TWI722718B - Group III nitride semiconductor light-emitting element and manufacturing method thereof - Google Patents

Abstract

The present invention provides a III-nitride semiconductor light-emitting device with high luminous output and excellent reliability and a method for manufacturing the same. The III-nitride semiconductor light-emitting device according to the present invention sequentially includes an n-type semiconductor layer, a light-emitting layer, a p-type AlGaN electron blocking layer, a p-type contact layer, and a p-side reflective electrode on a substrate, and light emission from the light-emitting layer The center wavelength is 250 nm or more and 330 nm or less, the Al composition ratio of the p-type AlGaN electron blocking layer is 0.40 or more and 0.80 or less, the film thickness of the p-type contact layer is 10 nm or more and 50 nm or less, and The p-type contact layer has a p-type AlGaN contact layer with an Al composition ratio of 0.03 or more and 0.25 or less.

Description

Group III nitride semiconductor light-emitting element and manufacturing method thereof

The present invention relates to a III-nitride semiconductor light-emitting device and its manufacturing method, and more particularly to a III-nitride semiconductor light-emitting device with high luminous output and excellent reliability and its manufacturing method.

Group III nitride semiconductors containing compounds of group III elements such as Al, Ga, In, and N are wide band gap semiconductors with a direct bandgap type band structure, and are expected to be used in sterilization, water purification, medical treatment, etc. Materials in a wide range of fields such as lighting and high-density optical recording. In particular, with regard to light-emitting elements using a group III nitride semiconductor in the light-emitting layer, the content ratio of the group III element can be adjusted to cover the deep ultraviolet light to the visible light region, thereby advancing the practical use of various light sources.

In general, the luminous efficiency of a deep ultraviolet light emitting element using a group III nitride semiconductor is extremely low, and it is difficult to achieve high output. However, in order to realize a small and high-output deep ultraviolet light-emitting element, in addition to improving the internal quantum efficiency, various attempts have been made to achieve high light extraction efficiency and low resistance characteristics.

The deep ultraviolet light emitting element that emits deep ultraviolet light is generally produced as follows. That is, a buffer layer is formed on a substrate such as sapphire or AlN single crystal, and an n-type semiconductor layer including a group III nitride semiconductor, a light-emitting layer, and a p-type semiconductor layer are sequentially formed. Thereafter, an n-side electrode electrically connected to the n-type semiconductor layer, A p-side electrode electrically connected to the p-type semiconductor layer. Here, so far, a p-type GaN contact layer that easily increases the hole concentration is generally formed on the p-side electrode side of the p-type semiconductor layer to obtain ohmic contact. However, the p-type GaN contact layer absorbs light with a wavelength of 360 nm or less due to its band gap.

Patent Document 1 discloses a group III nitride semiconductor device in which a GaN layer with a film thickness of 0.01 μm or more and 0.3 μm or less is provided on an AlGaInN layer having a relatively high Al composition ratio. In Patent Document 1, the growth mode of the GaN layer is grown in a state close to the single-layer growth (Frank-van der Merwe, FM) mode (pseudo FM mode), thereby making the GaN layer grow immediately after crystal growth. The surface is smooth. As a result, even when the film thickness of the GaN layer formed on the AlGaInN layer with a high Al composition ratio becomes thin, the surface can be smoothed.

[Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2010-232364

According to the technique of Patent Document 1, the film thickness of the p-type GaN contact layer can be made thin, and therefore light absorption by the layer can be suppressed, and it is expected that the light extraction efficiency of the group III nitride semiconductor device can be improved.

According to the experiments of the present inventors, when the film thickness of the p-type GaN contact layer is extremely thin to 50 nm or less, a group III nitride semiconductor device with a higher luminous output than the prior art can be obtained. However, in some samples of the III-nitride semiconductor light-emitting devices fabricated in this way, it has been confirmed that the following phenomenon occurs: the light-emitting output suddenly deteriorates to the extent that the light-emitting output at the initial stage is halved. In this specification, such a phenomenon of sudden deterioration of the luminous output is called "sudden death". Specifically, when a sample of a III-nitride semiconductor light-emitting device with a light-emitting area of 0.057 mm ² was energized at 20 mA to measure the initial luminous output, and then energized at 100 mA for 3 seconds, and then measured at 20 mA again, it was assumed that the relative Sudden death occurred in samples whose output dropped by more than half from the initial luminescence output. Here, when the light-emitting area of the III-nitride semiconductor light-emitting element is plotted against the light-emitting output of the forward current, the above-mentioned 20mA is the current value in the range where linearity is maintained, and the above-mentioned 100mA is the linearity loss of the output due to the heat of the light-emitting element. The current value of the range. In this way, the reliability of components with sudden deterioration in light output is insufficient, and the mixing of components with insufficient reliability into the product cannot be tolerated in the quality control of the product.

Therefore, an object of the present invention is to provide a III-nitride semiconductor light-emitting device that has both high luminous output and excellent reliability, and a method of manufacturing the same.

The inventors of the present invention have conducted diligent studies on methods to solve the above-mentioned problems. When the p-type GaN layer is extremely thinly formed to be 50 nm or less, defects are introduced due to the relaxation of large compressive strain, and the surface flatness is also deteriorated. When the p-type GaN layer is grown in the FM mode, if there are irregularities or dislocations in the AlGaN layer (the AlInGaN layer if In is included) that becomes the immediately underlying layer of the p-type GaN layer, the p-type GaN layer will be buried as described above. Concavities and convexities or dislocations grow in the direction, but it is estimated that compressive strain is easily relaxed and defects are easily introduced. Therefore, p-type GaN that cannot be buried Needless to say, the unevenness or dislocations of the layer immediately below it, even if the p-type GaN layer is flattened at first glance, new dislocations may occur. Considering the experimental facts, the inventors believe that the light-emitting element suddenly dies when the unevenness or dislocation is located in the electrode formation region. Therefore, it was found that by using an AlGaN layer having an Al composition ratio x of 0.03 or more and 0.25 or less as the p-type contact layer, sudden death of the light-emitting element can be prevented and high light-emitting output and excellent reliability can be achieved, and the present invention has been completed. That is, the gist of the present invention is configured as follows.

