JPS6151889A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain both an index guide type semiconductor laser and a gain guide type semiconductor laser positively while arbitrarily designing a semiconductor laser, to which both guide functions are formed partially, or a semiconductor laser having an intermediate function or the like easily by each shaping an optical absorption function and a current constriction function by different layers. CONSTITUTION:A first clad layer 12 consisting of AlzGa1-zAs having the same conduction type as an N type GaAs semiconductor substrate 11, a P type or N type active layer 13 composed of AlxGa1-xAs on the clad layer 12, a second clad layer 14 consisting of AlzGa1-zAs having a conduction type different from the first clad layer such as a P type on the active layer 13, and a cap layer 16 composed of a high-concentration GaAs layer having the same conduction type as the clad layer 14 such as the P type are formed onto the substrate 11. An optical absorption layer 21 consisting of AlyGa1-yAs having the same conduction type as the second clad layer such as the P type on the side, particularly, the side facing the active layer 13, and a current constriction layer 22 composed of AliGa1-iAs having a conduction type different from the second clad layer 14 such as the P type on the side reverse to the side facing the active layer 13 on the layer 21 are laminated and shaped in the second clad layer 14.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to semiconductor lasers.

[Conventional technology]

Conventional semiconductor lasers are broadly classified into refractive index guide (index guide) type and gain guide (r-in guide) type depending on their longitudinal mode light and carrier confinement mechanism.

These index-guided semiconductor lasers and gain-guided semiconductor lasers each have advantages and disadvantages.

In other words, the refractive index guide type has a single longitudinal mode, so when it is used as a light source for writing or reading an optical video disc, for example, it has the disadvantage that mode hopping noise occurs due to the returned light. be.

However, on the other hand, this refractive index guide type is located at the so-called beam waist position.
Po5ltion) exists near the tip surface of the light emitting region, which has the advantage that it is easy to set the focal point position in actual use. Also, a long distance image in a cross section parallel to the joint, the so-called far field view? The far field pattern is symmetrical and has the advantage that it is easy to obtain a spot shape with small distortion as a reading or writing light in actual use, for example.

In contrast, in gain-guided semiconductor lasers,
The beam waist position is located at a distance inward from the optical end face of the light emitting region, and furthermore, the farf f-
There are disadvantages in that the lens is often asymmetrical, and the astigmatism is large, resulting in relatively large spot distortion. However, since this gain-guided semiconductor laser has a multi-mode longitudinal mode, it has the advantage that mode hopping noise due to returned light is less likely to occur.

Accordingly, -C1 This type of semiconductor laser has been proposed to have a refractive index guide type structure or a gain guide type structure depending on its purpose and mode of use, and further proposals have been made to have a structure in which both types are mixed. ing.

As this type of refractive index guide type or gain guide type semiconductor radar, a structure shown in FIG. 8g3, for example, has been proposed.

This semiconductor radar uses, for example, a nu GaAa substrate (1
), a first cladding layer (2) made of N-type AZz Ga 11A s, and a P-type or N-type AZxG
an active layer (3) consisting of a 1-xA s and a P-type AZ
The second cladding layer (4
) and N embedded in this second cladding layer (4).
It has a light absorption and current narrowing layer (5) made of type AtyGa 1-yAs, and a cap layer (6) of P type with a high impurity concentration. The light absorption/current constriction layer (5) has, for example, a striped through hole (the part where the layer (5) is missing) having a width W extending in the direction perpendicular to the plane of the paper in FIG. 1 in the center thereof.
(5a). This light absorption and current narrowing layer (5
), whose energy gap (bandwidth) is the active layer (
It is smaller than that of 3), and its composition is selected so that the refractive index for light oscillated from the light emitting region of the active layer (3) is higher than that of the light emitting region, that is, the active layer (3). That is, in the compositions of the active layer (3) and the light absorption/current confining layer (5) described above, x>y is selected. In the figure (7) and (8) indicate counter electrodes ohmically deposited on the cap layer (6) and the substrate (1), respectively.

In such a configuration, when a predetermined forward voltage is applied between the electrodes (7) and (8), the first and second cladding layers (
Light is emitted in the active layer (3) confined by 2) and (4). In this case, the distance d2 between the active layer (3) and the light absorption/current constriction layer (5) is
When selecting the distance at which the oscillated light can reach the light absorption and current constriction layer (5), for example, d2 = 0.2 to 0.5 μ, the light absorption and current constriction layer (5) Light from the oozing active layer (3) passes through this light-absorbing and current-squeezing layer (5).
As a result, the area under the light absorption and current narrowing layer (5) and the area where this light absorption and current narrowing layer (5) does not exist (i.e., the striped hole in the center ( A difference in effective refractive index, that is, a difference Δn in refractive index in the horizontal direction is formed between the part corresponding to 5a) and the part where almost no light absorption occurs. In this case, the striped pores (5a) of the light absorption and current constriction layer (5)
The width W is selected to be, for example, 5 to 8μ, and the distance d described above is
In combination with the selection of 2, the through holes (5a) in the active layer (3)
The difference Δn”nl between the refractive index n1 of the part directly facing the central part (hereinafter referred to as the central part) and the refractive index n2 of both sides thereof
Adjust so that n2 is, for example, +10 to +10-3. In this case, the effect of confining the transverse oscillation state is produced in the central part of the active layer (3) facing the through hole (5a), and the refractive index guide type in which the light emitting region is regulated is produced here. semiconductor laser.

