JP7185867B2 - laser diode - Google Patents

Description

The present invention relates to semiconductor laser diodes.

Patent Document 1 discloses a laser diode having a structure in which a semiconductor layer is horizontally and vertically cut from a substrate by using a cleaving method using a crystal plane. Further, Patent Documents 2 and 3 disclose laser diodes having a structure in which horizontal and vertical cavity surfaces are formed by an etching method combining dry etching and wet etching.

JP-A-51-97390 JP-A-10-41585 JP 2008-108844 A

In the structures of the laser diodes disclosed in Patent Documents 1 to 3, optical noise may occur in which the output of the laser diode momentarily increases after packaging.

An object of the present invention is to provide a laser diode capable of reducing optical output noise.

To achieve the above object, a laser diode according to an aspect of the present invention includes a substrate, a light-emitting layer disposed above the substrate, and guide layers disposed above the substrate with the light-emitting layer interposed therebetween. , a lower clad layer formed between the substrate and the guide layer; and an upper clad layer formed on the guide layer, wherein the substrate comprises the lower clad layer, the guide layer and the upper The guide layer has a lamination surface on which a clad layer is laminated, the guide layer has an exit-side end face that intersects an axis in a resonance direction from which light emitted from the light-emitting layer is emitted, and the exit-side end face and the lamination plane is larger than 0 ° and smaller than 90°, and the upper cladding layer is disposed above the emission-side end face and forms an angle with the lamination plane It has a side end surface formed with a second angle smaller than the first angle .

According to one aspect of the present invention, optical output noise can be reduced.

1 is a perspective view showing a schematic configuration of a laser diode 1 according to one embodiment of the present invention; FIG. 1 is a main part side view showing a schematic configuration of a laser diode 1 according to one embodiment of the present invention; FIG. FIG. 4 is a diagram explaining the effect of the laser diode 1 according to one embodiment of the present invention; FIG. 5 is a side view of a main part showing a schematic configuration of a laser diode 1 according to a modification of one embodiment of the present invention;

A laser diode according to one embodiment of the present invention will be described with reference to FIGS. 1 to 4. FIG. First, a schematic configuration of a laser diode 1 according to this embodiment will be described with reference to FIG. In FIG. 1, a laser diode 1 is schematically illustrated.

As shown in FIG. 1, the laser diode 1 includes a substrate 11, a light-emitting layer 12 arranged above the substrate 11, a guide layer 13 arranged above the substrate 11 with the light-emitting layer 12 interposed therebetween, and the substrate 11. and a guide layer 13 and an upper clad layer 15 formed on the guide layer 13 . Although not shown, the laser diode 1 includes a package that covers the substrate 11, the lower clad layer 14, the light emitting layer 12, the guide layer 13 and the upper clad layer 15 and has a window made of glass.

The lower clad layer 14, the guide layer 13 and the upper clad layer 15 are laminated on the substrate 11 in this order. The guide layers 13 are arranged to sandwich the light emitting layer 12 from above and below. The light emitting layer 12 is arranged substantially in the center of the guide layer 13 in the layer thickness direction. In addition, the light emitting layer 12 may be arranged so as to be one side of the lower clad layer 14 and the upper clad layer 15 . A laminate 10 is composed of the lower clad layer 14 , the guide layer 13 , the light emitting layer 12 and the upper clad layer 15 . The laminate 10 has a mesa shape that slopes from the peripheral side of the substrate 11 toward the central side.

The substrate 11 has a rectangular shape of a thin plate. The substrate 11 has a lamination surface 11a on which the lower clad layer 14, the guide layer 13 and the upper clad layer 15 are laminated.

The lower clad layer 14 is made of an n-type semiconductor and laminated on the lamination surface 11 a of the substrate 11 . The lower clad layer 14 is formed to have a size one size smaller than that of the substrate 11 . As a result, the lamination surface 11 a is exposed around the lower clad layer 14 . The lower clad layer 14 has a first region 141 on which the guide layer 13 is laminated, and a second region 142 whose height from the lamination surface 11a is lower than that of the first region 141 . The lower clad layer 14 has a step at the boundary between the first region 141 and the second region 142 . An n-type electrode 161 is formed on the second region 142 . The n-type electrode 161 serves as a negative electrode for current injected into the light-emitting layer 12 . Electrons are supplied to the lower clad layer 14 via the n-type electrode 161 .

The guide layer 13 is laminated on the first region 141 of the lower clad layer 14 . The guide layer 13 is an undoped layer to which no dopant is added in order to suppress absorption of light. The guide layer 13 has an emission-side end surface 13a on the side from which the light emitted by the light-emitting layer 12 is emitted. Although the details will be described later, the first angle formed by the exit-side end surface 13a and the lamination surface 11a is larger than 0° and smaller than 90°. The exit-side end surface 13a of the guide layer 13 constitutes a half mirror, and the opposite surface of the guide layer 13 facing the exit-side end surface 13a constitutes a mirror. The guide layer 13 functions as a resonator that confines and amplifies light emitted from the light emitting layer 12 .

