JP2011187581A - Semiconductor light emitting device, method of manufacturing the same, light source for image display apparatus, and image display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor light emitting device for obtaining incoherent light to be high output by suppressing laser oscillation while beam quality is maintained. <P>SOLUTION: The semiconductor light emitting device 100 has an optical waveguide 115. The optical waveguide 115 includes an active layer 104, a first end face 111 and a second end face 112. The first end face 111 is arranged at one end of the optical waveguide 115. A second end face 112 is disposed at the other end of the optical waveguide 115. An optical reflectance ratio of the first end face 111 in a wavelength area of emission light is ≤1%, and that of the second end face 112 in the wavelength area of the emission light is ≥20%. The active layer 104 has a gain generation region and a gain wavelength generated in the gain generation region is nonuniform. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a semiconductor light emitting device, a method for manufacturing a semiconductor light emitting device, a light source for an image display device, and an image display device.

  Development of a projection type laser display (laser projector) using a visible light laser as a light source has been energetically advanced. Laser light has higher monochromaticity than a conventional lamp light source. For this reason, a display excellent in color reproducibility can be realized. Laser light is excellent in directivity. For this reason, the utilization efficiency of light is also high. Further, if a semiconductor laser that is small, highly efficient, and has excellent emission beam quality is used as a light source, it is possible to further reduce power consumption and downsize the apparatus. For this reason, the practical use of the visible semiconductor laser light source for displays is expected.

  However, the laser light has high coherence because the phases are aligned. For this reason, in the laser display, flicker called speckle may occur due to light randomly projected on the screen. The generation of speckle is a serious problem in realizing a laser display using a semiconductor laser as a light source.

  In order to suppress the generation of this speckle, it is necessary to reduce the temporal coherence of the laser beam. Examples of a method for reducing temporal coherence include a method in which a spatial phase modulator for spatially randomizing the phase is provided outside the light source, and a method in which light from a plurality of light sources is condensed. These methods are effective for large display applications. However, the provision of another mechanism for speckle reduction hinders downsizing, energy saving, and low cost of the laser display. For this reason, a simpler configuration is desirable from the viewpoint of cost reduction for small display applications utilizing the characteristics of semiconductor lasers. There is a demand for a small light source that can reduce speckle by a single semiconductor element and has excellent monochromaticity and directivity like a semiconductor laser.

  In order to achieve speckle reduction with a single light source, it is effective to increase the emission wavelength width. For example, since a light emitting diode (LED: Light Emitting Diode) has a light emission wavelength width much wider than that of a semiconductor laser, speckle is not a problem. However, the LED has a problem in terms of monochromaticity because of its wide spectrum width. Further, since the emitted beam has no directivity, it is not suitable for a small-sized and low power consumption display.

  A super luminescent diode (SLD) has been proposed as a semiconductor light source that can solve these problems and is promising for display applications (see Patent Documents 1 and 2). Similar to a semiconductor laser, the SLD is a device that has an optical waveguide structure and suppresses oscillation by increasing optical loss. The SLD can emit a directional beam in the same manner as a semiconductor laser due to its optical waveguide structure. Also, since temporal oscillation is suppressed, temporal coherence is reduced. In addition, since the optical waveguide structure receives the effect of amplification and loss by the active layer, the wavelength width can be narrower than that of the LED, and the monochromaticity is also advantageous compared to the LED.

  The SLD described in Patent Document 1 is intended to present a wide light spectrum emission characteristic having a spectrum half-value width greater than or equal to a predetermined value. Furthermore, the SLD described in Patent Document 2 is intended to obtain a relatively large light output without reducing the light emission efficiency.

International Publication No. 2006/0757559 Pamphlet JP 2002-76432 A

  However, the SLD that can obtain a relatively large light output without lowering the light emission efficiency like the SLD described in Patent Document 2 has the following problems.

  In the SLD described in Patent Document 2, a reflection film is formed on the reflection end face (rear end face) and an antireflection film is formed on the emission end face in order to increase the efficiency. The rear end surface intersects perpendicularly to the optical waveguide (vertical end). For this reason, wasteful emission from the rear end face can be reduced and the output of the SLD light can be increased. Here, when a reflective film is provided on the rear end face as in the SLD described in Patent Document 2, the front face light reflectance is close to 0 on the emission end face in order to stably suppress oscillation. The value needs to be very low. This is because, as described above, when the rear end face is a reflection face, the oscillation shifts to the oscillation operation if there is even a slight front reflection while the gain of the active layer is high.

  In order to make the front light reflectance at the light emitting end face extremely low to a value close to 0, for example, a method of providing an antireflection film on the light emitting end face can be considered. However, it is difficult to form such an antireflection film having a low light reflectance with good reproducibility. For this reason, in the SLD described in Patent Document 2, the front-surface light reflectance is substantially reduced by making the emission end face an oblique end that obliquely intersects the optical waveguide. That is, by making the exit end face an oblique end, light reflected by the light exit end face hardly returns to the optical waveguide. Thereby, in the SLD described in Patent Document 2, the effective light reflectance is suppressed and the oscillation is suppressed.

  In the SLD described in Patent Document 2, as described above, when the angle of the oblique end is increased in order to sufficiently suppress the effective light reflectance, the emission direction of the emission beam is a direction perpendicular to the element end face. Greatly deviated from. For this reason, beam quality degradation occurs such that the shape of the outgoing beam becomes asymmetrical.

  An object of the present invention is to provide a semiconductor light emitting device capable of obtaining incoherent light with high output by suppressing laser oscillation while maintaining beam quality, a method for manufacturing the semiconductor light emitting device, a light source for an image display device, and an image display To provide an apparatus.

In order to achieve the above object, the semiconductor light emitting device of the present invention comprises:
Having an optical waveguide,
The optical waveguide includes an active layer, a first end surface, and a second end surface,
The first end face is provided at one end of the optical waveguide;
The second end surface is provided at the other end of the optical waveguide;
The light reflectance of the first end face in the wavelength range of the emitted light is 1% or less,
The light reflectance of the second end face in the wavelength range of the emitted light is 20% or more,
The active layer has a gain generation region,
The gain wavelength generated in the gain generation region is non-uniform.

