TW201545372A - Epitaxial wafer, semiconductor light emission element, light emission device and manufacturing method of epitaxial wafer - Google Patents

Abstract

Provided is an epitaxial wafer that can substantially improve light emission output. The epitaxial wafer of the present invention comprises a GaN substrate having a surface at an off angle that is 0 degrees or greater and 30 degrees or less with respect to an m-plane as a major surface, an n-type conductive layer formed on the major surface on one side of the GaN substrate, and a light emission layer formed on the major surface on one side of the n-type conductive layer, wherein a PL peak wavelength of the light emission layer is 410 nm or greater and 460 nm or less, and a PL FWHM (Full Width at Half Maximum) of the light emission layer satisfies conditional formula (1). [Delta]l ≤ L*0.4-150 (1) L: PL peak wavelength (unit: nm) [Delta]l: PL FWHM (unit: nm).

Description

Epitaxial wafer, semiconductor light emitting device, light emitting device, and method for manufacturing epitaxial wafer

The present invention relates to an epitaxial wafer, a semiconductor light emitting device, a light emitting device, and a method of manufacturing an epitaxial wafer

Gallium nitride (GaN)-based materials are currently widely used in the manufacture of light-emitting elements such as semiconductor light-emitting elements (LEDs) or semiconductor lasers (LDs). In the conventional blue light-emitting device, an n-type layer and a p-type layer are formed in the c(+) direction ([0001] axis direction) mainly by using a sapphire substrate, and an InGaN system is formed between the n-type layer and the p-type layer. Quantum well illuminating layer. The light-emitting element thus produced is applied to, for example, a white light source, and it is required to solve the following problems in order to realize a light source of higher efficiency.

One of the problems is that a light-emitting element using a sapphire substrate cannot be prevented from being generated by a lattice constant mismatch between a substrate and a GaN-based material; another problem is that material properties occur along the c-axis direction. The internal electric field contributes to a small overlap between the fluctuation coefficient of the electrons and the holes and the luminous efficiency. Therefore, in the case of using a light-emitting element of a sapphire substrate, it is necessary to produce a quantum well layer having a thickness of 2 nm, which is extremely thin (Non-Patent Document 1).

The influence of the internal electric field is larger as the In composition is higher, and therefore, the luminous efficiency in the long-wave region above blue is particularly lowered. Furthermore, the attenuation phenomenon is also a profound problem, which is a cause of a decrease in efficiency in a high injection region. The reasons for the attenuation phenomenon have been extensive In general, it is generally considered that "the Ogg recombination caused by the increase in carrier density", "the overflow phenomenon that the carrier is not captured by the quantum well", and "the overflow of the carrier outside the MQW region" are the main reasons ( Non-patent document 2).

In order to solve the above problems, it has been considered effective in the past to use a GaN substrate having no difference in lattice constant as a substrate, and to use a surface orientation in which a piezoelectric electric field does not occur, or as a result, a m-plane of a quantum well layer in which a thick film can be formed ( 10-10) face.

For example, Patent Document 1 also discloses that an InGaN quantum well layer having a thick film of more than 10 nm can be formed on an m-plane GaN substrate, and actually has an LED having low attenuation characteristics.

Further, regarding the high luminous efficiency of the InGaN quantum well layer on the m-plane GaN substrate having a violet wavelength (407 nm), there is a review result in Patent Document 2. Here, the reason why the luminous efficiency of the m-plane is lowered is described as a composite of oxygen and a group III (gallium) existing on the slip surface of the crystal, and in order to improve the luminous efficiency, the vicinity of the crystal slip surface is set to a low In composition. The area is valid. The derivation of the growth conditions for this is complicated. An important feature is that it is preferable to set the growth condition of the InGaN quantum well layer to an ultra-high V/III ratio (10000 to 30000) (refer to paragraph 0101 of Patent Document 2).

On the other hand, as disclosed in Patent Document 1, the light-emitting characteristics of short-wavelength (purple) such as 400 nm are excellent in light-emitting output of 120% or more on the m-plane compared with the c-plane, and the attenuation is extremely small. It is also expected to obtain LEDs with high potential for high luminous efficiency on the m-plane, high efficiency and low attenuation characteristics that are not known.

As described above, attempts have been made to produce LEDs that emit light with high efficiency using an m-plane GaN substrate in a long wavelength region of a violet to blue wavelength or more.

However, on the m-plane GaN substrate which can eliminate the influence of the piezoelectric field and can reduce the transmission difference by the self-supporting substrate, it is reasonable to improve the luminous efficiency of the long wavelength region. However, contrary to the expectation, the report has a problem that the output is rapidly reduced as the wavelength is increased (Non-Patent Document 3). In Non-Patent Document 3, when the light emission wavelength is 400 nm, the light-emitting output is maximized, and thereafter, the light-emitting output is rapidly lowered at about 420 nm, and only one-half or less of the light output at 400 nm is obtained at 440 nm. This phenomenon is the same even if the thickness of the quantum well layer is changed.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2010-123803

[Patent Document 2] International Publication No. 2013/042297

[Non-patent literature]

[Non-Patent Document 1] A. Chakraborty et al., Japanese Journal of Applied Physics Vol. 44, No. 5, 2005, pp. L 173-L 175.

[Non-Patent Document 2] J. Piprek, Phys. Status Solidi A 207, No. 10, 2010, pp. 2217-2225.

[Non-Patent Document 3] H. Yamada et al., Appl. Phys. Express 1, 2008, 041101.

As described in Non-Patent Document 2, the LED on the m-plane GaN substrate having the InGaN quantum well layer has a maximum light emission output when the light emission wavelength is 400 nm, and thereafter, the In composition in the InGaN quantum well layer increases and emits light. The problem of irritable output is reduced.

In the inventors of the present invention, the LEDs using the m-plane GaN self-supporting substrate are also investigated for the substrate specifications such as the off-angle and the growth conditions such as the growth temperature, the growth pressure, and the growth rate when the respective layers of the InGaN multiple quantum well layer are formed. Dependence and the thickness of the InGaN quantum well layer, the thickness of the barrier layer when forming a multiple quantum well layer, and the structural dependence of the barrier layer composition. However, similarly to Non-Patent Document 2, when the light-emitting wavelength is 400 nm, the light-emitting output is maximized, and thereafter, the light-emitting output is rapidly lowered, and as a result, even if the LED of the polar substrate is used in the blue region (near the wavelength of 450 nm), Only a lower illuminating output is obtained.

Further, for the off angle of the m-plane GaN substrate, a substrate having an off angle of about ±5° in each axial direction was examined. As a result, the substrate which is gradually inclined to the off-angle of about -5° in the c-axis (-) direction from the substrate of 0° shows the wavelength dependence of the same luminous efficiency. Further, the m-plane GaN substrate having the other off angles (for example, a substrate inclined in the a-axis direction or a substrate inclined in the c-axis (+) direction or a substrate inclined toward both sides) includes a violet wavelength, Only lower luminescence properties are obtained.

The present invention has been made in view of such circumstances, and its main object is to provide an epitaxial wafer, a semiconductor light-emitting device, a light-emitting device, and a method for manufacturing an epitaxial wafer which can greatly improve light-emitting output.

Further, after this, when the yaw angle is described in the present specification, the inclination angle toward the c (+) direction is indicated. Further, as the accuracy of the numerical value of the declination, the influence of the decimal point or less on the crystal quality is substantially small, and there is a variation in the in-plane. Therefore, the effective number is rounded to the first decimal place as an integer. For example, in the case where the c (+) direction has an off angle of -5.2° and has an off angle of 0.1° in the a-axis direction, it is described as an off-angle substrate of -5°. Similarly, when the off angle is small, for example, a case where the c direction has a declination of +0.24° and a deviation angle of +0.13° in the a-axis direction is described as a 0° substrate.

In order to achieve the above object, the epitaxial wafer of the present invention includes a GaN substrate having a surface having an off angle of 0° or more and 30° or less with respect to the m-plane as a main surface, and is formed on the GaN substrate. An n-type conductive layer on a main surface of one side; and a light-emitting layer formed on a main surface of one side of the n-type conductive layer; wherein the PL wavelength of the light-emitting layer is 410 nm or more and 460 nm or less, and the light-emitting layer is The PL half value width satisfies the conditional expression (1) (hereinafter also referred to as an epitaxial wafer according to the first embodiment of the present invention).

△l≦L×0.4-150 (1)

L: PL peak wavelength (unit: nm); Δl: PL half value width (unit: nm)

Further, in the epitaxial wafer according to the first embodiment of the present invention, the PL lifetime of the light-emitting layer at room temperature of 25 ° C in the light-emitting layer is 1.3 nsec or more and 20 nsec or less.

Further, in the epitaxial wafer according to the first embodiment of the present invention, the fluctuation of the PL peak wavelength when the excitation light intensity of the light-emitting layer is changed by 1000 times is 0 nm or more and 10 nm or less.

Further, the epitaxial wafer according to another aspect of the present invention includes a GaN substrate having a surface having an off angle of 0° or more and 30° or less with respect to the m-plane as a main surface; and the GaN substrate is formed on the GaN substrate. An n-type conductive layer on one side of the main surface; and a light-emitting layer formed on a main surface of one side of the n-type conductive layer; wherein the light-emitting layer has a PL peak wavelength of 410 nm or more and 460 nm or less The PL lifetime of the light-emitting layer at room temperature of 25 ° C is 1.3 nsec or more and 20 nsec or less (hereinafter also referred to as an epitaxial wafer of the second embodiment of the present invention).

Moreover, the epitaxial wafer system according to the second embodiment of the present invention can be made up The fluctuation of the PL peak wavelength when the excitation light intensity of the light-emitting layer is changed by 1000 times is 0 nm or more and 10 nm or less.

Furthermore, the epitaxial wafer according to another aspect of the present invention includes a GaN substrate having a surface having an off angle of 0° or more and 30° or less with respect to the m-plane as a main surface; An n-type conductive layer on a main surface on one side of the substrate; and a light-emitting layer formed on a main surface on one side of the n-type conductive layer; wherein the PL peak wavelength of the light-emitting layer is 410 nm or more and 460 nm or less When the excitation light intensity of the light-emitting layer is changed by 1000 times, the fluctuation of the PL peak wavelength is 0 nm or more and 10 nm or less (hereinafter also referred to as an epitaxial wafer according to the third embodiment of the present invention).

In the epitaxial wafer of the present invention, for example, the light-emitting layer includes an InGaN layer.

Furthermore, the epitaxial wafer of the present invention preferably has a light-emitting layer of a quantum well structure and has at least one interface strain buffer layer between the quantum well layer and the barrier layer.

Further, in the epitaxial wafer of the present invention, it is preferable that the GaN substrate has a dark spot density of 2 × 10 ⁸ cm ^-2 or less.

Further, in the epitaxial wafer of the present invention, it is preferable that the main surface of the other side of the GaN substrate is roughened.

In order to achieve the above object, the semiconductor light-emitting device of the present invention includes an n-type conductive layer formed of a GaN-based semiconductor layer formed on a main surface of one side of a GaN substrate, the GaN The substrate has a surface having an off angle of 0° or more and 30° or less with respect to the m-plane as a main surface; a light-emitting layer formed on a main surface on one side of the n-type conductive layer; and a light-emitting layer formed on the light-emitting layer a p-type conductive layer on one side of the main surface; the light-emitting wavelength of the light-emitting layer is 410 nm or more and 460 nm or less, and the PL half-value width of the light-emitting layer satisfies the conditional expression (1) (hereinafter also referred to as the present invention) The semiconductor light-emitting device of the first embodiment).

△l≦L×0.4-150 (1)

L: PL peak wavelength (unit: nm); Δl: PL half value width (unit: nm)

Further, in the semiconductor light-emitting device of the first embodiment of the present invention, the PL lifetime of the light-emitting layer at room temperature of 25 ° C in the light-emitting layer is 1.3 nsec or more and 20 nsec or less.

In the semiconductor light-emitting device according to the first embodiment of the present invention, the light-emitting layer has a variation in the emission peak wavelength of 1 mA or more and 350 mA or less of 6 nm or less.

Further, the semiconductor light-emitting device of another aspect of the present invention may include an n-type conductive layer formed of a GaN-based semiconductor layer formed on a main surface of one side of the GaN substrate, the GaN The substrate has a surface having an off angle of 0° or more and 30° or less with respect to the m-plane as a main surface; a light-emitting layer formed on a main surface on one side of the n-type conductive layer; and a light-emitting layer formed on the light-emitting layer a p-type conductive layer on one side of the main surface; the light-emitting wavelength of the light-emitting layer is 410 nm or more and 460 nm or less; and the PL lifetime of the light-emitting layer of the light-emitting layer at room temperature of 25 ° C is 1.3 nsec or more and 20 nsec Hereinafter (hereinafter also referred to as a semiconductor light-emitting device of the second embodiment of the present invention).

In the semiconductor light-emitting device of the second embodiment of the present invention, the variation of the emission peak wavelength of the light-emitting layer of 1 mA or more and 350 mA or less is 6 nm or less.

Further, the semiconductor light-emitting device according to another aspect of the present invention may include an n-type conductive layer formed of a GaN-based semiconductor layer formed on a main surface of one side of the GaN substrate. The GaN substrate is a surface having an off angle of 0° or more and 30° or less with respect to the m-plane, and is formed as a main surface; a light-emitting layer on a main surface of one side of the n-type conductive layer; and a p-type conductive layer formed on a main surface on one side of the light-emitting layer; the light-emitting wavelength of the light-emitting layer is 410 nm or more and 460 nm or less. The variation of the emission peak wavelength of the light-emitting layer of 1 mA or more and 350 mA or less is 6 nm or less (hereinafter also referred to as a semiconductor light-emitting device of the third embodiment of the present invention).

Furthermore, in order to achieve the above object, a light-emitting device of the present invention includes a semiconductor light-emitting device and a wavelength conversion material. The semiconductor light-emitting device has an n-type conductive layer formed of a GaN-based semiconductor layer formed on a main surface on one side of a GaN substrate, the GaN substrate having 0 with respect to the m-plane a face having an off angle of not less than 30° as a main surface; a light-emitting layer formed on a main surface on one side of the n-type conductive layer; and a p-type formed on a main surface on one side of the light-emitting layer a conductive layer; the PL peak wavelength of the light-emitting layer is 410 nm or more and 460 nm or less, and a PL half-value width of the light-emitting layer satisfies conditional expression (1); and the wavelength conversion substance absorbs light emitted by the semiconductor light-emitting element At least a part of the light is converted into light of a longer wavelength (hereinafter also referred to as a light-emitting device according to the first embodiment of the present invention).

