JP2011258843A - Nitride semiconductor light-emitting element and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitride semiconductor light-emitting element exhibiting excellent emission characteristics and injection current uniformity, and having sufficient tolerance.SOLUTION: The nitride semiconductor light-emitting element comprises: a nitride semiconductor substrate 101 having a first principal surface 101a; a second principal surface 101b; a first nitride semiconductor layer 102 formed in contact with the first principal surface 101a; an n-type nitride semiconductor layer 103 formed on the first nitride semiconductor layer 102 on the side reverse to the side in contact with the first principal surface 101a; a laminate including an active layer 104 and a p-type nitride semiconductor layer 105; an n-side electrode 106 connected electrically with the n-type nitride semiconductor layer 103; and a p-side electrode 107 connected electrically with the p-type nitride semiconductor layer 105. The first nitride semiconductor layer 102 is an undoped nitride semiconductor layer. In the nitride semiconductor light-emitting element, the second principal surface 101b serves as a light extraction surface.

Description

  The present invention relates to a light emitting device represented by a light emitting diode (LED) including a nitride semiconductor layer on a nitride semiconductor substrate, and a method for manufacturing the same.

  Conventionally, many light emitting devices using III-V compound semiconductors are known. In particular, red light emitting elements made of AlGaAs-based materials and AlGaInP-based materials formed on gallium arsenide (GaAs) substrates, green light-emitting elements formed of GaAsP-based materials formed on gallium phosphide (GaP) substrates, and formed on GaAs substrates. A light emitting device such as an orange or yellow-green light emitting device has been realized using the AlGaInP-based material thus formed. In general, in these material-based light-emitting elements, a substrate and a semiconductor layer formed thereon are selected to have relatively close characteristics such as a lattice constant and a thermal expansion coefficient.

  On the other hand, light emitting diodes in a wide wavelength range from ultraviolet to purple, blue, green, and orange have been realized by AlGaInN-based materials using sapphire as a substrate, and have begun to be applied to a wide range of applications such as display devices and traffic signals. The sapphire substrate and the AlGaInN-based material formed on the sapphire substrate are not easy to form because the lattice constant and the thermal expansion coefficient are greatly different. However, the development of the low temperature deposition buffer layer technology has made it possible to obtain a flat film although there are many crystal defects such as dislocations. As a result, a light emitting device using an AlGaInN-based material has progressed rapidly. In addition to sapphire, silicon carbide (SiC), GaAs, silicon (Si), or the like is used as the substrate.

  Recently, a technique for producing a gallium nitride (GaN) substrate having a low dislocation density by using a vapor phase growth method has been established, and high-density light such as BD (Blu-ray disc) using an AlGaInN-based material using the GaN substrate. It is applied to the practical application of blue violet laser diode for recording (Laser Diode: LD) and blue laser diode for laser display.

  In response to the recent trend toward energy saving, white light-emitting diodes are most noted among light-emitting elements using AlGaInN-based materials. The white light-emitting diode is realized by combining a blue light-emitting diode or an ultraviolet light-emitting diode with a phosphor using an excitation light source. White light emitting diodes are attracting attention as a backlight light source for liquid crystal displays, and are used as a backlight light source for large liquid crystal televisions from small portable electronic devices. Furthermore, the development of lighting equipment that replaces incandescent bulbs and fluorescent lamps is underway. High output and high efficiency of blue light emitting diodes and ultraviolet light emitting diodes, which are excitation light sources, are extremely effective in improving the output of white light emitting diodes that can be used as next-generation lighting equipment. Industrial significance is very high.

  In order to increase the output of a light emitting diode, it is essential to improve the external quantum efficiency of the light emitting diode. The external quantum efficiency is a ratio between the electric energy given to the light emitting diode and the light energy that is converted into light energy inside the light emitting diode and finally extracted outside. For this reason, to improve the external quantum efficiency, it is necessary to improve the internal quantum efficiency in the active layer of the light emitting diode and to improve the light extraction efficiency for extracting the generated light energy from the light emitting diode.

  As a structure effective for improving the light extraction efficiency, a flip chip structure is generally known. In this flip-chip structure, a semiconductor layer that generates desired light emission is laminated on the surface of the substrate, an n-side electrode and a p-side electrode for current injection are formed on the opposite side of the semiconductor layer to the substrate side, and the back surface of the substrate Is the light extraction direction. For this reason, since the light emitted from the light emitting element is not blocked by the electrode, and the electrode can be used as a light reflecting surface, the light extraction efficiency is improved. Furthermore, by performing appropriate patterning on the back surface (light extraction surface) of the substrate, reflection of light to the inside can be suppressed and light extraction efficiency can be improved.

  In order to improve internal quantum efficiency, it is important to optimize the active layer structure and establish a high-quality film-forming technology with few defects in order to efficiently convert the applied electrical energy into light energy in the active layer. is there. In order to obtain crystals with few defects, it is effective to use a substrate with low dislocations together with adjustment of the growth conditions, and the GaN substrate used in laser diodes should also be used for the production of light emitting diodes. Is desirable.

  Further, apart from these, the improvement of the output of the light emitting diode is generally performed because the increase in the size of the element and the increase in input power are highly effective. However, when the element is increased in size, it is essential to ensure the uniformity of the emission intensity and emission wavelength and the uniformity of the injection current, and when the input power is increased, it is necessary to ensure the resistance against the increased power. Required.

  Since the optimization of the active layer structure can suppress power consumption and reduce heat generation during operation, it is very effective for increasing input power. Further, these techniques are not limited to light emitting diodes, and it goes without saying that similar improvements are necessary for laser diodes.

  Here, Patent Document 1 discloses a nitride semiconductor light emitting element using a sapphire substrate that can improve output and reduce power consumption.

  The nitride semiconductor light emitting device disclosed in Patent Document 1 includes a plurality of layers including first and second nitride semiconductor layers to which at least one of n-type impurities is added between a sapphire substrate and an active layer. A superlattice layer acting as an n-side contact layer. Patent Document 1 discloses forming an undoped nitride semiconductor layer between a sapphire substrate and a superlattice layer.

  The n-side contact layer needs to be composed of a layer with a high carrier concentration in order to form an n-electrode, but a thick film layer with a high impurity concentration tends to have poor crystallinity. Even if another nitride semiconductor such as an active layer is grown on a layer with poor crystallinity, the crystal defects cannot be improved because other layers take over the crystal defect, and as a result, high output light emission. An element cannot be realized. Therefore, in Patent Document 1, before growing the n-side contact layer, an undoped nitride semiconductor layer is grown as a buffer layer having a low impurity concentration and a good crystallinity, thereby increasing the carrier concentration and the crystallinity having a good crystallinity. A side contact layer is formed. It is disclosed that the thickness of the undoped nitride semiconductor layer as the buffer layer is desirably adjusted to 0.1 μm or more, more preferably 0.5 μm or more, and most preferably 1 μm or more and 20 μm or less. . If the thickness of the undoped nitride semiconductor layer is less than 0.1 μm, the n-side contact layer having a high impurity concentration must be grown thick, and the crystallinity of the n-side contact layer tends not to be improved much. Because. In addition, if the thickness of the undoped nitride semiconductor layer is greater than 20 μm, crystal defects tend to increase in the undoped nitride semiconductor layer itself.

