JP2006278554A - AlGaN-BASED DEEP-ULTRAVIOLET LIGHT-EMITTING ELEMENT AND ITS MANUFACTURING METHOD - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an AlGaN-based deep-ultraviolet light-emitting element with high luminous efficiency having a vertical electrode structure with a significantly reduced series resistance. <P>SOLUTION: The AlGaN-based deep-ultraviolet light-emitting element includes sequentially an n-type AlGaN layer, an AlGaN-based quantum well active layer, a p-type AlGaN layer, and a p-type GaN layer, as needed. Furthermore, an n-layer electrode is formed on at least part of the surface of the n-type AlGaN layer, a p-layer electrode is formed on at least part of the surface of the p-type AlGaN layer, or the p-type GaN layer so that a drive current flows in each layer substantially in a direction normal to respective boundary surfaces. An indium tin oxide (ITO) transparent electrode with a tin content of 10-20 mass% is used as the n-layer electrode. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an AlGaN-based deep ultraviolet light emitting device with high luminous efficiency.

  The ultraviolet light source has various application fields such as illumination, display, fluorescence analysis, photocatalytic chemistry, and high-resolution optical equipment. Nitride semiconductors are known as light-emitting elements for ultraviolet light sources. In particular, attention has been focused on aluminum / gallium nitride (AlGaN), which is a direct-transition wide-gap nitride semiconductor that can emit deep ultraviolet light with a wavelength of 200 to 350 nm. Yes.

  Since an AlGaN-based semiconductor layer is very difficult to produce a bulk substrate, it is usually formed by heteroepitaxial growth on a sapphire substrate. Also, in the case of an AlGaN-based light emitting device, when a p-type GaN layer is provided, it absorbs ultraviolet light, so that light cannot be extracted from the p-layer electrode side, and light must be extracted from the substrate side. Is useful. However, since the sapphire substrate has no electrical conductivity, the conventional AlGaN-based light-emitting element employs a lateral electrode structure in which the n-layer electrode is positioned on the side of the p-layer electrode (Patent Document 1).

JP-A-11-307811

  However, the lateral electrode structure in which the n-layer electrode is located on the side of the p-layer electrode has a problem that the series resistance increases because current must flow in the lateral direction in the n-type AlGaN layer. If the series resistance increases, the amount of self-heating during operation increases, and there is a concern about the adverse effect on the carrier injection efficiency. This problem becomes more prominent during high output operation. Furthermore, when taking out light through an electrode, the material with the high transmittance | permeability with respect to the wavelength of the said emitted light is calculated | required from a viewpoint of luminous efficiency.

  Therefore, the present invention has an element structure that increases drive efficiency by greatly reducing the series resistance, suppresses heat generation, and enables high-output operation, and further has high transparency in the deep ultraviolet region. An object of the present invention is to provide an AlGaN-based deep ultraviolet light-emitting device with improved luminous efficiency by employing the above.

  According to the present invention, an n-type AlGaN layer, an AlGaN-based quantum well active layer, a p-type AlGaN layer and, if necessary, a p-type GaN layer are included, and an n-layer electrode is formed on at least a part of the surface of the n-type AlGaN layer. And a p-layer electrode on at least a part of the surface of the p-type AlGaN layer or the p-type GaN layer so that the drive current flows in each layer in a substantially normal direction with respect to each boundary surface. An AlGaN-based deep ultraviolet light-emitting device using an indium tin oxide (ITO) transparent electrode having a tin content of 10 to 20% by mass as the n-layer electrode Is provided.

  According to the present invention, the realization of the vertical electrode structure in which the n-layer electrode and the p-layer electrode are positioned above and below dramatically reduces the series resistance of the AlGaN-based deep ultraviolet light-emitting device. For this reason, the drive efficiency of a light emitting element can be improved and the heat_generation | fever at the time of high output operation | movement can be suppressed. Furthermore, by adopting a high tin concentration ITO transparent electrode with increased transmittance in the deep ultraviolet region, the luminous efficiency of the AlGaN-based deep ultraviolet light emitting device is further improved.

  Further, according to the present invention, a GaN buffer layer, an n-type AlGaN layer, an AlGaN-based quantum well active layer, a p-type AlGaN layer and, if necessary, a p-type GaN layer are sequentially laminated on the sapphire substrate, and then the p-type AlGaN layer or the After forming a p-layer electrode on the p-type GaN layer, a conductive support is bonded on the p-layer electrode, and then irradiating a laser having a predetermined wavelength from the sapphire substrate side. The buffer layer is melted and removed together with the sapphire substrate, and at least part of the surface of the n-type AlGaN layer exposed thereby, indium tin oxide (ITO) having a tin content of 10 to 20% by mass as an n-layer electrode is formed. ) A method for producing an AlGaN-based deep ultraviolet light emitting device is provided, wherein the transparent electrode is formed by vapor deposition at a temperature of 400 ° C. or higher.

