JP5379703B2 - Ultraviolet semiconductor light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultraviolet semiconductor light emitting element, capable of improving the efficiency of luminescence of an ultraviolet light having a luminescent wavelength of 200 to 300 nm, and capable of improving reliability thereof. <P>SOLUTION: The ultraviolet semiconductor light emitting element having a luminescent wavelength in an ultraviolet region of 200 to 300 nm includes a light emitting layer 4 between an n-type nitride semiconductor layer 3 and a p-type nitride semiconductor layer 5. A p electrode 6 as one electrode in a pair of electrodes brought into contact with each of the n-type nitride semiconductor layer 3 and the p-type nitride semiconductor layer 5 consists of a transparent electrode including a transparent metallic layer 61 formed of a metal material whose optical absorption coefficient to the ultraviolet light having the luminescent wavelength is &le;5&times;10<SP>4</SP>cm<SP>-1</SP>. The ultraviolet semiconductor light emitting element includes a protective layer 9 protecting the p electrode 6 as the transparent electrode formed of a transparent insulating material in the luminescent wavelength of the ultraviolet light. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an ultraviolet semiconductor light emitting device.

  Ultraviolet semiconductor light-emitting elements that emit light in the ultraviolet wavelength region are expected to be applied to various fields such as hygiene, medicine, industry, lighting, and precision machinery.

  However, a general ultraviolet semiconductor light emitting device using a sapphire substrate as a single crystal substrate for epitaxial growth and a nitride semiconductor material as a material of a light emitting layer has lower luminous efficiency and light output than a blue semiconductor light emitting device. Currently, it is not widely industrialized.

  Here, the reason why the luminous efficiency of the ultraviolet semiconductor light emitting device is low is that the threading dislocation density is high, non-radiative recombination becomes dominant, the internal quantum efficiency is low, and the performance of the p-type nitride semiconductor layer is insufficient. The reason is that the light extraction efficiency of the emitted ultraviolet light to the outside is low. That is, in a general ultraviolet semiconductor light-emitting device, the laminated film of the n-type nitride semiconductor layer, the light-emitting layer, and the p-type nitride semiconductor layer on one surface side of the sapphire substrate has a mesa structure, and each is an opaque metal electrode. The horizontal electrode structure in which the n-electrode and the p-electrode are arranged in the lateral direction on the one surface side of the sapphire substrate is adopted, and light is taken out only from the sapphire substrate, and most of the light reaching the n-electrode and p-electrode is Light absorption efficiency is low because it is absorbed and not used. Note that the above-described mesa structure is formed by forming a laminated film of an n-type nitride semiconductor layer, a light emitting layer, and a p-type nitride semiconductor layer on the one surface side of the sapphire substrate by MOVPE or the like, and then performing n-type nitriding. The laminated film is formed by patterning so that a part of the physical semiconductor layer is exposed.

Therefore, in the field of ultraviolet semiconductor light emitting devices, a transparent electrode having high light transmittance and conductivity at an ultraviolet wavelength is desired. In general, an oxide-based material having a large band gap is used as a transparent conductive film used as a transparent electrode. However, as a transparent electrode with improved light transmittance in a transparent electrode in the ultraviolet region, a general ITO is used. An ITO film (see Patent Document 1) having a higher tin content and a higher film formation temperature than a film and a Ga ₂ O ₃ film (see Patent Document 2) formed by a pulse laser deposition method have been proposed. ing.

  In addition, it has also been proposed to use a highly conductive metal as a transparent conductive film by making it thin enough to prevent light absorption (Patent Document 3).

JP 2006-278554 A Japanese Patent No. 4083396 JP 2009-151963 A

  By the way, in the ultraviolet semiconductor light-emitting device described in the above-mentioned Patent Document 1, the wavelength of tin is 25% by mass in the ITO film constituting the transparent electrode and the substrate temperature during the deposition of the ITO film is 800 ° C. The transmittance can be improved to about 75% for ultraviolet light of 330 nm or more. However, when the wavelength is 300 nm, the light transmittance is reduced to 30%, and at a wavelength of 260 nm or less, the light transmittance is 0%. In short, the transparent electrode made of the ITO film of the ultraviolet semiconductor light-emitting device described in Patent Document 1 has insufficient transparency in the deep ultraviolet region with a wavelength of 200 nm to 300 nm, and particularly has transparency at a wavelength of 260 nm or less. I don't have it.

  The transparent electrode described in Patent Document 2 has an average light transmittance of 90% or more at a wavelength of 1000 nm to 250 nm, but has a transmittance of about 40% for ultraviolet light having a wavelength of 240 nm. The light transmittance is insufficient for use as a transparent electrode for light extraction of a light emitting device. Further, the transparent electrode described in Patent Document 2 must be formed by a special film formation method such as a pulsed laser deposition method, and film formation or annealing at a high temperature is necessary to obtain good conductivity. In addition, the process becomes complicated and the cost becomes high.

  Further, the transparent electrode described in Patent Document 3 is an AlAg thin film having a film thickness of 20 nm or less, and since many holes are formed in the AlAg thin film, when a pad is provided on the surface side of the transparent electrode, There is a concern that part of the pad comes into contact with the p-type nitride semiconductor layer underlying the transparent electrode through the hole, and the contact between the pad and the p-type nitride semiconductor layer does not become ohmic contact but becomes Schottky contact. . Further, the transparent electrode described in Patent Document 3 has problems in long-term stability and reliability.

