JP3185239B2 - Semiconductor laser device - 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 device, in particular, a semiconductor laser device in which a current is confined in a lateral direction of an active layer so as to reduce a threshold value. The present invention relates to a distributed feedback semiconductor laser device to be obtained.

[0002]

2. Description of the Related Art As a semiconductor laser having a low threshold current I _th, 1 single epitaxial growth SDH which is adapted to form the work (Separated Double Hetero Ju
(nction)
61-183987 and JP-A-2-174287.

As shown in a schematic enlarged cross-sectional view of an example of this SDH type semiconductor laser in FIG. 5 , first, for example, a substrate 1 made of, for example, GaAs having, for example, N-type and one principal surface having a {100} crystal plane is used. On one main surface, stripe-shaped mesa protrusions 2 extending in the <011> crystal axis direction orthogonal to the paper surface in FIG. 5 are formed, and normal MOCVD is sequentially formed on one main surface of the substrate 1 having the protrusions 2. (N-type buffer layer 13 and N-type buffer layer 13, for example) continuously by a (chemical vapor deposition using an organic metal) method, that is, a methyl MOCVD method.
Type first cladding layer 4, low impurity concentration or undoped active layer 5, for example, P-type second cladding layer 6
The semiconductor layers, for example, an N-type current blocking layer 8, a P-type third cladding layer 9, and a P-type cap layer 10, for example, are formed by a single epitaxial growth operation.

Here, the first cladding layer 4 and the second and third
The cladding layers 6 and 9 and the current blocking layer 8 are made of a material having a larger band gap, that is, a smaller refractive index than the active layer 5.

In this case, the crystal orientation with respect to the substrate 1 and the stripe-shaped mesa projections 2, the width and height of the projections 2, that is, the depth of the mesa groove 2A on both sides thereof, the first cladding layer 4, the active layer 5, the first cladding layer 4, the active layer 5, and the second cladding layer 5 on the mesa protrusion 2 are separated from those on the mesa groove 2A by selecting the thickness of the second cladding layer 6 and the like. Thus, a tom is formed by the slopes 7, and a triangular section 20 made of a stripe-shaped epitaxial growth layer divided by the slopes 7 is formed on the mesa protrusion 2.

This is because, in the case of the ordinary MOCVD method, that is, the MOCVD method using a methyl-based organic metal as a source gas, once a (111) B crystal plane is formed, epitaxial growth is unlikely to occur on this plane. Is used to form a striped triangular section 20. In this case, the current block layer 8 is divided on both sides of the stripe-shaped triangular section 20 with the triangular section 20 interposed therebetween, and both end faces generated by this division are separated from the other in the triangular section 20. The end faces of both sides of the active layer 5, that is, the end faces facing the slope 7 are abutted.

In this manner, the active layer 5 in the triangular section 20 on the mesa projection 2 is formed so as to be sandwiched by the current blocking layer 8 having a smaller refractive index, and is confined in the lateral direction to emit light. The third cladding layer 9, the current blocking layer 8, the second cladding layer 6, and the outer side of the triangular section 20 are formed on the outer side of the triangular section 20 due to the presence of the current blocking layer 8.
A pnpn thyristor is formed by the first cladding layer 4 to block a current therethrough, so that a current concentrates on the active layer 5 of the triangular section 20 on the mesa projection 2. In order to reduce the threshold current.

At this time, as a position selection of the current block layer 8, if the current block layer 8 is configured to cover both end faces of the active layer 5 of the triangular section 20 facing both slopes 7, an arrow in FIG. as shown by i _1, the third P-type on the mesa groove 2A cladding layer 9, N type current blocking layer 8, the first cladding layer 4 of N-type on the mesa projection 2, on the mesa projection 2 There is a current path that passes through the N-type buffer layer 13 to the N-type substrate 1, and there is a possibility that some leakage current may occur.

