JP3239528B2 - Manufacturing method of semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser, and more particularly to a semiconductor laser which can be formed by a single crystal growth without cleaving the cavity end face thereof and a method of manufacturing the same.

[0002]

2. Description of the Related Art In a semiconductor laser diode (LD) currently in practical use, a semiconductor crystal is cleaved and cut into individual semiconductor lasers to form an end face that regulates the cavity length of a laser emitting portion. I have. Therefore, it is difficult to monolithically integrate them to obtain an OEIC (Optical Electronic IC). In the case of cleavage, it is difficult to reduce the length of the resonator to about 100 μm or less, and it is difficult to reduce the threshold current by shortening the length of the resonator.

Further, RIE (reactive ion etching)
The end face of the resonator can be formed by performing etching in a direction perpendicular to the substrate by anisotropic dry etching such as RIE or RIBE (reactive ion beam etching).
However, in this case, there is a problem that the crystal is damaged.

[0004]

Accordingly, the applicant of the present invention has disclosed Japanese Patent Application Laid-Open No. Hei 4-349679 and Japanese Patent Application No. Hei 4-3.
In the application No. 5151, <01>
1) An inverted mesa-shaped step having an edge extending in the crystal axis direction or the <01-1> crystal axis direction is formed, and a semiconductor multilayer film having a double hetero structure is formed by one crystal growth, and resonance occurs at the same time. We have proposed a semiconductor laser in which a cavity can be formed without forming a device end face and performing cleavage and etching as described above.

As described above, in a semiconductor laser having a structure in which a resonator end face is formed on a structural substrate having a {100} crystal face as a main surface without cleavage or etching, the resonator end face portion has a (011) crystal face or a (011) crystal face. A vertical plane composed of (0-1-1) crystal plane and {111} A crystal plane, or a vertical plane composed of (01-1) crystal plane or (0-11) crystal plane and {11}
The active layer has a double hetero structure in which the active layer is sandwiched by the cladding layer surrounded by the 1｝ B crystal plane, and the end face of the active layer is also partially constituted by the {111} crystal plane.
In some cases, the light emission direction was not perpendicular to the end face of the resonator made of the {011} crystal plane, and was emitted slightly downward, for example, to the main surface of the substrate. Therefore, when a semiconductor laser having such a configuration is combined with an optical waveguide in a monolithic or hybrid manner, the coupling efficiency may be reduced.

In these structures, the area of the {011} crystal plane or {01-1} crystal plane serving as the cavity facet is relatively small. It is necessary to increase the thickness of the clad layer on the opposite side, and the series resistance and the thermal resistance may increase.

According to the present invention, the resonator end face can be formed by one crystal growth, and the emitted light is emitted in a direction perpendicular to the resonator end face, and the resonator end face having a sufficient area is formed. An object of the present invention is to provide a formed semiconductor laser and a method for manufacturing the same.

[0008]

The present invention SUMMARY OF THE INVENTION may, on the compound semiconductor base body having a major {100} crystal faces, <01-1>
The inverted mesa-shaped ripple di having an edge extending in the crystal axis direction <br/> formed, at least a first cladding on the ripple di
Layer, epitaxially growing the active So及 beauty second cladding layer.

Particularly, the growth rate of the {111} A crystal plane is represented by gr _{(111) A} , and the growth rate of the {100} crystal plane is represented by g.
r ₍₁₀₀₎ , the growth rate of the {011} crystal plane is gr ₍₀₁₁₎ , and the angle between the { 110} crystal plane and the {111} A crystal plane is θ, where (1) ) Φ ₁ = tan ⁻¹ [√2gr _{(111) A} / (√3 gr
₍₁₀₀₎ −gr _{(111) A} )] (2) φ ₂ = tan ⁻¹ [gr ₍₀₁₁₎ / (√3gr _{(111) A)}
− {2gr ₍₀₁₁₎ )] (3) The V / III ratio and the growth temperature are adjusted so that the angle α represented by α = 90 ° + φ ₂ −φ ₁ −θ satisfies ₍ 4) α ≦ 0 °. selection was carried out the Epita <br/> Kisharu growth.