The upper clad layer 15 is made of a p-type semiconductor and laminated on the guide layer 13 . Upper clad layer 15 has a ridge structure. That is, the upper cladding layer 15 has a flat plate portion 151 that contacts the guide layer 13 as a whole, and a bank-like protrusion 152 that protrudes upward from substantially the center of the flat plate portion 151 . The protrusion 152 may be provided not in the center of the flat plate portion 151 but on the side where the n-type electrode 161 is arranged. As the protrusion 152 approaches the n-type electrode 161, the current path through the multilayer body 10 is shortened, so that the resistance value of the current path formed in the multilayer body 10 can be reduced. A p-type electrode 162 is formed on the protrusion 152 . The p-type electrode 162 serves as a positive electrode for current injected into the light-emitting layer 12 . Holes are supplied to the upper clad layer 15 via the p-type electrode 162 .

If the upper clad layer 15 has a ridge structure, the threshold current for forming population inversion required for laser oscillation can be lowered. As shown in FIG. 1, the ridge structure of the laser diode 1 may be composed of a projecting part of the upper clad layer 15 and an electrode arranged on the projecting part. The ridge structure of the laser diode 1 includes a bank-like upper clad layer such as the protrusion 152 shown in FIG. It may be configured with an electrode placed in the By having such a ridge structure, the laser diode 1 can limit the current path in the upper clad layer 15 to the region immediately below the electrode. As a result, the horizontal current diffusion in the upper clad layer 15 is suppressed, so that the current flowing in the light emitting layer 12 should be concentrated directly below the protrusion (in this embodiment, the protrusion 152) of the upper clad layer 15. can be done. As a result, a population inversion state can be efficiently formed in the region of the protruding portion, and the threshold of laser oscillation can be kept low.

After the population inversion region is formed in the light-emitting layer 12 , the holes injected into the upper clad layer 15 and the electrons injected into the lower clad layer 14 recombine in the light-emitting layer 12 , thereby emitting light in the light-emitting layer 12 . occurs. The refractive index of the upper clad layer 15 and the lower clad layer 14 is higher than that of the guide layer 13 . Therefore, light emitted from the light-emitting layer 12 is reflected by the surfaces of the upper clad layer 15 and the lower clad layer 14 that are in contact with the guide layer 13 , so that the light is confined in the guide layer 13 . Since the exit-side end face 13a of the guide layer 13 and the side end face facing the exit-side end face 13a function as a mirror (reflection mirror), the light emitted from the light-emitting layer 12 travels back and forth while being amplified in the guide layer 13. Then stimulated emission occurs, resulting in laser oscillation. When the light amplified within the guide layer 13 becomes larger than the internal loss within the guide layer 13, the light is emitted to the outside.

Next, the relative relationship between the substrate 11 of the laser diode 1 and the laminate 10 and the effects of the laser diode 1 will be described with reference to FIG. 1 and FIGS. 2 and 3. FIG.

As shown in FIG. 2, a first angle .theta.1, which is an angle between the exit-side end surface 13a of the guide layer 13 and the lamination surface 11a of the substrate 11, is larger than 0.degree. and smaller than 90.degree. Here, the emission-side facet 13 a refers to a portion of the cavity facet on the laser emission facet of the laser diode 1 that corresponds to the side face of the guide layer 13 . The lamination surface 11a is a plane on which the substrate 11 is in contact with the laminate 10 composed of the guide layer 13 and the like. The first angle θ1 is an angle formed when the output-side end surface 13a and the lamination surface 11a intersect. The first angle θ1 includes an angle formed at a position where a virtual plane obtained by extending the output-side end surface 13a to the stacking surface 11a intersects the stacking surface 11a even if the output-side end surface 13a and the stacking surface 11a are not in direct contact with each other. .

The laser diode 1 is polished and processed with a focused ion beam (FIB) on a surface perpendicular to the substrate 11, and the cross section is observed with a scanning electron microscope (SEM) or a transmission electron microscope (TEM). ), it is possible to confirm the first angle θ1 by observing. Observation is performed using SEM because high-quality images can be obtained over a wide range and easily. For the purpose of keeping the output of the laser diode 1 high, the value of the first angle θ1 may be larger than 70° and smaller than 90° (70°<θ1<90°). Also, the value of the first angle θ1 may be greater than 80° and greater than 90°.

By the way, since a laser diode chip is generally mounted vertically on a package base when packaged, the glass surface of the package and the resonator surface of the laser diode are parallel. Since the light emitted by the laser diode has high directivity, part of the light may be reflected by the glass surface of the package and irradiate the light emitting layer of the laser diode. In this case, a photo-excited state is induced in the light-emitting layer, resulting in optical noise. Since a laser diode is required to have a stable output, it is usually desirable to emit a predetermined output in response to an applied current. is obtained.

On the other hand, if the emission side end surface 13a of the guide layer 13 is formed with respect to the lamination surface 11a of the substrate 11 so that the first angle θ1 is greater than 0° and less than 90°, as shown in FIG. , the incident angle at which the radiation L emitted from the laser diode 1 is incident on the inner side surface 17a of the package 17 facing the emission side end face 13a is substantially equal to the first angle .theta.1. In this embodiment, the inner surface 17a is the inner surface of a window 171 provided in the package 17, for example. The package 17 has a main structure of a support made of gold or lead, and has a window 171 made of glass in a region where the radiation light L emitted from the emission-side end surface 13a is incident. Therefore, the radiation L emitted from the laser diode 1 does not perpendicularly enter the inner surface 17a of the package 17 (that is, the inner surface of the window 171). As a result, the laser diode 1 emits most of the emitted light L incident on the window 171 to the outside as transmitted light T, and part of the emitted light L is reflected by the inner surface 17 a of the package 17 . Re-entering the light-emitting layer 12 as the return light R can be suppressed. As a result, the laser diode 1 can suppress photoexcitation of the active layer (light-emitting layer 12) and reduce output noise.

