JPH05283795A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To facilitate manufacture of a semiconductor laser of low threshold current by a method wherein clad layers are provided sandwiching an active layer and a current block layer between them respectively, and a rugged stripe is provided to the intermediate clad layer, extending in the lengthwise direction of a laser resonator, and a current block layer is formed on the rugged stripe. CONSTITUTION:A substrate 11 of N-type GaAs or the like has a primary surface of (100) crystal face, and an N-type GaAs first clad layer 1, an active layer 2 of material small in band gap such as GaAs, and a second clad layer 3 of GaAlAs doped with P-type impurities as a guide layer large in band gap to serve as an optical waveguide are formed on the substrate 11 through a continuous epitaxial growth method. Etching resists 12 are formed on the second clad layer 3 at a prescribed interval (d) in the lengthwise direction of a resonator, and stripe-like irregularities 6 are formed by etching, an N-type current block layer 4 is made to grow thereon, and then a P-type third clad layer 5 and a cap layer 13 are grown.

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 suitable for application to, for example, a distributed feedback semiconductor laser (hereinafter referred to as DFB laser).

[0002]

2. Description of the Related Art In a semiconductor laser, its threshold current I
In order to reduce th, it is required to efficiently inject a current into the optical waveguide or laser resonator, that is, the active layer. For this reason, a structure in which a current blocking layer (current constriction layer) that blocks current flow is often provided on both sides of the stripe-shaped resonator.

Further, in the DFB laser, since the uneven structure which causes the distributed feedback is required, in order to form the uneven structure by etching and to form the above-mentioned current blocking layer, each part of this semiconductor laser is required. The epitaxial growth process for forming the semiconductor layer needs to be interrupted at least twice, which not only complicates the work, but also leads to variations in characteristics and deterioration of characteristics, resulting in a problem in reliability.

[0004]

SUMMARY OF THE INVENTION In the present invention, in the semiconductor laser having the above-mentioned current blocking layer (current constriction layer), particularly in the DFB type laser, simplification of its structure,
This simplifies the manufacturing process and improves the reliability, so that the current can be efficiently injected into the optical waveguide or the resonator portion, and the threshold current Ith can be reduced.

[0005]

FIG. 1 is a schematic enlarged perspective view of an example of the present invention, and FIG. 2 is a schematic enlarged enlarged cross-sectional view of a main part of the cross section taken along the chain line a in FIG. As shown, the first cladding layer 1, the active layer 2, the second cladding layer 3, the current blocking layer 4, and the third cladding layer 5 are shown.
And a structure in which and are sequentially stacked.

Then, the concave and convex stripes 6 in which the concave portions 6G and the convex portions 6B are alternately and repeatedly arranged in the laser cavity length direction are formed on the second cladding layer 3, and the concave and convex portions 6G and the convex portions of the concave and convex stripes 6 are formed. The current blocking layer 4 is formed on 6B without being connected to each other.

[0007]

As described above, according to the present invention, in the second cladding layer 3, that is, in the DFB laser, for example, a so-called optical waveguide (guide layer) is formed with uneven stripes along the cavity length direction, and the concave portion 6G is formed. Since the current blocking layer 4 is formed independently in the inside and on the convex portion 6B, the current blocking layer 4 in the concave portion 6G is formed between the third cladding layer 5 and the second cladding layer 3. Current is injected through the periodically discontinuous portion of the current blocking layer 4 on the convex portion 6B (that is, a part of the side surface of the convex portion 6B) as schematically shown by an arrow b in FIGS.

That is, since the current can be injected only into the portion of the resonator that becomes the optical waveguide, the current density can be improved, the light emission efficiency can be increased, and the threshold current Ith can be reduced.

Further, in the structure of the present invention, the uneven period of the uneven stripe 6 is selected according to the oscillation wavelength, and the second cladding layer 3 is used as an optical guide layer, and the third cladding having a smaller refractive index than that.
By forming the clad layer 5 of, a DFB semiconductor laser having this as a DFB structure can be constructed.