  Further, according to Patent Document 1, it is shown that the superlattice layer functions as an n-side contact layer for forming an n-electrode and as a cladding layer having a large band gap energy with respect to the active layer. In the superlattice layer, it is desirable to increase the n-type impurity concentration of the layer having the larger band gap energy between the first layer and the second layer. When a superlattice layer to which a large number of n-type impurities are added is formed as a contact layer on the n-layer side toward a layer having a large band gap energy, the first layer and the band having a large band gap energy to which n-type impurities are added A superlattice layer in which an undoped second layer having a small gap energy is stacked is a heterojunction interface between an n-type impurity-added layer and an undoped layer, and the layer side having a large band gap energy is depleted. Electrons (two-dimensional electron gas) accumulate at the interface around the thickness of the small layer. In this way, since the two-dimensional electron gas is accumulated on the layer side having a small band gap energy, it is not scattered by impurities when the electron travels, so that the electron mobility of the superlattice layer is increased and the resistance is increased. It has been argued that the threshold voltage and the threshold current tend to decrease further, for example, in laser diodes. As the substrate, it is very preferable to use a nitride semiconductor substrate in addition to the sapphire substrate in order to improve the crystallinity of the nitride semiconductor. When this nitride semiconductor substrate is used as a substrate, it serves as a buffer layer. It is also clear that there is no need to grow an undoped nitride semiconductor layer.

  Another document (Patent Document 2) discloses a semiconductor light emitting device capable of improving the uniformity of light emission. According to Patent Document 2, an undoped GaN layer having a thickness of 2 μm is formed as a buffer layer on a GaN substrate, and then a laminated layer of undoped InGaN (film thickness 3 nm) and undoped GaN (film thickness 12 nm) as a light uniformizing layer (20 nm). The layer) structure is formed so that the thickness of the undoped GaN including the center thereof is 4 μm. Next, a Si-doped GaN layer having a thickness of 4 μm is formed as the first conductivity type (n-type) second cladding layer, and a Si-doped GaN layer having a thickness of 0.5 μm is formed as the first conductivity type (n-type) contact layer. In addition, an Si-doped AlGaN layer having a thickness of 0.1 μm is formed as a first conductivity type (n-type) first cladding layer. It is clearly shown that an active layer structure is further formed thereon. The light uniformizing layer is formed between the substrate and the n-side cladding layer and has a function of improving the uniformity of the emission intensity emitted from the light extraction surface.

  Further, another document (Non-Patent Document 1) shows recent technological trends in the field. Non-Patent Document 1 discloses a technique for manufacturing a standard flip chip structure light emitting diode on a sapphire substrate, and a technique for forming a thin film flip chip structure by peeling the sapphire substrate by a laser-assisted lift-off process after the fabrication. Is shown. According to the technology of Non-Patent Document 1, high light extraction efficiency and suppression of heat generation can be realized by backside processing after sapphire substrate peeling and flip chip mounting on a submount having high thermal conductivity.

JP 2000-068594 A JP 2007-329463 A

Appl. Phys. Lett. 89,071109 (2006)

  When a nitride semiconductor light emitting device such as a light emitting diode is formed using a GaN substrate, the nitride semiconductor layer formed on the GaN substrate needs to have good surface flatness as well as its crystallinity. It goes without saying that there is.

  As shown in Patent Document 1, it is very important to form an undoped nitride semiconductor layer for improving crystallinity on a low-temperature buffer layer in order to improve the performance of a light-emitting diode device manufactured using a sapphire substrate. It is effective.

  However, in order to achieve higher output, it is essential to use a nitride semiconductor substrate having a low dislocation density. However, Patent Document 1 describes problems and problems that occur when using a nitride semiconductor substrate. There is no explicit solution.

  In addition, Patent Document 2 discloses the use of a nitride semiconductor substrate, but Patent Document 2 also does not clearly disclose the problems that arise when using a nitride semiconductor substrate and the solutions therefor. .

A nitride semiconductor substrate typified by a GaN substrate is generally very difficult to fabricate and process, and although it is already on the market, the substrate itself still has many problems. For example, a GaN substrate formed by hetero-growth by vapor phase epitaxy has a threading dislocation density of about 1 × 10 ⁵ to 1 × 10 ⁶ cm ⁻³ , which is 2 to 3 digits compared to other compound semiconductor crystal substrates. There are also many defect gathering regions (usually called “cores”) where threading dislocations are gathered in the plane. This is because crystals are produced by hetero-growth, and the substrate has a large residual strain, warpage due to this residual strain, and in-plane distribution of crystal axes.

  When an n-type nitride semiconductor layer is epitaxially formed to form a light-emitting device using a nitride semiconductor substrate having such a defect assembly region, the growth method at the interface between the substrate and the epitaxial layer is not devised. Otherwise, the surface flatness will be deteriorated, leading to a problem that the light emitting characteristics are lowered and a light emitting element at a practical level cannot be realized.

Further, a nitride semiconductor layer (1 × 10 ¹⁸ cm ⁻³ or more) to which a donor impurity is added at a high concentration is formed as a low-resistance conductive layer on the nitride semiconductor substrate. However, in the case of a flip chip type device structure in which the substrate side (opposite side of the active layer) is the light extraction surface, free carrier loss occurs due to the nitride semiconductor layer to which the donor impurity is added at a high concentration. There is a problem that the output decreases.

  The present invention has been made in view of such problems, and an object of the present invention is to form a nitride semiconductor layer excellent in flatness and crystallinity on a nitride semiconductor substrate, and to emit light intensity and light emission wavelength. It is an object of the present invention to provide a nitride semiconductor light emitting device that has excellent uniformity of injection current and uniformity of injection current, and has sufficient resistance even at high input power, and a method for manufacturing the same.

  In order to solve the above problems, an embodiment of a nitride semiconductor light emitting device according to the present invention has a first main surface and a second main surface, and includes a nitride semiconductor substrate and the first main surface. A first nitride semiconductor layer formed in contact with the first nitride semiconductor layer, an n-type nitride semiconductor layer formed on a side opposite to the side in contact with the first main surface of the first nitride semiconductor layer, and an active layer And a stack including the p-type nitride semiconductor layer, an n-side electrode electrically connected to the n-type nitride semiconductor layer, and a p-side electrode electrically connected to the p-type nitride semiconductor layer The first nitride semiconductor layer is an undoped nitride semiconductor layer, and the second main surface is a light extraction surface.

  With this configuration, a nitride semiconductor light-emitting device having a flat surface can be formed in a stacked structure, so that uniform composition can be formed in a plane without unevenness in composition and thickness, and high internal quantum efficiency, light emission intensity, and light emission. It is possible to achieve uniformity of wavelength and injection current. Further, by forming an undoped nitride semiconductor layer in contact with the nitride semiconductor substrate, a nitride semiconductor film having excellent flatness can be realized as a thin film, so that the consumption of raw materials can be reduced, and the nitride semiconductor The manufacturing cost of the layer can be reduced.