△l≦L×0.4-150 (1)

L: PL peak wavelength (unit: nm); Δl: PL half value width (unit: nm)

Further, in the light-emitting device according to the first embodiment of the present invention, the PL lifetime of the light-emitting layer at room temperature of 25 ° C in the light-emitting layer is 1.3 nsec or more and 20 nsec or less.

Further, in the light-emitting device according to the first embodiment of the present invention, the variation of the emission peak wavelength of the light-emitting layer of 1 mA or more and 350 mA or less is 6 nm or less.

Moreover, the light-emitting device of the present invention includes a semiconductor light-emitting device and a wavelength conversion material. The semiconductor light-emitting device has an n-type conductive layer formed of a GaN-based semiconductor layer formed on a main surface on one side of a GaN substrate, the GaN substrate having 0 with respect to the m-plane a face having an off angle of not less than 30° as a main surface; a light-emitting layer formed on a main surface on one side of the n-type conductive layer; and a p-type formed on a main surface on one side of the light-emitting layer a conductive layer; the light-emitting wavelength of the light-emitting layer is 410 nm or more and 460 nm or less; and the PL lifetime of the light-emitting layer at room temperature of 25 ° C is 1.3 nsec or more and 20 nsec or less; and the wavelength conversion substance is absorbed by the above At least a part of the light emitted from the semiconductor light-emitting element is converted into light of a longer wavelength (hereinafter also referred to as a light-emitting device according to the second embodiment of the present invention).

Further, in the light-emitting device according to the first embodiment of the present invention, the light-emitting layer has a variation in the emission peak wavelength of 1 mA or more and 350 mA or less, which is 6 nm or less.

Furthermore, the light-emitting device of the present invention includes a semiconductor light-emitting device and a wavelength conversion material, and the semiconductor light-emitting device has an n-type conductive layer formed of a GaN-based semiconductor layer, and the GaN-based semiconductor layer is formed on the GaN substrate. On the main surface of one side, the GaN substrate has a surface having an off angle of 0° or more and 30° or less with respect to the m-plane as a main surface; and is formed on a main surface on one side of the n-type conductive layer. a light-emitting layer; and a p-type conductive layer formed on a main surface on one side of the light-emitting layer; wherein the light-emitting layer has an emission peak wavelength of 410 nm or more and 460 nm or less, and the light-emitting layer has an emission peak wavelength of 1 mA or more and 350 mA or less The change is below 6nm; The wavelength conversion material absorbs at least a part of the light emitted from the semiconductor light-emitting element and converts it into light of a longer wavelength (hereinafter also referred to as a light-emitting device according to a third embodiment of the present invention).

Further, in order to achieve the above object, the method for producing an epitaxial wafer of the present invention includes a first step of growing an n-type conductive layer formed of a GaN-based semiconductor layer, the GaN The semiconductor layer is formed on a main surface of one side of the GaN substrate, and the GaN substrate has a surface having an off angle of 0° or more and 30° or less with respect to the m-plane as a main surface; a second step of growing the light-emitting layer on the main surface on one side of the n-type conductive layer grown in the step; and at least the following step in the second step: the Mo group of the V-type raw material The ratio of the supply amount to the molar supply amount of the group III raw material, that is, the V/III ratio, is 500 or more and 4,000 or less, and the group V raw material and the group III raw material are supplied.

In the second step, it is preferable that the plurality of quantum well layers are grown as the light-emitting layer, and the multiple quantum well layer has a structure in which a quantum well layer and a barrier layer are alternately laminated, and the quantum well layer is grown. The V group raw material and the group III raw material are supplied so that the V/III ratio is 500 or more and 4,000 or less.

Further, in the second step, it is preferable to grow the quantum well layer formed of the InGaN layer as the quantum well layer.

Further, in the second step, it is preferable that the ratio of the supply amount of the indium raw material in the total supply amount of the group III raw material is 50% in the growth of the quantum well layer formed of the InGaN layer. The Group III raw material is supplied in the above 90% or less.

In the second step, it is preferred that the quantum well layer be grown at a growth rate of 1 nm/min or more and 8 nm/min.

Moreover, it is preferable that the method for producing an epitaxial wafer of the present invention further includes a third step of heat-treating the light-emitting layer in the air.

Further, in the first and second steps, it is preferable that the n-type conductive layer and the light-emitting layer are grown by MOCVD.

According to the present invention, an epitaxial wafer, a semiconductor light-emitting device, a light-emitting device, and a method of manufacturing an epitaxial wafer capable of greatly improving the light-emitting output can be realized.

1‧‧‧ epitaxial wafer

2‧‧‧m-plane GaN substrate

3‧‧‧1st undoped GaN layer

4‧‧‧n-type GaN contact layer

5‧‧‧AlGaN layer

6‧‧‧2nd undoped GaN layer

7‧‧‧Lighting layer

7A‧‧‧Quantum wells

7B‧‧‧Baffle layer

7C‧‧‧Interface strain buffer layer

8‧‧‧p-type AlGaN cladding

9‧‧‧p-type GaN contact layer

10‧‧‧p-type InGaN contact layer

11‧‧‧n side metal electrode

12‧‧‧p side contact electrode

13‧‧‧p side metal electrode

20‧‧‧Semiconductor light-emitting elements

21‧‧‧Package

22‧‧‧Translucent materials

23‧‧‧ wavelength conversion unit

30‧‧‧Lighting device

Fig. 1 is a graph showing the results of evaluating the wavelength dependence of the light output of a semiconductor light-emitting device fabricated under conventional conditions.

2(a) to 2(c) are graphs (halftone images) showing PL spectral imaging results in the plane of the substrate of the MQW structure fabricated under conventional conditions.

Fig. 3 is a graph showing the results of superimposing the PL spectrum at the position shown in Fig. 2 in the case where the all-polarized component is received and separated by the polarized light.

Fig. 4-1 is a graph showing the results of fitting the E//a component of the PL spectrum separated by polarization in Fig. 3 by a two-component Gauss peak.

Fig. 4-2 is a graph showing the results of fitting the E//c component of the PL spectrum separated by polarization in Fig. 3 by a two-component Gauss peak.

Fig. 5 is a graph showing the results of plotting the respective PL peak wavelengths obtained in Figs. 4-1 and 4-2 with the X position of Fig. 3 as the horizontal axis.

Figure 6 is a graph showing the X-ray diffraction (XRD) results for each position of Figure 2, and showing the positional dependence of the angle of the zero-chapter peak.

Figure 7 is a cross-sectional TEM image showing the MQW structure fabricated under conventional conditions. Photo.

Fig. 8 is a graph showing the result of superimposing the EL luminescence spectrum when changing the current value of the injection current of the semiconductor light-emitting element formed on the m-plane prepared by a known condition.

Fig. 9 is a graph showing the results of fitting the EL luminescence spectrum of Fig. 8 by a two-component Gauss peak.

Fig. 10 is a graph showing the results of PL luminescence spectra of Sample B and Sample C used in the Yang Electronics Elimination Experiment.

Figure 11 is a graph showing the S-W plots of Sample B and Sample C obtained in the Yang Electronics Elimination Experiment.

Fig. 12 is a schematic cross-sectional view showing an epitaxial wafer of the embodiment.

Fig. 13 is a schematic cross-sectional view showing a light-emitting layer of the embodiment.

Fig. 14 is a schematic view showing a semiconductor light emitting device of the embodiment, Fig. 14(a) is a plan view, and Fig. 14(b) is a cross-sectional view taken along line X-X of Fig. 14(a).

Fig. 15 is a schematic view showing a light-emitting device of the embodiment.

Fig. 16 is a flow chart showing a method of manufacturing an epitaxial wafer according to the embodiment.

Fig. 17 is a graph showing the wavelength dependence of the total radiation beam when the semiconductor light-emitting elements of Example 1, Example 2, and Comparative Example 1 were energized at 350 mA.

18 is a graph showing PL peak wavelength dependence and PL lifetime of PL half-value widths obtained from the semiconductor light-emitting elements of Example 1, Example 2, and Comparative Example 1. FIG.

19 is a view showing characteristics of the semiconductor light-emitting device of Example 1 and Comparative Example 1. FIG. 19(a) is a graph showing an EL luminescence spectrum, and FIG. 19(b) is a graph showing a current value dependence of an EL luminescence peak wavelength. Fig. 19(c) is a graph showing the dependence of the current value of the total radiation beam.

Figure 20 is a graph showing changes in the growth conditions of the LED structure and the MQW structure. A graph of the relationship between the PL peak wavelength and the PL half-value width.

Fig. 21 is a graph showing the relationship between the PL peak wavelength and the PL lifetime measured by changing the growth conditions of the LED structure and the MQW structure.

Fig. 22 is an indication of the intensity (relative value) of the excitation light of the PL peak wavelength.

Fig. 23 is a graph showing the relationship between the intensity of excitation light at room temperature and the lifetime of PL when the intensity of excitation light of the MQW structure of Example 6 is changed.

Figure 24 is a spectral imaging data (halftone image) of the half-value width of the CL spectrum obtained from the MQW structure of Example 7-1.

Figure 25 is a spectral imaging data (halftone image) of the CL spectral wavelength obtained from the MQW structure of Example 7-1.

Fig. 26 is a spectral imaging data (halftone image) of the half-value width of the CL spectrum obtained by the MQW structure of Comparative Example 7-1.

Fig. 27 is a spectral imaging material (halftone image) of the CL spectral wavelength obtained by the MQW structure of Comparative Example 7-1.

Figure 28 is a CL luminescence spectrum of the portion shown in Figure 26 as 1, 2, and 3.

Figure 29 is a CL luminescence spectrum of the portion shown in Figure 24 as 1, 2, and 3.

Fig. 30 is a schematic photograph showing the surface topography obtained by AFM on the InGaN single layer of Example 8-1, with the surface shape image on the left side and the phase image on the right side.

Fig. 31 is a schematic photograph showing the surface topography obtained by AFM on the InGaN single layer of Comparative Example 8-1, with the surface shape image on the left side and the phase image on the right side.

Fig. 32 is a graph showing the temperature dependence of the PL lifetime of the MQW structure of the ninth embodiment.

Fig. 33 is a graph showing the relationship between the PL peak wavelength and the PL half value width measured by changing the off angle of the m-plane GaN substrate and the growth conditions of the LED structure.

Fig. 34 is a schematic photograph showing the surface topography obtained by AFM on the InGaN quantum well layer (thickness: 0.9 nm) of Example 11-1, the surface shape image on the left side and the phase image on the right side.

Fig. 35 is a schematic photograph showing the surface topography obtained by AFM on the InGaN quantum well layer (about 4 nm thick) of Example 11-1, the surface shape image on the left side and the phase image on the right side.

Fig. 36 is a schematic photograph showing the surface topography obtained by AFM on the InGaN quantum well layer (about 50 nm thick) of Example 11-1, the surface shape image on the left side and the phase image on the right side.

Fig. 37 is a schematic photograph showing the surface topography obtained by AFM on the InGaN quantum well layer (thickness: 0.9 nm) of Comparative Example 11-1, the surface shape image on the left side and the phase image on the right side.

Fig. 38 is a schematic photograph showing the surface topography obtained by AFM on the InGaN quantum well layer (thickness: 4 nm) of Comparative Example 11-1, the surface shape image on the left side and the phase image on the right side.

39 is a pictorial representation of a surface topography obtained by AFM on an InGaN quantum well layer (about 50 nm thick) of Comparative Example 11-1, with a surface shape image on the left side and a phase image on the right side.

Fig. 40 is a view showing a surface atom arrangement pattern of GaN crystals.

(latitude and longitude)

The following description is the main motivation for the present inventors to achieve the present invention, focusing on an InGaN quantum well layer from an m-plane GaN substrate belonging to a non-polar surface. The luminescence spectrum has complex peaks. Here, as the target InGaN quantum well layer system, a light having a wavelength of 400 nm to 460 nm can be obtained, and the In composition is in the range of about 5% to 20%.

First, the inventors of the present invention fabricated a semiconductor light-emitting device using an InGaN quantum well layer on an m-plane GaN substrate using a conventional condition, that is, a high V/III ratio which is generally used, and evaluated the wavelength dependence of the light output. The results are shown in Figure 1. Here, the V/III ratio of the growth of the InGaN quantum well layer is a high V/III ratio of 8340 to 15480. The layer structure and growth conditions are shown in Tables 1 and 2. Further, the InGaN quantum well layer and the GaN barrier layer were laminated for three cycles. The substrate, the wafer structure, the mounting form, and the evaluation conditions are the same as those in the first embodiment to be described later.

In order to control the wavelength of light emitted from the InGaN quantum well layer, there are various methods, but here, the ratio of In mole supply in the group III by growing the InGaN quantum well layer ((MMI per minute of MMI) The supply amount) / (the molar supply amount per minute of TMI + the molar supply amount per minute of TMG)) is controlled by changing and/or adjusting the growth temperature of the light-emitting layer.

The examples and comparative examples shown in the present specification are any of the results of all the experiments conducted by the inventors of the present invention, and any of the conditions, regardless of the decrease in the growth temperature and the increase in the molar ratio of the In-mole supply under any of the conditions. Both can make the wavelength of the light longer. That is, there are a plurality of combinations for realizing a ratio of the growth temperature of a certain wavelength to the supply amount of the In mole. However, when the In molar supply ratio is in the range of 50% or more, the luminous efficiency or the luminescent layer quality described below is governed by the wavelength. That is, it was confirmed that the characteristics and quality of the produced light-emitting layer were the same regardless of the combination of the growth temperature and the In-mole supply ratio, and the other conditions were the same as the wavelength.

Here, as is clear from FIG. 1, the light-emitting output is rapidly reduced as it is long-wavelength. This tendency is completely the same as the above non-patent document 3.

As described in the above-mentioned problem, the improvement of the LED light-emitting output on the m-plane GaN substrate has not been found by the change of the growth conditions or the change in the type of the substrate such as the off-angle. Therefore, the inventors of the present invention thought that as the composition of In becomes higher and the quality of the light-emitting layer itself is lowered, in order to directly and accurately observe the quality of the light-emitting layer, the quality of the MQW structure is stopped before the p-type conductive layer is lowered. The reason for the improvement and improvement of the method.

The angling angle of the m-plane GaN substrate was examined in the vicinity of 0° to 5°, but the quality deterioration state was almost the same. Here, the LED on the m-plane GaN substrate having an off-angle of 0° will be described. The layer structure reviewed here is shown in Table 3. Further, the InGaN quantum well layer and the GaN barrier layer were laminated for three cycles. The V/III ratio of the InGaN quantum well layer grows with 8340 and higher values.

After the growth, the PL spectrum imaging measurement was performed on the entire substrate. The PL spectral imaging measurement was performed using a 325 nm He-Cd laser as an excitation light source, and the entire surface of the substrate was evaluated at a pitch of 0.5 mm. Fig. 2 (a) to (c) show spectral imaging results of PL peak wavelength, PL peak intensity, and PL half value width, respectively.

