WO2011077849A1 - Iii族窒化物半導体レーザ素子、iii族窒化物半導体レーザ素子を作製する方法、及びエピタキシャル基板 - Google Patents
Iii族窒化物半導体レーザ素子、iii族窒化物半導体レーザ素子を作製する方法、及びエピタキシャル基板 Download PDFInfo
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- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
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- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
- H01S5/343—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser
- H01S5/34333—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser with a well layer based on Ga(In)N or Ga(In)P, e.g. blue laser
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- H01S5/00—Semiconductor lasers
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/32—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures
- H01S5/3202—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures grown on specifically orientated substrates, or using orientation dependent growth
- H01S5/320275—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures grown on specifically orientated substrates, or using orientation dependent growth semi-polar orientation
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- H01S5/00—Semiconductor lasers
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
- H01S5/343—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser
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- H—ELECTRICITY
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- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/02—Structural details or components not essential to laser action
- H01S5/0201—Separation of the wafer into individual elements, e.g. by dicing, cleaving, etching or directly during growth
- H01S5/0202—Cleaving
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- H—ELECTRICITY
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- H01S5/00—Semiconductor lasers
- H01S5/02—Structural details or components not essential to laser action
- H01S5/0206—Substrates, e.g. growth, shape, material, removal or bonding
- H01S5/0207—Substrates having a special shape
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- H—ELECTRICITY
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- H01S5/00—Semiconductor lasers
- H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
- H01S5/22—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure
- H01S5/2201—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure in a specific crystallographic orientation
Definitions
- the present invention relates to a group III nitride semiconductor laser device, a method for manufacturing a group III nitride semiconductor laser device, and an epitaxial substrate.
- Patent Document 1 describes a laser device. If the surface inclined at 28.1 degrees from the ⁇ 0001 ⁇ plane toward the direction equivalent to the [1-100] direction is the main surface of the substrate, the secondary cleavage surface is both the main surface and the optical resonator surface. The ⁇ 11-20 ⁇ plane is perpendicular to the surface, and the laser device has a rectangular parallelepiped shape.
- Patent Document 2 describes a nitride semiconductor device.
- the back surface of the substrate for cleavage is polished to reduce the total thickness to about 100 ⁇ m.
- a dielectric multilayer film is deposited on the cleavage plane.
- Patent Document 3 describes a nitride-based compound semiconductor element.
- the substrate used for the nitride-based compound semiconductor element is made of a nitride-based compound semiconductor having a threading dislocation density of 3 ⁇ 10 6 cm ⁇ 2 or less, and the threading dislocation density is substantially uniform in the plane.
- Patent Document 4 describes a nitride semiconductor laser element.
- a cleavage plane is formed as follows. Using a laser scriber while avoiding the protrusions formed during the etching process of the resonator surface of the n-type GaN substrate with respect to the recesses formed by the etching process so as to reach the n-type GaN substrate from the semiconductor laser element layer
- the scribe grooves are formed in a broken line shape (at intervals of about 40 ⁇ m) in a direction orthogonal to the direction in which the ridge portion extends. Then, the wafer is cleaved at the position of the scribe groove.
- each element isolation surface is formed as a cleavage plane made of the (0001) plane of the n-type GaN substrate.
- Patent Document 5 describes a light emitting element. According to the light emitting element, long wavelength light emission can be easily obtained without impairing the light emission efficiency in the light emitting layer.
- Non-Patent Document 1 describes a semiconductor laser in which a waveguide is provided in the off direction on a semipolar (10-1-1) plane and a mirror is formed by a reactive ion etching method.
- the band structure of a gallium nitride semiconductor there are several transitions capable of laser oscillation.
- the laser beam is guided along a plane defined by the c-axis and the m-axis.
- the threshold current can be lowered when extending the waveguide.
- the mode with the smallest transition energy difference between conduction band energy and valence band energy
- the threshold is set. The current can be lowered.
- a conventional cleavage plane such as c-plane, a-plane or m-plane cannot be used for the resonator mirror.
- the dry etching surface of the semiconductor layer has been formed using reactive ion etching (RIE) for the fabrication of the resonator mirror.
- RIE reactive ion etching
- a resonator mirror formed by the RIE method is desired to be improved in terms of perpendicularity to a laser waveguide, flatness of a dry etching surface, or ion damage.
- derivation of process conditions for obtaining a good dry etching surface at the current technical level is a heavy burden.
- Another object of the present invention is to provide a group III nitride semiconductor laser device having a structure that can be improved, and to provide a method for manufacturing the group III nitride semiconductor laser device.
- Another object of the present invention is to provide an epitaxial substrate for the group III nitride semiconductor laser device.
- a group III nitride semiconductor laser device includes: (a) a support base made of a hexagonal group III nitride semiconductor and having a semipolar main surface; and the semipolar main surface of the support base A laser structure including the semiconductor region provided; and (b) an electrode provided on the semiconductor region of the laser structure.
- the semiconductor region includes a first cladding layer made of a gallium nitride semiconductor of a first conductivity type, a second cladding layer made of a gallium nitride semiconductor of a second conductivity type, the first cladding layer, and the first cladding layer.
- the first cladding layer, the second cladding layer and the active layer are arranged along a normal axis of the semipolar main surface.
- the active layer includes a gallium nitride based semiconductor layer, and the c-axis of the hexagonal group III nitride semiconductor of the support base is the normal axis in the direction of the m axis of the hexagonal group III nitride semiconductor.
- the laser structure is inclined at a finite angle ALPHA, and the laser structure intersects the mn plane defined by the m-axis and the normal axis of the hexagonal group III nitride semiconductor.
- the group III nitride semiconductor laser The laser resonator of the element includes the first and second fractured surfaces, the laser structure includes first and second surfaces, and the first surface is a surface opposite to the second surface.
- the first and second fractured surfaces extend from an edge of the first surface to an edge of the second surface.
- the angle formed between the normal axis and the c axis of the hexagonal group III nitride semiconductor is in the range of not less than 45 degrees and not more than 80 degrees, or not less than 100 degrees and not more than 135 degrees.
- the laser structure includes a laser waveguide extending on the semipolar main surface of the support base, wherein the laser waveguide is in a direction from one to the other of the first and second fractured faces.
- the c-axis vector extending in the direction of the waveguide vector directed to and indicating the c-axis direction of the hexagonal group III nitride semiconductor is parallel to the projection component parallel to the semipolar principal surface and the normal axis.
- the deviation angle between the waveguide vector and the projection component can be in the range of not less than ⁇ 0.5 degrees and not more than +0.5 degrees.
- an angle formed between the normal axis and the c axis of the hexagonal group III nitride semiconductor is in a range of 45 degrees to 80 degrees or 100 degrees to 135 degrees.
- the laser structure includes a laser waveguide extending on the semipolar main surface of the support base, wherein the laser waveguide is in a direction from one to the other of the first and second fractured faces.
- the laser structure exhibits a streaky emission image extending in the direction of a predetermined axis in a fluorescence microscope image by light excitation by a mercury lamp, and the laser structure exhibits a streak emission image extending in the direction of the waveguide vector
- the misalignment angle formed with the orthogonal direction perpendicular to the axis is in the range of not less than ⁇ 0.5 degrees and not more than +0.5 degrees.
- the first and second fractured sections serving as laser resonators are in the mn plane defined by the m axis and the normal axis of the hexagonal group III nitride semiconductor. Since they intersect, a laser waveguide extending in the direction of the intersecting line between the mn plane and the semipolar plane can be provided. Therefore, a group III nitride semiconductor laser device having a laser resonator that enables a low threshold current can be provided.
- this group III nitride semiconductor laser device at an angle of less than 45 degrees and greater than 135 degrees, there is a high possibility that the end face formed by pressing is an m-plane. Further, when the angle is more than 80 degrees and less than 100 degrees, the desired flatness and perpendicularity may not be obtained.
- the deviation angle when the deviation angle is in the range of not less than ⁇ 0.5 degrees and not more than +0.5 degrees, the oscillation yield is improved. Further, when the deviation angle is in the range of not less than ⁇ 0.3 degrees and not more than +0.3 degrees, the threshold variation is improved.
- an angle formed between the normal axis and the c axis of the hexagonal group III nitride semiconductor is 63 degrees or more and 80 degrees or less, or 100 degrees or more and 117 degrees. The following range is even better.
- this group III nitride semiconductor laser device in the range of 63 degrees to 80 degrees or 100 degrees to 117 degrees, there is a high possibility that the end face formed by pressing is nearly perpendicular to the substrate main surface. Become. Further, when the angle is more than 80 degrees and less than 100 degrees, the desired flatness and perpendicularity may not be obtained.
- the thickness of the support base is preferably 400 ⁇ m or less. This group III nitride semiconductor laser device is good for obtaining a high-quality fractured surface for a laser resonator.
- the thickness of the support base is not less than 50 ⁇ m and not more than 100 ⁇ m.
- the thickness is 50 ⁇ m or more, handling becomes easy and production yield is improved. If it is 100 ⁇ m or less, it is even better to obtain a high-quality fractured surface for the laser resonator.
- the laser light from the active layer is polarized in the a-axis direction of the hexagonal group III nitride semiconductor.
- a band transition capable of realizing a low threshold current has polarization.
- light in the LED mode in the group III nitride semiconductor laser device is polarized with the polarization component I1 in the direction of the a-axis of the hexagonal group III nitride semiconductor.
- the polarization component I2 is included in a direction in which the c-axis of the hexagonal group III nitride semiconductor is projected onto the principal surface, and the polarization component I1 is larger than the polarization component I2. According to this group III nitride semiconductor laser element, light having a large emission intensity in the LED mode can be laser-oscillated using the laser resonator.
- the semipolar principal surface includes ⁇ 20-21 ⁇ plane, ⁇ 10-11 ⁇ plane, ⁇ 20-2-1 ⁇ plane, and ⁇ 10- 1-1 ⁇ plane.
- the first and second flatness and perpendicularity sufficient to configure the laser resonator of the group III nitride semiconductor laser device on these typical semipolar planes.
- Two end faces can be provided.
- the semipolar principal surface includes ⁇ 20-21 ⁇ plane, ⁇ 10-11 ⁇ plane, ⁇ 20-2-1 ⁇ plane, and ⁇ 10- A surface having a slight inclination in a range of ⁇ 4 degrees to +4 degrees in the m-plane direction from any semipolar plane of the 1-1 ⁇ plane is also good as the main plane.
- the flatness and perpendicularity sufficient to configure the laser resonator of the group III nitride semiconductor laser device on the slightly inclined surface from these typical semipolar planes.
- the stacking fault density of the support substrate is preferably 1 ⁇ 10 4 cm ⁇ 1 or less.
- the stacking fault density is 1 ⁇ 10 4 cm ⁇ 1 or less, there is a low possibility that the flatness and / or the perpendicularity of the fractured section will be disturbed due to accidental circumstances.
- the support base may be made of any one of GaN, AlGaN, AlN, InGaN, and InAlGaN.
- the first and second end faces that can be used as a resonator can be obtained.
- an AlN substrate or an AlGaN substrate the degree of polarization can be increased, and light confinement can be enhanced by a low refractive index.
- an InGaN substrate the lattice mismatch rate between the substrate and the light emitting layer can be reduced, and the crystal quality can be improved.
- the group III nitride semiconductor laser device may further include a dielectric multilayer film provided on at least one of the first and second fractured faces.
- an end face coat can be applied to the fracture surface.
- the reflectance can be adjusted by the end face coating.
- the active layer may include a quantum well structure provided to generate light having a wavelength of 360 nm to 600 nm.
- This group III nitride semiconductor laser device can obtain a group III nitride semiconductor laser device that effectively utilizes polarized light in the LED mode by utilizing a semipolar plane, and can obtain a low threshold current.
- the active layer includes a quantum well structure provided to generate light having a wavelength of 430 nm or more and 550 nm or less.
- This group III nitride semiconductor laser device can improve quantum efficiency by reducing the piezoelectric field and improving the crystal quality of the light emitting layer region by utilizing a semipolar plane, and can generate light with a wavelength of 430 nm to 550 nm. good.
- an end face of the support base and an end face of the semiconductor region appear in each of the first and second fractured faces
- the angle formed between the end face of the active layer and the reference plane perpendicular to the m-axis of the support base made of the hexagonal nitride semiconductor is a first plane defined by the c-axis and the m-axis of the group III nitride semiconductor.
- the angle is in the range of (ALPHA-5) degrees to (ALPHA + 5) degrees.
- This group III nitride semiconductor laser device has an end face that satisfies the above-described perpendicularity with respect to an angle taken from one of the c-axis and the m-axis to the other.
- the angle is preferably in the range of ⁇ 5 degrees to +5 degrees in the first plane and the second plane orthogonal to the normal axis.
- This group III nitride semiconductor laser device has an end face that satisfies the above-mentioned perpendicularity with respect to an angle defined in a plane perpendicular to the normal axis of the semipolar plane.
- the electrode extends in the direction of a predetermined axis, and the first and second fractured surfaces intersect the predetermined axis.
- Another aspect of the present invention relates to a method for manufacturing a group III nitride semiconductor laser device.
- This method includes (a) a step of preparing a substrate made of a hexagonal group III nitride semiconductor and having a semipolar main surface; and (b) a semiconductor region formed on the semipolar main surface and the substrate.
- Forming a substrate product having a laser structure, an anode electrode, and a cathode electrode comprising (c) a first surface of the substrate product in the direction of the a-axis of the hexagonal group III nitride semiconductor; A step of partially scribing; and (d) separating the substrate product by pressing the substrate product against a second surface to form another substrate product and a laser bar.
- the first surface is a surface opposite to the second surface
- the semiconductor region is located between the first surface and the substrate
- the laser bar extends from the first surface to the first surface.
- the first and second end faces extending to the second face and formed by the separation, wherein the first and second end faces constitute a laser resonator of the group III nitride semiconductor laser element,
- An anode electrode and a cathode electrode are formed on the laser structure, and the semiconductor region is formed of a first cladding layer made of a first conductivity type gallium nitride semiconductor and a second conductivity type gallium nitride semiconductor.
- the active layer includes a gallium nitride based semiconductor layer, and the c-axis of the hexagonal group III nitride semiconductor of the substrate is in the direction of the m axis of the hexagonal group III nitride semiconductor with respect to the normal axis.
- the first and second end faces intersect the mn plane defined by the m-axis and the normal axis of the hexagonal group III nitride semiconductor.
- the angle formed between the normal axis and the c-axis of the hexagonal group III nitride semiconductor is in a range of 45 degrees to 80 degrees or 100 degrees to 135 degrees
- the laser structure includes the substrate A laser waveguide extending on a semipolar main surface, the laser waveguide extending in a direction of a waveguide vector directed from one to the other of the first and second fractured faces
- the c-axis vector indicating the direction of the c-axis of the hexagonal group III nitride semiconductor includes a projection component parallel to the semipolar principal surface and a vertical component parallel to the normal axis, and the waveguide vector and the The misalignment angle formed with the projection component is in the range of not less than ⁇ 0.5 degrees and not more than +0.5 degrees
- the semiconductor region of the substrate product indicates the direction of the a-axis of the hexagonal group III nitride semiconductor.
