Patent Application
20230275401
This application claims priority from Japanese Patent Application No. 2022-028541 filed on Feb. 25, 2022. The entire teachings of the above application are incorporated herein by reference.
The present disclosure relates to a semiconductor laser device.
Semiconductor lasers (LDs) are used as light sources for laser pointers. In particular, red and infrared LDs have been often used as a light source for pointers, and blue and green LDs are also used. In recent years, there has been an increasing demand to further make the light point of a pointer clearly visible or recognizable with sensors or cameras.
A semiconductor laser device has been known to have a structure with a ridge in the p-type cladding layer in semiconductor lasers used for optical pickup devices and the like.
When the present inventors observed the far-field pattern (FFP, far-field image), which is an image at a point that is irradiated with a semiconductor laser, they recognized a problem that the desired point could not be irradiated with the laser beam with sufficient focus because interference fringes occur around the periphery of the beam, specifically on the side of the beam.
After examining this problem, the present inventors have come to recognize that the cause of the problem originates from the insulating layer (SiO2 film) of the semiconductor laser device. That is, the SiO2 layers are provided on the side face of the ridge and the front face of the p-type cladding layer of the semiconductor laser device. Laser light seeping into the SiO2 insulating layer in the vicinity of the ridge causes interference in the SiO2 film, which in turn generates interference fringes in the FFP. The same problem also occurs on materials, such as oxide, nitride, and oxynitride in addition to SiO2, that have insulation properties and allow light to transmit or reflect. This recognition has not been taken as the general knowledge of those skilled in the art; however, it is the unique recognition of the present inventors.
Certain aspects of the present disclosure are made under such circumstances, and one of the exemplary purposes of the present disclosure is to provide a semiconductor laser that suppresses the generation of interference fringes in the FFP.
One aspect of the present disclosure relates to an edge-emitting semiconductor laser device. The semiconductor laser device includes a laser resonator including a layered structure in which a lower cladding layer, an active layer, and an upper cladding layer are formed over a semiconductor substrate, and a ridge that is formed on the upper cladding layer. The laser resonator emits laser light having a beam profile. When viewed in plan from a direction orthogonal to the semiconductor substrate, the laser resonator includes an emission area on its emission end face. When the emission end face of the laser resonator is viewed in front, a virtual line defined by the intensity being 1/e2 of the peak intensity of the beam profile of the laser light fits inside the upper cladding layer in the emission area.
Another aspect of the present disclosure relates to a method of manufacturing an edge-emitting semiconductor laser device. The manufacturing method includes forming a layered structure of a lower cladding layer, an active layer, and an upper cladding layer over a semiconductor substrate, undergoing ridge processing in the upper cladding layer in a manner that, when the emission end face of the laser resonator is viewed in front, a virtual line defined by the intensity being 1/e2 of the peak intensity of the beam profile of laser light fits inside the upper cladding layer in the emission area, and forming an insulating layer covering at least a side face of the ridge that has been formed on the upper cladding layer by the ridge processing.
Note that any combination of the above components, or mutual substitution of components or expressions among methods, devices, systems, etc., is also valid as an aspect of the present invention or disclosure. Furthermore, the description of this item (SUMMARY OF THE INVENTION) does not describe all the indispensable features of the present invention; hence, the sub-combinations of these features described can also be the present invention or disclosure.
An aspect of the present disclosure is capable of suppressing the generation of interference fringes in the FFP.
Hereinafter, an overview of some exemplary embodiments of the present disclosure will be described. This overview is intended as a preface to the detailed description that follows, or for a basic understanding of the embodiments. The overview describes some concepts of one or more embodiments in a simplified manner and is not intended to limit the scope of the invention or disclosure. In addition, the overview is not a comprehensive overview of all conceivable embodiments, nor does it limit the indispensable components of embodiments. For convenience, “an embodiment” may be used to refer to one embodiment (Example or Variation Example) or a plurality of embodiments (Examples or Variation Examples) disclosed in the present specification.