As can be seen from Fig. 2, the wavelength of the PL peak from the lower left side of the drawing to the upper right is long-wavelength, and the intensity of the PL peak is also lowered. The PL half-value width temporarily expands with long-wavelength, and is widest at around 440 nm, and further narrows near the upper right end of the drawing.

Further, in the PL luminescence spectrum obtained here, it can be found that when the intensity peak is two or that the intensity peak is one, the spectral shape is not bilaterally symmetrical, and swelling is also observed on one side (also referred to as shoulder). The case of a skewed shape, etc.

According to the review by the inventors of the present invention, the cause of the abnormality of these spectral shapes is that at least two intensity peaks are caused by the superposition of two or more kinds of light emission. Here, this phenomenon is referred to as a multi-peak of luminescence.

In order to investigate the above-described spectral imaging results in detail, the PL luminescence spectrum was evaluated again using another optical system at the point marked "X" on the substrate. Here, a picosecond pulsed laser having a wavelength of 385 nm is used as the excitation light, and the spot diameter is set to 100 μm. . The detailed conditions of the excitation light are the same as those used in the PL lifetime measurement. The indication points are indicated by the short-wave side on the substrate (the lower side of Figure 2), which are sequentially set to X1 and X2. . . X10.

In the evaluation of the PL luminescence spectrum, a polarization filter is inserted on the light-receiving side of the PL luminescence spectrum, and only a component that polarizes the electric field vector in the a-axis direction is received (E//). In the case of a) and the three conditions in which only the component (E//c) which polarizes the electric field vector in the c-axis direction is received, the spectrum is measured.

The purpose of evaluation by polarized light separation was to investigate whether or not the multi-peak of the PL luminescence spectrum is a band structure. The amount of InGaN on an m-plane GaN substrate is known The valence electron band of the sub-well layer is split due to the influence of in-plane anisotropic strain. The luminescence from the A-band with the lowest energy level at the base level (luminescence on the long-wave side) is E//a polarized light, from The high-level light (B-band) is E//c polarized light. Therefore, if the multi-wave peak is a band structure, it should be a superposition of two single-wave peaks with different polarizations, which can be separated into single-wave peaks by polarization separation.

The PL luminescence spectra measured under these three conditions are divided into respective polarization conditions, and the PL luminescence spectra at the respective positions are superimposed and depicted in FIG.

As can be seen from Fig. 3, both the E//a component and the E//c component are not single peaks but multi-peaks. That is, the reason for the multiple peaks of these is considered to be not the cause of the structure of the valence band. Furthermore, the scale of the vertical axis is appropriately expanded and reduced for easy viewing, and varies depending on the chart.

Next, in order to investigate which components such multi-wave peaks are composed, the respective PL spectra of the E//a component and the E//c component of the sample A are assumed to be superimposed and superimposed on the Gaussian peaks of the two components. The intensity of each PL peak. The results are shown in Figures 4-1 and 4-2. The vertical axis is the PL peak intensity, and the horizontal axis is the energy display (photon energy (eV)).

As can be seen from FIGS. 4-1 and 4-2, when the PL luminescence spectrum is a combination of two components, the respective peak shapes of the E//a component and the E//c component can be accurately reproduced. That is, these PL luminescence spectra are superimposed on the short-wave side emission mode (E high) and the long-wave side emission mode (E low).

In addition, FIG. 5 shows the peak wavelengths of the respective PL luminescence spectra separated by the peaks in FIGS. 4-1 and 4-2, and are drawn according to the respective positions.

As can be seen from Fig. 5, the peak wavelengths (hollow □ and Δ) of the original PL luminescence spectrum of the E//a component and the E//c component are PL luminescence spectra and peak wavelengths on the short-wave side near the violet wavelength side. Similar (meaning that the peak on the short wave side is dominant), along with the long wave The spectrum on the longer wavelength side becomes closer to the peak wavelength (meaning that the long-wave side luminescence is dominant).

The peak position shifted from the short wave side to the long wave side, depending on the E//a component and the E//c component, but either of them is around 430 nm.

Further, the peak wavelength of the original PL luminescence spectrum is a jump of the PL peak wavelength seen in X6 to X7. However, in order to investigate whether or not the In composition changes, the (300) reflection XRD evaluation of each position is performed. The source of the radiation uses a Cu source (λ = 1.5406 Å).

Here, the positions of X2, X4, X6, X7, X8, X9, and X10 were measured. The result is shown in Fig. 6. Moreover, the positional dependence of the angle of the 0th peak is shown in FIG. As can be seen from Fig. 6, from X6 to X7 and X8, the change in the accompanying peak reflecting the In composition is gentle. That is, the jump of the PL peak wavelength is not caused by the variation of the In composition.

In addition, in order to investigate whether such wavelength fluctuation or multi-peak generation is caused by crystal defects such as a sliding surface of a crystal or a laminated defect or a through-displacement as seen in Patent Document 2, a profile HAADF-TEM is implemented. Evaluation. The results are shown in Figure 7. As can be seen from Fig. 7, no defects were observed in the cross section of the InGaN quantum well layer, and the interface of the quantum well structure was flat, and the In deviation was not found to be too large.

Further, the inventors of the present invention investigated what kind of luminescence spectrum is available in terms of luminescence characteristics when a current is injected into an actual luminescence element. The luminescence spectrum obtained when the current is injected is referred to as an EL luminescence spectrum. In the same manner as the element structure used for the PL peak wavelength variation (described later), a substrate on which a p-type conductive layer was formed was produced, and a semiconductor light-emitting device was produced and evaluated. The results are shown in Figures 8 and 9.

As shown in Fig. 8, it was confirmed that the shape of the EL luminescence spectrum was changed depending on the injection current. Further, it is known that the shape is 2 Gauss as in the PL luminescence spectrum. The peaks are superimposed to fit well. Fig. 9 is a graph showing the EL luminescence spectrum of each of the injection current values, and the injection current value is indicated at the upper left of each spectrum. As shown in FIG. 9, the long-wave side light emission is mainly at a low carrier density (low current value), and the short-wave side light emission is mainly caused as the carrier density increases. That is, it was found that the relative luminous efficiency of the long-wave side luminescence is low when the carrier density is high.

In an attempt to investigate the cause of the quality degradation of the InGaN quantum well layer, the inventors of the present invention further used samples having different emission wavelengths to evaluate the condition and type of point defects by the positive electron elimination experiment. The evaluation of the point defect by the positive electron elimination experiment and the estimation of the defect type using the S-W drawing have been described by, for example, Uedono et al., Journal of Crystal Growth 311, 2009, pp. 3075-3079.

Regarding the point defect evaluation, in order to improve the evaluation sensitivity, the overall film thickness must be thickened. This time, the sample prepared for this purpose was formed by alternately stacking 4 nm of the InGaN quantum well layer and 4 nm of the GaN barrier layer on the m-plane GaN self-supporting substrate for 25 cycles. The sample system is made into two types of sample B and sample C. Sample B differs from sample C only in the composition of In, the composition of In in sample B is set to about 10%, and the composition of In in sample C is set to about 20%.

The growth conditions here are similar to those shown in Table 2. The difference from Table 2 is that the thickness and number of cycles of the above InGaN quantum well layer and GaN barrier layer are changed. Moreover, the V/III ratio at the time of growth of the InGaN quantum well layer is a high V/III condition of 8340 to 18080.

The sample B-based emission wavelength was 393 nm, and the sample C-based emission wavelength was 420 nm. The PL luminescence spectrum when Sample B and Sample C were evaluated using He-Cd laser excitation light is shown in FIG. The structure is different from the above sample A in which the multi-peak is reviewed. The PL spectrum of sample B is unimodal and the half-value width is narrow, and the sample C is PL spectrum jump. Multiple peaks occur. It is considered that the sample B reproduces a good quality when the In composition is low, and the sample C reproduces a situation in which a multi-peak occurs when the In composition is high, and the quality is lowered.

Figure 11 shows the SW plot obtained by the aging electron elimination experiment. Drawing on SW, it can indicate the size of the defect and the type of defect. It can be seen from Fig. 11 that sample B has almost no good quality of point defects; on the other hand, sample C has a point defect and teaches that the defect type is V _Ga -(V _N ) ₃ , that is, Ga hole and The possibility of a complex of N holes.

Further, Fig. 11 also shows points of the type of defects related to oxygen (e.g., V _Ga O _N or the like), and the relationship between the defects of oxygen and the defects of the sample C is small.

It is known that in an epitaxial growth film of an m-plane GaN substrate, the content of oxygen is generally large, but the sample B and the sample C which are only slightly different in wavelength cannot be considered to have extremely different oxygen concentrations, and thus it is also known that the defect is not Oxygen cause.

In summary, the luminescence from the InGaN quantum well layer on the m-plane GaN substrate is such that both PL and EL overlap in the luminescence spectrum of the two components, and it is not possible to describe the band structure, the In composition change, or the lattice defect or oxygen impurity. influences.

Due to the current value dependence of the EL luminescence spectrum, the luminescence on the long wavelength side becomes the main luminescence under the condition of low carrier density, but the decrease in luminescence efficiency becomes remarkable when the carrier density is increased.

Further, in the case where the long-wave side light emission occurs, the dot defect density increases. In suppressing this long-wave side luminescence, it is necessary to improve the luminescence characteristics. In the wavelength of purple to blue violet, the half-value width of the PL luminescence spectrum is broadened by the presence of long-wavelength luminescence, and it is understood that the PL half-value width narrowing system is an indicator of quality improvement by improvement of growth conditions and structure.

Furthermore, the PL lifetime is also an indicator of the quality of the light-emitting layer. room The PL life under temperature is dominated by non-radiative recombination, indicating the ease of elimination of the carrier (electrons and holes) in the crystal due to defects. The PL lifetime also varies greatly depending on the crystal polarity. However, since the influence of polarity can be eliminated on the m-plane GaN substrate, it can be said that the longer the PL lifetime is, the better the quality of the light-emitting layer is. In the present specification, the term "room temperature" means a temperature of about 25 °C.

In addition to the above, the intensity of the excitation light intensity of the PL peak wavelength also becomes an indicator of the light emission quality. As seen from the EL luminescence characteristics, the long-wave side luminescence has a low luminous efficiency at the high injection side, so that as the current value increases, the long-wave side luminescence shifts to the short-wave side peak, and as a result, the excitation wavelength intensity of the peak wavelength becomes larger. . The same phenomenon occurred in the PL luminescence spectrum measurement, and the carrier density at which the wavelength jump was observed was in the range of about 1 × 10 ¹⁶ cm ^-3 to 5 × 10 ²⁰ cm ^-3 . The amount of change in the wavelength of the PL peak when the excitation light intensity is changed by 1000 times in the range of the excitation light intensity is a good index for improving the quality of the light-emitting layer.

The evaluation of the dependence of the PL half-value width, the PL lifetime, and the PL peak wavelength on the excitation light intensity can also be performed in the structure of the light-emitting element, and can also be performed in the MQW structure without the p-type conductive layer. Therefore, the inventors of the present invention mainly conducted the above review based on the MQW structure in addition to the review of the light-emitting characteristics of the light-emitting elements.

In order to improve the optical quality of the quantum well layer, it is reviewed according to the following points. Conventionally, in the c-plane GaN substrate mainly used, there is a case where the crystallinity due to denitrification is deteriorated, and a high V/III ratio condition is usually used. In fact, it is expected from the atomic model that in the case where the N atom is attached to the crystal surface in the c(+) plane, it is bonded to one of the Ga atoms, and is unstable and easily detached. Therefore, it can be considered that the high V/III ratio condition can effectively function.

Conversely, the c(-) plane indicates the bond structure of the opposite atom. That is, the N atom is bonded by the three dangling bonds of the Ga atom from the surface, which is more stable. On the other hand, the group III atom attached to the surface is bonded by one dangling bond, and is considered to be more unstable. When the m-plane GaN substrate was subjected to the same review, the conditions were different depending on the off angle. For example, when the c(-) side has an inclined surface, a step including a c(-) plane exists on the surface, and the N atom of the step end is bonded to the Ga atom by three dangling bonds. Therefore, the stability of the N atom is considered to be good, and conversely, the stability of the group III atom is poor.

In the case of a m-plane GaN substrate having an off-angle of 0° or an m-plane GaN substrate having an off-angle of c(+) side, facets are likely to occur on the surface, and as a result, except for the step end on the c(+) side The step end on the c(-) side also appears on the surface. As a result, the same phenomenon as in the case of having the off angle of the c(-) side can be seen.

From such a viewpoint, the inventors of the present invention thought that it is not necessary to increase the V/III ratio in the m-plane GaN substrate as is conventionally performed on a c-plane GaN substrate, and conversely, the decrease in crystallinity is improved. By lowering the V/III ratio, the migration of the group III atoms is improved, and a good step flow growth can be expected. As a result, it is considered that it is possible to suppress crystal defects such as voids that can become non-radiative recombination centers or light-emitting peaks on the long-wave side.

However, when the step flow grows, the growth surface becomes flat, and as a result, the interface becomes extremely impatient. Therefore, at the interface between the InGaN quantum well layer and the GaN barrier layer, the composition changes rapidly, and the lattice constants are different from each other, so the local cumulative strain is accumulated. As a result, when the InGaN quantum well layer grows, the migration of surface atoms is hindered by local strain.

In order to avoid the influence of local strain, it is effective to provide an interface strain buffer layer between the quantum well layer and the barrier layer. The interfacial strain buffer layer can be realized by a layer having a lattice constant between the quantum well layer and the barrier layer.

According to the above, the step flow growth is achieved by lowering the V/III ratio, Further, by introducing an interface strain buffer layer, it is possible to realize a structure having superior surface flatness and a small local strain. As a result, it is possible to realize a good light-emitting layer in which the PL half-value width is narrowed and the non-light-emitting recombination center is small.

(Configuration of Epitaxial Wafer of the Present Embodiment)

Embodiments of the present invention will be described in detail below based on embodiments with reference to the drawings and tables. The present invention is not limited to the following description, and may be arbitrarily changed and implemented without departing from the spirit and scope of the invention. Further, the present invention and the embodiments schematically show the present invention, and some of them are emphasized, enlarged, reduced, or omitted for the purpose of deepening understanding, and the scale, shape, and the like of each constituent member are not accurately indicated. In addition, various numerical values and quantities used in the embodiment and the examples are exemplified, and various modifications can be made as needed. Further, in the present invention, all aspects can be used in combination.