- the substrate product extends on the semipolar main surface of the substrate.
- the laser waveguide extends in a direction of a waveguide vector directed from one to the other of the first and second fractured faces. The direction of the laser waveguide is determined based on the reference of the mark.
- the substrate product is separated by pressing the substrate product against the second surface.
- the first and second end faces are formed on the laser bar so as to intersect the mn plane defined by the m-axis and the normal axis of the hexagonal group III nitride semiconductor.
- the first and second end faces are provided with a mirror mirror surface having sufficient flatness, perpendicularity, or ion damage sufficient to constitute a laser resonator of the group III nitride semiconductor laser element.
- the laser waveguide extends in the direction of the c-axis inclination of the hexagonal group III nitride, and the cavity mirror end face that can provide this laser waveguide is not used as a dry etching surface. Is formed.
- the oscillation yield is improved when the deviation angle is in the range of not less than ⁇ 0.5 degrees and not more than +0.5 degrees. Further, when the deviation angle is in the range of not less than ⁇ 0.3 degrees and not more than +0.3 degrees, the threshold variation is improved.
- the substrate in the step of forming the substrate product, is subjected to processing such as slicing or grinding so that the thickness of the substrate is 400 ⁇ m or less.
- the surface may be a processed surface formed by the processing. Alternatively, it can be a surface including an electrode formed on the processed surface.
- the substrate in the step of forming the substrate product, is polished so that a thickness of the substrate is 50 ⁇ m or more and 100 ⁇ m or less, and the second surface is It can be a polished surface formed by polishing. Alternatively, it can be a surface including an electrode formed on the polished surface.
- the first and second end faces having sufficient flatness, perpendicularity, or ion damage sufficient to constitute a laser resonator of the group III nitride semiconductor laser element can be formed with high yield. .
- the angle ALPHA is preferably in the range of 63 degrees to 80 degrees and 100 degrees to 117 degrees. If the angle is less than 63 degrees or more than 117 degrees, the m-plane may appear in a part of the end face formed by pressing. Further, when the angle is more than 80 degrees and less than 100 degrees, desired flatness and perpendicularity cannot be obtained.
- the semipolar principal surface is a ⁇ 20-21 ⁇ plane, a ⁇ 10-11 ⁇ plane, a ⁇ 20-2-1 ⁇ plane, and a ⁇ 10-1-1 ⁇ plane. It is good to be either.
- first and second end faces without flatness, perpendicularity, or ion damage sufficient to constitute a laser resonator of the group III nitride semiconductor laser element.
- the semipolar principal surface is a ⁇ 20-21 ⁇ plane, a ⁇ 10-11 ⁇ plane, a ⁇ 20-2-1 ⁇ plane, and a ⁇ 10-1-1 ⁇ plane.
- a surface having a slight inclination in a range of ⁇ 4 degrees or more and +4 degrees or less in the m-plane direction from any of the semipolar planes is also preferable as the main surface.
- the first and second layers do not have sufficient flatness, perpendicularity, or ion damage that can constitute a laser resonator of the group III nitride semiconductor laser device. Can provide end face.
- the scribe is performed using a laser scriber, a scribe groove is formed by the scribe, and the length of the scribe groove is the length of the hexagonal group III nitride semiconductor. It is shorter than the length of the intersecting line between the an plane and the first plane defined by the a axis and the normal axis.
- another substrate product and a laser bar are formed by cleaving the substrate product.
- This cleaving is caused by using a scribe groove that is shorter than the cleaving line of the laser bar.
- the end face of the active layer in each of the first and second end faces is in relation to a reference plane perpendicular to the m-axis of the support base made of the hexagonal nitride semiconductor.
- an angle in the range of (ALPHA-5) degrees or more and (ALPHA + 5) degrees or less can be formed on the plane defined by the c-axis and m-axis of the hexagonal group III nitride semiconductor.
- the end face having the above-described perpendicularity can be formed with respect to the angle taken from one of the c-axis and the m-axis to the other.
- the substrate can be made of any one of GaN, AlN, AlGaN, InGaN, and InAlGaN. According to this method, when using a substrate made of these gallium nitride based semiconductors, the first and second end faces usable as a resonator can be obtained.
- the substrate may include an orientation flat indicating the a-plane of the hexagonal group III nitride semiconductor, and the mark may include the orientation flat.
- the substrate may include a cleavage plane in the a-plane of the hexagonal group III nitride semiconductor, and the mark may include the cleavage plane.
- the laser beam is irradiated to the substrate product and the laser arrayed in the a-axis direction of the hexagonal group III nitride semiconductor. A mark is formed, and the mark may include an array of the laser marks.
- the laser structure shows a streak emission image extending in the direction of a predetermined axis in a fluorescence microscope image by light excitation by a mercury lamp, and the orientation of the arrangement of the laser marks is the streak shape
- a deviation angle between the waveguide vector and an orthogonal direction orthogonal to the predetermined axis is determined based on the direction of the predetermined axis related to the emission image, and is ⁇ 0.5 degrees or more and +0.5 degrees or less. Can be in range.
- the epitaxial substrate includes (a) a substrate having a semipolar main surface made of a hexagonal group III nitride semiconductor, and (b) a semiconductor stack provided on the semipolar main surface of the substrate.
- the semiconductor stack includes a semiconductor region for a laser structure, and the semiconductor region includes a first clad layer made of a first conductivity type gallium nitride semiconductor and a second conductivity type gallium nitride semiconductor.
- the active layer includes a gallium nitride semiconductor layer, and the c-axis of the hexagonal group III nitride semiconductor of the substrate is the hexagonal system.
- the group III nitride semiconductor is inclined at an angle ALPHA with respect to the normal axis in the m-axis direction, and the angle formed between the normal axis and the c-axis of the hexagonal group III nitride semiconductor is 45 degrees or more. 80 degrees or less or 100 degrees to 135 degrees A circumference, wherein the semiconductor stack comprises a structure extending along a reference axis indicating a direction of the hexagonal Group III nitride semiconductor of the a-axis.
- This epitaxial substrate is good for a group III nitride semiconductor laser device including a laser stripe along the direction of the mn plane defined by the m-axis and normal axis of a hexagonal group III nitride semiconductor.
- the angle formed between the normal axis and the c-axis of the hexagonal group III nitride semiconductor is in the range of 45 degrees to 80 degrees or 100 degrees to 135 degrees.
- the semiconductor stack includes a band-shaped structure extending along the reference axis indicating the direction of the a-axis of the hexagonal group III nitride semiconductor, the structure is manufactured using the epitaxial substrate.
- a reference mark for orientation of the laser stripe and orientation of the laser cavity can be provided to the group III nitride semiconductor laser device.
- the structure has a length of 230 ⁇ m or more in the direction of the a-axis. According to this epitaxial substrate, a structure having a length of 230 ⁇ m or more is good for mask alignment in manufacturing a group III nitride semiconductor laser device.
- the structure may have a surface form extending in the direction of the a-axis on the upper surface of the semiconductor stack.
- the structure since the structure is a surface form on the epitaxial surface of the epitaxial substrate, the position of the structure is specified by observing the appearance of the epitaxial substrate.
- the structure may include a depression in the upper surface of the semiconductor stack.
- the position of the depression can be found by a reflection image or a transmission layer using ultraviolet rays, visible light, infrared rays, or the like.
- the structure may be provided at a position of a stacking fault reaching the upper surface of the semiconductor stack.
- this epitaxial substrate since the structure is formed at the position of the stacking fault that has reached the upper surface of the semiconductor stack, crystallographic information is reflected in the shape and orientation of the structure.
- the structure may have a deviation angle in a range of ⁇ 0.5 degrees or more and +0.5 degrees or less with respect to the direction of the a-axis. Furthermore, in still another aspect of the present invention, it is further preferable that the structure has a deviation angle in the range of ⁇ 0.3 degrees or more and +0.3 degrees or less with respect to the direction of the a-axis. According to this epitaxial substrate, for example, the stacking fault has a variation of about the above angle range.
- the structure may include a defect region that is observed as a dark region in a light emission image excited by a mercury lamp.
- the defect region is a defect related to crystal growth, crystallographic information is reflected in the shape and orientation of the structure.
- the dark region is enlarged by a heat treatment at a high temperature of 800 degrees Celsius or higher.
- the long side in the dark region in the light emission image extends in the direction of the reference axis, and the long side preferably has a length of 230 ⁇ m or more.
- a structure having a length of 230 ⁇ m or more is good for mask alignment in manufacturing a group III nitride semiconductor laser device.
- a deviation angle between the long side and the direction of the a-axis is preferably in a range of not less than ⁇ 0.5 degrees and not more than +0.5 degrees. Furthermore, in still another aspect of the present invention, it is further preferable that a deviation angle between the long side and the direction of the a-axis is in a range of not less than ⁇ 0.3 degrees and not more than +0.3 degrees. According to this epitaxial substrate, the dark region has a variation of about the angle range.
- the dark region may include crystal defects provided in the active layer. According to this epitaxial substrate, crystal defects are easily introduced into the active layer due to the growth temperature and quantum well structure, but these crystal defects can be used for mask alignment.
- a cross-sectional shape in a plane orthogonal to the a-axis may be a hexagon in at least a part of the crystal defects. According to this epitaxial substrate, crystal defects are easily introduced into the active layer due to the growth temperature and quantum well structure, but the shape of the crystal defects reflects crystallographic information.
- Another aspect of the present invention relates to a method for manufacturing a group III nitride semiconductor laser device.
- the method includes (a) a step of preparing the epitaxial substrate, (b) a step of forming a substrate product having an anode electrode and a cathode electrode using the epitaxial substrate, and (c) the structure.
- the laser bar has first and second end faces formed by the separation, and the first and second end faces constitute a laser resonator of the group III nitride semiconductor laser element
- the substrate product Includes a laser structure including the substrate having a semipolar principal surface made of a hexagonal group III nitride semiconductor and a semiconductor region formed on the semipolar principal surface, and the anode electrode and the cathode electrode include Formed on the laser structure, the first and second end faces intersect an mn plane defined by the m-axis and the normal axis of the hexagonal group III nitride semiconductor.
- the angle formed between the normal axis and the c-axis of the hexagonal group III nitride semiconductor is in the range of not less than 45 degrees and not more than 80 degrees or in the range of not less than 100 degrees and not more than 135 degrees.
- a scribe mark whose direction is defined with reference to a structure formed in the epitaxial region can be formed on the substrate product.
- the step of forming the substrate product includes a step of forming an insulating film that covers the semiconductor region of the laser structure, and the insulating film is based on the structure.
- a stripe-shaped opening having a defined orientation is formed, and either one of the anode electrode and the cathode electrode can contact the laser structure through the opening of the insulating film.
- the semiconductor region of the laser structure has a ridge structure, and the ridge structure has a stripe shape, and the ridge structure is formed when the ridge structure is formed.
- the direction of the stripe shape of the structure may be defined based on the structure. According to this method, it is possible to form a ridge structure whose orientation is defined with reference to the structure in the epitaxial substrate.
- a group III nitride semiconductor epitaxial substrate comprises (a) a support base composed of a hexagonal group III nitride semiconductor and having a semipolar main surface, and the semipolar main surface of the support base.
- a laser structure including a semiconductor region provided on the surface is provided.
- the semiconductor region includes a first cladding layer made of a gallium nitride semiconductor of a first conductivity type, a second cladding layer made of a gallium nitride semiconductor of a second conductivity type, the first cladding layer, and the first cladding layer.
- the first cladding layer, the second cladding layer and the active layer are arranged along a normal axis of the semipolar main surface.
- the active layer includes a gallium nitride based semiconductor layer, and the c-axis of the hexagonal group III nitride semiconductor of the support base is the normal axis in the direction of the m axis of the hexagonal group III nitride semiconductor.
- the angle formed by the normal axis and the c-axis of the hexagonal group III nitride semiconductor is in the range of 45 degrees to 80 degrees or 100 degrees to 135 degrees.
- Parallel to the a-axis direction in the epitaxial substrate Having a surface configured to Zhang.
- the surface form preferably has a length of 230 ⁇ m or more in the a-axis direction.
- the deviation angle between the surface form and the a-axis direction is preferably in the range of not less than ⁇ 0.5 degrees and not more than +0.5 degrees.
- a deviation angle between the surface form and the a-axis direction is preferably in the range of not less than ⁇ 0.3 degrees and not more than +0.3 degrees.
- the surface form is preferably a depression when a cross section from the a-axis direction is observed.
- a group III nitride semiconductor epitaxial substrate comprises (a) a support base composed of a hexagonal group III nitride semiconductor and having a semipolar main surface, and the semipolar main surface of the support base.
- a laser structure including a semiconductor region provided on the surface is provided.
- the semiconductor region includes a first cladding layer made of a gallium nitride semiconductor of a first conductivity type, a second cladding layer made of a gallium nitride semiconductor of a second conductivity type, the first cladding layer, and the first cladding layer.
- the first cladding layer, the second cladding layer and the active layer are arranged along a normal axis of the semipolar main surface.
- the active layer includes a gallium nitride based semiconductor layer, and the c-axis of the hexagonal group III nitride semiconductor of the support base is the normal axis in the direction of the m axis of the hexagonal group III nitride semiconductor.
- the angle formed by the normal axis and the c-axis of the hexagonal group III nitride semiconductor is in the range of 45 degrees to 80 degrees or 100 degrees to 135 degrees. In a luminescence image excited with a mercury lamp, c Axially symmetrical triangular or pentagonal dark regions are observed for.
- the long side in the dark region in the emission image extends in the a-axis direction, and has a length of 230 ⁇ m or more in the a-axis direction.
- a deviation angle between the long side and the a-axis direction is in a range of not less than ⁇ 0.5 degrees and not more than +0.5 degrees.
- a deviation angle between the long side and the a-axis direction is in a range of not less than ⁇ 0.3 degrees and not more than +0.3 degrees.
- the crystal structure of the well layer is partially observed as a hexagon.
- the dark region expands when heat treatment is performed at a high temperature of 800 degrees Celsius or higher.
- the laser resonance that enables a low threshold current on the semipolar plane of the support base in which the c-axis of the hexagonal group III nitride is inclined in the direction of the m-axis.
- a group III nitride semiconductor laser device having a resonator and a structure capable of improving the oscillation yield.
- a method for producing this group III nitride semiconductor laser device is provided.
- FIG. 1 is a drawing schematically showing a structure of a group III nitride semiconductor laser device according to the present embodiment.
- FIG. 2 is a drawing showing a band structure in an active layer in a group III nitride semiconductor laser device.
- FIG. 3 is a drawing showing the polarization of light emission in the active layer of the group III nitride semiconductor laser device.
- FIG. 4 is a drawing showing the relationship between the end face of the group III nitride semiconductor laser device and the m-plane of the active layer.
