JP2003046193A - Semiconductor laser and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ridge-type semiconductor laser together with its manufacturing method that can be manufactured at a low cost through one-time growth of crystal and has a structure to reduce contact resistance, as well as element resistance as a result. SOLUTION: This semiconductor laser has a refractive index guiding type ridge structure provided with a laminated body comprised of a plurality of compound semiconductor layers, an upper electrode, and a lower electrode. The uppermost layer of a ridge part is a contact layer 107 formed of a heavily doped compound semiconductor layer, and the width of the upper surface of a second semiconductor layer 106 that is positioned at the bottom of the contact layer and is in contact therewith is smaller than that of the bottom surface of the contact layer. The upper electrode 113 is directly in contact with at least one of the surface, both side surfaces and bottom surface of the contact layer in the ridge part, and the surface of the ridge part other than them is covered with an insulation film 111.

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 used as a light source for an optical disc system, information processing or optical communication.

[0002]

2. Description of the Related Art In a conventional manufacturing process of a semiconductor laser device, a first crystal growth in which at least a first conductivity type cladding layer, an active layer and a second conductivity type cladding layer are formed on a first conductivity type semiconductor substrate is performed. Then, through a stripe forming step of forming a region for injecting a current into the active layer, epitaxial growth for filling the stripe portion is performed to form a device.

For example, a manufacturing process of a ridge type semiconductor laser device as shown in FIG. 4 generally includes three steps of crystal growth (double hetero structure formation, current block layer formation, buried layer formation). . First, as shown in FIG. 4A, the n-type clad layer 2, the active layer 3, and the p-type clad layer 4 are sequentially deposited and grown on the n-type substrate 1 by the first crystal growth. Next, as shown in FIG. 4B, the p-type cladding layer 4 is etched by using a photolithography technique to form a ridge portion 4a. Next, as shown in FIG. 4C, the n-type current blocking layer 8 is formed by the second crystal growth. Next, as shown in FIG. 4D, the p-type buried layer 16 is formed by the third crystal growth, and the p-type buried layer 16 is further formed.
The mold contact layer 7 is formed. Finally, as shown in FIG. 4E, a p-side ohmic contact electrode 13 is formed on the p-type contact layer 7, and an n-side ohmic contact electrode 12 is formed on the bottom surface of the n-type substrate 1.

Even in the case of the groove type semiconductor laser device shown in FIG. 5, it is necessary to grow the crystal twice (double hetero structure formation, buried layer formation). First, as shown in FIG. 5A, the n-type cladding layer 2, the active layer 3, the p-type cladding layer 4, and the n-type current blocking layer 8 are sequentially formed on the n-type substrate 1 by the first crystal growth. Deposit and grow. Next in FIG.
As shown in (b), using photolithography technology,
The groove 8a is formed by etching the n-type current block layer 8. Next, as shown in FIG. 5C, the p-type buried layer 16 is formed by the second crystal growth, and the p-type contact layer 7 is further formed. Finally, as shown in FIG. 5D, p
The side ohmic contact electrode 13 and the n-side ohmic contact electrode 12 are formed.

Such crystal growth a plurality of times has been a major obstacle to reducing the manufacturing cost of laser chips. Therefore, as a method of producing a semiconductor laser device by one-time crystal growth by omitting embedded crystal growth, a ridge-type waveguide structure is formed, and current confinement and light are generated by a dielectric film such as SiO ₂ or Si ₃ N _4. A device for confining a laser has been developed and produced (for example, J. Hashimoto et. Al., IEEE J. Quantum
Electron, vol. 33, pp. 66-70, 1997). An example thereof is shown in FIG. First, as shown in FIG. 6A, an n-type cladding layer 2, an active layer 3, a p-type cladding layer 4, and a p-type contact layer 7 are sequentially deposited on the n-type substrate 1 by the first crystal growth. Grow and form a double heterostructure. Next, as shown in FIG. 6B, the p-type contact layer 7 and the p-type cladding layer 4 are etched by using a photolithography technique to form a ridge portion 4b. Next in FIG.
As shown in (c), an insulating film (dielectric film) 11 is formed, and a resist mask 11a is further patterned. Next, as shown in FIG. 6D, the insulating film (dielectric film) 11 is etched using the resist mask 11a to expose the p-type contact layer 7. Finally, as shown in FIG. 6E, a p-side ohmic contact electrode 13 and an n-side ohmic contact electrode 12 are formed.