In addition, the method for manufacturing a semiconductor light emitting device of the present invention includes
Including an optical waveguide forming step of forming an optical waveguide;
The optical waveguide forming step includes an active layer forming step for forming an active layer, a first end face forming step for forming a first end face, and a second end face forming step for forming a second end face,
In the first end face forming step,
Forming the first end face so that the light reflectance in the wavelength region of the emitted light is 1% or less;
In the second end face forming step,
Forming the second end face so that the light reflectance in the wavelength region of the emitted light is 20% or more;
In the active layer forming step,
An active layer having the gain generation region where the gain wavelength generated in the gain generation region is non-uniform is formed.

The light source for an image display device of the present invention is
The semiconductor light emitting device of the present invention or the semiconductor light emitting device manufactured by the manufacturing method of the present invention is included.

Moreover, the image display device of the present invention includes:
It includes the light source for an image display device of the present invention.

  According to the present invention, a semiconductor light emitting device capable of obtaining high output incoherent light by suppressing laser oscillation while maintaining beam quality, a method for manufacturing a semiconductor light emitting device, a light source for an image display device, and an image display A device can be provided.

(A) is a top view which shows the structure of an example in Embodiment 1 of the semiconductor light-emitting device of this invention. (B) is sectional drawing seen in the II direction of the semiconductor light-emitting device shown to Fig.1 (a). (C) is sectional drawing which shows the active layer in the semiconductor element shown to Fig.1 (a) in detail. It is sectional drawing which shows 1 process of the manufacturing method of the semiconductor light-emitting device shown in FIG. It is sectional drawing which shows the other process of the said manufacturing method. It is sectional drawing which shows the other process of the said manufacturing method. It is sectional drawing which shows the other process of the said manufacturing method. It is a graph which illustrates the gain spectrum concerning SLD and comparison object of the present invention. It is a graph which illustrates the relationship between the injection current density and SL optical output concerning SLD of this invention and a comparison object. It is a graph which illustrates the relationship between the light reflectivity and light emission intensity of the rear end surface in SLD of this invention. It is a graph which illustrates the emission spectrum of SL light concerning SLD of the present invention.

  In the present invention, unless otherwise specified, “on” may be in a state of being in direct contact with the upper surface, or other components may be disposed therebetween. The same applies to “under”. In the present invention, “on the upper surface” means a state in direct contact with the upper surface unless otherwise specified. The same applies to “on the bottom surface”.

  In the present invention, the “main surface” of a semiconductor laminate or substrate refers to the widest plane in the semiconductor laminate or substrate, that is, a so-called upper surface or lower surface, or front surface or back surface.

Further, in the present invention, “composition” refers to a quantitative relationship of the number of atoms of elements constituting a semiconductor layer or the like. “Composition ratio” refers to a relative ratio between the number of atoms of a specific element constituting the semiconductor layer and the like and the number of atoms of another element. For example, in the semiconductor layer represented by the composition of Al _x Ga _y In _1-xy N, the numerical value of x is “Al composition ratio”, the numerical value of y is “Ga composition ratio”, and the numerical value of 1-xy. Is called “In composition ratio”. In the present invention, when the composition or composition ratio of the semiconductor layer is defined, impurities (dopants) that develop conductivity and the like are not considered as elements constituting the semiconductor layer. For example, a p-type AlGaN layer and an n-type AlGaN layer are different in impurities (dopants) but have the same composition.

  Hereinafter, the semiconductor light emitting device and the method for manufacturing the semiconductor light emitting device of the present invention will be described in detail with examples. However, the present invention is not limited to the following embodiments. In addition, in the following FIG. 1 to FIG. In the drawings, for convenience of explanation, the structure of each part may be simplified as appropriate, and the dimensional ratio of each part may be different from the actual one. Further, the graph is an example of the theoretical calculation result, and the actual phenomenon in the semiconductor light emitting device of the present invention may not completely match the theoretical calculation.

(Embodiment 1)
The semiconductor light emitting device of this embodiment is a super luminescent diode (SLD) that is a gallium nitride (GaN) ridge waveguide device that emits light in the green wavelength band. FIG. 1 shows an exemplary configuration of the SLD of this embodiment. FIG. 1A is a plan view of the SLD of this embodiment. FIG.1 (b) is sectional drawing seen in the II direction of SLD shown to Fig.1 (a). FIG. 1C is a cross-sectional view showing in detail an active layer in the SLD shown in FIG. As illustrated, the SLD 100 has an optical waveguide 115. The optical waveguide 115 is formed on an n-type GaN substrate 101, an n-type AlGaN cladding layer 102 (first cladding layer), an InGaN lower optical waveguide layer 103, an InGaN / InGaN quantum well active layer 104, an InGaN upper optical waveguide layer 105, A p-type AlGaN cladding layer 106 (second cladding layer) is formed by being stacked in the above order. The p-type AlGaN cladding layer 106 constitutes a current confinement portion. The “InGaN / InGaN quantum well active layer” in this embodiment corresponds to the “active layer” of the present invention.

  The p-type AlGaN cladding layer 106 and the p-type GaN contact layer 107 provided thereon are processed into a ridge shape. Thereby, an optical waveguide is defined (ridge waveguide 115). This ridge shape functions as a current constriction. The ridge portion functions as a horizontal refractive index waveguide mechanism. The ridge width is, for example, 2.0 μm. A p-side electrode 108 is provided on the p-type GaN contact layer 107. An n-side electrode 109 is provided on the lower surface of the n-type GaN substrate 101. The upper surface (front surface) of the SLD 100 is covered with an insulating film 110 except for the portion where the ridge waveguide 115 and the p-side electrode 108 are provided. In FIG. 1A, for convenience of explanation, layers above the p-type AlGaN cladding layer 106 are omitted. The “ridge waveguide” in the present embodiment corresponds to the “optical waveguide” of the present invention.

  The InGaN / InGaN quantum well active layer 104 includes two periods of quantum wells. The two-period quantum well includes two InGaN quantum well layers 104a and three InGaN barrier layers 104b sandwiching them. The average layer thickness of the InGaN quantum well layer 104a is 2.5 nm, and the average indium composition is 17% (indium composition ratio: 0.17). The average layer thickness of the InGaN barrier layer 104b is 10 nm, and the average indium composition is 5% (indium composition ratio: 0.05).