- FIG. 5 is a process flow diagram showing the main steps of the method of manufacturing the group III nitride semiconductor laser device according to the present embodiment.
- FIG. 5 is a process flow diagram showing the main steps of the method of manufacturing the group III nitride semiconductor laser device according to the present embodiment.
- FIG. 6 is a drawing schematically showing main steps of a method for producing a group III nitride semiconductor laser device according to the present embodiment.
- FIG. 7 is a drawing showing a scanning electron microscope image of the resonator end face as well as the ⁇ 20-21 ⁇ plane in the crystal lattice.
- FIG. 8 is a drawing showing the structure of the laser diode shown in Example 1.
- FIG. 9 is a diagram showing the relationship between the obtained degree of polarization ⁇ and the threshold current density.
- FIG. 10 is a drawing showing the relationship between the inclination angle of the c-axis in the m-axis direction of the GaN substrate and the oscillation yield.
- FIG. 11 is a diagram showing the relationship between stacking fault density and oscillation yield.
- FIG. 7 is a drawing showing a scanning electron microscope image of the resonator end face as well as the ⁇ 20-21 ⁇ plane in the crystal lattice.
- FIG. 8 is a drawing showing the structure of the laser diode
- FIG. 12 is a diagram showing the relationship between the substrate thickness and the oscillation yield.
- FIG. 13 is a view showing an angle formed by the (20-21) plane and another plane orientation (index).
- FIG. 14 is a drawing schematically showing the structure of the gain guide laser.
- FIG. 15 is a drawing schematically showing the structure of an index guide laser having a ridge structure.
- FIG. 16 shows a Nomarski differential interference microscope image showing an area in the vicinity of the anode electrode on the epi surface of the substrate product, a light emission image excited by a mercury lamp, and a deviation between the streaky light emitting layer and the extending direction of the laser waveguide. It is drawing which shows.
- FIG. 17 is a top view showing a semiconductor laser intentionally having a large deviation angle.
- FIG. 17 is a top view showing a semiconductor laser intentionally having a large deviation angle.
- FIG. 18 is a drawing showing the relationship between the deviation angle between the direction of the laser waveguide and the direction of the c-axis projection component and the deviation angle between the ideal end face perpendicular to the waveguide and the actual end face.
- FIG. 19 shows the relationship between the deviation angle between the laser waveguide direction and the c-axis projection component (the direction in which the c-axis is projected onto the substrate main surface) and the oscillation yield, and the deviation angle between the laser waveguide and the c-axis projection component. It is drawing which shows the relationship with the dispersion
- FIG. 20 is a drawing showing atomic arrangements in the (20-21) plane, the ( ⁇ 101-6) plane, and the ( ⁇ 1016) plane.
- FIG. 21 is a drawing showing atomic arrangements in the (20-21) plane, the ( ⁇ 101-7) plane, and the ( ⁇ 1017) plane.
- FIG. 22 is a drawing showing atomic arrangements in the (20-21) plane, the ( ⁇ 101-8) plane, and the ( ⁇ 1018) plane.
- FIG. 23 shows a structure of a substrate having an orientation flat.
- FIG. 24 is a plan view showing a wafer that has been cleaved.
- FIG. 25 is a drawing showing a Nomarski differential interference microscope image of the outermost epi surface.
- FIG. 26 is a drawing showing a transmission electron microscope image in a cross section of a region in a box indicated by an arrow in FIG. FIG.
- FIG. 27 is a drawing schematically showing the stacking fault SF and the epi-surface defect G in the gallium nitride based semiconductor.
- FIG. 28 is a drawing showing a high-resolution transmission electron microscope (HR-TEM) image of the region BOX shown in FIG.
- FIG. 29 is a drawing showing a fluorescence image of an epitaxial substrate excited using a mercury lamp.
- HR-TEM transmission electron microscope
- FIG. 1 is a drawing schematically showing the structure of a group III nitride semiconductor laser device according to the present embodiment.
- group III nitride semiconductor laser device 11 has a gain guide type structure, the embodiment of the present invention is not limited to the gain guide type structure.
- the group III nitride semiconductor laser device 11 includes a laser structure 13 and an electrode 15.
- the laser structure 13 includes a support base 17 and a semiconductor region 19.
- the support base 17 is made of a hexagonal group III nitride semiconductor and has a semipolar main surface 17a and a back surface 17b.
- the semiconductor region 19 is provided on the semipolar main surface 17 a of the support base 17.
- the electrode 15 is provided on the semiconductor region 19 of the laser structure 13.
- the semiconductor region 19 includes a first cladding layer 21, a second cladding layer 23, and an active layer 25.
- the first cladding layer 21 is made of a first conductivity type gallium nitride semiconductor, and is made of, for example, n-type AlGaN, n-type InAlGaN, or the like.
- the second cladding layer 23 is made of a second conductivity type gallium nitride based semiconductor, for example, p-type AlGaN, p-type InAlGaN, or the like.
- the active layer 25 is provided between the first cladding layer 21 and the second cladding layer 23.
- the active layer 25 includes a gallium nitride based semiconductor layer, and this gallium nitride based semiconductor layer is, for example, a well layer 25a.
- the active layer 25 includes barrier layers 25b made of a gallium nitride semiconductor, and the well layers 25a and the barrier layers 25b are alternately arranged.
- the well layer 25a is made of, for example, InGaN
- the barrier layer 25b is made of, for example, GaN, InGaN, or the like.
- the active layer 25 can include a quantum well structure provided to generate light having a wavelength of 360 nm to 600 nm. Use of a semipolar surface is good for generation of light having a wavelength of 430 nm or more and 550 nm or less.
- the first cladding layer 21, the second cladding layer 23, and the active layer 25 are arranged along the normal axis NX of the semipolar principal surface 17a.
- the laser structure 13 includes the first fractured surface 27 and the first section 27 intersecting the mn plane defined by the m axis and the normal axis NX of the hexagonal group III nitride semiconductor. 2 split sections 29 are included.
- FIG. 1 an orthogonal coordinate system S and a crystal coordinate system CR are drawn.
- the normal axis NX is directed in the direction of the Z axis of the orthogonal coordinate system S.
- the semipolar principal surface 17a extends in parallel to a predetermined plane defined by the X axis and the Y axis of the orthogonal coordinate system S.
- FIG. 1 also shows a representative c-plane Sc.
- the c-axis of the hexagonal group III nitride semiconductor of the support base 17 is inclined at an angle ALPHA greater than zero with respect to the normal axis NX in the m-axis direction of the hexagonal group III nitride semiconductor.
- the direction of this c-axis is indicated by the c-axis vector VC.
- the c-axis vector VC includes a projection component VCP parallel to the semipolar principal surface 17a and a vertical component VCN parallel to the normal axis NX.
- the group III nitride semiconductor laser device 11 further includes an insulating film 31.
- the insulating film 31 covers the surface 19 a of the semiconductor region 19 of the laser structure 13, and the semiconductor region 19 is located between the insulating film 31 and the support base 17.
- the support base 17 is made of a hexagonal group III nitride semiconductor.
- the insulating film 31 has an opening 31a.
- the opening 31a extends in the direction of the intersection line LIX between the surface 19a of the semiconductor region 19 and the mn plane, and has, for example, a stripe shape.
- the electrode 15 is in contact with the surface 19a (for example, the second conductivity type contact layer 33) of the semiconductor region 19 through the opening 31a, and extends in the direction of the intersection line LIX.
- the laser waveguide includes the first cladding layer 21, the second cladding layer 23, and the active layer 25, and extends in the direction of the intersection line LIX.
- the opening 31a of the insulating film 31 has, for example, a stripe shape, and the direction of the laser waveguide is in the extending direction of the stripe opening.
- the semiconductor region 19 of the laser structure 13 has a ridge structure, and the direction of the laser waveguide is in the extending direction of the ridge structure.
- the waveguide vector LGV indicates the direction of the laser waveguide.
- the first fractured surface 27 and the second fractured surface 29 intersect the mn plane defined by the m-axis and the normal axis NX of the hexagonal group III nitride semiconductor.
- the laser resonator of the group III nitride semiconductor laser device 11 includes first and second fractured faces 27 and 29, and a laser waveguide is provided from one of the first fractured face 27 and the second fractured face 29 to the other. It is extended.
- the laser structure 13 includes a first surface 13a and a second surface 13b, and the first surface 13a is a surface opposite to the second surface 13b.
- the first and second fractured surfaces 27 and 29 extend from the edge 13c of the first surface 13a to the edge 13d of the second surface 13b.
- the first and second fractured surfaces 27 and 29 are different from conventional cleavage planes such as c-plane, m-plane, or a-plane.
- the group III nitride semiconductor laser device 11 According to the group III nitride semiconductor laser device 11, the first and second fractured surfaces 27 and 29 constituting the laser resonator intersect with the mn plane. Therefore, it is possible to provide a laser waveguide extending in the direction of the intersecting line between the mn plane and the semipolar plane 17a. Therefore, the group III nitride semiconductor laser device 11 has a laser resonator that enables a low threshold current.
- the angle ALPHA formed between the normal axis NX and the c axis of the hexagonal group III nitride semiconductor is in the range of 45 degrees to 80 degrees or 100 degrees to 135 degrees.
- the laser structure 13 includes a laser waveguide extending on the semipolar main surface 17 a of the support base 17. This laser waveguide extends in the direction of a waveguide vector LGV that faces in the direction from one of the first and second fractured surfaces 27 and 29 to the other.
- the c-axis vector VC indicating the direction of the c-axis of the hexagonal group III nitride semiconductor is defined by a projection component VCP parallel to the semipolar principal surface 17a and a vertical component VCN parallel to the normal axis NX.
- the deviation angle AV formed between the waveguide vector LGV and the projection component VCP shown in FIG. 1 can be in the range of not less than ⁇ 0.5 degrees and not more than +0.5 degrees.
- the laser structure 13 shows a streaky emission image extending in the direction of a predetermined axis in a fluorescence microscope image by light excitation by a mercury lamp.
- the deviation angle between the waveguide vector LGV and the orthogonal direction orthogonal to the predetermined axis PG is in the range of not less than ⁇ 0.5 degrees and not more than +0.5 degrees.
- the deviation angle between the waveguide vector LGV and the predetermined axial direction PG is in the range of ⁇ 89.5 degrees to +90.5 degrees.
- the deviation angle AV is in the range of not less than ⁇ 0.5 degrees and not more than +0.5 degrees, the oscillation yield is improved. Further, when the deviation angle AV is in the range of not less than ⁇ 0.3 degrees and not more than +0.3 degrees, the threshold variation is improved.
- the mismatch between the orientation of the end face and the orientation of the laser waveguide degrades the laser characteristics. If there is a deviation angle AV between the projection component VCP of the c-axis vector and the waveguide vector LGV, the end face produced by cleaving is unlikely to be perpendicular to the laser waveguide. The decrease in perpendicularity decreases the laser characteristics or increases the characteristic variation. When the parallelism between the waveguide vector LGV indicating the direction of the laser waveguide and the c-axis projection component VCP increases, the laser characteristics can be improved and the characteristic variation can be reduced.
- the oscillation yield can be 50% or more.
- the threshold variation can be improved to 15% or less.
- the group III nitride semiconductor laser device 11 includes an n-side light guide layer 35 and a p-side light guide layer 37.
- the n-side light guide layer 35 includes a first portion 35a and a second portion 35b, and the n-side light guide layer 35 is made of, for example, GaN, InGaN, or the like.
- the p-side light guide layer 37 includes a first portion 37a and a second portion 37b, and the p-side light guide layer 37 is made of, for example, GaN, InGaN, or the like.
- the carrier block layer 39 is provided, for example, between the first portion 37a and the second portion 37b.
- Another electrode 41 is provided on the back surface 17b of the support base 17, and the electrode 41 covers, for example, the back surface 17b of the support base 17.
- FIG. 2 is a drawing showing a band structure in an active layer in a group III nitride semiconductor laser device.
- FIG. 3 is a drawing showing the polarization of light emission in the active layer 25 of the group III nitride semiconductor laser device 11.
- FIG. 4 is a drawing schematically showing a cross section defined by the c-axis and the m-axis. Referring to FIG. 2A, there are three possible transitions between the conduction band and the valence band in the vicinity of the ⁇ point of the band structure BAND. The A band and the B band are relatively small energy differences.
- the light emission due to the transition Ea between the conduction band and the A band is polarized in the a-axis direction, and the light emission due to the transition Eb between the conduction band and the B band is polarized in the direction projected on the principal plane.
- the threshold value of the transition Ea is smaller than the threshold value of the transition Eb.
- the light in the LED mode includes a polarization component I1 in the direction of the a-axis of the hexagonal group III nitride semiconductor and a polarization component I2 in a direction of projecting the c-axis of the hexagonal group III nitride semiconductor on the main surface,
- the polarization component I1 is larger than the polarization component I2.
- the degree of polarization ⁇ is defined by (I1 ⁇ I2) / (I1 + I2).
- dielectric multilayer films 43a and 43b provided on at least one of the first and second fractured surfaces 27 and 29, or on each of them, can be further provided.
- An end face coat can also be applied to the fracture surfaces 27 and 29. The reflectance can be adjusted by the end face coating.
- the laser light L from the active layer 25 is polarized in the direction of the a-axis of the hexagonal group III nitride semiconductor.
- the band transition capable of realizing a low threshold current has polarization.
- the first and second fractured surfaces 27 and 29 for the laser resonator are different from conventional cleavage planes such as c-plane, m-plane or a-plane.
- the first and second fractured surfaces 27 and 29 have flatness and perpendicularity as mirrors for the resonator. Therefore, using the first and second fractured surfaces 27 and 29 and the laser waveguide extending between these fractured surfaces 27 and 29, as shown in FIG.
- the end surface 17c of the support base 17 and the end surface 19c of the semiconductor region 19 appear in each of the first and second fractured surfaces 27 and 29, and the end surface 17c and the end surface 19c are It is covered with a dielectric multilayer film 43a.
- An angle BETA formed by the normal vector NA of the end face 17c of the support substrate 17 and the end face 25c of the active layer 25 and the m-axis vector MA of the active layer 25 is defined by the c-axis and m-axis of the group III nitride semiconductor.
- component (BETA) 1 defined in one plane S1, and in a first plane S1 (referred to as “S1” in the drawing) and a second plane S2 (referred to as “S2” in the drawing) perpendicular to the normal axis NX Defined by component (BETA) 2 .
- the component (BETA) 1 is preferably in the range of (ALPHA-5) degrees to (ALPHA + 5) degrees in the first plane S1 defined by the c-axis and m-axis of the group III nitride semiconductor. This angle range is shown in FIG. 4 as an angle formed by a representative m-plane SM and the reference plane F A.
- a representative m-plane SM is depicted from the inside to the outside of the laser structure in FIG. 4 for ease of understanding.
- the reference plane F A extends along the end face 25c of the active layer 25.
- This group III nitride semiconductor laser device 11 has an end surface that satisfies the above-described perpendicularity with respect to an angle BETA taken from one of the c-axis and the m-axis to the other.
