JP7422496B2 - Structure, optical device, method for manufacturing optical device, method for manufacturing structure - Google Patents

Description

The present invention relates to a structure, an optical device, a method for manufacturing an optical device, and a method for manufacturing a structure.

Optical devices such as lasers are required to save power. In group III nitride semiconductors, forming devices on semipolar planes is expected to reduce the internal electric field and improve internal quantum efficiency.

Patent Document 1 describes that a quantum well structure is provided on a principal surface of a gallium nitride-based semiconductor region, which is a semipolar surface. Here, it is described that the thickness of the well layer is 4 nm or more.

Patent Document 2 describes that in a quantum well structure formed on a (20-2-1) plane, which is a semipolar plane of a nitride semiconductor, a corrugated portion is provided in a well layer. It is also stated that such a well layer can emit polarized luminescence.

Patent Document 3 describes that a multiple quantum well layer or the like is laminated on a u-GaN layer whose main surface is a {11-22} plane.

Patent Document 4 describes that a nitride semiconductor layer is epitaxially grown on a substrate having a main surface. Here, the substrate may be a nitride semiconductor substrate in which the normal to the main surface is inclined from the [11-22] axis of the nitride semiconductor in the +c-axis direction at an angle in the range of 5 degrees or more and 17 degrees or less. It is being

Non-Patent Document 1 describes the polarization ratio of light emitted from LDs and LEDs formed on the {20-21} plane, which is a semipolar plane, and the polarization ratio of light emitted from a single quantum well formed on the {11-22} plane. The polarization ratio of light emitted from the structure, etc. are described.

JP2012-109624A Japanese Patent Application Publication No. 2013-258275 International Publication No. 2013/128894 Japanese Patent Application Publication No. 2016-12717

Takashi Kyono and 7 others, “Optical Polarization Characteristics of InGaN Quantum Wells for Green Laser Diodes on Semi-Polar {2021} GaN Substrates”, Applied Physics Express, Japan Society of Applied Physics, January 8, 2010, No. 3 Volume, No. 1, p. 011003.1-011003.3

However, there is still room for consideration in obtaining a device that can be driven with high efficiency while suppressing the manufacturing cost of the device.

The present invention provides a technique for obtaining a device that can be driven with high efficiency while suppressing the manufacturing cost of the device.

According to the invention,
a group III nitride semiconductor substrate having a semipolar plane as a first principal surface;
A structure comprising a multilayer structure made of a group III nitride semiconductor stacked on the first main surface or the second main surface opposite to the first main surface of the substrate,
The multilayer structure includes a quantum well structure,
The polarization ratio Rp of the light emitted by photoluminescence is set as the c projection axis, which is the axis obtained by projecting the c axis onto the first principal surface, and the polarization ratio Rp of the light emitted by photoluminescence is Rp = (Intensity of the m axis polarized light component - Intensity of the c projection axis polarized light component)/(m It is expressed as: intensity of axial polarized light component + c intensity of projected axial polarized light component),
In a graph in which the horizontal axis is the peak wavelength λp [nm] of the maximum peak in the range of 360 nm or more and 560 nm or less of the photoluminescence spectrum and the vertical axis is the polarization ratio Rp, the photoluminescence of the structure with an excitation wavelength of 325 nm. The resulting plot is located inside the first parallelogram,
The first parallelogram is composed of straight line λp = 360, straight line λp = 560, straight line Rp = -0.005λp + 2.2, and straight line Rp = -0.005λp + 1.4,
A structure is provided in which the polarization ratio Rp obtained by photoluminescence of the structure with an excitation wavelength of 325 nm is less than 0.

According to the invention,
The above structure and
An optical device is provided comprising a first electrode and a second electrode electrically connected to the multilayer structure.

According to the invention,
A method of manufacturing an optical device is provided, which comprises forming, in the above structure, a first electrode and a second electrode electrically connected to the multilayer structure.

According to the invention,
A method for manufacturing a structure, the method comprising:
A group III nitride semiconductor is formed on the first main surface or the second main surface opposite to the first main surface of a group III nitride semiconductor substrate whose first main surface is a semipolar plane. comprising a forming step of growing to form a multilayer structure;
The multilayer structure includes a quantum well structure,
The polarization ratio Rp of the light emitted by photoluminescence is set as the c projection axis, which is the axis obtained by projecting the c axis onto the first principal surface, and the polarization ratio Rp of the light emitted by photoluminescence is Rp = (Intensity of the m axis polarized light component - Intensity of the c projection axis polarized light component)/(m It is expressed as: intensity of axial polarized light component + c intensity of projected axial polarized light component),
In a graph in which the horizontal axis is the peak wavelength λp [nm] of the maximum peak in the range of 360 nm or more and 560 nm or less of the photoluminescence spectrum and the vertical axis is the polarization ratio Rp, the photoluminescence of the structure with an excitation wavelength of 325 nm. The resulting plot is located inside the first parallelogram,
The first parallelogram is composed of straight line λp = 360, straight line λp = 560, straight line Rp = -0.005λp + 2.2, and straight line Rp = -0.005λp + 1.4,
A method for manufacturing a structure in which the polarization ratio Rp obtained by photoluminescence of the structure with an excitation wavelength of 325 nm is less than 0 is provided.

According to the present invention, it is possible to provide a technique for obtaining a device that can be driven with high efficiency while suppressing the manufacturing cost of the device.

FIG. 3 is a diagram illustrating the configuration of a structure according to the first embodiment. FIG. 3 is a diagram for explaining conditions related to polarization. FIG. 2 is a diagram illustrating the configuration of an apparatus that measures the intensity of the c-projection axis polarization component and the intensity of the m-axis polarization component of light emitted by photoluminescence. FIG. 2 is a diagram illustrating a structure having a multiple quantum well structure as a quantum well structure. FIG. 7 is a diagram illustrating the configuration of a structure according to a second embodiment. FIG. 3 is a diagram illustrating the configuration of an optical device according to a second embodiment. 3 is a diagram showing the configuration of a structure according to Example 1. FIG. FIG. 3 is a diagram showing the surface temperature in the formation process according to Example 1. FIG. 3 is a diagram showing the configuration of structures according to Examples 2 to 5; FIG. 6 is a diagram showing the surface temperature in the formation process according to Examples 2 to 5. FIG. 3 is a diagram showing the results of photoluminescence measurement performed on the structure of Example 1. FIG. 7 is a diagram showing the results of photoluminescence measurement performed on the structure of Example 2. FIG. 7 is a diagram showing the results of photoluminescence measurement performed on the structure of Example 3. FIG. 7 is a diagram showing the results of photoluminescence measurement performed on the structure of Example 4. FIG. 7 is a diagram showing the results of photoluminescence measurement performed on the structure of Example 5. 3 is a graph plotting the photoluminescence results of the structures of Examples 1 to 5. FIG.

Embodiments of the present invention will be described below with reference to the drawings. Note that in all the drawings, similar components are denoted by the same reference numerals, and descriptions thereof will be omitted as appropriate.