(1) A III-nitride semiconductor light-emitting element, which is provided with an n-type semiconductor layer, a light-emitting layer, a p-type AlGaN electron blocking layer, a p-type contact layer, and a p-side reflective electrode in this order on a substrate, and the III-nitride semiconductor The light-emitting element is characterized in that the emission center wavelength of the light emitted from the light-emitting layer is 250 nm or more and 330 nm or less, the Al composition ratio of the p-type AlGaN electron blocking layer is 0.40 or more and 0.80 or less, and the p-type contact layer has an Al composition ratio of 0.40 or more and 0.80 or less. The film thickness is 10 nm or more and 50 nm or less, and the p-type contact layer has a p-type AlGaN contact layer with an Al composition ratio of 0.03 or more and 0.25 or less.

(2) The group III nitride semiconductor light-emitting device according to (1), wherein the p-type contact layer includes only the p-type AlGaN contact layer.

(3) The group III nitride semiconductor light-emitting device according to (1), wherein the p-type contact layer has a p-type GaN contact layer between the p-type AlGaN contact layer and the p-side reflective electrode.

(4) Group III nitridation according to any one of (1) to (3) In a semiconductor light-emitting element, the thickness of the p-type AlGaN contact layer is 10 nm or more and 25 nm or less.

(5) A method for manufacturing a III-nitride semiconductor light-emitting device, comprising: forming an n-type semiconductor layer on a substrate; forming a light-emitting layer on the n-type semiconductor layer; forming a p-type semiconductor layer on the light-emitting layer A step of forming a p-type contact layer on the p-type AlGaN electron blocking layer; and a step of forming a p-side reflective electrode on the p-type contact layer, and the group III nitride The method for manufacturing a semiconductor light-emitting element is characterized in that the center wavelength of emission from the light-emitting layer is 250 nm or more and 330 nm or less, the Al composition ratio of the p-type AlGaN electron blocking layer is 0.40 or more and 0.80 or less, and the p-type contact The film thickness of the layer is 10 nm or more and 50 nm or less, and the p-type contact layer has a p-type AlGaN contact layer with an Al composition ratio of 0.03 or more and 0.25 or less.

According to the present invention, it is possible to provide a III-nitride semiconductor light-emitting device with high luminous output and excellent reliability, and a method for manufacturing the same.

10: substrate

10A: Surface

20: buffer layer

30: n-type semiconductor layer

40: luminescent layer

41: Well layer

42: barrier layer

60: p-type AlGaN electron barrier

70: p-type contact layer

71: p-type AlGaN contact layer

72: p-type GaN contact layer

80: p-side reflective electrode

90: n-side electrode

100: III-nitride semiconductor light-emitting device

FIG. 1 is a schematic cross-sectional view illustrating an embodiment of a group III nitride semiconductor light-emitting device according to the present invention.

2 is an enlarged schematic cross-sectional view illustrating one form of the p-type contact layer of the group III nitride semiconductor light-emitting device according to the present invention.

3 is a schematic cross-sectional view illustrating an embodiment of a method of manufacturing a group III nitride semiconductor light-emitting device according to the present invention.

4A is an Atomic Force Microscope (AFM) image of the surface of the p-type contact layer of Example 1. FIG.

4B is an AFM image of the surface of the p-type contact layer of Example 2. FIG.

4C is an AFM image of the surface of the p-type contact layer of Example 3. FIG.

4D is an AFM image of the surface of the p-type contact layer of Comparative Example 1. FIG.

Before describing the embodiments according to the present invention, the following aspects will be described in advance. First of all, in this specification, when the Al composition ratio is not clearly stated but only expressed as "AlGaN", it refers to any of the following compounds: the composition ratio of group III elements (the total of Al and Ga) and N is 1:1, And the ratio of group III elements Al to Ga is not fixed. In addition, in "AlGaN", even if there is no expression related to In as a group III element, In is contained within 5% of the total of Al and Ga as a group III element, and the description includes In. In the composition formula of, the Al composition ratio is set to x, and the In composition ratio is set to y (0≦y≦0.05), which is Al _x In _y Ga _1-xy N. In the case of only expressing "AlN" or "GaN", it means not including Ga and not including Al, respectively. Unless explicitly stated, by expressing only as "AlGaN", it does not exclude either AlN or GaN. In addition, the value of the Al composition ratio can be measured by photoluminescence measurement, X-ray diffraction measurement, or the like.

In addition, in this specification, a layer that electrically functions as a p-type is referred to as a p-type layer, and a layer that electrically functions as an n-type is referred to as an n-type layer. On the other hand, when a specific impurity such as Mg or Si is not intentionally added and does not function as p-type or n-type electrically, it is called "i-type" or "undoped". Inevitable impurities in the manufacturing process can be mixed into the undoped layer. Specifically, in this specification, when the carrier density is low (for example, less than 4×10 ¹⁶ /cm ³ ), it is called "undoped" . In addition, the value of the impurity concentration such as Mg or Si is set to be obtained by secondary ion mass spectroscopy (SIMS) analysis.

In addition, the overall film thickness of each layer formed by epitaxial growth can be measured using an optical interference type film thickness measuring device. Furthermore, regarding the thickness of each layer of each layer, when the composition of each adjacent layer is sufficiently different (for example, when the Al composition ratio is different from 0.01 or more), it can be determined from the cross-sectional observation of the growth layer by a transmission electron microscope. Calculate. In addition, regarding the boundary and film thickness of layers with the same or approximately the same Al composition ratio (for example, Al composition ratio less than 0.01) but different impurity concentrations in adjacent layers, the boundary between the two and the film thickness of each layer are based on the transmission electron Microscope-Energy Dispersion Spectrum (Transmission Electron Microscope-Energy Dispersion Spectrum, TEM-EDS) measurement. In addition, the impurity concentration of both can be determined by SIMS analysis. In addition, when the film thickness of each layer is thin like a superlattice structure, the film thickness can be measured using TEM-EDS.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, in principle, the same reference numerals are attached to the same constituent elements, and the description is omitted. In addition, in each figure, for convenience of description, the aspect ratio of the substrate and each layer is exaggerated from the actual ratio.

