to be because the absorption-luminescence process due to the donor-acceptor transition between the two is less likely to occur. 【0052】 Furthermore, in conventional AlN substrates, the absorption of ultraviolet light emitted from the active layer by the substrate reduces the total amount of ultraviolet light that can be extracted to the outside, thereby reducing the luminescence efficiency. To prevent this, for example, the absorption coefficient of the AlN substrate is set to 20 cm². -1 The following is preferable, and more preferably 10 cm -1 The following has been stated, and efforts have been made to lower the absorption coefficient. 【0053】 In contrast, in this embodiment, in order to ensure sufficient absorption to generate red light by absorbing deep ultraviolet light, the absorption coefficient of the active layer 23 with respect to light at the emission peak wavelength is set to 15 cm⁻¹. -1 That concludes the explanation. 【0054】 Absorption coefficient of 15cm -1 If the above conditions are met, sufficient red light emission that is visible to the naked eye can be obtained by appropriately setting the thickness of the substrate 13. In this embodiment, by setting the impurity concentration in the substrate 13 to a predetermined value or higher, the absorption coefficient can be set to 15 cm². -1 It is controlled to the above extent. 【0055】 [Internal transmittance] The amount of deep ultraviolet light absorbed by substrate 13 is such that the absorption coefficient is 15 cm⁻¹. -1 In the above cases, the absorption coefficient of the substrate 13 is determined by the thickness of the substrate 13, in addition to the absorption coefficient of the substrate 13. The balance between the amount of deep ultraviolet light absorbed by the substrate 13 and the total amount of deep ultraviolet light that can be extracted to the outside from the light-emitting surface 13S can be estimated by the internal transmittance of the substrate 13. When the absorption coefficient of the substrate 13 for light at the emission peak wavelength is α and the thickness of the substrate 13 is x, the internal transmittance τ is expressed by the following equation. 【0056】 【number】 From the viewpoint of extracting deep ultraviolet light with sufficient luminescence intensity and red light with sufficient luminescence intensity that is easily recognizable to the naked eye from the light-emitting surface 13S, the above internal transmittance is preferably 30% to 70%. 【0057】 If the internal transmittance is less than 30%, the amount of absorption of light at a wavelength of 265 nm increases, which allows for the acquisition of high-output light at a wavelength of approximately 600 nm. However, this also increases the decrease in light intensity at a wavelength of 265 nm, which is undesirable from the viewpoint of luminescence efficiency for deep ultraviolet and red light. 【0058】 When the internal transmittance exceeds 70%, the emission intensity at wavelength 265 nm is high because the absorption amount of light at wavelength 265 nm by the substrate 13 is small. However, because the absorption amount of light at wavelength 265 nm is small, a sufficient emission intensity of light at approximately 600 nm cannot be obtained, which is undesirable from the viewpoint of extracting red light. 【0059】 Considering the above points, the internal transmittance of the active layer 23 by the substrate 13 with respect to light at the emission peak wavelength is preferably 30% to 70%, and more preferably 40% to 60%. 【0060】 [Relationship between absorption coefficient and thickness of single-crystal AlN substrate] Furthermore, from a manufacturing standpoint for substrate 13, the absorption coefficient of substrate 13 for 265 nm light is 50 cm². -1 The following is preferable: Absorption coefficient of 50 cm -1 Beyond this point, variations in substrate thickness lead to significant variations in the absorption of 265nm light. In this case, variations in the manufacturing thickness of the substrate 13 will cause variations in the characteristics of the element. Therefore, to suppress variations in the thickness of the substrate 13, it is necessary to reduce the tolerance of the substrate 13's thickness. Thus, when the absorption coefficient exceeds 50 cm², -1 Considering that the requirements for manufacturing precision become stricter beyond this point, the absorption coefficient of substrate 13 should be set to 50 cm². -1 The following is preferable. 