[0010] The present invention also provides the above-mentioned manufacturing method, wherein :
Even without least epitaxially it is grown on the Lippo di {0
A window is formed so as to cover the end face made of the 11 ° crystal plane.

[0011]

[0012]

As described above, in the present invention, <01-
1) An inverted mesa-shaped ridge 2 having an edge extending in the crystal axis direction is formed, and a semiconductor layer is epitaxially grown thereon to form a laser resonator. Such a crystal plane and a crystal axis direction are selected, and an inverted mesa-shaped ridge, that is, a side surface thereof is inclined slightly inward from a plane perpendicular to the substrate 1, and an angle formed between the upper surface and the side surface of the ridge is 90 °. When a semiconductor layer is epitaxially grown by MOCVD (Chemical Vapor Deposition with Organometallic) or MBE (Molecular Beam Epitaxy) or the like, and the ridge 2 is formed to be smaller than the ridge 2, the edge 1 s of the ridge 2 is formed on the base 1. A crystal plane perpendicular to the main surface, that is, a {011} crystal plane naturally occurs.

In particular, in the present invention, each semiconductor layer is grown by selecting epitaxial growth conditions so that the angle α represented by the above formulas (1) to (3) is 0 ° or less. Incidentally, this angle α is a cross section orthogonal to the <01-1> crystal axis direction in which the ridge 2 extends, that is, <01-1>
1> FIG. 2 is a schematic cross-sectional view in a plane along the crystal axis direction. As shown in FIG. 2, each semiconductor layer has a {111} crystal plane along a top surface of the ridge 2, a {111} A crystal plane, and a top surface of the ridge 2. When growing while forming a {011} crystal plane perpendicular to the {111} A crystal plane, {1}
Ridge 2 at the intersection of the 00 crystal plane and the {011} crystal plane
Is the angle that represents the spread from the side of
It indicates the degree of growth of the 1｝ A crystal plane. Hereinafter, this will be described geometrically.

For simplicity, consider the model shown in FIG.
In FIG. 4, the line AB and the line ab are parallel, and the line BC and the line bc are parallel. Also, the intersection point between the extension line of the line BC and the line ab is d. The angle between the extension of the line BC and the line AB is θ ₀ , the angle between the extension of the line BC and the line Bb is φ ₀ ,
The distance between the line AB and the line ab g _A, the distance between the line BC and the line bc and g _B. Now, assuming that 交 Bbd is considered, and the intersection of the perpendicular line drawn from vertex b to side Bd and side Bd is e, Bd = Be + ed, Bd = g _A sin θ ₀ , Be =
g _B / tanφ _0, and since a _{ed = g B / tanθ 0,} (5) tanφ 0 = g B / (g A / sinθ 0 -g B /
tan θ ₀ ) is obtained.

From this analogy, the corner shown in FIG.
Degree φ₁, Φ_TwoAnd φ_ThreeIs found. Smell on the plane shown in FIG.
And the plane along the {100} crystal plane is_t, {111}
The plane along the A crystal plane is the solid line S_aAlong the {011} crystal plane
Solid line S_vGrows in a direction perpendicular to the side surface of the ridge 2.
The solid crystal plane_sIndicated by From the edge 2s of the ridge 2
Each solid line S_tAnd the solid line S_aIntersecting line, solid line S_aAnd the solid line S
_vIntersecting line, solid line S_vAnd the solid line S_sThe line going to the intersection with
These are shown as solid lines 1, m and n, respectively. In this case,
The angle α indicating the degree of expansion of the {111} A crystal plane is
The angle formed between the solid line 1 and the solid line m. Also the edge of ridge 2
Extends from part 2s, solid line S_a, Solid line S_v, Solid line S_sas well as
Solid line S_tAnd dashed lines k_a, K_v, K_sPassing
K _tAs shown.