A semiconductor laser device according to one embodiment is an edge-emitting semiconductor laser device. The semiconductor laser device includes a laser resonator including a layered structure in which a lower cladding layer, an active layer, and an upper cladding layer are formed over a semiconductor substrate, and a ridge that is formed on the upper cladding layer. The laser resonator emits laser light having a beam profile. When viewed in plan from a direction orthogonal to the semiconductor substrate, the laser resonator includes an emission area on its emission end face. When the emission end face of the laser resonator is viewed in front, a virtual line defined by the intensity being 1/e2 of the peak intensity of the beam profile of the laser light fits inside the upper cladding layer in the emission area.
In this configuration, the ridge is formed to expand in a width direction in the vicinity of the emission end face in a manner of having a sufficiently large cross section with respect to the beam diameter. Since 95% of the total light intensity is contained within a 1/e2 width of the beam, the intensity of light leaking from the upper cladding layer is smaller than 5% of the total light intensity. This suppresses light in the emission area from leaking from the upper cladding layer to the side. Therefore, this suppresses the beam emitted from the side of the upper cladding layer, suppressing the generation of interference fringes in the FFP.
In one embodiment, when the semiconductor laser device is viewed in plan from a direction orthogonal to the semiconductor substrate, the width of the ridge may widen at the boundary of the emission area, and the shape of the ridge may have a step shape, for example. This configuration can suppress the spread of the beam in the emission area.
In one embodiment, at least the side face of the ridge may be covered with an insulating layer. When the side face of the ridge of the upper cladding layer is covered with the insulating layer, light leaking into the insulating layer is emitted from the edge face of the insulating layer. The above configuration suppresses light leaking into the insulating layer, thereby suppressing the generation of interference fringes in the FFP.
In one embodiment, when the emission end face of the laser resonator is viewed in front, the cross-sectional shape of the ridge in the emission area of the laser resonator may be rectangular, and the width of the ridge may be larger than the 1/e2 width of the beam profile in the lateral direction.
In one embodiment, the width of the ridge may be three times or more as large as the 1/e2 width of the beam profile in the lateral direction. Since 99.97% of the total light intensity is contained within three times the beam 1/e2 width of the beam profile, light leaking from the upper cladding layer is smaller than 0.03% of the total light intensity. This further suppresses interference fringes in the FFP.
In one embodiment, the width of the ridge may be four times or more as large as the 1/e2 width of the beam profile in the lateral direction. In this case, light leaking from the upper cladding layer is smaller than 0.02% of the total light intensity. In one embodiment, the width of the ridge may be five times or more as large as the 1/e2 width of the beam profile in the lateral direction. In this case, light leaking from the upper cladding layer is smaller than 0.01% of the total light intensity. For practical use, three times is sufficient; however, when a sharper FFP is desired, the width of the rectangular upper cladding layer in the emission area may be designed to be increased to four times as large as the 1/e2 width, preferably 5 times or more.
In one embodiment, when the emission end face of the laser resonator is viewed in front, the width of the upper end of the ridge in the emission area may be narrower than the width of the lower end of the ridge.
In one embodiment, when the emission end face is viewed in front, the cross-sectional shape of the ridge in the emission area may have a lower rectangular portion having a first width and an upper rectangular portion having a second width narrower than the first width and being adjacent to and above the lower rectangular portion. The first width may be larger than the 1/e2 width of the beam profile in the lateral direction. In the longitudinal direction, the laser resonator has a waveguide structure in which a core layer is sandwiched by cladding layers, thus the beam spreads smaller in the longitudinal direction than in the lateral direction. Hence, expanding the width (first width) of the lower rectangular portion, which is the rise of the ridge, suppresses light leaking in the lateral direction.
In one embodiment, the first width may be three times or more as large as the 1/e2 width of the beam profile in the lateral direction. The first width may be four times or more as large as the 1/e2 width of the beam profile in the lateral direction or may be five times or more as large as the width thereof.
In one embodiment, when the emission end face of the laser resonator is viewed in front, the cross-sectional shape of the ridge in the emission area may be tilted from the upper end to the lower end. This tilt can be formed by using the isotropic nature of wet etching.
In one embodiment, the insulating layer may include at least one material selected from the group consisting of SiO2, SiNx, SiON, Al2O3, AlN, AlON, Ta2O5, and ZrO2.
