JP2000340887A - Semiconductor laser and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a semiconductor laser capable of self-oscillation at high yield, and a method for manufacturing the laser. SOLUTION: A self-oscillation semiconductor layer has a DH structure, in which a second p-type clad layer 7 which limits a current passage in a stripe- like state via an etch stopping layer 6 is provided on a first p-type clad layer 5 formed on an active layer 4. A lower-layer section 7a of the clad layer 7 is formed in a first ridge stripe shape, having a first stripe width W1 and the upper-layer section 7b of the layer 7 is formed in a second stripe shape, having a second stripe width W2 which is narrower than the first stripe width W1.

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 a method of manufacturing the same, and more particularly, to a self-pulsation type semiconductor laser and a method suitable for manufacturing the same.

[0002]

2. Description of the Related Art When a semiconductor laser is applied as a light source for an optical disk recording / reproducing apparatus, so-called return light noise generated when a laser beam from the semiconductor laser is reflected on the disk surface and returns to the semiconductor laser itself. It is important how to control this. As a means for solving the problem of the return light noise, a technique of making the longitudinal mode of the semiconductor laser multi-mode is adopted.

[0003] As a technique for achieving the multi-mode, a method of superimposing a high-frequency wave on a semiconductor laser and a method of self-excited oscillation of the semiconductor laser itself are known. Among them, the former method requires a circuit for performing high-frequency superposition, and therefore, when such a semiconductor laser is used in an optical disk recording / reproducing apparatus, the size, weight and cost of the semiconductor laser are reduced. Is disadvantageous. Therefore, the need for a self-pulsation type semiconductor laser that does not require a high-frequency superimposing circuit is increasing.

FIG. 16 shows an example of a conventional self-pulsation type semiconductor laser. This self-pulsation type semiconductor laser is an AlGaAs-based self-pulsation type semiconductor laser having a DH structure (Double Heterostructure).

As shown in FIG. 16, this conventional AlGa
In an As-based self-pulsation type semiconductor laser, n-type Ga
On an n-type semiconductor substrate 101 such as an As substrate, an n-type Al
Through a buffer layer 102 made of _0.3 Ga _0.7 As,
n-type cladding layer 10 made of n-type Al _0.47 Ga _0.53 As
3. Active layer 104 made of non-doped Al _0.13 Ga _0.87 As, first p-type clad layer 105 made of p-type Al _0.47 Ga _0.53 As, etching stop layer 106 made of p-type Al _0.3 Ga _0.7 As, and p-type Al _0.47 Ga _0.53 A
A second p-type cladding layer 107 made of s is sequentially laminated.

[0006] The etching stop layer 106 and the second p-type cladding layer 107 have a ridge stripe shape having a predetermined stripe width W extending in the resonator length direction. Sign 1
08 indicates the ridge stripe portion. The stripe width W of the ridge stripe portion 108 is 2.5 to 3.5 μ.
m.

On the first p-type cladding layer 105 on both sides of the ridge stripe portion 108 and on the second cladding layer 107
A current blocking layer 109 made of n-type GaAs is provided on the upper side, thereby forming a current confinement structure. The vicinity of the surface of the current blocking layer 109 is zinc (Zn).
Are made p-type by diffusion. Reference numeral 110 indicates the Z
5 shows an n diffusion region. The Zn diffusion region 110 has a second p region at a portion corresponding to the ridge stripe portion 108.
It has a depth reaching the upper part of the mold cladding layer 107.

On the Zn diffusion region 110, Ti / Pt / A
A p-side electrode 111 such as a u-electrode is provided in ohmic contact. On the other hand, an n-side electrode 1 such as an AuGe / Ni / Au electrode is provided on the back surface of the n-type GaAs substrate 101.
12 are provided in ohmic contact.

In the conventional self-sustained pulsation type semiconductor laser configured as described above, when a predetermined forward voltage is applied between the p-side electrode 111 and the n-side electrode 112 to conduct current, the current path becomes The current is limited to the stripe shape by the ridge stripe portion 108, and therefore, the current is reduced as shown by the arrow 113 in FIG.
Flowing inside. In this case, inside the active layer 104, the current spreads to a portion substantially corresponding to the ridge stripe portion 108.

On the other hand, in this self-sustained pulsation type semiconductor laser, a higher level is provided between the first p-type cladding layer 105 and the second p-type cladding layer 107 made of p-type Al _0.47 Ga _0.53 As. P-type Al _0.3 Ga _0.7 As with refractive index
By inserting the etching stop layer 106 made of, a refractive index difference necessary for performing optical waveguide in a direction (lateral direction) parallel to the heterojunction is formed. The difference in the refractive index between the corresponding high-refractive-index portion and the low-refractive-index portions on both sides thereof is smaller than that of a normal refractive index-guided semiconductor laser.
Therefore, light spreads beyond the portion corresponding to the ridge stripe portion 108 inside the active layer 104.