[0016] The angle formed between the case dashed k _a and ridges 2 of the surface theta, ₁ the angle formed by the solid line l and the broken line k _a phi, the angle formed between dashed lines k _v and solid m phi _2, a broken line k _s and solid line n
Is defined as φ _3, and the angle between the solid line m and the solid line n is defined as β to indicate the degree of growth of the {011} crystal plane. The angle γ indicates the angle formed by the solid line n and the broken line k _t.

At this time, the angle φ ₁ is defined by _a broken line ka and a solid line _Sa.
Are parallel to each other, in the above equation (5), θ ₀ is θ,
can be a a φ ₀ φ _1, g _a substituting distance L _t between the upper surface and the solid line S _t of the ridge 2 and g _B at a distance L _a between the broken line k _a and solid S _a represents a number 1 below .

[0018]

(Equation 1)

[0019] In this case, the distance L _t and L _a is the growth rate gr ₍₁₀₀₎ of each crystal plane or {100} crystal faces, {11
It can be shown as a film thickness obtained from the growth rate gr _{(111) A of the} 1｝ A crystal plane. Therefore, the above equation (1) can be changed to the following equation (2).

[0020]

(Equation 2)

Here, the angle θ between the {111} A crystal plane and the {100} crystal plane is given by cos θ = 1 from the crystal structure.
/ √3, which is approximately 54.7 °. Therefore, si
nθ = √2 / √3, since it is tan .theta = √2, the angle phi ₁ can be expressed as the number of the following 3 (same as the above-mentioned equation (1)).

[0022]

(Equation 3)

Similarly, the angle φ ₂ is defined by the broken line k _v and the solid line S
_{Since v} is parallel, θ ₀ in the above equation (5)
The can be represented by (90 ° -θ), φ ₀ the φ _2, g _a distance L _a, The following equation 4 by replacing g _B a distance L _v with a solid line S _v and dashed k _v.

[0024]

(Equation 4)

When this distance L _v is expressed as a film thickness obtained from the growth rate gr _{(011 )} of the {011} crystal plane perpendicular to the upper surface of the ridge 2, the above equation (4 ₎ can be expressed as follows.

[0026]

(Equation 5)

Where sin (90 ° −θ) = cos θ =
1 / √3, tan (90 ° -θ) = cotθ = 1 / √2
Therefore, the angle φ ₂ is given by the following equation (6)
(Same as the formula).

[0028]

(Equation 6)

Further, from the same consideration, the angle φ_ThreeIs Ridge 2
If the angle between the upper surface and the side surface of
In (5), θ₀Is (90 ° -ψ), φ₀Is φ_Three, G
_aTo gr ₍₀₁₁₎, G_BTo the solid line S_sSide of ridge 2 indicated by
Growth rate gr of the crystal plane growing along_BReplace with
It can be shown as Equation 7 below.

[0030]

(Equation 7)

From these φ ₁ , φ ₂ and φ ₃ , angles α, β and γ indicating the degree of expansion of each crystal plane are obtained. That is, α = 90 ° + φ ₂ −φ ₁ −θ β = 90 ° + φ ₃ −ψ−φ ₂ γ = ψ−φ ₃

Here, the crystal plane extending from the side of the ridge 2 is composed of a {100} crystal plane on the upper surface of the ridge 2, a {011} crystal plane perpendicular to the {100} crystal plane, and a plane along the side surface of the ridge 2. Then, when epitaxial growth is performed such that the angle α is 0 ° or less, the {011} crystal plane perpendicular to the upper surface of the ridge 2 grows dominantly,
The end face of the active layer 4 as well as the end face of the resonator can be naturally formed as a plane perpendicular to the upper surface of the ridge 2.
Therefore, in the thus formed semiconductor laser of the present invention, the traveling direction of the emitted light can be set to a direction substantially perpendicular to the cavity end face.

For this reason, according to the present invention, it is possible to avoid a decrease in coupling efficiency even when monolithically or hybridly combined with an optical waveguide, and to make the area of the {011} crystal plane which is the resonator end face relatively large. Therefore, it is not necessary to increase the thickness of the cladding layer above the active layer, and it is possible to avoid an increase in series resistance and thermal resistance.