FIG. 1 is a diagram illustrating the configuration of a structure 10 according to the first embodiment. Structure 10 includes a substrate 100 and a multilayer structure 200. The substrate 100 is a group III nitride semiconductor substrate with a first principal surface 101 having a semipolar surface. The multilayer structure 200 is a structure made of group III nitride semiconductors stacked on the first main surface 101 or the second main surface 102 of the substrate 100. Here, the second main surface 102 is the main surface of the substrate 100 on the opposite side to the first main surface 101. The multilayer structure 200 also includes a quantum well structure 220 . In a graph in which the horizontal axis is the peak wavelength λp [nm] of the photoluminescence spectrum and the vertical axis is the polarization ratio Rp of light emitted by photoluminescence, the photoluminescence obtained by the structure 10 with an excitation wavelength of 325 nm is shown. The resulting plot is located inside the first parallelogram. Here, the peak wavelength λp is the peak wavelength of the maximum peak in the range from 360 nm to 560 nm. Furthermore, when the c-axis is projected onto the first principal surface 101 as the c-projection axis, the polarization ratio Rp is Rp=(Intensity of m-axis polarized light component−Intensity of c-projection axis polarized light component)/(Intensity of m-axis polarized light component) +c projection axis polarization component intensity). The first parallelogram is composed of straight line λp=360, straight line λp=560, straight line Rp=−0.005λp+2.2, and straight line Rp=−0.005λp+1.4. The polarization ratio Rp obtained by photoluminescence of the structure 10 with an excitation wavelength of 325 nm is less than 0. This will be explained in detail below.

Note that a component whose vibration direction of the electric field of light is parallel to the m-axis is called an m-axis polarized light component. A component whose vibration direction of the electric field of light is parallel to the c-axis projection axis is called a c-projection axis polarization component. Furthermore, in the above graph, the fact that the plot of the result obtained from photoluminescence of the structure with an excitation wavelength of 325 nm is located inside the first parallelogram is also referred to as a "polarization-related condition."

When a device (eg, an optical device, an electronic device, etc.) is formed on the c-plane, which is the polar plane of a group III nitride semiconductor crystal, the internal quantum efficiency decreases due to the internal electric field. Particularly in a quantum well structure on a polar plane, as the In composition is increased in order to lengthen the wavelength, the internal electric field increases, which poses a problem. Therefore, attempts have been made to form a device on a so-called semipolar surface (a surface different from a polar surface and a non-polar surface). It is thought that if a device is formed on a semipolar plane, the internal electric field can be significantly reduced and the internal quantum efficiency can be increased compared to when a device is formed on a c-plane.

Further, when manufacturing a laser, the manufacturing cost of the device can be reduced by making the cleavage plane function as a mirror surface. In a group III nitride semiconductor, for example, the m-plane may be a cleavage plane, and the m-plane may be a mirror plane. In that case, a cavity will be provided in the m-axis direction.

The structure 10 according to this embodiment satisfies the above-described conditions regarding polarization. By doing so, when a laser is manufactured with the cleavage plane as a mirror surface, a large gain can be ensured in the cavity direction. Specifically, by increasing the proportion of the c-projection axis polarization component in the light emitted from the quantum well structure, the gain in the cavity direction can be increased. As a result, a highly efficient and energy-saving driving device can be obtained.

Note that although the structure 10 is suitably used for producing a laser, the use of the structure 10 is not particularly limited. The structure 10 may be used for manufacturing optical devices other than lasers.

FIG. 2 is a diagram for explaining conditions regarding polarization. The horizontal axis of the graph shown in this figure is the peak wavelength λp, and the vertical axis is the polarization ratio Rp. Also, in the graph, the lines λp=360, λp=560, Rp=-0.005λp+2.2, Rp=-0.005λp+1.4, and Rp=-0.005λp+1.6 are shown. The section is drawn. The four sides of the first parallelogram overlap with λp=360, straight line λp=560, straight line Rp=−0.005λp+2.2, and straight line Rp=−0.005λp+1.4, respectively. That is, the vertices of the first parallelogram are (λp, Rp) = (360, 0.4), (560, -0.6), (560, -1.4), (360, -0. 4).

The conditions regarding polarization are such that in this graph, the plot of the result obtained by photoluminescence of the structure 10 with an excitation wavelength of 325 nm is located inside the first parallelogram, and the structure with an excitation wavelength of 325 nm is The polarization ratio Rp obtained by photoluminescence of the body 10 is less than 0. Of the light emitted by the structure 10, the intensity of the c-projection axis polarized light component is greater than the intensity of the m-axis polarized light component. As a result, the optical gain in the cavity direction can be further improved when the m-plane is a mirror surface, and a highly efficient light emitting device can be realized.

In this graph, the plot of the results obtained from the photoluminescence of the structure 10 with an excitation wavelength of 325 nm may be further located inside the second parallelogram below. The second parallelogram is a parallelogram composed of straight line λp=360, straight line λp=560, straight line Rp=−0.005λp+2.2, and straight line Rp=−0.005λp+1.6. The vertices of the second parallelogram are (λp, Rp) = (360, 0.4), (560, -0.6), (560, -1.2), (360, -0.2) There are four points.

FIG. 3 is a diagram illustrating the configuration of an apparatus 40 for measuring the intensity of the c-axis polarized light component and the intensity of the m-axis polarized light component of light emitted by photoluminescence. In this figure, the path of light is shown by solid arrows and broken lines.

Light source 420 is a laser light source, specifically a He--Cd laser that emits light at a wavelength of 325 nm. Light emitted from the light source 420 enters the measurement object 500 (for example, the structure 10) via the mirror 421, the bright line cut filter 422, the mirror 423, the mirror 424, and the lens 425. Then, the light emitted from the measurement object 500 by photoluminescence is collimated by the lens 431, and a part of the light is incident on the polarizer 432. By changing the angle of the polarizer 432, the polarized light component to be transmitted can be switched. The light transmitted through the polarizer 432 is focused by a lens 433 onto a light receiving section 434, and is received by the light receiving section 434. The light receiver 435 is composed of a spectrometer and a CCD detector. The light received by the light receiving section 434 is separated into spectra by a spectroscope of a light receiver 435, and then received by a CCD detector. Then, the intensity of each wavelength is detected by a CCD detector.

Further, for the data obtained by the light receiver 435, in addition to the sensitivity correction of the CCD light receiver performed in normal photoluminescence measurement, the angle dependence of the polarizer transmitted intensity is corrected as follows, for example. First, using a c-plane InGaN quantum well structure (emission wavelength 450 nm) that emits unpolarized light, the intensity P ₀ when the polarizer angle is 0° and the intensity P ₉₀ when the polarizer angle is 90° are calculated. Measure. Then, the value of P ₉₀ /P ₀ is calculated for each wavelength, and the average value of the calculated values is determined. Then, by multiplying the average value by the measurement data of the measurement object 500 when the angle of the polarizer is 90 degrees, the corrected intensity is obtained.

