JPH08213706A - Manufacture of optical device - Google Patents

Abstract

PURPOSE: To enable wide growth of the 111}A crystal surface in an optical device in a semiconductor laser having a projected structure in the [011] crystal axis direction on the GaAs substrate having the main surface of 100} crystal surface and the 111}A crystal surface formed from the resonator end face of this semiconductor laser. CONSTITUTION: In the manufacture of an optical device including a semiconductor laser LD having a projected structure in the direction of [011] crystal axis on the GaAs substrate having the main surface of 100} crystal surface and the 111}A crystal surface which will become a reflecting mirror 7 formed of the resonator edge face of the semiconductor laser LD, the 111}A crystal surface is formed by setting the raw material supply ratio of group V and group III, namely, the V/III ratio x to 35<x<=200, preferably to 50<=x<=150.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical device such as a CLC (confocal laser coupler) element which is a novel optical coupling element, or a surface emitting laser.

[0002]

2. Description of the Related Art In a conventional optical device, for example, an optical pickup unit for a so-called optical disc such as a compact disc (CD) or a magneto-optical disc, optical components such as a grating and a beam splitter are individually assembled.
The configuration of the entire apparatus becomes complicated and large, and when assembling on a substrate in a hybrid manner, strict alignment accuracy is required when setting optical arrangement.

Further, in the optical system in the optical pickup section, the light always returns to the light emitting section, and therefore, in order to detect the returned light, it is necessary to split the light with a beam splitter or a hologram. Therefore, there is a disadvantage that the amount of light received by the light receiving unit is reduced.

[0004]

On the other hand, the applicant of the present invention has proposed an optical coupling element which is capable of simplifying the structure of the optical pickup section for the above-mentioned optical disc, downsizing the entire body, improving accuracy, and improving reliability. CLC (Confocal Laser Coupler) device was proposed. This CLC element is formed in a monolithic structure in which a light emitting portion made of a semiconductor laser and a light receiving portion made of a photodiode are close to each other.

The CLC element which is the optical coupling element will be described with reference to FIGS. In the figure, 1 is an optical coupling element, 2 is an irradiated portion, and 3 is a converging means, that is, a converging optical lens.

The optical coupling element 1 is formed by integrating the light emitting section 4 and the light receiving section 5 on a common semiconductor substrate 6, and the emitted light L _F from the light emitting section 4 converges and irradiates the irradiated section 2. The return light L _R reflected from the irradiated portion 2 is condensed by the converging means 3 and is received by the light receiving portion 5 arranged at the confocal position of the converging means 3 (strictly, near the confocal position). Is configured as follows. In this configuration, the light from the light emitting portion has its optical axis before and after being reflected by the irradiated portion 2, and its optical axis is represented by a chain line a.
As shown in, the light is received by the light receiving section 5 after passing through coaxial paths.

In this optical coupling element 1, as shown in the enlarged view of FIG. 5, the light emitting section 4 is composed of a semiconductor laser LD having a horizontal resonator (however, 9 is its stripe electrode), a reflecting mirror 7, and a light receiving section. Reference numeral 5 is a photodiode (PD). In the semiconductor laser LD, the outgoing light L _{F from this} is reflected by the reflecting mirror 7 so as to match the path to the irradiated portion 2.

The return light L _R directed to the light receiving section 5 is
The light is converged to near the light diffraction limit (that is, the diffraction limit of the lens), and at least a part of the light receiving surface of the light receiving unit 5 is within the light diffraction limit, that is, the wavelength of the light emitted from the light emitting unit 4 is λ, When the numerical aperture of the converging means 3 is NA, the distance from the optical axis a of the light emitted from the light emitting section 4 which crosses the arrangement reference plane S of the light receiving surface is set to a position within 1.22λ / NA. .

Further, in this case, as shown in FIGS. 4 and 6, the diameter φ _s of the emitted light L _F of the light emitting section 4 on the arrangement reference plane S of the light receiving surface of the light receiving section 5 is set to the above-mentioned optical diffraction limit. The diameter is smaller than the diameter φ _d , and the effective light receiving surface of the light receiving unit 5 is located outside the diameter φ _{s of} the emitted light. If a semiconductor laser is used as the light source of the light receiving unit 4, the diameter φ _{s of the} emitted light is about 1
It can be about 2 μm. On the other hand, the numerical aperture NA of the converging means 3 on the optical coupling element 1 side is, for example, 0.09 to 0.
1. When the wavelength λ of emitted light is about 780 nm, the diffraction limit, that is, φ _d, is about 1.22λ / NA≈10 μm.