Further, in the present invention, in addition to the above-described manufacturing method, a window 8A having a semiconductor layer having a larger energy band gap than the active layer 4 at both ends of the resonator as shown in FIG. With the configuration in which the 8B is provided, it is possible to suppress a decrease in power level due to COD (optical damage) near the resonator end face, and to improve the stability and reliability of characteristics.

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments according to the present invention will be described below in detail with reference to the drawings. In this example, a case is described in which an AlGaAs III-V compound semiconductor laser is formed on an n-type GaAs substrate.

First, a {01-1> crystal axis direction, for example, [01-1] in the <100-1> crystal plane of the compound semiconductor substrate 1 made of n-type GaAs
-1] An inverted mesa-shaped ridge 2 having an edge 2s extending in the crystal axis direction is formed to have a height not exceeding the end face of the resonator formed thereon, for example, a height exceeding 5 μm. The ridge 2 may be formed by, for example, etching with a mixed solution of an organic acid and hydrogen peroxide,
It can be manufactured by anisotropic etching such as IE. In this example, the ridge 2 is formed as a {111} B crystal plane in which the angle between the upper surface and the side surface is approximately 54.7 °, or a so-called off-plane slightly inclined from the {111} B crystal plane.

Then, over the ridge 2,
By normal pressure or reduced pressure, for example, normal pressure MOCVD (chemical vapor deposition with an organic metal) method, vapor phase growth is performed with a material such as a methyl-based material, such as trimethylaluminum, trimethylgallium, or arsine, and n-type Al _x Ga _{1 -x}
First cladding layer 3 made of As (for example, x = 0.5)
Is epitaxially grown to a thickness of, for example, 2 μm, and then an active layer 4 made of intrinsic Al _y Ga _{1 -y} As (for example, y = 0.13) is formed to a thickness of, for example, 0.05 μm, to form p-type Al.
_x Ga _1-x As (e.g. x = 0.5) having a thickness of, for example, 2μm a second cladding layer 5 made of such a high concentration of p-type GaA
The contact layer 7 made of s or the like is made to have a thickness of, for example, 0.5 μm, and is sequentially epitaxially grown.

At this time, as described above, the ridge 2 is formed in an inverted mesa shape, and the direction of extension of the edge is selected and epitaxial growth is performed as described above, whereby each semiconductor layer is formed on the main surface of the base 1. It grows while forming a plane perpendicular to the surface, and grows by being divided at the upper part of the ridge 2 and in the side grooves. Although a slightly higher-order crystal plane may grow from the abutting portion between the side surface of the ridge 2 and the bottom surface of the groove, by properly selecting the height of the ridge 2, it is ensured that the upper surface of the ridge 2 and the inside of the groove And can be grown separately.

Further, by appropriately selecting the V / III ratio and the growth temperature of the compound semiconductor, the surface of the crystal growth layer grown from the edge of the ridge 2 can have only the {100} crystal plane and the {011} crystal plane. And the above $ 11
The angle α indicating the degree of growth of the 1｝ A crystal plane can be set to 0 ° or less.

In FIG. 5, especially when an AlGaAs-based compound semiconductor is grown, V / III is used as a growth condition.
Ratio and growth temperature , that is, the supply amount of the group V element source gas and III
The measurement results are shown in which the ratio of the group element to the source gas supply amount and the condition range in which α ≦ 0 ° is obtained when the growth temperature is changed are shown. As a result of the inventor's diligent studies, when the growth conditions are selected in the range indicated by hatching in FIG.
The growth rate in the direction of the 11｝ crystal axis can be increased,
It was found that the crystal grows while forming a vertical plane without generating a {111} A crystal plane.

In this embodiment, the growth temperature is 750 ° C.
When each layer was epitaxially grown at a V / III ratio of 130, α = 0 ° and no {111} A crystal plane appeared, and the end faces 6A and 6B of each of the layers 3 to 5 were perpendicular to the main surface of the substrate 1, respectively. In this case, the (0-1-1) crystal plane and the (011) crystal plane.