  FIG. 1 shows a preferred example of an AlGaN-based deep ultraviolet light emitting device according to the present invention. The deep ultraviolet light emitting device according to the present invention includes an n-type AlGaN layer, an AlGaN-based quantum well active layer, a p-type AlGaN layer, and, if necessary, a p-type GaN layer sequentially stacked, and at least one surface of the n-type AlGaN layer. An ITO transparent electrode is formed as an n-layer electrode on the part, and a p-layer electrode is formed on at least a part of the surface of the p-type AlGaN layer (or p-type GaN layer when used). Since the deep ultraviolet light emitting device according to the present invention has a vertical electrode structure in which an n-layer electrode and a p-layer electrode are positioned above and below, deep ultraviolet light emission in which the series resistance between both electrodes has a conventional horizontal electrode structure. Compared with the structure, it drops dramatically, for example, to about 1/100.

As the material of the n-type AlGaN layer, an n-type AlGaN compound semiconductor designed to have a larger band gap than the material of an AlGaN quantum well active layer described later is used. A person skilled in the art can appropriately design such an n-type AlGaN-based compound semiconductor. A preferred example of the material of the n-type AlGaN layer is an n-type AlGaN compound semiconductor having an Al composition of about 30 atomic% (Ga composition is 70 atomic%). Examples of the n-type dopant doped in the n-type AlGaN compound semiconductor include Si sources such as silane and tetraethyl silicon. The n-type dopant may be doped in such an amount that the carrier concentration of the n-type AlGaN layer is about ^{2 to} 3 × 10 ¹⁸ cm ⁻² . The thickness of the n-type AlGaN layer may generally be in the range of 1 to 2 μm.

As the material of the AlGaN quantum well active layer, any AlGaN compound semiconductor capable of emitting deep ultraviolet light having a wavelength of 200 to 350 nm can be used. The material of the quantum well active layer is designed to have a smaller band gap than the material of the n-type AlGaN layer and the material of the p-type AlGaN layer described later. The quantum well active layer may have a single quantum well (SQW) structure or a multiple quantum well (MQW) structure. As a preferable example of the quantum well active layer, an Al _x Ga _1-x N / Al _y Ga _1-y N-based quantum well active layer (x = 0.15, y = 0.20), each having a film thickness An MQW structure in which 3 to 8 cycles of 3 nm / 8 nm are formed can be given.

As a material for the p-type AlGaN layer, a p-type AlGaN-based compound semiconductor designed to have a larger band gap than the material for the AlGaN-based quantum well active layer is used. Such a p-type AlGaN compound semiconductor can be designed as appropriate by those skilled in the art. A preferred example of the material of the p-type AlGaN layer is a p-type AlGaN-based compound semiconductor having an Al composition of about 24 to 30 atomic% (Ga composition is about 70 to 76 atomic%). Examples of the p-type dopant doped in the p-type AlGaN compound semiconductor include a Mg source such as biscyclopentadienyl magnesium. The p-type dopant may be doped in such an amount that the carrier concentration of the p-type AlGaN layer is about 1 × 10 ¹⁷ cm ⁻² . In general, the thickness of the p-type AlGaN layer may be in the range of 10 to 100 nm.

If necessary, a p-type GaN layer may be stacked in order to reduce contact resistance with a p-layer electrode described later. When used, as a material of the p-type GaN layer, a p-type GaN compound semiconductor designed to have a larger band gap than the p-type AlGaN layer is used. For example, in addition to p-type GaN, p-type AlGaN having a composition different from that of the p-type AlGaN constituting the p-type AlGaN layer may be used. Examples of the p-type dopant doped into the p-type GaN compound semiconductor include a Mg source such as biscyclopentadienyl magnesium. The p-type dopant may be doped in such an amount that the carrier concentration of the p-type GaN layer is about 5 × 10 ¹⁷ cm ⁻² . In general, the thickness of the p-type GaN layer may be in the range of 10 to 200 nm.