The structure of the structure 10 will be explained in detail below. For example, the substrate 100 may be a GaN substrate. Substrate 100 is a free-standing substrate. The thickness of the substrate 100 is not particularly limited, but from the viewpoint of ease of handling, it is preferably 100 μm or more. Further, from the viewpoint of downsizing the structure 10, the thickness of the substrate 100 is preferably 1.5 mm or less. The substrate 100 may be an undoped substrate, or may be an n-type or p-type semiconductor substrate.

The first main surface 101 of the substrate 100 is a {11-2n} plane or a plane whose off angle from the {11-2n} plane is within 10°, where n is a number of 0 or more. It is preferable that n is an integer satisfying 0≦n≦4, and particularly preferably n=3. The multilayer structure 200 may be formed on the first main surface 101 side of the substrate 100 or may be formed on the second main surface 102 side. The first principal surface 101 is, for example, a (11-2n) plane or a plane whose off angle from the (11-2n) plane is within 10°. In this case, the second principal surface 102 is a (-1-12-n) plane or a plane whose off angle from the (-1-12-n) plane is within 10°. In the structure 10, the multilayer structure 200 is in contact with the first main surface 101 or the second main surface 102 of the substrate 100. Multilayer structure 200 includes multiple layers stacked on top of each other.

It is preferable that the substrate 100 has a certain degree of high crystallinity. Specifically, the half-width of ω of (112) of the X-ray rocking curve (XRC) measured for the surface on the multilayer structure 200 side of the first principal surface 101 and second principal surface 102 of the substrate 100 is In the following m-axis incident measurement, 500 arcsec. It is preferably less than 200 arcsec. It is more preferable that it is below. Further, the half-width of ω of (112) of the X-ray rocking curve (XRC) measured for the side on which the multilayer structure 200 is formed among the first principal surface 101 and the second principal surface 102 of the substrate 100 is In the following c projection axis incident measurement, 500 arcsec. It is preferably less than 200 arcsec. It is more preferable that it is below. Note that the half width in the m-axis incident measurement and the c-projection axis incident measurement is, for example, 30 arcsec. It may be more than that.

The X-ray rocking curve measurement will be explained below. Since the space group of the unit cell of a group III nitride semiconductor is P63mc, it is impossible to obtain X-ray diffraction from the {11-23} plane, for example, due to the extinction law. Therefore, for example, rocking curve measurements are performed regarding the {11-22} plane, which is a plane relatively close to the {11-23} plane.

In particular, in the semipolar plane of a Group III nitride semiconductor, crystalline anisotropy often occurs in the m-axis direction and the c-projection axis direction with respect to the principal plane. Therefore, for example, X-ray rocking curves are measured in these two axial directions. Specifically, the evaluation of the XRC (112) ω half-value width is performed by making X-rays incident on the main surface of the measurement object parallel to the m-axis, and scanning the angle formed between the incident direction of the X-rays and the main surface. Two types of measurements are performed: axial incidence measurement and c-projection axis incidence measurement in which X-rays are incident parallel to the c-projection axis of the main surface of the measurement target and the angle formed between the X-ray incident direction and the main surface is scanned. . By doing so, the crystallinity in each direction can be evaluated.

For example, the off angle from the {11-23} plane can be calculated from the results of rocking curve measurement for the {11-22} plane. Specifically, in order to calculate the off angle in the m-axis direction and the c projection axis direction from the {11-23} plane on the main surface of the measurement target, the m-axis incident measurement and c For each projection axis incident measurement, the measurement is performed by rotating the substrate 100 by 180° in the in-plane direction of its main surface. Based on the off-angles in the m-axis direction and the c-projection axis direction obtained from the results of these measurements, the final off-angle, that is, the angle between the {11-23} plane and the main surface of the object to be measured can be calculated.

Further, among the first main surface 101 and the second main surface 102 of the substrate 100, the dark spot density of the surface on the multilayer structure 200 side is preferably 1×10 ⁷ cm ⁻² or less, and 3×10 ⁶ cm ⁻ More preferably, it is ² or less. Note that the dark spot density may be, for example, 1×10 ⁴ cm ⁻² or more. Dark spot density can be derived by cathodoluminescence (CL) measurements.

Of the first principal surface 101 and second principal surface 102 of the substrate 100, the radius of curvature of the surface on which the multilayer structure 200 is formed is preferably 0.5 m or more in the m-axis direction, and preferably 2 m or more. It is more preferable that Further, of the first main surface 101 and the second main surface 102 of the substrate 100, the radius of curvature of the surface on which the multilayer structure 200 is formed is preferably 0.5 m or more in the c projection axis direction. , more preferably 2 m or more. Note that the radius of curvature of the surface on which the multilayer structure 200 is formed may be, for example, 100 m or less. The radius of curvature in each direction can be calculated, for example, from the results of the X-ray rocking curve measurement described above.

Multilayer structure 200 includes a quantum well structure 220 . The quantum well structure 220 has a structure in which GaN layers 222 and InGaN layers 224 are stacked alternately. The quantum well structure 220 may be a single quantum well structure or a multiple quantum well structure. Other layers may or may not be present between quantum well structure 220 and substrate 100.

FIG. 1 is a diagram illustrating a structure 10 having a single quantum well structure as a quantum well structure 220. FIG. 4 is a diagram illustrating a structure 10 having a multiple quantum well structure as the quantum well structure 220. In the quantum well structure 220, an InGaN layer 224 is sandwiched between GaN layers 222, the InGaN layer 224 functions as a well layer, and the InGaN layer 224 functions as a barrier layer. The interface between the InGaN layer 224 and the GaN layer 222 is preferably flat, and the interface between the InGaN layer 224 and the GaN layer 222 is preferably free of irregularities with a height greater than the thickness of the InGaN layer 224. When the quantum well structure 220 is a multiple quantum well structure, the number of InGaN layers 224 included in the quantum well structure 220 is preferably 2 or more and 5 or less, for example.

The thickness of the InGaN layer 224 is preferably 3 nm or less, more preferably less than 3 nm, and even more preferably 2.5 nm or less. By doing so, lattice breakdown and defect generation can be suppressed, and a good 220 can be formed. Further, in order to obtain a more uniform film, the thickness of the InGaN layer 224 is preferably 1.5 nm or more.

In the quantum well structure of the III-nitride semiconductor, by increasing the In composition of the InGaN layer, the emission wavelength can be extended to green or the like. However, in the case of a semipolar surface, a higher In composition is required than that of a polar surface. On the other hand, when the In composition is increased, the lattice constant of the InGaN crystal increases and the mismatch with the GaN layer increases. As a result, the crystal structure becomes very easily broken due to lattice relaxation, lattice breakdown, etc.

Here, focusing on the thickness of the InGaN layer, a certain level of thickness is required to form a uniform film. On the other hand, if the film thickness becomes too thick, lattice failure occurs. Note that as the number of quantum wells increases, it becomes more difficult to obtain a better crystal structure. Therefore, in order to form a quantum well structure capable of emitting light at a long wavelength on a semipolar surface, it is necessary to highly control the In composition and film thickness.