  Furthermore, in one aspect of the nitride semiconductor light emitting device according to the present invention, the first nitride semiconductor layer is preferably an undoped GaN layer.

  With this configuration, a laminated structure of nitride semiconductor light-emitting elements having a very flat surface can be realized, so that uniform film formation can be achieved in a plane without unevenness in composition and thickness, and high internal quantum efficiency and emission intensity. In addition, it is possible to realize the uniformity of the emission wavelength and the injection current.

  Furthermore, in one aspect of the nitride semiconductor light emitting device according to the present invention, the n-type nitride semiconductor layer preferably includes an n-type AlGaN layer.

  With this configuration, a laminated structure of nitride semiconductor light emitting devices having a very flat surface can be realized, so that uniform film formation can be achieved in a plane with no uneven composition and thickness, and particularly high internal quantum efficiency and light emission. It is possible to achieve uniformity in intensity, emission wavelength, and injection current. Further, the n-type AlGaN layer acts as a barrier layer / carrier supply layer, and can store a two-dimensional electron gas at the interface of the undoped nitride semiconductor layer, which is a layer having a small band gap energy. By using this region as a region where electrons travel, the distribution of electrons in the element plane can be made uniform, and the injection of electrons into the active layer can be made more uniform. Furthermore, since the resistivity can be lowered, the operating voltage can also be reduced.

  Furthermore, in one aspect of the nitride semiconductor light emitting device according to the present invention, a second comprising an undoped AlGaN layer between the undoped GaN layer as the first nitride semiconductor layer and the n-type AlGaN layer. The nitride semiconductor layer is preferably included.

  With this configuration, a laminated structure of nitride semiconductor light emitting devices having a very flat surface can be realized, so that uniform film formation can be achieved in a plane with no uneven composition and thickness, and particularly high internal quantum efficiency and light emission. It is possible to achieve uniformity in intensity, emission wavelength, and injection current.

  Furthermore, in one aspect of the nitride semiconductor light emitting device according to the present invention, an n-type AlGaN layer in which the Al composition of the undoped AlGaN layer as the first nitride semiconductor layer is included in the n-type nitride semiconductor layer The Al composition is preferably the same as or smaller than the Al composition of the n-type AlGaN layer.

  With this configuration, the n-type AlGaN layer acts as a barrier layer / carrier supply layer, and the undoped AlGaN layer acts as a spacer layer, so that it is efficient at the interface of the first nitride semiconductor layer of the undoped GaN layer. It is possible to generate and store a two-dimensional electron gas. Then, by using this region as a region where electrons travel, it is possible to make the electron distribution in the element surface uniform and make the injection of electrons into the active layer uniform. Furthermore, since the resistivity can be lowered, the operating voltage can also be reduced.

  Furthermore, in one aspect of the nitride semiconductor light emitting device according to the present invention, the n-type semiconductor layer preferably contains Si as an impurity.

  With this configuration, electrons can be generated efficiently, so that the uniformity of the injection current and the reduction of the operating voltage can be realized.

Furthermore, in one aspect of the nitride semiconductor light emitting device according to the present invention, it is preferable that the Si concentration unintentionally contained in the first nitride semiconductor layer is 1 × 10 ¹⁷ cm ⁻³ or less.

  With this configuration, when current is injected, an increase in resistance due to impurity scattering can be suppressed, so that uniformity of the injected current and a reduction in operating voltage can be realized.

  Furthermore, in one aspect of the nitride semiconductor light emitting device according to the present invention, the nitride semiconductor substrate is preferably an n-type GaN substrate containing at least one of Si and O as an impurity.

  With this configuration, electrons are supplied not only from the n-type nitride semiconductor layer but also from the n-type GaN substrate side to the undoped nitride semiconductor layer. Can be reduced.

  An embodiment of the method for manufacturing a nitride semiconductor light emitting device according to the present invention includes a step of preparing a nitride semiconductor substrate having a first main surface and a second main surface and transparent to the emission wavelength. A step of forming a first nitride semiconductor layer in contact with the first main surface; a step of forming an n-type nitride semiconductor layer in contact with the first nitride semiconductor layer; and the n-type nitride A step of sequentially forming an active layer and a p-type nitride semiconductor layer on the oxide semiconductor layer, an n-side electrode electrically connected to the n-type nitride semiconductor layer, and the p-type nitride semiconductor layer And forming a p-side electrode electrically connected to the first nitride semiconductor layer, the first nitride semiconductor layer is an undoped nitride semiconductor layer, and the second main surface is a light extraction surface. is there.

  With this configuration, a laminated structure of nitride semiconductor light-emitting elements having a very flat surface can be realized, so that uniform film formation can be achieved in a plane without unevenness in composition and thickness, and high internal quantum efficiency and emission intensity. In addition, it is possible to realize the uniformity of the emission wavelength and the injection current.

  According to the nitride semiconductor light emitting device and the method for manufacturing the same according to the present invention, since the flatness of the nitride semiconductor layer formed on the nitride semiconductor substrate is improved, the active layer is particularly uniform in composition and thickness. Thus, it is possible to achieve high internal quantum efficiency, light emission intensity, light emission wavelength, and uniformity of injection current within the device surface. In addition, since an element structure with excellent flatness can be realized with a thin film, consumption of raw materials can be reduced, and manufacturing costs can be significantly reduced. Furthermore, since the supply of electrons using a two-dimensional electron gas can be realized, the resistivity is lowered, the carrier injection into the active layer can be made more uniform, and the operating voltage can be reduced.

Sectional drawing which shows the structure of the nitride semiconductor light-emitting device based on the 1st Embodiment of this invention Sectional drawing which shows the structure of the flip-chip type nitride semiconductor light-emitting device based on the 1st Embodiment of this invention Sectional drawing which shows the structure of the nitride semiconductor light-emitting device concerning a comparative example (A) A surface morphology photograph in the nitride semiconductor light emitting device according to the first embodiment of the present invention, (b) a surface morphology photograph in the nitride semiconductor light emitting device according to Comparative Example 1, and (c) a nitride according to Comparative Example 2. Surface morphology photo of semiconductor light emitting devices Surface morphology photograph of n-type GaN substrate used in nitride semiconductor light emitting device according to first embodiment and comparative example of the present invention The figure which shows the surface roughness of an n-type GaN substrate, and the figure which shows the relationship between the film thickness and surface roughness in the GaN layer formed on the n-type GaN substrate Sectional drawing which shows the structure of the nitride semiconductor light-emitting device based on the 3rd Embodiment of this invention.

  Hereinafter, a nitride semiconductor light emitting device and a manufacturing method thereof according to an embodiment of the present invention will be described in detail with reference to the drawings. In addition, the following embodiment shows the example and this invention is not limited to these embodiment.