As a result, saturable absorption regions 114 are formed in the active layer 104 at portions corresponding to the vicinity of both sides of the ridge stripe portion 108, and thereby self-pulsation is realized.

By the way, in the self-pulsation type semiconductor laser, the width of the saturable absorption region formed in the active layer is determined by a delicate difference between the spread of light and the spread of current in the active layer. Therefore, the self-pulsation type semiconductor laser is sensitive to the thickness and the impurity concentration of the semiconductor layer forming the laser structure. In particular, in the conventional self-pulsation type semiconductor laser shown in FIG. 16, the current spread inside the active layer 104 depends on the thickness of the cladding layer on both sides of the ridge stripe portion 108 (in this case, the first p-type). Depending on the thickness of the cladding layer 105) and the impurity concentration in that portion, characteristics such as the presence or absence of self-excited oscillation and the level of self-excited oscillation change. Here, the self-excited oscillation level refers to the maximum optical output capable of self-excited oscillation.

Therefore, in the conventional self-pulsation type semiconductor laser, in order to realize the self-pulsation, in other words, to stably form the saturable absorption region 114 in the active layer 104, It is necessary to precisely control the thickness and impurity concentration of the first p-type cladding layer 105.

[0014]

However, in the above-mentioned conventional self-pulsation type semiconductor laser, the semiconductor layer forming the laser structure is formed by a metal organic chemical vapor deposition (MOCVD) method or a molecular beam irradiation method. Epitaxy (MB
The thickness of the first p-type cladding layer 105 can be increased even when the first p-type cladding layer 105 is grown using a crystal growth method such as the E) method which has good reproducibility and good in-plane uniformity of film thickness and impurity concentration. Variations in the impurity concentration exceed the allowable value for realizing self-sustained pulsation, and at present, variations in thickness between wafers are several percent or more. Therefore, in the related art, when a self-pulsation type semiconductor laser is manufactured, there is a problem that the yield of the semiconductor laser becoming a self-pulsation type is low.

An object of the present invention is to provide a semiconductor laser capable of obtaining self-pulsation at a high yield and a method of manufacturing the same.

[0016]

To achieve the above object, a first aspect of the present invention is to provide a first conductive type first cladding layer, an active layer on the first cladding layer, A second cladding layer of a second conductivity type on the second cladding layer, and a third cladding layer of the second conductivity type provided on the second cladding layer to restrict a current path in a stripe shape. In the third cladding layer, the lower portion of the second cladding layer has a first stripe shape with a first stripe width, and the upper layer portion has a second stripe width smaller than the first stripe width. It is characterized by having two stripe shapes.

According to a second aspect of the present invention, there is provided a method of manufacturing a semiconductor laser, comprising: a first cladding layer of a first conductivity type, an active layer, a second cladding layer of a second conductivity type,
A step of sequentially growing a third cladding layer of a conductive type, and patterning the third cladding layer in a stripe shape. At this time, a lower layer portion of the third cladding layer on the side of the second cladding layer is formed as a first layer. And patterning the upper layer portion into a second stripe shape having a second stripe width smaller than the first stripe width, in addition to patterning the first stripe shape with the first stripe width. .

In the present invention, the semiconductor laser is typically a self-pulsation type semiconductor laser.

In the present invention, from the viewpoint of improving the controllability of etching when patterning the third cladding layer into a stripe shape, preferably, the third cladding layer is provided between the second cladding layer and the third cladding layer. And an etching stop layer made of a material having a different composition from the second cladding layer.

In the present invention, from the viewpoint of satisfactorily confining current, a current block layer is preferably provided on both sides of the stripe portion.

In the present invention, the lower and upper layers of the third cladding layer are preferably made of a material having the same composition, from the viewpoint of not adversely affecting the optical waveguide in the direction parallel to the hetero junction. Be composed. The third cladding layer is preferably made of a material having the same composition as that of the second cladding layer.

In the second aspect of the present invention, when the third cladding layer is patterned into a stripe shape,
The upper part of the third cladding layer is formed by the second stripe width of the second layer.
After patterning into the first stripe shape, the lower layer portion of the third cladding layer may be patterned into the first stripe shape having the first stripe width. Conversely, the entire third cladding layer may be patterned into the first stripe shape. After patterning into a first stripe shape having a width, the upper layer portion of the third cladding layer may be patterned into a second stripe shape having a second stripe width.