  The SLD of the present embodiment forms a spatial composition distribution so that the gain spectrum width of the entire quantum well is increased, and therefore the InGaN / InGaN quantum well activity is used under conditions that increase the composition fluctuation of indium. The layer 104 is manufactured. The composition fluctuation of indium described above can be adjusted by appropriately changing the semiconductor crystal growth conditions such as the composition of the supply gas (for example, V / III ratio, etc.), the temperature condition, the pressure condition, and the growth rate. it can. The composition fluctuation can be expressed by using the emission energy distribution as an index. In the case of the SLD of this embodiment, the composition fluctuation is about 100 meV. The gain peak wavelength λg of the InGaN / InGaN quantum well active layer 104 is approximately 450 nm.

  In the SLD 100 of this embodiment, the ridge waveguide 115 is provided with a light emission end face 111 at one end thereof. The ridge waveguide 115 has a rear end surface 112 at the other end. The planar shape of the ridge waveguide 115 is such that the light emitting end face 111 is inclined (obliquely inclined) from a plane orthogonal to the traveling direction of the ridge waveguide 115 (left-right direction in FIG. 1A). The inclination angle is 5 °. The rear end surface 112 is a vertical end surface. In order to connect the both end faces, the ridge waveguide structure 115 is bent. The shape of the bent portion is a gentle curve with a radius of curvature of about 3 mm in order to minimize the waveguide loss of light. A non-reflective coating multilayer film 113 is provided on the light emitting side end face 111. A reflective coating multilayer film 114 is provided on the rear end surface 112. The light reflectance of the light emitting end face 111 in the wavelength range of the emitted light from the SLD 100 is 1%. The light reflectance of the rear end face 112 in the wavelength range of the emitted light from the SLD 100 is 95%. The “light emitting end face” in the present embodiment corresponds to the “first end face” of the present invention. The “rear end surface” in the present embodiment corresponds to a “second end surface” of the present invention.

  Although the manufacturing method of the semiconductor light-emitting device of the present invention is not particularly limited, it is preferably manufactured by the manufacturing method of the present invention. In the production method of the present invention, the order in which the steps are performed is not particularly limited, and may be any order, and may be sequential or simultaneous. Hereinafter, an example of a method for manufacturing the SLD of this embodiment will be described with reference to FIGS. 2A to 2D.

  First, as shown in FIG. 2A, an n-type AlGaN cladding layer 102, an InGaN lower optical waveguide, and the like are formed on an n-type GaN substrate 101 using a metal organic vapor phase epitaxy (MOVPE: Metal Organic Vapor Phase Epitaxy). The layer 103, the InGaN / InGaN quantum well active layer 104, the InGaN upper optical waveguide layer 105, the p-type AlGaN cladding layer 106, and the p-type GaN contact layer 107 are stacked in the order described above to form the InGaN / GaN quantum well active layer 104. An optical waveguide is formed (optical waveguide forming step). In this step, the average layer thickness of the InGaN quantum well layer 104a in the InGaN / GaN quantum well active layer 104 is 2.5 nm, and the average indium composition is 17% (indium composition ratio: 0.17). The average layer thickness of the InGaN barrier layer 104b in the InGaN / GaN quantum well active layer 104 is 10 nm, and the average indium composition is 5% (indium composition ratio: 0.05). At this time, the composition fluctuation of indium is increased by changing the crystal growth conditions described above (active layer forming step).

  Next, an etching mask corresponding to the shape of the optical waveguide shown in FIG. 1A and the width of 2 μm is formed using a normal photolithography process. In this state, the p-type GaN contact layer 107 and the p-type AlGaN cladding layer 106 are etched halfway by dry etching using a chlorine-based gas. Thereby, as shown in FIGS. 2B and 2D, a ridge waveguide 115 having a width of about 2 μm is formed (ridge waveguide forming step). The value of the ridge width and the etching depth of the p-type cladding layer 106 are not particularly limited. However, since they affect the horizontal transverse mode characteristics, current-light output characteristics, current-voltage characteristics, etc. of the optical waveguide, required devices The optimum value is selected in consideration of characteristics and the like.

  Next, as shown in FIG. 2C, an insulating film 110 such as a silicon oxide film is formed on the entire semiconductor element using a chemical vapor deposition (CVD) method or the like (insulating film forming step). . Next, the insulating film 110 in the p-side electrode 108 forming portion is removed using a normal photolithography process. In this state, titanium and gold are vapor-deposited and heated under appropriate conditions to perform an alloy process. Thereby, the p-side electrode 108 is formed as shown in FIG. 2C. Further, titanium and gold are vapor-deposited on the back surface (the lower surface in FIG. 2C) of the n-type GaN substrate 101, and the alloy process is performed by heating under appropriate conditions. Thereby, the n-side electrode 109 is formed. (Electrode forming step).

  Further, the light emitting end face 111 and the rear end face 112 are exposed at both ends of the ridge waveguide 115 by cleavage. In this state, as shown in FIG. 2D, a non-reflective coating multilayer film 113 (light reflectance: 1%) made of a titanium oxide film and an aluminum oxide film is formed on the light emitting end face 111 by using a sputtering method or the like ( (Light emission end face forming step). Further, as shown in FIG. 2D, a highly reflective coated multilayer film 114 (light reflectivity: 95%) made of a titanium oxide film and an aluminum oxide film is formed on the rear end face by using a sputtering method or the like (rear end face forming step). ). Further, the inclination angle of the light emitting end face 111 is inclined by 5 °. For this reason, the effective light reflectivity at the light exit end face 111 is about 1/100 compared with the light reflectivity when the light exit end face is a vertical end face (effective light reflectivity). : 0.01%). In the present embodiment, the optical waveguide length of the semiconductor element is 1.0 mm. The optical waveguide length is not particularly limited and is determined by desired characteristics. In this way, the SLD of this embodiment can be manufactured. However, the method for manufacturing the SLD of the present embodiment is not limited to this example. The “light emitting end face forming step” in the present embodiment corresponds to the “first end face forming step” of the present invention. The “rear end face forming step” in the present embodiment corresponds to the “second end face forming step” of the present invention.

  Next, the operational effects obtained by the present invention will be described with reference to the drawings in comparison with a comparative nitride semiconductor light emitting device. The present invention is not limited or limited by the following description.