In one embodiment, the active layer may include at least one material selected from the group consisting of In, Ga, Al, As, P, and N.
In one embodiment, when the semiconductor laser device is viewed in plan from a direction orthogonal to the semiconductor substrate, the laser resonator may include a gain area adjacent to the emission area. The ridge in the gain area of the laser resonator may be designed such that the laser light has a transverse single mode.
In one embodiment, a light-shielding groove is formed at a location adjacent to the emission area or in the emission area of the semiconductor laser device, the light-shielding groove extending in a direction orthogonal to the laser resonator.
An edge-emitting semiconductor laser device according to one embodiment includes a laser resonator including a layered structure in which a lower cladding layer, an active layer, and an upper cladding layer are formed over a semiconductor substrate, and a ridge that is formed on the upper cladding layer. When viewed in plan from a direction orthogonal to the semiconductor substrate, the laser resonator includes an emission area on its emission end face and a gain area adjacent to the emission area. The width of the ridge of the upper cladding layer widens stepwise at the boundary between the gain area and the emission area, and the width of the ridge in the emission area is three times or more as large as the maximum width of the ridge in the gain area.
Hereinafter, the present disclosure will be described with reference to the drawings based on suitable embodiments. Identical or equivalent components, members, and processes shown in the respective drawings are marked with the same symbols, and duplicated explanations are omitted as appropriate. The embodiments are intended to be exemplary rather than to limit the disclosure, and all features and combinations thereof described in the embodiments are not necessarily essential to the disclosure.
The dimensions (thickness, length, width, etc.) of each member described in the drawings may be scaled as appropriate for ease of understanding. Furthermore, the dimensions of a plurality of members do not necessarily represent their size relationship; although one member A is drawn thicker than another member B on the drawing, the member A may be thinner than the member B.
The laser resonator 140 is formed on the semiconductor substrate 110. The laser resonator 140 includes a layered structure (multi-layered growth layer) 120 in which a lower cladding layer 122 that is an n-type cladding layer, a light-emitting layer 124 that is an active layer, an upper cladding layer 126 that is a p-type cladding layer, and a p-type contact layer 128 are formed. The upper cladding layer 126 is formed with a ridge 150 for current constriction through ridge processing. The ridge 150 includes a ridge 150_1, a ridge 150_2, and a ridge 150_3. At least the side face of the ridge 150 is covered with an insulating film, which is omitted in
In the figure, the x-axis denotes a direction of the width of the laser resonator 140, the y-axis denotes a direction perpendicular to the semiconductor substrate 110, and the z-axis denotes a direction of the length of the laser resonator 140, i.e., the waveguide direction of the laser beam. In the present specification, viewing the laser resonator 140 from plan means viewing the laser resonator 140 in plan from a direction orthogonal to the semiconductor substrate 110, i.e., viewing the laser resonator 140 along the y-axis. In addition, viewing the emission end face S1 of the laser resonator 140 from front means viewing the laser resonator 140 along the z-axis.
When the laser resonator 140 is viewed in plan, the laser resonator 140 includes a plurality of areas A1 to A3 adjacent in this order in the z-axis direction. The area A1 including the emission end face S1 is referred to as the emission area. The area A2 adjacent to the emission area A1 is referred to as the gain area. The area A3 having the reflection end face S2 is referred to as the reflection area. The ridges 150_1, 150_2, and 150_3 of the upper cladding layer 126 in the emission area A1, the gain area A2, and the reflection area A3 have different widths w1, w2, and w3, respectively. Specifically, the width w1 of the ridge 150_1 in the emission area A1 is sufficiently wider than the width w2 of the ridge 150_2 in the gain area A2.
Note that making the width w3 of the ridge 150_3 in the reflection area A3 equal to the width w1 of the ridge 150_1 can maintain the continuity of the laser resonator even when a dicing line (cleavage surface) is shifted during the process of cutting out the semiconductor laser device 100A from the wafer.
The shape of the ridge 150_2 in the gain area A2 determines a horizontal transverse mode of the laser beam. The ridge 150_2 is designed such that the laser beam guided thereinside has a single horizontal transverse mode. The width w2 of the ridge 150_2 can be about 2 μm, and its length can be approximately 1500 μm, for example.
