JPH11354882A - Semiconductor laser and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely constrict a current into a light-confining range by independently controlling a current-constriction width and a light-confining width in a semiconductor laser with a ridge structure and to manufacture the laser, moreover with high yield by suppressing the increase in element resistance. SOLUTION: In a semiconductor laser, where a ridge structure is formed on clad layers 17 and 20, the ridge structure is constituted of a first ridge part 31 that is relatively narrow and a second ridge part 32 that is formed at a side closer to an active layer 14 that the first ridge part 31 and has a discontinuous width and larger width as compared with that of the first ridge part 31.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser, and more particularly, to a semiconductor laser having a ridge structure formed in a cladding layer.

The present invention also relates to a method for manufacturing such a semiconductor laser.

[0003]

2. Description of the Related Art Conventionally, a semiconductor laser in which a ridge structure is formed in a cladding layer for controlling transverse mode of oscillation light and current confinement has been known.

FIG. 3 shows an example of a conventional semiconductor laser having a ridge structure. In the figure, 1 is a substrate, 2 and 6 are cladding layers, 3 and 5 are optical guide layers, 4 is an active layer, 7 is a contact layer, 8 is an insulating film, and 9 is an electrode. Then, two ridge grooves G extending in the waveguide direction (a direction perpendicular to the plane of the drawing) are formed in the portion including the upper cladding layer 6, and the ridge portion 10 is formed in a region sandwiched therebetween.
Are formed.

[0005]

In the conventional semiconductor laser having the ridge structure, the light confinement width (which is related to the transverse mode of the oscillation light) and the current confinement width are changed in the portion where the ridge groove G is formed. Although the control is performed by the remaining thickness d of the cladding layer 6, it is difficult to control the light confinement width and the current confinement width independently of each other.
Even if there is a remaining thickness d that satisfies both the light confinement width and the current confinement width, the dimensional accuracy required for the remaining thickness d is extremely severe. For this reason, the dimensional variation of the thickness d remaining in the surface of the clad layer is likely to occur, and the reproducibility of the dimensions is poor. Therefore, it is difficult to manufacture a semiconductor laser with a high yield.

Further, in the conventional semiconductor laser having the ridge structure, the current may spread until it reaches the active layer after passing through the ridge structure having the current constriction. In such a case, the driving current is changed. In this case, the light emitting area changes. In particular, when the drive current is increased in order to increase the light output, the light emitting region spreads out of the range where light confinement is effective due to the ridge structure, and the semiconductor laser cannot operate in an unstable mode caused thereby. It oscillates regularly, and tends to generate kinks and noises.

In view of the above problems, it is conceivable to reduce the electrode width in order to confine the current within the range of light confinement. However, the cladding layer in a semiconductor laser is generally 1 μm thick so that light that has permeated in the direction perpendicular to the bonding surface is not absorbed, and the current flows through the cladding layer having such a thickness. About 5-10 while passing
μm or more (20 μm or more on both sides). For this reason, when trying to confine the current on the contact layer, the
As shown in (1), it is necessary to greatly reduce the width wd of the electrode.

However, with such a structure, the contact area of the electrode with the contact layer is significantly reduced, and the contact resistance of the electrode is increased. As a result, an increase in element heat due to an increase in element resistance is caused, which causes problems such as generation of new kinks and noises and a reduction in element reliability due to a change in element temperature.

Further, in a conventional semiconductor laser having a ridge structure, a stress generated by ridge groove processing or a stress from a metal forming an insulating film or an electrode having a different coefficient of thermal expansion from that of a semiconductor is formed at a rising portion of the ridge. Therefore, uneven injection of electric current due to non-uniform refractive index and change in band structure is concentrated in this portion, and irregular light emission intensity variation occurs spatially or temporally.

The present invention has been made in view of the above circumstances, and the current confinement width and the light confinement width can be controlled independently of each other, whereby the current confinement is reliably performed within the light confinement range. It is an object of the present invention to provide a ridge-structured semiconductor laser which can be manufactured at a high yield while suppressing an increase in element resistance.

