Semiconductor laser element

Abstract

To provide a semiconductor laser element that is reduced in light loss.SOLUTION: There is provided a semiconductor laser element that has an n-side clad layer, an n-side guide layer, an active layer, a p-side guide layer, and a p-side clad layer, which are each made of a nitride semiconductor, upward in this order, and also emits ultraviolet light, and the semiconductor laser element comprises a first surface and a ridge part protruding upward from the first surface, wherein the first surface is present above a lower end of the p-side guide layer and also below an upper end of the p-side guide layer. Here, the n-side guide layer has a smaller thickness than the n-side clad layer and also has a smaller Al composition ratio than the n-side clad layer, and the p-side guide layer has a smaller thickness than the p-side clad layer and the n-side guide layer and also has a smaller Al composition ratio than the p-side clad layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a semiconductor laser device. [Background technology]

[0002] Conventionally, nitride-based semiconductor light-emitting elements that emit blue light have been known, but there is a demand for high-output nitride-based semiconductor light-emitting elements that emit ultraviolet light with shorter wavelengths (see, for example, Patent Document 1). For example, nitride-based semiconductor light-emitting elements can be used as light sources for exposure, processing, and the like. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-117509 Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure provides a semiconductor laser device with reduced optical loss. [Means for solving the problem]

[0005] In one embodiment, the semiconductor laser element is a semiconductor laser element that emits ultraviolet light and has, in this order from top to bottom, an n-side cladding layer, an n-side guide layer, an active layer, a p-side guide layer, and a p-side cladding layer, each of which is made of a nitride semiconductor, the semiconductor laser element has a first surface and a ridge portion protruding upward from the first surface, the first surface is located above a lower end of the p-side guide layer and below an upper end of the p-side guide layer, the thickness of the n-side guide layer is smaller than the thickness of the n-side cladding layer, the Al composition ratio of the n-side guide layer is smaller than the Al composition ratio of the n-side cladding layer, the thickness of the p-side guide layer is smaller than the thickness of the p-side cladding layer and smaller than the thickness of the n-side guide layer; The Al composition ratio of the p-side guide layer is smaller than the Al composition ratio of the p-side cladding layer. [Effects of the Invention]

[0006] A semiconductor laser device with reduced optical loss is realized. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic cross-sectional view of a semiconductor laser element. [Figure 2] 1 is a schematic diagram of an example of a layer structure from an n-side cladding layer to a p-side cladding layer of a semiconductor laser element. [Figure 3] 10 is a diagram showing the results of a simulation of fluctuations in light intensity with respect to the distance from the upper end of the p-side of the semiconductor laser elements in Example 1 and Comparative Example 1. FIG. [Figure 4] 1 is a diagram showing the relationship between the emission angle (radiation angle) from the light-emitting end facet and the radiation intensity in the slow-axis direction of the semiconductor laser elements in Example 1 and Comparative Example 1. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments for carrying out the present disclosure will be described with reference to the drawings. The following description is intended to embody the technical concept of the present disclosure and, unless otherwise specified, does not limit the present disclosure to the following description. In this disclosure, terms such as "upper" and "lower" may be used for ease of understanding. However, this does not limit the orientation of the semiconductor laser element during use; the orientation of the semiconductor laser element is arbitrary. In each drawing, components having the same function may be designated by the same reference numeral. For convenience, the embodiments may be shown separately to facilitate explanation or understanding of the main points. However, partial substitution or combination of the configurations shown in different embodiments or Example 1 is possible. In the embodiments shown later, differences from the previously shown embodiments will be mainly described, and overlapping descriptions of commonalities with the previously shown embodiments may be omitted. The size and positional relationship of components shown in each drawing may be exaggerated for clarity.

[0009] <Embodiment> Fig. 1 is a schematic cross-sectional view of a semiconductor laser device 10 according to an embodiment. This cross section is perpendicular to the resonance direction of the semiconductor laser device 10. Fig. 2 is a diagram schematically illustrating an example of the layer structure from the n-side cladding layer to the p-side cladding layer of the semiconductor laser device 10.

[0010] The semiconductor laser device 10 is a semiconductor laser device that emits ultraviolet light and has, in this order from top to bottom, an n-side cladding layer 2, an n-side guide layer 3, an active layer 4, a p-side guide layer 6, and a p-side cladding layer 7, each made of a nitride semiconductor. The semiconductor laser device has a first surface 611 and a ridge portion 610 that protrudes upward from the first surface 611. The first surface 611 is located above the lower end of the p-side guide layer 6 and below the upper end of the p-side guide layer 6. The thickness of the n-side guide layer 3 is smaller than the thickness of the n-side cladding layer 2. The Al composition ratio of the n-side guide layer 3 is smaller than the Al composition ratio of the n-side cladding layer 2. The thickness of the p-side guide layer 6 is smaller than the thickness of the p-side cladding layer 7 and is also smaller than the thickness of the n-side guide layer 3. The Al composition ratio of the p-side guide layer 6 is smaller than the Al composition ratio of the p-side cladding layer 7. With this configuration, in the distribution of light intensity in the stacking direction within the semiconductor laser device 10, the position at which the light intensity peaks can be moved away from the p-side guide layer 6 and closer to the n-side guide layer 3. Details of the distribution of the Al composition ratio of the semiconductor laser device 10 will be described later with reference to FIG.