  In the deep ultraviolet light emitting device according to the present invention, an indium tin oxide (ITO) transparent electrode containing tin at a high concentration is used as an n layer electrode formed on at least a part of the surface of the n type AlGaN layer. In the present invention, “high concentration” means a concentration higher than a tin content of 8 to 10% by mass of ITO generally used. Specifically, as the n-layer electrode according to the present invention, an ITO transparent electrode having a tin content of 10% by mass or more, preferably 12 to 25% by mass, more preferably 15 to 20% by mass is used. By containing tin at a high concentration, the transmittance in the deep ultraviolet light region is improved, and the emission efficiency of the emitted deep ultraviolet light is reduced because the loss due to the electrode is reduced. Since the high tin concentration ITO transparent electrode according to the present invention is highly permeable to deep ultraviolet light, the n-type electrode can cover the entire surface of the n-type AlGaN layer. Of course, the ITO transparent electrode may be formed only on a part of the surface of the n-type AlGaN layer. For example, the ITO transparent electrode can have a comb shape or a stripe shape, and light can be extracted from the gap. The thickness of the ITO transparent electrode is determined by the balance between conductivity and transparency, and is generally 100 to 500 nm, preferably 200 to 400 nm.

  The deep ultraviolet light-emitting device according to the present invention includes a p-layer electrode formed on at least a part of the surface of the p-type AlGaN layer (or p-type GaN layer when used). Since the deep ultraviolet light emitting device according to the present invention extracts emitted light from the ITO transparent electrode side, the translucency of the p-layer electrode is not a problem, and holes are efficiently injected into the p-type AlGaN layer or the p-type GaN layer. The material for the p-layer electrode is not particularly limited as long as it can be used. Preferred examples of the material for the p-layer electrode include Ni / Au, Pt / Pd / Au, Pt, Pd / Ni / Au, Pd / Ag / Au / Ti / Au, Ni / ITO, Pd / Re, Ni / ZnO, Ni (Mg) / Au, Ni (La) / Au, etc. are mentioned. The thickness of the p-layer electrode may generally be in the range of 20 to 3000 nm.

  Hereinafter, a method for manufacturing the above-described deep ultraviolet light emitting device according to the present invention will be described. FIG. 2 shows a preferred example of the production method according to the present invention. As shown in FIG. 2A, a GaN buffer layer, an n-type AlGaN layer, an AlGaN-based quantum well active layer, a p-type AlGaN layer, and, if necessary, a p-type GaN layer are sequentially stacked on a sapphire substrate. Here, the GaN buffer layer relaxes the lattice mismatch between the n-type AlGaN layer grown on the sapphire substrate and the GaN buffer layer, and the layers grown subsequently, thereby preventing misfit dislocations. In addition, it is provided for the purpose of melting and removing by laser irradiation described later. The thickness of the GaN buffer layer can be set in a wide range of 1 nm to several hundred μm. Since this GaN buffer layer is removed later and does not constitute a part of the deep ultraviolet light emitting device, the GaN buffer layer may be crystalline or amorphous, and further, when the thickness is several μm to several hundred μm. May be in the form of a commercially available thick GaN template wafer formed on a sapphire substrate. For the lamination of each layer, an epitaxial growth method known in the technical field, for example, a metal organic vapor phase volume method (MOCVD method) can be employed. Further, those skilled in the art can appropriately select the raw material gas, dopant gas, carrier gas, layer growth temperature, and other production conditions necessary for realizing the composition and characteristics of each layer described above.

  Next, as shown in FIG. 2B, a p-layer electrode is formed on the p-type GaN layer (or p-type AlGaN layer when the p-type GaN layer is not used), and if necessary, conductive adhesion is performed. A conductive support is bonded onto the p-layer electrode via an agent. The p-layer electrode can be formed by a vapor deposition method known in the art. The conductive support plays a role of supporting the light emitting element after removing the sapphire substrate and also has a function of injecting current into the p-layer electrode. Examples of the material for the conductive support include GaAs, SiC, Si, Ge, C, Cu, Al, Mo, Ti, Ni, W, Ta, and Au / Ni. The thickness of the conductive support may generally be in the range of 50 to 5000 μm. When using a conductive adhesive, for example, Au / Ge solder can be used at a thickness of about 0.5 to 100 μm. When the conductive adhesive is not used, the conductive support can be bonded to the p-layer electrode by placing the conductive support directly on the p-layer electrode and performing heat treatment. In particular, it is preferable not to use solder in that the substrate temperature at the time of vapor deposition of the ITO transparent electrode described later can be increased, and the deep ultraviolet light transmittance of the obtained ITO transparent electrode is further increased.

  Next, as shown in FIG. 2C, the GaN buffer layer is melted by irradiating a laser having a predetermined wavelength from the sapphire substrate side. As the laser, for example, the third harmonic (355 nm) or the fourth harmonic (266 nm) of an Nd-YAG laser may be used. By irradiating such a laser from the sapphire substrate side, the GaN buffer layer is melted and the sapphire substrate is easily removed.