  The graph of FIG. 3 shows the gain spectrum of the SLD of the present invention shown in Embodiment 1 and a comparative nitride semiconductor light emitting device (Comparative Object 1) obtained by simulation. Comparative object 1 is a nitride semiconductor light emitting device having the same configuration as the SLD of the present invention except that the crystal growth conditions of the active layer are different. The index of composition fluctuation of the active layer is about 10 meV. In the figure, the horizontal axis is the gain spectrum, and the unit is (nm). The vertical axis represents the gain, and the unit is an arbitrary unit (au). The solid line graph in the figure shows the SLD of the present invention. A broken line graph in FIG. As illustrated, in the SLD of the present invention and the comparison object 1, the gain peak values are substantially the same value. The operating current value at this time is smaller for the comparison target 1. In this spectrum, when the peak gain value exceeds the mirror loss and the optical loss of the optical waveguide, the oscillation operation is started. Compared with the SLD of the present invention, the comparative object 1 in which the composition fluctuation of the active layer is small can provide a high peak gain with a small current value. For this reason, when the active layer in the comparative object 1 is used as an active layer of a semiconductor laser that only needs to have a high gain in a very narrow wavelength range that contributes to oscillation, the oscillation threshold can be reduced. However, the rate of increase in peak gain (dg / dJ) with respect to the current is large in the active layer in Comparative Object 1. For this reason, it is easy to oscillate and it is difficult to suppress the oscillation. In particular, in the case of an AlGaInN-based active layer used for an element having a visible blue to green band wavelength, the state density of holes is extremely large as compared with an active layer of a GaAs-based or InP-based infrared wavelength band. For this reason, the dg / dJ tends to increase, and there is a further concern about the transition to the oscillation operation. In contrast, the active layer in the SLD of the present invention has a small rate of increase in peak gain (dg / dJ) with respect to current. For this reason, in the SLD of the present invention, incoherent light can be obtained while suppressing laser oscillation. Moreover, it has a high gain over a wide wavelength range. For this reason, the SL light output can be increased by the light emission in the entire wavelength range contributing.

  In the SLD aiming at obtaining a high output, such as the SLD described in Patent Document 2, the gain spectrum is broadened so that the rate of increase in the peak gain with respect to the current becomes small when considering further output improvement. There is a possibility that the output will be reduced. Thereby, there is a possibility of suppressing the effect of increasing the output. For this reason, it is considered unpreferable to apply the gain spectrum broadening due to the composition fluctuation or the like to the SLD described in Patent Document 2. On the other hand, in the semiconductor light emitting device of the present invention, as described above, the ratio of the peak gain increase to the current is reduced by widening the gain spectrum width. Since the semiconductor light emitting device of the present invention has a high gain over a wide wavelength range as described above, the SL light output can be increased.

  The graph of FIG. 4 shows the relationship between the injection current density and the SL light output in the SLD of the present invention, the SLD of the comparison object 1 and the comparison object 2. Comparative object 2 is a nitride semiconductor light emitting device having the same configuration as the SLD of the present invention except that the rear end face is made low reflective. In the figure, the horizontal axis represents the injection current density, and the unit is an arbitrary unit (au). The vertical axis represents the SL light output, and the unit is an arbitrary unit (au). The solid line graph in the figure shows the SLD of the present invention. A wide broken line graph in FIG. A broken line graph with a narrow interval in FIG. As shown in the drawing, in the comparison target 1, the light output rises at a current value lower than that of the SLD of the present invention. Here, in the comparative object 1, the current value at which the light output starts to increase and the current value leading to oscillation are very close. For this reason, in reality, the oscillation easily shifts to a slight change in operating conditions. As a result, a high SL light output cannot be obtained. On the other hand, in the SLD of the present invention, a larger current value is required for the optical output to rise as compared with the comparison target 1. However, the current value at which the optical output starts to increase is different from the current value that causes oscillation. For this reason, laser oscillation can be suppressed and incoherent light can be obtained. As a result, the SLD of the present invention can obtain an SL light output that is five times or more that of the nitride semiconductor light emitting device of Comparative Example 1. Here, in the comparative object 2 in which the reflectance of the rear end face is low similarly to the light emitting end face, since both the end faces have low reflectance, the possibility of oscillation is low. However, it can be seen that only a low SL light output can be obtained. Therefore, it can be seen that it is important to suppress the oscillation by widening the gain spectrum width while using the rear end face as the reflecting face.

  Here, as a light source for display, in order to ensure color reproducibility, it is necessary to maintain a certain degree of monochromaticity. For this reason, it is not preferable that the emission spectrum width is too wide. For example, in the case of a display using RGB three primary colors, in order to ensure the color reproducibility range, the wavelength peak width of each wavelength is, for example, about 20 nm or less. In SLD, if the gain spectrum width is too wide, the emission spectrum width of SL light becomes too wide. Therefore, the range of the gain spectrum width in which the optimum emission wavelength width can be obtained and the effects of the present invention can be obtained will be examined.

  When the gain spectrum width of the active layer is widened by composition fluctuation as in the SLD of the present invention, the emission wavelength width is affected by the optical waveguide length of the semiconductor element, the end face light reflectivity, and the like. First, the light emitting end face is a value in which the angle of the oblique end is within a range where the element characteristics and the like are not affected (for example, 5 °), and a non-reflective coated multilayer film having a reflectance of 1% is formed. The typical reflectance is about 0.01%. On the other hand, as shown in the graph of FIG. 5, the rear end face has an output improvement of about 10 times when the light reflectance is 20% and about 50 times when the light reflectance is 90%. I can expect. In the figure, the horizontal axis represents the light reflectance of the rear end face. The vertical axis represents the emission intensity, and the unit is 1 when the reflectance is 0. Therefore, in the present invention, the light reflectivity of the rear end face is 20% or more, and preferably 90% or more. In the present invention, the composition fluctuation is preferably 30 meV or more in order to obtain a sufficient oscillation suppressing effect with respect to the nitride semiconductor light emitting device of Comparative Example 1. Further, when the light reflectivity of the rear end face is 90% or more, the composition fluctuation is preferably about 50 meV or more. As a result, dg / dJ can be reduced and the transition to the oscillation state can be suppressed. On the other hand, regarding the emission wavelength width, for example, in the structure of this example, it is known that the emission wavelength width is about the same as the composition fluctuation to about 1.5 times. In this case, the composition fluctuation is preferably 100 meV or less in order to make the emission wavelength width 20 nm or less in the blue to green wavelength band. That is, when the gain spectrum width is expressed by composition fluctuation, the composition fluctuation is preferably in the range of 30 meV to 100 meV. The composition fluctuation is designed based on, for example, actual device characteristics or experimental values. As a result of the study by the present inventors, a good result was obtained when the full width at half maximum was in the range of 100 meV to 200 meV in the photoluminescence spectrum under strong excitation conditions.