According to the second aspect of the present invention, for example, the lower layer and the upper layer of the third cladding layer are made of materials having different compositions from each other, and the entire third cladding layer is formed into a predetermined stripe shape. After patterning, the upper layer portion of the third cladding layer is selectively etched from both sides of the stripe portion by utilizing the difference in chemical properties between the lower layer portion and the upper layer portion. By lowering the width of the upper layer portion relatively to the width of the lower layer portion by, for example, etching the upper layer portion under a high selectivity condition, the lower layer portion has a first stripe shape having a first stripe width. The upper layer portion may be patterned into a second stripe shape having a second stripe width smaller than the first stripe width. In this case, only one photoresist step is required for patterning the third cladding layer into a stripe shape. Such a method is used, for example, when the semiconductor laser to be manufactured is AlGaAs.
In the case of an s-based semiconductor laser, this can be realized by configuring the upper layer of the third cladding layer with AlGaAs having a larger Al composition than the lower layer.

In the second aspect of the present invention, for example, an intermediate portion made of a material having a different composition from the lower cladding layer is provided between the lower layer portion and the upper layer portion of the third cladding layer. When etching from the upper layer side, utilizing the difference in chemical properties between the upper layer portion and the intermediate portion, the etching rate in the depth direction is reduced when the intermediate portion is exposed, and during this time, the side etching of the upper layer portion is performed. The lower layer portion may be patterned into a first stripe shape having a first stripe width, and the upper layer portion may be patterned into a second stripe shape having a second stripe width smaller than the first stripe width. In this case, only one photoresist step is required for patterning the third cladding layer into a stripe shape. Such a method can be realized, for example, when the semiconductor laser to be manufactured is an AlGaAs-based semiconductor laser, by configuring the intermediate portion of the third cladding layer with AlGaAs having a smaller Al composition than the lower layer portion and the upper layer portion. . In this case, it is desirable that the Al composition in the intermediate portion be selected so that this portion does not become an etching stop layer when the third cladding layer is etched from the upper layer side. When the third clad layer is etched from the upper layer side, if the intermediate portion becomes an etching stop layer,
For example, the intermediate portion may be etched off using a phosphoric acid-based etchant.

According to the semiconductor laser and the method of manufacturing the same according to the present invention, the lower part of the third cladding layer on the side of the second cladding layer has the first stripe width. A second stripe width having a second stripe width smaller than the first stripe width
With this stripe shape, the spread of current can be narrowed with respect to the spread of light in the direction parallel to the hetero junction. As a result, the width of the saturable absorption region formed in the active layer can be made wider than in the conventional case, so that the margin of the self-sustained pulsation with respect to the variation in the thickness and impurity concentration of the second cladding layer can be increased. it can.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. In all the drawings of the embodiments, the same or corresponding portions are denoted by the same reference numerals.

First, a first embodiment of the present invention will be described. FIG. 1 is a sectional view of the self-pulsation type semiconductor laser according to the first embodiment of the present invention. This self-pulsation type semiconductor laser is an AlGaAs-based self-pulsation type semiconductor laser having a DH structure.

As shown in FIG. 1, in the self-pulsation type semiconductor laser according to the first embodiment, for example, an n-type G
On an n-type semiconductor substrate 1 such as an aAs substrate, for example, via a buffer layer 2 made of n-type Al _0.3 Ga _0.7 As,
For example, an n-type clad layer 3 made of n-type Al _0.47 Ga _0.53 As, for example, an active layer 4 made of non-doped Al _0.13 Ga _0.87 As, for example, a first p-type clad layer 5 made of p-type Al _0.47 Ga _0.53 As, for example p-type Al _0.3 Ga _0.7
Etching stop layer 6 made of As and, for example, p-type Al
_A second p-type cladding layer 7 made of _0.47 Ga _0.53 As is sequentially laminated.

The lower layer 7a of the etching stop layer 6 and the second p-type cladding layer 7 is formed by a first layer extending in the resonator length direction.
The first p-type cladding layer 7 has a first ridge stripe shape (first ridge stripe portion 8a) having a stripe width W1 of a second width.
Has a second ridge stripe shape (second ridge stripe portion 8b) having a stripe width W2 (W2 <W1). Reference numeral 8 denotes a ridge stripe portion composed of the first ridge stripe portion 8a and the second ridge stripe portion 8b. The stripe width W1 of the first ridge stripe portion 8a and the stripe width W2 of the second ridge stripe portion 8b respectively correspond to the width at the lower end.

The first of the portions on both sides of the ridge stripe portion 8
A current blocking layer 9 made of, for example, n-type GaAs is provided on the p-type cladding layer 5 and the second p-type cladding layer 7, thereby forming a current confinement structure. The vicinity of the surface of the current blocking layer 9 is made p-type by, for example, Zn diffusion. Reference numeral 10 indicates the Zn diffusion region. The Zn diffusion region 10 has a depth reaching the upper layer portion 7b of the second p-type cladding layer 7 in a portion corresponding to the ridge stripe portion 8.

On the Zn diffusion region 10, for example, Ti / P
A p-side electrode 11 such as a t / Au electrode is provided in ohmic contact. On the other hand, on the back side of the n-type semiconductor substrate 1, an n-type semiconductor such as an AuGe / Ni / Au electrode
The side electrode 12 is provided in ohmic contact.