Thereafter, as shown in FIG. 2D, an ITO transparent electrode having a high tin concentration is formed on at least a part of the surface of the n-type AlGaN layer exposed by removing the sapphire substrate and the GaN buffer layer. . Such an ITO transparent electrode can be formed by a vapor deposition method known in the art. For example, a mixture in which tin oxide (SnO ₂ ) and indium oxide (In ₂ O ₃ ) are mixed so that the Sn content is 10% by mass or more, preferably 12 to 25% by mass, more preferably 15 to 20% by mass. As a raw material, a vacuum deposition method using a laser can be employed. The ITO transparent electrode is generally deposited at a substrate temperature of about 200 ° C. However, according to the manufacturing method of the deep ultraviolet light emitting device according to the present invention, it is possible to set the substrate temperature at the time of vapor deposition of the high tin concentration ITO transparent electrode as high as possible within the range that does not adversely affect each layer. It is preferable for increasing the transmittance in the light region (wavelength 200 to 350 nm). In order to show this, FIG. 3 shows a graph showing the effect of the substrate temperature during ITO deposition on the deep ultraviolet light transmittance. From the graph, it can be seen that the deep ultraviolet light transmittance centered at a wavelength of 330 nm increases as the substrate temperature during deposition of ITO (tin concentration of 10% by mass) is increased to 400 ° C., 600 ° C., and 800 ° C. Therefore, the substrate temperature during the deposition of the high tin concentration ITO electrode is preferably 400 ° C. or higher, more preferably 600 ° C. or higher, and still more preferably 800 ° C. or higher. Thus, according to the manufacturing method of the present invention, a vertical electrode structure in which an n-layer electrode and a p-layer electrode are positioned vertically is realized for the first time in an AlGaN-based deep ultraviolet light-emitting device. By adopting the increased high tin concentration ITO transparent electrode as the n-layer electrode, the luminous efficiency of the AlGaN deep ultraviolet light emitting device is further improved.

Example 1
According to the manufacturing procedure shown in FIG. 2, an AlGaN-based deep ultraviolet light emitting device according to the present invention was manufactured as follows. For crystal growth of each layer, metal organic chemical vapor deposition (MOCVD) was used. Further, hydrogen (H ₂ ) was used as the carrier gas. However, the p-layer electrode and the conductive support were joined without using solder in order to increase the substrate temperature when the ITO electrode was deposited later.

A predetermined crystal growth apparatus was loaded with a C-plane sapphire substrate. Trimethylgallium (TMG) was supplied as a Ga source, and ammonia (NH ₃ ) was supplied as a nitrogen source, and a GaN layer having a thickness of 20 nm was grown as a buffer layer on a sapphire substrate at a temperature of 550 ° C.

Subsequently, the temperature is raised to 1120 ° C., TMG as a Ga source, trimethylaluminum (TMA) as an Al source, NH ₃ as a nitrogen source, and tetraethyl silicon (TESi) as an n-type dopant source are supplied, and GaN An n-type Al _0.3 Ga _0.7 N layer having a thickness of 1 μm was grown on the buffer layer.

Subsequently, while supplying TMG as a Ga source, TMA as an Al source, and NH ₃ as a nitrogen source while maintaining the temperature at 1120 ° C., by changing the flow rates of TMG and TMA, n-type Al _0.3 On the Ga _0.7 N layer, an AlGaN-based multi-quantum well active layer having an 8 nm thick Al _0.2 Ga _0.8 N barrier layer and a 3 nm thick Al _0.15 Ga _0.85 N well layer consisting of 5 periods was grown.

Subsequently, while maintaining the temperature at 1120 ° C., supply TMG as a Ga source, TMA as an Al source, NH ₃ as a nitrogen source, and biscyclopentadienyl magnesium (CP ₂ Mg) as a p-type dopant source Then, a p-type Al _0.3 Ga _0.7 N layer having a thickness of 40 nm was grown on the AlGaN-based multiple quantum well active layer.

Subsequently, the temperature was set to 1080 ° C., TMG was supplied as a Ga source, NH ₃ was supplied as a nitrogen source, and CP ₂ Mg was supplied as a p-type dopant source, and a 40 nm thick layer was formed on the p-type Al _0.3 Ga _0.7 N layer. A p-type GaN layer was grown.