  The present invention has been made in view of the above-mentioned reasons, and an object thereof is an ultraviolet semiconductor capable of improving the emission efficiency of ultraviolet light having an emission wavelength of 200 nm to 300 nm and improving long-term stability and reliability. The object is to provide a light emitting element.

The invention of claim 1 is an ultraviolet semiconductor light emitting device having an emission wavelength in an ultraviolet region of 200 nm to 300 nm, and has a light emitting layer between an n-type nitride semiconductor layer and a p-type nitride semiconductor layer , At least one electrode of the pair of electrodes in contact with the respective n-type nitride semiconductor layer and the p-type nitride semiconductor layer, the light absorption coefficient for ultraviolet light of the emission wavelength 5 × 10 ⁴ cm ^-1 Do a transparent electrode having at least a transparent metal layer formed by metal material is less than Ri, the transparent electrode on at least one surface side in the thickness direction of the transparent metal layer, a metal material different from that of the transparent metal layer And a blocking layer that prevents the reactive species that adversely affect the transparent metal layer from reaching the transparent metal layer, and the metal material of the block layer is made of Sb, Bi, or an alloy thereof. Characterized in that it is selected from.

According to this invention, at least one of the pair of electrodes is formed of a metal material having a light absorption coefficient of 5 × 10 ⁴ cm ⁻¹ or less for ultraviolet light having an emission wavelength in the ultraviolet region of 200 nm to 300 nm. By forming the transparent electrode having at least the transparent metal layer, absorption of the ultraviolet light emitted from the light emitting layer can be suppressed and the light extraction efficiency can be improved and the resistance of the transparent electrode can be reduced. from Figure is the improvement in luminous efficiency.
Further, according to the present invention, the transparent electrode is formed of a metal material different from the transparent metal layer on at least one surface side in the thickness direction of the transparent metal layer, and is a reactive species that adversely affects the transparent metal layer. Is provided with a block layer that prevents the transparent metal layer from reaching the transparent metal layer, so that even when the metal material of the transparent metal layer is a highly active metal material, the reactive species that adversely affect the transparent metal layer are blocked by the block layer. Since the long-term stability of the transparent metal layer can be improved, the degree of freedom in selecting a metal material for the transparent metal layer is increased.
According to the invention, since the metal material of the block layer is selected from the group of Sb, Bi, or alloys thereof, the metal material of the block layer is alloyed with the transparent metal layer to form the block layer. Since it becomes chemically stable, the long-term stability and reliability of the transparent electrode can be improved.
The invention of claim 2 is characterized in that, in the invention of claim 1, a protective layer is formed of an insulating material transparent at the emission wavelength of the ultraviolet light and protects the transparent electrode.
According to this invention, since the protective layer is formed of a transparent insulating material at the emission wavelength of the ultraviolet light and protects the transparent electrode, the transparent electrode is hardly deteriorated by oxidation or the like, and has long-term stability and reliability. Can improve the performance.

The invention of claim 3 is the invention of claim 2, the insulating material of the protective layer is characterized by a MgF _2.

According to the present invention, since the insulating material of the protective layer is MgF ₂ , the light caused by the protective layer is compared with the case where Al ₂ O ₃ , SiO ₂ or the like is used as the insulating material of the protective layer. Loss can be suppressed.

According to a fourth aspect of the present invention, in the first to third aspects of the invention, the metal material of the transparent metal layer is selected from the group of Na, K, Cs, and Rb.

  According to this invention, it has excellent light transmittance with respect to ultraviolet light having an emission wavelength in the ultraviolet region of 200 nm to 300 nm.

According to a fifth aspect of the present invention, in the first to fourth aspects of the invention, the transparent metal layer has a thickness of 50 nm to 100 nm.

  According to this invention, the current flowing through the transparent electrode can be easily diffused uniformly in the plane of the transparent electrode, the in-plane uniformity of the current density in the transparent electrode can be improved, and the luminous efficiency can be improved. I can plan.

A sixth aspect of the invention is characterized in that, in the first to fifth aspects of the invention, the thickness of the block layer is 5 nm or less.

  According to this invention, since the thickness of the block layer is 5 nm or less, even if the metal material of the block layer is a material having a low light transmittance with respect to the ultraviolet light of the emission wavelength, the absorption of the ultraviolet light in the block layer Can be suppressed.

According to a seventh aspect of the present invention, in the first to sixth aspects of the invention, the transparent electrode is made of a metal material that is in ohmic contact with the base of the light emitting layer on the light emitting layer side of the transparent metal layer. An ohmic contact layer is provided.

  According to this invention, since the transparent electrode includes the ohmic contact layer, the contact resistance between the transparent electrode and the base on the light emitting layer side can be reduced, so that the metal material of the transparent metal layer can be freely selected. As the degree increases, the luminous efficiency can be improved.

The invention of claim 8 is the invention of claim 7 , wherein the metal material of the ohmic contact layer is selected from the group consisting of Al, Ti, Hf, Zr, Cr, Au, Ni, Pt, Pd, In, or an alloy thereof. It is selected.

  According to the present invention, it is possible to obtain ohmic contact with the base by the ohmic contact layer regardless of the conductivity type (p-type, n-type) of the base of the transparent electrode.