[0011] (Semiconductor laser element 10) As shown in FIG. 1, the semiconductor laser device 10 includes a substrate 1, an n-side cladding layer 2, an n-side guide layer 3, an active layer 4, a p-side barrier layer 5, a p-side guide layer 6, a p-side cladding layer 7, a p-side electrode 8, and a p-side pad electrode 9. The semiconductor laser device 10 is, for example, an edge-emitting laser device having a light-emitting end face and a light-reflecting end face that intersect with the principal surfaces of the semiconductor layers. The stacking direction of the semiconductor laser device 10 may be referred to as the "upward direction," and the opposite direction from the "upward direction" may be referred to as the "downward direction." The stacking direction of the semiconductor laser device 10 is the direction of the p-side cladding layer 7 relative to the n-side cladding layer 2.

[0012] The semiconductor laser device 10 has a ridge portion 610 protruding upward from the p-side guiding layer 6. The ridge portion 610 has a shape in a top view that is long in the direction connecting the light-emitting end face and the light-reflecting end face, e.g., a rectangular shape with its short sides parallel to the light-reflecting end face and its long sides perpendicular to the light-reflecting end face. The portion of the active layer 4 directly below the ridge portion 610 and its vicinity constitutes an optical waveguide region. The semiconductor laser device also has a first surface 611. The first surface 611 is the surface of the p-side guiding layer 6 that continues from the side surface of the ridge portion 610. An insulating film 612 may be provided on the side surface of the ridge portion 610 and the first surface 611. The substrate 1 is made of, for example, an n-type semiconductor, and an n-side electrode 111 is provided on its bottom surface. A p-side electrode 8 is provided in contact with the top surface of the ridge portion 610, and a p-side pad electrode 9 is further provided thereon. The semiconductor laser device 10 can emit laser light, for example, in the ultraviolet region. Laser light in the ultraviolet region is, for example, light with a peak wavelength of 350 nm or more and 400 nm or less.

[0013] The light emitted from the light-emitting end face of the semiconductor laser element 10 may be divergent light having a spread. The divergent light (laser light) emitted from the semiconductor laser element 10 forms an elliptical far-field pattern (hereinafter referred to as "FFP") on a plane parallel to the light-emitting end face. The FFP refers to the shape and light intensity distribution of the emitted light at a position away from the light-emitting end face.

[0014] The light passing through the center of the elliptical shape of the FFP, in other words, the light with peak intensity in the light intensity distribution of the FFP, is called the light traveling along the optical axis. Also, the optical path of the light traveling along the optical axis is called the optical axis of that light. Also, in the light intensity distribution of the FFP, the light with a peak intensity of 1 / e 2 Light having an intensity equal to or greater than this will be referred to as the "main portion" of light.

[0015] In the elliptical shape of the FFP of light emitted from the semiconductor laser element 10, the minor axis direction of the ellipse is the parallel direction of the FFP, and the major axis direction is the perpendicular direction of the FFP. Multiple layers, including an active layer, that make up the semiconductor laser element are stacked in the perpendicular direction of the FFP.

[0016] (Substrate 1) The substrate 1 can be, for example, a nitride semiconductor substrate made of GaN or the like. Examples of semiconductors grown on the substrate 1 include semiconductors grown substantially in the c-axis direction. For example, a GaN substrate having a +c plane ((0001) plane) as its principal surface can be used, and each semiconductor layer can be grown on the +c plane. Here, having a +c plane as its principal surface may include a substrate having an off-angle of approximately ±1 degree or less. Using a substrate having a +c plane as its principal surface has the advantage of excellent mass productivity. The substrate 1 may contain impurities such as Ge, Si, etc.

[0017] (n-side cladding layer 2) The n-side cladding layer 2 is, for example, a layer made of AlGaN. The n-side cladding layer 2 is, for example, an n-type AlGaN layer. The n-side cladding layer 2 has a lower refractive index than the n-side guide layer 3. The n-side cladding layer 2 also serves to confine light. The n-side cladding layer 2 may be in contact with the substrate 1, or another layer may be disposed between the substrate 1 and the n-side cladding layer 2. The layer disposed between the substrate 1 and the n-side cladding layer 2 may be, for example, an n-side contact layer or a crack prevention layer. The crack prevention layer may be, for example, an InGaN layer. The lower surface of the n-side cladding layer 2 is preferably in contact with the crack prevention layer, which reduces the possibility of cracks occurring in the n-side cladding layer 2. The upper surface of the n-side cladding layer 2 is preferably in contact with the n-side guide layer 3, which allows the upper surface of the n-side cladding layer 2 to efficiently reflect light incident from the n-side guide layer 3.