Then, the light emitting portion 4 is arranged at the focal point position of the converging means 3 and the irradiated portion (eg optical disk) 2 is arranged at the resonance point position. The laser light emitted from the semiconductor laser LD of the light emitting section 4 is reflected by the reflecting mirror 7 in a substantially vertical direction, and is irradiated onto the irradiated section 2 through the converging means 3. At the time of focusing, the return light reflected from the irradiated portion 2, that is, the return light L _R reflected including the recording information in the irradiated portion 2
Is returned to the same optical path, is converged again by the converging means 3, and is incident on the photodiode of the light receiving section 5 arranged near the confocal position, and this return light L _R is detected by the light receiving section 5. become. That is, it is converted into an electric signal and taken out as a reproduction signal.

Incidentally, as a semiconductor laser for the above-mentioned CLC element, an SDH (separated double hetero) type semiconductor laser having a convex structure is one of the promising candidates because of its low threshold value and high efficiency. .

In this SDH type semiconductor laser, as shown in FIGS. 11 and 12, the main surface is a G having a {100} crystal plane.
The ridge stripe 12 is formed in the [011] crystal axis direction using the aAs substrate 11, and the semiconductor layer is formed by crystal growth of each semiconductor layer by MOCVD (Metal Organic Chemical Vapor Deposition) method. The ridge stripe 12 is formed by digging the groove 15 on both sides of the ridge formation portion by a known technique such as chemical etching, for example, RIE (reactive ion etching) (see FIG. 11).

That is, as shown in FIG. 12, on the main surface of the GaAs substrate 11 on which the ridge stripe 12 is formed, the first conductivity type, that is, the same conductivity type as the substrate 11, for example, A
The first clad layer 13 made of 1 GaAs, the active layer 14 made of, for example, undoped, GaAs, the second conductivity type different from that of the substrate 11, that is, AlGaAs, for example.
The lower second clad layer 16A, the first conductivity type first current blocking layer 17A and the second conductivity type second current blocking layer 17B each made of, for example, AlGaAs.
A third current blocking layer 17C of the first conductivity type, a second cladding layer 16B of the upper layer having the same composition as the second cladding layer 16A of the lower layer, and a cap layer 18 of the second conductivity type of GaAs, for example, are continuously epitaxy. Formed by.

In this case, as shown in FIG. 12, the epitaxial growth layer on the ridge stripe 12 is formed by the {111} B crystal plane from the edge along the extension direction of the ridge stripe 12, that is, the [011] crystal axis direction. Slope 19
a and 19b are generated. This is because the crystal growth rate of the {111} B crystal plane is low.
When the 1} B crystal plane is generated, the epitaxial growth on this plane is almost stopped to form slopes 19a and 19b, and on the ridge stripe 12,
It is sandwiched by the slopes 19a and 19b,
A semiconductor layer is formed by epitaxial growth with a triangular cross section, in which a and 19b abut at their upper edges. That is,
These slopes 19a and 19b separate the semiconductor layer from another portion, for example, from the inside of the groove 15.

In the triangular portion of the cross section sandwiched by the above-mentioned slopes 19a and 19b on the ridge stripe 12, for example, the semiconductor laser portion LD including the first cladding layer 13, the active layer 14, and the second cladding layer 16A below is formed. Limited configuration.

As a method of manufacturing a CLC element using an SDH type semiconductor laser, after the above-mentioned semiconductor layers are epitaxially grown on a GaAs substrate 11 having a stripe lis 12 formed thereon, RIE (so as to obtain a required horizontal resonator). A semiconductor laser LD is formed by etching by a reactive ion etching method or the like and having the etching surfaces as the cavity end faces 23A and 23B. Next, a mask layer, for example, an insulating film of SiO ₂ , SiN, or the like is formed so as to cover the formation portion of the semiconductor laser LD, and then Ga that is not covered by the mask layer is formed.
Selectively MOCV a GaAs layer, for example, on the As substrate 11.
Formed by D (in order to form the photodiode PD, GaAs of the first conductivity type is formed, and then the second
Forming conductivity type GaAs).