Returning to FIG. 2, the upper cladding layer 15 has a side end surface 15a which is arranged above the output side end surface 13a and formed so that the second angle θ2 formed with the lamination surface 11a is smaller than the first angle θ1. have. A side end surface 15 a of the upper clad layer 15 is an end surface of a layer above the guide layer 13 . Thus, in the present embodiment, the end surface of the layer above the guide layer 13 is the side end surface 15 a of the upper clad layer 15 . However, the end face above the guide layer 13 is not limited as long as it is a semiconductor layer laminated above the guide layer 13. Specifically, in addition to the side end face 15a of the upper cladding layer 15, for example, the guide layer If an electron blocking layer or a plurality of clad layers are laminated on the upper layer of 13, any one of them may be used.

The second angle .theta.2 is an angle formed when an end surface of a layer above the guide layer 13 (the side end surface 15a of the upper clad layer 15 in this embodiment) and the laminated surface 11a of the substrate 11 intersect. Even if the end surface of the layer above the guide layer 13 is not in direct contact with the stacking surface 11a of the substrate 11, the second angle θ2 is such that the virtual surface obtained by extending the end surface of the layer above the guide layer 13 to the stacking surface 11a is the stacking surface 11a. Also includes the angle formed at the intersection of For the first angle θ1 and the second angle θ2, the value obtained by subtracting the second angle θ2 from the first angle θ1 is larger than 0° and smaller than 60° (0°<(θ1−θ2 )<60°). Furthermore, from the viewpoint of facilitating the formation of a reflective material such as a dielectric multilayer film or a metal reflective film on the end face of the laminate 10, the first angle θ1 and the second angle θ2 are set to the second angle θ2 from the first angle θ1. The subtracted value is larger than 0° and smaller than 20° (0°<(θ1-θ2)<20°), or the subtracted value is larger than 0° and smaller than 10° (0°<(θ1-θ2)< 10°).

Assuming that the side end surface 15a of the upper clad layer 15 is formed such that the first angle θ1 and the second angle θ2 have the above relationship, the return light R (see FIG. 3) is irradiated to the upper clad layer 15. Also, the laser diode 1 can increase the amount of light reflected by the side facet 15 a without causing the return light R to enter the upper clad layer 15 again. As a result, the laser diode 1 can suppress optical excitation inside the upper cladding layer 15, so that optical output noise can be reduced.

As shown in FIG. 2, the lower cladding layer 14 has a side end surface 14a which is arranged below the output side end surface 13a and which forms a third angle θ3 with the lamination surface 11a which is smaller than the first angle θ1. ing. A side end surface 14 a of the lower clad layer 14 is an end surface of a layer below the guide layer 13 . Thus, in the present embodiment, the end surface of the layer below the guide layer 13 is the side end surface 14 a of the lower clad layer 14 . However, the end surface of a layer below the guide layer 13 is not limited as long as it is a semiconductor layer laminated below the guide layer 13. Specifically, in addition to the side end surface 14a of the lower clad layer 14, for example, the guide layer When a plurality of clad layers are laminated under the layer 13, any one of the plurality of clad layers may be used.

The third angle θ3 is an angle formed when an end surface of a layer below the guide layer 13 (the side end surface 14a of the lower clad layer 14 in this embodiment) and the lamination surface 11a of the substrate 11 intersect. Even if the end surface of the layer below the guide layer 13 does not directly contact the lamination surface 11a of the substrate 11, the third angle .theta. Also includes the angle formed at the intersection of For the first angle θ1 and the third angle θ3, the value obtained by subtracting the third angle θ3 from the first angle θ1 is larger than 0° and smaller than 60° (0°<(θ1−θ3 )<60°). Furthermore, from the viewpoint of facilitating the deposition of a reflective material such as a dielectric multilayer film or a metal reflective film on the end face of the laminate 10, the first angle θ1 and the third angle θ3 are set to the first angle θ1 to the third angle θ3. The subtracted value is greater than 0° and less than 20° (0°<(θ1-θ3)<20°), or the subtracted value is greater than 0 and less than 10° (0<(θ1-θ3)<10° ). Furthermore, the third angle θ3 may be larger than the second angle θ2 (θ2<θ3).

As shown in FIG. 1 , the lamination surface 11 a of the substrate 11 has a larger area than the contact surface of the guide layer 13 that contacts the light emitting layer 12 . Here, the area of the lamination surface 11a is the area of the contact surface with which the semiconductor layer (the lower clad layer 14 in this embodiment) on the lamination surface 11a is in contact, and the area of the semiconductor layer ( In this embodiment, the area is the sum of the area of the exposed surface that is not in contact with the lower clad layer 14). Specifically, the area of the contact surface between the lamination surface 11a and the guide layer 13 can be obtained by comparing the area of the substrate 11 and the area of the laminate 10 when the laser diode 1 is observed from the direction perpendicular to the substrate 11. Confirmation is possible. Actually, the area of the laminate 10 does not match the contact surface of the guide layer 13 , but the area of the laminate 10 observed by the above method is always larger than the area of the contact surface of the guide layer 13 . Therefore, when the area of the substrate 11 is larger than the area of the laminate 10 observed by the above method, it is possible to conclude that the area of the lamination surface 11a of the substrate 11 is necessarily larger than the area of the contact surface of the guide layer 13. .