(First embodiment)
First, a nitride semiconductor light emitting device according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view showing the structure of a nitride semiconductor light emitting device according to the first embodiment of the present invention. FIG. 2 is a cross-sectional view showing the structure of a flip-chip nitride semiconductor light emitting device according to the first embodiment of the present invention.

  The nitride semiconductor light emitting device 100 according to the first embodiment of the present invention is a nitride semiconductor light emitting diode, and as shown in FIG. 1, a first main surface (surface) 101a and a second main surface ( A nitride semiconductor substrate 101 having a back surface 101b, a first nitride semiconductor layer 102 formed on the first main surface 101a of the nitride semiconductor substrate 101, and a first conductivity type (n-type) n And a p-type nitride semiconductor layer 105 of a second conductivity type (p-type) which is a conductivity type different from the first conductivity type.

  The nitride semiconductor substrate 101 is a substrate that is transparent to the emission wavelength emitted by the active layer 104, and can extract light from the second major surface 101b. Here, “emission wavelength” means the wavelength of light generated by recombination of electrons and holes supplied to the active layer 104. In the present embodiment, the nitride semiconductor substrate 101 is an n-type GaN substrate in which the outermost surface of the first main surface 101a is inclined by 0.3 ° in the <11-00> direction with respect to the (0001) plane. Using. Further, silicon (Si) was added as a donor impurity to the nitride semiconductor substrate 101.

  The first nitride semiconductor layer 102 is an undoped nitride semiconductor layer formed in contact with the first main surface 101 a of the nitride semiconductor substrate 101. In the present embodiment, the first nitride semiconductor layer 102 is composed of an undoped GaN layer. Here, undoped means that no intentional addition of impurities is performed.

N-type nitride semiconductor layer 103 is an n-type cladding layer, and is in contact with the surface of first nitride semiconductor layer 102 that is opposite to the surface that is in contact with first main surface 101 a of nitride semiconductor substrate 101. It is formed as follows. In the present embodiment, the n-type nitride semiconductor layer 103 is an n-type AlGaN layer, and can be composed of, for example, n-Al _0.03 Ga _0.97 N.

The active layer 104 is formed so as to be in contact with the surface of the n-type nitride semiconductor layer 103 opposite to the surface in contact with the first nitride semiconductor layer 102. In this embodiment, the active layer 104 uses an active layer having a multiple quantum well structure, and is formed, for example, so as to sandwich a well layer made of In _0.15 Ga _0.85 N with a thickness of 3 nm and the well layer. An active layer having a triple quantum well structure with a barrier layer made of GaN having a thickness of 6.0 nm can be used.

The p-type nitride semiconductor layer 105 is a p-type cladding layer, and is formed on the surface of the active layer 104 opposite to the surface in contact with the n-type nitride semiconductor layer 103. In the present embodiment, the p-type nitride semiconductor layer 105 is a p-type AlGaN layer, and can be composed of, for example, p-Al _0.03 Ga _0.97 N.

  Further, as shown in FIG. 1, a part of the p-type nitride semiconductor layer 105, the active layer 104, and the n-type nitride semiconductor layer 103 is etched, and the surface of the n-type nitride semiconductor layer 103 is It is configured to be exposed. In FIG. 1, the surface of the n-type nitride semiconductor layer 103 is configured to be exposed, but etching is performed up to the first nitride semiconductor layer 102 so that the surface of the first nitride semiconductor layer 102 is exposed. You may make it.

  A p-side electrode 107 is formed on the surface of the p-type nitride semiconductor layer 105 that is not etched. An n-side electrode 106 is formed on the n-type nitride semiconductor layer 103 whose surface is exposed. When first nitride semiconductor layer 102 is exposed, n-side electrode 106 is formed on first nitride semiconductor layer 102 whose surface is exposed.

  The n-side electrode 106 is electrically connected to the n-type nitride semiconductor layer 103, and is composed of Ti / Au in this embodiment. Further, the p-side electrode 107 is electrically connected to the p-type nitride semiconductor layer 105, and in this embodiment, is constituted by Pd / Pt / Ag.

  Further, as shown in FIG. 2, by providing a metal solder 108 between each of the n-side electrode 106 and the p-side electrode 107 and the submount 109 and mounting the nitride semiconductor light emitting device 100 on the submount 109. The nitride semiconductor light emitting element 10 that is a flip chip mounting type light emitting diode that extracts light from the second main surface side (back surface side) of the nitride semiconductor substrate 101 can be manufactured. Note that a minute concavo-convex structure is formed on the second main surface of the nitride semiconductor substrate 101 which is a light extraction surface in order to improve light extraction efficiency.

  Next, a method for manufacturing the nitride semiconductor light emitting device shown in FIGS. 1 and 2 will be described in detail with reference to FIGS.

As shown in FIG. 1, first, as the nitride semiconductor substrate 101, for example, the outermost surface is inclined by 0.3 ° in the <11-00> direction with respect to the (0001) plane, and Si is used as a donor impurity. An n-type GaN substrate having a concentration of about 1 × 10 ¹⁸ cm ⁻³ is prepared.

  In the present embodiment, a nitride semiconductor multilayer structure is subsequently formed on the nitride semiconductor substrate 101 by metal organic chemical vapor deposition (MOCVD). In this embodiment, the nitride semiconductor stack is formed by the MOCVD method. However, if an appropriate growth condition is adjusted, the MOVPE (Metal Organic Vapor Phase Epitaxy) method, the MBE (Molecular Beam Epitaxy) method, and the PLD are used. Any film forming apparatus such as the (Pulsed Laser Deposition) method may be used, and any raw material to be used may be used.

Before growing the laminated structure of the nitride semiconductor layer, hydrogen (H ₂ ) and nitrogen (N ₂ ) are supplied as carrier gases to the nitride semiconductor substrate 101 and nitrogen is decomposed and desorbed from the substrate. A heat treatment is performed for 10 minutes in a state where ammonia (NH ₃ ), which is a group V source gas, is supplied as a gas for suppression. This heat treatment is performed to clean the surface of the GaN substrate and to remove a work-affected layer during surface polishing.

Thereafter, an undoped GaN layer having a thickness of 2.0 μm is formed as the first nitride semiconductor layer 102 on the first main surface 101a of the nitride semiconductor substrate 101 at a temperature of 1080 ° C. Trimethylgallium (TMG) was used as the Ga material, and NH ₃ was used as the N material. Here, undoped means that no intentional addition of impurities is performed as described above. In this embodiment, the residual donor concentration of the undoped GaN layer is 1 × 10 ¹⁶ cm ⁻³ to 1 × 10 ¹⁷ cm ⁻³ , and the source of the residual donor is not intentionally mixed from the members of the film forming apparatus. This is due to Si or the like.

Subsequently, an n-type cladding layer made of n-Al _0.03 Ga _0.97 N having a thickness of 50 nm is formed on the first nitride semiconductor layer 102 as the n-type nitride semiconductor layer 103. Si was used as the donor impurity so that the Si concentration was about 5 × 10 ¹⁸ cm ⁻³ . Further, monosilane (SiH ₄ ) was used as the Si raw material, and trimethylaluminum (TMA) was used as the Al raw material.