[0018] The n-side cladding layer 2 contains impurities. Examples of impurities include Si. The amount of Si contained in the n-side cladding layer 2 is 1×10 18 cm -3 More than 1×10 19 cm -3Examples of suitable thicknesses include the following. By setting the thickness within this range, the electrical conductivity of the n-side cladding layer 2 can be made suitable. The thickness of the n-side cladding layer 2 can be 500 nm or more and 1000 nm or less, and preferably 650 nm or more and 750 nm or less. By setting the thickness within this range, the light confinement performance of the n-side cladding layer 2 can be improved. The Al composition ratio of the n-side cladding layer 2 can be 6% or more and 13% or less, and preferably 8% or more and 11% or less. By setting the thickness within this range, the refractive index of the n-side cladding layer 2 can be made lower than that of the n-side guide layer 3, and the light confinement performance of the n-side cladding layer 2 can be improved.

[0019] (n-side guide layer 3) The n-side guide layer 3 is, for example, a layer made of AlGaN. The n-side guide layer 3 is, for example, an n-type AlGaN layer. The n-side guide layer 3 has a higher refractive index than the n-side cladding layer 2. The n-side guide layer 3 is a layer that functions as an optical waveguide. Since AlGaN has a lower absorption coefficient for ultraviolet light than GaN, when the n-side guide layer 3 is made of AlGaN, it is easy to reduce optical loss of ultraviolet light in the n-side guide layer. The n-side guide layer 3 is provided above the n-side cladding layer 2. The n-side guide layer 3 is preferably provided in contact with the n-side cladding layer 2, and this structure makes it possible to efficiently confine light to the n-side guide layer 3 side. The n-side cladding layer 2 contains impurities. Examples of impurities include Si. The amount of Si contained in the n-side guide layer 3 is 5×10 17 cm -3 More than 1×10 19 cm -3The following can be mentioned. By setting the thickness within this range, the electrical conductivity of the n-side guide layer 3 can be optimized. The amount of Si contained in the n-side guide layer 3 is less than the amount of Si contained in the n-side cladding layer 2. This configuration can optimize the carrier density in the n-side cladding layer 2 and the n-side guide layer 3. The thickness of the n-side guide layer 3 can be 150 nm or more and 300 nm or less, and preferably 200 nm or more and 250 nm or less. By setting the thickness within this range, the position where the light intensity peaks in the light intensity distribution in the stacking direction within the semiconductor laser device 10 can be moved away from the p-side guide layer 6 and closer to the n-side guide layer 3. Because p-type impurities have a stronger tendency to absorb light than n-type impurities, the p-side guide layer 6 and the p-side cladding layer 7 absorb light more easily than the n-side guide layer 3. Therefore, by moving the position where the light intensity peaks closer to the n-side guide layer 3, optical loss can be reduced. Furthermore, the thickness of the n-side cladding layer 2 is greater than the thickness of the n-side guide layer 3. This allows the light confinement efficiency of the n-side cladding layer 2 to be increased.

[0020] The Al composition ratio of the n-side guide layer 3 can be 3% or more and 9% or less, preferably 5% or more and 7% or less. By setting the Al composition ratio to 5% or more, the absorption coefficient for ultraviolet light emitted by the semiconductor laser device 10 decreases, thereby reducing optical loss. By setting the Al composition ratio to 7% or less, the refractive index of the n-side guide layer 3 can be made higher than that of the n-side cladding layer 2, thereby improving the optical confinement performance of the n-side cladding layer 2. As shown in FIG. 2, the Al composition ratio of the n-side guide layer 3 is smaller than that of the n-side cladding layer 2. This makes the refractive index of the n-side guide layer 3 higher than that of the n-side cladding layer 2, thereby strengthening the optical confinement to the n-side guide layer 3. Note that in layers made of AlGaN, the refractive index tends to increase as the Al composition ratio decreases. Therefore, when comparing the refractive indices of AlGaN layers, the refractive indices may be evaluated by comparing the Al composition ratios of those layers.

[0021] The active layer 4 is made of a nitride semiconductor layer such as GaN or InGaN. The semiconductor laser device 10 has a single quantum well structure or a multiple quantum well structure. The active layer 4 is a part of a single quantum well structure or a multiple quantum well structure. The active layer 4 is a well layer. The active layer 4 is undoped. The thickness of the active layer 4 is preferably 10 nm or more and 30 nm or less. By making the thickness 10 nm or more, deterioration due to operation of the semiconductor laser device 10 can be reduced. On the other hand, by making the thickness 30 nm or less, good crystallinity can be achieved during manufacturing.

[0022] The p-side barrier layer 5 is, for example, an undoped AlGaN layer. The p-side barrier layer 5 is provided for the purpose of confining carriers on the active layer 4 side and improving the probability of radiative recombination. The p-side barrier layer 5 has a higher Al composition ratio than the active layer 4. The p-side barrier layer 5 has a higher band gap energy than the active layer 4. Because the p-side barrier layer 5 is undoped, optical loss due to impurities inside the p-side barrier layer 5 can be reduced. The p-side barrier layer 5 is provided above the active layer 4. The lower surface of the p-side barrier layer 5 is preferably in contact with the active layer 4, thereby improving the probability of radiative recombination in the active layer 4. The thickness of the p-side barrier layer 5 is, for example, 60 nm to 250 nm, and preferably 80 nm to 200 nm. When the p-side barrier layer 5 is 80 nm or more, the probability of radiative recombination in the active layer 4 can be improved. On the other hand, when the p-side barrier layer 5 is 200 nm or less, the driving voltage of the semiconductor laser device 10 can be reduced. The Al composition ratio of the p-side barrier layer 5 is, for example, 3% to 9%, and preferably 5% to 7%. By setting the Al composition ratio in this range, the carrier confinement performance can be improved while reducing the possibility of an increase in series resistance.