In the structure 10 according to this embodiment, a high-quality quantum well structure 220 can be realized by making the thickness of the InGaN layer 224 thin to a certain extent, for example, 3 nm or less. Further, by setting the thickness of the InGaN layer 224 to 3 nm or less, the In composition of the InGaN layer 224 can be increased, and light emission at a long wavelength becomes possible. Furthermore, it is considered that in the thin InGaN layer 224, the compositional fluctuation of In is reduced, and transition can be caused between the same levels. Therefore, for example, when a laser is manufactured using the structure 10, it is assumed that laser oscillation becomes easier.

The composition of the InGaN layer 224 is expressed as In _x Ga _(1-x) N. Here, it is preferable that, for example, 0.1≦x≦0.75 holds true. However, in order to enable highly efficient light emission in the green wavelength region, it is more preferable that 0.28≦x≦0.5, and even more preferably that 0.3≦x≦0.4.

The thickness of the GaN layer 222 is not particularly limited, but is, for example, 10 nm or more and 100 nm or less. When the quantum well structure 220 is a multiple quantum well structure, it is particularly preferable that the thickness of the GaN layer 222 located between the two InGaN layers 224 is 10 nm or more and 50 nm or less. Note that the thicknesses of the plurality of GaN layers 222 in the quantum well structure 220 may or may not be the same. Further, the GaN layer 222 may be doped with Si. When the GaN layer 222 is doped with Si, the concentration of Si in the GaN layer 222 is preferably 5×10 ¹⁷ cm ⁻³ or more and 1×10 ¹⁹ cm ^{−3 or} less.

Preferably, a homoepitaxial GaN layer is included between substrate 100 and InGaN layer 224. By doing so, a high quality quantum well structure 220 can be formed. The homoepitaxial GaN layer may also serve as the GaN layer 222, which is a barrier layer. The thickness of the homoepitaxial GaN layer is preferably 10 nm or more and 10,000 nm or less.

The presence or absence of the quantum well structure 220 in the multilayer structure 200 can be confirmed, for example, by using a transmission electron microscope (TEM) or by performing X-ray diffraction measurement. If the existence of the quantum well structure 220 can be confirmed by at least one of these methods, it can be determined that the multilayer structure 200 includes the quantum well structure 220. Specifically, in the method using TEM, the film thicknesses of the InGaN layer and the GaN layer are checked. In the method of performing X-ray diffraction measurement, the main diffraction from the GaN layer, the main diffraction from the InGaN layer, and their fringes (periodic vibrations) are confirmed.

The peak wavelength λp obtained by photoluminescence of the structure 10 with an excitation wavelength of 325 nm can be 500 nm or more and 560 nm or less. According to such a structure 10, a device that emits green light can be realized. Furthermore, the half-value width of the maximum peak in the range of 360 nm or more and 700 nm or less of the photoluminescence spectrum of the structure 10 with an excitation wavelength of 325 nm can be, for example, 100 nm or less, and further can be 60 nm or less.

The peak intensity of the first peak appearing in the photoluminescence spectrum of the structure 10 with an excitation wavelength of 325 nm is preferably 1 times or more, and preferably 1.5 times or more, the peak intensity of the second peak. More preferred. Here, the first peak is a peak having the maximum peak intensity in the wavelength range of 500 nm or more and 560 nm or less. The first peak may be, for example, a peak whose peak wavelength is λp. The second peak is a peak having the maximum peak intensity in the wavelength range of 350 nm or more and 400 nm or less. The second peak is, for example, the emission peak of GaN. That is, when the structure 10 emits green light, it is preferable that the structure 10 includes the quantum well structure 220 with sufficient structural accuracy to have such a first peak of intensity.

Note that the peak wavelength λp of the photoluminescence spectrum of the structure 10 can be set by adjusting the In composition of the InGaN layer 224, etc. The emitted light color of the structure 10 is not limited to green, but may be red, blue, or the like. The peak wavelength λp may be, for example, in the range of 360 nm or more and 700 nm or less, or may be in the range of 360 nm or more and 560 nm or less.

The angle between at least one cleavage plane of the structure 10 and the first main surface 101 is preferably 75° or more and 105° or less, more preferably 80° or more and 100° or less, and 85° or more and 95° or more. It is more preferable that the temperature is less than or equal to . By doing so, a laser whose cleavage plane is a mirror surface can be easily manufactured using the structure 10. This cleavage plane is, for example, the m-plane.

Furthermore, the structure 10 may be a device. The structure 10 may further include an electrode.

The structure 10 according to this embodiment can be manufactured by a manufacturing method including a forming step. In the formation step, a group III nitride semiconductor is grown on the first main surface 101 or the second main surface 102 of the substrate 100 to form the multilayer structure 200. The substrate 100 is a group III nitride semiconductor substrate with a first principal surface 101 having a semipolar plane. The second main surface 102 is the main surface of the substrate 100 opposite to the first main surface 101 . Multilayer structure 200 includes a quantum well structure 220 . In a graph in which the horizontal axis is the peak wavelength λp [nm] of the photoluminescence spectrum and the vertical axis is the polarization ratio Rp of light emitted by photoluminescence, the photoluminescence obtained by the structure 10 with an excitation wavelength of 325 nm is shown. The resulting plot is located inside the first parallelogram. Here, the peak wavelength λp is the peak wavelength of the maximum peak in the range from 360 nm to 560 nm. Furthermore, when the c-axis is projected onto the first principal surface 101 as the c-projection axis, the polarization ratio Rp is Rp=(Intensity of m-axis polarized light component−Intensity of c-projection axis polarized light component)/(Intensity of m-axis polarized light component) +c projection axis polarization component intensity). The first parallelogram is composed of straight line λp=360, straight line λp=560, straight line Rp=−0.005λp+2.2, and straight line Rp=−0.005λp+1.4. The polarization ratio Rp obtained by photoluminescence of the structure 10 with an excitation wavelength of 325 nm is less than 0. This will be explained in detail below.

The multilayer structure 200 can be formed using, for example, MOCVD. Further, the group V source gas used to form the multilayer structure 200 is, for example, NH ₃ gas, and the group III source gas is an organometallic gas. Examples of the organic metal gas include trimethyl Ga (TMGa), triethyl Ga (TEGa), trimethyl In (TMIn), trimethyl Al (TMAl), and triethyl Al (TEAl). The group V source gas and the group III source gas are reactive gases that react with each other. Further, in the formation process, a carrier gas may be further supplied to the growth chamber of the MOCVD apparatus. The carrier gas is, for example, hydrogen (H ₂ ) gas and nitrogen (N ₂ ) gas, and does not react with the source gas. When TMGa gas is used as the Group III source gas, the temperature of the supplied TMGa gas is preferably -5°C or more and 25°C or less, more preferably 0°C or more and 20°C or less. Further, when TMIn gas is used as the Group III source gas, the temperature of the supplied TMIn gas is preferably 25°C or more and 55°C or less, more preferably 30°C or more and 50°C or less. However, the temperature of each gas can be appropriately set depending on the configuration of the MOCVD apparatus, the vapor pressure required for manufacturing the multilayer structure 200, and the like. Each gas to be supplied can be brought to a desired temperature using, for example, a constant temperature bath.