Another object of the present invention is to provide a method for manufacturing such a semiconductor laser.

[0012]

According to the present invention, there is provided a semiconductor laser having a ridge structure formed on a cladding layer as described above, wherein the ridge structure has a relatively narrow first ridge portion, The first ridge portion is formed closer to the active layer than the one ridge portion, and the first ridge portion has a discontinuous width and a wider width than the second ridge portion.

In this semiconductor laser, the maximum width of the first ridge portion is w1, the maximum width of the second ridge portion is w2,
Assuming that the current spread width from the first ridge portion to the second ridge portion is w3, it is desirable that w1 + w3 <w2.

On the other hand, according to a method of manufacturing a semiconductor laser according to the present invention, in the method of manufacturing a semiconductor laser having the above structure, a cladding layer is formed including an etching stop layer therebetween, and the etching is stopped at the etching stop layer. Thereby, the first ridge portion is formed by etching the clad layer portion on the side farther from the active layer than the etching stop layer, and then the etching stop layer is opened. Also, the second ridge portion is formed by etching a portion of the cladding layer near the active layer.

[0015]

According to the semiconductor laser of the present invention, current is mainly confined by the first ridge portion having a relatively small width, while light is mainly confined by the second ridge portion having a larger width. Become so. Therefore, the current confinement width and the light confinement width can be controlled independently of each other depending on the settings of the maximum widths w1 and w2 of the first and second ridge portions.

Further, since w1 <w2, the current can be reliably confined within the optical confinement range. If the current is confined within the optical confinement range by setting the maximum widths w1 and w2 of the first and second ridges,
It is not necessary to make the electrode width particularly small for realizing such current constriction. Therefore, the semiconductor laser of the present invention can be manufactured with a high yield while suppressing an increase in element resistance.

Further, in the semiconductor laser of the present invention, as described above, the current can be reliably confined within the range of light confinement. Therefore, even if the driving current is changed, the light emission intensity fluctuates at the ridge side end. Kinks and noise are suppressed.

Further, when the first ridge portion for performing current confinement is formed at a position away from the active layer with the second ridge portion interposed therebetween, uneven current injection into the active layer is suppressed, At the same time, since the current is confined within the range of light confinement, fluctuation of light confinement due to a change in the refractive index at the rising portion of the second ridge portion is suppressed, and a stable light emission pattern can be obtained.

When the current spreading width from the first ridge portion to the second ridge portion is w3, w1 + w3 <w
If it is 2, current leakage is effectively prevented.

As described above, the first ridge portion and the second ridge portion having different widths can be easily formed by applying the method of manufacturing a semiconductor laser according to the present invention having the above configuration.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a schematic cross-sectional shape of an infrared wavelength band semiconductor laser according to an embodiment of the present invention, and FIG. 2 shows a step of manufacturing the semiconductor laser in order.

First, the steps of fabricating the semiconductor laser of this embodiment will be described with reference to FIG. First, an n-type Al _x Ga _{1 -x is formed} on an n-type GaAs substrate 11 as shown in FIG.
As clad layer 12, Al _y Ga _1-y As light guide layer 13, A
l _z Ga _1-z As active layer _{14, Al y Ga 1-y} As optical guide layer
13 ', p-type Al _x Ga _1-x As cladding layer 15, p-type In
_0.5 Ga _0.5 P third etching stop layer 16, p-type Al _x Ga
_1-x As clad layer 17, p-type GaAs second etch stop layer 18, p-type In _0.5 Ga _0.5 P first etch stop layer 1
9, p-type Al _x Ga _{1 -x} As clad layer 20, p-type GaAs
The contact layers 21 are sequentially stacked by crystal growth.

Next, as shown in FIG. 3B, the epitaxial growth substrate is formed by photolithography as shown in FIG.
Three striped resist masks 24 are formed.