【0061】 For similar reasons, it is preferable that the thickness of the substrate 13 be 150 μm or more. If the thickness of the substrate 13 is less than 150 μm, the absorption coefficient of the substrate 13 needs to be high in order to obtain a sufficient amount of light with a wavelength of 265 nm, and as mentioned above, the tolerance of the thickness of the substrate 13 becomes small. 【0062】 In conventional single-crystal AlN substrates, the thickness required to obtain sufficient strength as a growth substrate for light-emitting elements is 90 to 100 μm. However, in this embodiment, it is preferable to have a thickness of 150 μm or more, depending on the relationship with the absorption coefficient at a wavelength of 265 nm. 【0063】 Furthermore, the thickness of the substrate 13 is preferably 500 μm or less, from a manufacturing standpoint, such as the fact that manufacturing costs increase when it exceeds 500 μm. 【0064】 Based on the above, and considering the manufacturing aspect, the substrate 13 has an absorption coefficient of 15 cm². -1 More than 50cm -1 The following is true, and it is preferable that the thickness is between 150 μm and 500 μm. 【0065】 [Control of impurity concentration in single-crystal AlN substrates] The control of impurity concentration in the substrate 13 in this invention will now be described. As described above, the substrate 13 contains C, Si, and O as impurities. These impurities are introduced during the growth of the substrate 13, and their concentrations are intentionally controlled. The concentrations of C, Si, and O in the substrate 13 can be measured by secondary ion mass spectrometry (SIMS). 【0066】 In the light-emitting device 10 of the present invention, as described above, the absorption and light emission process mainly caused by C among the impurities in the substrate 13 is utilized to absorb light with a wavelength of 265 nm from the active layer 23, generating red light with a wavelength of approximately 600 nm. Furthermore, as described above, the absorption at a wavelength of 265 nm (4.7 eV) is due to the substitution of nitrogen sites of AlN crystals in the substrate 13 with C. N It is presumed that this is the main cause. Therefore, in order to generate red light in the present invention, C in the substrate 13 N Controlling the concentration is important. 【0067】 It is known that carbon incorporated into AlN crystals preferentially displaces nitrogen sites (Non-Patent Document 3). Therefore, basically, the carbon concentration in the AlN crystal is determined by C N It can be considered as a concentration (C N Concentration ≒ C concentration). 【0068】 However, as shown in Table 1, if the Si concentration in the substrate 13 is higher than the C concentration, C N and Si Al C is a complex about N -Si Al C is formed by N Since the concentration decreases, the C concentration is reduced to C N It cannot be considered a concentration. The following explains the cases where the Si concentration is less than or equal to the C concentration, and where the Si concentration is higher than the C concentration. 【0069】 First, if the Si concentration in the substrate 13 is less than or equal to the C concentration (Si concentration ≤ C concentration), then C N -Si Al It is thought that little or no formation occurs or that it can be ignored. Therefore, the C concentration is C N It can be considered as a concentration, and by controlling the C concentration, C N The concentration can be controlled. 【0070】 Furthermore, the absorption coefficient α of the AlN crystal for light at 265 nm (4.7 eV) is determined by the amount of C in the AlN crystal. N It is known that this is determined by the concentration of (Non-Patent Literature 3). Therefore, in order to produce appropriate absorption and emission on the substrate 13 and obtain red light along with deep ultraviolet light, C N The concentration can be estimated based on the absorption coefficient α. 【0071】 The relationship between the carbon concentration in a single-crystal AlN substrate and the absorption coefficient α of the said single-crystal AlN substrate for light at 4.7 eV (≒265 nm) is disclosed in Non-Patent Documents 3 and 4. 【0072】 As mentioned above, 15cm -1Below this value, it is difficult to obtain red light regardless of the thickness of the substrate 13, and in this invention, the absorption coefficient α of the substrate 13 is set to 15 cm². -1 It is necessary to meet the above requirements. According to the relationship between C concentration and absorption coefficient α, the absorption coefficient of light with a wavelength of 265 nm is 15 cm². -1 The C concentration corresponding to this is 3 × 10 17 atoms / cm 3 It can be estimated as follows. 