For this reason, as a configuration for avoiding the generation of the current path, there has been proposed a structure shown in FIG. 6, parts corresponding to those in FIG. 5 are denoted by the same reference numerals, and redundant description will be omitted. In this case, the position of the current block layer 8 is selected so that the triangular cross section 20 is in contact with both side surfaces of the P-type second cladding layer 6 facing the two slopes 7. A configuration that does not cover both end surfaces of the layer 5, that is, a position that does not contact both side surfaces of the N-type first cladding layer 4 on the mesa protrusion 2 that faces both slopes 7 is adopted. Therefore, the current path indicated by the arrows i ₁ in FIG. 5 described above is not formed, it is possible to reduce the leakage current.

In this case, as shown by an arrow i ₂ in FIG.
There is a current path leading to the N-type substrate 1 through the P-type second cladding layer 6, the second cladding layer 6 on the mesa groove 2A, and the N-type buffer layer 13 of the triangular section 20 in cross section. In this case, the distance between the lower surface of the current block layer 8 that is in contact with the two slopes 7 of the triangular section 20 and the upper surface of the active layer 5 of the triangular section 20 are close to each other. The passage is narrowed, and the leak current can be practically suppressed.

However, when the active layer 5 is made of AlGaAs, there is a possibility that a leak current described below may cause a problem. That is, in such a configuration, the arrow i ₂
As shown in the figure, the current path from the P-type second cladding layer 6 on the mesa groove 2A to the upper surface of the mesa protrusion 2, that is, the N-type buffer layer 13 or the N-type substrate 1 (not shown) in this case. Although the current path exists, the built-in potential of the pn junction at this portion is smaller than the built-in potential between the second cladding layer 6 on the mesa protrusion 2 and the active layer 5, so that the mesa groove 2A The leakage current flowing from the P-type cladding layer 6 to the substrate 1 or the buffer layer 13 becomes dominant, and the current confinement in the lateral direction of the active layer 5 becomes insufficient, so that the threshold of the operating current can be reduced. It may be difficult to measure.

On the other hand, as a semiconductor laser device capable of realizing single-wavelength oscillation, a distributed feedback semiconductor laser, so-called DF, is used.
There is a B laser. This DFB laser is designed to emit a specific wavelength, that is, a single longitudinal mode, more selectively by emitting a diffraction grating, that is, a grating in the vicinity of an active layer. Research and development are progressing in various fields for application to transmission.

In general, in the manufacture of this type of DFB semiconductor laser, the epitaxial growth of each semiconductor layer is divided before and after the etching operation for forming the grating.

On the other hand, in this DFB semiconductor laser,
As described above, since a buried structure on a stripe for forming a light emitting operation region of the active layer is formed, the buried structure, that is, confinement of light and carriers, is performed. In order to take the structure to be performed, it is divided into two epitaxial growth operations with an etching operation for forming a groove therebetween.

However, when there is an interface divided by two epitaxial growths near the active layer formation portion, the epitaxial growth surface of the preceding stage is naturally oxidized between the two epitaxial growths, and the characteristics are deteriorated. Inconvenience such as

[0016]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problem of leakage current in a semiconductor laser device having an SDH structure and to reduce the threshold current.

Another object of the present invention is to provide a semiconductor laser device capable of lowering the threshold current and performing single wavelength oscillation.

[0018]

FIG. 1 is a schematic enlarged cross-sectional view of one example of a semiconductor laser device of the present invention. In the present invention, as shown in FIG. 1, an AlGaAs layer 3 is formed on a mesa projection 2 on a substrate 1 having a main surface 1S formed of a {100} crystal plane and having a mesa projection 2 extending in the <011> crystal axis direction. And
On the AlGaAs layer 3 on the mesa protrusion 2, at least a first cladding layer 4, an active layer 5, and a second cladding layer 6 grown by vapor phase epitaxy are provided. On the mesa groove 2A, Up
At least the first crack grown simultaneously with the vapor phase growth described above.
Layer 4, active layer 5, second cladding layer 6, and current
A second cladding layer 6 on the mesa groove 2A
The upper surface reaching the mesa protrusion 2 is the second surface on the mesa protrusion 2
To be in contact with both side surfaces of the cladding layer 6 of
The mesa protrusion 2 of the second cladding layer 6 on the mesa groove 2A
The lower surface leading to both sides of the AlGaAs layer 3 on the mesa protrusion 2
And the AlG on the mesa projection 2
The configuration is such that the amount of Al in the components of the aAs layer 3 is larger than the amount of Al in the components of the first and second cladding layers 4 and 6.