Next, an active layer 104 is formed on the n-type nitride semiconductor layer 103 as a triple quantum well composed of an In _0.15 Ga _0.85 N well layer having a thickness of 3 nm and a GaN barrier layer having a thickness of 6.0 nm. An active layer having a multiple quantum well structure is formed. Subsequently, a p-type cladding layer made of p-Al _0.03 Ga _0.97 N having a thickness of 140 nm is formed on the active layer 104 as the p-type nitride semiconductor layer 105.

Here, in this embodiment, the growth temperature of the In _0.15 Ga _0.85 N well layer was 720 ° C., and the carrier gas was changed to N ₂ without using H ₂ . The growth temperature was set to 960 ° C. during the growth of the GaN barrier layer and during the growth of the p-type cladding layer. The p-type nitride semiconductor layer 105, which is a p-type cladding layer, contains about 8 × 10 ¹⁹ cm ⁻³ of magnesium (Mg) as an acceptor impurity. In addition to acting as a cladding layer, it also acts as a contact layer. Note that biscyclopentadienyl magnesium (Cp ₂ Mg) was used as the Mg raw material.

After the crystal growth of each of the nitride semiconductor layers is finished, at the stage where the temperature is reduced to 920 ° C., the supply of NH _{3 as} the group V source gas is stopped, and the supply of the carrier gas H ₂ is also stopped. The temperature is continuously lowered to room temperature only with N ₂ carrier gas. In this way, the p-type cladding layer having a hole concentration of 4 to 5 × 10 ¹⁷ cm ⁻³ and a resistivity of 2 to ³ Ωcm is subjected to a special activation heat treatment outside the MOCVD furnace. And can be formed with good reproducibility.

Subsequently, SiO ₂ having a film thickness of 200 nm is deposited on the entire surface of the p-type nitride semiconductor layer 105, and is dry etched by standard photolithography and RIE (Reactive Ion Etching) to form the n side. A mask made of patterned SiO ₂ for forming the electrode 106 is formed.

Thereafter, the nitride semiconductor layer is etched to a depth of about 0.2 μm from the surface by ICP (Induction Coupled Plasma) dry etching using Cl ₂ gas or the like using SiO ₂ as a mask. As shown in FIG. The physical semiconductor layer 103 is partially exposed in the plane.

Next, after removing the SiO ₂ film used for the mask with a hydrofluoric acid solution (HF) or the like, a 100 nm SiO ₂ film is again deposited on the entire surface. Then, an opening for depositing the p-side electrode 107 is formed by photolithography and wet etching using a buffered hydrofluoric acid solution (BHF), and the p-side made of Pd / Pt / Ag is formed in the opening by electron beam evaporation. An electrode 107 is formed. Further, by subsequently etching part of the p-type nitride semiconductor layer 105, the active layer 104, and the n-type nitride semiconductor layer 103, an opening for depositing the n-side electrode 106 is formed. An n-side electrode 106 made of Ti / Au is formed in the opening.

  Thereafter, the second main surface (back surface) 101b of the nitride semiconductor substrate 101 is polished and thinned until the thickness of the substrate reaches about 80 μm. On the back surface of the polished substrate, an etching process using a sodium hydroxide (NaOH) solution is performed to form a texture structure having fine irregularities of several μm. This texture structure has an effect of suppressing a decrease in light extraction efficiency due to reflection on the light extraction surface, and can improve the light extraction efficiency as compared with the case where the texture structure is not formed.

  Next, dicing is performed from the second main surface (back surface) side of the nitride semiconductor substrate to obtain a 1.0 mm square chip shape. Thereby, the nitride semiconductor light emitting device 100 is completed.

  Thereafter, as shown in FIG. 2, metal solder 108 is provided between the n-side electrode 106 and the metal wiring of the submount 109 and between the p-side electrode 107 and the metal wiring of the submount 109. The p-side electrode 107 and the submount 109 are joined. Thus, the nitride semiconductor light emitting device 100 can be mounted on the submount 109, and a flip chip mounting type nitride semiconductor light emitting diode in which light is emitted from the back surface side of the nitride semiconductor substrate 101 is completed.

  Next, functions and effects of the nitride semiconductor light emitting device according to this embodiment will be described with reference to FIGS. FIG. 3 is a cross-sectional view showing the structure of a nitride semiconductor light emitting device according to a comparative example, which was produced for comparison with the nitride semiconductor light emitting device according to this embodiment.

  As shown in FIG. 3, the nitride semiconductor light emitting devices 10A and 100A according to the comparative example have the same basic structure as the nitride semiconductor light emitting devices 10 and 100 according to the first embodiment of the present invention shown in FIG. It is. The difference between the nitride semiconductor light emitting device 10A according to the comparative example and the nitride semiconductor light emitting device 10 according to the first embodiment of the present invention is the first nitride semiconductor layer, which is the first embodiment of the present invention. The first nitride semiconductor layer 102 in the nitride semiconductor light emitting device 10 according to the present invention was an undoped GaN layer, whereas the first nitride semiconductor layer 102A in the nitride semiconductor light emitting device 10A according to the comparative example was This is a Si-doped GaN layer. Note that the nitride semiconductor light emitting device 10A according to the comparative example was manufactured by the following method.

First, the same nitride semiconductor substrate 101 as the nitride semiconductor light emitting device 10 according to the first embodiment of the present invention is prepared, and before the nitride semiconductor layer stack structure is grown, the nitride semiconductor substrate 101 is grown. Then, heat treatment is performed for 10 minutes while supplying H ₂ and N ₂ as carrier gases and NH 3 as a gas for suppressing decomposition and desorption of nitrogen from the substrate. Thereafter, at a temperature of 1080 ° C., a first nitride semiconductor layer composed of a Si-doped GaN layer is added by adding Si as a donor impurity at a concentration of 5 × 10 ¹⁸ cm ⁻³ on the nitride semiconductor substrate 101. 102A is formed with a thickness of 2.0 μm. Thereafter, the n-type nitride semiconductor layer 103, which is an n-type cladding layer made of n-Al _0.03 Ga _0.97 N having a thickness of 50 nm, is replaced with the first nitride semiconductor layer by the same method as in the first embodiment. It is formed so as to be in contact with 102A. Next, an active layer 104 made of a triple quantum well composed of a well layer made of In _0.15 Ga _0.85 N with a thickness of 3 nm and a barrier layer made of GaN with a thickness of 6.0 nm, and a p-type with a thickness of 140 nm. A p-type nitride semiconductor layer 105 which is a p-type cladding layer made of -Al _0.03 Ga _0.97 N is sequentially formed. Thereafter, the n-side electrode 106 and the p-side electrode 107 are formed by the same method as in the first embodiment, and then diced into a 1.0 mm square chip shape and then mounted on the submount 109. Thus, a flip-chip mounting type nitride semiconductor light emitting diode is completed.

  FIG. 4 shows the surface of the GaN layer (first nitride semiconductor layer) formed on the GaN substrate in the nitride semiconductor light emitting device according to the first embodiment of the present invention and the nitride semiconductor light emitting device according to the comparative example. It is a morphological photograph.