(III nitride semiconductor light-emitting device)

As shown in FIG. 1, a III-nitride semiconductor light-emitting device 100 according to an embodiment of the present invention sequentially includes an n-type semiconductor layer 30, a light-emitting layer 40, a p-type AlGaN electron blocking layer 60, and a p-type contact layer on a substrate 10. 70 and p-side reflective electrode 80. Furthermore, the emission center wavelength of the light emitted from the light emitting layer 40 is 250 nm or more and 330 nm or less, the Al composition ratio of the p-type AlGaN electron blocking layer 60 is 0.40 or more and 0.80 or less, and the film thickness of the p-type contact layer 70 is 10 nm or more and 50 nm. Hereinafter, the p-type contact layer 70 includes a p-type AlGaN contact layer 71 having an Al composition ratio of 0.03 or more and 0.25 or less.

Furthermore, the preferred form of the III-nitride semiconductor light-emitting device 100 is as follows: as shown in FIG. 1, a buffer layer 20 is provided between the substrate 10 and the n-type semiconductor layer 30, and an exposed surface is provided on the n-type semiconductor layer 30. In addition, an n-side electrode 90 and the like are provided on the exposed surface. Hereinafter, the details of each configuration will be described in order.

<Substrate>

As the substrate 10 of the group III nitride semiconductor light-emitting element 100, a sapphire substrate can be used. It can also be used on an AlN template substrate with an epitaxially grown AlN layer on the surface of the sapphire substrate. As the sapphire substrate, any sapphire substrate can be used, the presence or absence of the off angle is arbitrary, and the crystal axis in the tilt direction when the off angle is provided The bit can be either the m-axis direction or the a-axis direction. For example, the main surface of the sapphire substrate may be a surface in which the C surface is inclined at an off angle θ of 0.5 degrees. When an AlN template substrate is used, it is preferable that the AlN layer on the surface of the sapphire substrate has excellent crystallinity. In addition, it is also preferable to provide an undoped AlGaN layer on the surface of the AlN template substrate. In addition, as the substrate 10, an AlN single crystal substrate may also be used.

<n-type semiconductor layer>

The n-type semiconductor layer 30 is provided on the substrate 10 via the buffer layer 20 as necessary. The n-type semiconductor layer 30 can also be directly disposed on the substrate 10. The n-type semiconductor layer 30 may use AlGaN doped with n-type dopants. If necessary, a group III element such as In can be introduced in a composition ratio of less than 5% to become AlGaInN or the like. Specific examples of n-type dopants include silicon (Si), germanium (Ge), tin (Sn), sulfur (S), oxygen (O), titanium (Ti), zirconium (Zr), and the like. The dopant concentration of the n-type dopant is not particularly limited as long as it is a dopant concentration at which the n-type semiconductor layer 30 can function as an n-type. For example, it can be set to 1.0×10 ¹⁸ atoms/cm ³ to 1.0× 10 ²⁰ atoms/cm ³ . In addition, the band gap of the n-type semiconductor layer 30 is preferably wider than the band gap of the light-emitting layer 40 (well layer 41 in the case of a quantum well structure), and is transparent to the emitted deep ultraviolet light. In addition, in addition to configuring the n-type semiconductor layer 30 to have a single-layer structure or a structure including multiple layers, it may also be configured to include a composition gradient layer or a superlattice in which the composition ratio of the group III element is inclined along the crystal growth direction. structure. The n-type semiconductor layer 30 not only forms a contact portion with the n-side electrode 90, but also has a function of improving the crystallinity from the substrate to the light-emitting layer.

<Light-emitting layer>

The light-emitting layer 40 is disposed on the n-type semiconductor layer 30, and the center wavelength of the emitted light is Deep ultraviolet light of 250nm or more and 330nm or less. The light-emitting layer 40 may be AlGaN, and the Al composition ratio may be appropriately set so that the desired center wavelength of emission can be obtained, for example, it may be set in the range of 0.17 to 0.70.

The light-emitting layer 40 may be a single-layer structure with a fixed Al composition ratio, or preferably a multiple quantum well (MQW) structure formed by repeatedly forming a well layer 41 and a barrier layer 42 of AlGaN with different Al composition ratios. . In any case, a group III element such as In can be introduced as an AlGaInN material or the like at a composition ratio of less than 5% as required, but it is more preferable to use only Al and Ga as a ternary AlGaN material of the group III element.

When the multiple quantum well structure is used, the Al composition ratio b of the barrier layer 42 is set to be higher than the Al composition ratio w of the well layer 41 (ie, b>w). Regarding the Al composition ratio b, under the condition of b>w, the Al composition ratio b of the barrier layer 42 can be set to, for example, 0.30 to 0.95. The central emission wavelength can be roughly adjusted based on the Al composition ratio w of the well layer 41. For example, when the Al composition ratio w of the well layer 41 in the light-emitting layer 40 is set to 0.17 to 0.68, the central wavelength of light emitted from the light-emitting layer 40 is 250nm~330nm.

In addition, the number of repetitions of the well layer 41 and the barrier layer 42 is not particularly limited. For example, it can be set to 1 to 10 times. It is preferable to set the both ends of the light-emitting layer 40 in the film thickness direction (that is, the first and the last) as barrier layers, and if the number of repetitions of the well layer 41 and the barrier layer 42 is set to n, in this case, it is expressed as " n.5 sets of well layer and barrier layer". In addition, the film thickness of the well layer 41 may be 0.5 nm to 5 nm, and the film thickness of the barrier layer 42 may be 3 nm to 30 nm.