- the component (BETA) 2 is preferably in the range of ⁇ 0.5 ° to + 0.5 ° in the second plane S2, and more preferably in the range of ⁇ 0.3 ° to + 0.3 °. good.
- BETA 2 (BETA) 1 2 + (BETA) 2 2 .
- the end faces 27 and 29 of the group III nitride semiconductor laser device 11 satisfy the above-described perpendicularity with respect to an angle defined in a plane perpendicular to the normal axis NX of the semipolar surface 17a.
- the thickness DSUB of the support base 17 is preferably 400 ⁇ m or less. This group III nitride semiconductor laser device is good for obtaining a high-quality fractured surface for a laser resonator. In the group III nitride semiconductor laser device 11, the thickness DSUB of the support base 17 is more preferably 50 ⁇ m or more and 100 ⁇ m or less. This group III nitride semiconductor laser device 11 is even better for obtaining a high-quality fractured surface for the laser resonator. Moreover, handling becomes easy and production yield can be improved.
- the angle ALPHA formed by the normal axis NX and the c-axis of the hexagonal group III nitride semiconductor is preferably 45 degrees or more, and preferably 80 degrees or less.
- the angle ALPHA is preferably 100 degrees or more and 135 degrees or less. If the angle is less than 45 degrees or more than 135 degrees, there is a high possibility that the end face formed by pressing is an m-plane. Further, when the angle is more than 80 degrees and less than 100 degrees, the desired flatness and perpendicularity may not be obtained.
- the angle ALPHA formed by normal axis NX and c-axis of hexagonal group III nitride semiconductor is more than 63 degrees, and travel is more than 80 degrees. Is good.
- the angle ALPHA is preferably 100 degrees or more, and preferably 117 degrees or less. If the angle is less than 63 degrees or more than 117 degrees, the m-plane may appear in a part of the end face formed by pressing. Further, when the angle is more than 80 degrees and less than 100 degrees, the desired flatness and perpendicularity may not be obtained.
- the semipolar main surface 17a can be any one of ⁇ 20-21 ⁇ plane, ⁇ 10-11 ⁇ plane, ⁇ 20-2-1 ⁇ plane, and ⁇ 10-1-1 ⁇ plane. Further, a surface slightly inclined from these surfaces within a range of ⁇ 4 degrees or more and +4 degrees or less is also preferable as the main surface.
- the first and second end surfaces 27 and 29 having sufficient flatness and perpendicularity that can constitute the laser resonator of the group III nitride semiconductor laser device 11 can be provided.
- an end face exhibiting sufficient flatness and perpendicularity can be obtained.
- the stacking fault density of the support base 17 can be 1 ⁇ 10 4 cm ⁇ 1 or less. Since the stacking fault density is 1 ⁇ 10 4 cm ⁇ 1 or less, there is a low possibility that the flatness and / or perpendicularity of the fractured section will be disturbed due to accidental circumstances.
- the support base 17 can be made of any one of GaN, AlN, AlGaN, InGaN, and InAlGaN. When these gallium nitride semiconductor substrates are used, end faces 27 and 29 that can be used as resonators can be obtained.
- the degree of polarization can be increased, and light confinement can be enhanced by a low refractive index.
- the lattice mismatch rate between the substrate and the light emitting layer can be reduced, and the crystal quality can be improved.
- FIG. 5 is a drawing showing the main steps of a method for producing a group III nitride semiconductor laser device according to the present embodiment.
- the substrate 51 is shown.
- step S101 a substrate 51 for preparing a group III nitride semiconductor laser device is prepared.
- the c-axis (vector VC) of the hexagonal group III nitride semiconductor of the substrate 51 is inclined at a finite angle ALPHA with respect to the normal axis NX in the m-axis direction (vector VM) of the hexagonal group III nitride semiconductor. ing. Therefore, the substrate 51 has a semipolar main surface 51a made of a hexagonal group III nitride semiconductor.
- a substrate product SP is formed.
- the substrate product SP is depicted as a substantially disk-shaped member, but the shape of the substrate product SP is not limited to this.
- the laser structure 55 is formed.
- the laser structure 55 includes a semiconductor region 53 and a substrate 51.
- the semiconductor region 53 is formed on the semipolar main surface 51a.
- a first conductivity type gallium nitride based semiconductor region 57, a light emitting layer 59, and a second conductivity type gallium nitride based semiconductor region 61 are sequentially grown on the semipolar main surface 51a.
- the gallium nitride based semiconductor region 57 can include, for example, an n-type cladding layer, and the gallium nitride based semiconductor region 61 can include, for example, a p-type cladding layer.
- the light emitting layer 59 is provided between the gallium nitride based semiconductor region 57 and the gallium nitride based semiconductor region 61, and may include an active layer, a light guide layer, an electron blocking layer, and the like.
- the gallium nitride based semiconductor region 57, the light emitting layer 59, and the second conductivity type gallium nitride based semiconductor region 61 are arranged along the normal axis NX of the semipolar principal surface 51a. These semiconductor layers are epitaxially grown.
- the substrate product SP includes a mark indicating the m-axis or a-axis direction of the hexagonal group III nitride semiconductor.
- an orientation flat (referred to as “OF”) of a GaN substrate can be used.
- an epitaxial substrate including the semiconductor region 53 is applied to the epitaxial substrate including the semiconductor region 53 by using a laser marker.
- An array of laser marks indicating the m-axis direction (for example, a row of grooves formed by laser beam irradiation) can be formed.
- the array of laser marks is preferably formed, for example, parallel to the OF of the wafer.
- the orientation flat orientation indicates the a-axis direction or the m-axis direction.
- the array of laser marks is used as an alignment mark. In the subsequent photolithography process using the mask aligner, the waveguide stripe and the OF are useful for accurately paralleling.
- the semiconductor region 53 is covered with an insulating film 54.
- the insulating film 54 is made of, for example, silicon oxide.
- An opening 54 a of the insulating film 54 is provided.
- the opening 54a has, for example, a stripe shape.
- the opening 54a is formed by, for example, a photolithography process using an array of laser marks.
- a mask for the ridge structure can be formed by a photolithography process using alignment with an array of laser marks.
- the direction of the laser waveguide (the direction of the waveguide vector LGV) is determined based on the above-described mark reference.
- the extending direction of the opening 54a of the insulating film 54 and the extending direction of the ridge structure are determined through photolithography based on the mark. The extending direction coincides with the direction of the waveguide vector.
- a ridge structure and / or electrodes (and stripe windows) are formed using the marks.
- the anode electrode 58 a and the cathode electrode 58 b are formed on the laser structure 55.
- the back surface of the substrate used for crystal growth is polished to form a substrate product SP having a desired thickness DSUB.
- the anode electrode 58a is formed on the semiconductor region 53
- the cathode electrode 58b is formed on the back surface (polishing surface) 51b of the substrate 51.
- the anode electrode 58a extends in the X-axis direction, and the cathode electrode 58b covers the entire back surface 51b.
- the substrate product SP is formed.
- the substrate product SP includes a first surface 63a and a second surface 63b located on the opposite side thereof.
- the semiconductor region 53 is located between the first surface 63 a and the substrate 51.
- step S105 the first surface 63a of the substrate product SP is scribed as shown in part (b) of FIG.
- This scribing is performed using a laser scriber 10a.
- a scribe groove 65a is formed by scribing.
- FIG. 6B five scribe grooves have already been formed, and the formation of the scribe groove 65b is being advanced using the laser beam LB.
- the length of the scribe groove 65a is shorter than the length of the intersection line AIS between the an plane and the first plane 63a defined by the a axis and the normal axis NX of the hexagonal group III nitride semiconductor.
- the laser beam LB is irradiated on a part of the AIS. By irradiation with the laser beam LB, a groove extending in a specific direction and reaching the semiconductor region is formed in the first surface 63a.
- the scribe groove 65a can be formed at one edge of the substrate product SP, for example.
- step S106 the substrate product SP is separated by pressing the substrate product SP against the second surface 63b to form the substrate product SP1 and the laser bar LB1.
- the pressing is performed using a breaking device such as a blade 69.
- the blade 69 includes an edge 69a extending in one direction and at least two blade surfaces 69b and 69c defining the edge 69a.
- the substrate product SP1 is pressed on the support device 70.
- the support device 71 includes a support surface 70a and a recess 70b, and the recess 70b extends in one direction.
- the recess 70b is formed in the support surface 70a.
- the substrate product SP1 is positioned on the recess 70b on the support device 70 by aligning the direction and position of the scribe groove 65a of the substrate product SP1 with the extending direction of the recess 70b of the support device 70.
- the direction of the edge of the breaking device is aligned with the extending direction of the recess 70b, and the edge of the breaking device is pressed against the substrate product SP1 from the direction intersecting the second surface 63b.
- the intersecting direction is preferably substantially perpendicular to the second surface 63b. Thereby, the substrate product SP is separated to form the substrate product SP1 and the laser bar LB1.
- the laser bar LB1 having the first and second end faces 67a and 67b is formed, and these end faces 67a and 67b are at least perpendicular to the light emitting layer and applicable to the resonant mirror of the semiconductor laser. It has flatness.
- the formed laser bar LB1 has first and second end surfaces 67a and 67b formed by the above separation, and each of the end surfaces 67a and 67b extends from the first surface 63a to the second surface 63b.
- the end faces 67a and 67b constitute a laser resonator of the group III nitride semiconductor laser element and intersect the XZ plane.
- This XZ plane corresponds to the mn plane defined by the m-axis and the normal axis NX of the hexagonal group III nitride semiconductor.
- the substrate product SP is pressed against the second surface 63b.
- the product SP is separated to form a new substrate product SP1 and a laser bar LB1. Therefore, the first and second end faces 67a and 67b are formed on the laser bar LB1 so as to intersect the mn plane.
- This end face formation provides sufficient flatness and perpendicularity to the extent that a laser resonator of the group III nitride semiconductor laser element can be formed on the first and second end faces 67a and 67b.
- the formed laser waveguide extends in the direction of the c-axis inclination of the hexagonal group III nitride.
- a resonator mirror end face capable of providing this laser waveguide is formed without using a dry etching surface.
- a new substrate product SP1 and a laser bar LB1 are formed by cleaving the substrate product SP1.
- separation by pressing is repeated to produce a large number of laser bars.
- This cleaving is caused by using a scribe groove 65a shorter than the breaking line BRAK of the laser bar LB1.
- step S108 a dielectric multilayer film is formed on the end faces 67a and 67b of the laser bar LB1 to form a laser bar product.
- step S109 the laser bar product is separated into individual semiconductor laser chips.
- the angle ALPHA can be in the range of 45 degrees to 80 degrees and 100 degrees to 135 degrees. If the angle is less than 45 degrees or more than 135 degrees, there is a high possibility that the end face formed by pressing is an m-plane. Further, when the angle is more than 80 degrees and less than 100 degrees, the desired flatness and perpendicularity may not be obtained.
- the angle ALPHA is more preferably in the range of 63 degrees to 80 degrees and 100 degrees to 117 degrees. If the angle is less than 45 degrees or more than 135 degrees, the m-plane may appear in a part of the end face formed by pressing.
- the semipolar main surface 51a can be any one of ⁇ 20-21 ⁇ plane, ⁇ 10-11 ⁇ plane, ⁇ 20-2-1 ⁇ plane, and ⁇ 10-1-1 ⁇ plane. Further, a surface slightly inclined from these surfaces within a range of ⁇ 4 degrees or more and +4 degrees or less is also preferable as the main surface. In these typical semipolar planes, it is possible to provide an end face for the laser resonator with sufficient flatness and perpendicularity that can constitute the laser resonator of the group III nitride semiconductor laser device.
- the substrate 51 can be made of any one of GaN, AlN, AlGaN, InGaN, and InAlGaN. When these gallium nitride semiconductor substrates are used, an end face that can be used as a laser resonator can be obtained.
- the substrate 51 is preferably made of GaN.
- step S104 for forming the substrate product SP the semiconductor substrate used for crystal growth was subjected to processing such as slicing or grinding so that the substrate thickness was 400 ⁇ m or less, and the second surface 63b was formed by polishing. It can be a machined surface. With this substrate thickness, end faces 67a and 67b free from flatness, perpendicularity, or ion damage sufficient to constitute a laser resonator of the group III nitride semiconductor laser device can be formed with high yield. It is even better if the second surface 63b is a polished surface formed by polishing and is polished to a substrate thickness of 100 ⁇ m or less. In order to handle the substrate product SP relatively easily, the substrate thickness is preferably 50 ⁇ m or more.
- the angle BETA described with reference to FIG. 3 is also defined for the laser bar LB1.
- the component (BETA) 1 of the angle BETA 1 is in a first plane (surface corresponding to the first plane S1 in the description with reference to FIG. 3) defined by the c-axis and the m-axis of the group III nitride semiconductor. It is preferable that the range is not less than (ALPHA-5) degrees and not more than (ALPHA + 5) degrees.
- the end faces 67a and 67b of the laser bar LB1 satisfy the above-described perpendicularity with respect to the angle component of the angle BETA taken from one of the c-axis and the m-axis to the other.
- the component (BETA) 2 of the angle BETA is preferably in the range of ⁇ 5 degrees or more and +5 degrees or less on the second plane (the plane corresponding to the second plane S2 shown in FIG. 3).
- the end faces 67a and 67b of the laser bar LB1 satisfy the above-described perpendicularity with respect to the angle component of the angle BETA defined by the plane perpendicular to the normal axis NX of the semipolar surface 51a.
- the end faces 67a and 67b are formed by a break by pressing against a plurality of gallium nitride based semiconductor layers epitaxially grown on the semipolar surface 51a. Because of the epitaxial film on the semipolar surface 51a, the end surfaces 67a and 67b are not cleaved surfaces with a low index such as the c-plane, m-plane, or a-plane that have been used as resonator mirrors. However, in the break of the lamination of the epitaxial film on the semipolar surface 51a, the end surfaces 67a and 67b have flatness and perpendicularity applicable as resonator mirrors.
- Example 1 A semipolar plane GaN substrate was prepared as follows, and the perpendicularity of the fractured surface was observed.
- the substrate used was a ⁇ 20-21 ⁇ plane GaN substrate cut from a (0001) GaN ingot grown thick by HVPE at an angle of 75 degrees in the m-axis direction.
- the main surface of the GaN substrate was mirror-finished and the back surface was polished and finished in a satin state.
- the thickness of the substrate was 370 ⁇ m.
- a marking line was put on the back side of the satin surface perpendicular to the direction in which the c-axis was projected onto the main surface of the substrate using a diamond pen, and then pressed to cleave the substrate.
- the substrate was observed from the a-plane direction using a scanning electron microscope.
- FIG. 7 (a) is a scanning electron microscope image obtained by observing the fractured surface from the a-plane direction, and the right end surface is the fractured surface. It can be seen that the split section has flatness and perpendicularity with respect to the semipolar principal surface.