  FIG. 6 shows the calculation result of the emission spectrum in the SLD of the present invention. In the figure, the horizontal axis is the emission spectrum, and the unit is (nm). The vertical axis represents the emission intensity, and the unit is an arbitrary unit (au). The solid line graph in the figure shows the SLD of the present invention having a composition fluctuation of 100 meV. The broken line graph in the figure shows the SLD of the present invention having a composition fluctuation of 50 meV. As shown in the figure, the wavelength width in the SLD of the present invention having a composition fluctuation of 100 meV is 19 nm. The wavelength width in the SLD of the present invention having a composition fluctuation of 50 meV is 9 nm. Any of the SLDs of the present invention can be said to be an SLD having a wavelength characteristic that satisfies the requirement of monochromaticity as a light source for display. In SLD, there is a case where vibration of a spectrum called ripple due to a resonance effect occurs. However, since the resolution of the wavelength perceived by the eye is wide, the occurrence of ripple due to a small wavelength difference is not a problem in applications such as displays. Moreover, the application of the semiconductor light emitting device of the present invention is not particularly limited.

  The SLD described in the above-mentioned Patent Document 1 is intended to present a wide light spectrum emission characteristic having a spectral half width of a predetermined value or more. For this reason, in the SLD described in Patent Document 1 described above, controlling the light reflectance of both end faces as described above (the emission spectrum is narrowed) is described in Patent Document 1 in which the light spectrum is widened. Contrary to the purpose of SLD. For this reason, it is considered that it is not preferable to apply the above-described control of the light reflectance of both end faces to the SLD of Patent Document 1. On the other hand, as described above, the semiconductor light emitting device of the present invention can suppress laser oscillation and obtain incoherent light by widening the gain spectrum width. Further, as described above, for example, the light emitting wavelength width of the semiconductor light emitting device of the present invention is preferably narrow to some extent (for example, 10 to 20 nm) in order to satisfy the requirement of monochromaticity as a light source for display. Here, the emission spectrum can be narrowed to some extent by making the above-mentioned light emitting end face low reflective and making the above-mentioned rear end face highly reflective. Therefore, in the present invention, it is preferable to control the light reflectance of both end faces as described above.

  In the above description, the method of controlling the composition fluctuation in the InGaN active layer by changing the crystal growth condition is described as an example of the method for expanding the gain spectrum width of the active layer. However, the present invention is not limited to this example. With a method that relaxes the sharp peak characteristics of the gain spectrum and is flattened near the peak, incoherent light can be obtained by suppressing laser oscillation while maintaining the emission intensity of the entire gain spectrum. Since it can do, it is more preferable.

  As a method for flattening the gain spectrum width near the peak, for example, there is a method using a plurality of quantum well layers having different thicknesses or compositions. For example, in a blue or green InGaN double quantum well (DQW), when providing a wavelength difference in the transition wavelength of each quantum well layer, the wavelength difference in the range of 10 to 20 nm is set due to the limitation of the emission wavelength width described above. It is preferable to provide it. When the quantum level is changed by changing the thickness of each quantum well layer, the difference in thickness in the range of 0.5 to 1.5 nm corresponds to the wavelength difference (10 to 20 nm) in each quantum well layer. . For this reason, it is preferable to use the DQW having a thickness of 2 nm and 3 nm, for example. When the indium composition of each quantum well layer is changed, the amount of change in the In composition in the range of 0.01 to 0.03 corresponds to the wavelength difference (10 to 20 nm) in each quantum well layer. Therefore, for example, in the case of a blue band, the DQW having In compositions of 0.2 and 0.22 can be used.

  In addition, in the case of blue or green InGaN quantum well layers, it is known that the indium composition changes locally even if the quantum well layers are produced under the same crystal growth conditions when the off-angle of the substrate is different (for example, JP 2009-49221 A). Therefore, the gain spectrum width can be widened by performing the crystal growth by providing the off-angle distribution of the substrate in the plane where the optical waveguide exists. As a result of studies by the present inventors, it has been found that in the blue to green wavelength band, a wavelength difference of about 5 to 10 nm is obtained when the off-angle difference is 0.1 °. Since the wavelength difference varies depending on crystal growth conditions and the like, the above description does not limit or limit the present invention. In order to obtain a desired gain spectrum width, it is preferable to use a substrate having an off-angle distribution of 0.1 ° to 0.4 °. In the case of using this substrate, for example, in the optical waveguide forming process shown in FIG. 2A, the above-mentioned off-angle distribution can be set by using a GaN substrate processed with a step with an appropriate aspect ratio. As a result, a desired gain spectrum width can be obtained. The step-processed GaN substrate is manufactured as follows, for example. That is, first, a striped etching mask having a width of 10 μm and a pitch of 20 μm is formed on an n-type GaN substrate by using a normal photolithography process. Using this mask, for example, etching is performed to a depth of 30 nm by performing dry etching using a chlorine-based gas. By this etching, a shallow mesa stripe having a width of 10 μm is formed. This mesa stripe has a convex mesa structure composed of a first portion having a higher surface on which a mask is disposed and a second portion having a lower surface by etching. In this way, the step-processed GaN substrate can be produced. Next, after removing the etching mask, an n-type AlGaN buffer layer is laminated on the n-type GaN substrate by the MOVPE method or the like. By laminating the n-type AlGaN buffer layer by about 0.5 μm, a substrate in which the stepped portion is embedded in a slope shape and the off angle continuously changes is formed. In this case, a base substrate having an off-angle distribution that gradually changes to approximately 0.2 ° near the center of the flat portion and gradually changes to approximately 0.5 ° at the slope portion is formed. Here, the surface of the n-type GaN substrate is inclined by about 0.2 ° from the c-plane. In an InGaN quantum well layer and the like grown on a substrate having such an off-angle distribution, depending on the growth conditions and wavelength band, the portion with a large off angle has a greater indium composition than the portion with a small off angle. Smaller and shorter wavelength. By using such a substrate and forming an optical waveguide so as to intersect with a stepped stripe formed on the substrate, a semiconductor light emitting device having a wide gain spectrum width can be manufactured. The method for manufacturing the step-processed GaN substrate or the step shape is not limited to this example. Moreover, you may produce the board | substrate which has off-angle distribution using another method.