FIG. 3 is a schematic enlarged sectional view of another example of the semiconductor laser device of the present invention. According to the present invention, as shown in FIG. 3, a diffraction grating 11 is formed on an AlGaAs layer 3 on a mesa projection 2 on a substrate 1.

[0020]

As described above, in the semiconductor laser device of the present invention, the main surface 1S is formed of a {100} crystal plane, and <011>
An AlGaAs layer 3 is provided on the mesa projection 2 on the substrate 1 having the mesa projection 2 extending in the crystal axis direction.
It has a first cladding layer 4, an active layer 5, a second cladding layer 6, and a current blocking layer 8 grown on the upper AlGaAs layer 3 by a vapor phase growth method.
By selecting the crystal plane of the crystal and the direction of the crystal axis in which the mesa protrusion 2 extends, the usual vapor phase growth method, ie, the methyl MOC
When each layer is epitaxially grown by the VD method, once a {111} B crystal plane which forms about 55 ° with respect to the main surface 1S from both side edges on the mesa protrusion 2 is generated,
Since the epitaxial growth by the methyl MOCVD method hardly occurs on the {111} B crystal plane, the first cladding layer 4, the active layer 5, and the second cladding layer 6 on the AlGaAs layer 3 on the mesa projection 2 The AlGaAs layer 3, the first cladding layer 4, the active layer 5 are formed on the mesa projection 2 and the inside of the mesa groove 2 </ b> A so as to be separated from each other.
The second cladding layer 6 is formed as a triangular section 20 having a triangular cross section sandwiched between the two inclined surfaces 7 made of the {111} B crystal plane.

According to one semiconductor laser device of the present invention, the AlGaAs layer 3 is provided on the mesa
The amount of Al in the components of the GaAs layer 3 is reduced by the first cladding layer 4 and
More than the Al content in the components of the second cladding layer 6 and
With this configuration, the built-in potential at the pn junction between the AlGaAs layer 3 and the second cladding layer 6 in the mesa groove 2A becomes large, so that the leakage current can be suppressed.

That is, as shown in an enlarged schematic sectional view of a main part of FIG. 2, in the case of such a structure, the second cladding layer 6 on the mesa projection 2 and the second cladding layer 6 on the mesa groove 2A are formed. There is a current path indicated by an arrow i toward the AlGaAs layer 3 on the mesa protrusion 2 through the cladding layer 6 of FIG.
Built-in potential at the pn junction between the second cladding layer 6 and the second cladding layer 6 on the mesa protrusion 2
Compared with the built-in potential between the active layer 5 having a small amount of Al in the component and that of the active layer 5, AlGa
Since the built-in potential for the As layer 3 is relatively large, the current passing through the active layer 5 becomes dominant, and as a result, the leakage current can be reduced. Therefore, even when the composition of the active layer 5 is an AlGaAs-based one, it is possible to sufficiently concentrate the current on the active layer 5, and to reduce the leak current equivalent to that of the conventional SDH semiconductor laser device. , It is possible to reduce the threshold current.

According to another semiconductor laser device of the present invention, since the diffraction grating 11 is provided on the AlGaAs layer 3 on the mesa projection 2, a normal methyl-based M
By epitaxially growing the layers 4, 5, 6, 8 and 9 by the OCVD method, it is possible to obtain a semiconductor laser device in which both side surfaces of the active layer 5 are buried.
As described above, the SDH having a low threshold current can be formed by reducing the leakage current, and the DFB is provided by the presence of the diffraction grating 11 near the active layer 5.
A semiconductor laser device capable of performing single-wavelength oscillation by operation can be configured.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS.
This will be described in detail with reference to FIG. In each case, N-type Ga
An example of a group III-V semiconductor laser device in which an AlGaAs-based compound semiconductor layer is stacked on an As substrate will be described.