Since the lamination surface 11a of the substrate 11 has a larger area than the contact surface of the guide layer 13 in contact with the light emitting layer 12, the effect of the present invention is hindered when the laser diode 1 is separated from the wafer or when the element is extracted afterward. Therefore, it is possible to suppress the particles from adhering to the cavity facet, which is the emission-side facet 13 a of the guide layer 13 . Adherence of particles to the cavity facet can be suppressed because the substrate 11 protrudes from the emission-side facet 13 a of the guide layer 13 , so that the cavity facet is in the shadow of the substrate 11 , and the cavity facet is located on the emission side of the guide layer 13 . This is because adhesion of particles to the end face 13a is suppressed.

The substrate 11 in this embodiment may have a single substrate structure, or may have a laminated structure in which semiconductors are laminated on a substrate. Examples of the laminated structure of the substrate 11 include a structure in which an AlN thin film is laminated on a sapphire substrate, a structure in which an AlN thin film and an n-type AlGaN thin film are laminated on a sapphire substrate, and the like.

As shown in FIG. 2, the projection length d of the substrate 11 from the side end surface 14a of the lower clad layer 14 may be longer than 5 μm and shorter than 1000 μm (5 μm<d<1000 μm). The protruding length d of the substrate 11 is the distance from the side end surface 14a of the lower clad layer 14 to the side end surface 11b of the substrate 11 on the surface where the substrate 11 and the lower clad layer 14 contact (that is, the lamination surface 11a). The protrusion length d of the substrate 11 can be confirmed by the same method as the method of comparing the area of the substrate 11 and the area of the guide layer 13 .

By satisfying the range that the protruding length d of the substrate 11 from the side end surface 14a of the lower clad layer 14 is longer than 5 μm and shorter than 1000 μm, the laser diode 1 can be separated from the wafer or extracted after that according to the present invention. It is possible to suppress the adhesion of particles that impede the effect to the cavity facet, which is the emission-side facet 13 a of the guide layer 13 . Adherence of particles to the cavity facets can be suppressed because the substrate 11 protrudes from the side facets 14 a of the lower clad layer 14 , so that the cavity facets are in the shadow of the substrate 11 and are located on the emission side of the guide layer 13 . This is because adhesion of particles to the end face 13a is suppressed. The protruding length d of the substrate 11 may be longer than 5 μm and shorter than 400 μm (5 μm<d<400 μm), or longer than 5 μm and shorter than 100 μm (5 μm<d<100 μm). Thereby, the number of laminates 10 obtained from one wafer can be increased.

As shown in FIG. 2, the thickness t of the substrate 11 may be longer than 50 μm and shorter than 10000 μm (50 μm<t<10000 μm). The thickness t of the substrate 11 can be confirmed by the same method as the projecting length d of the substrate 11 . The thickness t of the substrate 11 can also be measured from the side surface of the laser diode 1 by optical microscope or SEM observation. SEM observation is suitable for more accurate length measurement, and an optical microscope is suitable for measuring a thickness exceeding 100 μm.

When the thickness t of the substrate 11 satisfies the above range, the mechanical strength of the element can be maintained when the laser diode 1 is sandwiched and extracted from the wafer, and cracking of the wafer during assembly can be suppressed. The thickness t of the substrate 11 may be longer than 50 μm and shorter than 500 μm (50 μm<t<500 μm) or longer than 50 μm and shorter than 200 μm (50 μm<t<200 μm). Further, when the ratio of the protruding length d of the substrate 11 to the thickness t of the substrate 11 is larger than 0.01 and smaller than 2 (0.01<d/t<2), the mechanical strength of the laser diode 1 is easier to hold. As a result, the heat of the laser diode 1 can be efficiently released to the external package 17 side through the substrate 11 while maintaining the strength of the device.

Substrate 11 can use a material other than a nitride semiconductor as a base material. When the substrate 11 is made of a material other than a nitride semiconductor and dry etching is used to form the laminate 10, the etching rate difference caused by the material difference between the laminate 10 made of semiconductor and the substrate 11 is reduced. By using this, dry etching can be accurately stopped at the lamination surface 11a of the substrate 11 . As the base material of the substrate 11, specifically, sapphire, silicon carbide, silicon, gallium oxide, zinc oxide, and the like can be used. Thereby, the production reproducibility of the laminate 10 is improved. The material forming the substrate 11 can be analyzed by a technique such as energy dispersive X-ray spectrometry (EDX) or Auger electron spectroscopy (AES).

As shown in FIG. 2, a fourth angle θ4, which is an angle formed between the exit-side end surface 13a of the guide layer 13 and the inner surface 17a of the package 17, is greater than 0° and less than 5° (0°<θ4< 5°). In FIG. 2, for ease of understanding, the output-side end surface 13a is translated toward the inner surface 17a of the package 17 to show the fourth angle .theta.4. FIG. 2 also shows part of the package 17 that covers the substrate 11 and the laminate 10 as a whole. The fourth angle θ4 is obtained by taking a cross-sectional SEM image of the laser diode 1 in a state where both the laminate 10 and the package 17 are resin-sealed and fixed, and comparing the emission side end surface 13a and the inner side surface 17a of the package 17. A square angle θ4 can be measured.

By setting the fourth angle θ4 within the above range, the radiation light L emitted from the laser diode 1 is suppressed from being reflected again by the inner surface 17a of the package 17, and a high-power laser diode package product is produced. It is possible.