Fig. 12 is a schematic cross-sectional view showing an epitaxial wafer of the embodiment. The epitaxial wafer 1 has a GaN substrate (m-plane GaN substrate) having a surface having an off angle of 0° or more and 30° or less on the m-plane as a main surface, and is formed on a main surface on one side of the GaN substrate. An n-type conductive layer; a light-emitting layer formed on a main surface on one side of the n-type conductive layer; and a p-type conductive layer formed on a main surface on one side of the light-emitting layer. Further, the term "main surface" does not necessarily mean that it is directly above, as long as it is located on the upper side of the main surface.

Specifically, as shown in FIG. 12, the epitaxial wafer 1 has: an m-plane GaN substrate 2; a first undoped GaN layer 3; an n-type GaN contact layer (n-type conductive layer) 4; an AlGaN layer 5; a second undoped GaN layer 6; a light-emitting layer 7; a p-type AlGaN cladding layer 8; a p-type GaN contact layer (p-type conductive layer) 9; and a p-type InGaN contact layer 10. The m-plane GaN substrate 2 and each of the layers 3 to 10 are laminated in the order described above.

The m-plane GaN substrate 2 may be a GaN substrate with an off-angle of 0°, or An angulated GaN substrate is imparted. The off angle is usually within 30 °, preferably within 25 °, more preferably within 20 °, and even more preferably within 15 °. From the viewpoint of narrowing the PL half-value width, it is preferably within 15°. From the viewpoint of the exclusion of the internal electric field, it is preferably within 10 °, more preferably within 6 °. The angle between the thickness direction of each layer formed on the m-plane GaN substrate 2 and the m-axis of the GaN-based semiconductor constituting each layer is equal to the off angle of the m-plane GaN substrate 2. Further, the m-plane GaN substrate 2 is generally preferably a self-supporting substrate having good crystallinity.

In addition, the inventors of the present invention presume the following, and the reason why the effect of the present invention can be exerted in the range of the yaw angle of the m-plane is from 0 to 30.

As a result of review by the inventors of the present invention, it has been found that the m-plane is less likely to cause Intake by atomic arrangement than the c-plane, causing an initial problem. Therefore, the surface atomic arrangement of various plane orientations will be compared and illustrated by FIG. 40. As shown in Fig. 40, in the case where the c-plane atoms are arranged in a hexagonal shape, it is considered that even if In atoms having a large atomic radius are mixed, the degree of freedom in which the strain is uniformly dispersed in the plane is obtained, and In is easily taken. On the other hand, in the m-plane Ga atom and the N atom arranged linearly in the a-axis direction, the strains of the a-axis and the c-axis are different, and it is considered that the strain cannot be uniformly dispersed in the plane. It is not easy to ingest In under certain conditions. Further, Fig. 40 shows the plane orientation between the c-plane and the m-plane, which is inclined by about 10° (30-3-1) plane from the m-plane toward the c--direction and by about 15° from the m-plane toward c(-). (20-2-1) Surface model of the face. As shown in FIG. 40, in the same plane direction as in the m-plane, the atom is arranged linearly in the a-axis direction. Therefore, as described in the following paragraph 0270, similarly to the m-plane (offset angle of 0°), there is a case where the PL half-value width is enlarged due to the three-dimensionalization of the initial growth of InGaN. In other words, even in the (20-2-1) plane or the (30-3-1) plane, in order to uniformly introduce In, it is preferable that In is a liquid growth mode, that is, reducing NH ₃ and lowering V / The growth pattern of the III ratio.

When the conditions for growing the InGaN quantum well layer are set to a low V/III ratio of 500 or more and 4,000 or less, or a temperature of 790 ° C or more and 830 ° C or less, it is expected to be formed at an angle of 15°. The half value width of the light-emitting element on the surface GaN substrate is narrower. Thereby, regardless of the polarity due to the increase in the off angle, a high light output can be achieved.

In addition, when the yaw angle is 15 or more, in addition to the conditional expression (1) described later, further improvement in the light-emission output can be expected by satisfying the following conditional expression (2).

△l≦L×0.4-160 (2)

L: PL peak wavelength (unit: nm); Δl: PL half value width (unit: nm)

The first undoped GaN layer 3 is produced, for example, by using TMG (trimethylgallium) or NH ₃ (ammonia) as a raw material. The thickness of the first undoped GaN layer 3 is, for example, 1 nm or more and 1000 nm or less, preferably 2 nm or more and 20 nm or less. The growth temperature of the first undoped GaN layer 3 is usually about 900 ° C or more and about 1100 ° C or less. The first undoped GaN layer 3 has a function of stabilizing the surface of the m-plane GaN substrate 2 and improving the quality of each layer on the upper surface.

The n-type GaN contact layer 4 is doped with an n-type impurity such as Si (germanium) or Ge (germanium). The n-type GaN contact layer 4 is produced, for example, using SiH ₄ (decane), TMG, or NH ₃ as a raw material. The thickness of the n-type GaN contact layer 4 is, for example, 1 μm or more and 6 μm or less, preferably 2 μm or more and 4 μm or less, and the growth temperature is the same as that of the first undoped GaN layer 3 . The n-type impurity concentration is, for example, 2 × 10 ¹⁸ cm ^-3 or more and 2 × 10 ¹⁹ cm ^-3 or less, preferably 5 × 10 ¹⁸ cm ^-3 or more and 1 × 10 ¹⁹ cm ^-3 or less.

The Al GaN layer 5 is made of, for example, TMG, TMA (trimethylaluminum), or NH ₃ as a raw material. The thickness of the AlGaN layer 5 is, for example, 5 nm or more and 100 nm or less, preferably 5 nm or more and 20 nm or less.

The AlGaN layer 5 has an effect of reducing crystal defects which are likely to occur during MOCVD growth on an m-plane GaN substrate having an off angle of 2 or more, and has a function of improving the quality of the light-emitting layer formed on the upper portion.

The second undoped GaN layer 6 is produced, for example, using TMG or NH ₃ as a raw material. The thickness of the second undoped GaN layer 6 is, for example, 20 nm or more and 1000 nm or less, preferably 50 nm or more and 200 nm or less.

Further, the first undoped GaN layer 3, the Al GaN layer 5, and the second undoped GaN layer 6 may be omitted as appropriate. That is, the n-type GaN contact layer 4 may be provided directly on the m-plane GaN substrate 2, and the light-emitting layer 7 may be provided directly on the n-type GaN contact layer 4. Further, the Al GaN layer 5 may be undoped or doped.

The light-emitting layer 7 may be a single layer including InGaN or InAlGaN, and may preferably have a multiple quantum well layer (MQW) having a structure in which a quantum well layer and a barrier layer are alternately laminated. The quantum well layer is preferably formed of a GaN-based semiconductor containing In as in InGaN or InAlGaN. When the light-emitting layer 7 is an InGaN quantum well layer/GaN barrier layer, the InGaN quantum well layer is made of, for example, TMI (trimethylindium), TMG, and NH ₃ as a raw material. The GaN barrier layer is produced, for example, using TMG or NH ₃ as a raw material. The thickness of the quantum well layer is, for example, 2 nm or more and 15 nm or less, preferably 3 nm or more and 10 nm or less. The thickness of the barrier layer is, for example, 2 nm or more and 30 nm or less, preferably 4 nm or more and 20 nm or less. Further, the number of repetition periods of the quantum well layer and the barrier layer is usually in the range of 2 cycles to 12 cycles.

In the production of the quantum well layer and the barrier layer of the light-emitting layer 7, as the gallium material, TEG (triethylgallium) or a mixed gas of TMG and TEG may be used instead of TMG.

Further, the barrier layer is a GaN-based semiconductor having a band gap energy larger than that of the quantum well layer. Alternatively, a GaN layer may be used, or an In composition layer having a smaller composition than a quantum well layer.

The p-type Al GaN cladding layer 8 is, for example, Al _y Ga _1-y N having a larger band gap energy with respect to either of the light-emitting layer 7 and the p-type GaN contact layer 9 (preferably 0.04 ≦ y ≦ 0.2) ) formed. The p-type AlGaN cladding layer 8 is doped with a p-type impurity such as Mg (magnesium) or Zn (zinc). The thickness of the p-type AlGaN cladding layer 8 is, for example, 10 nm or more and 200 nm or less, preferably 10 nm or more and 50 nm or less. The p-type impurity concentration is, for example, 1 × 10 ¹⁹ cm ^-3 or more and 5 × 10 ²⁰ cm ^-3 or less.

Further, the p-type AlGaN cladding layer 8 can be omitted. That is, the p-type GaN contact layer 9 may be disposed directly on the light-emitting layer 7.

The p-type GaN contact layer 9 is doped with a p-type impurity such as Mg or Zn. The thickness of the p-type GaN contact layer 9 is, for example, 40 nm or more and 200 nm or less. The p-type impurity concentration is, for example, 1 × 10 ¹⁹ cm ^-3 or more and 5 × 10 ²⁰ cm ^-3 or less, and the impurity concentration may be intentionally changed inside. Al is mixed with the p-type GaN contact layer 9, and a p-type Al _x Ga _1-x N (preferably 0.01 ≦ x ≦ 0.05) contact layer can also be formed.

The p-type InGaN contact layer 10 is formed of, for example, In _x Ga _1-x N (preferably 0.01 ≦ x ≦ 0.05), and is doped with a p-type impurity such as Mg or Zn. The thickness of the p-type InGaN contact layer 10 is, for example, 1 nm or more and 20 nm or less, preferably 10 nm or less, and particularly preferably 5 nm or less. The composition of the p-type InGaN contact layer 10 is preferably determined such that the band gap energy is larger than the band gap energy of the light-emitting layer 7 (the band gap energy of the quantum well layer when the active layer is MQW).

Still, the p-type InGaN contact layer 10 can be omitted. That is, the epitaxial growth can be completed at the time of the p-type GaN contact layer 9.

Further, a layer not described above may be added. Specifically, an n-type layer may be added between the second undoped GaN layer 6 and the light-emitting layer 7. Or in the luminescent layer and p A p-type layer having no doping or a low Mg concentration is added between the AlGaN cladding layers 8. By adding these layers, there is a situation in which reliability can be improved.

As described above, the configuration of the p-type conductive layer, the n-type conductive layer, and the light-emitting layer is indispensable for producing an LED element or a laser element, and in order to improve the quality or quality of the light-emitting layer which is a problem in the present invention, It is preferred not to have a p-type conductive layer. The reason for this is that when the p-type conductive layer is provided, when photoluminescence measurement (hereinafter referred to as PL measurement) is performed, it is necessary to irradiate the excitation light by the p-type conductive layer, and the excitation light is attenuated depending on the structure of the p-type conductive layer. Further, since photoluminescence (hereinafter referred to as PL light) generated by the light-emitting layer is also received by the p-type conductive layer, the PL light is attenuated depending on the structure of the p-type conductive layer.

In the present description, in view of the above situation, the experimental review is mainly based on the structure without the p-type conductive layer. Here, crystal growth is terminated in the case of a multiple quantum well layer (MQW layer). Hereinafter, a structure in which a p-type conductive layer is not formed is referred to as an MQW structure, and a structure formed up to a p-type conductive layer is referred to as an LED structure.

However, in the present specification, the intensity of the PL light which is affected by the attenuation of the p-type conductive layer does not cause a problem, and only the shape of the PL luminescence spectrum becomes a problem, so that the MQW structure and the LED structure can be compared with each other.

In the first embodiment of the present invention, the PL peak wavelength of the light-emitting layer 7 is 410 nm or more and 460 nm or less, and the PL half-value width Δ1 of the light-emitting layer 7 satisfies the following conditional expression (1).

△l≦L×0.4-150 (1)

L: PL peak wavelength (unit: nm); Δl: PL half value width (unit: nm)

Since the shape of the PL luminescence spectrum depends on the intensity of the excitation light, it is necessary to use a weak excitation condition that more sensitively reflects the optical quality. Here, the He-Cd laser (wavelength 325 nm) using a simple method is used to adjust the radiation beam on the substrate to 0.7 mJ/sec (0.7 mW) per second, and the irradiation size is set to about 0.1 mm. And evaluate. The density per carrier area is 8.9 W/cm ² , and the density of the carrier formed in the InGaN quantum well layer in the light-emitting layer is preferably about 5 × 10 ¹⁷ cm ^-3 or less, which is preferable because it is weakly excited.

The evaluation of the PL luminescence spectrum must be evaluated with an excitation light intensity equal to or lower than the above-described excitation light intensity. Further, the PL luminescence spectrum can be obtained by measuring the PL light by a spectroscope and measuring it by a light receiving device. The PL half value width of the light-emitting layer 7 means the full width at half maximum of the PL light-emitting spectrum described above.

For reference, an example of the relationship between the PL peak wavelength and the PL half value width satisfying the conditional expression (1) is shown. For example, when the PL peak wavelength is 420 nm, the PL half value width satisfying the formula (1) is 18 nm or less. Further, when the PL peak wavelength is 430 nm, the PL half value width satisfying the formula (1) is 22 nm or less. Further, when the PL peak wavelength is 440 nm, the PL half value width satisfying the formula (1) is 26 nm or less.

In the second embodiment of the present invention, the PL peak wavelength of the light-emitting layer 7 is 410 nm or more and 460 nm or less, and the PL lifetime obtained by the time-decomposition PL measurement of the light-emitting layer 7 at room temperature is 1.3 nsec or more and 20 nsec or less. Further, the PL lifetime is preferably 1.5 nsec or more and 15 nsec or less, more preferably 1.7 nsec or more and 10 nsec or less.

Here, the time-decomposed PL measurement system was measured at room temperature using a time-dependent single photon coefficient method. The light source uses a mode-locked Ti: sapphire laser and a wavelength-variable pulsed laser formed by crystallization of high-frequency waves. The number of repetition frequencies of the pulse was set to 80 MHz, and the pulse width was set to 2 ps.

In order to directly evaluate the optical quality of a quantum well layer having a single layer or a plurality of layers inherent in the active layer structure, it is effective to perform time-decomposed PL measurement by selective excitation. In order to selectively excite the quantum well layer, in the construction of this embodiment, Excitation light having a larger energy band than the InGaN quantum well layer and having a smaller band gap than the materials constituting the other layers (here, GaN and AlGaN) is selected. Therefore, the wavelength of the variable wavelength pulse laser is set to 385 nm.

Next, the pulse energy was adjusted by the ultraviolet ND filter, and then irradiated to the sample attached to the sample stage. The PL light from the sample is passed through a collecting lens and dispersed by a beam splitter, and then guided to a photomultiplier.

The pulse energy irradiated to the sample is obtained by measuring the power by a power meter and dividing by the number of repetition frequencies. The beam path of the laser is at the sample position. 0.1mm. Thereby, the pulse energy density per unit area was 1.6 μJ/cm ² , and the excited excess carrier density was estimated to be about 1 × 10 ¹⁷ cm ^-3 .