FIG. 4A is a surface morphology photograph of the nitride semiconductor light emitting device 10 according to the first embodiment of the present invention, and is an undoped GaN layer having a thickness of 2.0 μm formed on the n-type GaN substrate (first). 2 shows the surface morphology of one nitride semiconductor layer 102). FIG. 4B is a surface morphology photograph in the nitride semiconductor light emitting device 10A according to Comparative Example 1. The Si doped GaN layer having a Si concentration of 5 × 10 ¹⁷ cm ⁻³ and a film thickness of 2.0 μm. The surface morphology is shown. FIG. 4C is a surface morphology photograph of the nitride semiconductor light emitting device 10A according to Comparative Example 2, in which the Si-doped GaN layer having a Si concentration of 5 × 10 ¹⁸ cm ⁻³ and a film thickness of 2.0 μm. The surface morphology is shown. 4A to 4C show the state immediately before forming the n-type nitride semiconductor layer 103 made of n-Al _0.03 Ga _0.97 N.

  As shown in FIGS. 4A to 4C, the GaN layer in the nitride semiconductor light emitting device 10 according to the first embodiment of the present invention is extremely excellent in flatness and crystallinity, and has an impurity concentration. It can be seen that the flatness and crystallinity deteriorate as the value increases. Thus, it can be seen that the GaN layer formed on the GaN substrate is preferably an undoped GaN layer as in the nitride semiconductor light emitting device 10 according to the first embodiment of the present invention. That is, by using an GaN layer formed on the GaN substrate as an undoped layer as in the present invention, a GaN layer having excellent flatness and crystallinity can be formed. This will be considered below.

  Conventionally, when a light-emitting element using a compound semiconductor is manufactured, a semiconductor layer formed on a substrate has the same conductivity type as that of the substrate and is generally grown epitaxially while being doped. However, as a result of intensive studies by the inventors of the present application, when an n-type GaN substrate is used, the surface morphology is greatly deteriorated by doping, and an active layer having a uniform film in the plane is formed. Thus, it was found that a light-emitting element at a practical level could not be manufactured.

  The inventors of the present application have investigated in detail the cause of the problem of rough surface morphology, and found that a large amount of donor impurity Si is adsorbed on the interface between the substrate and the epitaxial film and incorporated into the crystal. I found. This will be described with reference to FIG.

  FIG. 5 is a surface morphology photograph of the n-type GaN substrate used in the nitride semiconductor light emitting device according to the first embodiment of the present invention and the comparative example before film formation of the GaN layer.

  Nitride semiconductors are generally known to be difficult to process due to the very robust properties of the material itself. This also applies to the production of a nitride semiconductor substrate. As shown in FIG. 5, many scratch marks, which are scratches generated during surface polishing, are formed on the surface of the nitride semiconductor substrate, or are formed during surface polishing. A work-affected layer remains as a layer having many point defects. In order to remove such a work-affected layer, the n-type GaN substrate is subjected to a heat treatment before growing the laminated structure of the nitride semiconductor layer. It was found that the surface morphology was greatly deteriorated. When an Si-doped GaN layer is formed on the n-type GaN substrate with the surface morphology deteriorated while doping, Si, which is a large amount of donor impurity, is taken into the interface between the substrate and the epitaxial film as described above. Thus, the film formation proceeds in a shape that leaves the scratch mark as it is, and the surface morphology of the GaN layer is also deteriorated as shown in FIGS. 4B and 4C.

  The inventors of the present application have studied variously thereafter, and even if the GaN substrate has a scratch mark as shown in FIG. 5, by forming an undoped GaN layer on the GaN substrate, the substrate and the epitaxial film are formed. It has been found that the surface morphology of the GaN layer can be improved by suppressing the incorporation of impurities such as Si at the interface with the GaN layer.

  FIG. 6 is a diagram showing the surface roughness of the n-type GaN substrate shown in FIG. 5 and the relationship between the film thickness and the surface roughness in the GaN layers shown in FIGS. 4 (a) to 4 (c). In FIG. 6, the horizontal axis indicates the film thickness of the GaN layer. However, for the n-type GaN substrate, only the surface roughness is shown (the film thickness is shown as 0 μm). In FIG. 6, the vertical axis indicates the RMS (Root Mean Square) value of the surface roughness. The RMS value shows the result of quantification using a scanning white interferometer. The RMS value is a result of measurement in a rectangular range of about 300 μm on the surface of the GaN substrate and the GaN layer.

  As indicated by “◯” in FIG. 6, although the n-type GaN substrate has many scratch marks, the RMS value before the heat treatment of the n-type GaN substrate is 1.4 nm and is very small. On the other hand, it can be seen that scratch marks become apparent by performing heat treatment, and the RMS value of the n-type GaN substrate increases to exceed 6 nm.

  When an undoped GaN layer is formed on a heat-treated n-type GaN substrate while changing the film thickness, the RMS value once decreases as the film thickness increases, as indicated by “●” in FIG. When the film is formed to a thickness of 3 μm, it is almost the minimum, and the RMS value is about 2 nm. Thereafter, the RMS value increases once more as the film thickness increases. This is a phenomenon for promoting step bunching as the film thickness increases and making it macro stepped. In practice, the RMS value is desirably 3 nm or less. When an undoped GaN layer is used, the film thickness is preferably 0.3 μm or more and 2 μm or less.

  On the other hand, as shown by “▲” or “■” in FIG. 6, when the Si-doped GaN layer is used, the surface roughness varies depending on the Si concentration contained in the crystal, and the RMS value increases as the Si concentration increases. Can be seen to grow. In any case, when a Si-doped GaN layer is used, it is difficult to realize an RMS value of 3 nm or less that is practically required with good reproducibility.

  As described above, according to the nitride semiconductor light emitting devices 10 and 100 according to the first embodiment of the present invention, the first nitride semiconductor which is an undoped nitride semiconductor layer on the nitride semiconductor substrate 101. By forming the layer 102, the first nitride semiconductor layer 102 excellent in flatness and crystallinity can be obtained. As a result, the various nitride semiconductor layers formed on the first nitride semiconductor layer 102 can be semiconductor layers having excellent in-plane uniformity. As a result, the active layer can be formed without unevenness in the In composition and thickness, and the active layer made of quantum wells can be uniformly formed in the device surface, so that high internal quantum efficiency, emission intensity, and emission wavelength can be obtained. Can be realized. In addition, since the In composition is uniform, the band gap non-uniformity in the element plane can be reduced, and uniform current injection into the active layer can be realized.