[0023] The p-side guide layer 6 is, for example, a layer made of AlGaN. The p-side guide layer 6 is, for example, p-type AlGaN. The p-side guide layer 6 has a higher refractive index than the p-side cladding layer 7. The p-side guide layer 6 is a layer that functions as an optical waveguide. The p-side guide layer 6 is provided above the p-side barrier layer 5. That is, the p-side barrier layer 5 is provided below the p-side guide layer 6. It is preferable that the upper end of the p-side guide layer 6 is provided in contact with the p-side cladding layer 7, and this structure makes it possible to efficiently confine light to the p-side guide layer 6 side. The p-side guide layer 6 may contain impurities. Examples of impurities include Mg. The amount of Mg contained in the p-side guide layer 6 is 1×10 17 cm -3 More than 1×10 19 cm -3 The following are examples of the Al composition ratio of the p-side guide layer 6. By setting the thickness within this range, the electrical conductivity of the p-side guide layer 6 can be made suitable. The thickness of the p-side guide layer 6 can be, for example, 60 nm or more and 200 nm or less, and preferably 80 nm or more and 150 nm or less. By setting the thickness within this range, the position where the light intensity peaks in the light intensity distribution in the stacking direction within the semiconductor laser device 10 is moved away from the p-side guide layer 6 side, thereby reducing optical loss due to the p-side guide layer 6 and the p-side cladding layer 7. Furthermore, the Al composition ratio of the p-side guide layer 6 can be, for example, 3% or more and 9% or less, and preferably 5% or more and 7% or less. By setting the thickness within this range, the refractive index of the p-side guide layer 6 can be made higher than that of the p-side cladding layer 7, and the light confinement performance of the p-side cladding layer 7 can be improved.

[0024] A part of the upper surface of the p-side guiding layer 6 is the first surface 611. The semiconductor laser device 10 also has a ridge portion 610 protruding upward from the first surface 611. A part of the ridge portion 610 is the p-side guiding layer 6. The lower end of the p-side guiding layer 6 is located below the first surface 611, and the upper end of the p-side guiding layer 6 is located above the first surface 611. The thickness of the p-side guiding layer 6 can be defined as the sum of the distance from the lower end of the p-side guiding layer 6 to the first surface 611 and the distance from the first surface 611 to the upper end of the p-side guiding layer 6. The distance from the lower end of the p-side guiding layer 6 to the first surface 611 is preferably 60 nm or more and 70 nm or less. By setting the distance within this range, deterioration of the side portions of the ridge portion 610 can be reduced. The distance from the first surface 611 to the upper end of the p-side guiding layer 6 is preferably 35 nm or more and 45 nm or less. By setting the distance within this range, deterioration of the side portions of the ridge portion 610 can be reduced.

[0025] The thickness of the p-side guide layer 6 is smaller than the thickness of the n-side guide layer 3. This allows the position of the peak light intensity in the light intensity distribution in the stacking direction within the semiconductor laser device 10 to be moved away from the p-side guide layer 6 and closer to the n-side guide layer 3, thereby reducing optical loss. Furthermore, the sum of the thickness of the p-side barrier layer 5 and the thickness of the p-side guide layer 6 is smaller than the thickness of the n-side guide layer 3. This configuration further enhances the effect of moving the light intensity peak closer to the n-side guide layer 3, thereby reducing optical loss. Furthermore, the thickness from the upper end of the active layer 4 to the upper end of the p-side guide layer 6 is smaller than the thickness of the n-side guide layer 3. This configuration further enhances the effect of moving the light intensity peak closer to the n-side guide layer 3, thereby reducing optical loss.

[0026] The p-side cladding layer 7 is, for example, a layer made of AlGaN. The p-side cladding layer 7 is, for example, p-type AlGaN. The p-side cladding layer 7 has a lower refractive index than the p-side guide layer 6. The p-side cladding layer 7 is a layer that plays a role in confining light. The p-side cladding layer 7 is provided above the p-side guide layer 6. It is preferable that the lower end of the p-side cladding layer 7 is provided in contact with the p-side guide layer 6, and this structure makes it possible to efficiently confine light to the p-side guide layer 6 side. The p-side cladding layer 7 may contain impurities. Examples of impurities include Mg. The amount of Mg contained in the p-side cladding layer 7 is 1×10 18 cm -3 More than 1×10 20 cm -3 The following can be mentioned. By setting the thickness within this range, the electrical conductivity of the p-side cladding layer 7 can be made suitable. The amount of Mg contained in the p-side cladding layer 7 is greater than the amount of Mg contained in the p-side guide layer 6. This configuration can make the carrier density in the p-side guide layer 6 and the p-side cladding layer 7 suitable. The thickness of the p-side cladding layer 7 is, for example, 300 nm to 500 nm, and preferably 350 nm to 450 nm. By setting the thickness within this range, the light confinement efficiency of the p-side cladding layer 7 can be improved. The thickness of the p-side cladding layer 7 is greater than the thickness of the p-side guide layer 6. This can improve the light confinement efficiency of the p-side cladding layer 7. As shown in FIG. 2, the Al composition ratio of the p-side cladding layer 7 is greater than the Al composition ratio of the p-side guide layer 6. This makes the refractive index of the p-side guide layer 6 greater than the refractive index of the p-side cladding layer 7, thereby strengthening the light confinement to the p-side guide layer 6. The Al composition ratio of the p-side cladding layer 7 is, for example, 6% to 13%, and preferably 7.5% to 10.5%. By setting it in this range, light confinement to the p-side guide layer 6 can be strengthened.