Embodiment 1 A description will be given with reference to FIG. 1 and FIG. As shown in FIG.
For example, on a {100} crystal plane on an N-type GaAs substrate 1, for example, a main surface 1S composed of a (100) crystal plane, an N-type A
After epitaxially growing an AlGaAs layer 3 of l _x1 Ga _1-x1 As with a thickness of, for example, 1 μm,
With a required width on the aAs layer 3, <01
1> A stripe-shaped etching mask extending along, for example, the [011] crystal axis direction in the crystal axis direction is formed by, for example, application of a photoresist and pattern exposure, and crystallography is performed from above the AlGaAs layer 3 using the etching mask as a mask. Then, a stripe-shaped mesa protrusion 2 composed of the substrate 1 and the AlGaAs layer 3 is formed by performing a periodic etching to extend along the [011] crystal axis direction. That is, in this case, the direction perpendicular to the plane of FIG. 1 is the [011] crystal axis direction.

After removing the etching mask,
The first cladding layer 4 made entirely of N-type Al _x2 Ga ₁ -x2 As, including the inside of the mesa groove 2A, is undoped by a normal MOCVD method, that is, an MOCVD method using a methyl-based organic metal as a source gas. Alternatively, a low concentration of Al _y Ga
Active layer 5 made of _1-y As or the like and P-type Al _x2 Ga _{1- x2}
A second cladding layer 6 made of As or the like is epitaxially grown.

At this time, epitaxial growth is performed on the mesa protrusion 2 and in the mesa groove 2A. On the upper surface of the mesa protrusion 2, the angle with respect to the (100) crystal plane is about 55 ° (1).
11) The slope 7 composed of the B crystal plane is spontaneously generated from both sides of the mesa projection 2 and the methyl MO
Since the epitaxial growth by the CVD method does not easily progress, the layers 4, 5, and 6 are formed on the mesa protrusion 2 and in the mesa groove 2A so as to be separated from each other.

By appropriately selecting the width and height of the mesa projection 2 and the thickness of each of the layers 4, 5 and 6, the lower surface of the second cladding layer 6 reaching the mesa projection 2 on the mesa groove 2A can be formed. The two slopes 7 on the mesa projection 2 intersect during the growth of the second clad layer 6 so as to contact the two side faces of the AlGaAs layer 3 on the substrate 1. A triangular section 20 having a triangular cross section is formed on each of the layers 4, 5 and 6 and extends in the direction of the [011] crystal axis.

Then, the growth of the P-type second cladding layer 6 is further continued so that the upper surface in the mesa groove 2A crosses both side surfaces of the active layer 5 on the mesa protrusion 2 facing both slopes 7, and this is second to a position about to reach both sides of the cladding layer 6 is grown, Al _x2 Ga _1-x2 a N-type followed thereon on the
Similarly, the current blocking layer 8 having a lower refractive index than the active layer 5 is epitaxially grown by MOCVD, and the upper surface of the current blocking layer 8 The thickness and the impurity concentration are selected so as not to cover both side surfaces of the clad layer 6.

Further, for example, a P-type Al _x2 G
a third cladding layer 9 made of a _1-x2 As or the like;
A cap layer 10 made of As or the like is epitaxially grown. At this time, epitaxial growth does not initially occur on the slope 7 composed of the (111) B crystal plane on the mesa projection 2, but as the growth progresses in the mesa groove 2 A, the butted portion except for the (111) B crystal plane Is formed, and the third cladding layer 9 is entirely grown so as to cover the triangular section 20 on the mesa projection 2.

Then, although not shown, on the cap layer 10,
Electrodes made of Al or the like are respectively deposited on the back surface of the substrate 1 and
The semiconductor laser device of the present invention can be obtained by being applied by sputtering or the like.