  Subsequently, the semiconductor laminate formed by the above-described crystal growth method is taken out from the crystal growth apparatus, and activation of p-type is performed at 850 ° C. in a nitrogen atmosphere for 30 minutes in an electric furnace (manufactured by Vacuum Riko Co., Ltd .: HPC-5000). Annealing was performed. Next, after performing activation annealing, the laminate subjected to surface treatment with aqua regia at 70 ° C. for 10 minutes is mounted on a vapor deposition apparatus (manufactured by Anerva Co., Ltd .: Model VI-43N), and on the p-type GaN layer. A 20 nm thick Ni and a 700 nm thick gold were successively deposited. After vapor deposition, the laminate is taken out from the vapor deposition apparatus, and annealed in an electric furnace (manufactured by Vacuum Riko Co., Ltd .: HPC-5000) in a mixed gas atmosphere having a nitrogen content of 80% and an oxygen content of 20% at 450 ° C for 5 minutes. A p-type electrode was formed. After forming the p-type electrode, the laminate was cut into an appropriate size for the bonding process. A conductive support made of GaAs having a thickness of 350 μm for supporting the laminate was cut into an appropriate size, washed with acetone, methanol, and ultrapure water and dried. After drying, a 40 [mu] m thick gold germanium alloy (gold: 12%) is placed on the support, and then the p-type electrode surface of the laminate is placed down, and an electric furnace (manufactured by Vacuum Riko Co., Ltd .: HPC) -5000) in a nitrogen atmosphere at 450 ° C. for 5 minutes to bond the laminate and the support.

  Next, from the sapphire substrate side, a GaN buffer layer was melted by irradiation with a Q-switched LD-pumped Nd: YVO laser (Spectra Physics Co., Ltd .: model BL6S-266Q) (wavelength 266 nm). Thereafter, the semiconductor laminate was heated to about 50 ° C. to remove the sapphire substrate.

The surface of the n-type AlGaN layer exposed by removing the sapphire substrate was polished by CMP. Next, using a laser deposition apparatus (manufactured by Nippon Vacuum Co., Ltd.), from a mixture obtained by mixing SnO ₂ and In ₂ O _{3 so} that the Sn content is 15% by mass, at a temperature of 800 ° C., n-type Al _0.3 Ga _0.7 An n-layer electrode composed of a 300-nm-thick high tin concentration ITO electrode was deposited on the N layer.

  When the emission spectrum was measured by injecting a current of 10 mA into the light-emitting device obtained by depositing the ITO electrode, it was found that the light-emitting device obtained in Example 1 had a peak near the wavelength of 330 nm in the deep ultraviolet region. . Further, when the series resistance of this light emitting element was measured, it was about 1Ω. This value is 1/100 of the series resistance of about 100Ω in the AlGaN-based deep ultraviolet light-emitting device having the conventional lateral electrode structure. Furthermore, since the ITO electrode was deposited at 800 ° C., the transmittance at the wavelength of deep ultraviolet light was increased, and the light emission efficiency of the light emitting device was improved.

1 is a schematic cross-sectional view showing a layer structure of an AlGaN deep ultraviolet light emitting device having a vertical electrode structure according to the present invention. It is a general | schematic cross-sectional view which shows the one aspect | mode of the manufacturing procedure of the AlGaN-type deep ultraviolet light emitting element by this invention. It is a graph which shows the influence which the substrate temperature at the time of ITO vapor deposition has on the transmittance | permeability in a deep ultraviolet light region.

Claims (2)

  An n-type AlGaN layer, an AlGaN-based quantum well active layer, a p-type AlGaN layer, and a p-type GaN layer as necessary, and an n-layer electrode on at least a part of the surface of the n-type AlGaN layer, and AlGaN-based depth in which a p-layer electrode is formed on at least a part of the surface of the p-type GaN layer or the p-type GaN layer so that the driving current flows in each layer in a direction substantially normal to each boundary surface An AlGaN-based deep ultraviolet light emitting element, wherein an indium tin oxide (ITO) transparent electrode having a tin content of 10 to 20% by mass is used as the n-layer electrode.   A GaN buffer layer, an n-type AlGaN layer, an AlGaN-based quantum well active layer, a p-type AlGaN layer and, if necessary, a p-type GaN layer are sequentially stacked on the sapphire substrate, and then on the p-type AlGaN layer or the p-type GaN layer. After forming a p-layer electrode, a conductive support is bonded on the p-layer electrode, and then the GaN buffer layer is melted by irradiating a laser having a predetermined wavelength from the sapphire substrate side. An indium tin oxide (ITO) transparent electrode having a tin content of 10 to 20% by mass as an n-layer electrode is formed on at least a part of the surface of the n-type AlGaN layer that is removed together with the sapphire substrate and exposed at a temperature of 400. A method for producing an AlGaN-based deep ultraviolet light-emitting device, wherein vapor deposition is performed at a temperature equal to or higher than ° C.

Images