【0073】 In the light-emitting device 10 of the present invention, the C concentration in the substrate 13 is set to 3 × 10 17 atoms / cm 3 By controlling it as described above, the absorption coefficient α for light with a wavelength of 265 nm by the substrate 13 is set to 15 cm -1 The system is controlled to ensure the above conditions are met. 【0074】 Furthermore, according to the relationship between the C concentration and the absorption coefficient α described above, the upper limit of the absorption coefficient α considering the substrate thickness tolerance is 50 cm². -1 The corresponding C concentration is 3 × 10 18 atoms / cm 3 Therefore, the C concentration can be estimated as C N If it can be considered as a concentration, the absorption coefficient α is set to 15 cm -1 More than 50cm -1 The preferred range of C concentration for this purpose is 3 × 10 17 atoms / cm 3 The above 3 x 10 18 atoms / cm 3 The following applies: 【0075】 Next, we will explain the case where the Si concentration is higher than the C concentration (Si concentration > C concentration). As mentioned above, when the Si concentration is greater than the C concentration, C N and Si Al C is a complex about N -Si Al C is formed. N -Si Al It shows absorption of 5.5 eV and does not absorb light at 265 nm (4.7 eV). Also, C N -Si Alshows luminescence at 4.3 eV and does not emit red light with a wavelength of 600 nm (= 2.07 eV). 【0076】 In this case, the concentration of C N cannot be regarded as approximately equal to the concentration of C, and the concentration of C N is the concentration obtained by subtracting the concentration of C N -Si Al from the concentration of C, that is, "the concentration of C N ≈ the concentration of C - (the concentration of C N -Si Al ). Therefore, even with the same concentration of C, the absorption coefficient α for light at 265 nm becomes smaller compared to the case where the Si concentration is less than or equal to the concentration of C. Therefore, the concentration of C in the substrate 13 needs to be set higher by the amount used for the formation of C N -Si Al . 【0077】 Actually, when the Si concentration is higher than the concentration of C and the absorption coefficient α is 20 cm -1 , and the concentration of C is 6 × 10 18 atoms / cm 3 and the Si concentration is 2.5 × 10 18 atoms / cm 3 , using a sample of C N -Si Al , when calculating the concentration of C 18 atoms / cm 3 , it becomes approximately 5 × 10 N . For the calculation of the concentration of C -12 , the relational expression of α = 5.672E 0.6978 (X is the concentration of C N ) was used. 【0078】 From the above calculation results, when the Si concentration is higher than the concentration of C, the concentration of C for making the absorption coefficient α be 15 cm -1 or more and 50 cm -1 or less can be estimated to be 5.3 × 10 18 atoms / cm 3 or more and 8.0 × 10 18 atoms / cm 3 or less. 【0079】 Furthermore, considering not only the case where the Si concentration is lower than the C concentration, but also the case where the Si concentration is higher than the C concentration, in the present invention, the absorption coefficient of the substrate 13 for light with a wavelength of 265 nm is set to 15 cm⁻¹. -1 More than 50cm -1 The preferred range of C concentration for this purpose is 3 × 10 17 atoms / cm 3 The above 8 x 10 18 atoms / cm 3 It can be estimated as follows: 【0080】 Furthermore, the inventors of this application have found that by controlling the sum of the Si concentration and O concentration in the substrate 13 to be higher than the C concentration in the substrate 13 (Si concentration + O concentration > C concentration), it is possible to obtain sufficient deep ultraviolet light emission intensity, which is the main objective, and to emit visible red light. 【0081】 This is because if the sum of the Si concentration and O concentration is higher than the C concentration in the substrate 13, C N -Si Al C is formed N This is thought to be because the absorption of light at a wavelength of 265 nm caused by this is suppressed, preventing the transmittance from dropping too low. 【0082】 The impurity in question may be one that is naturally introduced during the manufacturing of the substrate 13. In that case, a substrate containing the desired concentration of impurity can be selected as the substrate 13. 【0083】 Referring to Figures 3 to 6, the luminescence characteristics of Sample A and Sample B of this embodiment will be compared and explained. 