In the self-pulsation type semiconductor laser according to the first embodiment configured as described above, the etching stop layer 6 and the second p-type semiconductor layer are formed in the ridge stripe portion 8 for limiting the current path in a stripe shape. Mold cladding layer 7
The first ridge stripe portion 8a formed of the lower layer portion 7a has the first stripe width W1 and the second stripe
The second ridge stripe portion 8b composed of the upper layer portion 7b of the p-type cladding layer 7 has a second stripe width W2 smaller than the first stripe width W1, thereby suppressing the current from spreading in the lateral direction. Is characteristic.

The difference W1-W2 between the stripe width W1 of the lower first ridge stripe portion 8a and the stripe width W2 of the upper second ridge stripe portion 8b of the ridge stripe portion 8. Is, for example, 0.5μ
m. After satisfying this relationship, the first stripe width W1 is, for example, about 2.5 to 3.5 μm,
Is selected to be, for example, about 2.0 μm to 3.0 μm. However, if the impurity concentration of the first p-type cladding layer 5 and the second p-type cladding layer 7 changes, the spread of the current also changes, and accordingly the first stripe width W1 and the second stripe width W2 needs to be set. Specifically, for example, when the impurity concentration of the first p-type cladding layer 5 is increased (for example, about 1 × 10 ¹⁸ / cm ³ ) to improve the temperature characteristics,
The spread of the current in the mold cladding layer 5 increases, and the semiconductor laser hardly oscillates by itself. In such a case, the first
Of the stripe width W1 and the second stripe width W2 are
It is set smaller than the above range.

The lower limit of the thickness T of the ridge stripe portion 8 depends on the output of the semiconductor laser and the like, but from the viewpoint of reducing the absorption loss by the current block layer 9 which leads to an increase in the operating current, for example, 0. .8 μm. On the other hand, the upper limit of the thickness T of the ridge stripe portion 8 is selected to be, for example, about 1.4 μm from the viewpoint of reducing the series resistance that leads to an increase in heat generation. At this time, the thickness T1 of the first ridge stripe portion 8a on the lower layer side and the thickness T2 of the second ridge stripe portion 8b on the upper layer side are determined from the viewpoint of effectively suppressing the lateral spread of the current. T1
<T2 is preferable. The thickness T
It is necessary to change the ratio of 1 and T2 according to the impurity concentration of the first p-type cladding layer 5 and the second p-type cladding layer 7 as in the case of the stripe widths W1 and W2. In particular, when the impurity concentration of the first p-type cladding layer 5 is high, the second ridge stripe 8b is made thicker (T2 / T1 is larger) than the first ridge stripe portion 8a, and the current spreads. Is desirable.

Next, the operation of the self-pulsation type semiconductor laser according to the first embodiment will be described. During operation of the self-pulsation type semiconductor laser, a predetermined forward voltage is applied between the p-side electrode 11 and the n-side electrode 12. At this time, the current path is formed in the second layer on the upper layer side of the ridge stripe portion 8.
Therefore, the current flows inside the ridge stripe portion 8 as shown by an arrow 13 in FIG. in this case,
In the inside of the active layer 4, the current spreads substantially to a portion corresponding to the second ridge stripe portion 8b.

On the other hand, in this self-sustained pulsation type semiconductor laser, a higher level is provided between the first p-type cladding layer 5 and the second p-type cladding layer 7 made of p-type Al _0.47 Ga _0.53 As. By inserting the etching stop layer 6 made of p-type Al _0.3 Ga _0.7 As having a refractive index, a difference in the refractive index necessary for performing the optical waveguide in the lateral direction is created. In this case, the ridge stripe portion is formed. 8 (first ridge stripe portion 8a), the difference in the refractive index between the high-refractive-index portion and the low-refractive-index portions on both sides of the high-refractive-index portion is smaller than that of a normal refractive index-guided semiconductor laser. . Therefore, inside the active layer 4, the light spreads beyond the portion corresponding to the first ridge stripe portion 8a.

As a result, according to the difference between the spread of light and the spread of current in the active layer 4, as shown in FIG. An absorption region 14 is formed, whereby self-pulsation is realized. In this case, while the light spreads over the portion corresponding to the first ridge stripe portion 8a,
Since the current is limited by the second ridge stripe portion 8b having a small width, a state in which the current distribution is narrow and the light distribution is wide in the active layer 4 is realized. 14 are secured.

Next, a method of manufacturing the self-pulsation type semiconductor laser according to the first embodiment will be described.