In this case, the surface of the GaAs layer selectively epitaxially grown on the substrate 11 facing the cavity end face 23A is a {111} A crystal plane, and the angle formed with the plate surface of the substrate 11 is 54.7 °. Becomes The {111} A crystal plane occurs as a slope having a good morphology, and this slope serves as the reflecting mirror 7.

By the way, when the required laser resonator is formed by RIE, due to the convex structure peculiar to the SDH type semiconductor laser, resist unevenness or the like that occurs during mask alignment appears,
After etching by RIE, as shown in FIGS. 7 and 8, the ridge stripe 12 is slightly recessed. Moreover, since it has a convex structure, it remains in a convex shape on the etching bottom surface 21, making it difficult to form the reflecting mirror 7 for the CLC element. The normal growth conditions (growth temperature T = 800 ° C., selective MOCVD) on the states of FIGS.
According to the V group and III group material supply ratio, that is, V / III ratio = 3
When GaAs selective growth is performed in 5), the result is as shown in FIG. 9, and the reflecting mirror region 7 of the {111} A crystal plane of the GaAs layer 22 becomes extremely narrow. FIG. 10 is a side view of FIG. 9.

In the case of an SDH type semiconductor laser, a typical far field pattern is θ // = 30 °, θ⊥ = 45 °
Therefore, only a part of the emitted light may be reflected in the narrow reflector area 7. That is, since the reflecting mirror region 7 is small, the emitted light from the semiconductor laser is eclipsed, and only a part of the emitted light is reflected.

Such a problem also applies to a so-called surface emitting laser other than the CLC element, for example, a laser light from a semiconductor laser having a horizontal resonator is reflected by a reflecting mirror and emitted upward.

In view of the above points, the present invention is an optical device such as a CLC device or a surface emitting laser, which has a convex structure as a laser structure thereof, but is capable of freely controlling the reflection mirror region and forming it in a required area. The present invention provides a method of manufacturing an optical device that is made possible.

[0022]

In the method for manufacturing an optical device according to the first aspect of the present invention, a Ga whose main surface is a {100} crystal plane is used.
A semiconductor laser LD having a convex structure in the [011] crystal axis direction on an As substrate and a cavity end face 23A of this semiconductor laser.
In manufacturing an optical device having a {111} A crystal plane 7 formed from, a group V raw material supplied by selective MOCVD and II
The raw material supply ratio of the group I raw material, that is, the V / III ratio x, is 35 <x
≦ 200, preferably 50 ≦ x ≦ 150 and {11
1} A crystal plane 7 is formed.

In the method of manufacturing an optical device according to the second aspect of the present invention, the growth of the {111} A crystal plane 7 surrounded by the {100} crystal planes and the {110} crystal planes is performed with V of 35 <x≤200.
It is characterized in that it is controlled by the / III ratio.

[0024]

According to the first aspect of the present invention, when forming the {111} A crystal face 7 from the resonance end facet 23A of the semiconductor laser LD having a convex structure, the raw material supply ratio of the group V raw material and the group III raw material, that is, By setting the V / III ratio x to 35 <x ≦ 200, the area of the {111} A crystal plane 7 can be increased. When the V / III ratio x is 35 or less, {111} A
The area of the crystal plane becomes narrow, and when the V / III ratio x exceeds 200, the area of the {111} A crystal plane saturates and remains unchanged.

According to the second aspect of the present invention, the growth of the {111} A crystal plane 7 surrounded by {100} crystal planes and {110} crystal planes is controlled by the V / III ratio x of 35 <x≤200. By doing so, the area of the {111} A crystal plane 7 can be freely changed. Therefore, by selecting the V / III ratio x, it is possible to selectively grow {111} A crystal planes over a wide area.

[0026]

Embodiments of the present invention will be described below with reference to the drawings.

CLC element which is an optical coupling element, that is, SDH
The case of application to the manufacture of a CLC element using a semiconductor laser of the type will be described.