As shown in FIG. 2, the distance M from the light emitting layer 12 to the inner surface 17a of the package 17 may be 1 mm or more and 100 mm or less, preferably 1 mm or more and 10 mm or less. The distance M can be measured by the same method as the projecting length d of the substrate 11 .

Since the distance M from the light emitting layer 12 to the inner side surface 17a of the package 17 is within the above range, the return light R from the inner side surface 17a of the package 17 is incident again on the active layer (light emitting layer 12) of the laser diode 1. It is possible to further reduce the probability of

Next, a laser diode 1 according to a modified example of this embodiment will be described with reference to FIG.

Substrate 11 may be formed of a nitride semiconductor. In this case, an oxide 111 having a thickness of 0.5 nm or more and 100 nm or less may be formed on part or all of the surface of the substrate 11 (that is, the lamination surface 11a). If the substrate 11 is composed only of a nitride semiconductor, the surface of the substrate 11 may be additionally etched during wet etching after dry etching for forming the laminate 10 . Therefore, the surface of the substrate 11 after dry etching is treated with O ₂ plasma, treated with a chemical containing an oxidant, or heat-treated at a high temperature to form an oxide 111 on the surface as shown in FIG. This can prevent the substrate 11 from being etched away from the surface during wet etching. The oxide 111 on the surface can be subjected to length measurement and composition analysis by performing TEM-EDX analysis of the cross section of the substrate 11 . Nitride semiconductors for forming the substrate 11 include aluminum nitride, gallium nitride, boron nitride, and mixed crystals containing two or more of these.

As shown in FIG. 4, when the lower clad layer 14 and the upper clad layer 15 are made of AlGaN, they have AlGaNO films 143 and 153 having a thickness of 0.5 nm or more and 100 nm or less in part or all. You may have More specifically, the lower clad layer 14 may have an AlGaNO film 143 on part or all of the side facet 14a. Also, the upper clad layer 15 may have an AlGaNO film 153 partially or entirely on the side facet 15a. The AlGaNO films 143 and 153 can be subjected to length measurement and material analysis by taking TEM and EDX of the cross section of the laminate 10 . The AlGaNO film 143 may be exposed on the side end surface 14a of the lower clad layer 14, and the AlGaNO film 143 may be further covered with an insulating protective layer such as a dielectric multilayer film. Similarly, the AlGaNO film 153 may be exposed on the side end face 15a of the upper cladding layer 15, and the AlGaNO film 153 may be further covered with an insulating protective layer such as a dielectric multilayer film. As a result, corrosion of the side facet 14a of the lower clad layer 14 and the side facet 15a of the upper clad layer 15 during use of the laser diode 1 is suppressed. It becomes possible to suppress the change of the angle θ2. The AlGaNO film means that the main constituent elements of the film are Al, Ga, N, and O, and examples thereof include Al _0.5 Ga _0.7 N _0.95 O _0.05 . The AlGaNO film may contain trace impurities such as C, H, F, Cl, Br, Si, and Mg. In addition, the composition ratio of the end face of the lower clad layer 14, the end face of the upper clad layer 15, and the end face of the guide layer 13 may be different. The composition ratio of AlGaNO in may be non-uniform.

As shown in FIG. 4, the guide layer 13 may have a dielectric multilayer film 131 formed on the emission-side end surface 13a. The dielectric multilayer film 131 including the light-emitting layer 12 is formed on the emission-side facet 13a and functions as a half mirror. Furthermore, the dielectric multilayer film 131 also functions as an insulating protective layer. This suppresses corrosion of the emission-side facet 13a during use of the laser diode 1, and makes it possible to suppress a change in the first angle θ1 of the emission-side facet 13a.

As shown in FIG. 4, the light-emitting layer 12 is made of _Alx1Gay1N , and the _{upper cladding layer 15 is composed of an Alx2Gay2N layer 15b and an Alx3 Gay2N layer 15b above the Alx2Gay2N} layer 15b. and a _Gay3N layer 15c. The compositions of the light emitting layer ₁₂ , the _Alx2Gay2N layer 15b and the _Alx3Gay3N layer 15c may satisfy the relationships x1+ _y1 =1, x2+y2=1, x3+y3=1, x2<x1 and x2<x3. . As a result, the _Alx2Gay2N layer 15b serves as a stop layer, and the layers _below the upper cladding layer 15 in the region below the _Alx2Gay2N layer 15b are side _- etched in the wet etching during the formation of the laminate 10. can be suppressed. Wet etching progresses not only from the side surface of the upper clad layer 15 but also from the upper surface of the upper clad layer 15. For example, when etching is performed with an alkaline chemical such as a KOH aqueous solution, the Al _x3 Ga _y3 N layer 15c is etched. Since the _Alx2Gay2N layer 15b, which has a slow etching rate, suppresses etching from _the upper surface of the upper clad layer 15, side etching is suppressed. The thin film structure of the upper clad layer 15 can be identified by cross-sectional TEM and EDX. The thickness of _{the Alx2Gay2N} layer 15b may be greater than 0 nm and less than 200 nm.