A light-shielding groove 160 extending in the x-axis direction kept away from the ridge 150 is formed in an area close to the emission area A1 and also in the gain area A2.
In the present embodiment, the width w1 of the ridge 150 in the emission area A1 of the laser resonator 140 is determined such that the virtual line 2 above the light-emitting layer 124 fits in the upper cladding layer 126 in the emission area A1, in other words, the upper half of the virtual line 2 avoids extending beyond the upper cladding layer 126. Specifically, the width w1 of the ridge 150_1 in the emission area A1 is larger than the emission spot diameter ϕx.
In the present embodiment, when the emission end face S1 of the laser resonator 140 is viewed in front, the ridge 150 of the upper cladding layer 126 in the emission area A1 of the laser resonator 140 has a rectangular cross-sectional shape. Hence, the width w1 of the ridge 150_1 is the width of a rectangle.
The width w1 of the rectangular ridge 150_1 is preferably 3 times or more as large as the emission spot diameter ϕx. The width w1 of the rectangular ridge 150_1 is more preferably 4 times or more as large as the emission spot diameter ϕx and further preferably 5 times or more as large as the emission spot diameter ϕx.
In
The disclosure is not limited to this embodiment; the p-type contact layer 128 may be formed on the upper side of the ridge 150_1 even in the emission area A1, as is similar to in the gain area A2, and the insulating film 134 may be formed on the p-type contact layer 128.
The lower part of
As mentioned above, the width w1 of the ridge 150_1 is larger than the emission spot diameter ϕx (ϕx<w1) at the emission end face S1. Since dx≤ϕx is always true in the emission area A1, dx<w1 is always true in the emission area A1. In other words, most of the laser beam is guided without leaking out from the upper cladding layer 126 to the insulating film 134 in the emission area A1.
In this configuration, the ridge 150_1 in the emission area A1 is formed in the width direction (x-axis direction) in a manner of having a sufficiently large cross section with respect to the emission spot diameter ϕx. Since 95% of the total light intensity is contained in the 1/e2 width of the beam, the light leaking from the upper cladding layer 126 to the insulating film 134 is smaller than 5% of the total light intensity. Hence, this configuration suppresses the light leaking from the upper cladding layer 126 to the insulating film 134 on the side in the emission area A1. This suppresses the beam emitted from the side of the upper cladding layer 126, suppressing the generation of interference fringes in the FFP.
With respect to the optical intensity distribution of the laser beam, 99.9% of the total light intensity is contained in a range of three times the 1/e2 beam width. Hence, when the width w1 of the rectangular ridge 150_1 is set to be three times or more as large as the emission spot diameter ϕx, the light leaking from the upper cladding layer 126 is smaller than 0.03% of the total light intensity. This further suppresses interference fringes in the FFP.
Similarly, with respect to the optical intensity distribution of the laser beam, 99.98% of the total light intensity is contained in a range of four times the 1/e2 beam width. Hence, when the width w1 of the rectangular ridge 150_1 is set to be four times or more as large as the emission spot diameter ϕx, the light leaking from the upper cladding layer 126 is smaller than 0.02% of the total light intensity. In addition, 99.99% of the total light intensity is contained in a range of five times the 1/e2 beam width. Hence, when the width w1 of the rectangular ridge 150_1 is set to be five times or more as large as the emission spot diameter ϕx, the light leaking from the upper cladding layer 126 is smaller than 0.01% of the total light intensity. Hence, setting the width w1 of the rectangular ridge 150_1 to be larger further suppresses light leaking to the side face. For practical use, it is sufficient that the width w1 of the rectangular ridge 150_1 is 3 times as large as the 1/e2 beam width; however, when sharper FFP is desired, it is recommended to design the width of the rectangular upper cladding layer in the emission area 4 times or more, preferably 5 times or more, as large as the 1/e2 beam width. In edge-emitting semiconductor lasers, the beam shape (spot diameter) at the emission end face has typically a larger dimension in the x-axis direction, which is a direction of the epitaxially grown plane, than that in the y-axis direction, which is a stacking direction. The dimension of the spot diameter dy in the y-axis direction is sufficiently small compared to the thickness of the cladding layer 126.
