JPH10190123A - Light emitting element and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily control the reflectance at the end face of a resonator by forming a diffraction grating having a cyclic recessing and projecting structure on the end face of the resonator. SOLUTION: In a light emitting element 10, a semiconductor laser LD comprises a laminated semiconductor layer 12 formed by successively forming first and second clad layers on a semiconductor substrate 11. Both front ends of the layer 12 respectively contain the front and rear end faces 13A and 13B of a resonator so that a horizontal stripe-like resonator having a grating formed by etching may be composed of the laser LD. In addition, current blocking areas 14 are formed on both sides of the stripe-like area constituting the horizontal resonator. The grating constituting the end faces 13A and 13B of the resonator has a cyclic recessing and projecting structure which controls the reflectance and transmittance of the end faces 13A and 13B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device such as a semiconductor laser having a cavity facet having a different reflectivity and a method of manufacturing the same.

[0002]

2. Description of the Related Art As one type of semiconductor laser, an etched facet laser having a cut surface formed by etching as an end face of a resonator, or an etched facet laser.
In a pseudo surface emitting laser in which a rising mirror is integrated and formed on a laser, a conventional cleavage plane is used as a resonator end face for controlling the reflectance of the resonator end face such as increasing or decreasing the reflectance. Multilayer thin film coatings have been used as well as lasers.

[0003] The multilayer thin film coating is an established technique, and is an essential technique for controlling the reflectance of a cleaved laser beam processed in units of bars divided from a wafer.

[0004]

However, when the cavity facet can be formed by a wafer process by dry etching instead of cleavage, such as an etched facet laser or a pseudo surface emitting laser, the multilayer thin film coating is not necessarily suitable. Not.

That is, when a multi-layer thin film is coated on a wafer, the incidence of particles of the coating material becomes fairly oblique on the end face. For this reason, the coating film thickness distribution becomes uneven and the film quality deteriorates in the wafer surface, and as a result, the reflectivity varies in the wafer surface and the reflectance changes over time. Further, inconveniences such as formation of a coating film in a region other than the end face of the resonator also occur.

[0006] Therefore, a multilayer thin film coating is performed after cleavage into a bar instead of a wafer, and the advantage of an etched facet laser that it can be manufactured by a full wafer process without coating is sufficiently used. Couldn't make the most of it. Furthermore, in particular, in a pseudo surface emitting laser in which a rising mirror is integrated and formed on an etched facet laser, even after being cleaved into a bar, the rising mirror makes it necessary to form a coating film at oblique incidence. As a result, it has been difficult to completely solve the above problem.

[0007] In order to solve the above-mentioned problems, the present invention provides a light emitting device and a method for manufacturing the same, which can easily control the reflectance of the cavity end face.

[0008]

The light emitting device according to the present invention has a structure in which a diffraction grating having a periodic structure of irregularities is formed on the end face of the resonator.

According to the configuration of the present invention described above, the end face reflectivity at the end face of the resonator can be controlled by the diffraction grating having the periodic structure of irregularities formed on the end face of the resonator.

According to the method of manufacturing a light emitting device of the present invention, when the cavity facet of the light emitting element is formed by etching, the shape of the etching mask is made to have a periodic structure of concavities and convexities, and one or both of the cavity facets are provided with irregularities. And a step of forming a diffraction grating having a periodic structure.

According to the method of the present invention described above, the shape of the etching mask has a periodic structure of irregularities, and by etching the end face of the resonator, the end face of the resonator can be formed as a periodic structure of irregularities. A resonator end face having end face reflectivity can be formed. In addition, it is possible to form a cavity end face with the end face reflectivity set in the state of a wafer.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is a light emitting device in which a diffraction grating having a concave-convex periodic structure is formed on a cavity end face of the light emitting device.

Further, according to the present invention, in the above-described light emitting device, the reflectance of the cavity facet is controlled by setting the period of the diffraction grating, the ratio of the concave portion to the convex portion, and the amplitude of the concave / convex periodic structure.