This condition is a sufficiently low excitation condition for evaluating the luminescence quality of the quantum well layer, and when evaluating the luminescence quality, it is necessary to use an excitation condition equal to or lower than this.

Here, the measurement of the PL luminescence spectrum is first performed, and then the peak wavelength of the PL luminescence spectrum is selected by the spectroscope to perform time-decomposition PL measurement. Next, the PL lifetime is obtained from the transient response (attenuation curve) of the PL intensity after the pulse excitation with respect to time. The time from the maximum intensity to the 1/e intensity of the maximum intensity in the attenuation curve of the PL intensity is defined as the PL lifetime. In general, most of the decay curves in the time-decomposed PL measurement do not become a single exponential function, but the PL lifetime is defined as described above. In fact, the attenuation curve obtained in this example shows a curve close to a single exponential function.

Furthermore, in the third embodiment of the present invention, the PL peak wavelength of the light-emitting layer 7 is 410 nm or more and 460 nm or less, and the wavelength variation of the light-emitting layer 7 when the excitation intensity is changed by the excitation density dependency is 0 nm or more and 10 nm or less. In addition, the wavelength fluctuation when the excitation intensity is changed by the excitation density dependency is preferably 0 nm or more and 8 nm or less, more preferably 0 nm or more and 6 nm or less. The wavelength variation here means that the density of the carrier generated in the InGaN quantum well layer is in the range of about 1×10 ¹⁶ cm ⁻³ to 5×10 ²⁰ cm ^{−3 ,} and the excitation light intensity is varied by 1 to 1000 times. The component of the change in the wavelength of the PL peak. At the time of measurement, the excitation light is collected by the objective lens to have a high energy density, and then the energy density (relative value) is changed to 1 or more and 1000 or less by using an ND filter.

Figure 13 is a schematic cross-sectional view of a light-emitting layer 7 of the present invention. The light-emitting layer 7 preferably contains an InGaN layer. Further, as shown in FIG. 13, the light-emitting layer 7 preferably includes a multiple quantum well layer having a structure in which the quantum well layer 7A and the barrier layer 7B are alternately laminated, between the quantum well layer 7A and the barrier layer 7B, including The interface strain buffer layer 7C having a lattice constant between the quantum well layer 7A and the barrier layer 7B and a strain between the quantum well layer 7A and the barrier layer 7B is at least one layer. By providing at least one interface strain buffer layer, the effect of avoiding the influence of local strain is more preferable, and it is more preferable that the interface strain buffer layer is provided between the quantum well layer 7A and the barrier layer 7B. The interfacial strain buffer layer 7C is preferably formed of a GaN-based semiconductor containing In, like InGaN or InAlGaN. The In composition of the interfacial strain buffer layer 7C is a composition between the quantum well layer 7A and the barrier layer 7B, and may be a single-layer layer, or the composition may be changed stepwise. Further, the thickness is, for example, 0.1 nm or more and 3 nm or less, preferably 0.5 nm or more and 2 nm or less.

Further, the interface strain buffer layer 7C may be omitted. That is, the light-emitting layer 7 may be a multiple quantum well layer having a structure in which only the quantum well layer 7A and the barrier layer 7B are alternately laminated.

Further, the dark spot density of the m-plane GaN substrate 2 is preferably 2 × 10 ⁸ cm ^-2 or less. More preferably 2 × 10 ⁷ cm ^-2 or less, still more preferably 2 × 10 ⁶ cm ^-2 or less. Here, the dark spot density of the m-plane GaN substrate 2 refers to the density at which a lattice defect such as a mismatch difference in the crystal is observed in a dark spot after the cathodoluminescence image. In order to achieve such a low dark point density, it can be realized by using a GaN self-supporting substrate instead of a heterogeneous substrate.

Further, the main surface on the other side of the m-plane GaN substrate 2 is preferably roughened. Here, the m-plane GaN substrate 2 is roughened to mean that a surface unevenness shape capable of improving light extraction efficiency is formed, and the substrate can be provided with a surface treatment such as dry etching. The surface roughness of the roughened m-plane GaN substrate 2 is preferably 50% or less of the flat surface having the original plane orientation.

(Configuration of Semiconductor Light Emitting Element of the Present Invention)

Figure 14 is a schematic illustration of a semiconductor light emitting device 20 of the present invention. Fig. 14 (a) is a plan view, and Fig. 14 (b) is a cross-sectional view taken along line X-X of Fig. 14 (a).

The semiconductor light-emitting device 20 is produced by performing etching, electrode formation, element separation, and the like on the epitaxial wafer 1 described above. The semiconductor light-emitting device 20 includes an n-type conductive layer including a GaN-based semiconductor layer having a surface having an off-angle of 0° or more and 30° or less on the m-plane as a main surface, and is formed on one side of the n-type conductive layer. a light-emitting layer on the main surface; and a p-type conductive layer formed on the main surface on one side of the light-emitting layer.

In the light-emitting layer of the semiconductor light-emitting device of the first embodiment of the present invention, the PL emission peak wavelength is 410 nm or more and 460 nm or less, and the PL half-value width of the light-emitting layer is in a range satisfying the following conditional expression (1).

△l≦L×0.4-150 (1)

L: PL peak wavelength (unit: nm); Δl: PL half value width (unit: nm)

Further, the PL light emission peak wavelength of the light-emitting layer 7 of the semiconductor light-emitting device of the second embodiment of the present invention is 410 nm or more and 460 nm or less, and is emitted at room temperature. The PL lifetime of the time-separated PL measurement of the optical layer 7 is preferably 1.3 nsec or more and 20 nsec or less.

Further, in the semiconductor light-emitting device 20 according to the third embodiment of the present invention, the wavelength variation due to current injection can be made smaller. For example, when the luminescence peak wavelength is 420 nm, the wavelength variation due to the current injection at 350 mA is 6 nm or less, and preferably the decomposition energy (about 1 nm) or less of the measurement system.

Specifically, the semiconductor light emitting element 20 has an m-plane GaN substrate 2, a first undoped GaN layer 3, an n-type GaN contact layer (n-type conductive layer) 4, and an AlGaN layer, as shown in FIG. 14(b). 5; second undoped GaN layer 6; light-emitting layer 7; p-type AlGaN cladding layer 8; p-type GaN contact layer (p-type conductive layer) 9; p-type InGaN contact layer 10; n-side metal electrode 11; The side contact electrode 12; and the p-side metal electrode 13. Further, the m-plane GaN substrate 2 can also be removed by peeling or the like.

The n-side metal electrode 11 is formed on the exposed surface of one of the n-type GaN contact layers 4 as shown in FIG. 14(b). Further, the p-side contact electrode 12 is formed on the upper surface of the p-type InGaN contact layer 10 as shown in FIG. 14(b). The p-side contact electrode 12 may also be, for example, ITO, nickel, platinum, titanium, silver, tungsten, chromium, or an alloy containing such metals. Further, the p-side metal electrode 13 is formed as a pad electrode on one portion of the p-side contact electrode 12.

The semiconductor light emitting element 20 of the present invention can exhibit high output by injection of a current of 410 nm or more. The relationship between the wavelength of the luminescence peak at the time of injection of 350 mA and the luminescence output is as follows. For example, when the luminescence peak wavelength is about 420 nm, the luminescence output is 490 mW or more. Further, when the emission peak wavelength is about 430 nm, the light emission output is 370 mW or more. Further, when the emission peak wavelength is about 440 nm, the light emission output is 350 mW or more.

Further, the semiconductor light-emitting device 20 of the present invention has been described with respect to the case where the n-side metal electrode 11 is formed on the surface on which one of the n-type GaN contact layers 4 is exposed. However, the present invention is not limited thereto, and may be, for example, m. The main surface of the other side of the surface GaN substrate 2 forms the n-side metal electrode 11, and is applicable to other various semiconductor light-emitting elements.

(Configuration of Light Emitting Device of the Present Invention)

Figure 15 is a cross-sectional view showing a light-emitting device 30 of the present invention. The light-emitting device 30 includes the semiconductor light-emitting element 20, and at least a part of the light emitted from the semiconductor light-emitting element 20 is absorbed and converted into a wavelength-converting substance of light having a longer wavelength. Specifically, the light-emitting device 30 includes a semiconductor light-emitting device 20, a package 21 that houses the semiconductor light-emitting device 20, a light-transmitting material 22, and a wavelength conversion portion 23.

The semiconductor light-emitting device 20 has the same configuration as the semiconductor light-emitting device 20 of the present invention, and is, for example, a semiconductor light-emitting device that emits blue-violet light to blue light having an emission peak wavelength of 410 nm or more and 460 nm or less.

The package 21 is a known package. For example, a heat-resistant resin such as a polyamide resin, an epoxy resin, or a polyoxymethylene resin may be integrally molded with a lead frame, and various types of packages may be applied. As the light transmissive material 22, for example, polyphthalocyanine resin, glass, or the like can be used. Further, the light transmissive material 22 may be omitted, and the semiconductor light emitting element 20 and the wavelength conversion portion 23 may be hollow.

The wavelength conversion unit 23 includes, for example, a yellow phosphor belonging to a wavelength conversion substance, and the yellow fluorescent system converts one of blue-violet light to blue light emitted from the semiconductor light-emitting element 20 into yellow light. Then, the wavelength conversion unit 23 releases the white light generated by mixing the surface blue light and the yellow light to the outside.

The use of the light-emitting device 30 of the present invention includes illumination, a display, a backlight of a liquid crystal display device, an indicator, and the like, but is not limited thereto.

(Method of Manufacturing Epitaxial Wafer of the Present Invention)

Figure 16 is a flow chart showing a method of manufacturing the epitaxial wafer 1 of the present invention. The method of manufacturing the epitaxial wafer 1 of the present invention has an n-type on a main surface on one side of a GaN substrate having a surface having an off angle of 0° or more and 30° or less on the m-plane as a main surface. The first step of growing the conductive layer; and the second step of growing the light-emitting layer on the main surface of the one side of the n-type conductive layer grown in the first step.

Specifically, in the method of manufacturing the epitaxial wafer 1, first, the first undoped GaN layer 3 is formed by metal organic vapor phase epitaxy (MOCVD) on the main surface of one side of the m-plane GaN substrate 2. The n-type GaN contact layer 4, the AlGaN layer 5, and the second undoped GaN layer 6 are respectively grown in a predetermined condition (step SP1).

Next, in the method of manufacturing the epitaxial wafer 1, on the main surface on one side of the second undoped GaN layer 6, by the organometallic vapor phase growth method, the V/III ratio is made according to the predetermined conditions. The repeating structure of the quantum well layer 7A, the barrier layer 7B, and the interfacial strain buffer layer 7C which are grown by supplying the V-group raw material and the group III raw material in a manner of 500 or more and 4,000 or less is laminated and grown to form the light-emitting layer 7 (step SP2).

Here, in the method of manufacturing the epitaxial wafer 1, it is preferable that the quantum well layer 7A grows a quantum well layer including an InGaN layer. Furthermore, in the growth of the quantum well layer including the InGaN layer, it is preferable to supply the group III so that the molar ratio of the supply amount of the indium raw material in the total supply amount of the group III raw material is 50% or more and 90% or less. raw material. The molar ratio of the supply amount of the indium raw material is preferably 70% or more and 90% or less, and more preferably 80% or more and 90% or less.

Further, as the growth condition of the light-emitting layer 7, it is preferable to grow at a relatively low speed of a growth rate of 1 nm/min or more and 8 nm/min or less. The growth rate here is more preferably 1 nm/min or more and 7 nm/min or less.

Next, in the method of manufacturing the epitaxial wafer 1, the p-type AlGaN cladding layer 8 and the p-type GaN are respectively contacted by the organometallic vapor phase growth method on the main surface on one side of the light-emitting layer 7 under predetermined conditions. The layer 9 and the p-type InGaN contact layer 10 are laminated and grown (step SP3).

[Examples]

The results of experiments conducted by the inventors and the like are described below. However, the invention is not limited by the construction of the methods or samples used in such experiments.

(Example 1)

The epitaxial wafer and the semiconductor light emitting element of the first embodiment have the same configuration as the epitaxial wafer 1 and the semiconductor light emitting element 20 shown in FIGS. 12 to 14 . The epitaxial wafer and the semiconductor light-emitting device of Example 1 were produced according to the following procedures.

(Elevation Growth)

First, an m-plane GaN substrate having a length × width × thickness of 8 mm × 20 mm × 330 μm was prepared in an MOVPE apparatus. The m-plane GaN substrate carrier concentration is in the range of 1.0 × 10 ¹⁷ cm ^-3 to 5.0 × 10 ¹⁷ cm ^-3 , and the off angle in the +c direction is -5°. On the polished surface of the prepared m-plane GaN substrate, the semiconductor laminate was subjected to epitaxial growth using an atmospheric pressure MOVPE method. That is, the first undoped GaN layer, the n-type GaN contact layer, the AlGaN layer, the second undoped GaN layer, the light-emitting layer, and the p-type AlGaN cladding layer are formed on the main surface on one side of the m-plane GaN substrate. The p-type GaN contact layer and the p-type InGaN contact layer are sequentially epitaxially grown.

In the first undoped GaN layer, the substrate temperature was set to 900 ° C, and TMG and NH _{3 were} used as raw materials to grow to a thickness of 10 nm. The growth rate at this time was 15 nm/min. Further, the n-type GaN contact layer has a substrate temperature of 900 ° C, and is grown to have a Si concentration of about 7 × 10 ¹⁸ cm ^-3 and 1500 nm thick using TMG, NH ₃ or SiH _{4 as a} raw material. The growth rate at this time was 17 nm/min. The AlGaN layer system was set to have a substrate temperature of 900 ° C, and was grown to a thickness of 6 nm using TMG, TMA, and NH _{3 as a} raw material. In the second undoped GaN layer, the substrate temperature was 820 ° C, and TMG and NH _{3 were} used as raw materials to grow to a thickness of 100 nm.

The light-emitting layer is formed by using TMG, TMI, and NH _{3 as} raw materials, and forming a four-layer GaN barrier layer and three layers of InGaN quantum well layers alternately so that the lowermost layer and the uppermost layer become barrier layers. Further, an interfacial strain buffer layer is interposed between the GaN barrier layer and the InGaN quantum well layer. A standby time of 5 seconds is set between the growth of the quantum well layer and the interface strain buffer layer. When the growth temperature is in the interface strain buffer layer and the InGaN quantum well layer, the growth temperature is constant, and it is set in the range of 750 ° C to 770 ° C. The growth temperature of the GaN barrier layer is set to be in the range of 790 ° C to 810 ° C, and the growth temperature of the InGaN quantum well layer is 40 ° C higher. When the growth temperature is changed between the interface strain buffer layer and the barrier layer, a standby time of 2 minutes is set. Here, a complex structure having different wavelengths is produced by adjusting the temperature. The thickness of the InGaN quantum well layer was set to 3.6 nm, the thickness of the GaN barrier layer was set to 18 nm, the thickness of the interface strain buffer layer was set to 1 nm, and the In composition was set to be about 4%. No impurities were added to the light-emitting layer.