As described above, according to the structure of the present invention, the DFB structure and the current constriction can be formed by the same structure portion, so that the manufacturing can be simplified, and as will be more apparent from the following description. Since the epitaxial growth process in the manufacture of this semiconductor laser needs to be interrupted only once, the manufacturing process can be simplified, the characteristic deterioration due to the interruption of the epitaxial growth can be avoided, and the yield can be improved as compared with the conventional method.

[0011]

EXAMPLE A current confinement type D of a semiconductor laser according to the present invention
The case of application to an FB laser will be described.

In order to facilitate the understanding, a detailed description will be given together with the manufacturing method.

In this case, as shown in FIG. 3A, a substrate 11 is prepared, and a first clad layer 1, an active layer 2 and a second clad layer 3 are successively formed thereon by continuous epitaxial growth.

Substrate 11 is, for example, (100)
It is made of n-type GaAs having a crystal plane as a main surface, and the first cladding layer 1 is also made of n-type GaAlAs. The active layer 2 is formed of a non-doped or low impurity concentration layer made of, for example, GaAs having a bandgap smaller than that of the first cladding layer 1. The second cladding layer 3 is
As a guide layer having a bandgap larger than that of the active layer 2 and serving as an optical waveguide in the DFB, for example, GaA doped with an impurity of a conductivity type different from that of the first cladding layer 1, for example, p-type
It is composed of 1As.

Thus, the first cladding layer 1, the active layer 2 and the second cladding layer 3 are formed as the first epitaxial growth step by continuous epitaxial growth.

Then, the etching resist 1 is formed on the second cladding layer 3 with a predetermined distance d and a pitch P _B.
2 are arrayed at predetermined intervals d in the resonator length direction so that the width in the direction orthogonal to the paper surface of FIG. 3A corresponds to the finally obtained resonator width. The etching resist 12 can be formed, for example, by forming a photoresist, performing pattern exposure by electron beam pattern exposure or interference exposure, and performing development processing.

Next, as shown in FIG. 3B, the second clad layer 3 is etched to a required depth by using the etching resist 12 as a mask, so that the convex portions 6B and the concave portions 6G are sequentially arranged in a predetermined cycle, that is, the pitch P. Striped irregularities 6 arranged with _B and a space d are formed. In this case, the stripe direction of the uneven stripes 6, that is, the direction along the paper surface of FIG. 3 is defined as the <01-1> axis direction, and the width direction of the stripe, that is, the direction orthogonal to the paper surface in FIG. 3B is defined as <01-1>.
1> Select in the axial direction.

The etching for forming the uneven stripes 6 is, for example, RIE (reactive ion etching).
Alternatively, it can be performed by so-called reverse mesa etching shown in FIG. 5 by chemical etching.

Next, as shown in FIG. 4, the etching resist 12 is removed to form the concave portions 6G and the convex portions 6B of the concave and convex stripes 6.
A conductivity type different from that of the second clad layer 3 is formed on the n-type current blocking layer 4 in this example, the current blocking layers 4 in the concave portion 6G and on the convex portion 6B are discontinuous with each other, that is, independent of each other. Grow as you are. This growth is, for example, methyl-based M
It can be formed by utilizing the difference in the growth rate of crystal planes by OCVD, that is, by a growth method having a high growth rate in the (100) plane and a low growth rate with respect to the (011) plane. Then, successively, the second clad layer 3, the p-type third clad layer 5 of the same conductivity type, and, if necessary, the cap layer 13 of the same conductivity type and a high impurity concentration are continuously formed. Grow by epitaxy. That is, each layer 4, 5, 13 is formed as a second epitaxial growth step.

The third clad layer 5 has a larger band gap than the second clad layer 3 as a guide layer and has the same composition as that of the first clad layer 1, for example, GaAlA.
s. Also, the cap layer 1
3 may be composed of GaAs, for example. Then, the first electrode 21 is ohmic-deposited in a stripe shape, for example, immediately above the concave-convex stripe 6, and the counter electrode, that is, the second electrode 22 is ohmic-deposited on the other surface of the substrate 11. To do.