On the other hand, in the structure shown in FIG. 3 described above, the distance d2 between the active layer and the light absorption and current narrowing layer (5) is made sufficiently large so that the light from the active layer (3) is absorbed and current narrowed. The light absorption effect of the light absorption layer (5) is eliminated or reduced, while the width W of the through hole (5a) of the light absorption/current narrowing layer (5) is reduced to strengthen current concentration. (3) Thickness dl
When increasing the value, the negative refractive index change -Δn due to the injected carriers becomes dominant compared to the refractive index change Δn due to cropping. Difference in effective refractive index between and both sides ΔW (where Δ=Δn−Δn
) or −10 to 10, thereby providing a gain-guided structure.

[Problem that the invention seeks to solve]

As mentioned above, according to the semiconductor laser having the configuration explained in FIG. Since the actions of the upper parts affect each other, the refractive index guide type and the gain guide type cannot be selected independently, and since they influence each other, there is little freedom in design. Another drawback is that it is difficult to reliably obtain a semiconductor laser with desired characteristics.

In the present invention, each characteristic of such a refractive index-guided semiconductor laser and a gain-guided semiconductor laser can be designed independently, so that a refractive index-guided semiconductor laser 1 or a gain-guided semiconductor laser having desired characteristics can be designed. It is possible to easily and reliably obtain a guide type laser or a semiconductor radar in which these types are mixed in the same semiconductor laser so that the positions of both types of semiconductor radars are complemented.

[Means for solving problems]

In the present invention, the first cladding layer, the active layer, the second cladding layer, and the second cladding layer have a smaller energy gap than the active layer and absorb light oscillated from the active layer. It has a structure in which a light absorption layer having the effect of

[For production]

As described above, in the semiconductor laser according to the present invention, the light absorption layer and the current confinement layer are separately provided so that the functions of both can be made to be dominant independently, or the functions of both can be made to work together. Then, the refractive index can be used as a semiconductor laser with an id-type function, a semiconductor laser with a gain-guided type function, a semiconductor laser with properties intermediate between the refractive index-guided type and the gain-guided type, or oscillation. It is possible to reliably obtain a semiconductor laser in which both characteristics are mixed by partially existing in each part of the region.

〔Example〕

An example of a semiconductor laser according to the present invention will be explained with reference to FIG. In this example, the same 281! Type AZ2Ga, 1A
A first cladding layer (6) made of A, further on this a P-type or N-type active layer CLJ made of AtXGa1-xAs, and further on this a conductive layer different from the first cladding layer. A second cladding α layer made of, for example, P-type At, Ga 1-, As, and a cap NαQ made of a high-concentration, for example, P-type GaAs layer of the same conductivity type are provided. In the layer α, in particular, in the present invention, on the side facing the active layer cL3, there is a light absorbing NQ layer made of P-type AtyGal-yAII of the same conductivity type as the second cladding layer, and an active layer above this layer. A second cladding layer α (a) and a current constriction layer (c) of a different conductivity type, such as P-type AttGa 1-i As, are laminated on the side opposite to the side facing the layer (to). Provided.

Is there a light absorption layer here? ]) and the current constriction layer (b) are each width W
1 and W2, striped through holes (21a) and (22a) are provided in the center thereof, respectively.

Here, the distance d2 between the active layer α1 and the light absorbing layer is selected to be, for example, 0.2 to 0.5 μm, which is a distance that allows the light emitted by the active layer α1 to leak into the light absorbing layer at a distance υ.

Here, the light absorption layer 01) is arranged so that its energy gap is smaller than that of the active layer α→, that is, X>y≧OV
c Select. The fc current constriction layer (c) has i>y so that its energy gap is larger than that of the light absorption layer hn.
For example, it can be selected as l y z.

Each of these [1-V group compound semiconductor layer (6), α3. α→
.

ati, an, h are MOCVD (Me
Chemi cm 1) method, or MBEt, Mo1
It can be formed by the ecular BeamEp-1taxy method or the like. Specifically, on the board αη [whistle 1
cladding layer α, active layer (2), second cladding layer a
A part (lower) layer of 4 and on top of this a light absorption layer 4 &η,
Current squeezing layer 2 sequentially, the first continuous shrimp,
The taxi is formed by, for example, the above-mentioned MOCVD method or MBE method, and then a through hole (a) having a required width W2 is formed in the current confining layer by photoetching, and further, for example, a narrow W, A through hole (21a) is formed in the light absorbing layer Q, and then a second continuous epitaxy process is performed to open the second cladding layer from the other part (upper layer).
is epitaxially grown so as to fill the through holes (21a) and (22a) and the light absorption layers Q1) and (c), and then the cap layer aQ is epitaxially grown. Further, a pair of opposing electrodes α force and α barrel are ohmically attached on the cap 76 layer aQ and on the back surface of the substrate (11).