Also in this example, FIG. 11 and FIG.
Similar to 2, the ridge stripe along the [011] crystal axis direction is formed by digging grooves 15 on both sides of the GaAs substrate 11 whose main surface is a {100} crystal surface by a well-known technique such as RIE. 12 is formed. Then, a first clad layer 13 of, for example, AlGaAs of the first conductivity type, that is, the same conductivity type as the substrate 11, a non-doped active layer 14 of, for example, GaAs, and a conductivity type different from that of the substrate 11 are sequentially formed thereon by MOCVD. Ie the second
Clad layer 16A, a first conductivity type first current blocking layer 17A, a second conductivity type second current blocking layer 17B, and a first conductivity type third layer, which are each made of, for example, AlGaAs.
Current blocking layer 17C, and, for example, the upper second clad layer 16 having the same composition as the lower second clad layer 16A.
B, cap layer 18 of the second conductivity type, for example, GaAs
Are continuously epitaxially grown.

The epitaxial growth layer on the ridge stripe 12 is formed as shown in FIG.
The slopes 19a and 19b formed by the {111} B crystal planes are generated from the edge portion along the extension direction of 2, that is, the [011] direction, and as a result, both slopes 19 are formed on the ridge stripe 12.
A semiconductor layer is formed by epitaxial growth with a triangular cross section where a and 19b meet at the upper edge. Therefore, these slopes 19a and 19b separate the semiconductor layer from other portions, for example, the semiconductor layer grown from inside the groove 15.

A slope 19a on the ridge stripe 12
The semiconductor laser LD is constituted by the first clad layer 13, the active layer 14, and the second clad layer 16A which is the lower layer in the triangular portion of the cross section sandwiched between and 19b.

Next, leaving at least a portion of the epitaxially grown semiconductor layer as the semiconductor laser LD, at least the portion where the reflecting mirror 7 is finally formed is etched by RIE or the like. Then, both end surfaces of the semiconductor layer formed by this etching surface are made into resonator end surfaces 23A and 23B, respectively, and an SDH type semiconductor laser LD is constituted between both end surfaces 23A and 23B (see FIG. 2).

The state of the etching surface by this RIE is
Similar to the above-described FIGS. 7 and 8, the ridge stripe 12 is slightly recessed, and the etching bottom surface 21 remains convex.

Next, in this embodiment, a mask layer such as SiO 2 is formed so as to cover the constituent portion of the SDH type semiconductor laser LD.
_2. After forming an insulating film such as SiN, select MOCV on the GaAs substrate 12 not covered by the mask layer.
A state in which the source supply ratio of the group V source and the group III source, that is, the V / III ratio x is increased by D, that is, 35 <x ≦ 200, preferably in the range of 50 ≦ x ≦ 150, for example, a GaAs layer is formed. To do. Growth temperature T
Is set to 800 ° C. which is the same as usual. By selectively growing GaAs under the growth condition in which the V / III ratio x is made higher than usual, as shown in FIG. 1 and FIG.
{111} surrounded by 0} and {110} crystal faces
The reflector area 7 formed by the A crystal plane is enlarged.

By sequentially forming the GaAs layers of the first conductivity type and the second conductivity type during the growth of the GaAs layer 24, it is possible to form the photodiode PD as the light receiving portion on the reflecting mirror region 7 side. .

FIG. 3 shows the relationship between the V / III ratio x and the size of the reflecting mirror area 7. The straight line I plotted by the ● marks.
Is the length A of the bottom of the reflector area, a straight line plotted with a circle
II indicates the width B of the reflecting mirror region 7 on the extension of the position of the active layer 14 of the SDH type semiconductor laser, and this straight line II is considered to be the effective reflecting mirror region 7.

The far field pattern of the SDH semiconductor laser LD is as wide as θ // = 30 °, and the cavity end face 2 is used.
When the distance between 3A and the reflecting mirror region 7 is about 2 to 3 μm, the width B of the reflecting mirror region 7 on the extension of the active layer needs to be about 5 μm. Under these conditions, V / III
It is desired that the ratio be 70 or more.