The invention according to claim 9 is the invention according to claim 7 or 8, wherein the ohmic contact layer has a thickness of 5 nm or less.

  According to the present invention, since the thickness of the ohmic contact layer does not exceed 5 nm, even if the metal material of the ohmic contact layer is a material having low light transmittance with respect to ultraviolet light having the emission wavelength, The absorption of ultraviolet light can be suppressed.

In a tenth aspect of the present invention, in the first to ninth aspects of the present invention, a part of the surface of the transparent electrode is provided with a pad formed of a material selected from the group of Au, Al, or an alloy thereof. It is characterized by that.

  According to the present invention, since a pad formed of a material selected from the group of Au, Al, or an alloy thereof is provided, it becomes easy to connect a wiring such as a general bonding wire. Electrical connection between the element and the external circuit is facilitated.

  In the invention of claim 1, there is an effect that the luminous efficiency of ultraviolet light having a wavelength of 200 nm to 300 nm can be improved.

The ultraviolet semiconductor light emitting element of embodiment is shown, (a) is a schematic sectional drawing, (b) is a schematic plan view, (c) is a principal part schematic sectional drawing. It is a schematic sectional drawing of the other structural example of the principal part in an ultraviolet semiconductor light emitting element same as the above.

  The ultraviolet semiconductor light emitting device of this embodiment is an ultraviolet light emitting diode having an emission wavelength (emission peak wavelength) of 200 nm to 300 nm, and as shown in FIGS. 1A and 1B, a single crystal substrate for epitaxial growth N-type nitride semiconductor layer 3 is formed on one surface side of buffer 1 via buffer layer 2, light-emitting layer 4 is formed on the surface side of n-type nitride semiconductor layer 3, and p-type is formed on the surface side of light-emitting layer 4. A nitride semiconductor layer 5 is formed.

  In addition, the ultraviolet semiconductor light emitting device of this embodiment has a cylindrical mesa structure on the one surface side of the single crystal substrate 1, and includes an n electrode (cathode electrode) 7 and a p electrode (anode electrode) as a pair of electrodes. 6) adopts a horizontal electrode structure in which 6 are aligned in the horizontal direction on the one surface side of the single crystal substrate 1. That is, in the ultraviolet semiconductor light-emitting device of this embodiment, the p-electrode 6 is formed on the surface side of the p-type nitride semiconductor layer 5 (on the side opposite to the light-emitting layer 4 side in the p-type nitride semiconductor layer 5). An n electrode 7 is formed on the side of the n-type nitride semiconductor layer 3 where the light emitting layer 4 is laminated. Note that, as described later, the above-described mesa structure is a stacked film of a buffer layer 2, an n-type nitride semiconductor layer 3, a light emitting layer 4, and a p-type nitride semiconductor layer 5 on the one surface side of the single crystal substrate 1. Is formed by patterning the laminated film so that a part of the n-type nitride semiconductor layer 3 is exposed. Thus, the n-electrode 7 is formed by sequentially growing the buffer layer 2, the n-type nitride semiconductor layer 3, the light emitting layer 4, and the p-type nitride semiconductor layer 5 on the one surface side of the single crystal substrate 1. A predetermined region of the laminated film of the layer 2, the n-type nitride semiconductor layer 3, the light emitting layer 4, and the p-type nitride semiconductor layer 5 is formed in the middle of the n-type nitride semiconductor layer 3 from the surface side of the p-type nitride semiconductor layer 5. Is formed on the surface of n-type nitride semiconductor layer 3 exposed by etching.

  By the way, in the ultraviolet semiconductor light emitting device of this embodiment, the p electrode 6 is constituted by a transparent electrode, and is formed on the surface side of the p-type nitride semiconductor layer 5 by an insulating material transparent at the emission wavelength of ultraviolet light. A protective layer 9 for protecting the electrode 6 is provided. Thus, the ultraviolet light emitted from the light emitting layer 4 can be efficiently extracted through the p electrode 6 and the protective layer 9 made of a transparent electrode. In other words, the absorption of ultraviolet light emitted from the light emitting layer 4 at the p-electrode 6 can be suppressed, and the light extraction efficiency can be improved.

  Here, the planar shape of the p electrode 6 and the protective layer 9 is circular, and the diameter of the protective layer 9 is slightly smaller than that of the p electrode 6. In this embodiment, since the mesa structure is cylindrical, the planar shape of the p electrode 6 and the protective layer 9 is circular, but the shape of the mesa structure is not particularly limited, and the p electrode 6 and the protective layer 9 are not limited. The planar shape is not particularly limited. However, it is desirable that the planar shape of the p electrode 6 and the protective layer 9 is similar to the upper surface of the mesa structure (here, the surface of the p-type nitride semiconductor layer 5), and the area of the light extraction surface is increased.

On the other hand, the n-electrode 7 is formed in an annular shape surrounding the p-electrode 6 over the entire circumference in plan view. An insulating film 8 made of an insulating material (for example, SiO ₂ or the like) is formed across the side surface of the mesa structure and a part of the upper surface, and the peripheral portion of the p electrode 6 and the p-type nitride semiconductor layer 5 are formed. A part of the insulating film 8 is interposed between the two. In short, an opening 8 a for contact between the p-electrode 6 and the p-type nitride semiconductor layer 5 is formed in a portion of the insulating film 8 formed on the surface of the p-type nitride semiconductor layer 5. The insulating film 8 can prevent a short circuit between the p electrode 6 and the n electrode 7.