【0084】 Sample A is an example of the light-emitting device 10 of this embodiment, in which the absorption coefficient of the substrate 13 is set to 20 cm². -1 Sample B has a substrate thickness of 400 μm. Sample B differs from Sample A only in that the substrate thickness of Sample B is 100 μm; otherwise, it is configured the same as Sample A. 【0085】 Therefore, in both Sample A and Sample B, the absorption coefficient of the substrate 13 is 20 cm². -1 Furthermore, the impurity concentrations in the substrate 13 for sample A and sample B are as follows: C concentration is 6 × 10 18 atoms / cm 3 , Si concentration is 2.5 × 10 18 atoms / cm 3 , O concentration is 4.5 × 10 18 atoms / cm 3 Therefore, in samples A and B, the sum of the Si concentration and O concentration in the substrate 13 is controlled to be greater than the C concentration ((Si+O) / C=1.17). A photodetector was placed on the light emission surface 13S of each of samples A and B, and the light output and emission spectrum were measured when the drive current was varied from 5mA to 70mA. 【0086】 Figure 3 shows the optical output at a wavelength of 265 nm as the drive current increases for samples A and B. As shown in Figure 3, for both samples A and B, the optical output at a wavelength of 265 nm increases as the drive current increases. Also, at the same drive current, the optical output value of sample A is lower than that of sample B. 【0087】 This is because sample A has a thicker substrate 13 than sample B, resulting in lower internal transmittance and thus greater absorption of light at a wavelength of 265 nm. Specifically, for light at a wavelength of 265 nm, the internal transmittance of sample A is approximately 45%, while the internal transmittance of sample B is approximately 82%. 【0088】 When actually using the light-emitting device 10, it will be driven with a larger drive current of approximately 400 mA than in this experiment. In that case, even using the light-emitting device of sample A, a sufficient light output of, for example, 30 mW or more, can be obtained for sterilization and other applications. 【0089】 Figure 4 shows the optical output at a wavelength of 600 nm for samples A and B as a function of the drive current. In Figure 4, the line representing the visible optical output level of 0.15 μW is shown as a dashed line. 【0090】 As shown in Figure 4, up to a drive current of 30 mA, both Sample A and Sample B show an increase in optical output at a wavelength of 600 nm as the drive current increases. Furthermore, both Sample A and Sample B exceed the visible optical output level of 0.15 μW when the drive current is 30 mA or higher. 【0091】 When the drive current exceeds 30mA, sample A shows an increase in optical output at a wavelength of 600nm as the drive current increases. In contrast, for sample B, when the drive current exceeds 30mA, the increase in optical output at 600nm becomes smaller even as the drive current increases, and when the drive current exceeds 50mA, the optical output at 600nm stops increasing. In sample B, when the drive current exceeds 30mA, there is a shortage of absorption sites for light at a wavelength of 265nm, and it is thought that the optical output at 600nm tends to saturate. 【0092】 Figure 5 shows the emission spectra of sample A between 400 nm and 800 nm wavelengths for each drive current, when the drive current was varied from 5 mA to 70 mA. As shown in Figure 5, in the emission spectrum of sample A, the emission intensity is maximum at a wavelength of approximately 600 nm for all drive currents. In other words, in the emission spectrum of sample A, the emission peak in the wavelength range from 450 nm to 800 nm is within the range of 590 nm to 610 nm. 【0093】 Thus, when the emission intensity is maximum at a wavelength of approximately 600 nm within the visible light range, orange to red light can be perceived by the naked eye. 【0094】 Furthermore, the position of the emission peak at approximately 600 nm does not change from approximately 600 nm even when the drive current is changed. Therefore, for sample A, even when the drive current is increased to a practical drive current of about 400 mA as described above, it is considered that the tendency for the emission peak in the wavelength range of 450 nm to 800 nm to be within the range of 590 nm to 610 nm will be maintained. 【0095】 Therefore, when sample A is driven with a drive current of approximately 400 mA, orange to red visible light is emitted from the light-emitting surface 13S of sample A along with deep ultraviolet light, and it is easy to recognize at a glance that it is being driven by this visible light. 