- Example 2 In Example 1, in a GaN substrate having a semipolar ⁇ 20-21 ⁇ plane, a fractured surface obtained by pressing with a marking line perpendicular to the direction in which the c-axis is projected onto the substrate main surface is formed on the substrate main surface. On the other hand, it was found to have flatness and perpendicularity. Therefore, in order to investigate the usefulness of this split section as a laser resonator, the laser diode shown in FIG. 8 was grown by metal organic vapor phase epitaxy as follows. Trimethylgallium (TMGa), trimethylaluminum (TMAl), trimethylindium (TMIn), ammonia (NH 3 ), and silane (SiH 4 ) were used as raw materials.
- TMGa Trimethylgallium
- TMAl trimethylaluminum
- TMIn trimethylindium
- NH 3 ammonia
- SiH 4 silane
- a substrate 71 was prepared.
- a substrate 71 is cut from a (0001) GaN ingot grown thick by HVPE using a wafer slicing device at an angle in the range of 0 to 90 degrees in the m-axis direction, and an inclination angle ALPHA of the c-axis in the m-axis direction.
- a GaN substrate having a desired off angle in the range of 0 to 90 degrees was produced.
- a ⁇ 20-21 ⁇ plane GaN substrate is obtained, which is indicated by reference numeral 71a in the hexagonal crystal lattice shown in FIG. 7 (b).
- the substrate was observed by the cathodoluminescence method in order to investigate the stacking fault density of the substrate.
- cathodoluminescence the emission process of carriers excited by an electron beam is observed, but if a stacking fault exists, carriers are not re-emitted in the vicinity, and thus are observed as dark lines.
- the density per unit length of the dark line was determined and defined as the stacking fault density.
- the cathodoluminescence method of nondestructive measurement was used, but a transmission electron microscope of destructive measurement may be used.
- a defect extending in the m-axis direction from the substrate toward the sample surface is a stacking fault included in the support base, and as in the case of the cathodoluminescence method.
- the line density of stacking faults can be determined.
- an epitaxial layer was grown by the following growth procedure. First, an n-type GaN layer 72 having a thickness of 1000 nm was grown. Next, an n-type InAlGaN cladding layer 73 having a thickness of 1200 nm was grown on the GaN layer 72. Subsequently, after growing an n-type GaN guide layer 74a having a thickness of 200 nm and an undoped InGaN guide layer 74b having a thickness of 65 nm, a three-period MQW 75 composed of a GaN thickness of 15 nm / InGaN thickness of 3 nm was grown.
- an undoped InGaN guide layer 76a having a thickness of 65 nm, a p-type AlGaN blocking layer 77 having a thickness of 20 nm, and a p-type GaN guide layer 76b having a thickness of 200 nm were grown.
- a p-type InAlGaN cladding layer 77 having a thickness of 400 nm was grown.
- a stripe window having a width of 10 ⁇ m was formed by wet etching using photolithography.
- contact windows in the stripe direction were formed in the following two ways. Laser stripes are (1) in the M direction (the contact window is along a predetermined plane defined by the c-axis and m-axis) and (2) in the A direction: ⁇ 11-20> direction. .
- a p-side electrode 80a made of Ni / Au and a pad electrode made of Ti / Al were deposited.
- the back surface of the GaN substrate (GaN wafer) was polished with diamond slurry to produce a substrate product with the back surface in a mirror state.
- the thickness of the substrate product was measured using a contact-type film thickness meter. The thickness may be measured by a microscope from a sample cross section. As the microscope, an optical microscope or a scanning electron microscope can be used.
- An n-side electrode 80b made of Ti / Al / Ti / Au was formed on the back surface (polished surface) of the GaN substrate (GaN wafer) by vapor deposition.
- a laser scriber using a YAG laser having a wavelength of 355 nm was used for manufacturing the resonator mirror for these two types of laser stripes.
- the following conditions were used for forming the scribe grooves: laser light output 100 mW; scanning speed 5 mm / s.
- the formed scribe groove was, for example, a groove having a length of 30 ⁇ m, a width of 10 ⁇ m, and a depth of 40 ⁇ m.
- a scribe groove was formed by directly irradiating the epitaxial surface with laser light through an insulating film opening portion of the substrate at a pitch of 800 ⁇ m.
- the resonator length was 600 ⁇ m.
- 7B shows a case where laser stripes are provided in the (1) M direction, and end faces 81a and 81b for the laser resonator are shown together with the semipolar surface 71a.
- the end surfaces 81a and 81b are substantially orthogonal to the semipolar surface 71a, but are different from conventional cleavage surfaces such as the conventional c-plane, m-plane, or a-plane.
- FIG. 7B shows a case where laser stripes are provided in the (1) M direction, and end faces 81a and 81b for the laser resonator are shown together with the semipolar surface 71a.
- the end surfaces 81a and 81b are substantially orthogonal to the semipolar surface 71a, but are different from conventional cleavage surfaces such as the conventional c-plane, m-plane, or a-plane.
- FIG. 7 (c) shows a case where laser stripes are provided in the (2) ⁇ 11-20> direction.
- End faces 81c and 81d for the laser resonator are shown together with the semipolar surface 71a.
- the end surfaces 81c and 81d are substantially orthogonal to the semipolar surface 71a and are composed of a-planes.
- the flatness (size of irregularities) of the fractured surface is estimated to be 20 nm or less. Further, the perpendicularity of the cut surface to the sample surface was within a range of ⁇ 5 degrees.
- a dielectric multilayer film was coated on the end face of the laser bar by vacuum deposition.
- the dielectric multilayer film was configured by alternately laminating SiO 2 and TiO 2 .
- Each film thickness was adjusted in the range of 50 to 100 nm and designed so that the central wavelength of reflectance was in the range of 500 to 530 nm.
- the reflective surface on one side was set to 10 periods, the design value of reflectivity was designed to about 95%, the reflective surface on the other side was set to 6 periods, and the design value of reflectivity was about 80%.
- Evaluation by energization was performed at room temperature.
- a pulse power source having a pulse width of 500 ns and a duty ratio of 0.1% was used, and electricity was applied by dropping a needle on the surface electrode.
- the light output the light emission from the end face of the laser bar was detected by a photodiode, and the current-light output characteristic (IL characteristic) was examined.
- the emission wavelength the light emitted from the end face of the laser bar was passed through an optical fiber, and the spectrum was measured using a spectrum analyzer as a detector.
- the polarization state was examined by rotating the light emitted from the laser bar through the polarizing plate.
- the LED mode light the light emitted from the surface was measured by arranging the optical fiber on the laser bar surface side.
- the oscillation wavelength was 500 to 530 nm.
- the polarization state of LED mode was measured with all lasers.
- the polarization component in the a-axis direction is defined as I1
- the polarization component in the direction in which the m-axis is projected onto the principal surface is defined as I2
- (I1-I2) / (I1 + I2) is defined as the degree of polarization ⁇ .
- FIG. 9 was obtained as a result of investigating the relationship between the obtained degree of polarization ⁇ and the minimum value of the threshold current density. From FIG. 9, it can be seen that, when the degree of polarization is positive, (1) the laser current in the direction of the laser stripe M greatly reduces the threshold current density.
- the threshold current density is greatly reduced when the degree of polarization is positive (I1> I2) and the waveguide is provided in the off direction.
- the data shown in FIG. 9 is as follows. Threshold current, threshold current. Polarization degree, (M direction stripe), ( ⁇ 11-20> stripe). 0.08, 64, 20. 0.05, 18, 42. 0.15, 9, 48. 0.276, 7, 52. 0.4 6.
- FIG. 10 is a plot of a substrate having a stacking fault density of 1 ⁇ 10 4 (cm ⁇ 1 ) or less and a laser stripe of (1) M direction laser.
- FIG. 10 shows that the oscillation yield is very low when the off angle is 45 degrees or less.
- the off angle when the off angle is in the range of 63 degrees to 80 degrees, the verticality is improved and the oscillation yield is increased to 50% or more. From these facts, the optimum range of the off-angle of the GaN substrate is 63 degrees or more and 80 degrees or less. Similar results can be obtained even in the range of 100 degrees to 117 degrees, which is the angle range in which the crystallographically equivalent end faces are provided.
- the data shown in FIG. 10 is as follows. Tilt angle, yield. 10, 0.1. 43, 0.2. 58, 50. 63, 65. 66, 80. 71, 85. 75, 80. 79, 75. 85, 45. 90, 35.
- FIG. 11 As a result of investigating the relationship between the stacking fault density and the oscillation yield, FIG. 11 was obtained.
- the definition of the oscillation yield is the same as described above. From FIG. 11, it can be seen that when the stacking fault density exceeds 1 ⁇ 10 4 (cm ⁇ 1 ), the oscillation yield rapidly decreases.
- the sample having a reduced oscillation yield did not have a flat split surface with severe end face unevenness. The cause is thought to be a difference in the ease of cracking due to the presence of stacking faults. For this reason, the stacking fault density included in the substrate needs to be 1 ⁇ 10 4 (cm ⁇ 1 ) or less.
- the data shown in FIG. 11 is as follows. Stacking fault density (cm ⁇ 1 ), yield. 500, 80. 1000, 75. 4000, 70. 8000, 65. 10000, 20. 50000, 2.
- FIG. 12 As a result of investigating the relationship between the substrate thickness and the oscillation yield, FIG. 12 was obtained.
- the definition of the oscillation yield is the same as described above.
- the plotting is performed in the case where the stacking fault density of the substrate is 1 ⁇ 10 4 (cm ⁇ 1 ) or less and the laser stripe is (1) M direction laser. From FIG. 12, when the substrate thickness is thinner than 100 ⁇ m and thicker than 50 ⁇ m, the oscillation yield is high. This is because if the substrate thickness is thicker than 100 ⁇ m, the perpendicularity of the fractured surface deteriorates. On the other hand, when the thickness is less than 50 ⁇ m, handling is difficult and the chip is easily broken.
- the optimal thickness of the substrate is 50 ⁇ m or more and 100 ⁇ m or less.
- the data shown in FIG. 12 is as follows. Substrate thickness, yield. 48, 10. 80, 65. 90, 70. 110, 45. 150, 48. 200, 30. 400, 20.
- Example 3 In Example 2, a plurality of epitaxial films for a semiconductor laser were grown on a GaN substrate having a ⁇ 20-21 ⁇ plane. As described above, the end face for the optical resonator was formed by forming and pressing the scribe groove. In order to find candidates for these end faces, a plane orientation different from the a-plane with an angle of about 90 degrees with the (20-21) plane was obtained by calculation. Referring to FIG. 13, the following angles and plane orientations have angles close to 90 degrees with respect to the (20-21) plane. Specific plane index, angle with respect to ⁇ 20-21 ⁇ plane. (-1016): 92.46 degrees. ( ⁇ 1017): 90.10 degrees. (-1018): 88.29 degrees.
- Example 4 Laser diodes were grown by metalorganic vapor phase epitaxy as follows. Trimethylgallium (TMGa), trimethylaluminum (TMAl), trimethylindium (TMIn), ammonia (NH 3 ), and silane (SiH 4 ) were used as raw materials.
- TMGa Trimethylgallium
- TMAl trimethylaluminum
- TMIn trimethylindium
- NH 3 ammonia
- SiH 4 silane
- a 2-inch ⁇ 20-21 ⁇ plane GaN substrate grown by the HVPE method was used as the substrate.
- the GaN substrate has an orientation flat (denoted as “OF”) indicating the a-plane.
- the surface accuracy indicating the deviation angle between the OF surface and the a surface was measured by a surface inspection device, and the surface accuracy was 0.1 degrees or less.
- the direction of the projection component obtained by projecting the c-axis onto the main surface of the GaN substrate and the end surface indicating the a-plane are in an angular range of ⁇ 0.1 degrees or more and +0.1 degrees or less Parallel with accuracy of.
- an epitaxial layer for an epitaxial substrate as shown in FIG. 14 was grown on the GaN substrate by the following growth procedure. First, an n-type GaN layer having a thickness of 1100 nm was grown. Next, an n-type InAlGaN cladding layer having a thickness of 1200 nm was grown. Subsequently, an n-type GaN guide layer having a thickness of 250 nm and an n-type InGaN guide layer having a thickness of 115 nm were grown.
- a quantum well structure composed of GaN (thickness 10 nm) / InGaN (thickness 3 nm) was grown.
- an undoped InGaN guide layer having a thickness of 65 nm, a p-type AlGaN block layer having a thickness of 20 nm, a p-type InGaN guide layer having a thickness of 50 nm, and a p-type GaN guide layer having a thickness of 250 nm were grown.
- An epitaxial substrate was produced by this growth process.
- a plurality of laser marks arranged in parallel with OF are formed on the surface of the epitaxial substrate in order to make the waveguide stripe and OF parallel with high accuracy. It was formed on a predetermined line. Since the OF length is about 15 mm, for example, and the alignment accuracy at the time of the laser mark is about 2 ⁇ m, for example, the parallelism between the OF and the laser mark is in the range of ⁇ 0.01 degrees to +0.01 degrees. It becomes. This accuracy is an order of magnitude lower than the accuracy of the OF orientation.
- the orientation accuracy of the OF is substantially reflected in the accuracy of the parallelism between the waveguide stripe direction and the direction of the projection component obtained by projecting the c-axis onto the principal surface.
- a semipolar GaN substrate having no OF it is possible to determine the a-axis direction of the semipolar substrate. More specifically, it is possible to determine the a-axis direction by cleaving the epitaxial substrate and causing the a-plane of the GaN substrate to appear. By using the edge produced by this cleavage as a reference, the direction of the laser waveguide can be accurately determined at an angle of not less than ⁇ 0.1 degrees and not more than +0.1 degrees. Another method is to use surface morphology.
- a linear surface morphology parallel to the a-axis may appear.
- This surface morphology is formed by reflecting defects in the substrate, the influence of the substrate edge, and the roughness of the substrate surface, and is observed with a fluorescence microscope by photoexcitation of a mercury lamp. In this microscopic image, linear or streaky emission lines appear.
- the epitaxial substrate is rotated at an angle of 90 degrees therefrom, and then a line-shaped laser mark can be formed. .
- This method can also determine the laser waveguide direction (the direction of the stripe window or the direction of the ridge) with the same accuracy.
- the orientation of the arrangement of the laser marks can be determined with reference to the direction of the axis related to the streak emission image.
- the laser mark for example, scribe mark
- laser waveguide direction stripe window orientation or ridge orientation
- a stripe window having a width of 10 ⁇ m was formed by wet etching using photolithography.
- the stripe direction was determined with reference to the laser mark described above. Specifically, the patterning of the stripe window was performed so that the stripe and the laser mark were parallel or intentionally provided with an angular difference.
- a p-side electrode AND1 made of Ni / Au and a pad electrode made of Ti / Au were deposited.
- the back surface of the GaN substrate (GaN wafer) was polished with diamond slurry to produce a substrate product with the back surface in a mirror state.
- an n-side electrode CTD1 made of Ti / Al / Ti / Au was formed by vapor deposition.