In order to manufacture the self-pulsation type semiconductor laser according to the first embodiment, first, as shown in FIG.
A buffer layer 2 made of n-type Al _0.3 Ga _0.7 As and an n made of n-type Al _0.47 Ga _0.53 As on an n-type semiconductor substrate 1 such as an n-type GaAs substrate by, for example, MOCVD.
A cladding layer 3, an active layer 4 of undoped Al _0.13 Ga _0.87 As, a first p-type cladding layer 5 of p-type Al _0.47 Ga _0.53 As, an etching stop layer 6 of p-type Al _0.3 Ga _0.7 As, sequentially growing a p-type Al _0.47 Ga _0. consisting ₅₃ As the second p-type cladding layer 7 and cap layer 21 made of GaAs. Here, the cap layer 21 is made of a second p-containing layer containing Al during the manufacturing process of the semiconductor laser.
It has a role of preventing the surface of the mold clad layer 7 from being oxidized.

Next, as shown in FIG.
A stripe-shaped resist pattern 22 having a predetermined width and extending in one direction is formed thereon by, for example, a lithography method. Next, using this resist pattern 22 as a mask,
For example, the second clad layer 7 is etched to an intermediate depth in the thickness direction by a reactive ion etching (RIE) method or a wet etching method. As a result, the upper layer portion 7b of the second p-type cladding layer 7 extends in the resonator length direction and is patterned into a ridge stripe shape having a desired stripe width W2. 8b are formed. After that, the resist pattern 22 used as the etching mask is removed.

Next, as shown in FIG. 4, a resist pattern 23 having a predetermined shape is formed so as to cover the second ridge stripe portion 8b. Next, using the resist pattern 23 as a mask, the remaining thickness of the second p-type cladding layer 7 is exposed until the surface of the etching stop layer 6 is exposed, for example, by a wet etching method using an HF-based etchant. Etch. Next, as shown in FIG. 5, using the resist pattern 23 as a mask, the etching stop layer 6 is removed by, for example, a wet etching method using a phosphoric acid-based etchant. As a result, the lower layer portion 7a of the etching stop layer 6 and the second p-type clad layer 7 extends in the resonator length direction and is patterned into a ridge stripe shape having a desired stripe width W1, and
Is formed. Through the steps so far, a desired ridge stripe structure is formed.
After that, the resist pattern 23 used as the etching mask is removed.

Next, after removing the cap layer 21, FIG.
As shown in (1), a current block layer 9 made of, for example, n-type GaAs is grown on the first p-type cladding layer 5 and the second p-type cladding layer 7 on both sides of the ridge stripe portion 8 by, for example, MOCVD. Let it.

Next, as shown in FIG. 7, a resist pattern 24 having a predetermined shape having an opening 24a at a portion corresponding to the ridge stripe portion 8 is formed on the current block layer 9 by lithography. Next, using the resist pattern 24 as a mask, the current confinement layer 9 in the opening 24a is etched by, for example, RIE or wet etching so that the second p-type cladding layer 7 thereunder is not exposed. After that, the resist pattern 24 used as the etching mask is removed.

Next, as shown in FIG. 8, by diffusing Zn over the entire surface, the vicinity of the surface layer of the current blocking layer 9 is made p-type. At this time, the diffusion depth of Zn is controlled so that the Zn diffusion front near the ridge stripe portion 8 reaches the upper layer portion 7b of the second p-type cladding layer 7. Thereby, the Zn diffusion region 1 as the p-side electrode contact portion
0 is formed.

Next, as shown in FIG.
The n-side electrode 12 is formed on the back surface of the n-type semiconductor substrate 1 while the p-side electrode 11 is formed on the semiconductor substrate 1. Thereafter, the two cavity end faces are formed by cleaving the n-type semiconductor substrate 1 on which the laser structure is formed as described above into a bar shape, and if necessary, both cavity end faces are subjected to end face coating. Bars are chipped. Thus, the intended self-pulsation type semiconductor laser is manufactured.

As described above, according to the first embodiment, the etching stop layer 6 and the second p-type clad layer 7
The lower layer portion 7a has a first stripe shape having a first stripe width, and the upper layer portion 7b of the second p-type cladding layer 7 has a second stripe width having a second stripe width smaller than the first stripe width. By having the shape, the active layer 4
In this case, the current spread (current distribution) can be made narrower than the horizontal light spread (light distribution). As a result, the width of the saturable absorption region 14 formed in the active layer 4 can be made wider than in the conventional case.
The margin of the self-sustained pulsation with respect to the variation of the thickness and the impurity concentration of the p-type cladding layer 5 can be increased,
A self-pulsation type semiconductor laser can be obtained with a high production yield.

Next, a second embodiment of the present invention will be described. In the above-described first embodiment, the first ridge stripe portion 8a is formed through two photoresist steps.
And a ridge stripe portion 8 composed of a second ridge stripe portion 8b. In the second embodiment, the lower layer portion 7a and the upper layer portion 7b of the second p-type cladding layer 7 have different compositions. A similar ridge stripe portion 8 is formed by using a material and utilizing the difference between the two etching rates.