In the growth of the light-emitting layer, the NH ₃ flow rate was set to a constant 2.8 SLM. The supply molar flow rates of TMI and TMG in the InGaN quantum well layer were 61 μmol/min and 14 μmol/min, respectively, and the ratio of the supply of the V-type raw materials to the supply of the Group III raw materials, that is, the V/III ratio was 1,670. The supply flow rates of TMI and TMG at the strain buffer layer of the InGaN interface were 10 μm/min, 14 μm/min, respectively, and the V/III ratio was 5,160. The supply flow rate of TMG in the GaN barrier layer was 14 μm/min, and the V/III ratio was 8930. The growth rate of the InGaN quantum well layer was 2.2 nm/min.

The p-type AlGaN cladding layer was formed to have a substrate temperature of 900 ° C, and was grown to a thickness of 50 nm using TMG, TMA, Cp ₂ Mg (dicyclopentadienyl magnesium) or NH ₃ as a raw material. The p-type AlGaN cladding layer is doped with Mg, and the Mg concentration is about 2 × 10 ¹⁹ cm ^-3 . The flow rates of TMG and TMA were adjusted in such a manner that the crystal composition became Al _0.1 Ga _0.9 N.

The p-type GaN contact layer was set to have a substrate temperature of 900 ° C, and was grown to a thickness of 40 nm using TMG, TMA, NH ₃ , and Cp ₂ Mg as a raw material. The p-type GaN contact layer is doped with Mg, and the Mg concentration is about 7 × 10 ¹⁹ cm ^-3 . Immediately after the growth of the p-type GaN contact layer, the supply of NH _{3 was} stopped, and the substrate heating was stopped and cooled to 820 ° C.

The p-type InGaN contact layer was formed to have a substrate temperature of 820 ° C, and was grown to a thickness of 1 nm using TMG, TMI, NH ₃ , or Cp ₂ Mg as a raw material. Although the p-type InGaN contact layer is doped with Mg, the Mg concentration is unknown because it is a surface layer.

The above crystal growth was carried out by using N ₂ (nitrogen) as a carrier gas. Thereby, the epitaxial wafer of Example 1 was produced.

When the crystal growth is completed, the heating and cooling of the epitaxial wafer are stopped immediately, and the blowing of N ₂ as a carrier gas is continued until the epitaxial wafer is cooled to 500 °C.

Table 4 shows the structure of each layer of the epitaxial wafer of Example 1, the amount of NH ₃ supplied, the amount of raw material supplied, the V/III ratio, the growth temperature, the thickness, and the dopant.

(formation of mesa and p-side contact electrodes)

An ITO layer having a thickness of 210 nm was formed as a p-side contact electrode on the entire surface of the p-type InGaN contact layer of the epitaxial wafer obtained by the above procedure. Thereafter, heat treatment was performed at 520 ° C for 20 minutes in an atmosphere using a quartz heating furnace. Thereafter, etching is performed by an RIE apparatus until reaching the n-type GaN contact layer, and a mesa is formed.

(formation of n-side metal electrode)

Next, an n-side metal electrode is formed on the surface of the n-type GaN contact layer 4 which is partially exposed by the mesa. The n-side metal electrode is a laminated film containing an Al layer (thickness: 100 nm) and an Au layer (thickness: 300 nm) in this order. The pattern of the n-side metal electrode is performed by a usual lift off method.

(formation of p-side metal electrode)

Next, as a pad electrode, a laminated film containing a Ti-W layer (thickness: 108 nm) and an Au layer (thickness: 300 nm) was sequentially formed on the p-side contact electrode, and then a heat treatment furnace was used, and the temperature was 500 ° C in an N ₂ atmosphere. Heat treatment (alloy treatment) was performed for 1 minute to form a p-side metal electrode.

(roughening of the main surface on the other side of the substrate)

For the roughening of the main surface on the other side of the m-plane GaN substrate, a circular SiO ₂ having a thickness of 1.0 μm and a diameter of 2.0 μm was masked, and a triangular lattice was formed with a center distance between adjacent masks of 6.0 μm. shape. Thereafter, dry etching was performed using chlorine gas to form protrusions having a height of 4.0 μm.

Finally, use a diamond scribe to divide the epitaxial wafer into A semiconductor light-emitting device of Example 1 was produced by using 550 μm × 550 μm square.

(Example 2)

The epitaxial wafer and the semiconductor light-emitting device of Example 2 were produced in the same manner as the semiconductor light-emitting device of Example 1 except that the InGaN interfacial strain buffer layer was not interposed between the GaN barrier layer and the InGaN quantum well layer.

(Comparative Example 1)

The epitaxial wafer and the semiconductor light-emitting device of Comparative Example 1 mainly increase the flow rate of NH ₃ in addition to the growth of the InGaN quantum well layer, increase the V/III ratio of the light-emitting layer, and the GaN barrier layer and the InGaN quantum well. The same procedure as in the semiconductor light-emitting device of Example 1 was carried out except that the InGaN interfacial strain buffer layer was not interposed between the layers.

In the light-emitting layer of Comparative Example 1, four layers of GaN barrier layers and three layers of InGaN quantum well layers are alternately grown by using TMG, TMI, and NH _{3 as} raw materials, and the lowermost layer and the uppermost layer are barrier layers. . The growth temperature is in the range of 790 ° C to 810 ° C in the GaN barrier layer and in the range of 750 ° C to 770 ° C in the InGaN quantum well layer. The growth temperature of the GaN barrier layer is a temperature 40 ° C higher than the growth temperature of the InGaN quantum well layer. The thickness of the InGaN quantum well layer was set to 3.6 nm, and the thickness of the GaN barrier layer was set to 18 nm. No impurities were added to the light-emitting layer.

In the growth of the luminescent layer, the NH ₃ flow rate is set to a certain 14 SLM. The supply flow rate of TMI and TMG in the InGaN quantum well layer was 61 μm/min, 14 μm/min, and the V/III ratio was 8340. The supply flow rate of TMG to the GaN barrier layer was 14 μm/min, and the V/III ratio was 43520.

Epitaxial crystals after epitaxial growth of Examples 1 and 2 The circle is flat when viewed by an optical microscope. Further, even in the evaluation by a fluorescent microscope using a mercury lamp, the inside of the field of view was uniform, and no special structure was observed. From the above results, it was considered that crystal defects did not occur in Example 1 and Example 2, and the In concentration in the plane was relatively uniform.

(Evaluation)

Fig. 17 shows the wavelength dependence of the light-emission output (total radiation beam) when the semiconductor light-emitting elements of Example 1, Example 2, and Comparative Example 1 were energized at 350 mA.

The V/III ratios of the quantum well layers of Examples 1 and 2 were 1670 in common, and the TMI molar supply ratio in the Group III raw materials was 81%. On the other hand, the V/III ratio of the quantum well layer of Comparative Example 1 was 8340. As can be seen from Fig. 17, the light-emitting outputs of the semiconductor light-emitting elements of Example 1 and Example 2 were higher than the light-emitting output of the semiconductor light-emitting device of Comparative Example 1 by 100 mW or more when the EL light-emitting peak wavelengths were the same.

Fig. 18 shows the PL peak wavelength dependence of the PL half-value width obtained from the semiconductor light-emitting elements of Example 1, Example 2, and Comparative Example 1.

As is clear from Fig. 18, the PL half-value widths of the semiconductor light-emitting devices of Example 1 and Example 2 are significantly smaller than the PL half-value width of the semiconductor light-emitting device of Comparative Example 1 when the PL light-emitting peak wavelengths are the same. Further, the PL lifetimes of the semiconductor light-emitting devices of Example 1 and Example 2 were significantly longer than those of the semiconductor light-emitting device of Comparative Example 1 when the PL emission peak wavelengths were the same.

19(a) to 19(c) show the dependence of the EL luminescence spectrum, the current value of the EL luminescence peak wavelength, and the current value of the total radiation beam in the semiconductor light-emitting elements of Example 1 and Comparative Example 1, respectively.

The V/III ratio of the quantum well layer of Example 1 is 1670, in the Group III raw material. The TMI molar supply ratio is 81%. On the other hand, the V/III ratio of the quantum well layer of Comparative Example 1 was 8340. As is clear from Fig. 19(a), the EL luminescence spectrum was unimodal with respect to Example 1, and Comparative Example 1 showed multi-peak luminescence having a peak shoulder on the short-wave side. Further, as is clear from Fig. 19(b), the wavelength of the light emission peak did not change with respect to the current injection in the range of 1 mW to 350 mW in the first embodiment, and in the comparative example 1, the current injection value was increased to be shorter than 10 nm.

In Comparative Example 1 in which the long-wave side light emission with low efficiency occurred, the EL light-emitting peak was strongly affected by the long-wave side light emission in the low current region, but if the injection current value became large, the short-wave side light emission became relatively strong, and EL light emission was obtained. The crest is strongly affected by the short-wave side illumination. It is shown that the wavelength is sharply short-waved due to an increase in the current injection value.

The EL luminescence spectrum of Comparative Example 1 is a state in which the luminescence peak is shifted from the long-wave side to the short-wave side, and swelling is observed on the short-wave side of the spectral shape. However, in Example 1 in which the crystallinity was good, since the long-wave side luminescence was reduced, the EL spectral shape was almost unimodal, and even if the current value was changed, the luminescence mode was maintained to be uniform. As a result, the current density dependence of the EL luminescence peak wavelength becomes extremely small.

(Example 3)

In the third embodiment, the relationship between the PL peak wavelength and the PL half value width measured by changing the growth conditions of the LED structure and the MQW structure is shown in FIG.

Example 3-1 is the semiconductor light-emitting device of Example 1, and Example 3-2 is the semiconductor light-emitting device of Example 2. Embodiment 3-3 is a similar configuration of the semiconductor light-emitting device of Embodiment 1, and forms an LED structure up to the p-type conductive layer; Embodiment 3-4 is a similar structure of the semiconductor light-emitting element of Embodiment 1, and no p-type is formed. The conductive layer forms an MQW structure up to the multiple quantum well layers.

The m-plane GaN substrate used in the LED structure of the embodiment 3-3 and the MQW structure of the embodiment 3-4 is a m-plane GaN substrate of 2 Å, the substrate fabrication method and the small-sized rectangular m-plane GaN of the first embodiment. The substrates are different (details are described later). The V/III ratio of the LED structure of Example 3-3 and the InGaN quantum well layer of the MQW structure of Example 3-4 was 1670 as in the case of Example 1.

Example 3-5 Example-based semiconductor light-emitting element of the structure of an MQW structure is changed when the NH ₃ flow rate of the light emitting layer is grown, NH InGaN quantum well layer when the flow rate of ₃ grown 5.6SLM, V / III ratio of 3340 The growth rate is 2.2 nm/min. Example 3-6 is a similar structure of the semiconductor light-emitting device of Example 2, which is an MQW structure, further reducing the TIM molar supply amount to 74%, and the V/III ratio of the InGaN quantum well layer growing to 2280, the growth rate It is 2.2 nm/min.

The LED half-value width of the LED structure of the embodiment 3-3 and the MQW structure of the embodiment 3-4 to the embodiment 3-6 is the PL half-value width of the semiconductor light-emitting element of the first embodiment and the second embodiment, Although they all increase with the PL peak wavelength, they are narrow overall.

Comparative Example 3-1 is a similar structure of the semiconductor light-emitting device of Comparative Example 1, and has an MQW structure. The NH ₃ flow rate at the time of growth of the InGaN quantum well layer is 14 SLM, and the V/III ratio is 15480. Comparative Example 3-2 is the MQW structure shown in Table 2 above. The InGaN quantum well layer has a NH ₃ flow rate of 14 SLM and a V/III ratio of 8340. The angle of deviation of the m-plane GaN substrate used in Comparative Example 3-2 was 0°, and the growth conditions of the substrate were different from those of the substrate having an off angle of -5°.

Comparative Example 3-3 is a similar structure of the semiconductor light-emitting device of Example 1, and was made into an MQW structure, and the TIM molar supply amount when the InGaN quantum well layer was grown was reduced to 1/4 of that of Example 1, and the V/III ratio was made. Increased to 4240.

The PL half-value width of the MQW structure of Comparative Example 3-1 to Comparative Example 3-3 is the same as the PL half-value width of the semiconductor light-emitting elements of Embodiments 1 and 2 at the same PL peak wavelength. Shows a significantly wider value.

Table 5 shows the structures or growth conditions of the semiconductor light-emitting elements from Example 1 and Example 2 (Table 4) of Example 3-1 to Example 3-6 and Comparative Example 3-1 to Comparative Example 3-3. Change point.

As can be seen from FIG. 20, the longer the PL peak wavelength and the wider the PL half-value width, the more the examples and the comparative examples are, the distribution is significantly different from the comparative example, and the line of the conditional expression (1) is demarcated. Split into two parts.

In Examples 3-1 to 3-6, the PL peak wavelength dependence of the PL half-value width was almost the same.

The method for producing the 2吋m-plane GaN substrate used in Example 3-3 and Example 3-4 is shown below. The 2吋m-plane GaN substrate is manufactured by the following procedure.

(i) a GaN template on a C-plane sapphire having a mask pattern formed on the main surface is used for seeding, and a primary GaN crystal is grown by a hydride vapor phase growth method (HVPE method), and c is cut out from the primary GaN crystal ( -) Surface substrate (primary substrate).

(ii) A primary substrate is used for seed crystals, and secondary GaN crystals are grown by an ammonothermal method, and an m-plane GaN substrate (secondary substrate) is cut out from the secondary GaN crystal.

(iii) A secondary substrate is used for seed crystals, and cubic GaN crystals are grown by an ammonothermal method, and an m-plane GaN substrate (third substrate) is cut out from the cubic GaN crystal.

(iv) A cubic substrate was used for seeding, and a target 2 μm-face GaN substrate (four-time substrate) was produced by the HVPE method.

(Example 4)

In the fourth embodiment, the relationship between the PL peak wavelength and the PL lifetime measured by changing the growth conditions of the LED structure and the MQW structure is shown in FIG.

Embodiment 4-1 is a semiconductor light-emitting device of Embodiment 1, and Embodiment 4-2 is a similar structure of the semiconductor light-emitting device of Embodiment 2, and has an MQW structure. Further, the PL half value width was 20.4 nm, and the PL peak wavelength was 426.9 nm. LED structures and MQW structures of Examples 4-3 to 4-6 and Examples 3-3 to 3-6 Don't be the same. Comparative Example 4-1 and Comparative Example 4-2 were the same as the MQW structures of Comparative Example 3-1 and Comparative Example 3-2, respectively.