- an index guide laser having a ridge structure shown in FIG. 15 can be manufactured by the following method.
- a mask having a pattern with a width of 2 ⁇ m made of a positive resist was provided by photolithography.
- the laser waveguide direction was oriented to be parallel to the direction of the projection component obtained by projecting the c-axis vector onto the main surface.
- a ridge structure was produced by dry etching using Cl 2 .
- the etching depth is 0.7 ⁇ m, for example, and the semiconductor region of the epitaxial substrate was etched until the AlGaN block layer was exposed. After the etching, the resist mask was removed.
- a stripe mask having a width of about 2 ⁇ m was left on the ridge structure using photolithography.
- the direction of the stripe mask was adjusted to the direction of the ridge structure.
- SiO 2 was deposited on the side surface of the ridge using a vacuum deposition method.
- SiO 2 on the ridge was removed by a lift-off method to form an insulating film having a stripe-shaped opening.
- an anode electrode AND2 and a cathode electrode CTD2 were formed to obtain a substrate product.
- a laser scriber using a YAG laser with a wavelength of 355 nm was used to manufacture the resonator mirror for these laser stripes.
- a scribe groove is formed using a laser scriber and a break is made, the oscillation chip yield can be improved as compared with the case where a diamond scribe is used.
- the following were used as the scribe groove formation conditions.
- Laser light output 100 mW.
- the scanning speed is 5 mm / s.
- the scribe groove formed under these conditions was, for example, a groove having a length of 100 ⁇ m, a width of 10 ⁇ m, and a depth of 40 ⁇ m. Scribe grooves were periodically formed by directly irradiating the surface of the substrate with laser light through the electrode openings at intervals of 300 ⁇ m corresponding to the width of the semiconductor chip.
- the resonator length was 600 ⁇ m.
- a resonant mirror was prepared by cleaving.
- a laser bar was produced by breaking at the end on the back side of the substrate by pressing.
- a split section for the laser resonator is formed by a method in which an end surface perpendicular to the laser waveguide provided in parallel to the direction in which the c-axis is projected onto the main surface is a mirror surface on the semipolar plane. This split section is different from the cleaved surface of the m-plane, a-plane, or c-plane that becomes the end face for the optical resonator in a conventional laser on the c-plane principal plane or m-plane principal plane.
- the end face of the laser bar was coated with a dielectric multilayer film by vacuum deposition.
- the dielectric multilayer film was configured by alternately laminating SiO 2 and TiO 2 .
- the film thickness was adjusted in the range of 50 to 100 nm, and the central wavelength of the reflectance was adjusted to be in the wavelength range of 500 to 530 nm.
- the reflective surface on one side was set to 10 periods, the design value of reflectivity was designed to about 95%, the reflective surface on the other side was set to 6 periods, and the design value of reflectivity was about 80%.
- Evaluation by energization was performed at room temperature.
- a pulse power source having a pulse width of 500 ns and a duty ratio of 0.1% was used, and electricity was applied by dropping a needle on the surface electrode.
- the light output the light emission from the end face of the laser bar was detected by a photodiode, and the current-light output characteristic (IL characteristic) was examined.
- the emission wavelength the light emitted from the end face of the laser bar was passed through an optical fiber, and the spectrum was measured using a spectrum analyzer as a detector.
- the oscillation wavelength was 500 to 530 nm.
- the emission image was observed using a fluorescence microscope having a mercury lamp as an excitation light source.
- a streak emission image parallel to the a-axis can be obtained.
- the parallelism between the c-axis and the laser waveguide was estimated by examining the perpendicularity between the shape of the structure such as the electrode or the ridge structure and the streaky emission line in the a-axis direction.
- the angle of deviation between the end face formed by cleaving and the waveguide was estimated by observing the device surface with an optical microscope.
- Part (a) of FIG. 16 is a drawing showing a Nomarski differential interference microscope image of an area in the vicinity of the anode electrode on the epitaxial surface of the substrate product.
- Part (b) of FIG. 16 is a drawing showing a fluorescent image (a light emission image excited by a mercury lamp) indicating the area indicated by a broken line in part (a) of FIG. In the fluorescent image, streaky emission lines extend in the a-axis direction.
- Part (c) of FIG. 16 is a diagram showing a deviation between the streaky emission line and the extending direction of the laser waveguide in the area shown in part (a) of FIG. 16.
- FIG. 17 shows a top view of an intentionally formed semiconductor laser having a large deviation angle.
- FIG. 17 (a) an optical microscope image showing the upper surface of an area including three chips of the laser bar is shown.
- part (b) of FIG. 17 an enlarged view showing an upper surface near the end face of the laser bar in the section BOX1 shown in part (a) of FIG. 17 is shown.
- FIG. 18 is a drawing showing the relationship between the deviation angle between the direction of the laser waveguide and the direction of the c-axis projection component and the deviation angle between the ideal end face perpendicular to the waveguide and the actual end face.
- the abscissa indicates a deviation angle (referred to as “deviation angle 1”) between the direction of the laser waveguide and the direction of the c-axis projection component.
- the deviation angle between the ideal end face and the actual end face (referred to as “deviation angle 2”) is shown.
- the deviation angle 2 can be reduced by reducing the deviation angle 1. Specifically, if the deviation angle 1 is within the range of ⁇ 1 degree to +1 degree, the deviation angle 2 does not vary greatly. When the misalignment angle 1 exceeds the angle represented by the absolute value, the misalignment angle 2 varies greatly.
- the relationship between the deviation angle between the laser waveguide direction and the c-axis projection component (the direction in which the c-axis is projected onto the main surface of the substrate) and the oscillation yield were investigated.
- the oscillation yield was improved when the absolute value of the deviation angle was small.
- the oscillation yield can be increased to 50% or more.
- the misalignment angle is in the range of ⁇ 0.25 degrees or more and +0.25 degrees or less
- the oscillation yield can be 75% or more.
- the oscillation yield can be 15% or more.
- the deviation angle between the laser waveguide and the c-axis projection component and the variation in threshold current density were investigated. As a result, as shown in part (b) of FIG. 19, when the absolute value of the deviation angle is small, the variation in the threshold current density (standard deviation ⁇ ) was reduced. If the deviation angle is in the range of not less than ⁇ 0.3 degrees and not more than +0.3 degrees, this variation can be reduced to 15% or less. Since the variation in a semiconductor laser with a deviation angle of 0 degrees is about 10%, when the deviation angle is in the range of not less than ⁇ 0.3 degrees and not more than +0.3 degrees, 1 of the threshold current density of the semiconductor laser with a deviation angle of 0 degrees. It is suppressed to about 5 times.
- the deviation angle is in the range of not less than ⁇ 0.25 degrees and not more than +0.25 degrees, this variation can be reduced to 13% or less.
- the absolute value of the deviation angle exceeds 0.3 degrees, the change in the variation of the threshold current density becomes large. If the deviation angle is in the range of ⁇ 0.75 degrees or more and +0.75 degrees or less, this variation can be made 40% or less.
- FIG. 20 is a drawing showing atomic arrangements in the (20-21) plane, the ( ⁇ 101-6) plane, and the ( ⁇ 1016) plane.
- FIG. 21 is a drawing showing atomic arrangements in the (20-21) plane, the ( ⁇ 101-7) plane, and the ( ⁇ 1017) plane.
- FIG. 22 is a drawing showing atomic arrangements in the (20-21) plane, the ( ⁇ 101-8) plane, and the ( ⁇ 1018) plane.
- the local atomic arrangement indicated by the arrow indicates the arrangement of electrically neutral atoms, and the electrically neutral atomic arrangement appears periodically.
- this charge-neutral atomic arrangement appears periodically, which suggests that the generation of the split section is relatively stable. There is sex.
- the angle ALPHA can be in the range of 45 degrees to 80 degrees and 100 degrees to 135 degrees. In order to improve the oscillation chip yield, the angle ALPHA can be in the range of 63 degrees to 80 degrees and 100 degrees to 117 degrees. It can be any of a typical semipolar principal surface, ⁇ 20-21 ⁇ surface, ⁇ 10-11 ⁇ surface, ⁇ 20-2-1 ⁇ surface, and ⁇ 10-1-1 ⁇ surface. Furthermore, it can be a slightly inclined surface from these semipolar surfaces.
- the semipolar principal surface is an m-plane direction from any one of ⁇ 20-21 ⁇ , ⁇ 10-11 ⁇ , ⁇ 20-2-1 ⁇ , and ⁇ 10-1-1 ⁇ planes. Further, it can be a slightly inclined surface that is turned off within a range of ⁇ 4 degrees or more and +4 degrees or less.
- the semiconductor wafer can be provided with a notch indicating a crystal orientation called, for example, an orientation flat (hereinafter referred to as “orientation flat”) OF.
- chamfers (chamfers) CHF1 and CHF2 are formed in this orientation flat in order to avoid unexpected wafer breakage.
- an orientation flat provided with a chamfer it is not easy to improve the focusing accuracy during patterning using a mask aligner. Since the chamfered portion of the orientation flat is provided with an inclined surface that is inclined with respect to the main surface of the wafer, the distance between the mask aligner and the orientation flat changes in the inclined surface with respect to the direction perpendicular to the main surface of the wafer. Because of this change, the alignment using the mask aligner can focus on any position on the inclined surface of the orientation flat chamfer.
- the alignment accuracy depends on which position in the range of the chamfer width of the orientation flat is focused, and as a result, there is a limit to the improvement of the alignment accuracy.
- chipping occurs during polishing of the substrate, and the edge of the orientation flat may be rough rather than straight as shown in FIG. This roughening results in a limit in improving alignment accuracy.
- the epitaxial substrate in a GaN wafer having a c-plane main surface, in order to increase alignment accuracy, the epitaxial substrate is cleaved before the process in the process after epitaxial growth, and the edge where the m-plane appears is obtained. Form.
- This m-plane edge can be used as a reference for mask alignment.
- this m-plane edge formation method is applied to a semipolar epitaxial substrate such as ⁇ 20-21 ⁇ plane semipolar, an a-plane edge is formed instead of the m-plane.
- an epitaxial substrate having a ⁇ 20-21 ⁇ plane as a semipolar plane is taken as an example.
- FIG. 24 is a plan view showing a wafer that has been cleaved.
- the broken edge has a linearly extending portion PLN, but the crack meanders as a whole.
- the formation of the a-plane edge makes it difficult for the GaN-based semiconductor to break linearly along the a-plane as compared to the m-plane.
- the inventors' careful observation has revealed that defects inherent to semipolarity are formed in an epitaxial semiconductor region grown on a semipolar surface substrate.
- FIG. 25 is a drawing showing a Nomarski differential interference microscope image of the outermost epi surface. As shown in FIG. 25, a linear morphology almost parallel to the a-axis direction was observed on the surface. In order to investigate this morphology, the epitaxial substrate was observed using a transmission electron microscope (TEM).
- FIG. 26 is a drawing showing a transmission electron microscope image in a cross section of a region in a box indicated by an arrow in FIG. Referring to FIG. 26, a depression is observed on the epi surface, and this depression is observed as a linear morphology.
- FIG. 26 is a drawing showing a transmission electron microscope image in a cross section of a region in a box indicated by an arrow in FIG. Referring to FIG. 26, a depression is observed on the epi surface, and this depression is observed as a linear morphology.
- FIG. 26 is a drawing showing a transmission electron microscope image in a cross section of a region in a box indicated by an arrow in FIG. Referring to FIG. 26, a
- FIG. 27 is a drawing schematically showing stacking faults SF and episurface defects (for example, grooves) G in the gallium nitride based semiconductor. As shown in the schematic diagram of FIG. 27, a defect propagating from the substrate at the bottom of the photograph is observed at the substrate position at the depression.
- FIG. 28 Images with different magnifications are shown in FIG. 28 (a), FIG. 28 (b) and FIG. 28 (c).
- FIG. 28C Images with different magnifications are shown in FIG. 28C.
- the laminated structure of the crystal plane changes from ABABAB ... to BCBCBC ... as shown in FIG. Is shown. Therefore, this defect is a stacking fault. Further, since the stacking fault exists in the c plane, it extends in the a-axis direction (exactly [-12-10] direction as shown in FIG. 28).
- the epitaxial substrate according to the present embodiment includes a structure including a stacking fault provided in the c-plane and a linear depression related to the stacking fault.
- the direction of the depression and the stacking fault indicates the a-axis direction very accurately.
- the waveguide can be mask-aligned so as to be perpendicular to the mark. Therefore, it is possible to align the mask with high accuracy in the direction perpendicular to the a-axis direction and with high accuracy parallel to the direction in which the c-axis is projected onto the main surface.
- the above stacking fault occurs accidentally at the time of crystal growth on the substrate, but is preferably included in the wafer surface at a density of 0.2 (cm ⁇ 1 ) or more. In such a case, it is unlikely that stacking faults are produced in the substrate used for epitaxial growth for laser production.
- stacking faults are desirably included in the wafer surface at a density of 10 (cm ⁇ 1 ) or less. If the density exceeds this value, the yield of laser elements is affected.
- the length of the stacking fault on the epi surface (the length of the dent) is preferably 230 ⁇ m or more. When the mark length is 230 ⁇ m or more, accurate mask alignment is possible.
- Example 6 An epitaxial multilayer structure for a laser structure is grown on a ⁇ 20-21 ⁇ plane GaN substrate.
- the epitaxial stacked structure includes an n-type semiconductor region, an active layer, and a p-type semiconductor region, and the active layer has a single quantum well structure including an InGaN well layer.
- excitation was performed using a mercury lamp (wavelength 365 nm), and a fluorescence image on the upper surface of the epitaxial substrate was observed.
- FIG. 29 (a) is a drawing showing a fluorescent image of the upper surface of the epitaxial substrate when excited using a mercury lamp. As shown in part (a) of FIG.
- a dark region (a region that does not emit light due to mercury lamp excitation) in the emission image from the upper surface is observed.
- the dark region has a pentagonal shape, for example.
- the longest side (long side) of the pentagon is substantially parallel to the a-axis direction.
- the cross section of the dark region has a typical cross-sectional shape as shown in part (b) of FIG. 29, part (c) of FIG. 29, and part (d) of FIG.
- it has a trapezoid such as a pentagon and an isosceles trapezoid
- a triangle such as an isosceles triangle.
- each of the triangle and the pentagon is symmetric with respect to an axis passing through one vertex and orthogonal to the long side.
- this precipitate extends in the a-axis direction. Moreover, the cross section of the precipitate has substantially the same cross-sectional shape in the depth direction of the precipitate. Therefore, by performing mask alignment of the waveguide parallel to the long side of the dark region when observed from the surface of the epitaxial substrate, it is accurately perpendicular to the a-axis direction and accurately to the direction in which the c-axis is projected onto the main surface. It is possible to perform mask alignment in parallel.
- the dark region may include crystal defects provided in the active layer.
- the well layer has crystal defects due to the growth temperature and the quantum well structure.
- this crystal defect can be used as an alignment mark.
- the dark region is likely to occur when the growth temperature of the p-type semiconductor layer after growing the light emitting layer is too high or the growth time is long.