That is, as shown in FIG. 9, in the self-pulsation type semiconductor laser according to the second embodiment, the upper layer 7b of the second p-type cladding layer 7 has a higher Al composition than the lower layer 7a. It is made of a large p-type AlGaAs. However, in the second p-type cladding layer 7, if the difference in the Al composition between the lower layer portion 7a and the upper layer portion 7b is extremely changed, it may affect the refractive index difference inside and outside the stripe. The composition of the lower layer portion 7a and the upper layer portion 7b is as follows:
It is selected in consideration of this point. Here, the lower layer portion 7a of the second cladding layer 7a is, for example, p-type Al _0.47 Ga _0.53 A
s, and the upper layer portion 7b is made of, for example, p-type Al _0.5 G
a _0.5 As.

The other configuration of the self-pulsation type semiconductor laser according to the second embodiment is the same as that of the self-pulsation type semiconductor laser according to the first embodiment, and the description is omitted.

Next, a method of manufacturing the self-pulsation type semiconductor laser according to the second embodiment will be described.

In order to manufacture the self-pulsation type semiconductor laser according to the second embodiment, first, an MO is formed on the n-type semiconductor substrate 1 by following the same steps as in the first embodiment.
The buffer layer 2, the n-type cladding layer 3, the active layer 4, the first p-type cladding layer 5, the etching stop layer 6,
The second p-type cladding layer 7 and the cap layer 21 are sequentially grown. However, when growing the second p-type cladding layer 7, p-type Al _0.47 Ga _0.53 As is grown on a portion having a predetermined thickness corresponding to the lower layer portion 7a, and the remaining thickness corresponding to the upper layer portion 7b is formed. A p-type Al _0.5 Ga _0.5 As is grown in the portion.

Next, as shown in FIG.
A resist pattern 31 having a predetermined width extending in one direction is formed on the substrate 1 by lithography. Next, using the resist pattern 31 as a mask, etching is performed by, for example, RIE or wet etching until the surface of the etching stopper layer 6 is exposed. Thereby, the second p
The mold cladding layer 7 is patterned into a predetermined ridge stripe shape.

Next, as shown in FIG. 11, for example, by a wet etching method using an HF-based etchant,
The second p-type cladding layer 7 patterned in the ridge stripe shape is etched from both sides. At this time, in the second p-type cladding layer 7, both the lower layer portion 7a and the upper layer portion 7b are side-etched, but since the etching rate is higher in the upper layer portion 7b having a large Al composition, the upper layer portion 7b is Side etching is performed faster than the portion 7a. As a result, as shown in FIG.
Becomes relatively narrow, and a step occurs between the lower layer portion 7a and the upper layer portion 7b. Next, as in the first embodiment, the etching stop layer 6 is removed by a wet etching method using a phosphoric acid-based etchant. Thereby, the lower layer portion 7a of the etching stop layer 6 and the second p-type cladding layer 7 extends in the resonator length direction and is patterned into a first ridge stripe shape having a first stripe width W1. The upper layer portion 7b of the second p-type cladding layer 7 extends in the resonator length direction and is patterned into a second ridge stripe shape having a second stripe width W2 to form a desired ridge stripe structure. You. As described above, in the second embodiment, the number of masks and the number of steps can be reduced because only one photoresist step is required when forming the ridge stripe portion 8.

Thereafter, the steps are advanced in the same manner as in the first embodiment, and the intended self-pulsation type semiconductor laser is completed as shown in FIG.

According to the second embodiment, the same advantages as in the first embodiment can be obtained.

Next, a third embodiment of the present invention will be described. In the above-described first embodiment, the first ridge stripe portion 8a is formed through two photoresist steps.
A ridge stripe portion 8 including a second ridge stripe portion 8b is formed. In the third embodiment, the ridge stripe portion 8 is formed between the lower layer portion 7a and the upper layer portion 7b of the second p-type cladding layer 7. An intermediate portion 7c made of a material having a different composition is provided, and a similar ridge stripe portion 8 is formed by utilizing a difference in etching rate between the upper layer portion 7a and the intermediate portion 7c.

That is, as shown in FIG.
In the self-pulsation type semiconductor laser according to the embodiment,
The lower portion 7a and the upper portion 7b of the second p-type cladding layer 7 have a smaller A than that of the lower portion 7a and the upper portion 7b.
An intermediate portion 7c made of p-type AlGaAs having a small l-composition is provided. The lower layer portion 7a of the etching stop layer 6 and the second p-type cladding layer 7 has a first stripe shape having a first stripe width W1 extending in the resonator length direction,
Middle part 7c and upper part 7b of second p-type cladding layer 7
Has a second stripe shape with a second stripe width W2 extending in the resonator length direction. The lower layer portion 7a and the upper layer portion 7b of the second cladding layer 7a are, for example, p-type Al _0.47 Ga
_The intermediate portion 7c is made of, for example, such that the intermediate portion 7c does not become an etching stop layer when the second p-type clad layer 7 is etched from the upper layer portion 7b side as described later. Al composition is 0.35 to 0.38
It is composed of about p-type AlGaAs.