In the above configuration, the case where α = 0 ° has been described, but the case where α <0 ° will be briefly described. As described above, as a method for forming the inverted mesa-shaped ridge 2, wet etching using a mixed solution of an organic acid and hydrogen peroxide, RIE, or the like can be used. As schematically shown, the edge 2s of the ridge 2 is not formed at an acute angle, and for example, an inclined surface such as a {111} A crystal plane is microscopically formed on the shoulder, and the edge 2s is formed.
A case may occur where s is formed gently.

In such a configuration, the angle α is 0
° when performing epitaxial growth to be less than
The semiconductor layer 11 grown thereon constitutes a {111} A crystal plane, but this plane gradually disappears, and by appropriately selecting the thickness, the end face of the semiconductor layer 11 can be formed into a vertical plane S.
It can be composed of only _v . That is, compared to the growth rate of the upper surface of the ridge 2 indicated by the arrow g ₀ in FIG. 6, the {111} A crystal plane when the growth rate of indicated by the arrow g ₁ {111} A crystal face becomes large extinction As a result, a vertical plane is formed.

That is, in the above-mentioned growth condition where the angle α ≦ 0 °, the growth rate of the {111} A crystal plane is larger than the growth rate of the other crystal planes, and the growth rate is at least for a predetermined time (predetermined thickness).
As described above, it can be seen that when the crystal is grown, the {111} A crystal plane does not appear and the other crystal planes, for example, the {100} crystal plane and the {011} crystal plane are dominantly grown. Therefore, when this is applied to the manufacture of a semiconductor laser, by appropriately selecting the thicknesses of the first cladding layer 3 and the active layer 4, it is possible to ensure that the end of the active layer 4 is formed by a vertical plane. You can do it.

After the structure shown in FIG. 1 is obtained in this way, the structure shown in FIG.
The contact layer 7 is patterned in a stripe shape having a width of, for example, 6 μm extending in the direction along the plane of the drawing, and further, although not shown, for example, ohmic electrodes are formed on the contact layer 7 and on the back surface of the substrate 1 to form a vertical resonator. It is possible to obtain a semiconductor laser in which the end face is formed spontaneously and the current is confined in the lateral direction.

In this case, since the end face of the active layer 4 is formed as a vertical face as described above, light emitted from the active layer 4 becomes almost perpendicular to the end face of the resonator and is monolithically or hybridly combined with the optical waveguide. In this case, the coupling efficiency does not decrease, and even if the thickness of the second cladding layer 5 is made small, the area of the cavity end face can be made sufficiently large to avoid an increase in series resistance and thermal resistance. can do.

A window can be formed in such a semiconductor laser. An example will be described with reference to FIGS. First, as shown in FIG. 3A, for example, an n-type A having a larger energy band gap than the active layer 4.
A semiconductor layer 8a of l _0.5 Ga _0.5 As is grown thickly over the contact layer 7 so as to fill the grooves on both sides of the end faces 6A and 6B, for example.

Next, as shown in FIG. 3B, the entire surface is etched by anisotropic etching such as RIE to remove the semiconductor layer 8a on the contact layer 7.

Then, as shown in FIG.
Of electrodes 9 and 1 on the upper part of
After 0 is formed ohmic, it is cleaved with a predetermined length to obtain a semiconductor laser in which windows 8A and 8B are formed.

The window structure is not limited to this example, but may take various other structures. For example, as shown in FIG. 7A, first, the entire surface including the upper surface of the contact layer 7,
The semiconductor layer 8a made of n-type Al _0.5 Ga _0.5 As is deposited at a growth temperature of, for example, 830 ° C. using a material such as triethylaluminum, trimethylgallium, arsine or the like.