Furthermore, it is preferable to set the conductivity type of the barrier layer 42 to the n-type. This is because In order to increase the electron concentration, there is an effect of compensating for crystal defects in the well layer 41. Furthermore, the light-emitting layer 40 can be a general multiple quantum well (MQW: Multiple Quantum Well) structure in which the barrier layer 42 and the well layer 41 are repeatedly formed and sandwiched by the barrier layer 42, or the p can be removed as needed. The structure of the last barrier layer 42 on the side of the type AlGaN electron blocking layer 60.

<p-type AlGaN electron barrier layer>

The p-type AlGaN electron blocking layer 60 is provided on the light emitting layer 40. The p-type AlGaN electron blocking layer 60 is used as a layer for blocking electrons and injecting electrons into the light-emitting layer 40 (the well layer 41 in the case of the MQW structure) to improve electron injection efficiency. In the present invention, as the p-type AlGaN electron blocking layer, p-type Al _z Ga _1-z N (0.40≦z≦0.80) whose Al composition ratio is 0.40 or more and 0.80 or less can be used. If necessary, a quaternary AlGaInN material in which a group III element such as In is introduced at a composition ratio of less than 5% may be used. However, it is more preferable to use a ternary AlGaN material that uses only Al and Ga as group III elements. When the Al composition ratio is within the range, relatively many dislocations are formed on the p-type AlGaN electron blocking layer 60, and therefore it is effective to use the p-type contact layer 70 according to the present invention in this case. When the Al composition ratio is 0.60 or more and 0.70 or less, dislocations are particularly likely to be formed.

The film thickness of the p-type AlGaN electron blocking layer 60 is not particularly limited, and for example, it is preferably 10 nm to 80 nm. If the film thickness of the p-type AlGaN electron blocking layer 60 is within the above-mentioned range, a high luminous output can be reliably obtained. Furthermore, the film thickness of the p-type AlGaN electron blocking layer 60 is preferably thicker than the film thickness of the barrier layer 42. In addition, as the p-type dopant doped in the p-type AlGaN electron blocking layer 60, magnesium (Mg), zinc (Zn), calcium (Ca), beryllium (Be), manganese (Mn), etc. can be exemplified. Use Mg. As long as the dopant concentration of the p-type AlGaN electron blocking layer 60 is a dopant concentration that can function as a p-type layer, it is not particularly limited. For example, it can be set to 1.0×10 ¹⁸ atoms/cm ³ to 5.0×10 ²¹ atoms/cm ³ .

<p-type contact layer>

The p-type contact layer 70 is directly disposed on the p-type AlGaN electron blocking layer 60. The p-type contact layer 70 is a layer for reducing the contact resistance between the p-side reflective electrode 80 and the p-type AlGaN electron blocking layer 60 provided on the outermost surface thereof. In the present invention, the film thickness of the p-type contact layer 70 is 10 nm or more and 50 nm or less. In addition, the p-type contact layer 70 has a p-type AlGaN contact layer 71 whose Al composition ratio x is 0.03 or more and 0.25 or less. Furthermore, the p-type AlGaN contact layer 71 is formed to be in contact with directly above the p-type AlGaN electron blocking layer 60, and _{the Al composition ratio x of the composition formula Al x} Ga _1-x N can be 0.03≦x≦0.25. The inventors’ experiments confirmed that the p-type contact layer 70 has the p-type AlGaN contact layer 71 directly above the p-type AlGaN electron blocking layer 60 to prevent sudden death of the III-nitride semiconductor light-emitting device 100. It is believed that the reason is that instead of forming a p-type GaN layer directly above the p-type AlGaN electron blocking layer 60, a p-type AlGaN contact layer 71 (Al _x Ga _1-x N, 0.03≦x≦0.25) is formed to control the deterioration of the surface flatness The adverse effects of, and inhibit the occurrence of dislocations formed in the early stages of growth.

In order to obtain the effect of the present invention, it is sufficient that the p-type contact layer 70 has the above-mentioned p-type AlGaN contact layer 71 directly above the p-type AlGaN electron blocking layer 60. The p-type contact layer 70 may include only the p-type AlGaN contact layer 71 (refer to FIG. 1). On the other hand, the p-type contact layer 70 may be located between the p-type AlGaN contact layer 71 and the p-side A p-type GaN contact layer is included between the reflective electrodes 80 (refer to FIG. 2). In either case, the film thickness of the p-type AlGaN contact layer 71 may be 10 nm or more and 50 nm or less, and the film thickness of the entire p-type contact layer 70 may be 10 nm or more and 50 nm or less. Furthermore, in order to increase the light-emitting output of the III-nitride semiconductor light-emitting element 100 while obtaining the effects of the present invention, it is more preferable that the film thickness of the p-type AlGaN contact layer 71 be 10 nm or more and 25 nm or less. In addition, in order to more reliably suppress sudden death to zero, it is more preferable to set the thickness of the p-type contact layer 70 to 15 nm or more.

Furthermore, although not shown, the p-type contact layer 70 is preferably on the side opposite to the p-type AlGaN electron blocking layer 60 (in other words, the side in contact with the p-side reflective electrode 80), and has a Mg concentration of 3 In the high concentration region of ×10 ²⁰ atoms/cm ³ or more, it is more preferable that the Mg concentration in the high concentration region is 5×10 ²⁰ atoms/cm ³ or more. Increasing the hole concentration of the p-type contact layer 70 can reduce the forward voltage Vf of the III-nitride semiconductor light-emitting device 100. Furthermore, although it is not intended to limit the upper limit, if industrial productivity is considered, in this embodiment, the upper limit of the Mg concentration in the high-concentration region can be set to 1×10 ²¹ atoms/cm ³ . In this case, the Mg concentration in the region on the p-type AlGaN electron blocking layer 60 side of the p-type contact layer 70 can be set to a general range, which is usually 5×10 ¹⁹ atoms/cm ³ or more and less than 3×10 ²⁰ atoms/cm ³ . In addition, the Mg concentration in the p-type contact layer is the average concentration in each region measured by SIMS. In order to maintain the crystallinity of the p-type contact layer 70, the film thickness of the high concentration region is usually 15 nm or less.