By placing the substrate 100 in a growth chamber of an MOCVD apparatus and supplying a group III source gas containing Ga and a group V source gas, layers made of GaN such as the GaN layer 222 can be grown. Furthermore, by supplying a group III source gas containing Ga, a group III source gas containing In, and a group V source gas, layers made of InGaN such as the InGaN layer 224 can be grown.

In the formation process, the surface temperature, growth pressure, and supply amount of each gas can be controlled. Here, the surface temperature is the temperature of the surface on which a crystal is to be grown, that is, the temperature of the surface to which the raw material gas is supplied. The surface temperature may be either the temperature of the main surface of the substrate 100 or the temperature of the surface of a crystal layered on the substrate 100. Surface temperature can be measured using a pyrometer, for example. Note that the surface temperature during crystal growth is also particularly referred to as growth temperature.

The first to third conditions for manufacturing the structure 10 will be described below. By satisfying all of the first to third conditions in the formation process, it is possible to obtain a structure 10 that includes a high-quality multilayer structure 200 and satisfies the conditions regarding polarization. In particular, it is preferable that at least the first to third conditions are satisfied when forming the quantum well structure 220. However, the method for manufacturing the structure 10 is not particularly limited as long as the conditions regarding polarization are satisfied. A method that satisfies the first to third conditions is an example of a method for manufacturing the structure 10.

The first condition is that the formation step includes a step of interrupting film formation or a step of supplying hydrogen gas, which will be described below.

The interrupting step is a step of interrupting growth between at least one layer. Specifically, for example, crystal growth is stopped by stopping the supply of at least one of the Group III raw material gas and the Group V raw material gas in the interruption step. During the interruption step, the surface temperature may be changed to increase or decrease as described above. In addition, in the interruption step, the supply of one of the Group III source gas and the Group V source gas may be continued. For example, in the interruption step, group V source gas is supplied without supplying group III source gas. Preferably, the interruption step is performed each time the surface temperature is changed. Further, the interruption process is preferably performed between all the layers included in the quantum well structure 220, and more preferably performed between all the layers included in the multilayer structure 200. Each interruption step is preferably 30 seconds or more and 180 seconds or less.

The hydrogen gas supply step is a step of supplying hydrogen when forming a boundary between layers. Preferably, the hydrogen gas supply step is performed when at least one boundary portion is formed. The interruption step and the hydrogen gas supply step do not need to be performed at the same time. In the hydrogen gas supply step, H ₂ gas is supplied toward the substrate 100 while crystal growth continues. That is, while supplying hydrogen gas, the type of raw material gas is switched or the surface temperature is changed. By doing so, it is possible to obtain an etching effect due to hydrogen flow, to remove excess atoms at the boundary, and to obtain a steep interface between layers. Also, thin layers can be grown uniformly. The amount of hydrogen gas supplied in the hydrogen gas supply step is preferably, for example, 0.5 slm or more and 10 slm or less.

The second condition is to perform appropriate temperature adjustment. Specifically, the growth temperature in the formation step is preferably 500°C or more and 1000°C or less, more preferably 700°C or more and 1000°C or less. In particular, it is preferable that the growth temperature of the GaN layer 222 be higher than the growth temperature of the InGaN layer 224. The growth temperature of the InGaN layer 224 is preferably 700° C. or more and 850° C. or less. By keeping the growth temperature low to a certain extent, the efficiency of In uptake can be increased. Furthermore, by not setting the growth temperature too low, a good crystal structure and interface can be obtained.

The third condition is to appropriately set the V/III ratio in the source gas. The V/III ratio indicates the ratio of the number of group V atoms supplied to the number of group III atoms supplied. Note that each number of supplies is the number of supplies by raw material gas. The V/III ratio in the forming step is preferably 5,000 or more and 20,000 or less. Namely. The number of Group V atoms supplied is preferably 5,000 to 20,000 times the number of Group III atoms supplied. Further, in the formation step, the number of group V atoms supplied is more preferably 6000 times or more and 17000 times or less the number of group III atoms supplied.

Note that when growing InGaN, the number of In atoms supplied is preferably 0.4 times or more and 0.8 times or less, and 0.5 times or more and 0.7 times or less of the total number of group III atoms supplied. It is more preferable that By doing so, it is possible to suppress the half-width of the emission peak, increase the emission intensity, and stably emit light throughout.

Note that in the formation step, the pressure inside the growth chamber is preferably 100 Torr or more and 500 Torr or less.

Furthermore, in the method for manufacturing the structure 10, the surface of the substrate 100 may be thermally cleaned prior to the formation step. In thermal cleaning, for example, the surface temperature of the substrate 100 is maintained at 900° C. or more and 1100° C. or less for 5 minutes or more. Note that the time for thermal cleaning can be 60 minutes or less.

Next, the functions and effects of this embodiment will be explained. According to this embodiment, since the structure 10 satisfies the conditions regarding polarization, it is possible to obtain a device that can be driven with high efficiency while suppressing the manufacturing cost of the device.

(Second embodiment)
FIG. 5 is a diagram illustrating the configuration of the structure 10 according to the second embodiment. The structure 10 according to the present embodiment is similar to the first embodiment except that the multilayer structure 200 includes at least one of a guide layer, a cladding layer, an electron block layer, and a contact layer in addition to the quantum well structure 220. It is the same as the structure 10 according to.

In the example shown in the figure, the multilayer structure 200 includes an n-type cladding layer 251, an n-GaN guide layer 233, an InGaN guide layer 231, a quantum well structure 220, an InGaN guide layer 231, an electron block layer 240, a p-GaN guide layer 234 , a p-type cladding layer 252, and a p-type contact layer 260 in this order from the substrate 100 side. Further, the substrate 100 is n-type GaN. By using such a structure 10, a good laser device can be manufactured.

The InGaN guide layer 231 is made of InGaN, and the quantum well structure 220 is located between the two InGaN guide layers 231 . Further, the n-GaN guide layer 233 is made of n-type GaN, and the p-GaN guide layer 234 is made of p-type GaN. Quantum well structure 220 is located between n-GaN guide layer 233 and p-GaN guide layer 234. Furthermore, an electron blocking layer 240 is located between the InGaN guide layer 231 and the p-GaN guide layer 234. The electron block layer 240 is made of p-type AlGaN, for example.

The cladding layer is made of AlGaN having a composition expressed as Al _y Ga _(1-y) N, for example. Specifically, the n-type cladding layer 251 is made of n-type AlGaN, and the p-type cladding layer 252 is made of p-type AlGaN. Here, y is preferably 0.1 or more, more preferably 0.15 or more. Moreover, it is preferable that y is 0.25 or less. Quantum well structure 220 is located between n-type cladding layer 251 and p-type cladding layer 252. A p-type contact layer 260 is located at the end of the multilayer structure 200 opposite to the substrate 100 side. P-type contact layer 260 is made of p-type GaN, for example.