As shown in FIG. 4, the laser diode 1 may include an insulating protective film 18 partially or entirely above the upper clad layer 15 . At least part of the insulating protective film 18 protrudes from the upper cladding layer 15 toward the side end surface 11 b of the substrate 11 . The structure in which the laser diode 1 is provided with the insulating protective film 18 can be specified by performing cross-sectional SEM and EDX. Since the laser diode 1 is provided with the insulating protective film 18, it becomes a "hook" when the dielectric multilayer film 131 and the AlGaNO films 143 and 153 are laminated. In other words, the insulating protective film 18 has an anchor effect when laminating the dielectric multilayer film 131 and the AlGaNO films 143 and 153 . As a result, the adhesion between the dielectric multilayer film 131 and the emission side end surface 13a of the guide layer 13, the adhesion between the AlGaNO film 143 and the side end surface 14a of the lower clad layer 14, and the adhesion between the AlGaNO film 153 and the upper clad layer 15 are improved. Adhesion to the end surface 15a can be improved. The insulating protective film 18 may be made of SiO ₂ , or may be made of Al ₂ O ₃ , SiN, SnO ₂ , ZrO, HfO ₂ or the like.

The light-emitting layer 12 is formed to emit light having an emission wavelength of 360 nm or less. The laser diode 1 according to the present embodiment has a particularly large refractive index and is effective for an ultraviolet light emitting element with a wavelength of 360 nm or less where light is easily refracted.

(Manufacturing method)
Next, a method for manufacturing the laser diode 1 according to this embodiment will be described. In order to form the laser diode 1, a wafer having a predetermined thickness within a range of more than 50 μm and less than 10000 μm is prepared. In the laser diode 1, a semiconductor layer that will eventually become the lower clad layer 14, a semiconductor layer that will eventually become the guide layer 13 in the region below the light emitting layer 12, and finally the light emitting layer 12 will be formed on this wafer. A semiconductor layer is formed by stacking a semiconductor layer, a semiconductor layer that will eventually become the guide layer 13 in the region above the light emitting layer 12, and a semiconductor layer that will finally become the upper clad layer 15. Then, as shown in FIG. After that, by dry etching and wet etching a part of this semiconductor laminate into a predetermined shape, a plurality of laminates 10 are formed on the wafer. Although the details will be described later, in this embodiment, a positive resist is used when forming the laminate 10 , that is, the guide layer 13 , the upper clad layer 15 and the lower clad layer 14 . After that, the wafer is cut at a predetermined position to separate the laminate 10 into pieces, and the substrate 11 and the laminate 10 are covered and fixed with a package to complete the packaged laser diode 1 .

A method for forming the exit-side end surface 13a of the guide layer 13 will be described.
When patterning the resist, a photomask is used to provide a gap (for example, 3 μm or 5 μm) between the resist and the photomask during contact exposure to allow light to leak. As a result, a resist pattern mask having inclined resist pattern end surfaces is formed. Using a resist pattern mask with an inclined facet as a mask, part of the side portion of the semiconductor laminate is dry-etched, so that the cavity facet, that is, the emission-side facet 13a of the guide layer 13 is inclined by more than 0° to 90°. It can be tilted at a smaller first angle θ1.

A method of forming the side end surface 15a of the upper clad layer 15 will be described.
When patterning the resist, a photomask is used to provide a gap (for example, 3 μm or 5 μm) between the resist and the photomask during contact exposure to allow light to leak. As a result, a resist pattern mask having inclined resist pattern end surfaces is formed. After forming a resist pattern mask with an inclined end surface, a photomask having an opening wider than the upper surface of the opening of the resist pattern mask for forming the guide layer 13 is used to form a gap between this photomask and the resist pattern mask. By exposing and developing with a gap, a resist pattern mask having an end surface with a two-stage inclination is formed. Dry etching is performed using this resist pattern mask to form the upper clad layer 15 having side end surfaces 15a with a second angle θ2 smaller than the first angle θ1.

A method of forming the side end surface 14a of the lower clad layer 14 will be described.
A two-step inclined resist pattern mask is formed in the same manner as the resist pattern mask for forming the upper clad layer 15 . By appropriately setting the etching time using this resist pattern mask, the lower clad layer 14 having the side end surface 14a with the third angle θ3 smaller than the first angle θ1 is formed.

A method for forming the lamination surface 11a of the substrate 11 will be described.
By stopping the etching while leaving the wafer that will eventually become the substrate 11 by a method similar to the method of forming the guide layer 13, the guide layer 13 has a larger area than the surface of the guide layer 13 in contact with the light emitting layer 12. A region that will eventually become the lamination surface 11a is formed.

A method for forming the protruding length d of the substrate 11 will be described.
When dividing the substrate 11, a dividing line is drawn in the wafer so that the protruding length of the substrate 11 from the side end surface 14a of the lower clad layer 14 is longer than 5 μm and shorter than 1000 μm, and the wafer is divided along the dividing line. As a result, the substrate 11 having an adjusted length protruding from the side end surface 14a of the lower clad layer 14 is formed.

A method of forming the oxide 111 (see FIG. 4) will now be described.
After forming a region that has a larger area than the surface of the guide layer 13 in contact with the light emitting layer 12 and will eventually become the lamination surface 11a, this region of the wafer is subjected to O ₂ plasma treatment and treatment with a chemical solution containing an oxidant. Alternatively, the oxide 111 is formed by heat treatment at a high temperature.

A method of forming the package 17 so that the angle formed with the guide layer 13 is the fourth angle θ4 (see FIG. 2) will be described.
After the laminated body 10 is formed and the wafer is singulated, the package 17 is tilted with the fourth angle .theta.4 formed by the exit-side end face 13a of the guide layer 13 and the inner side face 17a, and the window 171 is attached and fixed. .