  In addition, the GaN substrate has a large number of defect collection regions called cores in which threading dislocations are gathered, but the donor impurity concentration and resistivity are different in the plane around the core and other parts, and the core In the peripheral portion, the donor impurity concentration is high and the resistivity tends to be low. In this case, when a current is supplied to the n-type GaN substrate, a current easily flows around the core having a low resistance, and as a result, current injection into the active layer tends to be uneven. In addition, the concentration of current around the core, which is the defect collection region, causes the growth of defects, and the increase in leakage current reduces the breakdown voltage. However, according to the nitride semiconductor light emitting devices 10 and 100 according to the first embodiment of the present invention, the first nitride semiconductor layer 102 that is an undoped nitride semiconductor layer is formed on the nitride semiconductor substrate 101. Therefore, no current is applied to the n-type GaN substrate. As a result, the increase in the leakage current can be suppressed, and as a result, the breakdown voltage can be increased, and even if the element size of the nitride semiconductor light emitting diode is increased, the yield does not decrease, and the light emission output is further improved. Can be realized.

  In this embodiment, as the nitride semiconductor substrate 101, an n-type GaN substrate tilted by 0.3 ° in the <11-00> direction with respect to the (0001) plane and containing Si as a donor impurity is used. However, it is not limited to this. For example, as the nitride semiconductor substrate 101, all nitride semiconductor substrates made of AlGaN, GaInN, AlGaInN, or the like can be used in addition to GaN. In addition to Si, oxygen (O) or selenium (Se) can also be used as a donor impurity. Further, the plane orientation of the substrate is not limited to the (0001) plane of the polar plane, and the (000-1) plane, the {1-100} plane or the {11-20} plane of the nonpolar plane, It can be applied to all of the {11-22} plane, {10-1-3} plane, {10-1-1} plane, etc. of the semipolar plane, and the tilt direction and tilt angle of the crystal axis of the substrate surface It is not limited to the above.

In this embodiment, no intentional impurity is added to the undoped GaN layer, but the same effect can be obtained if Si as a donor impurity is 1 × 10 ¹⁷ cm ⁻³ or less as a residual impurity. Therefore, in this embodiment, the n-side electrode 106 is formed on the n-type nitride semiconductor layer 103 partially exposed by dry etching, but the n-side electrode 106 is an undoped GaN layer exposed by the same means. The first nitride semiconductor layer 102 may be formed. This is because the GaN layer exhibits n-type conductivity even if it is not intentionally added with impurities, and an ohmic contact with low resistance can be achieved by appropriately selecting the deposition conditions for the n-side electrode 106. An electrode can be formed, and this structure can also serve as the n-side electrode 106 that is electrically connected to the n-type nitride semiconductor layer 103. In this case, the thickness of the first nitride semiconductor layer 102 made of the undoped GaN layer is preferably set thin. Thereby, electrons are also supplied from donor impurities contained in the nitride semiconductor substrate 101 which is an n-type GaN substrate.

In the present embodiment, the nitride semiconductor substrate 101 is an n-type GaN substrate using Si as a donor impurity and having a Si concentration of about 1 × 10 ¹⁸ cm ^−3. Since an undoped GaN layer is used as the region where the flowing electrons travel, an n-type GaN substrate having a Si concentration of 1 × 10 ¹⁸ cm ⁻³ or less may be used as the nitride semiconductor substrate. As a result, in the flip chip type element structure, the region where the donor impurity is added at a high concentration can be reduced on the light extraction surface side. Therefore, a decrease in light output due to free carrier loss can be suppressed, so that the light emission output can be improved.

(Second Embodiment)
Next, a nitride semiconductor light emitting device according to the second embodiment of the present invention will be described.

  The nitride semiconductor light emitting device according to the second embodiment of the present invention has the same basic configuration as the nitride semiconductor light emitting device according to the first embodiment of the present invention. Therefore, in the description of the nitride semiconductor light emitting device according to the second embodiment of the present invention, FIGS. 1 and 2 are used, and the nitride semiconductor light emitting device according to the first embodiment shown in FIGS. The same reference numerals are used as the constituent elements.

  The difference between the nitride semiconductor light emitting device according to the second embodiment of the present invention and the nitride semiconductor light emitting device according to the first embodiment of the present invention is the film thickness of the first nitride semiconductor layer 102. . Other components are the same.

  In the nitride semiconductor light emitting device according to the second embodiment of the present invention, the thickness of the first nitride semiconductor layer 102 which is an undoped GaN layer is set to 0.3 to 1.0 μm. In particular, in the present embodiment, the thickness of the first nitride semiconductor layer 102 is set to 0.5 μm. In the first embodiment, the thickness of the first nitride semiconductor layer 102 is 2.0 μm.

  The nitride semiconductor light emitting device according to this embodiment can be manufactured by the same method as in the first embodiment. As a result, a flip-chip mounted nitride semiconductor light emitting diode in which the thickness of the undoped GaN layer is 0.5 μm can be obtained.

  In the nitride semiconductor light emitting device according to this embodiment, the first nitride semiconductor layer 102 which is an undoped GsN layer has a thickness of 0.3 to 1.0 μm. Accordingly, as can be seen from FIG. 6, an extremely flat undoped GaN layer having an RMS value of about 2 or less and having a small RMS value can be manufactured with good reproducibility.

  As described above, the nitride semiconductor light-emitting diode according to the present embodiment can form an undoped GaN layer with excellent flatness, and thus is more active than the nitride semiconductor light-emitting diode according to the first embodiment. The surface morphology during layer growth can be further improved. As a result, high internal quantum efficiency can be realized with good reproducibility, and the yield can be improved. In addition, the consumption of raw materials can be reduced and the growth time can be shortened. Therefore, since the throughput of the MOCVD facility can be improved, the manufacturing cost of the nitride semiconductor light emitting diode can be reduced.

(Third embodiment)
Next, a nitride semiconductor light emitting device according to a third embodiment of the present invention will be described with reference to FIG. FIG. 7 is a cross-sectional view showing a configuration of a nitride semiconductor light emitting device according to the third embodiment of the present invention. In FIG. 7, the same components as those of the nitride semiconductor light emitting device according to the first embodiment of the present invention shown in FIG. 2 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The nitride semiconductor light emitting device 20 according to the third embodiment of the present invention shown in FIG. 7 is different from the nitride semiconductor light emitting device 10 according to the first embodiment of the present invention shown in FIG. This is a configuration of an n-type nitride semiconductor layer formed on the nitride semiconductor layer 102. Other configurations are the same as those of the nitride semiconductor light emitting device 10 according to the first embodiment.

  As shown in FIG. 7, the nitride semiconductor light emitting device 20 according to the third embodiment of the present invention includes a plurality of undoped layers and doped layers on a first nitride semiconductor layer 102 that is an undoped layer. An n-type nitride semiconductor layer 203 that is an n-type cladding layer is formed. The n-type nitride semiconductor layer 203 includes three layers of a second nitride semiconductor layer 203a that is an undoped layer, a nitride semiconductor layer 203b that is a doped layer, and a third nitride semiconductor layer 203c that is an undoped layer. Consists of structure. In the present embodiment, the second nitride semiconductor layer 203a and the third nitride semiconductor layer 203c are undoped AlGaIn layers, and the nitride semiconductor layer 203b is an n-type AlGaN layer.