Among the layers included in the multilayer structure 200, a layer made of an n-type Group III nitride semiconductor can be formed, for example, by further supplying a doping gas containing an n-type dopant during growth. The n-type dopant is, for example, one or more selected from the group consisting of Si, Ge, and O.

Among the layers included in the multilayer structure 200, a layer made of a p-type Group III nitride semiconductor can be formed, for example, by further supplying a doping gas containing a p-type dopant during growth and performing an activation process. The activation treatment is heat treatment or electron beam irradiation. The p-type dopant is, for example, one or more selected from the group consisting of Mg, Zn, Cd, and Be.

Among the layers included in the multilayer structure 200, the layer made of AlGaN can be formed by supplying a group III source gas containing Ga, a group III source gas containing Al, and a group V source gas during growth. .

FIG. 6 is a diagram illustrating the configuration of an optical device 30 according to the second embodiment. Optical device 30 includes structure 10, first electrode 310, and second electrode 320. First electrode 310 and second electrode 320 are electrically connected to multilayer structure 200. In the example shown in the figure, the first electrode 310 is in contact with the substrate 100, and the second electrode 320 is in contact with the layer at the end of the multilayer structure 200 on the opposite side from the substrate 100.

The optical device 30 can be manufactured by forming a first electrode 310 and a second electrode 320 on the structure 10. Specifically, etching or the like is performed on the surface of the substrate 100 opposite to the multilayer structure 200 side as necessary, and the first electrode 310 is formed. Further, a second electrode 320 is formed on the surface of the p-type contact layer 260 opposite to the substrate 100 side. Each electrode is made of at least one metal such as Pd, Pt, Au, and In. Note that each electrode may have a laminated structure of a plurality of metal layers. Further, the shape may be processed by cleaving or dicing the structure 10 as necessary.

Optical device 30 is, for example, a laser. Here, it is preferable that the cleavage plane, which is the side surface of the structure 10, functions as a mirror surface. By doing so, the optical device 30 can be operated as a highly efficient laser. As a result, lasers can be manufactured at low cost. For example, the m-plane is preferable as the cleavage plane used as the mirror plane.

The structures of the structure 10 and the optical device 30 according to this embodiment are not limited to the examples shown in FIGS. 5 and 6, respectively. Further, the optical device 30 is not limited to a laser, and may be a wavelength conversion element, a light emitting diode, a sensor, or the like. When the optical device 30 is a light emitting device such as a laser or a light emitting diode, the emission wavelength of the optical device 30 can be, for example, 500 nm or more and 560 nm or less. That is, a device that emits green light can be manufactured using the structure 10. Note that the emission wavelength of the optical device 30 can be set by adjusting the In composition of the InGaN layer 224, etc. The emitted light color of the optical device 30 is not limited to green, but may be red, blue, or the like.

Next, the functions and effects of this embodiment will be explained. According to this embodiment, the same actions and effects as in the first embodiment can be obtained. In addition, devices can be easily obtained using the structure 10.

Hereinafter, this embodiment will be described in detail with reference to Examples. Note that this embodiment is in no way limited to the description of these examples.

In Example 1, a structure including a single quantum well structure (SQW) was manufactured. In Examples 2 to 5, structures including multiple quantum well structures (MQW) were fabricated. Here, the In composition was changed in Examples 1 to 5. Then, the polarization characteristics of the structures of each example were evaluated.

FIG. 7 is a diagram showing the structure of the structure according to Example 1, and FIG. 8 is a diagram showing the surface temperature in the formation process according to Example 1. Further, Table 1 shows the manufacturing conditions of the structure according to Example 1.

In this example, first, a GaN free-standing substrate having a square shape of 10 mm x 10 mm and whose first principal surface was a (11-23) plane was prepared, and the substrate was evaluated. Thereafter, the substrate was divided into 2 mm x 3 mm rectangular substrates, which were used to form a multilayer structure.

The results of evaluation performed on a 10 mm x 10 mm square substrate are as follows. First, the thickness of the substrate and the CL dark spot density on the first principal surface were evaluated. The evaluation results were as follows.
Thickness: 408μm
CL scotoma density: 1.53×10 ⁶ cm ^-2

Next, the XRC (112)ω half-width, the off angle from the {11-23} plane, and the radius of curvature of the first principal surface were evaluated using the method described in the first embodiment.
XRC (112) ω half-width: m-axis incident measurement 138 arcsec. , c projection axis incident measurement 66.4 arcsec.
Off angle in each axis direction from the {11-23} plane: -0.06° in the m-axis direction, 0.16° in the c-projection axis direction (the angle between the {11-23} plane and the main surface of the measurement target is It was confirmed that the angle was within 10°.)
Radius of curvature: -2.69m in m-axis direction, +8.79m in c-projection axis direction
Note that + in the radius of curvature indicates that the radius of curvature of the crystal axis is in the convex direction on the main surface of the measurement object, and - indicates that the radius of curvature of the crystal axis is in the concave direction.

The divided substrates were attached to an MOCVD apparatus, and a single quantum well structure was fabricated under the conditions shown in Table 1. First, the substrate surface was thermally cleaned by raising the surface temperature from room temperature (RT) and maintaining it at 980° C. for 20 minutes. During thermal cleaning, NH ₃ gas, H ₂ gas, and N ₂ gas were supplied to the growth chamber at the flow rates shown in Table 1, respectively.

Next, a homoepitaxial GaN layer (HT-GaN), an InGaN layer (GaInN), and a cap-GaN layer were grown in this order on the first main surface of the substrate to obtain the structure of Example 1. The growth conditions for each layer are as shown in Table 1. In Table 1, "atomic ratio" refers to the atomic ratio between group V and group III (V/III ratio) or the atomic ratio between In and group III (In/III ratio) contained in the raw material gas. ) is shown. "Pressure" indicates the pressure inside the growth chamber of the MOCVD apparatus.

As shown in Table 1, an interruption step was provided between the growth of the homoepitaxial GaN layer and the growth of the InGaN layer to lower the surface temperature without causing crystal growth. Further, the growth temperature in the formation step was set in a range of 700°C or more and 1000°C or less. Then, the V/III ratio of the raw material gas to be supplied was set in a range of 6,000 to 17,000.

FIG. 9 is a diagram showing the structure of the structure according to Examples 2 to 5, and FIG. 10 is a diagram showing the surface temperature in the formation process according to Examples 2 to 5. Further, Table 2 shows manufacturing conditions for the structures according to Examples 2 to 5. The surface temperature shown in A in this table was 830°C in Example 2, 750°C in Example 3, 770°C in Example 4, and 800°C in Example 5.

In Examples 2 to 5, the same GaN free-standing substrate as in Example 1 was divided into rectangles of about 2 mm x 3 mm and used as substrates. A multilayer structure was then formed on the (11-23) plane, which is the first principal surface of the substrate, to obtain a structure. Note that the formation of the multilayer structure was performed separately in Examples 2 to 5.

As in Example 1, the divided substrates were attached to an MOCVD apparatus, and a multiple quantum well structure was produced under the conditions shown in Table 2. First, as in Example 1, thermal cleaning of the substrate surface was performed.