Further, according to the present invention, in the above-mentioned light emitting device, the period of the concave-convex periodic structure in the diffraction grating is set to be shorter than the wavelength of light emitted from the light emitting device.

According to the present invention, when the cavity facet of the light emitting element is formed by etching, the shape of the etching mask is made a periodic structure of irregularities, and a diffraction grating of the periodic structure is formed on one or both of the cavity end faces. 5 is a method for manufacturing a light-emitting element having a step of forming.

According to the present invention, in the method of manufacturing a light emitting device, the reflectance of the cavity facet is controlled by selecting the period of the diffraction grating, the ratio between the concave portion and the convex portion, and the amplitude of the periodic structure.

Further, according to the present invention, in the above-described method for manufacturing a light emitting device, the period of the concave / convex periodic structure in the etching mask is made shorter than the wavelength of light emitted from the light emitting device.

Hereinafter, embodiments of a light emitting device of the present invention and a method of manufacturing the same will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an example of a light emitting device of the present invention, in this example, an example in which the present invention is applied to an etched facet laser in which the end face of the resonator is formed by etching.

The light emitting element 10 has a first conductivity type, for example, n
A first cladding layer made of, for example, AlGaAs having the same conductivity type as the semiconductor substrate 11 is formed on a semiconductor substrate 11 made of a GaAs substrate having a {100} crystal plane as a main surface.
an active layer made of aAs and a second layer different from the first cladding layer.
A laminated semiconductor layer 12 is formed by sequentially laminating a second clad layer made of a conductive type, for example, p-type AlGaAs, and the laminated semiconductor layer 12 constitutes a semiconductor laser LD.

The two end faces of the laminated semiconductor layer 12 have a resonator end face, that is, a front end face (front end face) 13A and a rear end face (rear end face) 13B on which a grating formed by etching is formed. Face 13
A horizontal cavity of the semiconductor laser LD having a stripe shape is formed between A and 13B. Further, the semiconductor laser LD has a current blocking region 14 formed by, for example, ion implantation of impurities so as to sandwich the stripe-shaped region constituting the horizontal resonator.

In the light emitting device 10, the cavity facet 1
The gratings constituting 3A and 13B have an uneven periodic structure. Then, the end surface reflectivity and transmittance of the cavity end surfaces 13A and 13B are defined by the concave-convex periodic structure.

The period of the periodic structure is preferably shorter than the wavelength of the light emitted from the light emitting element 10 so that the emitted light is not diffracted by the periodic structure of the grating. Thus, the light emitted from the light emitting element can be emitted as a single light beam.

FIG. 2 shows another example of the light emitting device of the present invention.
In this example, a schematic configuration diagram of an example in which the present invention is applied to a pseudo surface emitting laser in which a rising mirror is further integrated with the above-described etched facet laser in which the end face of the resonator is etched is further illustrated.

The light emitting device 20 is different from the light emitting device 10 of FIG. 1 in that a rising mirror 15 is provided on a part of the semiconductor substrate 11 so as to face the front end face 13A of the horizontal resonator. Also in this light emitting element 20, the gratings forming the resonator end faces 13A and 13B have a concave-convex periodic structure.
The end face reflectance and transmittance of 3A and 13B are defined.

In the light emitting devices 10 and 20 shown in FIGS. 1 and 2, gratings are formed on both the front end face (front end face) 13A and the rear end face (rear end face) 13B of the resonator. The grating may be formed only on the surface.

The grating structure having the irregular period shown in FIGS. 1 and 2 can be easily formed by using a mask pattern 30 as shown in FIG. This mask pattern 30 has a period d, a width b of the convex portion,
It has a rectangular concavo-convex periodic structure with a height h of the convex portion.

That is, by performing etching using this mask pattern, the portions indicated by oblique lines in FIG. 3 are not etched because they are covered with, for example, SiO ₂ , but the other portions are etched. As a result, as shown in FIGS. 1 and 2, the cavity end faces 13A, 13B
Then, a grating structure having the same cross-sectional shape as the mask pattern 30 of FIG. 3 can be formed.