Similar ridge type semiconductor lasers are disclosed in Japanese Patent Laid-Open Nos. 63-90879 and 5-327113.
Japanese Patent Laid-Open No. 12-164986. Most of these adopt the ridge portion formation method by regrowth (selective growth), and in terms of manufacturing cost, FIG.
It is expected to be higher than the configuration shown in. On the other hand, in common with these configurations, in addition to the fact that the buried growth can be omitted in the ridge type semiconductor laser, the contact layer is formed on the uppermost layer of the ridge portion, and the electrode is directly formed without forming the insulating film on the contact layer. The point is that the contact is formed by doing so. Therefore, the contact layer is limited to a narrow region above the ridge, and the contact area is narrowed, so that an increase in device resistance becomes a serious problem. As shown in FIGS. 4 and 5, in the semiconductor laser of the conventional structure in which the buried growth is performed, the contact layer can be formed over a wide area on the device surface, so that the contact area with the electrode can be widened and the contact resistance does not increase. .

FIG. 7 shows a manufacturing method for forming a ridge portion by selective growth using an insulating film as a mask. First, Fig. 7
As shown in (a), the n-type substrate 1 is formed by the first crystal growth.
An n-type clad layer 2, an active layer 3, and a p-type clad layer 4 are sequentially deposited and grown thereon, and an antioxidant layer 70 is further laminated. Next, as shown in FIG. 7B, a protective film 71, which is an insulating layer, is deposited, and the protective film 71 in the outer region is removed by using a photolithography technique.
The n-type current blocking layer 8 is formed by the selective growth of the second time. Further, as shown in FIG. 7C, a p-type second cladding layer 72 is formed by a second selective growth after forming an opening for forming a ridge in the central portion of the protective film 71 by using a photolithography technique. The p-type contact layer 73 is sequentially deposited and grown. Finally, as shown in FIG. 7D, a p-side ohmic contact electrode 13 and an n-side ohmic contact electrode 12 are formed.

In this method, since no insulating film exists near the contact layer, the contact can be formed by directly forming the electrode after the selective growth (contact layer formation) as shown in FIG. 7D. However, FIG.
As shown in (d), the crystal growth is required a plurality of times, so that there is a problem that the manufacturing cost becomes high.

On the other hand, when the ridge portion is formed by selective etching as shown in FIG. 6, it is necessary to open the insulating film on the contact layer because the insulating film is formed after the ridge is formed.

In Japanese Patent Laid-Open No. 4-329688, in order to manufacture a ridge type semiconductor laser in which a current is confined by a dielectric film, a ridge type semiconductor laser in which buried crystal growth is omitted is formed by lift-off to form a pattern of an insulating film. An example of doing is disclosed. This example is shown in FIG. First, FIG.
As shown in FIG. 8A, after forming a double hetero structure, a resist mask 80 is formed and etching is performed to form a resist mask 80, as shown in FIG.
A ridge portion is formed as shown in FIG. Next, leaving the resist mask 80 having an eaves, an insulating film (dielectric film) 11 is formed by a sputtering method as shown in FIG. 8C. Next, as shown in FIG. 8D, the resist mask 8
The insulating film 11 on the ridge is lifted off together with 0 to form a current injection portion of the ridge portion. Finally Figure 7
Electrodes are formed as shown in FIG.

This method has a problem that the size of the eaves of the resist mask 80 greatly affects the shape of the insulating film on the ridge slope. If the eaves are large, it is difficult to form the insulating film on the slope of the ridge portion. Therefore, it is desirable that the eaves are not formed on the contact layer after the formation of the ridge portion. Therefore, FIG.
As shown in (a), it has a ridge shape similar to that produced by selective growth, and it is theoretically difficult to increase the surface area of the contact layer by forming an eave.

Further, as a known method for selectively removing the insulating film on the ridge, there is an etchback method by dry etching. For example, after forming the ridge portion, an insulating film is formed on the entire surface, a resist is applied so that the upper portion of the ridge becomes thinnest, and the resist is etched by O ₂ plasma treatment, so that the thinnest resist on the upper surface of the ridge portion is completely etched. After that, the insulating film is selectively etched. In this case, the insulating film on the ridge portion can be selectively removed, but it is considered that there are problems in process complexity, cost increase, and stability of in-plane distribution. Further, in principle, this method only removes the insulating film on the surface of the contact layer as shown in FIG. 9B, and a sufficient contact area cannot be obtained, and it is considered difficult to significantly reduce the element resistance. .