At this time, the amount of Al in the components of the layers 4, 5, 6, and 8 is set to x ₂ > y, and the active layer is compared with the first and second cladding layers 4 and 6, and the current blocking layer 8. The band gap of No. 5 is made small, that is, the refractive index is made large so as to confine light. On the other hand, assuming that the amount of Al in the components of the layers 3, 4, 5, and 6 is x ₁ > x ₂ > y, the built-in potential between the second cladding layer 6 on the mesa groove 2A and the AlGaAs layer 3 is defined as the mesa. The second clad layer 6 in the mesa groove 2A and the AlG are formed so as to be larger than the built-in potential of the second clad layer 6 on the protrusion 2 and the active layer 5.
The generation of a leak current at the interface with the aAs layer 3 is suppressed.

In this case, the P-type third cladding layer 9, the current blocking layer 8, the P-type second cladding layer 6, and the N-type first cladding layer 4 in the mesa groove 2A. P-
The NPN thyristor structure is formed, and the built-in potential at the interface between the AlGaAs layer 3 on the mesa protrusion 2 and the P-type second cladding layer 6 on the mesa groove 2A is made relatively large as described above. By making the built-in potential at the interface between the second cladding layer 6 and the active layer 5 of the triangular section 20 on the mesa projection 2 relatively small, the active layer of the triangular section 20 on the mesa projection 2 can be reduced. 5, the current is concentrated on the substrate 5, the leakage current in the mesa groove 2A can be remarkably suppressed, and the threshold current can be reduced.

When the AlGaAs layer 3 having a relatively high Al concentration is epitaxially grown on the GaAs substrate 1, the crystallinity of the first cladding layer 4 and the active layer 5 epitaxially grown on the AlGaAs layer 3 may be deteriorated. However, as described above, the influence of such crystal distortion can be suppressed by selecting the AlGaAs layer 3 to have a relatively large thickness of about 1 μm. It has been confirmed that in order to avoid such crystal distortion of the upper epitaxial growth layer, the sum of the thickness of the AlGaAs layer 3 and the thickness of the first cladding layer 4 thereon should be about 1 μm. .

In this case, AlGaAs is formed on the mesa projection 2.
Since the clad layer having a smaller refractive index exists with respect to the s-layer 3, that is, the active layer 5, the thickness of the first clad layer 4 can be reduced as compared with the conventional case, and as a result, Since the height of the mesa protrusion 2, that is, the depth of the mesa groove 2 </ b> A can be reduced, the mesa protrusion 2 can be formed by etching with more controllability, and the uniformity of the shape of the mesa protrusion 2 can be improved. The reliability can be improved by improving the uniformity of the semiconductor laser device.

Embodiment 2 A description will be given with reference to FIGS. 4A to 4C showing an example of a manufacturing method for easy understanding, together with the sectional view of FIG. 3, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted.

In this case, first, for example, as shown in FIG. 4A, an AlGaAs layer 3 is epitaxially grown on a substrate 1 made of GaAs or the like.

Thereafter, as shown in FIG. 4B, a mesa projection 2 extending in the [011] crystal axis direction is formed by crystallographic etching, for example, as in the first embodiment. 2A is a mesa groove.

Then, as shown in FIG. 4C, a diffraction grating 11 is formed on the AlGaAs layer 3 at a predetermined pitch by a known two-beam interference exposure method. In this example, the diffraction grating 11 is configured by an array of a number of parallel grooves extending along the width direction of the stripe-shaped mesa projections 2. For example, a photoresist is applied over the mesa projections 2 to cover the entire surface. On the other hand, after performing interference fringe exposure with two light beams, development processing is performed, and using this as a mask, A
Etching is performed on the lGaAs layer 3 to obtain grooves arranged in parallel so as to be perpendicular to the extension direction of the mesa protrusion 2 at a required pitch that satisfies the Bragg reflection condition for obtaining a desired single mode oscillation. be able to.

After forming the diffraction grating 11 in this manner, as shown in FIG.
6, 8, 9 and 10 are epitaxially grown. Also in this case, although not shown, an electrode made of Al or the like is formed on the cap layer 10 and the back surface of the substrate 1 so as to obtain the semiconductor laser device of the present invention.