As is apparent from the graph of FIG. 3, the width B of the reflecting mirror region 7 depends on the group V and II in the selective MOCVD.
By controlling the V / III ratio x at the time of supplying the group I raw material, it becomes possible to freely change it. However, V / II
When the I ratio x is 35 or less, the light emitted from the semiconductor laser LD is eclipsed by the reflecting mirror 7. Further, when the V / III ratio x exceeds 200, the size of the reflecting mirror region 7 is saturated, and it is not possible to expect further expansion of the area.

In the above example, the present invention is applied to a CLC device as an optical coupling device, but it can also be applied to a surface emitting laser in which light emitted from a semiconductor laser by a horizontal resonator is raised by a reflecting mirror to make surface emission.

According to this embodiment, in the CLC device or the simple surface emitting laser to which the SDH type semiconductor laser LD is applied, when forming the reflecting mirror 7, the V / III ratio x is higher than that under the normal growth condition, that is, 35 <x ≦ 200,
Preferably, by setting 50 ≦ x ≦ 150, it is possible to form the reflecting mirror region 7 having a large area and thus a large width B. Therefore, the emitted light from the SDH type semiconductor laser can be reflected upward without being lost in the reflecting mirror region 7.

[0040]

According to the first aspect of the present invention, the main surface is {10.
When manufacturing a semiconductor laser having a convex structure in the [011] crystal axis direction on a GaAs substrate, which is a 0} crystal plane, and an optical device having a {111} A crystal plane formed from the cavity facets of the semiconductor laser, High V / II of 35 <x ≦ 200
By forming the {111} A plane by using the I ratio x, it is possible to increase the area of the {111} A plane which becomes the reflecting mirror area and prevent the laser light from being eclipsed in the reflecting mirror area. You can Therefore, CL with good performance, for example
C element or surface emitting laser can be manufactured.

According to the second aspect of the present invention, the growth of {111} A crystal planes surrounded by {100} crystal planes and {110} crystal planes is controlled by the V / III ratio x of 35 <x≤200. Thus, the area of the {111} A plane can be freely changed. Therefore, even when the SDH laser is used as the CLC element or the surface emitting laser, the area of the {111} A plane that serves as the reflecting mirror can be formed to be wide, and the CLC element with good performance without the laser beam being eclipsed. Alternatively, a surface emitting laser can be manufactured.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of an optical coupling element obtained by a manufacturing method according to the present invention.

FIG. 2 is a side view showing an example of an optical coupling element obtained by a manufacturing method according to the present invention.

FIG. 3 is a graph showing the relationship between the V / III ratio and the width of the reflecting mirror area according to the present invention.

FIG. 4 is a configuration diagram of an optical coupling element.

5 is an enlarged perspective view of a main part of FIG.

FIG. 6 is an explanatory diagram of an optical coupling element.

FIG. 7 is a state diagram of the SDH type semiconductor laser after RIE.

FIG. 8 is a plan view of FIG.

FIG. 9 is a perspective view of an optical coupling element using an SDH semiconductor laser having a reflecting mirror formed under normal growth conditions.

FIG. 10 is a side view of FIG. 9.

FIG. 11 is a process drawing of the manufacture of the SDH type semiconductor laser.

FIG. 12 is a sectional view of an essential part of an SDH type semiconductor laser.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical coupling element 2 Irradiated part 3 Converging means 4 Light emitting part 5 Light receiving part 6 Light receiving part substrate 7 Reflecting mirror, reflecting mirror area ({111} A plane) LD semiconductor laser (SDH type laser) 12 Ridge stripe 13 First Cladding layer 14 Active layer 15 Groove 16 [16A, 16B] Second cladding layer 17 [17A, 17B, 17C] Current blocking layer 18 Cap layer 19a, 19b Slope ({111} B surface)

Claims (2)

[Claims] 1. A GaAs whose main surface is a {100} crystal surface.
In manufacturing an optical device having a semiconductor laser having a convex structure in the [011] crystal axis direction on a substrate and a {111} A crystal plane formed from the cavity facets of the semiconductor laser, V
/ III ratio x is set to 35 <x ≦ 200, and {111} A
A method for manufacturing an optical device, which comprises forming a crystal plane. 2. The growth of {111} A crystal planes surrounded by {100} crystal planes and {110} crystal planes is 35 <x≤2.
A method for manufacturing an optical device, which is controlled by a V / III ratio x of 00.