【0096】 Figure 6 shows the emission spectra of sample B between wavelengths of 400 nm and 800 nm for each drive current, when the drive current is varied from 5 mA to 70 mA. As shown in Figure 6, in the emission spectrum of sample B, the emission intensity is maximum at a wavelength of approximately 600 nm up to a drive current of 30 mA. Also, as shown in Figure 4, the optical output level exceeds 0.15 μW, which is the level of optical output that can be seen by the naked eye, at a drive current of 30 mA or higher. Therefore, it can be said that red light can be perceived by driving sample B, at least under the condition of a drive current of 30 mA. 【0097】 However, in Figure 6, in the spectra for 50mA and 70mA, the intensity at a wavelength of 600nm does not increase even when the drive current increases from 50mA to 70mA. Instead, the emission intensity of light with wavelengths between 450nm and 600nm, i.e., light in the visible light region with wavelengths shorter than 600nm, increases. This is thought to be due to emission from the contact layer 31, which is a p-type GaN layer. 【0098】 In such cases, the visible color of the emitted light tends to be bluish-white to white (hereinafter also simply referred to as bluish-white light), rather than orange to red, due to the mixing of light with a wavelength of approximately 600 nm and light with a wavelength between 450 nm and 600 nm. 【0099】 For example, in the case of sample B, if the drive current is increased to a practical drive current of about 400mA, the emission intensity at a wavelength of approximately 600nm will not increase further, and it is thought that the tendency for high emission intensity at wavelengths between 450nm and 600nm will be maintained. 【0100】 Therefore, when sample B is driven with a drive current of approximately 400 mA, deep ultraviolet light and bluish-white light may be emitted from the light-emitting surface 13S of sample B. Although the driving of sample B can be recognized by the emission of this visible light, bluish-white light tends to be less recognizable than red light, and sample A, which emits red light, is more preferable. 【0101】 In this embodiment, a blue-white emission spectrum was observed in sample B, which originated from the contact layer 31, a p-type GaN layer as described above. The intensity of this blue-white emission varies depending on the quality and thickness of the pGaN contact layer, and in some cases it may be difficult to see. 【0102】 Furthermore, as was evident in Sample A, in the present invention, the emission spectrum of the light-emitting device 10 has a peak of approximately 600 nm in the 450-800 nm region. This wavelength of 600 nm is C N This is primarily due to an absorption-luminescence process and is basically unchanging. However, this peak wavelength may become shorter as the excitation density (current density) increases, or longer as the temperature increases. Even considering these factors, the peak wavelength in the 450-800 nm region due to the absorption-luminescence process of C impurities in substrate 13 is thought to be within 600 nm ± 5 nm, and even with a generous estimate, it will be within 600 nm ± 10 nm. 【0103】 [Method for manufacturing single-crystal AlN substrates] The substrate 13 can be manufactured, for example, by the physical vapor transport (PVT) method. In the PVT method, an AlN raw material such as polycrystalline AlN is heated and sublimated to grow crystals on a seed substrate placed opposite the crucible containing the raw material. 【0104】 For example, by using an AlN raw material with a low initial impurity content, the impurity concentration in the growing single-crystal AlN substrate can be reduced. 【0105】 Furthermore, by controlling temperature conditions such as the temperature of the raw materials during crystal growth and pressure conditions within the reactor, the amount of impurities in the gas phase changes, and consequently, the amount of impurities incorporated into the AlN single crystal can be controlled. For example, lowering the temperature tends to decrease the impurity concentration. 【0106】 Furthermore, by adding impurity raw materials such as Si pieces and carbon pieces along with the AlN raw material, and controlling the amount of these additions, as well as the temperature and pressure conditions mentioned above, the impurity concentration in the single-crystal AlN substrate can be increased or decreased. 