  In the ultraviolet semiconductor light emitting device of this embodiment, a pad 10 is formed so as to cover the transparent electrode 8 and the protective layer 9 on the surface side of the p-type nitride semiconductor layer 5. An opening 10a that exposes a part of the surface of 9 is formed. In short, the pad 10 is formed on a part of the surface of the p-electrode 6 and is patterned so that light can be extracted from the protective layer 9 (opening 10a is formed).

  Here, the single crystal substrate 1 is a sapphire substrate having one surface with a (0001) plane, that is, a c-plane. However, the single crystal substrate 1 is not limited to a sapphire substrate. For example, a spinel substrate Alternatively, a silicon substrate, a silicon carbide substrate, a zinc oxide substrate, a gallium phosphide substrate, a gallium arsenide substrate, a magnesium oxide substrate, a zirconium boride substrate, a group III nitride semiconductor crystal substrate, or the like may be used.

  The buffer layer 2 is provided in order to reduce threading dislocations in the n-type nitride semiconductor layer 3 and to reduce residual strain in the n-type nitride semiconductor layer 3, and is composed of an AlN layer. The nitride semiconductor layer is not limited to a layer but may be any nitride semiconductor layer containing Al as a constituent element, and is composed of an AlGaN layer, an AlInN layer, or the like.

The n-type nitride semiconductor layer 3 is for injecting electrons into the light emitting layer 4, and the film thickness and composition are not particularly limited. For example, the Si-doped n-type Al formed on the buffer layer 2 is used. It is composed of a _0.55 Ga _0.45 N layer. The n-type nitride semiconductor layer 3 is not limited to a single layer structure, and may be a multilayer structure. For example, a Si-doped n-type Al _0.7 Ga _0.3 N layer on the buffer layer 2 and the n-type Al _0.7 Ga _0.3 N layer The upper Si-doped n-type Al _0.55 Ga _0.45 N layer may be used.

Further, the light emitting layer 4 has a quantum well structure, and barrier layers and well layers are alternately stacked. For example, in the light emitting layer 4, the barrier layer may be composed of an Al _0.55 Ga _0.45 N layer having a thickness of 8 nm, and the well layer may be composed of an Al _0.40 Ga _0.60 N layer having a thickness of 2 nm. In addition, each composition of a barrier layer and a well layer is not limited, For example, what is necessary is just to set suitably according to the desired light emission wavelength in the range of 200 nm-300 nm. Further, the number of well layers in the light emitting layer 4 is not particularly limited, and the light emitting layer 4 is not limited to a multiple quantum well structure having a plurality of well layers, but adopts a single quantum well structure having one well layer. May be. Further, the thicknesses of the barrier layer and the well layer are not particularly limited. In addition, the light emitting layer 4 has a single layer structure, and the light emitting layer 4 and the layers on the both sides in the thickness direction of the light emitting layer 4 (n-type nitride semiconductor layer 3 and p-type nitride semiconductor layer 5) have a double hetero structure. May be formed.

  The p-type nitride semiconductor layer 5 is for injecting holes into the light emitting layer 4, and the film thickness and composition are not particularly limited. For example, p-type nitride semiconductor layer 5 formed on the light emitting layer 4 may be used. A first p-type nitride semiconductor layer made of an AlGaN layer, and a second p-type nitride semiconductor layer 7b made of an Mg-doped p-type AlGaN layer formed on the first p-type nitride semiconductor layer; And a third p-type nitride semiconductor layer made of an Mg-doped p-type GaN layer formed on the second p-type nitride semiconductor layer. Here, each composition of the first p-type nitride semiconductor layer and the second p-type nitride semiconductor layer is such that the band gap energy of the first p-type nitride semiconductor layer is the second p-type nitride semiconductor layer. It is set to be larger than the band gap energy. The composition of the second p-type nitride semiconductor layer is set so that the band gap energy is the same as that of the barrier layer. The p-type nitride semiconductor layer 5 has a thickness of the first p-type nitride semiconductor layer of 15 nm, a thickness of the second p-type nitride semiconductor layer of 50 nm, and a third p-type nitride semiconductor layer. Although the film thickness is set to 15 nm, the film thickness is not particularly limited. Further, the nitride semiconductor employed in the p-type nitride semiconductor layer 5 is not particularly limited, and for example, AlGaInN may be used. Further, in addition to AlGaInN, InGaN may be used for the third p-type nitride semiconductor layer.

The transparent electrode constituting the p-electrode 6 was formed of a metal material having a light absorption coefficient of 5 × 10 ⁴ cm ⁻¹ or less with respect to ultraviolet light having an emission wavelength of the light-emitting layer 4 as shown in FIG. A transparent metal layer 61 is provided. Here, if the metal material of the transparent metal layer 61 is selected from the group of Na, K, Cs, and Rb, the light absorption coefficient is 5 × 10 ⁴ cm ⁻¹ or less, and light is emitted in the ultraviolet region of 200 nm to 300 nm. Excellent optical transparency with respect to ultraviolet light having a wavelength. When the light absorption coefficient is 5 × 10 ⁴ cm ⁻¹ , the light transmittance (without considering reflection) when the film thickness is 100 nm is about 60%, and the light absorption coefficient is more than 5 × 10 ⁴ cm ^−1. A high metal material has a light transmittance of 50% or less, and transparency as a transparent electrode becomes insufficient.