In the example shown in Fig. 1, an index-guided semiconductor laser is configured, and in this case, the light absorption layer Q
The width W1 of the through-hole portion (21a) in 1) is selected to be, for example, 4 to 8μ. In this case, the through hole (2) of the current narrowing N (c)
The width W2 in 2a) is set to W2)Wl to substantially prevent the aforementioned dyne guide operation due to current constriction from occurring. That is, as mentioned above, there is a difference in effective refractive index between the part where the light absorption Wi (c) exists and the through hole (21a), that is, the part where the light absorption layer Q does not exist, that is, the difference in the effective refractive index, that is, the difference in the horizontal direction.
A difference Δn in refractive index is formed, and this difference Δn in refractive index
is made to be, for example, a positive value of +10 to +10-3, thereby producing an effect of confining the lateral oscillation state in the center of the active layer (3) and regulating the light emitting region there.

According to the above configuration, the light absorption layer Q°C has the same conductivity type as the second cladding layer, so there is no current narrowing effect, whereas the current narrowing layer (A) has the same conductivity type as the second cladding layer. It has a current narrowing effect because it is selected to have the same conductivity type as the cladding layer, but it has no light absorption effect because its energy earlag is larger than the active layer. F and B have only one of the effects of light absorption and current narrowing, respectively, independently of each other.

Next, with reference to FIG. 2, the present invention will be explained using an example of a case in which a gain-guided semiconductor radar is constructed. In FIG. 2, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and repeated explanation will be omitted. In this case, the width W2 of the through-hole portion (22a) of the current narrowing layer gradient is set to be sufficiently narrow, for example, 5 to 8
μm so that stripe-like current concentration occurs, and a negative refractive index change -Δn due to the stripe-like injected carriers is created in the center of the active layer α■. The active layer (
3) Difference in effective refractive index between the center and both sides Jn?-1
0 to -10"-3. In this case, the width of the through hole (21a) in the light absorption layer is 1w.
, > w2 so that there is no substantial difference in the refractive index due to the light absorption layer (a) K.

Further, the specific method for manufacturing this gain-guided semiconductor laser is to sequentially form the semiconductor layers (6) and (2) by the first epitaxy in the same manner as described above.

α→, (2υJ (goods) are formed on the substrate αη, and then striped through holes (
After selectively forming 22a), the difference in etching rate based on the difference in red content between the layer gradient and the layer 00 below this results in /j! (C) is passed through the hole (22m) of the current narrowing Nj (A) with a large At content, and by over-etching the light absorption layer (20) below it, a wide striped hole (21a) is formed. ) are bored.Then, these through holes (21a) and (22a) are filled and multilayered Cυ.

), a second cladding layer α→ is epitaxially grown in connection with the second cladding layer below, and a cap layer αQ is continuously epitaxially grown thereon.

Note that in the examples shown in FIGS. 1 and 2 described above, the refractive index guided semiconductor laser and the gain guided semiconductor laser are configured independently, respectively, but the refractive index guided semiconductor laser and the gain guided semiconductor laser are configured separately. In order to compensate for the drawbacks of both types of radar, the present invention can be used to obtain a semiconductor radar in which both types of guide portions are arranged in the longitudinal direction of a striped light oscillation region so that both characteristics coexist. It can also be applied. That is, for example, a compound semiconductor laser is constructed in which a stripe-shaped oscillation section has a refractive index guide type structure as explained in FIG. It can also be configured.

Alternatively, by appropriately selecting the valley widths W1 and W2 of the through-hole portions (21a) and (22a) of the above-mentioned light absorption layer Cυ and current confining layer), it is possible to create an intermediate between the dual refractive index guide type and the gain guide type. It is also possible to construct a semiconductor radar having similar characteristics.

〔Effect of the invention〕

As described above, in the present invention, by forming the light absorption function and the current narrowing function in different layers, it is possible to reliably obtain both a refractive index guided semiconductor laser and a gain guided semiconductor laser. With,
A semiconductor laser in which both guide functions are partially formed or a semiconductor laser having an intermediate function can be arbitrarily and easily designed.

[Brief explanation of drawings]

1 and 2 are respectively enlarged linear sectional views of the valley side of a semiconductor laser according to the present invention, and FIG. 3 is an enlarged linear sectional view of an example of a conventional semiconductor laser. α...Substrate, (6)...First cladding layer, (G)...Active layer, α→...Second cladding layer, Cυ・
...Light absorption layer, (Incorporated Foundation)...Current constriction layer, αQ...Cap layer, α and α→... Electrode Figure 1 Figure 2

Claims (1)

[Claims] It has a first cladding layer, an active layer, and a second cladding layer, and the second cladding layer has a smaller energy gap than the active layer and absorbs light from the active layer. an absorption layer having a conductivity type different from that of the second cladding layer,
A semiconductor laser provided with a current constriction layer that restricts a current path.