【0107】 Furthermore, the substrate 13 is not limited to the PVT method; for example, it can also be grown by hydride vapor deposition (HVPE), molecular beam epitaxy (MBE), or MOCVD, and these methods can also be combined. 【0108】 Furthermore, considering the long growth time for MBE or MOCVD, and the high cost of the HVPE method, it is preferable to grow the substrate 13 using the PVT method. 【0109】 As described in detail above, the light-emitting device 10 of this embodiment is configured by mounting an ultraviolet semiconductor light-emitting element 11 on a submount substrate. The ultraviolet semiconductor light-emitting element 11 has a single-crystal AlN substrate, an n-type cladding layer, an active layer having an emission peak wavelength of 250 nm to 280 nm, and a p-type cladding layer, and the C concentration in the single-crystal AlN substrate is 3 × 10⁻¹⁶ 17 atoms / cm 3 That's all. 【0110】 In other words, the ultraviolet semiconductor light-emitting element 11 has an emission peak in the wavelength range of 450 nm to 800 nm in its emission spectrum, which is in the range of 590 nm to 610 nm. 【0111】 With the above configuration, the single-crystal AlN substrate absorbs a portion of the deep ultraviolet light, which is the emission peak wavelength of the active layer, and emits light in the wavelength range of 590 nm to 610 nm in response to the absorption of the deep ultraviolet light. From the light-emitting surface of the light-emitting device 10, light in the wavelength range of 590 nm to 610 nm is emitted along with the deep ultraviolet light. Light in the wavelength range of 590 nm to 610 nm can be easily recognized by the naked eye as orange to red light. With this red emission, which is easily visible and generally signifies a warning or prohibition, the user of the light-emitting device 10 can recognize at a glance that the ultraviolet semiconductor light-emitting element 11 is operating, thereby improving the safety of the worker. 【0112】 Therefore, according to this embodiment, it is possible to provide an ultraviolet semiconductor light-emitting element that allows the user to easily confirm whether or not it is being driven and emitting deep ultraviolet light. [Examples] 【0113】 Figure 7 is a top view of the light-emitting device 50 according to Example 2. As shown in Figure 7, the light-emitting device 50 is configured to include an ultraviolet semiconductor light-emitting element 51. The ultraviolet semiconductor light-emitting element 51 differs from the configuration of Example 1 in that it has a substrate 53 which is a single crystal AlN substrate, but is otherwise configured similarly to the ultraviolet semiconductor light-emitting element 11 of Example 1. 【0114】 The substrate 53 has two regions, region 53A and region 53B, when viewed from above. Region 53A of the substrate 53 is thicker than region 53B. In other respects, the substrate 53 is configured the same as the substrate 13 of Example 1. 【0115】 In Figure 7, the region on the lower surface of the substrate 53 where the active layer 23 is formed is indicated by a dashed line. As shown in Figure 7, the region 53A where the substrate 53 is thicker overlaps with the region where the active layer 23 is formed. 【0116】 Figure 8 is a cross-sectional view of the light-emitting device 50 taken along the line 8-8 in Figure 7. As shown in Figure 8, the substrate 53 is thicker in region 53A than in region 53B. 【0117】 Specifically, for example, the absorption coefficient of substrate 53 is 20 cm² in all regions. -1 Region 53A of substrate 53 has a thickness of 400 μm, similar to sample A in Example 1, and its internal transmittance to light with a wavelength of 265 nm is approximately 45%. Region 53B of substrate 53 has a thickness of 100 μm, similar to sample B in Example 1, and its internal transmittance to light with a wavelength of 265 nm is approximately 82%. 【0118】 In other words, the substrate 53 has a region in plan view where the internal transmittance to light at the emission peak wavelength of the active layer 23 is between 30% and 70%. When the light-emitting device 50 is driven, red light is extracted from region 53A of the substrate 53. High output of deep ultraviolet light is obtained from region 53B, and no red light is emitted. For example, as in the case of sample B of Example 1, blue-white to white visible light can be emitted from region 53B. 