<p-side electrode>

The p-side reflective electrode 80 may be disposed directly above (on the outermost surface) of the p-type contact layer 70. The p-side reflective electrode 80 is preferably used with respect to the violet radiated from the self-luminous layer 40 Metal with high reflectivity (for example, 60% or more) of external light. Examples of metals having such reflectance include rhodium (Rh), platinum (Pt), iridium (Ir), ruthenium (Ru), molybdenum (Mo), tungsten (W), tantalum (Ta), and at least containing these Any of these alloys. If it is these metals or alloys, the reflectivity to deep ultraviolet light is high, and a good ohmic contact can also be obtained between the p-type contact layer 70 and the p-side reflective electrode 80, so it is preferable. Furthermore, from the viewpoint of reflectivity, among these, it is preferable that the p-side reflective electrode 80 contains rhodium (Rh) in the form of a single body or an alloy. In addition, the film thickness, shape, and size of the p-side reflective electrode 80 can be appropriately selected according to the shape and size of the group III nitride semiconductor light-emitting element 100. For example, the film thickness of the p-side reflective electrode 80 can be 30 nm to 45 nm.

The group III nitride semiconductor light-emitting element 100 of the present embodiment described above can have both high light-emitting output and excellent reliability.

Hereinafter, a specific form that can be applied to the present embodiment will be described, but the present embodiment is not limited to the following form.

<Buffer layer>

It is also preferable to provide a buffer layer 20 between the substrate 10 and the n-type semiconductor layer 30 to alleviate the inconsistency of the crystal lattice between the substrate 10 and the n-type semiconductor layer 30, as shown in FIG. As the buffer layer 20, an undoped group III nitride semiconductor layer may be used, for example, undoped AlN may be used. The buffer layer 20 may have a superlattice structure. One or more buffer layers selected from the group consisting of an AlGaN layer, a composition gradient layer, and a superlattice layer may be further provided between the buffer layer 20 and the n-type semiconductor layer 30.

<n-side electrode>

The n-side electrode 90 that can be provided on the exposed surface of the n-type semiconductor layer 30 can be, for example, a metal composite film having a Ti-containing film and an Al-containing film formed on the Ti-containing film. The film thickness, shape, and size of the n-side electrode 90 can be appropriately selected according to the shape and size of the light-emitting element. The n-side electrode 90 is not limited to being formed on the exposed surface of the n-type semiconductor layer 30 as shown in FIG. 1, as long as it is electrically connected to the n-type semiconductor layer.

<p-type guide layer>

Furthermore, although not shown in FIG. 1, it is possible to provide AlGaN or AlN with an Al composition ratio higher than that of the p-type AlGaN electron blocking layer 60 between the light-emitting layer 40 and the p-type AlGaN electron blocking layer 60. The p-type guide layer. By providing the guide layer, the injection of holes into the light-emitting layer 40 can be promoted.

<n-type guide layer>

In addition, although not shown in FIG. 1, an n-type guide layer may be provided between the light-emitting layer 40 and the n-type semiconductor layer 30. It is preferable to use AlGaN for the n-type guiding layer, and the Al composition ratio thereof is preferably greater than or equal to the Al composition ratio of the n-type semiconductor layer 30 and the Al composition ratio b of the barrier layer 42 or less. The film thickness can be 3nm~30nm. In addition, it is preferable that the n-type guide layer is doped with an n-type dopant (impurity) as in the n-type semiconductor layer 30, but the amount of the dopant is preferably lower than that of the n-type layer.

Furthermore, the III-nitride semiconductor light-emitting device 100 according to this embodiment forms the p-side reflective electrode 80 with a reflective electrode material and reflects deep ultraviolet light, thereby enabling the substrate side or the substrate horizontal direction as the main light extraction direction. In addition, the group III nitride semiconductor light-emitting element 100 can be in a so-called flip chip form.

(Manufacturing Method of Group III Nitride Semiconductor Light-emitting Device)

Next, an embodiment of the method for manufacturing the above-mentioned group III nitride semiconductor light-emitting element 100 will be described with reference to FIG. 3. An embodiment of the method of manufacturing the III-nitride semiconductor light-emitting device 100 according to the present invention includes: forming an n-type semiconductor layer 30 on the substrate 10 (refer to step A); forming a light-emitting layer 40 on the n-type semiconductor layer 30 The step of forming a p-type AlGaN electron blocking layer 60 on the light-emitting layer 40 (refer to step B); a step of forming a p-type contact layer 70 on the p-type AlGaN electron blocking layer 60 (refer to step C); and A step of forming the p-side reflective electrode 80 on the type contact layer 70 (refer to step D). Here, in one embodiment of the manufacturing method, the emission center wavelength of the light emitted from the light-emitting layer 40 is 250 nm or more and 330 nm or less, the Al composition ratio of the p-type AlGaN electron blocking layer 60 is 0.40 or more and 0.80 or less, and the p-type contact layer The film thickness of 70 is 10 nm or more and 50 nm or less. In addition, the p-type contact layer 70 forms a p-type AlGaN contact layer 71 having an Al composition ratio of 0.03 or more and 0.25 or less.

Hereinafter, referring to FIG. 3 showing a flowchart of a preferred embodiment according to this embodiment, the details of each step will be sequentially described together with a specific aspect, regarding each configuration of the group III nitride semiconductor light-emitting element 100 , Repeated description is omitted.