The configuration of the semiconductor laser device 100A has been described with focusing on the relationship between the width w1 of the ridge 150_1 in the emission area A1 and the emission spot diameter ϕx; however, the characteristics of the semiconductor laser device 100A can also be described from the relationship between the width w1 of ridge 150_1 in the emission area A1 and the width w2 of ridge 150_2 in the gain area A2.
The emission spot diameter ϕx is highly dependent on the width w2 of the ridge 150_2 in the gain area A2. However, when the width w1 of the emission area A1 is wide as shown in the configuration of the present disclosure, the light will travel in a direction in which the width of the ridge is wider than the width w2 specified in the gain region A2. In other words, when the length of the emission area A1 in the direction of the resonator is longer, the emission spot diameter ϕx is larger than the width w2 of ridge 150_2. In contrast, when the length of the emission area A1 in the direction of the resonator is longer, the non-gain area becomes longer for the semiconductor laser device, resulting in poor light-emitting efficiency. In the present disclosure, the emission spot diameter ϕx estimated from the length of emission area A1 in the direction of the resonator is twice or less as large as the width w2, and at most, it does not exceed 3 times. In other words, designing the ridges 150_1 and 150_2 in a manner of satisfying w1>w2×3 suppresses the laser light from leaking in the lateral direction in the emission area A1.
In other words, designing the ridges 150_1 and 150_2 to satisfy w1>w2×k with using k (k≥3) as a parameter further suppresses laser light from leaking in the lateral direction in the emission area A1. Making k larger such as 4, 5, . . . 10 further suppresses interference fringes.
Note that the width w1 of the ridge 150_1 in the emission area A1 can be considered as a width wL in the case of Embodiments 2 to 4.
Hereinafter, the manufacturing method of the semiconductor laser device 100A will now be described.
Referring to
The lower cladding layer 122 is, for example, an n-type cladding layer made of AlGaInP or AlGaAs having a thickness of 2.0 μm, for example.
The light-emitting layer 124 is an active layer having a quantum well structure. The active layer includes, for example, a barrier layer and a well layer, and is made of one or more materials selected from the group consisting of In, Ga, Al, As, P, and N. The barrier layer may have a four-layer structure including an AlGaInP layer with a thickness of 6 nm, for example. The well layer may have a three-layer structure including a GaInP layer with a thickness of 5 μm, for example. The active layer may be a single layer structure including (Al)GaInP or (Al)GaAs. The active layer may also be made of GaN, InGaN, AlGaN, or other nitride semiconductors.
The upper cladding layer 126 is a P-type cladding layer made of AlGaInP or AlGaAs with a thickness of 2.0 μm, for example.
The p-type contact layer 128 is made of GaAs with a thickness of 0.5 μm, for example.
Referring to
Referring to
Referring to
Referring to
The manufacturing method of the semiconductor laser device 100A has been described above.
The following is Variation Examples related to Embodiment 1.
The light-shielding groove 160 may be omitted.
In
Specifically, in Embodiment 2, when the emission end face S1 is viewed in front, the cross-sectional shape of the ridge 150_1 in the emission area A1 includes a lower rectangular portion 152 and an upper rectangular portion 154. The width wL of the lower rectangular portion 152 is wider than the width wU of the upper rectangular portion 154. The width wU of the upper rectangular portion 154 is equal to the width w2 of the ridge 150_2 in the gain area A2.
In Embodiment 2, as is similar to Embodiment 1, the width of the ridge 150_1 is extended in a manner that the virtual line 2 above the light-emitting layer 124 fits in the ridge 150_1 in the emission area A1. Specifically, the width wL of the lower rectangular portion 152 in the emission area A1 is larger than the emission spot diameter ϕx (1/e2 width).
The width wL of the lower rectangular portion 152 is preferably wL>3×ϕx because setting wL to be larger further reduces the laser light leaking to the side face. Moreover, setting wL>4×ϕx or wL>5×ϕx will further reduce the leaked light.