【0119】 Thus, in this embodiment, the absorption coefficient of the substrate 53 for 265 nm light is set to 15 cm². -1 In addition to the above, the thickness was varied depending on the region. By doing so, in regions where the substrate 53 is thin and has high internal transmittance, absorption of 265nm light by the substrate 53 is suppressed, ensuring high light output of deep ultraviolet light, while in regions where the substrate is thick and has low internal transmittance, red light with a wavelength of approximately 600nm, which can be easily seen, can be emitted. 【0120】 In Example 2, it is sufficient to increase the thickness of a portion of the substrate 53, and it is arbitrary which region's thickness to increase. For example, as described above, by making the region 53A at the edge of the substrate 53 thicker in a top view, it is possible to avoid the region 53A obstructing the emission of deep ultraviolet light. 【0121】 Furthermore, as shown in Figures 7 and 8, it is preferable to provide region 53A in a region that overlaps with the region where the active layer 23 is formed when viewed from above. By doing so, the light emitted from the active layer 23 can be reliably incident on region 53A, and red light can be reliably emitted. 【0122】 In this embodiment, the substrate 53 can be formed, for example, by protecting the semiconductor laminate 20 with a resist or the like after forming the semiconductor laminate 20, and then forming region 53B by a method such as wet etching of a single crystal AlN substrate. 【0123】 In this embodiment, instead of changing the thickness of a portion of the substrate 53, the impurity concentration of a portion of the substrate 53 may be changed to cause red light to be emitted from that portion. [Examples] 【0124】 Figure 9 is a top view of the light-emitting device 60 according to Example 3. As shown in Figure 9, the light-emitting device 60 is configured to include an ultraviolet semiconductor light-emitting element 61. The ultraviolet semiconductor light-emitting element 61 differs from the configuration of Example 1 in that it has a substrate 63 which is a single crystal AlN substrate, but is otherwise configured similarly to the ultraviolet semiconductor light-emitting element 11 of Example 1. 【0125】 The substrate 63 has two types of regions, region 63A and region 63B, when viewed from above. As shown in Figure 9, the substrate 63 has a rectangular top surface shape. Region 63A is a rectangular region provided at the four corners of the substrate 63. Region 63B is the remaining region of the substrate 63 after removing region 63A. 【0126】 The substrate 63 is thicker in region 63A than in region 63B. In other respects, the substrate 63 is configured the same as the substrate 13 of Example 1. 【0127】 Specifically, for example, the absorption coefficient of substrate 63 is 20 cm² in all regions. -1Region 63A of substrate 63 has a thickness of 400 μm, similar to sample A in Example 1, and its internal transmittance to light with a wavelength of 265 nm is approximately 45%. Region 63B of substrate 63 has a thickness of 100 μm, similar to sample B in Example 1, and its internal transmittance to light with a wavelength of 265 nm is approximately 82%. 【0128】 In other words, the substrate 63 has a region in plan view where the internal transmittance to light at the emission peak wavelength of the active layer 23 is between 30% and 70%. When the light-emitting device 60 is driven, red light with a peak at approximately 600 nm in the wavelength range of 450-800 nm is extracted from region 63A of the substrate 63. In region 63B, the absorption of light at 265 nm is small, a high output of deep ultraviolet light is obtained, and almost no red light is emitted. For example, as in the case of sample B of Example 1, bluish-white to white visible light can be emitted from region 63B. 【0129】 In this embodiment, since the thicker regions 63A are placed at the four corners of the substrate 63, it is possible to confirm whether or not red light is emitted from the four regions 63A, or whether or not red light is emitted from the four regions 63A with a certain intensity. This allows for indirect confirmation of whether or not deep ultraviolet light is emitted uniformly. 【0130】 The upper surface shape of region 63A can be any shape; in addition to the rectangle shown in Figure 9, it may also be a sector shape centered on the four corners of the substrate 63, for example. 【0131】 [Differentiation] Figure 10 is a top view of a modified light-emitting device 70 according to Example 3. As shown in Figure 10, the light-emitting device 70 is configured to include an ultraviolet semiconductor light-emitting element 71. The ultraviolet semiconductor light-emitting element 71 differs from the configuration of Example 3 in that it has a substrate 73 which is a single crystal AlN substrate, but is otherwise configured similarly to the ultraviolet semiconductor light-emitting element 61 of Example 3. 