The other configuration of the self-pulsation semiconductor laser according to the third embodiment is the same as that of the self-pulsation semiconductor laser according to the first embodiment, and therefore the description is omitted.

Next, a method of manufacturing the self-pulsation type semiconductor laser according to the third embodiment will be described.

In order to manufacture the self-pulsation type semiconductor laser according to the third embodiment, first, an MO is formed on the n-type semiconductor substrate 1 according to the same steps as in the first embodiment.
The buffer layer 2, the n-type cladding layer 3, the active layer 4, the first p-type cladding layer 5, the etching stop layer 6,
The second p-type cladding layer 7 and the cap layer 21 are sequentially grown. However, when the second p-type cladding layer 7 is grown, p-type Al _0.47 Ga _0.53 As is grown on a portion having a predetermined thickness corresponding to the lower layer portion 7a, and a predetermined thickness corresponding to the intermediate layer 7c is formed. In the portion of, the Al composition is 0.35 to 0.38.
Is grown, and p-type Al _0.47 Ga _0.53 As is grown on the remaining thickness corresponding to the upper layer portion 7b.

Next, as shown in FIG.
After a resist pattern 41 having a predetermined shape is formed on the substrate 1 by lithography, the cap layer 21 is selectively etched by RIE or wet etching using the resist pattern 41 as a mask.

Next, using the resist pattern 41 as a mask, the second p-type clad layer 7 is etched from the upper layer portion 7b side by, for example, a wet etching method using an HF-based etchant. At this time, the upper layer portion 7b of the second p-type cladding layer 7 is gradually etched, and as shown in FIG.
When the intermediate portion 7c made of p-type AlGaAs having a smaller Al composition than lGaAs is exposed on the surface, the etching rate in the vertical direction decreases. Lower part 7 of p-type cladding layer 7
The etching of "a" is started when the intermediate portion 7c is removed, and ends when the etching stop layer 6 is exposed. At this time, while the intermediate portion 7c is being etched, side etching proceeds in the upper layer portion 7b. As a result, as shown in FIG. 15, the width of the upper layer portion 7b becomes relatively narrow, and a step is generated between the lower layer portion 7a and the upper layer portion 7b. Next, as in the first embodiment,
The etching stop layer 6 is removed by a wet etching method using a phosphoric acid-based etchant. This allows
The lower layer portion 7a of the etching stop layer 6 and the second p-type cladding layer 7 extends in the resonator length direction, and is patterned into a first ridge stripe shape having a first stripe width W1 and a second ridge stripe shape. Intermediate portion 7c of p-type cladding layer 7
And upper layer portion 7b extends in the resonator length direction, and
Is patterned into a second ridge stripe shape having a stripe width W2, thereby forming a desired ridge stripe structure. As described above, in the third embodiment, the number of masks and the number of steps can be reduced because only one photoresist step is required when forming the ridge stripe portion 8. In the third embodiment, when the second p-type cladding layer 7 is etched from the upper layer portion 7b side, its Al composition is selected so that the intermediate portion 7c does not become an etching stop layer. A
If the l composition is selected as small as about 0.3, for example, and the intermediate portion 7c becomes an etching stop layer in the step shown in FIG. 14, then, for example, a phosphoric acid-based etchant is used to form the intermediate portion 7c. 7c may be removed.

Thereafter, the steps are advanced in the same manner as in the first embodiment to complete the intended self-pulsation type semiconductor laser as shown in FIG.

According to the third embodiment, the same advantages as in the first embodiment can be obtained.

Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above embodiments, and various modifications based on the technical concept of the present invention are possible.

For example, the numerical values, structures, materials, processes, and the like described in the first to third embodiments are merely examples, and different numerical values, structures,
Materials, processes and the like may be used. Specifically, the composition of each semiconductor layer forming the laser structure described in the above-described first to third embodiments is merely an example, and a composition different from that exemplified as needed may be used. Good. Also,
As for the laser structure, a laser structure different from the illustrated one may be employed.

For example, in the above-described first to third embodiments, the growth of the semiconductor layer forming the laser structure is performed by MOC.
Although the method is performed by the VD method, it can be performed by another method such as the MBE method.

In the first to third embodiments, the conductivity types of the semiconductor layers forming the substrate and the laser structure may be reversed.

In the first to third embodiments, the case where the present invention is applied to a self-pulsation type semiconductor laser having a DH structure has been described.
It is also possible to apply to a self-pulsation type semiconductor laser having a structure (Separate Confinement Heterostructure).