[0027] In some blue-light-emitting semiconductor laser devices, a transparent electrode such as ITO is provided on the p-side guiding layer instead of a p-side cladding layer, and is used as a light confinement layer. However, ITO has a large absorption coefficient for ultraviolet light, and its use as a p-side cladding layer in an ultraviolet-emitting semiconductor laser device results in significant optical loss. On the other hand, AlGaN has a smaller absorption coefficient for ultraviolet light than ITO. Therefore, by providing a p-side cladding layer 7 made of AlGaN above the p-side guiding layer 6, optical confinement can be achieved on the p-side guiding layer 6 side while reducing optical loss. Furthermore, because AlGaN tends to have a higher refractive index than ITO, when the p-side cladding layer 7 is made of AlGaN, the position of the peak optical intensity in the optical intensity distribution in the stacking direction within the semiconductor laser device 10 is closer to the p-side cladding layer 7 than when the p-side cladding layer is made of ITO. Therefore, by making the thickness of the p-side guide layer 6 smaller than the thickness of the n-side guide layer 3, the position where the light intensity peaks can be moved away from the p-side cladding layer 7 side, thereby reducing optical loss.

[0028] The insulating film 612 is a film provided on the side surfaces of the ridge portion 610 and the first surface 611. The insulating film 612 can be formed of a single layer film or a multilayer film of an oxide or nitride of, for example, Si, Al, Zr, Ti, Nb, Ta, etc. The insulating film 612 has electrical insulating properties.

[0029] The p-side electrode 8 is provided on the upper surface of the ridge portion 610. Examples of materials for the p-side electrode 8 include a single-layer film or a multi-layer film of a metal or alloy such as Ni, Rh, Cr, Au, W, Pt, Ti, or Al, or a conductive oxide containing at least one selected from Zn, In, and Sn. Examples of conductive oxides include ITO (indium tin oxide), IZO (indium zinc oxide), and GZO (gallium-doped zinc oxide). The thickness of the electrode may generally be sufficient to function as an electrode for a semiconductor element. For example, the thickness may be approximately 0.05 μm to 2 μm.

[0030] The p-side pad electrode 9 is provided above the p-side electrode 8 and the insulating film 612. The material of the p-side pad electrode 9 may be, for example, the same as the material of the p-side electrode 8. The width of the p-side pad electrode 9 in a direction perpendicular to the resonance direction of the semiconductor laser element 10 and perpendicular to the stacking direction of the semiconductor laser element 10 (hereinafter also referred to as the lateral direction) is preferably longer than the width of the ridge portion 610 in the same direction. This structure makes it possible to secure a large space on the upper surface of the p-side pad electrode 9 for providing wires, etc.

[0031] The thickness of the p-side barrier layer 5 is greater than the distance from the lower end of the p-side guide layer 6 to the first surface 611. This increases the distance from the upper end of the active layer 4 to the first surface 611. This structure weakens the light confinement in the lateral direction in the active layer 4, and therefore the radiation angle θ of the light in the slow axis direction of the light emitted from the light-emitting end facet of the semiconductor laser device 10 is x Here, the radiation angle θ of light in the slow axis direction is x is based on the light intensity distribution of the FFP, and is 1 / e 2 It can be defined as an angle equivalent to more than twice the amount of light.

[0032] Incidentally, the radiation angle θx of light in the slow axis direction is M 2 There is a relationship between the factors and the following formula 1: M 2 The factor is an index of the spread from an ideal Gaussian beam, and for an ideal Gaussian beam, M 2 The factor is 1. That is, the M 2 Knowing this factor tells us how much the laser light spreads compared to an ideal Gaussian beam.

[0033] M 2 =πdθ x / 4λ...(Formula 1) Here, d is the beam diameter at the light-emitting end face of the semiconductor laser device 10, and is approximated to the lateral width of the ridge portion 610. Also, λ is the wavelength of the laser light in a vacuum, and π is the ratio of the circumference of a circle to its diameter.

[0034] That is, the radiation angle θ of light in the slow axis direction x As M becomes smaller, 2 The value of the factor decreases, improving the quality of light emitted from the semiconductor laser device 10. Therefore, by setting the thickness of the p-side barrier layer 5 to a value greater than the distance from the lower end of the p-side guiding layer 6 to the first surface 611, the quality of light emitted from the semiconductor laser device 10 can be improved.