FIG. 4 shows the relationship between the end face reflectivity and transmittance, the grating period d, and the grating height h, specifically calculated for a GaAs semiconductor laser. However, the cross-sectional shape of the grating is rectangular, and the ratio of the rectangular projections, that is, the duty (corresponding to b / d when the width of the projections is b) is 1/2 (50%).
Was assumed. From FIG. 4, the end face reflectance can be changed from almost 0% (point X in FIG. 4B) to almost 10% by selecting d and h.
It can be controlled to 0% (point Y in FIG. 4A).

According to the detailed calculation results, the reflectivity also depends on the shape of the grating. That is, the values of the parameters d, b / d, and h that give the desired reflectance are different between the rectangular cross-sectional shape and the triangular cross-sectional shape shown in FIG. 5A or the gentle mountain-shaped cross-sectional shape shown in FIG. 5B. In either case, the reflectance can be controlled from approximately 0% to 100%.

According to FIG. 4, it is necessary to form a fine pattern having a period of 200 nm to 400 nm in order to control the end face reflectance and transmittance. Such a fine pattern can be transferred to the laminated semiconductor layer 12 made of a compound semiconductor or the like by a technique such as RIE (reactive ion etching).

According to the present invention, a high-output laser that requires a high reflectivity on the rear side and a low reflectivity on the front side in order to complete the reflectivity control at the same time as etching the cavity facet is used. Even in the case of manufacturing, a full wafer process for forming a cavity end face in a wafer state can be applied as in the case of a non-coated semiconductor laser.

Next, with reference to the drawings,
A method for manufacturing the light emitting device 10 of FIG. 1 will be described. First, as shown in FIG. 6A, a first conductivity type, for example, n-type # 1
Each semiconductor layer constituting the semiconductor laser LD is epitaxially grown on a semiconductor substrate 11 made of a GaAs substrate having a principal plane of the 00 ° crystal plane. That is, for example, a first cladding layer 1 made of n-type AlGaAs of the same conductivity type as the semiconductor substrate 11, for example, an active layer 2 made of GaAs, and a second conductivity type different from the first cladding layer 1, for example, p-type AlGa
A second semiconductor layer 12 is formed by sequentially epitaxying the second cladding layer 3 made of As with the MOCVD method or the like.

Next, as shown in FIG. 6B, etching is performed while leaving a part of the epitaxially grown laminated semiconductor layer 12 as a semiconductor laser LD. At this time, for example, using a mask pattern having a shape as shown in FIG.
By performing etching by RIE (reactive ion etching) or the like, a grating having a periodic structure of irregularities is formed on the side surface of the stacked semiconductor layer 12. The two end surfaces of the laminated semiconductor layer 12 on which the grating having the periodic structure is formed by this etching are used as cavity end surfaces 13A and 13B, respectively, and both end surfaces 13A and 13B
A horizontal resonator of the semiconductor laser LD is formed therebetween.

Further, although not shown, a current blocking region is formed by ion implantation of impurities so as to sandwich the region constituting the resonator of the semiconductor laser LD finally. Thus, the light emitting device 10 having the configuration shown in FIG. 1 can be manufactured.

By manufacturing the light emitting element 10 in this manner, the etching of the resonator end faces 13A and 13B is performed using the mask 30 having the periodic uneven structure, so that the end faces of the resonator end faces 13A and 13B are simultaneously etched when the resonator end faces 13A and 13B are etched. Rate control can be performed. This makes it possible to control the end face reflectivity by a full wafer process, in which the end face reflectivity is controlled by etching in the state of the wafer.

Next, a method of manufacturing the light emitting device 20 of FIG. 2 according to the method of the present invention will be described with reference to the drawings.
First, as shown in FIG. 7A, similarly to FIG. 6A, the semiconductor layers constituting the semiconductor laser LD are epitaxially grown on the semiconductor substrate 11 to form the laminated semiconductor layer 12.