- the long side in the dark region in the emission image excited by the mercury lamp extends in the direction of the a-axis, for example, and the long side preferably has a length of 230 ⁇ m or more.
- a defect region observed as a dark region in a light emission image excited with a mercury lamp is a defect related to crystal growth, crystallographic information is reflected in the shape and orientation of the structure.
- the dark region is characterized by being enlarged by heat treatment at a high temperature of 800 degrees Celsius or higher.
- the epitaxial substrate for the group III nitride semiconductor laser device can have the following structure.
- the epitaxial substrate includes a substrate having a semipolar main surface made of a hexagonal group III nitride semiconductor, and a semiconductor stack provided on the semipolar main surface of the substrate.
- the semiconductor stack includes a semiconductor region for the laser structure, the semiconductor region comprising a first cladding layer made of a gallium nitride semiconductor of a first conductivity type and a first cladding layer made of a gallium nitride semiconductor of a second conductivity type. 2 cladding layers and an active layer.
- the active layer includes a gallium nitride based semiconductor layer.
- the c-axis of the hexagonal group III nitride semiconductor of the substrate is inclined at an angle ALPHA with respect to the normal axis in the m-axis direction of the hexagonal group III nitride semiconductor.
- the semiconductor stack includes the above structure that extends along the reference axis indicating the direction of the a-axis of the hexagonal group III nitride semiconductor.
- This epitaxial substrate is suitable for the shape of a group III nitride semiconductor laser element including a laser stripe along the direction of the mn plane defined by the m-axis and the normal axis of a hexagonal group III nitride semiconductor.
- the group III nitride semiconductor laser device is formed on a semipolar plane substrate.
- the semiconductor stack includes a band-shaped structure having an edge extending along the reference axis indicating the direction of the a-axis of the hexagonal group III nitride semiconductor, the structure is formed using the epitaxial substrate.
- Laser beam orientation and laser cavity orientation can be provided for the manufactured group III nitride semiconductor laser device.
- the angle ALPHA formed by the normal axis and the c-axis of the hexagonal group III nitride semiconductor is preferably in the range of 45 degrees to 80 degrees or 100 degrees to 135 degrees.
- the active layer is provided between the first cladding layer and the second cladding layer, and the first cladding layer, the second cladding layer, and the active layer are arranged along the normal axis of the semipolar main surface. ing.
- the structure can have a surface form extending in the direction of the a-axis on the upper surface of the semiconductor stack. At this time, the structure can be confirmed by observing the appearance of the epitaxial substrate.
- the position of the depression can be specified by reflected light or transmitted light using ultraviolet rays, visible light, infrared rays, or the like.
- the structure (for example, the long side of the dark region or the groove on the epi surface) in the epitaxial substrate has a deviation angle in the range of ⁇ 0.5 degrees or more and +0.5 degrees or less with respect to the a-axis direction. Is good.
- the structure has a deviation angle in the range of ⁇ 0.3 degrees or more and +0.3 degrees or less with respect to the direction of the a-axis.
- a group III nitride semiconductor laser device can be manufactured by the following process using this epitaxial substrate.
- Mask alignment can be performed using a linear morphology such as a groove provided on the epi surface.
- the linear morphology can be detected using the mask aligner sensor device or visually.
- the position and orientation of the semiconductor product on the mask aligner is determined so that the direction of the waveguide is perpendicular to the linear morphology.
- Mask alignment can be performed using a dark region in an excitation image by a mercury lamp.
- a semiconductor product is installed in the laser scriber device.
- a light emission image is obtained by excitation using a mercury lamp.
- the semiconductor product is aligned on the laser scriber device.
- a mark is formed on a semiconductor product using a laser scriber device.
- Mask alignment is performed using this mark as a reference. By this procedure, it is possible to match the waveguide and the crystal orientation with high accuracy.
- a low threshold current is enabled on the semipolar plane of the support base in which the c-axis of the hexagonal group III nitride is inclined in the m-axis direction.
- a group III nitride semiconductor laser device having a laser resonator and a structure capable of improving the oscillation yield is provided.
- a method for manufacturing this group III nitride semiconductor laser device is provided.
- an epitaxial substrate for the group III nitride semiconductor laser device is provided.
- SYMBOLS 11 Group III nitride semiconductor laser element, 13 ... Laser structure, 13a ... 1st surface, 13b ... 2nd surface, 13c, 13d ... Edge, 15 ... Electrode, 17 ... Support base
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Abstract
Description
以下の通り、半極性面GaN基板を準備し、割断面の垂直性を観察した。基板には、HVPE法で厚く成長した(0001)GaNインゴットからm軸方向に75度の角度で切り出した{20-21}面GaN基板を用いた。GaN基板の主面は鏡面仕上げであり、裏面は研削仕上げされた梨地状態であった。基板の厚さは370μmであった。
実施例1では、半極性{20-21}面を有するGaN基板において、c軸を基板主面に投影した方向に垂直にケガキ線を入れて押圧して得た割断面は、基板主面に対して平坦性及び垂直性を有することがわかった。そこでこの割断面をレーザの共振器としての有用性を調べるため、以下の通り、図8に示されるレーザーダイオードを有機金属気相成長法により成長した。原料にはトリメチルガリウム(TMGa)、トリメチルアルミニウム(TMAl)、トリメチルインジウム(TMIn)、アンモニア(NH3)、シラン(SiH4)を用いた。基板71を準備した。基板71には、HVPE法で厚く成長した(0001)GaNインゴットからm軸方向に0度から90度の範囲の角度でウェハスライス装置を用いて切り出し、m軸方向へのc軸の傾斜角度ALPHAが、0度から90度の範囲の所望のオフ角を有するGaN基板を作製した。例えば、75度の角度で切り出したとき、{20-21}面GaN基板が得られ、図7の(b)部に示される六方晶系の結晶格子において参照符号71aによって示されている。
図9に示されたデータは以下のものである。
しきい値電流、 しきい値電流。
偏光度、(M方向ストライプ)、(<11-20>ストライプ)。
0.08、 64、 20。
0.05、 18、 42。
0.15、 9、 48。
0.276、 7、 52。
0.4 6。
図10に示されたデータは以下のものである。
傾斜角、歩留まり。
10、 0.1。
43、 0.2。
58、 50。
63、 65。
66、 80。
71、 85。
75、 80。
79、 75。
85、 45。
90、 35。
図11に示されたデータは以下のものである。
積層欠陥密度(cm-1)、歩留まり。
500、 80。
1000、 75。
4000、 70。
8000、 65。
10000、 20。
50000、 2。
図12に示されたデータは以下のものである。
基板厚、歩留まり。
48、 10。
80、 65。
90、 70。
110、 45。
150、 48。
200、 30。
400、 20。
実施例2では、{20-21}面を有するGaN基板上に、半導体レーザのための複数のエピタキシャル膜を成長した。上記のように、スクライブ溝の形成と押圧とによって光共振器用の端面が形成された。これらの端面の候補を見いだすために、(20-21)面に90度近傍の角度を成し、a面とは異なる面方位を計算により求めた。図13を参照すると、以下の角度及び面方位が、(20-21)面に対して90度近傍の角度を有する。
具体的な面指数、{20-21}面に対する角度。
(-1016): 92.46度。
(-1017): 90.10度。
(-1018): 88.29度。
以下の通り、レーザーダイオードを有機金属気相成長法により成長した。原料にはトリメチルガリウム(TMGa)、トリメチルアルミニウム(TMAl)、トリメチルインジウム(TMIn)、アンモニア(NH3)、シラン(SiH4)を用いた。基板として、HVPE法で成長した2インチ{20-21}面GaN基板を用いた。GaN基板は、a面を示すオリエンテーションフラット(「OF」と記す)を有する。OF面とa面とのズレ角度を示す面精度を面検査器にて測定し、面精度は0.1度以下であった。このため、GaN基板主面にc軸を投影した投影成分の方向とa面を示す端面(例えばOF又は、a面のへき開面)は、-0.1度以上+0.1度以下の角度範囲の精度で平行である。
レーザ光出力100mW。
走査速度は5mm/s。
この条件で形成されたスクライブ溝は、例えば、長さ100μm、幅10μm、深さ40μmの溝であった。半導体チップ幅に対応する300μm間隔で基板の表面に電極の開口部と通して直接レーザ光を照射することによって、スクライブ溝を周期的に形成した。共振器長は600μmとした。
既に述べたように、半導体レーザにおいては、導波路と共振器端面を精度よく垂直にすることにより、半導体レーザの特性を良好かつ安定化させることができる。その故に、端面の割れやすさは結晶方位に大きく依存するので、結晶方位を正確に示す目印を見出すとともに、その目印を基準にしてその目印に対して平行又は垂直にマスクアライメントを行うことができるとき、マスクアライメントの精度を高めることが可能である。半導体ウエハには、図23の(a)部に示されるように、例えばオリエンテーションフラット(以下、「オリフラ」として参照する)OFと呼ばれる結晶方位を示す切り欠きを設けることができる。
{20-21}面GaN基板上にレーザ構造のためのエピタキシャル積層構造を成長する。エピタキシャル積層構造は、n型半導体領域、活性層及びp型半導体領域を含み、活性層は、InGaN井戸層を含む単一量子井戸構造を有する。この成長の後に、水銀ランプ(波長365nm)を用いて励起してエピタキシャル基板の上面の蛍光像を観察した。図29の(a)部は、水銀ランプを用いて励起した際のエピタキシャル基板の上面の蛍光像を示す図面である。図29の(a)部に示すように、上面からの発光像における暗領域(水銀ランプ励起で発光しない領域)が観測される。暗領域は例えば五角形の形状を成している。五角形の最も長い辺(長辺)は、a軸方向にほぼ平行である。また、発明者らの観察によれば、暗領域の断面は、図29の(b)部、図29の(c)部及び図29の(d)部に示すような典型的な断面形状、例えば五角形、等脚台形といった台形、二等辺三角形といった三角形を有しており、これらの断面形状は、最長の辺に直交する軸に関して左右対称である。例えば三角形及び五角形の各々は、一頂点を通過し長辺に直交する軸に関して左右対称である。
Claims (46)
- III族窒化物半導体レーザ素子であって、
六方晶系III族窒化物半導体からなり半極性主面を有する支持基体、及び前記支持基体の前記半極性主面上に設けられた半導体領域を含むレーザ構造体と、
前記レーザ構造体の前記半導体領域上に設けられた電極と、
を備え、
前記半導体領域は、第1導電型の窒化ガリウム系半導体からなる第1のクラッド層と、第2導電型の窒化ガリウム系半導体からなる第2のクラッド層と、前記第1のクラッド層と前記第2のクラッド層との間に設けられた活性層とを含み、
前記第1のクラッド層、前記第2のクラッド層及び前記活性層は、前記半極性主面の法線軸に沿って配列されており、