[0035] However, if the thickness of the p-side barrier layer 5 is set to a value greater than the distance from the lower end of the p-side guide layer 6 to the first surface 611, the lateral confinement of light will be weakened, and the drive current of the semiconductor laser device 10 will increase. That is, the characteristics of the semiconductor laser device 10 will deteriorate. Therefore, by configuring the p-side guide layer 6 to be thinner than the n-side guide layer 3, the position where the light intensity peaks will be closer to the n-side guide layer 3, reducing optical loss and compensating for the deteriorated characteristics. That is, by configuring the thickness of the p-side barrier layer 5 to be thicker than the distance from the lower end of the p-side guide layer 6 to the first surface 611 and by configuring the thickness of the p-side guide layer 6 to be thinner than the n-side guide layer 3, it is possible to reduce optical loss while improving the quality of light.

[0036] The thickness of the p-side barrier layer 5 is greater than the distance from the first surface 611 to the upper end of the p-side guide layer 6. This increases the distance from the upper end of the active layer 4 to the first surface 611, resulting in an improvement in the quality of light emitted from the semiconductor laser device 10. Furthermore, by making the thickness of the p-side barrier layer 5 greater than the distance from the first surface 611 to the upper end of the p-side guide layer 6 and making the thickness of the p-side guide layer 6 smaller than the thickness of the n-side guide layer 3, it is possible to improve the quality of light and reduce optical loss. Furthermore, the distance from the lower end of the p-side barrier layer 5 to the first surface 611 is greater than the thickness of the p-side guide layer 6. This increases the distance from the upper end of the active layer 4 to the first surface 611, resulting in an improvement in the quality of light emitted from the semiconductor laser device 10. Furthermore, by making the distance from the lower end of the p-side barrier layer 5 to the first surface 611 greater than the thickness of the p-side guide layer 6 while making the thickness of the p-side guide layer 6 smaller than the thickness of the n-side guide layer 3, it is possible to improve the quality of light while reducing optical loss.

[0037] The distance from the lower end of the p-side guiding layer 6 to the first surface 611 is greater than the distance from the first surface 611 to the upper end of the p-side guiding layer 6. This reduces deterioration of the side portions of the ridge portion 610 below the first surface 611, and reduces deterioration of the characteristics of the semiconductor laser device 10.

[0038] The thickness of the p-side barrier layer 5 is preferably 90% or more and 110% or less of the thickness of the p-side guide layer 6. By setting the thickness in this range, the distance from the upper end of the active layer 4 to the first surface 611 increases, and as a result, the quality of the light emitted from the semiconductor laser device 10 can be improved.

[0039] The Al composition ratio of the n-side guide layer 3 is 5% or more. The Al composition ratio of the p-side guide layer 6 is preferably 5% or more. Since ultraviolet light is easily absorbed by AlGaN, which has a low Al composition ratio, by setting the Al composition ratio at this value or more, optical loss in the n-side guide layer 3 and / or the p-side guide layer 6 can be reduced.

[0040] The distance from the lower end of the p-side barrier layer 5 to the upper end of the p-side guide layer 6 is 0.5 to 0.95 times the thickness of the n-side guide layer 3. With this configuration, in the light intensity distribution in the stacking direction within the semiconductor laser device 10, the light intensity peak can be moved closer to the n-side guide layer 3, thereby reducing optical loss. Furthermore, the thickness of the p-side guide layer 6 is 0.3 to 0.95 times the thickness of the n-side guide layer 3. With this configuration, the light intensity peak can be moved closer to the n-side guide layer 3, thereby reducing optical loss.

[0041] (Manufacturing method) A manufacturing method of the semiconductor laser device 10 according to the embodiment includes, for example, the following first to sixth steps. The first step is a step of forming an n-side cladding layer 2 on a substrate 1. The second step is a step of forming an n-side guide layer 3 on the n-side cladding layer 2. The third step is a step of forming an active layer 4 on the n-side guide layer 3. The fourth step is a step of forming an undoped p-side barrier layer 5 on the active layer 4. The fifth step is a step of forming a p-side guide layer 6 on the p-side barrier layer 5. The sixth step is a step of forming a p-side cladding layer 7 on the p-side guide layer 6. The manufacturing method of the semiconductor laser device 10 may further include a seventh step of forming an upwardly protruding ridge portion 610 by removing a part of the stacked structure including the p-side cladding layer 7 and the p-side guide layer 6. The effects and preferred configurations of the layers obtained by each step are as described above.

[0042] Example 1 As Example 1, a semiconductor laser device 10 was fabricated. An MOCVD apparatus was used to fabricate an epitaxial wafer that would become the semiconductor laser device 10. Furthermore, trimethylgallium (TMG), triethylgallium (TEG), trimethylaluminum (TMA), trimethylindium (TMI), ammonia (NH), silane gas, and bis(cyclopentadienyl)magnesium (CpMg) were used as appropriate as raw materials.