  In the present invention, any method may be used as long as the active layer has a gain generation region and the gain wavelength generated in the gain generation region can be non-uniform. For example, when a strained InGaN quantum well layer is grown on a polar plane substrate, the gain spectrum width can be widened by the internal electric field effect. In this case, for example, in order to increase the thickness of the quantum well layer or to increase the influence of the strain, by using the reverse strain AlGaN barrier layer, the internal electric field effect can be used positively. It is possible to widen a single spectrum. Compared with an active layer used in a normal semiconductor laser, the light emission intensity in the entire spectrum can be maintained while lowering the peak gain dg / dJ by devising to widen the gain spectrum width. It is possible to suppress the shift to laser oscillation and improve the characteristics of the SLD element.

  In the embodiment and the examples described later, the case where the optical waveguide length is 1.0 mm, the light reflectivity of the rear end face is 95%, and the optical waveguide width is 2 μm has been described as an example. However, the present invention is not limited to this example. In the semiconductor light emitting device of the present invention, it is important for high output design to provide an appropriate effective waveguide length (gain length) according to the gain of the active layer. That is, as the gain increases, the effect of increasing the effective waveguide length increases. On the other hand, since it is close to the oscillation condition, a design corresponding to the active layer is required. In the InGaN-based quantum well active layer as in the above embodiment, if the optical reflectivity of the rear end face is 50% or more, the optical waveguide length is about 0.5 mm or more, and almost sufficient light output is obtained. Estimated. Further, the light reflectivity of the rear end face is preferably closer to 100%, but it is estimated that a sufficient effect can be obtained at 20% or more as described above.

  In the embodiment and the examples described later, the optical waveguide width (ridge waveguide width) is 2 μm. The reason for this setting is that an element that optically emits a single mode beam is desirable when used as a light source for a projection display by mirror scanning. However, the present invention is not limited to this example. For example, when priority is given to higher output, or when the mode characteristics of the beam are not limited, it is possible to use a wider optical waveguide or a tapered optical waveguide.

  Further, in the embodiment and the examples to be described later, the angle of the light emitting end surface which is an oblique end is described as 5 °. However, the present invention is not limited to this example. In the semiconductor light emitting device of the present invention, as described above, by increasing the gain spectrum width of the active layer, laser oscillation can be suppressed and incoherent light can be obtained with high output. For this reason, for example, it is not necessary to set the angle of the oblique end to 7 ° or more unlike the SLD described in Patent Document 2 described above (for example, in the embodiment and the examples described later, the angle of the oblique end is 5 °). Is). As described above, since it is not necessary to set a large oblique end angle in order to suppress laser oscillation, it is possible to suppress degradation of beam quality that may occur when the oblique end angle is large, such as the beam shape being left-right asymmetric. Thus, the beam quality can be maintained. In order to maintain the above-mentioned beam quality by reducing the angle of the oblique end, it is necessary to control the light reflectivity to be extremely low by a non-reflective coating on the light exit end face. However, with respect to the manufacturing accuracy of a general coating film that does not use special film thickness control, the light reflectance that can be stably obtained with the wavelength controllability taken into consideration is, for example, about 0.5%. For this reason, as in the present invention, without increasing the gain spectrum width of the active layer, the light reflectance (for example, low enough to suppress oscillation stably in a desired wavelength range corresponding to the SL light output) In order to realize (0.001% or less), at least an oblique end must be used, for example, an angle of 7 ° or more. It is practically difficult to realize a sufficiently low light reflectance at an angle shallower than this. Therefore, in the case of an angle shallower than this, there is a concern that the oscillation operation is easily shifted. For example, in the above-described comparison object 1 (the angle of the oblique end is 5 °), the oscillation operation is easily performed. For example, when a non-reflective coating is applied to a 5 ° oblique end, which is considered to have a small effect on beam quality, a light reflectance (effective light reflectance) of about 0.005% is a realistic range. It is thought that. The semiconductor light-emitting device of the present invention can obtain incoherent light with high output by suppressing laser oscillation while maintaining beam quality within such a practical range. As a result, the semiconductor light-emitting device of the present invention is effective as a low-cost and compact display light source that can reduce speckle while maintaining beam quality, for example. Note that the present invention is not limited to this example.

  Further, the angle of the oblique end of the light emitting end face is preferably set in consideration of beam characteristics or ease of mounting and a desired effective light reflectance value. The optimum value varies depending on the gain characteristic or refractive index of the active layer. On the other hand, when the angle is less than 2 °, the effect of reducing the light reflectance by the oblique end becomes small. For this reason, the effect of suppressing oscillation according to the present invention is also reduced. However, this is not the case when a highly accurate non-reflective coating is possible or when an oscillation suppressing means is provided in addition to the light reflecting film. The light emitting end face may be, for example, a vertical end face. On the other hand, from the viewpoint of beam quality, even in the configurations shown in the embodiments and the examples described later, if the angle is 10 ° or less, the problem of left-right asymmetry of the beam shape can be suppressed. Further, from the viewpoint of the beam emission direction, in the GaN-based materials used in the embodiments and examples, SL light is emitted in an angle direction that is about 2.2 times the angle of the light emission end face. That is, when the angle is 5 °, the light is emitted in the direction of about 11 °. When mounting on an optical system, the mounting is performed by inclining this angle. Considering this point, from the viewpoint of beam quality, the angle of the light exit end face is preferably less than 7 °. As described above, in the present invention, the oblique end angle of the light emitting end face is, for example, in the range of 2 ° or more and less than 7 °. In this case, particularly SL light can be obtained effectively.