Next, a homoepitaxial GaN layer (HT-GaN) was formed on the substrate, and three barrier GaN layers and three InGaN layers (GaInN) were alternately formed. Thereafter, a cap-GaN layer was formed to obtain structures of Examples 2 to 5. In Table 2, "atomic ratio" refers to the atomic ratio between group V and group III (V/III ratio) or the atomic ratio between In and group III (In/III ratio) contained in the raw material gas. ) is shown.

As shown in Table 2, an interruption step was provided between the layers to prevent crystal growth. In addition, each interruption process was within the range of 30 seconds or more and 180 seconds or less. Further, the growth temperature in the formation step was set in a range of 700°C or more and 1000°C or less. Then, the V/III ratio of the source gas to be supplied was set in the range of 6,000 to 17,000.

11 to 15 are diagrams showing the results of photoluminescence measurements performed on the structures of Examples 1 to 5 using the apparatus shown in FIG. 3, respectively. In FIGS. 11 to 14, the c-projection axis polarization component is shown by a solid line, and the m-axis polarization component is shown by a dotted line. Photoluminescence measurements were performed at room temperature. The excitation wavelength was 325 nm.

Further, Table 3 shows the results of photoluminescence measurements of the structures according to Examples 1 to 5 at an excitation wavelength of 325 nm. Further, FIG. 16 is a graph plotting the photoluminescence results of the structures of Examples 1 to 5. This graph is the same as described in the first embodiment, with the horizontal axis representing the peak wavelength λp and the vertical axis representing the polarization ratio Rp. This graph includes parts of straight line λp=360, straight line λp=560, straight line Rp=-0.005λp+2.2, straight line Rp=-0.005λp+1.4, and straight line Rp=-0.005λp+1.6. They are drawn together. In addition, as a comparative example, this graph plots the polarization ratio of light emitted from a single quantum well structure formed on the {11-22} plane, which is described in Non-Patent Document 1.

As a result of photoluminescence measurements of the structures according to Examples 1 to 5, the peak wavelengths λp were all within the range of 360 nm or more and 560 nm or less. Moreover, the half-value width of the maximum peak in the range of 360 nm or more and 700 nm or less of the photoluminescence spectrum was all 100 nm or less.

As can be seen from FIGS. 11 to 15, the intensity of the c-projection axis polarization component was higher than the intensity of the m-axis polarization component in all structures. That is, the polarization ratio Rp was less than 0. As can be seen from FIG. 16, all the plots in the examples were located inside the first parallelogram described in the first embodiment, and further inside the second parallelogram. On the other hand, the plots of the comparative examples were all located above the first parallelogram. That is, the ratio of the c-projection axis polarization component of the structure according to the example was higher than the ratio of the c-projection axis polarization component of the structure according to the comparative example. Therefore, it was confirmed that when the structure according to the example was used, the gain in the cavity direction could be increased more than when the structure according to the comparative example was used. Therefore, it is considered that the structure according to the example can realize a highly efficient device.

In both Examples and Comparative Examples, the polarization ratio Rp tended to decrease as the emission wavelength increased.

Although the embodiments of the present invention have been described above with reference to the drawings, these are merely examples of the present invention, and various configurations other than those described above may also be adopted.
Below, examples of reference forms will be added.
1. a group III nitride semiconductor substrate having a semipolar plane as a first principal surface;
A structure comprising a multilayer structure made of a group III nitride semiconductor stacked on the first main surface or the second main surface opposite to the first main surface of the substrate,
The multilayer structure includes a quantum well structure,
The polarization ratio Rp of the light emitted by photoluminescence is set as the c projection axis, which is the axis obtained by projecting the c axis onto the first principal surface, and the polarization ratio Rp of the light emitted by photoluminescence is Rp = (Intensity of the m axis polarized light component - Intensity of the c projection axis polarized light component)/(m It is expressed as: intensity of axial polarized light component + c intensity of projected axial polarized light component),
In a graph in which the horizontal axis is the peak wavelength λp [nm] of the maximum peak in the range of 360 nm or more and 560 nm or less of the photoluminescence spectrum and the vertical axis is the polarization ratio Rp, the photoluminescence of the structure with an excitation wavelength of 325 nm. The resulting plot is located inside the first parallelogram,
The first parallelogram is composed of straight line λp = 360, straight line λp = 560, straight line Rp = -0.005λp + 2.2, and straight line Rp = -0.005λp + 1.4,
A structure in which the polarization ratio Rp obtained by photoluminescence of the structure with an excitation wavelength of 325 nm is less than 0.
2. 1. In the structure described in
The first principal surface is a {11-2n} plane or a plane whose off angle from the {11-2n} plane is within 10°,
A structure where n is a number greater than or equal to 0.
3. 2. In the structure described in
A structure where n=3.
4. 1. From 3. In the structure described in any one of
A structure in which the angle formed by at least one cleavage plane of the structure and the first principal surface is 75° or more and 105° or less.
5. 1. From 4. In the structure described in any one of
The quantum well structure has a structure in which GaN layers and InGaN layers are alternately laminated.
6. 5. In the structure described in
The composition of the InGaN layer is represented by In _x Ga _(1-x) N,
A structure that satisfies 0.28≦x≦0.5.
7. 1. From 6. In the structure described in any one of
A structure in which λp obtained by photoluminescence of the structure with an excitation wavelength of 325 nm is 500 nm or more and 560 nm or less.
8. 1. From 7. In the structure described in any one of
A structure in which a photoluminescence spectrum of the structure with an excitation wavelength of 325 nm has a maximum peak half width of 100 nm or less in a range of 360 nm or more and 700 nm or less.
9. 1. From 8. In the structure described in any one of
The multilayer structure includes a cladding layer made of AlGaN with a composition represented by Al _y Ga _(1-y) N,
A structure in which y is 0.1 or more.
10. 1. From 9. A structure described in any one of
An optical device comprising a first electrode and a second electrode electrically connected to the multilayer structure.
11. 10. In the optical device described in
An optical device that is a laser in which the cleavage plane of the structure is a mirror surface.
12. 1. From 9. A method for manufacturing an optical device, comprising forming a first electrode and a second electrode electrically connected to the multilayer structure in the structure according to any one of the above.
13. A method for manufacturing a structure, the method comprising:
A group III nitride semiconductor is formed on the first main surface or the second main surface opposite to the first main surface of a group III nitride semiconductor substrate whose first main surface is a semipolar plane. comprising a forming step of growing to form a multilayer structure;
The multilayer structure includes a quantum well structure,
The polarization ratio Rp of the light emitted by photoluminescence is set as the c projection axis, which is the axis obtained by projecting the c axis onto the first principal surface, and the polarization ratio Rp of the light emitted by photoluminescence is Rp = (Intensity of the m axis polarized light component - Intensity of the c projection axis polarized light component)/(m It is expressed as: intensity of axial polarized light component + c intensity of projected axial polarized light component),
In a graph in which the horizontal axis is the peak wavelength λp [nm] of the maximum peak in the range of 360 nm or more and 560 nm or less of the photoluminescence spectrum and the vertical axis is the polarization ratio Rp, the photoluminescence of the structure with an excitation wavelength of 325 nm. The resulting plot is located inside the first parallelogram,
The first parallelogram is composed of straight line λp = 360, straight line λp = 560, straight line Rp = -0.005λp + 2.2, and straight line Rp = -0.005λp + 1.4,
A method for manufacturing a structure in which the polarization ratio Rp obtained by photoluminescence of the structure with an excitation wavelength of 325 nm is less than 0.
14. 13. In the method for manufacturing a structure described in
A method for manufacturing a structure, wherein the growth temperature in the formation step is 500°C or more and 1000°C or less.
15. 13. or 14. In the method for manufacturing a structure described in
The method for manufacturing a structure, wherein the forming step includes a step of interrupting growth between at least one layer.
16. 13. or 14. In the method for manufacturing a structure described in
The method for manufacturing a structure includes the step of supplying hydrogen when forming at least one boundary between layers.
17. 13. From 16. In the method for manufacturing a structure according to any one of
In the forming step, the number of Group V atoms supplied by the source gas is 5000 to 20000 times the number of Group III atoms supplied.