[0043] An n-type GaN substrate (substrate 1) with the +c plane as the upper surface was prepared, and a 500 nm thick Si-doped Al 0.013 Ga 0.987 An N layer is formed, and a 150 nm thick In layer doped with Si is then formed on top of it. 0.046 Ga 0.954 An N layer is formed, and then a 700 nm thick Al layer containing Si is formed on top of it. 0.096 Ga 0.904 An N layer (n-side cladding layer 2) was formed.

[0044] After the formation of the n-side cladding layer 2, a 231 nm thick Al 0.057 Ga 0.943 An N layer (n-side guide layer 3) was formed.

[0045] After the formation of the n-side guide layer 3, a 10.5 nm thick Al 0.06 Ga 0.94 An N layer is formed, and a 17.5 nm thick In layer is formed on it without adding impurities. 0.01 Ga 0.99 The N layer (active layer 4) was formed as a well layer.

[0046] After the active layer 4 is formed, a 100 nm thick Al 0.06 Ga 0.94 An N layer (p-side barrier layer 5) was formed.

[0047] After the formation of the p-side barrier layer 5, a 3.8 nm thick Al 0.19 Ga 0.81 An N layer was formed, and then an 8.5 nm thick Mg-doped Al layer was formed on top of it. 0.22 Ga 0.78 An N layer is formed, and a 105 nm thick Al layer is formed on it without adding impurities. 0.057 Ga 0.943 An N layer (p-side guide layer 6) was formed.

[0048] After the p-side guide layer 6 is formed, a 400 nm thick Mg-doped Al 0.09 Ga 0.91 An N layer (p-side cladding layer 7) was formed, and an Mg-doped GaN layer having a thickness of 15 nm was formed thereon.

[0049] The epitaxial wafer on which the above layers were formed was then removed from the MOCVD apparatus, and a ridge portion 610, an insulating film 612, a p-side electrode 8, a p-side pad electrode 9, and an n-side electrode 111 were formed thereon. Reflective films were formed on the light-emitting end facet and the light-reflecting end facet, respectively, and the wafer was singulated to obtain semiconductor laser devices 10. The height of the ridge portion 610 was approximately 455 nm. That is, the ridge portion 610 was formed so that its lower end was located in the p-side guide layer 6. The peak wavelength of the laser light emitted by the semiconductor laser device 10 in Example 1 was 377 nm.

[0050] (Comparative Example 1) The semiconductor laser device according to Comparative Example 1 was fabricated in the same manner as the semiconductor laser device 10 according to Example 1, except that the n-side guiding layer 3 had a thickness of 140 nm, the p-side barrier layer 5 had a thickness of 50 nm, the p-side guiding layer 6 had a thickness of 155 nm, and the ridge portion 610 had a different height. The depth of the ridge portion 610 was approximately 505 nm. The peak wavelength of the laser light emitted from the semiconductor laser device according to Comparative Example 1 was 377 nm.

[0051] (distance from the top of the p-side and light intensity) FIG. 3 shows the simulation results of the fluctuation in optical intensity with respect to the distance from the top end of the p-side for the semiconductor laser elements of Example 1 and Comparative Example 1. In the graph of FIG. 3, the horizontal axis represents the distance from the top end of the p-side, and the vertical axis represents the optical intensity. In FIG. 3, the solid line represents Example 1, and the dashed line represents Comparative Example 1. As shown in FIG. 3, the optical intensity peak in Example 1 is located farther from the top end of the p-side than in Comparative Example 1. In other words, it can be said that Example 1 reduces optical loss and improves optical output. This is thought to be the effect of reducing optical loss due to impurities in the p-side guide layer 6 and the p-side cladding layer 7.

[0052] (radiation angle) FIG. 4 shows the relationship between the emission angle (radiation angle) from the light-emitting end facet in the slow-axis direction and the radiation intensity of the semiconductor laser elements of Example 1 and Comparative Example 1. In the graph of FIG. 4, the horizontal axis represents the radiation angle, and the vertical axis represents the radiation intensity. In FIG. 4, the solid line represents Example 1, and the dashed line represents Comparative Example 1. As shown in FIG. 4, in Example 1, the width of the graph showing the radiation intensity is narrower overall, and the half-value width and radiation angle are also narrower, compared to Comparative Example 1. That is, in Example 1, the radiation angle is reduced, thereby reducing M 2 It was confirmed that the factor was reduced and the quality of the light improved.