  However, Na, which is one of the group of metal materials described above, is transparent only in the wavelength region of 210 nm or less. Further, the light absorption rate of K in the above-described group of metal materials is 12.3% when the film thickness is 100 nm, 6.5% when the film thickness is 50 nm, and 3.3% when the film thickness is 25 nm. The light absorption rate of Rb is 22.9% when the film thickness is 100 nm, 11.7% when the film thickness is 50 nm, and 6.1% when the film thickness is 25 nm, and the light absorption rate of Cs is When the film thickness is 50 nm, it is 24.3%, and when the film thickness is 25 nm, it is 13.2%.

  Therefore, by setting the thickness of the transparent metal layer 61 to 100 nm or less (that is, the upper limit of the thickness of the transparent metal layer 61 is set to 100 nm), the ultraviolet light having an emission wavelength in the ultraviolet region of 200 nm to 300 nm is light. It can be seen that the transparency of the absorption rate of 25% or less can be realized. On the other hand, the lower limit of the transparent metal layer 61 is preferably 50 nm from the viewpoint of increasing the conductivity of the p-electrode 6 and ensuring a sufficient function as an electrode. If the thickness of the transparent metal layer 61 is 50 nm to 100 nm, the current flowing in the transparent electrode can be easily diffused uniformly in the plane of the transparent electrode, and the in-plane uniformity of the current density in the transparent electrode can be improved. The luminous efficiency can be improved.

  Here, although the transparent metal layer 61 can be used alone as a transparent electrode, the metal material of the transparent metal layer 61 described above is an alkali metal, has a low melting point, and has high reactivity in the atmosphere ( High activity). Therefore, in order to operate more stably as the electrode of the ultraviolet semiconductor light emitting element, the p electrode 6 is formed on at least one surface in the thickness direction of the transparent metal layer 61 by a metal material different from the transparent metal layer 61. It is preferable to form a block layer 62 that prevents the reactive species (for example, oxygen, moisture, semiconductor, metal, etc.) that adversely affect the layer 61 from reaching the transparent metal layer 61. Here, in the example shown in FIG. 1C, the block layers 62 are formed on both surfaces in the thickness direction of the transparent metal layer 61.

  By providing such a block 62, even if the metal material of the transparent electrode 61 is a highly active metal material, reactive species that adversely affect the transparent metal layer 61 can be prevented by the block layer 62. Since the long-term stability of the layer 61 can be improved, the degree of freedom in selecting the metal material of the transparent metal layer 61 is increased.

  The metal material of the block layer 62 is preferably selected from the group of Sb, Bi, or alloys thereof that can be alloyed with the transparent metal layer 61 to form a relatively stable metal. If selected from this group, the metal material of the block layer 62 is alloyed with the transparent metal layer 61 and the block layer 62 becomes chemically stable, so that the long-term stability and reliability of the transparent electrode can be improved. However, since the metal material of the block layer 62 is not transparent with respect to light having a wavelength of 200 nm to 300 nm, it is preferably formed with a thickness of 5 nm or less (that is, not exceeding 5 nm). Here, if the thickness of the block layer 62 is 5 nm or less, even if the metal material of the block layer 62 is a material having a low light transmittance with respect to the ultraviolet light of the emission wavelength, the absorption of the ultraviolet light in the block layer 62 is suppressed. can do.

  Furthermore, in the present embodiment, in order to obtain good ohmic contact with the p-type nitride semiconductor layer 5, the transparent electrode constituting the p electrode 6 is disposed on the light emitting layer 4 side of the transparent metal layer 61 (see FIG. 1C). In the example, between the block layer 62 and the p-type nitride semiconductor layer 5) and ohmic contact with the base on the light emitting layer 4 side (p-type nitride semiconductor layer 5 in the example of FIG. 1C). An ohmic contact layer 63 made of a metal material is provided. In the present embodiment, since the transparent electrode includes the ohmic contact layer 63, the contact resistance between the transparent electrode and the base on the light emitting layer 4 side can be reduced, so the degree of freedom in selecting the metal material of the transparent metal layer 61 is increased. In addition, the luminous efficiency can be improved.

  The metal material of the ohmic contact layer 63 may be selected from the group of Al, Ti, Hf, Zr, Cr, Au, Ni, Pt, Pd, In, or an alloy thereof. Regardless of the conductivity type (p-type, n-type) of the base of the electrode, the ohmic contact layer 63 can make ohmic contact with the base. However, since this group of metal materials does not have transparency with respect to light having a wavelength of 200 nm to 300 nm, it is preferably formed with a thickness of 5 nm or less (that is, not exceeding 5 nm). In other words, if the thickness of the ohmic contact layer 63 is 5 nm or less, even if the metal material of the ohmic contact layer 63 is a material having a low light transmittance with respect to the ultraviolet light of the emission wavelength, the ultraviolet light in the ohmic contact layer 63 is reduced. Absorption can be suppressed.