Next, as shown in FIG. 7B, etching is performed on at least a portion where a rising mirror is finally formed, leaving a part of the epitaxially grown laminated semiconductor layer 12 as a semiconductor laser LD. At this time, for example, by using a mask pattern having a shape as shown in FIG. By this etching, both end surfaces of the laminated semiconductor layer 12 on which the grating having the concave-convex periodic structure is formed are cavity end surfaces 13A and 13B, respectively.
And a horizontal cavity of the semiconductor laser LD are configured between 13B and 13B.

Subsequently, as shown in FIG. 7C, a mask layer 4 for selective MOCVD, for example, SiO ₂ , SiN is formed so as to cover the laminated semiconductor layer 12 left on the semiconductor substrate 11, ie, the constituent part of the semiconductor laser LD. And the like.

Next, as shown in FIG. 8D, a semiconductor layer 5 of, for example, GaAs of the first conductivity type, for example, n-type GaAs is selectively formed on the semiconductor substrate 11 not covered by the mask layer 4.
It is formed by OCVD.

In this case, the slope R of the semiconductor layer selectively epitaxially grown on the semiconductor substrate 11 of FIG. 8D, in this example, the first semiconductor layer 5 is opposed to the end face of the resonator. For example, the end face 13 of the semiconductor laser
When the direction of the cavity length of the horizontal cavity of the semiconductor laser formed between A and 13B, that is, the direction indicated by the arrow x in FIG. 8D is the [011] crystal axis direction, the opposing surface is {111}.
It occurs as a slope due to the A crystal plane, and the direction b is [0-11].
When the direction is the crystal axis direction, it is generated as a slope due to the {111} B crystal plane, and the angle between the substrate and the plate surface is 54.7 in each case.
°. When the direction b is set to the [100] crystal axis direction, the opposing surface is formed as a {110} crystal plane, and forms 45 ° with respect to the surface of the substrate. Each of them is formed as a slope R having good morphology due to an atomic plane.

Therefore, as shown in FIG. 8F, the slope R formed by the specified crystal plane formed as described above reflects the light emitted from the end face of the horizontal resonator of the semiconductor laser LD and is directed to a predetermined direction. The mirror, ie, the rising mirror 15, can be used. Thereafter, as shown in FIG. 8E, for example, after the mask layer 4 is removed by etching, the semiconductor laser LD is formed on the semiconductor laser LD including the laminated semiconductor layer 12.
One electrode 6 is ohmic-coated, and the semiconductor substrate 11
The other electrode 7 of the semiconductor laser LD is ohmically adhered to the back surface of the semiconductor laser LD. Thus, the light emitting device 20 shown in FIG.
Can be manufactured.

By manufacturing the light emitting element 20 in this manner, the end face reflectivity can be controlled simultaneously with the etching of the resonator end faces 13A and 13B, as in the previous example. The reflectance can be controlled.

The reflecting mirror R of the rising mirror 15 may be formed by etching. According to the above-described manufacturing process, since the reflecting surface R of the rising mirror 15 is formed by the crystal plane, the mirror surface is more excellent than when it is formed by etching, and the inclination thereof is set accurately.

In the above example, the rising mirror 15 is used as a reflecting mirror. However, as shown in FIG. 9, for example, a second semiconductor layer of a second conductivity type of the opposite conductivity type, for example, p-type GaAs is provided in the semiconductor layer 5. 21 is selectively formed by MOCVD, and the photodiode PD is formed by the semiconductor layer 5 and the second semiconductor layer 21 so that the rising mirror 15 has a function as a light receiving element by the photodiode PD. You can also. 22 is one electrode of the photodiode PD, 23 is the semiconductor laser L
D and the photodiode PD. The second semiconductor layer 21 may be formed by ion implantation instead of selective MOCVD. With this configuration, the semiconductor laser LD and the photodiode PD can be formed on the same semiconductor substrate 11, so that the optical element having both the light-emitting element and the light-receiving element can be made smaller.

The relationship as shown in FIG. 4 is not limited to the semiconductor laser made of GaAs, and the conditions for setting the optimum periodic periodic structure exist for light emitting elements of other materials. Therefore, similarly, as shown in FIGS. 1 and 2, an etched facet laser and a pseudo surface emitting laser in which the end face reflectance is controlled by forming an uneven periodic structure on the end face of the resonator are shown in FIGS. Lasers are feasible.