  The embodiments of the present invention have been described above. However, the present invention is not limited to the configurations and methods specifically shown in these embodiments, and various variations are conceivable as long as they are within the spirit of the invention. For example, in the above embodiment, an example of a nitride blue semiconductor laser (SLD) using an InGaN quantum well as an active layer is adopted. However, the present invention is not limited to this example. The present invention can also be applied to other visible light sources for displays such as AlGaInP red semiconductor light emitting elements or nitride green semiconductor light emitting elements. However, in display applications, it is important to reduce speckle in a green light source having the highest visibility among RGB. For this reason, the significance of applying the present invention to a nitride semiconductor capable of emitting light in this wavelength band is great.

  Next, the operational effects obtained by the present invention will be described by comparison with a comparative example. The present invention is not limited or restricted by the following examples and comparative examples.

[Example 1]
The SLD 100 shown in FIG. 1 was produced. That is, the optical waveguide forming step, the ridge waveguide forming step, the insulating film forming step, the electrode forming step, the light emitting end surface forming step, and the rear end surface forming step were performed to produce the SLD 100 of this example. . The index of composition fluctuation of the active layer in this SLD 100 was 100 meV. The light reflectance of the light emitting end face 111 was 1%. The light reflectance of the rear end face 112 was 95%. The oblique angle of the light emitting end face 111 was 5 °. The optical waveguide length was 1.0 mm. The SLD in this example corresponds to the “SLD of the present invention in which the composition fluctuation is 100 meV” in the above-described simulation.

[Example 2]
An SLD of this example was fabricated in the same manner as in Example 1 except that the active layer was formed so that the composition fluctuation index of the active layer was 50 meV. The SLD in this example corresponds to the “SLD of the present invention in which the composition fluctuation is 50 meV” in the above-described simulation.

[Comparative Example 1]
A nitride semiconductor light emitting device of this comparative example was fabricated in the same manner as in Example 1 except that the crystal growth conditions of the active layer were different. The index of composition fluctuation of the active layer was about 10 meV. The nitride semiconductor light emitting device of this comparative example corresponds to “Comparison 1” in the above-described simulation.

[Comparative Example 2]
A nitride semiconductor light emitting device of this comparative example was fabricated in the same manner as in Example 1 except that the reflective coat multilayer film was not formed on the rear end face. The nitride semiconductor light emitting device of this comparative example corresponds to “Comparison 2” in the above-described simulation.

  The gain spectra of Example 1 and Comparative Example 1 were measured. This measurement result was in good agreement with the result obtained by the theoretical calculation shown in the graph of FIG.

  In Example 1, Comparative Example 1 and Comparative Example 2, the SL light output according to the injection current density was measured. This measurement result was in good agreement with the result obtained by the theoretical calculation shown in the graph of FIG.

  The emission spectra in Example 1 and Example 2 were measured. This measurement result was in good agreement with the result obtained by the theoretical calculation shown in FIG.

  The semiconductor light emitting device of the present invention can obtain incoherent light with high output by suppressing laser oscillation while maintaining beam quality. Therefore, the semiconductor light-emitting device of the present invention can be used as a semiconductor light-emitting device having beam characteristics and emission wavelength width suitable for display applications, in which speckle can be reduced particularly with a single light source. Moreover, the semiconductor light emitting device of the present invention can be used as, for example, a visible light semiconductor light emitting device used as a light source for general displays (image display devices). The semiconductor light emitting device of the present invention preferably emits light in a visible light wavelength band (for example, 400 to 750 nm), more preferably emits light in a blue to red visible light wavelength band (for example, 430 to 750 nm), and blue. It is particularly preferable to emit light in a green visible light wavelength band (for example, 430 to 570 nm). As described above, the light source for the image display device of the present invention includes the semiconductor light emitting element of the present invention, and the image display device of the present invention includes the light source for the image display device of the present invention. To do. As the image display device of the present invention, for example, a laser projector (laser display) is preferable. According to the laser projector (laser display) of the present invention, for example, it is possible to obtain effects such as dramatic improvement in color reproducibility, energy saving and low cost, large screen and high definition, and ultra-compact optical system. It is. Specifically, the laser projector (laser display) of the present invention includes, for example, a mobile projector, a next generation rear projection TV (digital projection), a digital cinema, a retina scanning display (RSD), a head-up display ( An HUD (Head Up Display) or a built-in projector for a mobile phone, a digital camera, a notebook personal computer, and the like can be used, and application to a wide range of markets is possible. Further, the semiconductor light emitting device of the present invention is not limited to an image display device. For example, the semiconductor light emitting device may be used as a light emitting device for products such as optical coherence tomography (OCT), optical fiber gyroscope, and optical fiber break point detection. It can be used. Therefore, the semiconductor light-emitting device of the present invention can be applied to a wide range of fields such as the medical / bio field and various sensing fields.

  A part or all of the above embodiment can be described as in the following supplementary notes, but is not limited to the following.

(Additional remark 1) It has an optical waveguide,
The optical waveguide includes an active layer, a first end surface, and a second end surface,
The first end face is provided at one end of the optical waveguide;
The second end surface is provided at the other end of the optical waveguide;
The light reflectance of the first end face in the wavelength range of the emitted light is 1% or less,
The light reflectance of the second end face in the wavelength range of the emitted light is 20% or more,
The active layer has a gain generation region,
A semiconductor light emitting device characterized in that a gain wavelength generated in the gain generation region is non-uniform.

(Supplementary note 2) The semiconductor light emitting element according to supplementary note 1, wherein an effective light reflectance of the first end face is 0.005% or more.

(Additional remark 3) The said 1st end surface inclines from the plane orthogonal to the advancing direction of the said optical waveguide in the end surface, The angle of the said inclination is less than 7 degrees, The additional remark 1 or 2 characterized by the above-mentioned. The semiconductor light-emitting device described in 1.

(Supplementary Note 4) The gain generation region in the active layer is formed of Al _x Ga _y In _1-xy N (0 ≦ x <1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1),
4. The semiconductor light emitting element according to any one of appendices 1 to 3, wherein at least one of x and y is not uniform in the gain generation region.

(Supplementary Note 5) The gain generation region in the active layer is formed of Al _x Ga _y In _1-xy N (0 ≦ x <1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1), and The semiconductor light-emitting element according to appendix 4, wherein the composition fluctuation is in the range of 30 to 100 meV in terms of emission energy.