  By the way, the laminated structure of the transparent electrode which comprises the p electrode 6 is not restricted to the example of FIG.1 (c) and FIG.2 (a), For example, the laminated structure shown to FIG.2 (b)-(e) may be sufficient. FIG. 2B differs from FIG. 2A in that the block layer 62 is not provided, and FIG. 2C does not include the ohmic contact layer 63 as compared to FIG. FIG. 4D is different from FIG. 1A in that the block layer 62 and the ohmic contact layer 63 on the light emitting layer 4 (see FIG. 1C) side in the transparent metal layer 61 are not provided. FIG. 4E is different from FIG. 1A in that the block layer 62 on the light emitting layer 4 (see FIG. 1C) side of the transparent metal layer 61 is not provided.

Further, in the present embodiment, the outermost surface of the transparent electrode (in the example of FIG. 1C, the surface of the upper block layer 62) so that the transparent electrode constituting the p electrode 6 operates stably for a long time. The above-described protective layer 9 for protecting the transparent electrode is formed thereon. Here, since the conductive property is not necessary for the protective layer 9, an insulating material transparent to ultraviolet light having an emission wavelength of 200 to 300 nm can be used, and MgF ₂ is optimal. In the present embodiment, since the insulating material of the protective layer 9 is MgF ₂ , the optical loss caused by the protective layer 9 compared to the case where Al ₂ O ₃ , SiO ₂ or the like is adopted as the insulating material of the protective layer 9. Can be suppressed.

  In the present embodiment, the above-described pad 10 is provided on a part of the surface of the transparent electrode. Here, the pad 10 is preferably formed of a material selected from the group of Au, Al, or an alloy thereof. By providing the pad 10 formed of such a material, a package, a wiring board, or the like is provided. When mounting on the mounting member, it is easy to connect common wiring such as bonding wires (gold fine wire, Al thin wire), so that the electrical connection between the ultraviolet semiconductor light emitting element and the external circuit formed on the mounting member is possible. It becomes easy. However, the pad 10 is not necessarily provided with a hole.

  The film forming method on the transparent electrode and the pad 10 is not particularly limited, but a resistance heating type vacuum vapor deposition method, an electron beam vapor deposition method, a sputtering method, or the like may be appropriately employed depending on the type of metal material. That's fine.

  The n-electrode 7 is composed of a laminated film of a Ti film having a thickness of 20 nm, an Al film having a thickness of 100 nm, a Ti film having a thickness of 20 nm, and an Au film having a thickness of 200 nm. The n electrode 7 is in electrical contact with the n-type nitride semiconductor layer 3, and the material, film thickness, laminated structure, and the like are not particularly limited as long as the contact resistance is small and ohmic contact is possible. Here, in the present embodiment, an example in which only the p electrode 6 is configured by a transparent electrode has been described. However, only the n electrode 7 may be configured by a transparent electrode, or both the p electrode 6 and the n electrode 7 are transparent. In any case, the transparent electrode may have the same structure as that of the p-electrode 6 described above.

  Hereinafter, a specific manufacturing method of the ultraviolet semiconductor light emitting device shown in FIG. 1 will be described.

After the single crystal substrate 1 made of a sapphire substrate is introduced into the reactor of the MOVPE apparatus, the substrate temperature is kept at a predetermined temperature (for example, 1250 ° C. while maintaining the pressure in the reactor at a predetermined growth pressure (for example, 10 kPa≈76 Torr). ), The one surface of the single crystal substrate 1 is cleaned by heating for a predetermined time (for example, 10 minutes), and then the substrate temperature is set to the same growth temperature (here, 1250 ° C.) as the predetermined temperature. ), The flow rate of trimethylaluminum (TMAl) that is a raw material of aluminum is set to 0.05 L / min (50 SCCM) in a standard state, and the flow rate of ammonia (NH ₃ ) that is a raw material of nitrogen is set to after setting the 0.05L / min (50SCCM) under standard conditions, single sintered started supplying to the TMAl and NH ₃ at the same time reactor Growing a buffer layer 2 made of AlN layer. The buffer layer 2 is not limited to a single crystal AlN layer but may be a single crystal AlGaN layer.

As growth conditions for the n-type nitride semiconductor layer 3, the growth temperature is 1200 ° C., the growth pressure is the predetermined growth pressure (here, 10 kPa), TMAl is used as the aluminum source, and trimethylgallium (TMGa) is used as the gallium source. NH _{3 is used} as a nitrogen source, tetraethylsilane (TESi) is used as a silicon source that is an impurity imparting n-type conductivity, and H ₂ gas is used as a carrier gas for transporting each source. Here, the flow rate of TESi is set to 0.0009 L / min (0.9 SCCM) in a standard state. Each raw material is not particularly limited. For example, triethylgallium (TEGa) may be used as a gallium raw material, a hydrazine derivative may be used as a nitrogen raw material, and monosilane (SiH ₄ ) may be used as a silicon raw material.

The growth conditions of the light emitting layer 4 are as follows: the growth temperature is 1200 ° C., which is the same as that of the n-type nitride semiconductor layer 3, the growth pressure is the predetermined growth pressure (here, 10 kPa), the aluminum source is TMAl, and the gallium source TMGa and NH ₃ are used as a raw material of nitrogen. Here, the growth conditions of the barrier layer of the light emitting layer 4 are set to be the same as the growth conditions of the n-type nitride semiconductor layer 3 except that TESi is not supplied. As for the growth conditions of the well layer of the light emitting layer 4, the molar ratio of TMAl ([TMAl] / {[TMAl] + [TMGa]}) in the group III material is set so as to obtain a desired composition. It is set smaller than the growth conditions. In this embodiment, the barrier layer is not doped with impurities. However, the present invention is not limited to this, and n-type impurities such as silicon may be doped with an impurity concentration that does not deteriorate the crystal quality of the barrier layer.