前記活性層は窒化ガリウム系半導体層を含み、
前記支持基体の前記六方晶系III族窒化物半導体のc軸は、前記六方晶系III族窒化物半導体のm軸の方向に前記法線軸に対して角度ALPHAで傾斜しており、
前記レーザ構造体は、前記六方晶系III族窒化物半導体のm軸及び前記法線軸によって規定されるm-n面に交差する第1及び第2の割断面を含み、
当該III族窒化物半導体レーザ素子のレーザ共振器は前記第1及び第2の割断面を含み、
前記レーザ構造体は第1及び第2の面を含み、前記第1の面は前記第2の面の反対側の面であり、
前記第1及び第2の割断面は、それぞれ前記第1の面のエッジから前記第2の面のエッジまで延在し、
前記角度ALPHAは、45度以上80度以下又は100度以上135度以下の範囲であり、
前記レーザ構造体は、前記支持基体の前記半極性主面上に延在するレーザ導波路を含み、前記レーザ導波路は、前記第1及び第2の割断面の一方から他方への方向に向く導波路ベクトルの方向に延在し、
前記六方晶系III族窒化物半導体のc軸の方向を示すc軸ベクトルは、前記半極性主面に平行な投影成分と、前記法線軸に平行な垂直成分とを含み、
前記導波路ベクトルと前記投影成分との成すズレ角は-0.5度以上+0.5度以下の範囲にある、III族窒化物半導体レーザ素子。 - III族窒化物半導体レーザ素子であって、
六方晶系III族窒化物半導体からなり半極性主面を有する支持基体、及び前記支持基体の前記半極性主面上に設けられた半導体領域を含むレーザ構造体と、
前記レーザ構造体の前記半導体領域上に設けられた電極と、
を備え、
前記半導体領域は、第1導電型の窒化ガリウム系半導体からなる第1のクラッド層と、第2導電型の窒化ガリウム系半導体からなる第2のクラッド層と、前記第1のクラッド層と前記第2のクラッド層との間に設けられた活性層とを含み、
前記第1のクラッド層、前記第2のクラッド層及び前記活性層は、前記半極性主面の法線軸に沿って配列されており、
前記活性層は窒化ガリウム系半導体層を含み、
前記支持基体の前記六方晶系III族窒化物半導体のc軸は、前記六方晶系III族窒化物半導体のm軸の方向に前記法線軸に対して角度ALPHAで傾斜しており、
前記レーザ構造体は、前記六方晶系III族窒化物半導体のm軸及び前記法線軸によって規定されるm-n面に交差する第1及び第2の割断面を含み、
当該III族窒化物半導体レーザ素子のレーザ共振器は前記第1及び第2の割断面を含み、
前記レーザ構造体は第1及び第2の面を含み、前記第1の面は前記第2の面の反対側の面であり、
前記第1及び第2の割断面は、それぞれ前記第1の面のエッジから前記第2の面のエッジまで延在し、
前記角度ALPHAは、45度以上80度以下又は100度以上135度以下の範囲であり、
前記レーザ構造体は、前記支持基体の前記半極性主面上に延在する導波路を含み、前記導波路は、前記第1及び第2の割断面の一方から他方への方向に向く導波路ベクトルの方向に延在し、
前記レーザ構造体は、水銀ランプによる光励起による蛍光顕微鏡像において所定の軸の方向に延在する筋状発光像を示し、
前記導波路ベクトルと前記所定の軸に直交する直交方向との成すズレ角は、-0.5度以上+0.5度以下の範囲にある、III族窒化物半導体レーザ素子。 - 前記法線軸と前記六方晶系III族窒化物半導体のc軸との成す角度は、63度以上80度以下又は100度以上117度以下の範囲である、請求項1又は請求項2に記載されたIII族窒化物半導体レーザ素子。
- 前記支持基体の厚さは400μm以下である、請求項1~請求項3のいずれか一項に記載されたIII族窒化物半導体レーザ素子。
- 前記支持基体の厚さは、50μm以上100μm以下である、請求項1~請求項4のいずれか一項に記載されたIII族窒化物半導体レーザ素子。
- 前記活性層からのレーザ光は、前記六方晶系III族窒化物半導体のa軸の方向に偏光している、請求項1~請求項5のいずれか一項に記載されたIII族窒化物半導体レーザ素子。
- 当該III族窒化物半導体レーザ素子におけるLEDモードにおける光は、前記六方晶系III族窒化物半導体のa軸の方向に偏光成分I1と、前記六方晶系III族窒化物半導体のc軸を主面に投影した方向に偏光成分I2を含み、
前記偏光成分I1は前記偏光成分I2よりも大きい、請求項1~請求項6のいずれか一項に記載されたIII族窒化物半導体レーザ素子。 - 前記半極性主面は、{20-21}面、{10-11}面、{20-2-1}面、及び{10-1-1}面のいずれかの面から-4度以上+4度以下の範囲でオフした微傾斜面である、請求項1~請求項7のいずれか一項に記載されたIII族窒化物半導体レーザ素子。
- 前記半極性主面は、{20-21}面、{10-11}面、{20-2-1}面、及び{10-1-1}面のいずれかである、請求項1~請求項8のいずれか一項に記載されたIII族窒化物半導体レーザ素子。
- 前記支持基体の積層欠陥密度は1×104cm-1以下である、請求項1~請求項9のいずれか一項に記載されたIII族窒化物半導体レーザ素子。
- 前記支持基体は、GaN、AlGaN、AlN、InGaN及びInAlGaNのいずれかからなる、請求項1~請求項10のいずれか一項に記載されたIII族窒化物半導体レーザ素子。
- 前記第1及び第2の割断面の少なくともいずれか一方に設けられた誘電体多層膜を更に備える、請求項1~請求項11のいずれか一項に記載されたIII族窒化物半導体レーザ素子。
- 前記活性層は、波長360nm以上600nm以下の光を発生するように設けられた発光領域を含む、請求項1~請求項12のいずれか一項に記載されたIII族窒化物半導体レーザ素子。
- 前記活性層は、波長430nm以上550nm以下の光を発生するように設けられた量子井戸構造を含む、請求項1~請求項13のいずれか一項に記載されたIII族窒化物半導体レーザ素子。
- 前記第1及び第2の割断面の各々には、前記支持基体の端面及び前記半導体領域の端面が現れており、
前記半導体領域の前記活性層における端面と前記六方晶系窒化物半導体からなる支持基体のm軸に直交する基準面との成す角度は、前記III族窒化物半導体のc軸及びm軸によって規定される第1平面において(ALPHA-5)度以上(ALPHA+5)度以下の範囲の角度を成す、請求項1~請求項14のいずれか一項に記載されたIII族窒化物半導体レーザ素子。 - 前記ズレ角は-0.3度以上+0.3度以下の範囲にある、請求項1~請求項14のいずれか一項に記載されたIII族窒化物半導体レーザ素子。
- III族窒化物半導体レーザ素子を作製する方法であって、
六方晶系III族窒化物半導体からなり半極性主面を有する基板を準備する工程と、
前記半極性主面上に形成された半導体領域と前記基板とを含むレーザ構造体、アノード電極、及びカソード電極を有する基板生産物を形成する工程と、
前記六方晶系III族窒化物半導体のa軸の方向に前記基板生産物の第1の面を部分的にスクライブする工程と、
前記基板生産物の第2の面への押圧により前記基板生産物の分離を行って、別の基板生産物及びレーザバーを形成する工程と、
を備え、
前記第1の面は前記第2の面の反対側の面であり、
前記半導体領域は前記第1の面と前記基板との間に位置し、
前記レーザバーは、前記第1の面から前記第2の面にまで延在し前記分離により形成された第1及び第2の端面を有し、
前記第1及び第2の端面は当該III族窒化物半導体レーザ素子のレーザ共振器を構成し、
前記アノード電極及びカソード電極は、前記レーザ構造体上に形成され、
前記半導体領域は、第1導電型の窒化ガリウム系半導体からなる第1のクラッド層と、第2導電型の窒化ガリウム系半導体からなる第2のクラッド層と、前記第1のクラッド層と前記第2のクラッド層との間に設けられた活性層とを含み、
前記第1のクラッド層、前記第2のクラッド層及び前記活性層は、前記半極性主面の法線軸に沿って配列されており、
前記活性層は窒化ガリウム系半導体層を含み、
前記基板の前記六方晶系III族窒化物半導体のc軸は、前記六方晶系III族窒化物半導体のm軸の方向に前記法線軸に対して角度ALPHAで傾斜しており、
前記第1及び第2の端面は、前記六方晶系III族窒化物半導体のm軸及び前記法線軸によって規定されるm-n面に交差し、
前記角度ALPHAは、45度以上80度以下又は100度以上135度以下の範囲であり、
前記レーザ構造体は、前記基板の前記半極性主面上に延在するレーザ導波路を含み、前記レーザ導波路は、前記第1及び第2の割断面の一方から他方への方向に向く導波路ベクトルの方向に延在し、
前記六方晶系III族窒化物半導体のc軸の方向を示すc軸ベクトルは、前記半極性主面に平行な投影成分と、前記法線軸に平行な垂直成分とを含み、
前記導波路ベクトルと前記投影成分との成すズレ角は-0.5度以上+0.5度以下の範囲にあり、
前記基板生産物の前記半導体領域は、前記六方晶系III族窒化物半導体のa軸の方向を示すマークを含み、
前記基板生産物を形成する工程では、前記レーザ導波路の向きは前記マークの基準に決定される、III族窒化物半導体レーザ素子を作製する方法。 - 前記ズレ角は-0.3度以上+0.3度以下の範囲にある、請求項17に記載されたIII族窒化物半導体レーザ素子を作製する方法。
- 前記角度ALPHAは、63度以上80度以下又は100度以上117度以下の範囲である、請求項17又は請求項18に記載されたIII族窒化物半導体レーザ素子を作製する方法。
- 前記基板生産物を形成する前記工程において、前記基板は、前記基板の厚さが400μm以下になるようにスライス又は研削といった加工が施され、
前記第2の面は前記加工により形成された加工面、又は前記加工面に上に形成された電極を含む面である、請求項17~請求項19のいずれか一項に記載されたIII族窒化物半導体レーザ素子を作製する方法。 - 前記基板生産物を形成する前記工程において、前記基板は、前記基板の厚さが50μm以上100μm以下になるように研磨され、
前記第2の面は前記研磨により形成された研磨面、又は前記研磨面に上に形成された電極を含む面である、請求項17~請求項20のいずれか一項に記載されたIII族窒化物半導体レーザ素子を作製する方法。 - 前記スクライブは、レーザスクライバを用いて行われ、
前記スクライブによりスクライブ溝が形成され、前記スクライブ溝の長さは、前記六方晶系III族窒化物半導体のa軸及び前記法線軸によって規定されるa-n面と前記第1の面との交差線の長さよりも短い、請求項17~請求項21のいずれか一項に記載されたIII族窒化物半導体レーザ素子を作製する方法。 - 前記半極性主面は、{20-21}面、{10-11}面、{20-2-1}面、及び{10-1-1}面のいずれかである、請求項17~請求項22のいずれか一項に記載されたIII族窒化物半導体レーザ素子を作製する方法。
- 前記第1及び第2の端面の各々における前記活性層の端面は、前記六方晶系窒化物半導体からなる支持基体のm軸に直交する基準面に対して、前記六方晶系III族窒化物半導体のc軸及びm軸によって規定される平面において(ALPHA-5)度以上(ALPHA+5)度以下の範囲の角度を成す、請求項17~請求項23のいずれか一項に記載されたIII族窒化物半導体レーザ素子を作製する方法。
- 前記基板は、GaN、AlGaN、AlN、InGaN及びInAlGaNのいずれかからなる、請求項17~請求項24のいずれか一項に記載されたIII族窒化物半導体レーザ素子を作製する方法。
- 前記基板は、前記六方晶系III族窒化物半導体のa面を示すオリエンテーションフラットを含み、
前記マークは、前記オリエンテーションフラットを含む、請求項17~請求項25のいずれか一項に記載されたIII族窒化物半導体レーザ素子を作製する方法。 - 前記基板は前記六方晶系III族窒化物半導体のa面におけるへき開面を含み、
前記マークは、前記へき開面を含む、請求項17~請求項26のいずれか一項に記載されたIII族窒化物半導体レーザ素子を作製する方法。 - 前記基板生産物を形成する工程では、レーザ光を前記基板生産物に照射して、前記六方晶系III族窒化物半導体のa軸の方向に配列されたレーザマークを形成しており、
前記マークは、前記レーザマークの配列を含む、請求項17~請求項27のいずれか一項に記載されたIII族窒化物半導体レーザ素子を作製する方法。 - 前記レーザ構造体は、水銀ランプによる光励起による蛍光顕微鏡像において所定の軸の方向に延在する筋状発光像を示し、
前記レーザマークの配列の向きは、前記筋状発光像に係る前記所定の軸の方向を基準にして決定され、
前記導波路ベクトルと前記所定の軸に直交する直交方向との成すズレ角は、-0.5度以上+0.5度以下の範囲にある、請求項28に記載されたIII族窒化物半導体レーザ素子を作製する方法。 - III族窒化物半導体レーザ素子のためのエピタキシャル基板であって、
六方晶系III族窒化物半導体からなる半極性主面を有する基板と、
前記基板の前記半極性主面上に設けられた半導体積層と、
を備え、
前記半導体積層はレーザ構造体のための半導体領域を含み、
前記半導体領域は、第1導電型の窒化ガリウム系半導体からなる第1のクラッド層と、第2導電型の窒化ガリウム系半導体からなる第2のクラッド層と、前記第1のクラッド層と前記第2のクラッド層との間に設けられた活性層とを含み、
前記第1のクラッド層、前記第2のクラッド層及び前記活性層は、前記半極性主面の法線軸に沿って配列されており、
前記活性層は窒化ガリウム系半導体層を含み、
前記基板の前記六方晶系III族窒化物半導体のc軸は、前記六方晶系III族窒化物半導体のm軸の方向に前記法線軸に対して角度ALPHAで傾斜しており、
前記法線軸と前記六方晶系III族窒化物半導体のc軸との成す角度ALPHAは、45度以上80度以下又は100度以上135度以下の範囲であり、
前記半導体積層は、前記六方晶系III族窒化物半導体のa軸の方向を示す基準軸に沿って延在する構造物を含む、エピタキシャル基板。 - 前記構造物は前記a軸の方向に230μm以上の長さを有する、請求項30に記載されたエピタキシャル基板。
- 前記構造物は、前記半導体積層の上面において前記a軸の方向に延在する表面形態を有する、請求項30又は請求項31に記載されたエピタキシャル基板。
- 前記構造物は、前記半導体積層の上面における窪みを含む、請求項30~請求項32のいずれか一項に記載されたエピタキシャル基板。
- 前記構造物は、前記半導体積層の上面に到達した積層欠陥の位置に設けられている、請求項30~請求項33のいずれか一項に記載されたエピタキシャル基板。
- 前記構造物は、前記a軸の方向に対して-0.5度以上及び+0.5度以下の範囲のズレ角を成す、請求項30~請求項34のいずれか一項に記載されたエピタキシャル基板。
- 前記構造物は、前記a軸の方向に対して-0.3度以上及び+0.3度以下の範囲のズレ角を成す、請求項30~請求項35のいずれか一項に記載されたエピタキシャル基板。
- 前記構造物は、水銀ランプで励起した発光像において暗領域として観察される欠陥領域を含む、請求項30に記載されたエピタキシャル基板。
- 前記発光像中の暗領域における長辺は前記基準軸の方向に延在しており、
前記長辺は230μm以上の長さを有する、請求項37に記載されたエピタキシャル基板。 - 前記長辺と前記a軸の方向との成すズレ角は-0.5度以上+0.5度以下の範囲にある、請求項37又は請求項38に記載されたエピタキシャル基板。
- 前記長辺と前記a軸の方向との成すズレ角は-0.3度以上+0.3度以下の範囲にある、請求項37~請求項39のいずれか一項に記載されたエピタキシャル基板。
- 前記暗領域は、前記活性層に設けられた結晶欠陥を含む、請求項37~請求項40のいずれか一項に記載されたエピタキシャル基板。
- 前記a軸に直交する平面における断面形状が前記結晶欠陥の少なくとも一部において六角形である、請求項37~請求項41のいずれか一項に記載されたエピタキシャル基板。
- 前記暗領域は、摂氏800度以上の温度おける熱処理により拡大される、請求項37~請求項42のいずれか一項に記載されたエピタキシャル基板。
- III族窒化物半導体レーザ素子を作製する方法であって、
請求項30~請求項42のいずれか一項に記載されたエピタキシャル基板を準備する工程と、
前記エピタキシャル基板を用いて、アノード電極及びカソード電極を有する基板生産物を形成する工程と、
前記エピタキシャル基板の前記構造物を基準にして向きを規定したスクライブマークを前記基板生産物に形成する工程と、
前記基板生産物の押圧により前記基板生産物の分離を行って、別の基板生産物及びレーザバーを形成する工程と、
を備え、
前記レーザバーは、前記分離により形成された第1及び第2の端面を有し、
前記第1及び第2の端面は当該III族窒化物半導体レーザ素子のレーザ共振器を構成し、
前記基板生産物は、六方晶系III族窒化物半導体からなる半極性主面を有する前記基板と前記半極性主面上に形成された半導体領域とを含むレーザ構造体を含み、
前記アノード電極及びカソード電極は、前記レーザ構造体上に形成され、
前記第1及び第2の端面は、前記六方晶系III族窒化物半導体のm軸及び前記法線軸によって規定されるm-n面に交差する、III族窒化物半導体レーザ素子を作製する方法。 - 前記基板生産物を形成する工程は、前記レーザ構造体の前記半導体領域を覆う絶縁膜を形成する工程を含み、
前記絶縁膜にはストライプ形状の開口が形成されており、
前記開口の形成の際に、前記開口の向きは前記構造物を基準にして規定されており、
前記アノード電極及びカソード電極のいずれか一方は、前記絶縁膜の前記開口を介して前記レーザ構造体に接触する、請求項44に記載されたIII族窒化物半導体レーザ素子を作製する方法。 - 前記レーザ構造体の前記半導体領域はリッジ構造を有しており、
前記リッジ構造はストライプ形状を有しており、
前記リッジ構造の形成の際に、前記リッジ構造のストライプ形状の向きは前記構造物を基準にして規定される、請求項44又は請求項45に記載されたIII族窒化物半導体レーザ素子を作製する方法。
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KR20120099136A (ko) | 2012-09-06 |
CN102668281B (zh) | 2014-05-28 |
US8507305B2 (en) | 2013-08-13 |
CN103606817A (zh) | 2014-02-26 |
JP2011151349A (ja) | 2011-08-04 |
US20110158277A1 (en) | 2011-06-30 |
US20120258557A1 (en) | 2012-10-11 |
TW201134040A (en) | 2011-10-01 |
EP2518840A4 (en) | 2014-12-31 |
CN102668281A (zh) | 2012-09-12 |
JP5327154B2 (ja) | 2013-10-30 |
EP2518840A1 (en) | 2012-10-31 |
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