(Appendix 6) Further, it has a substrate,
The optical waveguide is formed on the substrate;
The gain generation region in the active layer is formed of Al _x Ga _y In _1-xy N (0 ≦ x <1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1),
6. The semiconductor light emitting device according to appendix 4 or 5, wherein off-angles of the substrate are distributed with a width of 0.1 to 0.4 °.

(Supplementary note 7) The semiconductor light-emitting element according to any one of Supplementary notes 1 to 6, which is a superluminescent diode.

(Additional remark 8) The optical waveguide formation process which forms an optical waveguide is included,
The optical waveguide forming step includes an active layer forming step for forming an active layer, a first end face forming step for forming a first end face, and a second end face forming step for forming a second end face,
In the first end face forming step,
Forming the first end face so that the light reflectance in the wavelength region of the emitted light is 1% or less;
In the second end face forming step,
Forming the second end face so that the light reflectance in the wavelength region of the emitted light is 20% or more;
In the active layer forming step,
A method of manufacturing a semiconductor light emitting device, comprising: forming an active layer having the gain generation region where the gain wavelength generated in the gain generation region is non-uniform.

(Supplementary note 9) The method for manufacturing a semiconductor light-emitting element according to supplementary note 8, wherein an effective light reflectance of the first end face is 0.005% or more.

(Supplementary Note 10) In the first end face forming step,
10. The semiconductor light-emitting element according to appendix 8 or 9, wherein the first end face is inclined from a plane perpendicular to the traveling direction of the optical waveguide at the end face, and the inclination angle is less than 7 °. Production method.

(Supplementary Note 11) In the active layer formation step, the gain generation region in the active layer from Al _x Ga _y In _1-xy N (0 ≦ x <1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) Form the
11. The method for manufacturing a semiconductor light-emitting element according to any one of appendices 8 to 10, wherein in the gain generation region, at least one of x and y is not uniform.

(Supplementary Note 12) In the active layer forming step,
The gain generation region in the active layer is formed from Al _x Ga _y In _1-xy N (0 ≦ x <1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1), and the composition fluctuation is The method for producing a semiconductor light-emitting element according to appendix 11, wherein the emission energy is in the range of 30 to 100 meV.

(Supplementary note 13) In the optical waveguide forming step,
The optical waveguide is formed on a substrate having an off-angle distributed with a width of 0.1 to 0.4 °,
In the active layer forming step,
Additional remark 11 or forming the gain generating region in the active layer from Al _x Ga _y In _1-xy N (0 ≦ x <1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) 12. A method for producing a semiconductor light-emitting device according to 12.

(Additional remark 14) It is set as a super luminescent diode, The manufacturing method of the semiconductor light-emitting device as described in any one of Claim 8 to 13 characterized by the above-mentioned.

(Supplementary note 15) Light source for an image display device comprising the semiconductor light-emitting device according to any one of supplementary notes 1 to 7 or the semiconductor light-emitting device produced by the production method according to any one of supplementary notes 8 to 14 .

(Additional remark 16) The image display apparatus characterized by including the light source for image display apparatuses of Additional remark 15.

(Supplementary note 17) The image display device according to supplementary note 16, which is a laser projector.

100 Superluminescent diode (semiconductor light emitting device)
101 n-type GaN substrate (substrate)
102 n-type AlGaN cladding layer 103 InGaN lower optical waveguide layer 104 InGaN / GaN quantum well active layer (active layer)
104a InGaN quantum well layer 104b InGaN barrier layer 105 InGaN upper optical waveguide layer 106 p-type AlGaN cladding layer 107 p-type GaN contact layer 108 p-side electrode 109 n-side electrode 110 Insulating film 111 Light emitting end face (first end face)
112 Rear end face (second end face)
113 Non-reflective coated multilayer film 114 Reflective coated multilayer film 115 Ridge waveguide (optical waveguide)

Claims (10)

Having an optical waveguide,
The optical waveguide includes an active layer, a first end surface, and a second end surface,
The first end face is provided at one end of the optical waveguide;
The second end surface is provided at the other end of the optical waveguide;
The light reflectance of the first end face in the wavelength range of the emitted light is 1% or less,
The light reflectance of the second end face in the wavelength range of the emitted light is 20% or more,
The active layer has a gain generation region,
A semiconductor light emitting device characterized in that a gain wavelength generated in the gain generation region is non-uniform. 2. The semiconductor light emitting element according to claim 1, wherein an effective light reflectance of the first end face is 0.005% or more. 3. The semiconductor according to claim 1, wherein the first end face is inclined from a plane perpendicular to the traveling direction of the optical waveguide at the end face, and the inclination angle is less than 7 °. Light emitting element. The gain generation region in the active layer is formed of Al _x Ga _y In _1-xy N (0 ≦ x <1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1),
4. The semiconductor light emitting element according to claim 1, wherein at least one of x and y is not uniform in the gain generation region. 5. The gain generation region in the active layer is formed of Al _x Ga _y In _1-xy N (0 ≦ x <1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1), and the composition fluctuation is 5. The semiconductor light emitting device according to claim 4, wherein the light emission energy is in the range of 30 to 100 meV. Furthermore, it has a substrate,
The optical waveguide is formed on the substrate;
The gain generation region in the active layer is formed of Al _x Ga _y In _1-xy N (0 ≦ x <1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1),
6. The semiconductor light emitting device according to claim 4, wherein off-angles of the substrate are distributed with a width of 0.1 to 0.4 [deg.]. The semiconductor light-emitting device according to claim 1, wherein the semiconductor light-emitting device is a superluminescent diode. Including an optical waveguide forming step of forming an optical waveguide;
The optical waveguide forming step includes an active layer forming step for forming an active layer, a first end face forming step for forming a first end face, and a second end face forming step for forming a second end face,
In the first end face forming step,
Forming the first end face so that the light reflectance in the wavelength region of the emitted light is 1% or less;
In the second end face forming step,
Forming the second end face so that the light reflectance in the wavelength region of the emitted light is 20% or more;
In the active layer forming step,
A method of manufacturing a semiconductor light emitting device, comprising: forming an active layer having the gain generation region where the gain wavelength generated in the gain generation region is non-uniform. A light source for an image display device comprising the semiconductor light emitting device according to claim 1 or the semiconductor light emitting device manufactured by the manufacturing method according to claim 8. An image display device comprising the light source for an image display device according to claim 9.

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