The method of manufacturing the semiconductor laser device 100B according to Embodiment 2 is basically similar to the method of manufacturing the semiconductor laser device 100A according to Embodiment 1. In the method of manufacturing the semiconductor laser device 100B, etching the ridge 150_1 is modified in two steps.
The following is Variation Examples related to Embodiment 2.
The light-shielding groove 160 may be added to the semiconductor laser device 100B of
In
In Embodiment 3, the width of the ridge 150_1 is extended in a manner that the virtual line 2 above the light-emitting layer 124 fits in the ridge 150_1 in the emission area A1. Specifically, the width (width at foot) wL of the lower end of the ridge 150_1 is larger than the emission spot diameter ϕx (1/e2 width). The width wL of the lower end of the ridge 150_1 is preferably wL>3×ϕx because setting the width wL larger further reduces the laser light leaking to the side face. Moreover, setting wL>4×ϕx or wL>5×ϕx will further reduce the leaked light.
The cross-sectional shape of the ridge 150_1, i.e., the width wU and height of the upper end, or in other words, the extent of the tilt, may be determined in a manner that the tilted portion of the ridge 150_1 does not intersect with the virtual line 2.
The method of manufacturing the semiconductor laser device 100C according to Embodiment 3 is basically similar to the method of manufacturing the semiconductor laser device 100A according to Embodiment 1. In the method of manufacturing the semiconductor laser device 100C, the slope of the ridge 150_1 can be formed using the isotropic nature of wet etching.
The following is Variation Examples related to Embodiment 3.
The light-shielding groove 160 may be added to the semiconductor laser device 100C of
In
Embodiment 4 can also have an effect similar to Embodiments 1-3.
The following is Variation Examples related to Embodiment 4.
In
The shape of the gain area A2 is not limited to that shown in
In embodiment 5, the cross-sectional shape of the ridge 150_1 in the emission area A1 includes a trapezoidal portion 156 and a rectangular portion 158. The trapezoidal portion 156 is tilted (tapered) from its upper end to its lower end. The slope (foot) of the trapezoidal portion 156 may vary gently. The width wU of the upper end is equal to the width w2 of the ridge 150_2 in the gain area A2.
The cross-sectional shape of the trapezoidal portion 156 of the ridge 150_1, i.e., the width of the upper end wU and the height, in other words, the extent of the tilt, is determined in a manner that the tilted portion of the trapezoidal portion 156 does not intersect with the virtual line 2.
Finally, Variation Examples related to the whole will be described.
In Embodiments 1 to 4, the case in which the side faces of the ridge 150 are covered with the insulating film 134; however, the present disclosure is not limited to the case. Even in the case in which the insulating film 134 is absent, the presence of a void, a metal layer, or other materials adjacent to the ridge 150 can cause light leaking from the ridge 150 to emit from the area adjacent to the ridge 150, generating interference fringes. Hence, the technique of widening the width of the ridge 150_1 in the emission area A1 can be applied regardless of the presence or absence of the insulating film 134.
The cross-sectional shape of the ridge 150_1 in the emission area A1 is not limited to those described in the embodiments; the virtual line indicating 1/e2 of the peak intensity can be spread out in a shape that fits inside the upper cladding layer 126.
A bank may be formed in the upper cladding layer 126 adjacent to the ridge 150. The bank is formed on each of both side faces of the ridge 150 over the entire length in the direction of the resonator to protect the ridge 150 and the like. The bank can have the same height (thickness in the y direction) as that of the ridge 150.
The application of the semiconductor laser device 100 is not limited to laser pointers, but can also be used for levelers, rangefinders, sensors, light sources for projectors, etc.
In the case of focusing the light emitted from the semiconductor laser device 100 for use, a poor beam profile makes the minimum spot diameter large. According to the present embodiment, it is also possible to reduce the minimum spot diameter in the case of focusing the light emitted from the semiconductor laser device 100, making the semiconductor laser device applicable to optical disk pickups, for example.
The embodiments merely show the principles and applications of the present disclosure or invention, and many variation examples and modifications in the arrangement are allowed for the present embodiment to the extent that does not depart from the idea of the disclosure or invention stipulated in the scope of the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-028541 | Feb 2022 | JP | national |