The growth conditions of the first p-type nitride semiconductor layer and the second p-type nitride semiconductor layer of the p-type nitride semiconductor layer 5 include a growth temperature of 1050 ° C. and a growth pressure of the predetermined growth pressure (here, 10 kPa), TMAl as the aluminum source, TMGa as the gallium source, NH ₃ as the nitrogen source, and biscyclopentadienylmagnesium (Cp ₂ Mg) as the source of magnesium which is an impurity imparting p-type conductivity. H ₂ gas is used as a carrier gas for transporting each raw material. The growth condition of the third p-type nitride semiconductor layer is basically the same as the growth condition of the second p-type nitride semiconductor layer, except that the supply of TMAl is stopped. Here, in any growth of the first to third p-type nitride semiconductor layers, the flow rate of Cp ₂ Mg is 0.02 L / min (20 SCCM) in the standard state, and the first to third p-type nitrides are used. The molar ratio (flow rate ratio) of the group III raw material is appropriately changed according to the composition of each semiconductor layer.

  The crystal growth step of sequentially growing the buffer layer 2, the n-type nitride semiconductor layer 3, the light emitting layer 4, and the p-type nitride semiconductor layer 5 on the one surface side of the single crystal substrate 1 under the above-described growth conditions is completed. After that, the single crystal substrate 1 having a laminated structure of the buffer layer 2, the n-type nitride semiconductor layer 3, the light emitting layer 4, and the p-type nitride semiconductor layer 5 is taken out from the reactor of the MOVPE apparatus.

  Then, the electrode formation process which forms the n electrode 7 and the p electrode 6 is performed.

  In this electrode formation step, first, the upper surface of the mesa structure is supported in the laminated film of the buffer layer 2, the n-type nitride semiconductor layer 3, the light emitting layer 4, and the p-type nitride semiconductor layer 5 by using a photolithography technique. A resist layer (hereinafter referred to as a first resist layer) is formed on the region to be formed. Subsequently, the mesa structure is formed by etching from the surface side of the p-type nitride semiconductor layer 5 to the middle of the n-type nitride semiconductor layer 3 by reactive ion etching using the first resist layer as a mask. The area and shape of the mesa structure are not particularly limited.

After forming the above mesa structure, the first resist layer is removed, and then the SiO ₂ film that forms the basis of the insulating film 8 is formed on the entire surface of the single crystal substrate 1 on the one surface side by PECVD. Then, using a photolithography technique, a resist layer (hereinafter, referred to as a portion of the SiO ₂ film that overlaps with a region where the n electrode 7 and the p electrode 6 are to be formed is opened on the one surface side of the single crystal substrate 1. (Referred to as a second resist layer). Subsequently, the exposed portion of the SiO ₂ film is removed by wet etching using BHF (buffered hydrofluoric acid) using the second resist layer as a mask, whereby the insulating film 8 made of the patterned SiO ₂ film is removed. Form.

Next, the single crystal substrate 1 is patterned so that only the region where the n electrode 7 is to be formed on the one surface side (that is, a part of the n-type nitride semiconductor layer 3 where the thickness is reduced) is exposed. A third resist layer is formed. Thereafter, the n-electrode 7 is formed by electron beam evaporation and lift-off is performed to remove the third resist layer and the unnecessary film on the third resist layer. Thereafter, an RTA process (rapid thermal annealing process) is performed in an N ₂ gas atmosphere so that the contact between the n electrode 7 and the n-type nitride semiconductor layer 3 is an ohmic contact. The n electrode 7 is a laminated film of a Ti film having a thickness of 20 nm, an Al film having a thickness of 100 nm, a Ti film having a thickness of 20 nm, and an Au film having a thickness of 200 nm. For example, the annealing temperature may be 900 ° C. and the annealing time may be 1 minute.

Next, a fourth resist layer patterned so that only the p electrode formation scheduled region (that is, part of the surface of the p-type nitride semiconductor layer 5) on the one surface side of the single crystal substrate 1 is exposed. Form. Thereafter, a Ni film having a thickness of 2 nm as a base of the ohmic contact layer 63 in the p-electrode 6 is formed by electron beam evaporation, and lift-off is performed, so that the fourth resist layer and the fourth resist layer are unnecessary. The film (unnecessary Ni film) is removed. Subsequently, the ohmic contact layer 63 is formed by performing thermal annealing at a predetermined annealing temperature (for example, 700 ° C.) and annealing time (20 minutes) in an N ₂ gas atmosphere.

  Thereafter, an Sb film having a film thickness of 2 nm is formed on the ohmic contact layer 63 using a metal mask in which a portion corresponding to the ohmic contact layer 63 (that is, a portion corresponding to a region where the p electrode 6 is to be formed) is opened. A laminated film of a block layer 62, a transparent metal layer 61 made of a K film having a film thickness of 50 nm, and a block layer 62 made of an Sb film having a film thickness of 2 nm is vacuum-deposited by the resistance heating vacuum deposition method. Films were continuously formed using an apparatus.