The light-emitting device of the present invention and the method of manufacturing the same are not limited to the above-described examples, and may take various other configurations without departing from the gist of the present invention.

[0047]

According to the light emitting device of the present invention described above,
By providing the concave-convex periodic structure diffraction grating on the resonator end face, the reflectance at the resonator end face can be controlled. By setting the period of the diffraction grating, the ratio between the concave and convex portions, and the amplitude of the periodic structure of the concave and convex to appropriate values, the end face reflectivity can be controlled to approximately 0% to 100%. By setting the period of the concave / convex periodic structure in the diffraction grating to be shorter than the wavelength of the light emitted from the light emitting element, the emitted light can be emitted as a single light beam without being diffracted by the concave / convex periodic structure. .

According to the above-described method for manufacturing a light emitting device of the present invention, the end face reflectance is controlled simultaneously with the end face of the resonator by etching the end face of the resonator by using the mask having the periodic structure of irregularities. be able to.
As a result, it is possible to control the end face reflectivity of a high-output etched facet laser or a pseudo-surface emitting laser by the full wafer process, which has conventionally been difficult to perform the full wafer process.

Therefore, since the light emitting element can be manufactured at a time by the full wafer process and the reflectance of the end face can be controlled, the manufacturing cost can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an example of a light emitting device according to the present invention.

FIG. 2 is a schematic configuration diagram of another example of a light emitting device according to the present invention.

FIG. 3 is an example of the shape of a mask pattern in the manufacturing method of the present invention.

FIG. 4 is a diagram showing the relationship between the end face reflectivity and transmittance, the grating period d, and the grating height h, calculated for semiconductor lasers made of A and B GaAs.

FIGS. 5A and 5B are examples of shapes of a concave-convex periodic structure.

6A and 6B are manufacturing process diagrams of the light emitting device of FIG. 1;

7A to 7C are manufacturing process diagrams of the light emitting device of FIG. 2;

8A to 8D are manufacturing process diagrams of the light emitting device of FIG. 2;

9 is a schematic configuration diagram of an example in which a light receiving element is further formed on the light emitting element of FIG.

[Explanation of symbols]

Reference Signs List 1 n-type cladding layer, 2 active layer, 3 p-type cladding layer, 4 mask layer, 5 semiconductor layer, 6,7 semiconductor laser electrode, 10,20 light emitting element, 11 semiconductor substrate, 1
2 laminated semiconductor layer, 13A front end face of resonator, 13B
Rear end face of resonator, 14 current blocking region, 15 rising mirror, 21 second semiconductor layer, 22 electrode of photodiode, 23 electrode common to semiconductor laser and photodiode, 30 mask pattern, LD semiconductor laser,
PD photodiode, dperiod of periodic structure, h
Height of the periodic uneven structure, b Width of the periodic periodic structure, R slope

Claims (6)

[Claims] 1. A light emitting device, wherein a diffraction grating having a periodic concave-convex structure is formed on a cavity end face of the light emitting device. 2. The reflectance of the resonator end face according to claim 1, wherein the period of the diffraction grating, the ratio of the concave portion to the convex portion, and the amplitude of the periodic structure are controlled. Light emitting element. 3. The light emitting device according to claim 1, wherein a period of the concave-convex periodic structure in the diffraction grating is set shorter than a wavelength of light emitted from the light emitting device. 4. When a cavity facet of a light emitting element is formed by etching, the shape of an etching mask is a periodic uneven structure, and a diffraction grating having a concave / convex periodic structure on one or both of the resonator end faces. Forming a light-emitting element. 5. The reflectivity of the resonator end face according to claim 4, wherein the period of the diffraction grating, the ratio between the concave and convex portions and the amplitude of the concave and convex periodic structure are selected to control the reflectance of the resonator end face. A method for manufacturing a light-emitting element. 6. The method for manufacturing a light emitting device according to claim 4, wherein the period of the concave-convex periodic structure in the etching mask is shorter than the wavelength of light emitted from the light emitting device.