Next, the p-type Al _x Ga _{1 -x} As clad layer 20 and the p-type
The GaAs contact layer 21 is etched to have a sectional shape shown in FIG.
The first ridge groove (stripe groove) G1 of the stripe is processed. At this time, as an etching solution, p-type In _0.5 Ga _0.5 P first
It is difficult to etch the etching stop layer 19, and the etching stop layer 19 and the p-type Al _x Ga _{1 -x} As clad layer
An etchant having a sufficient selectivity between 20 and the p-type GaAs contact layer 21, for example, a citric acid-based etchant is used.

Next, an etching solution having a sufficient selectivity between the p-type In _0.5 Ga _0.5 P first etching stop layer 19 and the p-type GaAs second etching stop layer 18, for example, a hydrochloric acid type etching solution was used. A window is formed in the p-type In _0.5 Ga _0.5 P first etching stop layer 19 by etching as shown in FIG.

Next to spread the width of the first ridge groove G1, while etching the p-type Al _x Ga _1-x As cladding layer 20, as the etching solution at that time, p-type GaAs second etching stop layer 18 and p-type In _0.5 Ga _0.5 P first
An etchant that is difficult to etch the etching stop layer 19, for example, an etchant obtained by mixing sulfuric acid, hydrogen peroxide solution, and water is used. By this etching, p-type Al _x Ga _{1 -x} As
The clad layer 20 and the p-type GaAs contact layer 21 are processed as shown in FIG.

In order to form another stripe groove (second ridge groove) in the next step, a p-type Al _x Ga _{1 -x} A is formed.
The s-cladding layer 17 is etched.
Since the l _x Ga _{1 -x} As clad layer 20 and the p-type GaAs contact layer 21 are simultaneously etched, the amount of etching is determined in consideration of the amount of etching in the next step.

Next, the p-type In _0.5 Ga _0.5 P with the window opened
Using the first etching stopper layer 19 as a mask, the p-type GaAs second etching stopper layer 18 is etched and processed as shown in FIG. At this time, the p-type I
n _0.5 Ga _0.5 P first etching stop layer 19 and p-type Al
_{A material in which the} xGa ₁ -xAs clad layer 20 is difficult to etch, for example, a mixed solution of ammonium water and hydrogen peroxide solution is used.

In the above-described etching for expanding the width of the first ridge groove G1, if an etching solution that does not etch GaAs is used, the p-type GaAs contact layer 21 is not etched and the p-type Al _x Ga _{1 -x} As cladding is used. Only layer 20 is etched. Therefore, the p-type GaAs contact layer 21 is left over the both ends of the ridge-shaped cladding layer 20 in an eaves-like manner (the state is not shown in FIG. 2E). In this case, in the etching of the p-type GaAs second etching stop layer 18, the p-type GaAs contact layer 21 that protrudes like an eave can be removed together.

Next, it is difficult to etch the p-type In _0.5 Ga _0.5 P third etching stop layer 16, and the p-type Al _x Ga _{1 -x} As
An etching solution for selectively etching the cladding layer 15,
For example, using a citric acid-based etching solution, the p-type Al
_The xGa1 _- xAs cladding layer 15 is etched. Thereby, as shown in FIG. 2G, a second ridge groove G2 having a smaller width than the first ridge groove G1 is formed below the first ridge groove G1.

Thereafter, the same processing as in the manufacturing process of the semiconductor laser having the usual ridge structure is performed. That is, after the resist is first removed, for example, Si
Approximately 100 of the O ₂ and SiNx by a plasma CVD method or the like
An insulating film 22 is formed by depositing about 200 nm. Next, a contact window is opened by photolithography on the top of the central mesa, and, for example, Ti / Pt / Au
A p-side electrode 23a is formed. On the other hand, on the back side of the n-type GaAs substrate 11, an n-side electrode 23b made of, for example, AuGe / Ni / Au is formed.