Thus, the first clad layer, the active layer 2, the second clad layer 3, the current blocking layer 4, and the third clad layer are formed.
And the clad layer 5 are sequentially laminated to form a concavo-convex stripe 6 on the second clad layer 3 in which concave portions 6G and convex portions 6B are alternately and repeatedly arranged in the laser cavity length direction.
A semiconductor laser according to the present invention is formed in which the current blocking layer 4 is formed on the concave portions 6G and the convex portions 6B of the concave and convex stripes 6 without being connected to each other.

The semiconductor laser having the above-described structure is similar to that shown in FIG.
As is clear from the above, since the current blocking layer 4 blocks the current injection into the second cladding layer 3, that is, the guide layer, as shown by the arrow b in FIGS. 1 and 2, only in the stripe portion. Since the current can be intensively injected in stripes along the resonance length direction only in the discontinuous portions of the current blocking layer 4, a semiconductor laser having high emission efficiency and low threshold current can be constructed.

Further, since the uneven stripes 6 can be constructed as a DFB structure by selecting the period thereof, a gain coupling type DFB laser can be constructed.

In the above example, the second clad layer 3 and the third clad layer 5 are formed by layers having different band gaps, that is, different refractive indexes, and the uneven stripes 6 form a DFB structure. However, by providing the second cladding layer 3 and the third cladding layer 5 with the same composition, that is, with the same refractive index, not only the DFB type laser but also the usual gain waveguide type It is also possible to configure a semiconductor laser. Further, not limited to the illustrated example, various modifications can be made such that each part can be selected as a conductivity type opposite to the illustrated conductivity type.

In the above example, GaAlAs
Although the present invention is applied to a semiconductor laser of a system, the present invention can be applied to other various compound semiconductor lasers and the like.

[0026]

As described above, according to the present invention, in the second cladding layer 3, that is, the DFB laser, for example,
Since the uneven stripes 6 are formed in the so-called optical waveguide, that is, the guide layer along the cavity length direction, and the current blocking layer 4 is formed independently in the concave portions 6G and the convex portions 6B, respectively. 3 between the clad layer 5 and the second clad layer 3, the current blocking layer 4 in the concave portion 6G and the periodic discontinuous portion of the current blocking layer 4 on the convex portion 6B (that is, a part of the convex portion 6B). Current is injected through the side surface of FIG. 1) as schematically shown by an arrow b in FIGS.

That is, since the current can be injected only into the portion which becomes the optical waveguide of the resonator, the current density can be improved, the light emission efficiency can be increased, and the threshold current Ith can be reduced.

Further, by selecting the period of the unevenness with the formation portion of the current blocking layer 4, this is set to D
Since the DFB semiconductor laser can be configured as the FB structure portion, the structure can be simplified and the manufacturing can be simplified.
It is possible to simplify the manufacturing process, avoid the characteristic deterioration due to the simplification, and improve the yield as compared with the conventional case.

[Brief description of drawings]

FIG. 1 is a schematic enlarged view of an example of a semiconductor laser according to the present invention.

FIG. 2 is a schematic enlarged cross-sectional view of a main part on line a in FIG.

FIG. 3 is a manufacturing process diagram (1) of a method for manufacturing a semiconductor laser according to the present invention.

FIG. 4 is a similar manufacturing process diagram (No. 2).

FIG. 5 is a cross-sectional view in another manufacturing process of another example.

[Explanation of symbols]

 1 1st clad layer 2 active layer 3 2nd clad layer 4 current blocking layer 5 3rd clad layer 6 concave-convex stripe 6G concave part 6B convex part

Claims (1)

[Claims] 1. A first clad layer, an active layer, a second clad layer, a current blocking layer, and a third clad layer are sequentially laminated, and a laser resonator is provided in the second clad layer. An uneven stripe in which concave portions and convex portions are alternately arranged in the longitudinal direction is formed repeatedly, and the current blocking layer is formed in the concave portion and the convex portion of the uneven stripe without being connected to each other. A semiconductor laser characterized by: Detailed Description of the Invention