10 Structure 30 Optical device 40 Device 100 Substrate 101 First main surface 102 Second main surface 200 Multilayer structure 220 Quantum well structure 222 GaN layer 224 InGaN layer 231 InGaN guide layer 233 n-GaN guide layer 234 p-GaN guide layer 240 Electron block layer 251 N-type cladding layer 252 P-type cladding layer 260 P-type contact layer 310 First electrode 320 Second electrode 420 Light sources 421, 423, 424 Mirror 422 Bright line cut filter 425, 431, 433 Lens 432 Polarizer 434 Light receiving section 435 Light receiver 500 Measurement target

Claims (15)

a group III nitride semiconductor substrate having a semipolar plane as a first principal surface;
A structure comprising a multilayer structure made of a group III nitride semiconductor stacked on the first main surface or the second main surface opposite to the first main surface of the substrate,
The multilayer structure includes a quantum well structure,
The polarization ratio Rp of the light emitted by photoluminescence is set as the c projection axis, which is the axis obtained by projecting the c axis onto the first principal surface, and the polarization ratio Rp of the light emitted by photoluminescence is Rp = (Intensity of the m axis polarized light component - Intensity of the c projection axis polarized light component)/(m It is expressed as: intensity of axial polarized light component + c intensity of projected axial polarized light component),
In a graph in which the horizontal axis is the peak wavelength λp [nm] of the maximum peak in the range of 360 nm or more and 560 nm or less of the photoluminescence spectrum and the vertical axis is the polarization ratio Rp, the photoluminescence of the structure with an excitation wavelength of 325 nm. The resulting plot is located inside the first parallelogram,
The first parallelogram is composed of straight line λp = 360, straight line λp = 560, straight line Rp = -0.005λp + 2.2, and straight line Rp = -0.005λp + 1.4,
The polarization ratio Rp obtained by photoluminescence of the structure with an excitation wavelength of 325 nm is less than 0,
The m-axis polarized light component is a component in which the vibration direction of the electric field is parallel to the m-axis,
The c projection axis polarization component is a component in which the vibration direction of the electric field is parallel to the c projection axis,
The first principal surface is a {11-23} plane, or a plane whose off angle from the {11-23} plane is within -0.06° in the m-axis direction and within 0.16° in the c-projection axis direction. Structure. The structure according to claim 1,
A structure in which the angle formed by at least one cleavage plane of the structure and the first principal surface is 75° or more and 105° or less. The structure according to claim 1 or 2,
The quantum well structure has a structure in which GaN layers and InGaN layers are alternately laminated. The structure according to claim 3,
The composition of the InGaN layer is represented by In _x Ga _(1-x) N,
A structure that satisfies 0.28≦x≦0.5. The structure according to any one of claims 1 to 4,
A structure in which λp obtained by photoluminescence of the structure with an excitation wavelength of 325 nm is 500 nm or more and 560 nm or less. The structure according to any one of claims 1 to 5,
A structure in which a photoluminescence spectrum of the structure with an excitation wavelength of 325 nm has a maximum peak half width of 100 nm or less in a range of 360 nm or more and 700 nm or less. The structure according to any one of claims 1 to 6,
The multilayer structure includes a cladding layer made of AlGaN with a composition represented by Al _y Ga _(1-y) N,
A structure in which y is 0.1 or more. A structure according to any one of claims 1 to 7,
An optical device comprising a first electrode and a second electrode electrically connected to the multilayer structure. The optical device according to claim 8,
An optical device that is a laser in which the cleavage plane of the structure is a mirror surface. A method for manufacturing an optical device, comprising forming a first electrode and a second electrode electrically connected to the multilayer structure in the structure according to any one of claims 1 to 7. A method for manufacturing a structure, the method comprising:
The {11-23} plane, or the semipolar plane whose off angle from the {11-23} plane is within -0.06° in the m-axis direction and within 0.16° in the c-projection axis direction, is the first principal surface. forming a multilayer structure by growing a group III nitride semiconductor on the first main surface or the second main surface opposite to the first main surface of a group III nitride semiconductor substrate; including the process,
The multilayer structure includes a quantum well structure,
The polarization ratio Rp of the light emitted by photoluminescence is set as the c projection axis, which is the axis obtained by projecting the c axis onto the first principal surface, and the polarization ratio Rp of the light emitted by photoluminescence is Rp = (Intensity of the m axis polarized light component - Intensity of the c projection axis polarized light component)/(m It is expressed as: intensity of axial polarized light component + c intensity of projected axial polarized light component),
In a graph in which the horizontal axis is the peak wavelength λp [nm] of the maximum peak in the range of 360 nm or more and 560 nm or less of the photoluminescence spectrum and the vertical axis is the polarization ratio Rp, the photoluminescence of the structure with an excitation wavelength of 325 nm. The resulting plot is located inside the first parallelogram,
The first parallelogram is composed of straight line λp = 360, straight line λp = 560, straight line Rp = -0.005λp + 2.2, and straight line Rp = -0.005λp + 1.4,
The polarization ratio Rp obtained by photoluminescence of the structure with an excitation wavelength of 325 nm is less than 0,
The m-axis polarized light component is a component in which the vibration direction of the electric field is parallel to the m-axis,
The c-projection axis polarization component is a component in which the vibration direction of the electric field is parallel to the c-projection axis. The method for manufacturing a structure according to claim 11,
A method for manufacturing a structure, wherein the growth temperature in the formation step is 500°C or more and 1000°C or less. The method for manufacturing a structure according to claim 11 or 12,
The method for manufacturing a structure, wherein the forming step includes a step of interrupting growth between at least one layer. The method for manufacturing a structure according to claim 11,
The method for producing a structure includes a step in which the forming step includes a step of switching the type of raw material gas while supplying hydrogen when forming at least one boundary between the layers. The method for manufacturing a structure according to any one of claims 11 to 13,
In the forming step, the number of group V atoms supplied by the source gas is 5000 to 20000 times the number of group III atoms supplied.

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