Reference Example 4-1 is a similar structure of the semiconductor light-emitting device of Example 2, which is an MQW structure, which increases the TMG flow rate when the InGaN quantum well layer is grown, increases the growth rate to 8.4 nm/min, and adjusts the growth time to make the quantum. The thickness of the well layer is equivalent, the V/III ratio is 2740, and the TMI molar supply ratio is 48%. The PL half value width is 28.1 nm, and the PL peak wavelength is 445.4 nm.

As can be seen from Fig. 21, the lifespans of the examples 4-1 to 4-6 were all sufficiently longer than 1.3 nsec, and the display optical quality was good. On the other hand, in Comparative Example 4-1 and Comparative Example 4-2, the PL life was short, and the display optical quality was poor. Further, by comparison of Examples 4-1 to 4-6 with Reference Example 4-1, it was revealed that the PL lifetime can be sufficiently increased by setting the growth rate to a specific range.

(Example 5)

In the fifth embodiment, the excitation light intensity dependence of the PL peak wavelength measured by changing the growth conditions of the LED structure and the MQW structure is shown in FIG.

Examples 5-1 and 5-2 are the same as the MQW structure of Example 3-6, and the portions in which the PL peak wavelengths in the plane are different are used. Example 5-3 is the same as the MQW structure of Example 3-4. Comparative Example 5-1 was the same as the MQW structure of Comparative Example 3-2.

As is clear from Fig. 22, the intensity of the excitation light intensity of the PL peak wavelength was hardly present with respect to Example 5-1 to Example 5-3, and Comparative Example 5-1 had a large PL peak wavelength as the excitation light intensity became high. change.

(Example 6)

Example 6 is a relationship between the excitation light intensity at room temperature and the PL lifetime when the excitation light intensity of the MQW structure is changed, and is shown in Fig. 23 .

Example 6-1 is the same as the MQW structure of Example 4-4. Comparative Example 6-1 was the same as the MQW structure of Comparative Example 4-2.

The measurement was performed using substantially the same conditions and methods as the time-resolved PL measurement. In order to investigate the PL lifetime behavior under a wide range of weak excitation light intensity, the pulse energy density per unit area was 1.6 nJ using an ND filter. /cm ^{2 was} changed to 1.6 μJ/cm ² .

With respect to the short PL lifetime of about 1 nsec in all the measurement ranges in Comparative Example 6-1, in Example 6-1, the maximum value was 0.16 μJ/cm ^{2 ,} and thus the PL light lifetime was confirmed when the excitation light intensity was small. A tendency to decrease slightly. However, the longer PL lifetime of 2 nsec or more is still shown in Example 6-1. Even in the weak excitation conditions which have a strong influence on the excited excess carrier and the non-light-emitting recombination process, such a long PL lifetime is exhibited, so that the optical quality of Example 6-1 is good.

(Example 7)

Example 7-1 is a low V/III ratio MQW structure similar to that of Example 3-4, and the uppermost barrier layer is obtained by cathodoluminescence (CL) spectral imaging of the MQW structure belonging to the GaN barrier layer, as shown in FIG. And Figure 25.

Fig. 24 is a view showing a half-value width of a CL spectrum obtained at each point in the plane; and Fig. 25 is a view showing a peak wavelength of a CL spectrum obtained at each point in the plane. The measurement was carried out at room temperature using a SEM-CL apparatus, the acceleration voltage was 5 kV, the beam current value was 1 nA, the SEM observation magnification was 20,000 times, and the measurement interval was 50 nm pitch. 80 x 80 points were measured.

Comparative Example 7-1 is a high V/III ratio structure similar to that of Comparative Example 3-1, but the substrate is a 0° declination, and the CL imaging of the structure in which the quantum well layer is a single layer is obtained, as shown in FIG. And Figure 27.

Fig. 26 is a view showing a half-value width of a CL spectrum obtained at each point in the plane, and Fig. 27 is a view showing a peak wavelength of a CL spectrum obtained at each point in the plane. The measurement was carried out using the same conditions and methods as in Example 7-1.

As can be seen from Fig. 24 to Fig. 27, the peak wavelength in the plane is uniform and the half-value width of the CL is narrow and uniform with respect to Example 7-1. In Comparative Example 7-1, the peak wavelength distribution is large, and the half-value width is also uniform. It is wider, and then a part is an area of extremely wide half-value width. Moreover, the distribution of the half-value width is related to the wavelength distribution, but the distribution of the half-value width is large. Because of the above, in Example 7-1, even a small area can obtain an overall uniform and sharp spectrum; in contrast, in Comparative Example 7-1, the wavelength is not uniform, and the half value width is more uneven in the submicron size, Some are extremely wide areas.

Fig. 28 is a CL luminescence spectrum obtained at each of points 1 to 3 illustrated in Fig. 26. As can be seen from Fig. 28, in Comparative Example 7-1, the luminescence spectrum of the Gaussian shape which is almost bilaterally symmetrical is displayed at a point where the half value width is narrow; relatively, the point where the half value width is wide is the peak shoulder on the long wave side of the spectrum. Therefore the half value width is wider. As apparent from the above, the reason why the half value width of Comparative Example 7-1 is wide is that the light peak of low energy (long wave) locally appears.

Fig. 29 is a CL luminescence spectrum obtained at each of points 1 to 3 illustrated in Fig. 24. As is apparent from Fig. 29, in any of Examples 7-1, an emission spectrum of a Gaussian shape narrower than the narrowest spectrum of Comparative Example 7-1 was exhibited, and highly uniform luminescence characteristics were obtained.

(Example 8)

Example 8-1 is a low V/III ratio MQW structure similar to that of Example 3-4, and is used to directly lower the temperature after growing the InGaN quantum well layer of the first layer and then growing the GaN barrier layer. The surface image is shown in Fig. 30. The measurement was carried out on an 2 μm square using an atomic force microscope (AFM) apparatus. The left side of the figure is the surface shape image, and the right side is the phase image. The specifications are all 2μm on one side.

Comparative Example 8-1 is a high V/III ratio MQW structure similar to that of Comparative Example 3-1. Similarly to Example 8-1, FIG. 31 shows that after the InGaN quantum well layer is grown, the GaN barrier is not subsequently formed. The surface is grown to directly reduce the surface image at temperature. The measurement was carried out on a 2 μm square using an AFM apparatus. The left side of the figure is the surface shape image, and the right side is the phase image. The specifications are all 2μm on one side.

As can be seen from Fig. 30 and Fig. 31, in the embodiment 8-1, a large number of light-emitting convex portions on the surface were layered on the base layer, whereas in Comparative Example 8-1, the surface was flat on the atomic level.

The convex portion of Example 8-1 can be considered to be a droplet solidified person of a Group III metal mainly composed of In. Since V/III is relatively low, the intake of In is lowered, and the surface is cured as a metal, and the residue is cured together with a decrease in the substrate temperature. However, it is not clear whether the droplet is formed or the entire surface of the coating is grown. It is known that these droplets are re-evaporated and destroyed by raising the substrate temperature and setting the growth standby time when the barrier layer is grown. Therefore, these droplets have little effect on the actual device characteristics.

(Example 9)

In Example 9, the temperature dependence of the PL lifetime of the MQW structure is plotted in FIG.

Example 9-1 is a low V/III ratio MQW structure similar to that of Example 3-4. The substrate was placed in a cryostat and the sample temperature dependence of the PL lifetime was measured. The temperature adjustment uses a freezer and heater from 2.3K to 300K. The PL life measurement conditions are the same as those described above. Further, the PL half value width at 300 K was 20.4 nm, and the PL peak wavelength was 426.9 nm.

In Comparative Example 9-1, a high V/III ratio MQW structure similar to Comparative Example 3-1 was subjected to the same measurement as in Example 9-1. Further, the PL half value width at 300 K was 31.0 nm, and the PL peak wavelength was 449.9 nm.

As can be seen from Fig. 32, in Example 9-1, the PL lifetime was as short as 0.77 nsec at extremely low temperature (2.3 K), but the PL lifetime increased together with the rise in the sample temperature, and the PL lifetime became 1.87 at 300 K = 27 ° C (room temperature). Nsec.

On the other hand, the PL lifetime at the extremely low temperature in Comparative Example 9-1 was also shorter than that in Example 9-1 and was 0.62 nsec, but the PL lifetime hardly changed with respect to the temperature rise, even though the PL lifetime was still at room temperature. Very short 0.79nsec.

From the above investigation, it can be considered that the influence caused by the non-light-emitting recombination process at a very low temperature is small, and the PL life is mainly determined by the luminescence recombination life. Therefore, although the PL lifetime is extremely short, the probability of existence of the excess carrier at the bottom of the defect in the k-space due to the influence of photon scattering is reduced, so that the luminescence lifetime is prolonged.

On the other hand, the non-light-emitting recombination process system which has a small influence at an extremely low temperature, together with the temperature rise, has a large influence degree. As a result, along with the increase in sample temperature, the dominant factor of PL life is gradually transferred to the non-lighting recombination process.

In Example 9-1, it can be considered that since the influence of the non-light-emitting recombination process is small, together with the temperature rise, it is mainly affected by the luminescence recombination process and the PL lifetime On the other hand, in Comparative Example 9-1, it can be considered that the influence of the temperature rise rather than the luminescence recombination process is increased, and the PL lifetime is kept short and becomes constant.

(Embodiment 10)

In the tenth embodiment, the relationship between the PL peak wavelength and the PL half value width measured by changing the off angle of the m-plane GaN substrate and/or the growth condition of the LED structure is shown in FIG.

Examples 10-1 to 10-3 have the same structure as the LED structure of Example 2, and the m-plane GaN substrate used in the LED structures of Examples 10-1 and 10-2 has an off angle of 10°, and Example 10 The off-angle of the m-plane GaN substrate used for the LED structure of -3 was 15°. The growth conditions of the LED structure of Example 10-1 were the same as in Example 2.

Table 6 shows the structures of the respective layers of the epitaxial wafers of Examples 10-2 and 10-3, the supply amount of NH _{3 ,} the supply amount of the raw material, the V/III ratio, the substrate temperature, the thickness, and the dopant. The V/III ratio at the time of growth of the InGaN quantum well layer of the LED structures of Examples 10-2 and 10-3 was 1130.

In Comparative Example 10-1, the same LED structure as in Comparative Example 1 was used. The m-plane GaN substrate used in the LED structure of Comparative Example 10-1 had an off angle of 10°.

The LED structures and growth conditions of Examples 10-1 to 10-3 and Comparative Example 10-1 are shown in Table 7. Further, none of the LED structures of Examples 10-1 to 10-3 and Comparative Example 10-1 was inserted into the interface strain buffer layer. Further, the growth temperature in Table 7 indicates the temperature at which the quantum well layer was grown.

As apparent from Fig. 33, the examples show a tendency that the PL peak wavelength is longer and the PL half value width is wider. On the other hand, the comparative example compares the PL half-value width when the PL peak wavelength is 425 nm to 430 nm and the PL half-value width when the PL peak wavelength is about 435 nm to 445 nm, which clearly shows that the latter PL half-value width is wide. . Further, in the comparative example, the half-value width of the PL peak wavelength of about 435 nm to 445 nm is almost constant. It can be seen that the distributions in the examples and the comparative examples are significantly different, and are divided into two parts by dividing the line of the conditional expression (1) as a boundary.

In Example 10-1 and Example 10-2 in which the off-angle was 10°, the PL peak wavelength dependence of the PL half-value width was almost the same. In Example 10-3, in which the eccentric angle was 15°, the PL peak wavelength was shifted from the long wavelength side to the low wave side, and the PL half value width was sharply narrowed.

(Example 11)

The low V/III ratio MQW structure similar to that of the embodiment 3-4 in the embodiment 11-1 is used after forming the layers of 2 to 6 in FIG. 12 and the GaN barrier layer of 7B on the m-plane GaN substrate. After the 7A InGaN quantum well layer was produced, it immediately stopped growing at 0.9 nm and was taken out from the growth furnace. The surface image is shown in Fig. 34. The measurement was carried out on a 2 μm square using an atomic force microscope (AFM) apparatus. In the figure, the left side is the surface shape image, and the right side is the phase image. The specifications are all 2μm on one side. The growth conditions of Example 1 were used for the production conditions.

Similarly, the surface image of the InGaN quantum well layer grown by 4 nm is shown in FIG.

Further, a surface image of a thick film (about 50 nm) in which an InGaN quantum well layer is laminated in the same manner is shown in Fig. 36.

Comparative Example 11-1 is a high V/III ratio MQW similar to Comparative Example 3-4. The structure is used to form the layers of 2 to 6 in FIG. 12 and the GaN barrier layer of 7B on the m-plane GaN substrate, and then start growing the InGaN quantum well layer of 7A, and immediately stop growing at 0.9 nm. Remover. The surface image is shown in Fig. 37. The measurement was carried out on a 2 μm square using an atomic force microscope (AFM) apparatus. In the figure, the left side is the surface shape image, and the right side is the phase image. The specifications are all 2μm on one side. The production conditions were the growth conditions of Comparative Example 1.

Similarly, the surface image of the InGaN quantum well layer grown by 4 nm is shown in FIG. 38.

Further, a surface image of a thick film (about 50 nm) in which an InGaN quantum well layer is laminated in the same manner is shown in Fig. 39.

In Example 11-1, on the gentle base layer of Fig. 34, a plurality of circular structures which appeared to be In droplet marks were observed. From this, it is presumed that Example 11-1 achieved flat crystal growth, but In the growth, In was a liquid-coated surface. On the other hand, as is clear from Fig. 37, in the case of Comparative Example 1, the whole was rough, and it was found that InGaN was grown in three dimensions.

Similarly, as can be seen from a comparison between FIG. 35 and FIG. 38, when the InGaN quantum well layer was grown to 4 nm and subjected to AFM observation, the condition of Comparative Example 1 was able to obtain a flatter surface than the condition of Example 1.

Further, as shown in FIG. 39, when the InGaN layer was formed into a thick film (about 50 nm) and subjected to AFM observation, the columnar crystal was grown under the growth conditions of Comparative Example 1. Moreover, it is dark brown even under visual observation. On the other hand, under the growth conditions of Example 1, it was transparent under visual conditions, and the AFM results also showed stratum aggregation and In droplet marks, and the crystallinity was good.

(examine)

With respect to Comparative Example 1, the reason for the increase in the output of Example 1 and Example 2 was caused by improving the quality of the InGaN quantum well layer by changing the growth condition of the InGaN quantum well layer to a low V/III ratio condition. By suppressing the light emission on the long-wave side by the low V/III ratio growth condition, the multi-peak peaks appearing in the luminescence spectrum are mono-peaked, and the luminous efficiency is rapidly increased.