A method of forming the AlGaNO films 143 and 153 (see FIG. 4) will be described.
After forming the lamination surface 11a having a larger area than the surface of the guide layer 13 in contact with the light emitting layer 12, O ₂ An AlGaNO film 143 is formed on the side facet 14a of the lower clad layer 14 and an AlGaNO film 153 is formed on the side facet 15a of the upper clad layer 15 by plasma treatment, treatment with a chemical solution containing an oxidant, or heat treatment at a high temperature. .

A method of forming the insulating protective film 18 (see FIG. 4) will be described.
An insulating layer is formed on the semiconductor laminate that will eventually become the laminate 10, and dry etching is performed in the same manner as the method for forming the guide layer 13, followed by wet etching with an alkaline chemical solution (eg, KOH aqueous solution or TMAH solution). A portion of the upper clad layer 15 is side-etched by , forming the insulating protective film 18 protruding from the upper clad layer 15 toward the side end surface 11 b of the substrate 11 . In addition, the insulating protective film 18 is formed so as to expose at least a portion of the p-type electrode 162 .

As described above, the laser diode 1 according to this embodiment includes a substrate 11, a light emitting layer 12 arranged above the substrate 11, and a guide layer 13 arranged above the substrate 11 with the light emitting layer 12 interposed therebetween. , a lower clad layer 14 formed between the substrate 11 and the guide layer 13 , and an upper clad layer 15 formed on the guide layer 13 . The substrate 11 has a lamination surface 11a on which the lower clad layer 14, the guide layer 13 and the upper clad layer 15 are laminated. 13a, and the first angle θ1 formed by the output-side end surface 13a and the lamination surface 11a is larger than 0° and smaller than 90°.

According to the laser diode 1 having this configuration, it is possible to suppress the return light R reflected by the inner surface 17 a of the package 17 from entering the light emitting layer 12 again. As a result, the laser diode 1 can suppress photoexcitation of the light emitting layer 12 and reduce output noise.

The present invention is not limited to the above embodiments, and various modifications are possible.
Although the guide layer 13 is an undoped layer in the above embodiment, the present invention is not limited to this. The guide layer 13 may be doped with, for example, a dopant so that the region below the light emitting layer 12 is made of an n-type semiconductor and the region above the light emitting layer 12 is made of a p-type semiconductor. In this case, the laminated body 10 is formed of a p-type semiconductor in the upper layer than the light emitting layer 12 and an n-type semiconductor in the lower layer of the light emitting layer 12 .

In the above embodiment, the end faces of the protrusion 152 and the p-type electrode 162 are formed flush with the side end face 15a and the opposing side end face facing the side end face 15a, but the present invention is not limited to this. The projecting portion 152 may have both end faces at positions inside (for example, 5 μm to 10 μm) from the side end face 15a and the opposing side end face. In addition, the p-type electrode 162 may have an end surface at a position (for example, 2 μm to 10 μm) inside the end surface of the protrusion 152 .

Although the lamination surface 11a of the substrate 11 is exposed around the lower clad layer 14 in the above embodiment, the present invention is not limited to this. For example, the lamination surface 11 a of the substrate 11 does not have to be exposed around the lower clad layer 14 . In this case, the lamination surface 11a of the substrate 11 and the lower surface of the lower clad layer 14 (the surface in contact with the lamination surface 11a) may have the same area. It may have the same shape as the lower surface.

1 Laser diode 10 Laminate 11 Substrate 11a Laminated surface 11b Side end surface 12 Light emitting layer 13 Guide layer 13a Emission side end surface 14 Lower clad layer 14a Side end surface 15 Upper clad layer 15a Side end surface 15b Al _x2 Ga _y2 N layer 15c Al _x3 Ga _y3 N-layer layer 17 package 17a inner surface 18 insulating protective film 111 oxide 131 dielectric multilayer film 141 first region 142 second regions 143, 153 AlGaNO film 151 flat plate portion 152 protrusion 161 n-type electrode 162 p-type electrode 171 window L Emitted light M Distance R Returned light T Transmitted light θ1 First angle θ2 Second angle θ3 Third angle θ4 Fourth angle

Claims (18)