First, as shown in step A and step B in FIG. 3, an n-type semiconductor layer 30, a light-emitting layer 40 and a p-type AlGaN electron blocking layer 60 are sequentially formed on the substrate 10. In these steps, the metal organic chemical vapor deposition (MOCVD: Metal Organic Chemical Vapor Deposition) method or molecular beam epitaxy (MBE: Each layer is formed by well-known epitaxial growth techniques such as Molecular Beam Epitaxy) method and sputtering method.

When forming each layer of the n-type semiconductor layer 30, the light-emitting layer 40, and the p-type AlGaN electron blocking layer 60, the growth temperature, growth pressure, and growth time for epitaxial growth can be set to correspond to the Al composition ratio of each layer And general conditions of film thickness. As a carrier gas for epitaxial growth, it is only necessary to supply hydrogen, nitrogen, or a mixed gas of both, etc. into the chamber. Furthermore, with regard to the source gas for the growth of each layer, as the source gas of the group III element, trimethyl aluminum (TMA), trimethyl gallium (Trimethyl gallium, TMG), etc. can be used as the group V element gas _{, NH 3} gas can be used. Regarding the molar ratio of the group V element to the group III element calculated based on the growth gas flow rate of the group V element gas such as NH _{3 gas and the group III element gas such as TMA gas (hereinafter referred to as the V/III ratio), as long as} Just set it as a general condition. Furthermore, as the gas for the dopant source, as far as the p-type dopant is concerned, cyclopentadienyl magnesium gas (CP ₂ Mg) as the Mg source is suitably selected, and for the n-type dopant, for example, Si The monosilane gas (SiH ₄ ) as the source, the zinc chloride gas (ZnCl ₂ ) as the Zn source, etc., can be supplied into the chamber at a predetermined flow rate.

Next, in the p-type contact layer forming step shown in step C of FIG. 3, a p-type AlGaN contact layer 71 is formed on the p-type AlGaN electron blocking layer 60. The content of the film thickness range of the p-type contact layer 70, the conditions of the Al composition ratio of the p-type AlGaN contact layer 71, and the formation of the p-type GaN contact layer 72 (not shown in FIG. 3; refer to FIG. 2) are as described above. In addition, the p-type contact layer 70 may be crystal grown by epitaxial growth using the MOCVD method or the like, similarly to the p-type AlGaN electron blocking layer 60 and the like. Furthermore, the growth conditions are not particularly limited, but it is preferable to adjust the gas flow rate, V/III ratio, and growth temperature so that the growth rate in the thickness direction is 0.03μm/h~0.50μm/h, more preferably 0.03μm/h ~0.19μm/h, it is best to make the growth rate in the thickness direction be 0.10μm/h~0.15μm/h. Furthermore, it is preferable to use H ₂ as the carrier gas.

In addition, in order to make the Mg concentration of the p-type contact layer 70 high, it is only necessary to appropriately adjust the Mg/group III element gas ratio.

In addition, as shown in step D of FIG. 3, a part of the light-emitting layer 40, the p-type AlGaN electron blocking layer 60, and the p-type contact layer 70 can be removed by etching or the like to form an n-side electrode on the exposed n-type semiconductor layer 30 90. Furthermore, the p-side reflective electrode 80 and the n-side electrode 90 can be formed into a film by a sputtering method, a vacuum evaporation method, or the like. In addition, it is also preferable to form a buffer layer 20 on the surface 10A of the substrate 10.

[Example]

Hereinafter, the present invention will be explained in more detail using examples, but the present invention is not limited to the following examples at all.

(Example 1: Wavelength 280nm)

A sapphire substrate (diameter: 2 inches, film thickness: 430 μm, surface orientation: (0001), m-axis direction deviation angle θ: 0.5 degrees) was prepared. Thereafter, an AlN layer with a central film thickness of 0.60 μm (average film thickness of 0.61 μm) was grown on the sapphire substrate by the MOCVD method to prepare an AlN template substrate. At this time, the growth temperature of the AlN layer was 1300° C., the growth pressure in the chamber was 10 Torr, and the growth gas flow rates of ammonia gas and TMA gas were set so that the V/III ratio became 163. The flow rate of the group V element gas (NH ₃ ) is 200 sccm, and the flow rate of the group III element gas (TMA) is 53 sccm. Regarding the film thickness of the AlN layer, an optical interference-type film thickness measuring machine (Nanospec M6100A; manufactured by Nanometrics) was used to measure the total dispersion at equal intervals including the center of the wafer surface. The film thickness of 25 locations was measured.

Next, the AlN template substrate was introduced into a heat treatment furnace, the pressure was reduced to 10 Pa, and nitrogen gas was purged to normal pressure to make the furnace a nitrogen atmosphere, and then the temperature in the furnace was raised to heat the AlN template substrate. At this time, the heating temperature was set to 1650°C, and the heating time was set to 4 hours.

Next, as an undoped AlGaN layer by the MOCVD method, an undoped AlGaN layer with a thickness of 200 nm with an Al composition ratio of 0.85 to 0.65 in the direction of crystal growth was formed. Next, as the n-type semiconductor layer, an n-type layer containing Al _0.65 Ga _0.35 N and doped with Si with a film thickness of 2 μm was formed. Furthermore, as a result of SIMS analysis, the Si concentration of the n-type layer was 1.0×10 ¹⁹ atoms/cm ³ .

Next, _{an n-type guide layer containing Al 0.65} Ga _0.35 N and a film thickness of 20 nm doped with Si was formed on the n-type layer, and a 4 nm Al _0.65 Ga _0.35 N was formed as a barrier layer. Next, two well layers with a thickness of 3 nm _{including Al 0.45} Ga _0.55 N and a barrier layer with a _{thickness of 4 nm including Al 0.65} Ga _0.35 N were alternately formed, and a well with a thickness of 3 nm _{including Al 0.45} Ga _{0.55 N was formed.} Floor. That is, the number of well layers and the number of barrier layers N are both 3, the Al composition ratio b of the barrier layer is 0.65, and the Al composition ratio w of the well layer is 0.45. Furthermore, Si is doped in the formation of the barrier layer.