【0132】 The substrate 73 has two types of regions, region 73A and region 73B, when viewed from above. As shown in Figure 10, the substrate 73 has a rectangular top surface shape. Region 73A is an annular region provided along the outer edge of the substrate 73. Region 73B is the remaining region of the substrate 73 after removing region 73A. 【0133】 The substrate 73 is thicker in region 73A than in region 73B. In other respects, the substrate 73 is configured the same as the substrate 63 of Example 3. In this embodiment, since the thicker region 73A is arranged along the outer edge of the substrate 73, it is possible to confirm whether or not red light is emitted uniformly from region 73A. This makes it possible to more reliably confirm whether or not deep ultraviolet light is emitted uniformly. 【0134】 Furthermore, for example, in a top view, the thicker region 73A may be provided in a shape along two intersecting lines. For example, the thicker region 73A may be placed on the diagonal of the substrate 73. Doing so can enhance the meaning of the warning or attention-gathering effect of the red light emission. 【0135】 The configurations in the above-described examples and manufacturing methods are merely illustrative and can be modified as appropriate depending on the application. 【0136】 For example, the above embodiment describes an example in which the ultraviolet semiconductor light-emitting element is mounted in a flip-chip configuration, but it is not limited to this. The side opposite to the single-crystal AlN substrate may be used as the light-emitting surface. In that case as well, the light that has undergone the absorption and emission process by the single-crystal AlN substrate is emitted from the light-emitting surface. [Explanation of symbols] 【0137】 10 Light-emitting device 11. Ultraviolet semiconductor light-emitting element 13 circuit boards 13S light exit surface 15 Submount board 20 Semiconductor Stacks 21 n-type cladding layer 23 Active layer 25 p-type semiconductor layer 27 Electron Block Layer 29 p-type cladding layer 31 Contact Layer 33 n electrode 37p electrode

Claims

[Claim 1] Single crystal AlN substrate and The n-type AlGaN layer formed on the single-crystal AlN substrate, An active layer formed on the n-type AlGaN layer, having an emission peak wavelength of 250 nm or more and 280 nm or less, The active layer has a p-type AlGaN layer formed on it, In the emission spectrum, the emission peak in the wavelength range of 450 nm to 800 nm is in the range of 590 nm to 610 nm. The single-crystal AlN substrate has an absorption coefficient of 15 cm⁻¹ or more for light at the emission peak wavelength of the active layer. An ultraviolet semiconductor light-emitting element having an output of 0.15 μW or more of light with a wavelength of 590 nm to 610 nm during operation. [Claim 2] The ultraviolet semiconductor light-emitting element according to claim 1, wherein the single-crystal AlN substrate absorbs a portion of the light emitted from the active layer and emits light in the wavelength range of 590 nm to 610 nm in response to the absorption of the emitted light. [Claim 3] The ultraviolet semiconductor light-emitting element according to Claim 1, wherein the carbon concentration in the single crystal AlN substrate is 3 × 10¹⁷ atoms / cm³ or more. [Claim 4] The ultraviolet semiconductor light-emitting element according to claim 3, wherein the sum of the Si concentration and O concentration in the single crystal AlN substrate is higher than the C concentration. [Claim 5] The ultraviolet semiconductor light-emitting element according to Claim 1, wherein the single-crystal AlN substrate has a region in which, in a plan view, the internal transmittance τ, expressed by the following formula (1), is 30% or more and 70% or less, when the absorption coefficient of the active layer with respect to the emission peak wavelength is α and the thickness of the single-crystal AlN substrate is x. [Math 1] [Claim 6] The ultraviolet semiconductor light-emitting element according to claim 5, wherein the single-crystal AlN substrate has a region in which the internal transmittance τ is 40% or more and 60% or less in a plan view. [Claim 7] The ultraviolet semiconductor light-emitting element according to claim 5 or 6, wherein the region is along the outer edge of the upper surface of the single crystal AlN substrate.