a substrate;
a light-emitting layer disposed above the substrate;
a guide layer disposed above the substrate with the light-emitting layer interposed therebetween;
a lower clad layer formed between the substrate and the guide layer;
and an upper clad layer formed on the guide layer,
The substrate has a lamination surface on which the lower clad layer, the guide layer and the upper clad layer are laminated,
The guide layer has an emission-side facet that intersects the axis in the resonance direction from which the light emitted by the light-emitting layer is emitted,
a first angle formed by the exit-side end surface and the lamination surface is larger than 0° and smaller than 90°,
The upper cladding layer has a side end surface disposed above the output side end surface and forming a second angle smaller than the first angle with the lamination surface.
laser diode. a substrate;
a light-emitting layer disposed above the substrate;
a guide layer disposed above the substrate with the light-emitting layer interposed therebetween;
a lower clad layer formed between the substrate and the guide layer;
an upper clad layer formed on the guide layer;
with
The substrate has a lamination surface on which the lower clad layer, the guide layer and the upper clad layer are laminated,
The guide layer has an emission-side facet that intersects the axis in the resonance direction from which the light emitted by the light-emitting layer is emitted,
a first angle formed by the exit-side end surface and the lamination surface is larger than 0° and smaller than 90°,
The lower clad layer has a side end face that is arranged below the output side end face and that forms a third angle with the lamination plane that is smaller than the first angle.
laser diode. 2. The laser diode according to claim 1 , wherein the lower cladding layer has a side facet disposed below the emission side facet and having a third angle formed with the lamination face that is smaller than the first angle. 4. The laser diode according to any one of claims 1 to 3, wherein the laminated surface has an area larger than the surface of the guide layer that contacts the light emitting layer. The protruding length of the substrate from the side end surface of the lower clad layer is longer than 5 μm and 1000 μm.
5. Laser diode according to any one of claims 1 to 4, shorter than m. 6. A laser diode according to any one of claims 1 to 5, wherein the substrate has a thickness greater than 50 [mu]m and less than 10000 [mu]m. 7. The laser diode according to any one of claims 1 to 6, wherein the substrate is made of a material other than a nitride semiconductor. a substrate;
a light-emitting layer disposed above the substrate;
a guide layer disposed above the substrate with the light-emitting layer interposed therebetween;
a lower clad layer formed between the substrate and the guide layer;
an upper clad layer formed on the guide layer;
with
The substrate has a lamination surface on which the lower clad layer, the guide layer and the upper clad layer are laminated,
The guide layer has an emission-side facet that intersects the axis in the resonance direction from which the light emitted by the light-emitting layer is emitted,
a first angle formed by the exit-side end surface and the lamination surface is larger than 0° and smaller than 90°,
The substrate is made of a nitride semiconductor,
An oxide having a thickness of 0.5 nm or more and 100 nm or less is formed on part or all of the surface of the substrate.
laser diode. The substrate is made of a nitride semiconductor,
7. The laser diode according to any one of claims 1 to 6, wherein an oxide having a thickness of 0.5 nm or more and 100 nm or less is formed on part or all of the surface of the substrate. A package formed of glass covering the substrate, the lower clad layer, the light emitting layer, the guide layer and the upper clad layer,
10. The laser diode according to any one of claims 1 to 9 , wherein a fourth angle formed by said emitting end surface and said inner surface of said package is larger than 0[deg.] and smaller than 5[deg.]. 11. The laser diode according to claim 10 , wherein the distance from the light emitting layer to the inner surface of the package is 1 mm or more and 10 mm or less. a substrate;
a light-emitting layer disposed above the substrate;
a guide layer disposed above the substrate with the light-emitting layer interposed therebetween;
a lower clad layer formed between the substrate and the guide layer;
an upper clad layer formed on the guide layer;
with
The substrate has a lamination surface on which the lower clad layer, the guide layer and the upper clad layer are laminated,
The guide layer has an emission-side facet that intersects the axis in the resonance direction from which the light emitted by the light-emitting layer is emitted,
a first angle formed by the exit-side end surface and the lamination surface is larger than 0° and smaller than 90°,
The lower clad layer and the upper clad layer are made of AlGaN and have AlGaNO with a thickness of 0.5 nm or more and 100 nm or less on part or all of the side facets.
laser diode. The lower clad layer and the upper clad layer are made of AlGaN , and have AlGaNO with a thickness of 0.5 nm or more and 100 nm or less on part or all of the side facets. Laser diode as described. a substrate;
a light-emitting layer disposed above the substrate;
a guide layer disposed above the substrate with the light-emitting layer interposed therebetween;
a lower clad layer formed between the substrate and the guide layer;
an upper clad layer formed on the guide layer;
with
The substrate has a lamination surface on which the lower clad layer, the guide layer and the upper clad layer are laminated,
The guide layer has an emission-side facet that intersects the axis in the resonance direction from which the light emitted by the light-emitting layer is emitted,
a first angle formed by the exit-side end surface and the lamination surface is larger than 0° and smaller than 90°,
The light-emitting layer is made of Al _x1 Ga _y1 N,
The _upper cladding layer includes _{an Alx2Gay2N} layer and _{an Alx3Gay3N} layer provided on the _Alx2Gay2N layer,
The compositions of the light emitting layer, the Al _x2 Ga _y2 N layer and the Al _x3 Ga _y3 N layer satisfy the relationships x1+y1=1, x2+y2=1, x3+y3=1, x2<x1 and x2<x3.
laser diode. The light-emitting layer is made of Al _x1 Ga _y1 N,
The _upper cladding layer includes _{an Alx2Gay2N} layer and _{an Alx3Gay3N} layer provided on the _Alx2Gay2N layer,
The compositions of the light-emitting layer, the _Alx2Gay2N layer and the _Alx3Gay3N layer satisfy the relationships x1+ _y1 =1, x2+y2=1, x3+y3=1, _x2 <x1 and x2<x3. 14. Laser diode according to any one of claims 13 to 13 . An insulating protective film is provided on part or all of the upper cladding layer,
16. The laser diode according to any one of claims 1 to 15 , wherein at least part of said insulating protective film protrudes from said upper cladding layer toward a side end surface of said substrate. a substrate;
a light-emitting layer disposed above the substrate;
a guide layer disposed above the substrate with the light-emitting layer interposed therebetween;
a lower clad layer formed between the substrate and the guide layer;
an upper clad layer formed on the guide layer;
with
The substrate has a lamination surface on which the lower clad layer, the guide layer and the upper clad layer are laminated,
The guide layer has an emission-side facet that intersects the axis in the resonance direction from which the light emitted by the light-emitting layer is emitted,
a first angle formed by the exit-side end surface and the lamination surface is larger than 0° and smaller than 90°,
The light-emitting layer emits light having an emission wavelength of 360 nm or less.
laser diode. 17. The laser diode according to any one of claims 1 to 16 , wherein the light emitting layer emits light having an emission wavelength of 360 nm or less.

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