Then, on the third well layer, using nitrogen as a carrier gas, an undoped AlN guide layer was formed. The film thickness of the AlN guiding layer is 1 nm. Next, while the supply of TMA gas is stopped, the nitrogen of the carrier gas is stopped and hydrogen is supplied while the ammonia gas is continuously supplied. After the carrier gas is changed to hydrogen, the TMA gas and TMG which are the source gases of group III elements are supplied again Gas, thereby forming _{an electron blocking layer containing Al 0.68} Ga _0.32 N and having a thickness of 40 nm doped with Mg.

Next, the growth of the electron blocking layer was stopped, the carrier gas was switched to nitrogen, the gas flow rate was changed to _{the setting conditions of the p-type Al 0.08} Ga _0.92 N contact layer, and the carrier gas was switched to hydrogen to form a Mg doped film with a thickness of 20 nm The p-type Al _0.08 Ga _0.92 N contact layer (hereinafter, abbreviated as "p-type contact layer" in the examples). As a result of SIMS analysis, the Mg concentration of the p-type contact layer averaged 1.2×10 ²⁰ atoms/cm ³ . In addition, the growth rate in the thickness direction when forming the p-type contact layer was set to 0.12 μm/h.

Thereafter, a mask is formed on the p-type contact layer, and mesa etching is performed by dry etching to expose a part of the n-type semiconductor layer, thereby forming a p-side electrode including Ni/Au on the p-type contact layer , And an n-side electrode including Ti/Al is formed on the exposed n-type layer. Furthermore, in the p-side electrode, the film thickness of Ni is 50 Å, and the film thickness of Au is 1500 Å. In addition, in the n-side electrode, the film thickness of Ti is 200 Å, and the film thickness of Al is 1500 Å. Finally, contact annealing (rapid thermal annealing (RTA)) is performed at 550°C to form each electrode.

Table 1 shows the structure of each layer of the group III nitride semiconductor light-emitting device of Example 1 produced as described above.

(Examples 2 to 5, Examples 8 to 11, Comparative Example 1, Previous Example 1, Comparative Examples 4 to 7: Wavelength 280nm)

As shown in Table 2, the film thickness and Al composition ratio of the p-type contact layer of Example 1 were changed as described in Table 2. Other than that, Examples 2 to 5, Comparative Example 1, and III of the previous example 1 were produced in the same manner as in Example 1. Group nitride semiconductor light-emitting element. Furthermore, in Example 3, a p-type Al _0.08 Ga _{0.92 N contact layer with a film thickness of 20 nm was formed on the p-type Al 0.68} Ga _0.32 N electron blocking layer, and then a p-type GaN contact layer with a film thickness of 20 nm was formed. In addition, as shown in Table 2, except that the film thickness and Al composition ratio of the p-type contact layer of Example 1 were changed, the III of Examples 8 to 11 and Comparative Examples 4 to 7 were produced in the same manner as in Example 1. Group nitride semiconductor light-emitting element.

(Example 6, Examples 12 to 13, Comparative Example 2, Previous Example 2: Wavelength 310nm)

The Al composition ratio w: 0.45 of the well layer in Example 1 was changed to 0.30, and the Al composition ratio of the undoped layer was changed to 0.55, and the n-type semiconductor The Al composition ratio of the layer was changed to 0.45, the Al composition ratio of the n-type guide layer and the barrier layer was changed to 0.55, the Al composition ratio of the p-type electron blocking layer was changed to 0.58, and the p-type contact layer was changed as described in Table 2. Except for the film thickness of and the Al composition ratio x, the Group III nitride semiconductor light-emitting devices of Example 6, Comparative Example 2, and Previous Example 2 were produced in the same manner as Example 1. In addition, except that the film thickness and Al composition ratio of the p-type contact layer of Example 6 were changed as described in Table 2, the Group III nitride semiconductor light-emitting elements of Example 12 and Example 13 were produced in the same manner as in Example 6.

(Example 7, Example 14, Comparative Example 3, Previous Example 3: Wavelength 265nm)

The Al composition ratio w: 0.45 of the well layer in Example 1 was changed to 0.58, and then the Al composition ratio of the barrier layer was changed to 0.76, and the film thickness of the p-type contact layer was changed as described in Table 2. Except for the Al composition ratio x, the group III nitride semiconductor light-emitting elements of Example 7, Comparative Example 3, and Previous Example 3 were produced in the same manner as in Example 1. In addition, a group III nitride semiconductor light-emitting device of Example 14 was produced in the same manner as in Example 7 except that the film thickness and Al composition ratio of the p-type contact layer of Example 7 were changed as described in Table 2.

(Evaluation 1: Measurement of film thickness of each layer and Al composition)

For Examples 1 to 7, Examples 8 to 14, Comparative Examples 1 to 3, Comparative Examples 4 to 7, and Previous Examples 1 to 3, respectively, the optical interference type film thickness meter was used to measure the growth shape by epitaxial growth. The thickness of each layer. In addition, the thickness of each layer including the barrier layer and the electron blocking layer is as thin as several nm to several tens of nm. Using TEM-EDS when the cross section of each layer is observed with a transmission electron microscope, the film thickness and Al composition ratio of each layer are measured. . In addition, the measurement position of the film thickness of each layer is the center of the wafer.