In the first to third embodiments, the case where the present invention is applied to an AlGaAs-based self-pulsation type semiconductor laser has been described.
For example, a self-oscillation type semiconductor laser using another group III-V compound semiconductor such as an AlGaInP-based self-oscillation type semiconductor laser, a self-oscillation type semiconductor laser using a II-VI group compound semiconductor, and a nitride semiconductor Physical system III-V
It is also possible to apply to a self-pulsation type semiconductor laser using a group III compound semiconductor.

[0071]

As described above, according to the semiconductor laser and the method of manufacturing the same according to the present invention, the lower part of the third cladding layer on the side of the second cladding layer has the first stripe width of the first stripe width. A second stripe having a second stripe width having a stripe shape and an upper layer portion having a width smaller than the first stripe width.
With this stripe shape, the spread of current can be narrowed with respect to the spread of light in the direction parallel to the hetero junction. As a result, the width of the saturable absorption region formed in the active layer can be made wider than in the conventional case, so that the margin of the self-sustained pulsation with respect to the variation in the thickness and impurity concentration of the second cladding layer can be increased. As a result, a self-pulsation type semiconductor laser can be obtained with a high manufacturing yield.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a self-pulsation type semiconductor laser according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view for explaining the method for manufacturing the self-pulsation type semiconductor laser according to the first embodiment of the present invention.

FIG. 3 is a cross-sectional view for explaining the method for manufacturing the self-pulsation type semiconductor laser according to the first embodiment of the present invention.

FIG. 4 is a cross-sectional view for explaining the method for manufacturing the self-pulsation type semiconductor laser according to the first embodiment of the present invention.

FIG. 5 is a sectional view for explaining the method for manufacturing the self-pulsation type semiconductor laser according to the first embodiment of the present invention.

FIG. 6 is a sectional view for explaining the method of manufacturing the self-pulsation type semiconductor laser according to the first embodiment of the present invention.

FIG. 7 is a sectional view for explaining the method for manufacturing the self-pulsation type semiconductor laser according to the first embodiment of the present invention.

FIG. 8 is a sectional view for explaining the method for manufacturing the self-pulsation type semiconductor laser according to the first embodiment of the present invention.

FIG. 9 is a sectional view of a self-pulsation type semiconductor laser according to a second embodiment of the present invention.

FIG. 10 is a cross-sectional view for explaining the method for manufacturing the self-pulsation type semiconductor laser according to the second embodiment of the present invention.

FIG. 11 is a cross-sectional view for explaining the method for manufacturing the self-pulsation type semiconductor laser according to the second embodiment of the present invention.

FIG. 12 is a sectional view of a self-pulsation type semiconductor laser according to a third embodiment of the present invention.

FIG. 13 is a cross-sectional view for explaining the method for manufacturing the self-pulsation type semiconductor laser according to the third embodiment of the present invention.

FIG. 14 is a sectional view for explaining the method for manufacturing the self-pulsation type semiconductor laser according to the third embodiment of the present invention.

FIG. 15 is a cross-sectional view for explaining the method for manufacturing the self-pulsation type semiconductor laser according to the third embodiment of the present invention.

FIG. 16 is a sectional view of a conventional self-pulsation type semiconductor laser.

[Explanation of symbols]

1 ... n-type semiconductor substrate, 2 ... buffer layer, 3 ...
-N-type cladding layer, 4 ... active layer, 5 ... first p
Mold clad layer, 6 etching stop layer, 7 second p-type clad layer, 7a lower layer part, 7b upper layer part, 8 ridge stripe part, 8a ... First ridge stripe portion, 8b... Second ridge stripe portion, 9... Current blocking layer, 10... Zn diffusion region, 11.

Claims (4)

[Claims] 1. A first cladding layer of a first conductivity type, an active layer on the first cladding layer, and a second cladding layer of a second conductivity type on the active layer, In a semiconductor laser provided with a third cladding layer of a second conductivity type for limiting a current path in a stripe shape on a second cladding layer, the third cladding layer is a lower layer on the second cladding layer side. A semiconductor laser having a first stripe shape having a first stripe width and an upper layer having a second stripe shape having a second stripe width smaller than the first stripe width. 2. The semiconductor laser according to claim 1, wherein an etching stop layer is provided between said second clad layer and said third clad layer. 3. The semiconductor laser according to claim 1, wherein said lower layer portion and said upper layer portion of said third cladding layer are made of a material having the same composition. 4. A first cladding layer of a first conductivity type, an active layer, a second cladding layer of a second conductivity type, and a second cladding layer on a substrate.
A step of sequentially growing a third cladding layer of a conductive type; and patterning the third cladding layer into a stripe shape. Is patterned into a first stripe shape having a first stripe width, and the upper layer portion is formed into a second stripe having a second stripe width smaller than the first stripe width.
Patterning into a stripe shape as described above.