Through the above steps, a semiconductor laser having the structure shown in FIG. 1 is obtained. The ridge structure formed in the central portion of the semiconductor laser is composed of a relatively narrow first ridge portion 31 formed in the p-type Al _x Ga _{1 -x} As clad layer 20.
The first ridge portion 31 is composed of a second ridge portion 32 formed in the p-type Al _x Ga _{1 -x} As clad layer 17 having a discontinuous width and a wider width.

In the semiconductor laser of the present embodiment having the above-described structure, the current is confined mainly by the first ridge portion 31 having a relatively small width, and the light is mainly confined by the second ridge portion 32 having a larger width. Is made. Therefore, the current confinement width and the light confinement width can be controlled independently of each other depending on the settings of the maximum widths w1 and w2 of the first and second ridge portions. Further, since w1 <w2, the current can be reliably confined within the optical confinement range.

The first ridge portion 31 to the second ridge portion 32
Assuming that the current spread width toward is w3, w1 + w3
<W2 is effective in preventing current leakage. The current spreading width w3 is defined by the distance from the first ridge portion 31 where the current is confined to the active layer 14 which becomes the light emitting region and the resistivity of each layer. The value of this current spread width w3 is
Usually, it is about several to 10 μm.

In the case of this embodiment, the current spreading width w3 changes according to the thicknesses d1 and d2 of the p-type Al _x Ga _{1 -x} As clad layer 17 and the p-type Al _x Ga _{1 -x} As clad layer 15, respectively. It is necessary to increase the difference between w1 and w2 as the sum of the thicknesses d1 and d2 is larger.

The embodiment in which the present invention is applied to an AlGaAs semiconductor laser has been described above. However, the present invention is not limited to this, and a semiconductor laser having an active layer formed of InGaAs, an InGaAsP semiconductor laser,
The same can be applied to an lGaInP-based semiconductor laser or the like.

For these semiconductor lasers, the first ridge portion and the second ridge portion having different widths can be easily formed by combining an appropriate etching solution and an etching stop layer. .

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a semiconductor laser according to an embodiment of the present invention.

FIG. 2 is a schematic view showing a step of manufacturing the semiconductor laser.

FIG. 3 is a schematic sectional view showing an example of a conventional semiconductor laser having a ridge structure.

FIG. 4 is a schematic sectional view showing another example of a conventional semiconductor laser having a ridge structure.

[Explanation of symbols]

11 n-type GaAs substrate 12 n-type Al _x Ga _1-x As cladding layer _{13,13 'Al y Ga 1-y} As optical guide layer 14 Al _z Ga _1-z As active layer 15 _p-type Al _x Ga _1-x As cladding layer 16 p-type In _0.5 Ga _0.5 P third etching stop layer 17 p-type Al _x Ga _{1 -x} As cladding layer 18 p-type GaAs second etching stop layer 19 p-type In _0.5 Ga _0.5 P first etching stop layer 20 p-type Al _x Ga _{1 -x} As cladding layer 21 p-type GaAs contact layer 22 insulating film 23 a p-side electrode 23 b n-side electrode 31 first ridge portion 32 second ridge portion

Claims (3)

[Claims] 1. A semiconductor laser having a ridge structure formed in a cladding layer, wherein the ridge structure is formed on a first ridge portion having a relatively small width and on a side closer to the active layer than the first ridge portion, A semiconductor laser comprising a first ridge portion and a second ridge portion having a discontinuous width and a wider width. 2. When the maximum width of the first ridge portion is w1, the maximum width of the second ridge portion is w2, and the current spreading width from the first ridge portion to the second ridge portion is w3, w1
2. The semiconductor laser according to claim 1, wherein + w3 <w2. 3. The method for manufacturing a semiconductor laser according to claim 1, wherein the cladding layer is formed by including an etching stop layer therebetween, and the etching is stopped at the etching stop layer. The first ridge portion is formed by etching a portion of the cladding layer farther from the active layer than the etching stop layer, and then the opening of the etching stop layer is opened. A method for manufacturing a semiconductor laser, wherein a second ridge portion is formed by etching a portion of a cladding layer closer to a layer.