Thereafter, the protective layer 9 made of an MgF ₂ film having a thickness of 200 nm is formed using another metal mask without breaking the vacuum in the same vacuum deposition apparatus.

  Thereafter, a pad 10 made of an Al film having a film thickness of 300 nm is formed using another metal mask without breaking the vacuum in the same vacuum vapor deposition apparatus, whereby the ultraviolet semiconductor light emission having the configuration of FIG. An element is obtained.

  In manufacturing the above-described ultraviolet semiconductor light-emitting device, all steps until the formation of the pad 10 is completed at the wafer level, and then the dicing process is performed to divide into individual ultraviolet semiconductor light-emitting devices.

The ultraviolet semiconductor light emitting device of the present embodiment described above has at least one of a pair of electrodes (p electrode 6 and n electrode 7) in contact with the n-type nitride semiconductor layer 3 and the p-type nitride semiconductor layer 5, respectively. The electrode comprises a transparent electrode having at least a transparent metal layer 61 formed of a metal material having a light absorption coefficient of 5 × 10 ⁴ cm ⁻¹ or less for ultraviolet light having an emission wavelength in the ultraviolet region of 200 nm to 300 nm, The absorption of the ultraviolet light emitted from the light emitting layer 5 at the electrode can be suppressed, the light extraction efficiency can be improved, and the resistance of the transparent electrode can be reduced, so that the light emission efficiency can be improved. In addition, since the protective layer 9 is formed of a transparent insulating material at the ultraviolet light emission wavelength and protects the transparent electrode, deterioration due to oxidation of the transparent electrode hardly occurs and long-term stability and reliability can be improved.

  In the above-described embodiment, the method of manufacturing the ultraviolet semiconductor light emitting element using the MOVPE method is exemplified. However, the crystal growth method is not limited to the MOVPE method. For example, the halide vapor phase growth method (HVPE method) is used. ), Molecular beam epitaxy (MBE), or the like.

  In the ultraviolet semiconductor light emitting device of the above embodiment, since the light emission wavelength of the light emitting layer 4 is appropriately set within the range of 200 nm to 300 nm, a light emitting diode having a light emission wavelength in the ultraviolet region can be realized. It can be used as an alternative light source for a deep ultraviolet light source such as a lamp.

DESCRIPTION OF SYMBOLS 1 Single crystal substrate 2 Buffer layer 3 N-type nitride semiconductor layer 4 Light emitting layer 5 P-type nitride semiconductor layer 6 P electrode (transparent electrode)
7 n electrode 9 protective layer 10 pad 61 transparent metal layer 62 block layer 63 ohmic contact layer

Claims (10)

An ultraviolet semiconductor light emitting device having an emission wavelength in an ultraviolet region of 200 nm to 300 nm, having a light emitting layer between an n-type nitride semiconductor layer and a p-type nitride semiconductor layer , wherein the n -type nitride semiconductor layer good beauty at least one electrode of the pair of electrodes in contact with the p-type nitride semiconductor layer, respectively, formed of a metallic material light absorption coefficient of 5 × 10 ⁴ cm ^-1 or less with respect to ultraviolet light of the emission wavelength Ri Do a transparent electrode having at least a transparent metal layer, the transparent electrode, the at least one side in the thickness direction of the transparent metal layer, wherein the transparent metal layer is formed by a metal material different from the transparent metal layer comprising a blocking layer for blocking the arrival of the adverse effects of reactive species of the transparent metal layer, the metal material of the blocking layer, this being selected Sb, Bi or from the group of their alloys, Ultraviolet semiconductor light-emitting device characterized. The ultraviolet semiconductor light-emitting element according to claim 1, further comprising a protective layer that is formed of a transparent insulating material at the emission wavelength of the ultraviolet light and protects the transparent electrode . The insulating material of the protective layer, the ultraviolet semiconductor light emitting element 請 Motomeko 2 wherein you being a MgF _2. 4. The ultraviolet semiconductor light emitting element according to claim 1, wherein the metal material of the transparent metal layer is selected from the group of Na, K, Cs, and Rb . 5. The ultraviolet semiconductor light-emitting element according to any one of claims 1 to 4, wherein the transparent metal layer has a thickness of 50 nm to 100 nm . Ultraviolet semiconductor light-emitting element mounting serial to any one of claims 1 to 5, wherein the thickness of the block layer is 5nm or less. The transparent electrode according to claim 1 to claim, characterized in that it comprises an ohmic contact layer made of a metal material for the ohmic contact with the underlying light-emitting layer side to the light-emitting layer side of the transparent metal layer ultraviolet semiconductor light-emitting element mounting serial any to one of 6. Metallic material of the ohmic contact layer, Al, Ti, Hf, Zr , Cr, Au, Ni, Pt, Pd, In or No placement claim 7 Symbol characterized in that it is selected from the group of their alloys, Ultraviolet semiconductor light emitting device. Ultraviolet semiconductor light-emitting device according to claim 7 or請 Motomeko 8 wherein you wherein the thickness of the ohmic contact layer is 5nm or less. 10. The pad according to claim 1, further comprising a pad formed of a material selected from a group of Au, Al, or an alloy thereof on a part of the surface of the transparent electrode. serial mounting of ultraviolet semiconductor light-emitting device.

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