Specifically, a first nitride semiconductor layer 102 made of an undoped GaN layer having a thickness of 0.5 μm is formed on a nitride semiconductor substrate 101 made of a GaN substrate. Further, on the first nitride semiconductor layer 102, a second nitride semiconductor layer 203a made of undoped Al _0.03 Ga _0.97 N having a thickness of 10 nm and a Si concentration of 5 × 10 ¹⁸ cm ⁻³ are formed. A three-layer n-type structure comprising a nitride semiconductor layer 203b made of n-Al _0.03 Ga _0.97 N having a thickness of 30 nm and a third nitride semiconductor layer 203c made of undoped Al _0.03 Ga _0.97 N having a thickness of 10 nm. An n-type nitride semiconductor layer 203 which is a cladding layer is formed.

  The nitride semiconductor light emitting device 20 according to this embodiment can be manufactured by the same method as the nitride semiconductor light emitting device 10 according to the first embodiment. Thereby, a flip-chip mounting type nitride semiconductor light emitting diode can be obtained.

  In the nitride semiconductor light emitting devices 20 and 200 according to the third embodiment of the present invention, the thickness of the first nitride semiconductor layer 102 made of an undoped GaN layer is reduced as in the second embodiment. Therefore, the surface morphology during active layer growth can be further improved as compared with the first embodiment, and high internal quantum efficiency can be realized with good reproducibility.

Furthermore, since the nitride semiconductor light emitting device 20 according to the third embodiment of the present invention includes the n-type nitride semiconductor layer 203 which is the n-type clad layer having the three-layer structure, the undoped Al _0.03 Ga _0.97 N The second nitride semiconductor layer 203a can serve as a spacer layer, and the n-Al _0.03 Ga _0.97 N nitride semiconductor layer 203b can serve as a barrier layer / carrier supply layer. Thereby, the two-dimensional electron gas can be effectively stored at the interface of the first nitride semiconductor layer 102 of the undoped GaN layer. By using this region as a region where electrons travel, the distribution of electrons in the device surface can be made uniform, and carriers can be more uniformly injected into the active layer in the device surface. Since the rate can be lowered, the operating voltage can also be reduced.

Note that the second nitride semiconductor layer 203a of undoped Al _0.03 Ga _0.97 N functions as a spacer layer and also acts as a barrier layer to the active layer for electrons, so the second nitride semiconductor layer 203a With respect to the film thickness, the influence of impurity scattering by Si, which is a donor impurity added to the nitride semiconductor layer 203b acting as a carrier supply layer, can be reduced, and no increase in resistance is caused in current injection into the active layer. It is desirable to set the range. Further, the Al composition of the second nitride semiconductor layer 203a is higher than that of the first nitride semiconductor layer 102 in order to cause the second nitride semiconductor layer 203a to act as a spacer that can reduce the influence of impurity scattering. In addition, it is desirable to set the Al composition of the third nitride semiconductor layer 203c in the same range or less so that the resistance does not increase in current injection into the active layer.

  As described above, the nitride semiconductor light emitting device and the manufacturing method thereof according to the present invention have been described based on the embodiments, but the present invention is not limited to the above embodiments.

  For example, in the nitride semiconductor light emitting device according to the present invention, as described above, the nitride semiconductor substrate is not limited to the GaN substrate, and all nitride semiconductor substrates such as AlGaN, GaInN, and AlGaInN are used. A desired nitride semiconductor layer can be formed on these nitride semiconductor substrates. In addition, the method for manufacturing a nitride semiconductor substrate is not limited to a method using a vapor phase growth method, but can be applied to a substrate manufactured by any method such as a liquid phase growth method and a high-pressure synthesis method. Further, the substrate surface orientation can be applied to all surface orientations regardless of their polarities.

  In addition, the embodiment can be realized by arbitrarily combining the components and functions in each embodiment without departing from the scope of the present invention, or a form obtained by subjecting each embodiment to various modifications conceived by those skilled in the art. Forms are also included in the present invention.

  The present invention relates to a light-emitting diode having a nitride semiconductor layer on a GaN substrate that is operated by applying a large current as a light source or other light-emitting device used for a display device, illumination, or backlight of a liquid crystal display. Or as a semiconductor laser diode used for an optical disk device.

10, 10A, 20, 100, 100A, 200 Nitride semiconductor light emitting device 101 Nitride semiconductor substrate 101a First main surface 101b Second main surface 102, 102A First nitride semiconductor layer 103, 203 n-type nitride Semiconductor layer 104 Active layer 105 p-type nitride semiconductor layer 106 n-side electrode 107 p-side electrode 108 metal solder 109 submount 203a second nitride semiconductor layer 203b nitride semiconductor layer 203c third nitride semiconductor layer

Claims (9)

A nitride semiconductor substrate having a first main surface and a second main surface;
A first nitride semiconductor layer formed in contact with the first main surface;
A laminate including an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer, formed on the opposite side of the first nitride semiconductor layer from the side in contact with the first main surface;
An n-side electrode electrically connected to the n-type nitride semiconductor layer;
A p-side electrode electrically connected to the p-type nitride semiconductor layer,
The first nitride semiconductor layer is an undoped nitride semiconductor layer;
The nitride semiconductor light emitting device, wherein the second main surface is a light extraction surface. The nitride semiconductor light-emitting element according to claim 1, wherein the first nitride semiconductor layer is an undoped GaN layer. The nitride semiconductor light emitting device according to claim 2, wherein the n-type nitride semiconductor layer includes an n-type AlGaN layer. The nitride semiconductor according to claim 3, further comprising a second nitride semiconductor layer made of an undoped AlGaN layer between the undoped GaN layer as the first nitride semiconductor layer and the n-type AlGaN layer. Light emitting element. The Al composition of the undoped AlGaN layer that is the first nitride semiconductor layer is the same as the Al composition of the n-type AlGaN layer included in the n-type nitride semiconductor layer, or the n-type AlGaN layer The nitride semiconductor light-emitting element according to claim 3 or 4, wherein the nitride semiconductor light-emitting element is smaller than the Al composition. The nitride semiconductor light-emitting element according to claim 1, wherein the n-type nitride semiconductor layer contains Si as an impurity. The nitride semiconductor light emitting device according to any one of claims 1 to 6, wherein a Si concentration unintentionally contained in the first nitride semiconductor layer is 1 x ¹⁰¹⁷ cm- ³ or less. The nitride semiconductor light-emitting element according to claim 1, wherein the nitride semiconductor substrate is an n-type GaN substrate containing at least one of Si and O as an impurity. Preparing a nitride semiconductor substrate having a first main surface and a second main surface and transparent to the emission wavelength;
Forming a first nitride semiconductor layer in contact with the first main surface;
Forming an n-type nitride semiconductor layer in contact with the first nitride semiconductor layer;
Forming an active layer and a p-type nitride semiconductor layer in order on the n-type nitride semiconductor layer;
Forming an n-side electrode electrically connected to the n-type nitride semiconductor layer and a p-side electrode electrically connected to the p-type nitride semiconductor layer,
The first nitride semiconductor layer is an undoped nitride semiconductor layer;
The method for manufacturing a nitride semiconductor light emitting device, wherein the second main surface is a light extraction surface.