(Evaluation 2: Reliability Evaluation)

For the light-emitting elements obtained from Examples 1 to 7, Examples 8 to 14, Comparative Examples 1 to 3, Comparative Examples 4 to 7, and Previous Examples 1 to 3 (measured number 24), a constant current voltage power supply was used at 20 mA The current was energized to measure the luminescence output, and then 100 mA was energized for 3 seconds, and then 20 mA was energized again to measure the luminescence output, and the change in the luminescence output relative to the initial luminescence output was measured. At this time, the area that emits light by energization is 0.057 mm ² . It was confirmed that the number of light-emitting elements that had sudden death occurred when the light-emitting output after 3 seconds of energizing at 100 mA dropped to less than half of the initial light-emitting output. In Examples 1 to 7 and the previous examples 1 to 3, there was no significant change after the current was applied to 100mA. However, in Comparative Examples 1 to 3, it was confirmed that there was no spot in the wafer after the current was applied to 100mA. A light-emitting element that is bright or has an output that is less than half of the initial light-emitting output (that is, the occurrence of sudden death is confirmed). Table 2 shows the rate of occurrence of sudden death as the rate of non-lighting or that the luminous output is drastically reduced to less than half of the initial luminous output. In addition, when measuring the luminous output Po, an integrating sphere was used. Table 2 shows the results of the average value of the initial light emission output and the occurrence rate of sudden death. Furthermore, the emission center wavelength of each sample was measured by a fiber spectrometer. The emission center wavelength is also shown in Table 2.

(Evaluation 3: Measurement of surface roughness Ra)

As a representative example, for the p-type contact layer of Examples 1 to 5 and Comparative Example 1, the most On the surface, an AFM image is acquired with an atomic force microscope (AFM: Atomic Force Microscope), and Ra (average roughness; according to Japanese Industrial Standards (JIS) B 0601:2001) is measured as an index of surface roughness. In addition, the measurement location is the center of the wafer. The measured value of Ra is shown in Table 2. In addition, regarding Examples 1 to 5 and Comparative Example 1, the presence or absence of pits under substrate observation are also shown. Furthermore, FIGS. 4A to 4D show AFM images of Examples 1 to 3 and Comparative Example 1, respectively.

(Examination of evaluation results)

In Examples 1 to 7 in accordance with the conditions of the present invention, when the same wavelength is used for comparison, the luminous output can be increased compared with the previous examples 1 to 3 while the reliability is ensured. In Comparative Examples 1 and 2, since the p-type contact layer was made thin, the light absorption from the light-emitting layer could be suppressed. As a result, although the light-emitting output could be increased, it was confirmed that sudden death occurred. In Comparative Example 3, sudden death occurred frequently since the initial energization, and even the luminescence output could not be measured.

According to the AFM images shown in FIGS. 4A to 4D and the surface roughness Ra values of Examples 1 to 5 and Comparative Example 1, it was confirmed that sudden death occurred even if the surface roughness was sufficiently small. Based on the observation of pits in Examples 1, 2, 4 and Comparative Example 1, it can be considered that while embedding the irregularities or dislocations of the electron blocking layer, suppressing the increase of crystal defects accompanying the relaxation of compressive strain is important for It is important to prevent sudden death.

In addition, comparing Examples 1 to 5 and Examples 8 to 11 with a wavelength of 280 nm with Comparative Examples 1, 4 to 7, and Previous Example 1, it can be seen that the Al of the p-type contact layer The composition ratio is in the range of 0.03 to 0.25, and the film thickness is in the range of 10 nm to 50 nm, no sudden death occurs, and a light-emitting element with a larger light-emitting output than the prior art can be obtained. In addition, the results indicate that the same results can be seen in Examples 6, 12, and 13 with a wavelength of 310 nm and Examples 7, 14 with a wavelength of 265 nm.

From the above results, it was confirmed that by forming a p-type contact layer that satisfies the conditions of the present invention, a high light-emitting output can be obtained and reliability can be achieved.

[Industrial availability]

According to the present invention, it is possible to provide a III-nitride semiconductor light-emitting device with high luminous output and excellent reliability, and a method for manufacturing the same.

10: substrate

20: buffer layer

30: n-type semiconductor layer

40: luminescent layer

41: Well layer

42: barrier layer

60: p-type AlGaN electron barrier

70: p-type contact layer

71: p-type AlGaN contact layer

80: p-side reflective electrode

90: n-side electrode

100: III-nitride semiconductor light-emitting device

Claims (5)

A III-nitride semiconductor light-emitting element, which includes an n-type semiconductor layer, a light-emitting layer, a p-type AlGaN electron blocking layer, a p-type contact layer, and a p-side reflective electrode on a substrate in sequence, and is characterized in that: light from the light-emitting layer The emission center wavelength of the p-type AlGaN electron blocking layer is greater than or equal to 250 nm and less than 280 nm, the Al composition ratio of the p-type AlGaN electron blocking layer is greater than or equal to 0.40 and less than 0.80, the film thickness of the p-type contact layer is greater than or equal to 10 nm and less than 50 nm, and the p The type contact layer has a p-type AlGaN contact layer with an Al composition ratio of 0.03 or more and 0.25 or less. The III-nitride semiconductor light-emitting device according to claim 1, wherein the p-type contact layer includes only the p-type AlGaN contact layer. The III-nitride semiconductor light-emitting device according to claim 1, wherein the p-type contact layer has a p-type GaN contact layer between the p-type AlGaN contact layer and the p-side reflective electrode. The III-nitride semiconductor light-emitting device according to any one of claims 1 to 3, wherein the film thickness of the p-type AlGaN contact layer is 10 nm or more and 25 nm or less. A method of manufacturing a III-nitride semiconductor light-emitting element, comprising: forming an n-type semiconductor layer on a substrate; and forming a light-emitting layer on the n-type semiconductor layer; The step of forming a p-type AlGaN electron blocking layer on the light-emitting layer; the step of forming a p-type contact layer on the p-type AlGaN electron blocking layer; and the step of forming a p-side reflective electrode on the p-type contact layer , And the method for manufacturing the III-nitride semiconductor light-emitting element is characterized in that the center wavelength of light emission from the light-emitting layer is 250 nm or more and 280 nm or less, and the Al composition ratio of the p-type AlGaN electron blocking layer is 0.40 or more and 0.80 or less, the film thickness of the p-type contact layer is 10 nm or more and 50 nm or less, and the p-type contact layer has a p-type AlGaN contact layer with an Al composition ratio of 0.03 or more and 0.25 or less.

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