Then, as shown in FIG. 7B, an opening 8c is provided on the upper surface of the contact layer 7 by applying photolithography or the like, an electrode 9 is applied ohmicically, and the back surface of the compound semiconductor substrate 1 is similarly formed. The electrodes 10 are applied in an ohmic manner, and windows 8A and 8B having band gaps larger than those of the active layer 4 are formed on the end faces 6A and 6B of the active layer 4.
A semiconductor laser having a window structure provided with is provided. In this example, it is possible to form the window without cleavage.

When the windows 8A and 8B are provided in this manner, COD (optical damage) near the cavity end face is required.
, The power level is reduced, and the stability and reliability of the characteristics can be improved.

It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made by changing the composition of the above-mentioned AlGaAs-based compound or in the current confinement structure, the window structure, and the like. The material is not limited to the methyl type, but may be the ethyl type, and not only the MOCVD but also the growth by MBE is possible. Further, in addition to AlGaAs-based compounds, for example, InGaAs-based, InG
AlGaAs such as aAsP, InP, ZnSe, etc.
A similar effect can be obtained by applying the present invention to a semiconductor laser made of a material having a so-called cubic zinc sulfide type crystal structure similar to that of the system.

[0054]

As described above, according to the present invention, the end face of the resonator can be spontaneously formed by one crystal growth, and the end face of the active layer has the same vertical face as the end face of the resonator. Since it can be formed with a surface, it is possible to avoid instability in the light emission direction, emit the emitted light almost perpendicular to the cavity end face, and reduce the coupling efficiency even when monolithically or hybridly combined with the optical waveguide. Can be avoided.

Further, even if the thickness of the second cladding layer 5 is made small, the area of the cavity end face can be made sufficiently large, and an increase in the series resistance and thermal resistance of the laser diode can be avoided.

According to the present invention, the windows 8A and 8A
By providing B, CO2 in the vicinity of the resonator end face is reduced.
A decrease in power level due to D (optical damage) can be suppressed, and stability and reliability of characteristics can be improved.

[Brief description of the drawings]

FIG. 1 is a manufacturing process diagram of an embodiment of the present invention.

FIG. 2 is a schematic sectional view for explaining the present invention.

FIG. 3 is a manufacturing process diagram of one embodiment of the present invention.

FIG. 4 is a diagram provided for explanation of the present invention.

FIG. 5 is a diagram showing a range of epitaxial growth conditions according to the present invention with respect to changes in V / III ratio and growth temperature in an AlGaAs-based semiconductor.

FIG. 6 is a schematic sectional view for explaining the present invention.

FIG. 7 is a manufacturing process diagram of another embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 compound semiconductor substrate 2 ridge 2s edge 3 first cladding layer 4 active layer 5 second cladding layer 6A end face 6B end face 7 contact layer 8A window 8B window 9 electrode 10 electrode

Claims (2)

(57) [Claims] An inverted mesa-shaped ridge having an edge extending in the <01-1> crystal axis direction is formed on a compound semiconductor substrate having a {100} crystal plane as a main surface, Then, a first clad layer, an active layer and a second clad layer are epitaxially grown, and the growth rate of the {111} A crystal plane is set to gr _{(111) A} , {100}.
The growth rate of the crystal plane is gr ₍₁₀₀₎ , the growth rate of the {011} crystal plane is gr ₍₀₁₁₎ , and the {110} crystal plane and {111} A
When the angle between the crystal plane and θ is θ, φ ₁ = tan ⁻¹ [√2gr _{(111) A} / (√3gr ₍₁₀₀₎ −
gr _{(111) A} )] φ ₂ = tan ⁻¹ [gr ₍₀₁₁₎ / (√3 gr _{(111) A} −√2
gr ₍₀₁₁₎ )] The above epitaxial growth is performed by selecting the V / III ratio and the growth temperature so that the angle α represented by α = 90 ° + φ ₂ −φ ₁ −θ satisfies α ≦ 0 °. A method for manufacturing a semiconductor laser, comprising: 2. The method according to claim 1, wherein a window is formed so as to cover at least an end face made of a {011} crystal plane epitaxially grown on the ridge.