With this structure, a PNPN thyristor structure is formed in the mesa groove 2A, and the AlGaAs layer 3 and the mesa groove 2 are formed in the same manner as in the first embodiment.
By increasing the built-in potential of the active layer 5 on the mesa protrusion 2 with respect to the second clad layer 6 in A, current concentration is performed on the active layer 5 and the leakage current is reduced. As a result, a semiconductor laser device capable of performing single-wavelength oscillation can be obtained by forming the diffraction grating 11 while reducing the threshold current.

Also in this case, since the AlGaAs layer 3 serving as a cladding layer is formed on the active layer 5 on the mesa projection 2, the mesa groove 2 is formed in the same manner as in the first embodiment.
The depth A can be reduced, the uniformity of the mesa protrusion 2 can be improved, and the reliability of the semiconductor laser device can be improved.

In each of the above embodiments, the substrate 1, the AlG
aAs layer 3, first cladding layer 4, and current blocking layer 8
Is N-type, and the second and third cladding layers are P-type. However, the conductivity type may be opposite to this.

[0044]

As described above, according to the semiconductor laser device of the present invention, a PN-PN thyristor structure is formed in the mesa groove 2A to block a current in this portion, and the mesa protrusion 2 is formed. The upper side of both sides of the upper active layer 5, that is, the second
Even when the current blocking layer 8 is in contact with both side surfaces of the cladding layer 6 facing the two slopes 7, the built-in potential in the current path from the mesa groove 2A to the mesa protrusion 2 is increased, and the active layer 5 on the mesa protrusion 2 Current concentration can be performed to lower the threshold current.

Further, since the AlGaAs layer 3 is formed on the mesa protrusion 2, the depth of the mesa groove 2A can be reduced, and the semiconductor laser can be made uniform in shape of the mesa protrusion 2. The reliability of the device can be improved.

In another semiconductor laser device of the present invention, A
By forming the diffraction grating 11 on the lGaAs layer 3, single wavelength oscillation can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic enlarged cross-sectional view of an example of a semiconductor laser device of the present invention.

FIG. 2 is a schematic enlarged sectional view of a main part of an example of the semiconductor laser device of the present invention.

FIG. 3 is a schematic enlarged cross-sectional view of another example of the semiconductor laser device of the present invention.

FIG. 4 is a manufacturing process diagram showing a manufacturing method of another example of the semiconductor laser device of the present invention.

FIG. 5 is a schematic enlarged cross-sectional view of an example of a conventional semiconductor laser device.

FIG. 6 is a schematic enlarged cross-sectional view of another example of the conventional semiconductor laser device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Mesa protrusion 2A Mesa groove 3 AlGaAs layer 4 First clad layer 5 Active layer 6 Second clad layer 7 Slope 8 Current block layer 9 Third clad layer 10 Cap layer 11 Diffraction grating

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-119285 (JP, A) JP-A-2-283087 (JP, A) JP-A-3-30485 (JP, A) JP-A-2- 122585 (JP, A) JP-A-63-213385 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 5/00-5/50

Claims (2)

(57) [Claims] 1. The method according to claim 1, wherein the main surface comprises a {100} crystal plane, and <0
11> An AlGaAs layer is provided on the mesa protrusion on the substrate having the mesa protrusion extending in the crystal axis direction. At least a first layer grown by a vapor deposition method on the AlGaAs layer on the mesa protrusion is provided. Cladding layer, active layer,
A second clad layer is provided, and at least the mesa groove is grown on the mesa groove simultaneously with the vapor phase growth.
The first cladding layer, the active layer, the second cladding layer, and
And a second cladding layer on the mesa groove extends to the mesa protrusion.
Upper surfaces of the second clad layer on the mesa protrusions
And a second clip on the mesa groove is provided.
The lower surface of the lad layer reaching the mesa protrusion is above the mesa protrusion.
Is provided so as to be in contact with both side surfaces of the AlGaAs layer.
It becomes Te, semiconductor laser device Al content in component of the AlGaAs layer on the mesa projection, characterized in that it contains more than the amount of Al in the component of the first and second cladding layers. 2. The Al on the mesa protrusion on the substrate.
2. The semiconductor laser device according to claim 1, wherein a diffraction grating is formed on the GaAs layer.