In particular, the wavelength dependence of the conventional light-emitting output is such that when the wavelength exceeds the violet wavelength (405 nm), the light-emitting output is rapidly lowered. However, as a result of the 420 nm of the first embodiment, the present invention is characterized in that no output reduction occurs at around 405 nm to 420 nm. .

A sufficiently high light-emitting output can be obtained from the second embodiment without the interface buffer layer. However, if the wavelength dependency of the light-emitting output of the first embodiment is inserted and compared with the wavelength according to the second embodiment, the first embodiment can be estimated. Get a higher output. The reason for this is that it has an interface strain buffer layer and is suitable for a structure with higher output.

For example, in the latitude and longitude term, the characteristics of the multi-wave peak are described. The light emission on the short-wave side of the original illuminating system is the derivative of the long-wave side. However, when the excitation density is small, the light-emitting level on the long-wave side where the band gap is small flows into the carrier, and the light emission on the long-wave side becomes dominant.

The long-wave side light-emitting system corresponds to the off-angle of the substrate, and is determined by the wavelength difference from the original light-emitting wavelength. Further, since the light is emitted in accordance with the mode of both, the half value width of the PL and EL luminescence spectra increases.

Further, since the long-wave side light emission is relatively low in light emission efficiency with respect to the light emission from the original InGaN quantum well due to an increase in the carrier density (current), the influence of the original light-emitting wavelength is increased by current injection, and the light-emitting wavelength is Short-wave.

Regarding the emission wavelength of Comparative Example 1, the pattern of the peak of the short-wave side appeared to be the light emission from the original InGaN quantum well, and the peak wavelength of the spectrum of Example 1 was almost the same wavelength. Therefore, in the case of high current injection, Comparative Example 1 and Example 1 have the same peak wavelength.

In the case where such an emission spectrum of the specific long-wave side occurs, the PL lifetime which corresponds to an increase in the dot defect density and an increase in the non-luminescence recombination center is reduced, and the luminous efficiency is lowered.

In summary, the occurrence of long-wave side luminescence increases with the half-value width of the luminescence spectrum, decreases the luminescence efficiency, increases the dot defect density, increases the non-luminescence recombination center, decreases the PL lifetime, and changes the peak wavelength of the carrier density. The changes are all related.

These various physical systems express an essence only from other angles. Therefore, it can be said that regardless of the index used, the light quality is reflected.

In the results of Example 3, the PL half-value widths of Comparative Examples 3-1 and 3-2 were wide. Among them, the half value width of Comparative Example 3-1 was wider. In this case, when the long-wave side light emission occurs as described above, the half-value width is widened, but the difference in energy between the peak wavelengths of the original light-emitting spectrum is different depending on the off-angle of the substrate. In the 0° offset substrate of Comparative Example 3-1, the long-wave side emission system largely deviated from the original luminescence of the InGaN quantum well, and the long-wave side luminescence of the -5° deviation from the substrate of Comparative Example 3-2 was closer to the original luminescence.

However, in any case, when the half value width is wider than the straight line in the drawing, it is said that a plurality of peaks occur, and the state in which the luminous efficiency is lowered regardless of the difference in size does not change. In the case of PL evaluation, for example, the wavelength decomposition ability is set to be low, and it is possible to separate the multi-wave peaks by the measurement conditions, but if the half-value width is greater than or equal to the straight line, multi-peak peaks are generated. reduce.

From Example 3-1 and Example 3-2, it is understood that the PL half-value width can be narrowed by reducing the V/III ratio at the time of growth of the InGaN quantum well layer. In Example 3-3 and Example 3-4, a two-layer substrate having a different manufacturing method was used as the substrate, but the wavelength dependence of the half-value width did not change. In other words, if it is an m-plane, it does not depend on the substrate. law.

Further, with respect to Example 3-5, NH _{3 was} slightly increased to adopt a slightly higher V/III ratio of 3340, but although the PL half-value width was extremely small, a sufficiently narrow spectrum was obtained. However, when the V/III ratio is further increased, the long-wave side light emission is rapidly generated, and it is understood that the half-value width of the PL spectrum is increased.

Conversely, experiments were also conducted to reduce the lower limit of the V/III ratio by reducing NH ₃ . At this time, the incorporation of In into the crystal is deteriorated, and there is a problem that it is difficult to grow the wave and the In droplet is likely to occur on the surface of the substrate. However, even if In droplets are generated, they can be easily removed by a HCl solution, and the overall crystallinity is good.

Further, although the In mole supply ratio was lowered in Example 3-6, no significant difference was observed in this range (74-81%), and the half value width was kept narrow.

With respect to the results of Example 4, all of Examples 4-1 to 4-6 having a relatively low V/III gave a longer PL lifetime. The PL lifetime at room temperature is dominated by non-luminous recombination, meaning that the longer the PL lifetime, the smaller the effect of defects. With respect to Comparative Example 4-1 and Comparative Example 4-2 having the same structures as those of Comparative Example 1 and Comparative Example 2, it was found that multi-peaks occurred, and since the quality was lowered in this case, the PL life was also shortened. .

Reference Example 4-1 sets the V/III ratio to a lower value of 2740, and achieves a narrower PL half-value width by the MQW structure of the PL peak wavelength of 460 nm or less. On the other hand, the growth rate condition is increased faster than in Examples 4-1 to 4-6. Although it is considered that the most dominant in-mole-weighted InGaN quality is the V/III ratio, it can be said that the optical quality can be further improved by using the growth rate or the In-mole supply ratio as an appropriate value in a certain range.

The mechanism shown in Example 5 is the same as the current value dependence of the peak wavelength of the EL luminescence spectrum described in Example 1. This becomes the m-side quality of the problem The decrease is accompanied by the occurrence of long-wave side luminescence, and in the case where this luminescence occurs, the long-wave side luminescence becomes dominant at a low carrier concentration. When the carrier density is high, since the main peak wavelength shifts to the light emission on the short-wave side of the original luminescence center, the carrier density dependence of the luminescence peak wavelength becomes large.

In Example 5-1 and Example 5-2, which only saw good quality and original luminescence from InGaN quantum wells, even if the PL excitation intensity was changed, the luminescence wavelength was single and the wavelength change was small; however, on the long wave side In Comparative Example 5-1 in which light was emitted, the light emission on the long-wave side of the low-excitation side was mainly changed, and the short-wave side light emission was shifted by increasing the excitation intensity, so that the wavelength was changed.

In Example 7-1, which only saw good quality and original luminescence from InGaN quantum wells, the luminescence spectrum from the original InGaN was obtained in the in-plane full region, and the wavelength and half-value width were uniform; however, long-wavelength luminescence occurred. In Comparative Example 7-1, a long-wave side peak occurred in part. Therefore, a region having a wide half-value width can be partially observed. The origin of these localized long-wave luminescence has not yet been elucidated, but it is clear that this condition is closely related to the condition of reduced optical quality.

In Comparative Example 8-1 and Comparative Example 8-1, Comparative Example 8-1 in which the optical quality was lowered was found to have a flat surface morphology. That is, the occurrence of the long-wave peak is independent of the surface itself, and is an abnormality at the atomic level, and it can be considered that it cannot be detected by the AFM.

From Example 9-1 and Comparative Example 9-1, the temperature characteristics of the PL lifetime reflecting the optical quality were obtained. In general, it is considered that the in-plane diffusion of the carrier is likely to occur together with the rise in the temperature of the sample, and the influence of the non-light-emitting recombination center becomes large. In Comparative Example 9-1, it was found that the influence of the non-light-emitting recombination center was strong; on the other hand, the ideal physical phenomenon was observed in Example 9-1, that is, the photon scattering was affected together with the temperature rise and the PL lifetime was long. The situation.

As a result of the embodiment 10, by using a substrate having a declination within a specific range, the V/III ratio at the time of growth of the InGaN quantum well layer is lowered, and the PL half-value width can be narrowed, and the PL peak wavelength and the PL half value are obtained. The relationship of the width satisfies the conditional expression (1), and the luminous efficiency can be expected to be improved.

As a result of the example 11, it is shown that the conventional example is three-dimensionally formed in the initial stage of growth of InGaN, and although it is temporarily flat, when it grows into a thick film, the result is three-dimensionally intense again. In the initial three-dimensional growth, it is difficult to ingest In to the surface of the GaN on the m-plane, and it is considered that this phenomenon occurs due to uneven intake of In at the initial stage of growth.

When such three-dimensional growth at the initial stage of growth occurs, the crystallinity (mainly strain distribution) fluctuates. Once the crystal layer is changed in the underlayer (the initial growth layer), In is easily taken in, and uniform and flat InGaN can be formed in the range of the thickness of the quantum well.

However, it is considered that three-dimensionality occurs again due to the influence of the strain fluctuation caused by the three-dimensionalization of the underlayer at the time of thick film formation. From the above, the peak on the long-wave side seen in PL is highly likely to reflect the strain change at the initial stage of growth. That is, since it is difficult for In to be ingested onto the surface of the m-plane GaN, it is important that the GaN-InGaN interface does not impair the crystallinity and uniformly introduces In.

It is understood from the droplet marks that, under the conditions of Example 1, in the growth of In, the crystal surface is coated in a liquid state, and it is considered that In is ingested into the crystal by liquid-solid phase diffusion. The reason why In is in a liquid state is to lower the NH ₃ flow rate, reduce the V/III ratio, and supply excess TMI. The MOCVD growth is basically a vapor phase growth. Although it is not known to use such a condition, it is preferable to form an In liquid phase on the surface as in Example 1.

Claims (16)

An epitaxial wafer characterized by comprising: a GaN substrate having a surface having an off angle of 0° or more and 30° or less with respect to an m-plane as a main surface; and an n-type conductive layer formed on the same a main surface on one side of the GaN substrate; and a light-emitting layer formed on a main surface on one side of the n-type conductive layer; wherein the PL wavelength of the light-emitting layer is 410 nm or more and 460 nm or less, and the light-emitting layer is The PL half-value width satisfies the conditional expression (1); Δl ≦ L × 0.4 - 150 (1) L: PL peak wavelength (unit: nm); Δl: PL half-value width (unit: nm). The epitaxial wafer according to claim 1, wherein the light-emitting layer has a PL lifetime of the light-emitting layer at room temperature of 25 ° C of 1.3 nsec or more and 20 nsec or less. The epitaxial wafer of the first aspect of the invention, wherein the fluctuation of the PL peak wavelength when the excitation light intensity of the light-emitting layer is changed by 1000 times is 0 nm or more and 10 nm or less. The epitaxial wafer of claim 1, wherein the light-emitting layer comprises an InGaN layer. The epitaxial wafer of claim 1, wherein the light-emitting layer is formed by a multiple quantum well layer having a structure in which a quantum well layer and a barrier layer are alternately laminated; in the quantum well layer and the barrier layer And an interfacial strain buffer layer having at least one layer for buffering strain between the quantum well layer and the barrier layer; the interfacial strain buffer layer having a lattice constant between the quantum well layer and the barrier layer. The epitaxial wafer of claim 1, wherein the GaN substrate has a dark spot density of 2 × 10 ⁸ cm ^-2 or less. The epitaxial wafer of claim 1, wherein the main surface of the other side of the GaN substrate is roughened. A semiconductor light emitting device comprising: an n-type conductive layer formed of a GaN-based semiconductor layer formed on a main surface of one side of a GaN substrate, wherein the GaN substrate is a surface having an off angle of 0° or more and 30° or less with respect to the m-plane as a main surface; a light-emitting layer formed on a main surface on one side of the n-type conductive layer; and a p-type conductive layer formed On the main surface of one side of the light-emitting layer; the light-emitting wavelength of the light-emitting layer is 410 nm or more and 460 nm or less; and the PL half-value width of the light-emitting layer satisfies the conditional expression (1); Δl≦L×0.4- 150 (1) L: PL peak wavelength (unit: nm); Δl: PL half-value width (unit: nm). A light-emitting device comprising a semiconductor light-emitting device and a wavelength conversion material, the semiconductor light-emitting device having an n-type conductive layer formed of a GaN-based semiconductor layer formed on a GaN substrate On the main surface of one side, the GaN substrate has a surface having an off angle of 0° or more and 30° or less with respect to the m-plane as a main surface; and a light-emitting layer formed on one side of the n-type conductive layer And a p-type conductive layer formed on a main surface of one side of the light-emitting layer; the PL peak wavelength of the light-emitting layer is 410 nm or more and 460 nm or less, and a PL half-value width of the light-emitting layer satisfies Conditional expression (1); wherein the wavelength converting substance absorbs at least a part of the light emitted by the semiconductor light emitting element and converts it into light of a longer wavelength; Δl≦L×0.4-150 (1) L: PL peak wavelength (unit: nm); Δl: PL half-value width (unit: nm). A method for producing an epitaxial wafer, comprising: a first step of growing an n-type conductive layer, wherein the n-type conductive layer is formed of a GaN-based semiconductor layer, and the GaN-based semiconductor layer is formed On the main surface on one side of the GaN substrate, the GaN substrate has a surface having an off angle of 0° or more and 30° or less with respect to the m-plane as a main surface; and a second step of growing the light-emitting layer, The light-emitting layer is grown on the main surface on one side of the n-type conductive layer grown in the first step; and in the second step, at least the following step is included: the molar supply amount of the V-type raw material The group V raw material and the group III raw material are supplied so that the ratio of the molar supply amount of the group III raw material, that is, the V/III ratio is 500 or more and 4,000 or less. The method for producing an epitaxial wafer according to claim 10, wherein in the second step, the multiple quantum well layer is grown as the light-emitting layer, and the multiple quantum well layer has a quantum well layer In the structure in which the barrier layers are alternately laminated, when the quantum well layer is grown, the V-type raw material and the group III raw material are supplied so that the V/III ratio is 500 or more and 4,000 or less. The method for producing an epitaxial wafer according to claim 10, wherein in the second step, the quantum well layer formed of the InGaN layer is grown as the quantum well layer. The method for producing an epitaxial wafer according to claim 10, wherein in the second step, when the quantum well layer formed of the InGaN layer is grown, the total supply amount of the group III raw material is The group III raw material is supplied so that the ratio of the supply amount of the indium raw material in the medium is 50% or more and 90% or less. The method for manufacturing an epitaxial wafer according to claim 10, wherein, in the above In the second step, the quantum well layer is grown at a growth rate of 1 nm/min or more and 8 nm/min. The method for producing an epitaxial wafer according to claim 10, further comprising a third step of heat-treating the light-emitting layer in the atmosphere. The method for producing an epitaxial wafer according to claim 10, wherein in the first and second steps, the n-type conductive layer and the light-emitting layer are grown by MOCVD.