[0053] Embodiments of the present disclosure may include the following configurations. (Section 1) A semiconductor laser device that emits ultraviolet light, comprising, in this order from top to bottom, an n-side cladding layer made of AlGaN, an n-side guide layer made of AlGaN, an active layer made of InGaN, a p-side guide layer made of AlGaN, and a p-side cladding layer made of AlGaN, the semiconductor laser element has a first surface and a ridge portion protruding upward from the first surface, the first surface is located above a lower end of the p-side guide layer and below an upper end of the p-side guide layer, the thickness of the n-side guide layer is smaller than the thickness of the n-side cladding layer, the Al composition ratio of the n-side guide layer is smaller than the Al composition ratio of the n-side cladding layer, the thickness of the p-side guide layer is smaller than the thickness of the p-side cladding layer and smaller than the thickness of the n-side guide layer; The Al composition ratio of the p-side guide layer is smaller than the Al composition ratio of the p-side cladding layer. (Section 2) the semiconductor laser element further includes a p-side barrier layer above the active layer and below the p-side guide layer; Item 2. The semiconductor laser device according to item 1, wherein the sum of the thickness of the p-side barrier layer and the thickness of the p-side guide layer is smaller than the thickness of the n-side guide layer. (Section 3) Item 3. The semiconductor laser device according to item 1 or 2, wherein the thickness from the upper end of the active layer to the upper end of the p-side guide layer is smaller than the thickness of the n-side guide layer. (Section 4) 4. The semiconductor laser device according to any one of items 1 to 3, wherein the thickness of the p-side barrier layer is greater than the distance from the lower end of the p-side guiding layer to the first surface. (Section 5) 5. The semiconductor laser device according to any one of items 1 to 4, wherein the thickness of the p-side barrier layer is greater than the distance from the first surface to the upper end of the p-side guiding layer. (Section 6) 6. The semiconductor laser device according to any one of items 1 to 5, wherein the distance from the lower end of the p-side barrier layer to the first surface is greater than the thickness of the p-side guiding layer. (Section 7) Item 7. The semiconductor laser device according to any one of items 1 to 6, wherein the p-side barrier layer is undoped. (Section 8) 8. The semiconductor laser device according to claim 1, wherein the distance from the lower end of the p-side guide layer to the first surface is greater than the distance from the first surface to the upper end of the p-side guide layer. (Section 9) Item 9. The semiconductor laser device according to any one of items 1 to 8, wherein the Al composition ratio of the n-side guide layer is 5% or more, and the Al composition ratio of the p-side guide layer is 5% or more. (Section 10) Item 10. The semiconductor laser element according to any one of items 1 to 9, wherein a distance from a lower end of the p-side barrier layer to an upper end of the p-side guide layer is 0.5 to 0.95 times the thickness of the n-side guide layer. (Section 11) Item 11. The semiconductor laser device according to any one of items 1 to 10, wherein the thickness of the p-side guide layer is 0.3 to 0.95 times the thickness of the n-side guide layer. [Explanation of symbols]

[0054] 10 Semiconductor laser element 1 board 111 n-side electrode 2. N-side cladding layer 3 n-side guide layer 4 Active layer 5 p-side barrier layer 6 p-side guide layer 610 Ridge 611 Page 1 612 insulating film 7 p-side cladding layer 8 p side electrode 9 p-side pad electrode

Claims

1. A semiconductor laser element that emits ultraviolet light, having, in this order from top to bottom, an n-side cladding layer, an n-side guide layer, an active layer, a p-side guide layer, and a p-side cladding layer, each of which is made of a nitride semiconductor, the semiconductor laser element comprises a first surface and a ridge portion protruding upward from the first surface, the first surface is located above a lower end of the p-side guide layer and below an upper end of the p-side guide layer, the thickness of the n-side guide layer is smaller than the thickness of the n-side cladding layer, the Al composition ratio of the n-side guide layer is smaller than the Al composition ratio of the n-side cladding layer, the thickness of the p-side guide layer is smaller than the thickness of the p-side cladding layer and smaller than the thickness of the n-side guide layer; The Al composition ratio of the p-side guide layer is smaller than the Al composition ratio of the p-side cladding layer.

2. the semiconductor laser device further includes a p-side barrier layer above the active layer and below the p-side guide layer; 2. The semiconductor laser device according to claim 1, wherein the sum of the thickness of said p-side barrier layer and the thickness of said p-side guide layer is smaller than the thickness of said n-side guide layer.

3. 3. The semiconductor laser device according to claim 2, wherein a thickness from an upper end of said active layer to an upper end of said p-side guide layer is smaller than a thickness of said n-side guide layer.

4. 4. The semiconductor laser device according to claim 2, wherein the thickness of said p-side barrier layer is greater than the distance from a lower end of said p-side guide layer to said first surface.

5. 4. The semiconductor laser device according to claim 2, wherein the thickness of said p-side barrier layer is greater than the distance from the first surface to the upper end of said p-side guide layer.

6. 4. The semiconductor laser device according to claim 2, wherein a distance from a lower end of said p-side barrier layer to said first surface is greater than a thickness of said p-side guide layer.

7. 4. The semiconductor laser device according to claim 2, wherein the p-side barrier layer is undoped.

8. 4. The semiconductor laser device according to claim 1, wherein a distance from a lower end of said p-side guide layer to said first surface is greater than a distance from said first surface to an upper end of said p-side guide layer.

9. 4. The semiconductor laser device according to claim 1, wherein the Al composition ratio of said n-side guide layer is 5% or more, and the Al composition ratio of said p-side guide layer is 5% or more.

10. 4. The semiconductor laser device according to claim 2, wherein the distance from the lower end of said p-side barrier layer to the upper end of said p-side guide layer is 0.5 to 0.95 times the thickness of said n-side guide layer.

11. 4. The semiconductor laser device according to claim 1, wherein the thickness of said p-side guide layer is 0.3 to 0.95 times the thickness of said n-side guide layer.

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