[0013]

As described above, in the ridge type semiconductor laser in which the embedded growth is omitted, the ridge portion is not affected by the selective growth method or the selective etching method. In this structure, the part directly contacts the electrode. In particular, in the selective etching method, it is not easy to accurately manufacture the size and position of the contact window portion, so that the increase and variation of the contact resistance and thus the element resistance become a problem.

In a low-cost ridge type semiconductor laser device (hereinafter referred to as a low-cost laser) in which crystal growth is performed once as shown in FIG. 6D, a selective etching method is indispensable for forming a ridge portion. The configuration requires a step of selectively removing the insulating film on the contact layer surface of the ridge portion. Since the buried layer is not grown, the surface area of the contact layer is reduced, and in general, the size and position accuracy of the contact window are not sufficiently high as described above, so that the contact area with the electrode cannot be large. Therefore, it was more difficult to reduce the contact resistance as compared with the case of the selective growth method.

The present invention provides a structure of a ridge type semiconductor laser which can be manufactured at a low cost by one crystal growth process at a low cost, and as a result, a semiconductor laser structure which can reduce the element resistance, and a manufacturing method thereof. To aim.

[0016]

A semiconductor laser according to the present invention is a semiconductor laser having a refractive index guided ridge structure including a laminate of a plurality of compound semiconductor layers, an upper electrode and a lower electrode. The second semiconductor layer located under the contact layer and in contact with the contact layer has a top surface that is narrower than a bottom surface of the contact layer. The upper electrode is in direct contact with the surface of the contact layer in the ridge, and at least one of the side surfaces and the bottom of the contact layer, and the other surface of the ridge is covered with an insulating film.

With the above structure, not only the surface of the contact layer but also both side surfaces or the bottom surface of the contact layer contacts the upper electrode, so that the contact area is increased and the contact resistance is reduced. Moreover, since the electrode does not directly contact the second semiconductor layer (clad layer) which is generally a high Al composition,
Problems such as electrode peeling do not occur. Further, the contact layer is preferably a semiconductor layer having a low Al composition (Al composition <20%) such as GaAs in order to suppress electrode peeling.

Further, as in the above structure, by narrowing the width of the lower layer of the contact layer so that the contact layer becomes the eaves, the surface area of the contact layer is increased and the contact area with the upper electrode is further increased. Further, the contact resistance can be further reduced.

However, if the eaves are too large, the eaves will be damaged during the diffusion process. Therefore, the thickness of the contact layer is d, the bottom width of the contact layer in the direction perpendicular to the stripe direction is A, and the bottom width is A. Assuming that the upper surface width of the two semiconductor layers in the direction perpendicular to the stripe direction is B, 0.1 <d <1.
0 μm, (A−B) / B <2, 0.5 μm <A <10 μ
It is desirable that it is m.

Instead of the above structure, the uppermost layer of the ridge portion is a contact layer made of a highly-doped compound semiconductor layer, and the upper electrode is directly attached to the surface and both side surfaces of the contact layer of the ridge portion. It may be in contact with each other, and the other surface of the ridge portion may be covered with an insulating film.

According to the method of manufacturing a semiconductor laser of the present invention, a double hetero structure in which an active layer is sandwiched by a clad layer having a band gap larger than that of the active layer on an n-type semiconductor substrate, and a highly-doped p-type contact is formed. A layer and an n-type or undoped semiconductor layer in this order, a step of removing a part or all of the n-type or undoped semiconductor layer, and a step of removing a part of the p-type contact layer and the clad layer from each other. a step of selectively removing the p-type contact layer so as to form an eaves; a step of coating the surface of the wafer with an insulating film; a step of forming a resist so that the surface of the p-type contact layer has an opening; And a step of selectively removing the insulating film with the mask as a mask, and a step of forming an electrode by coating the surface of the wafer with a metal electrode.

The eaves of the contact layer (high concentration layer) can be easily realized by forming the ridge portion by etching as in this method, and it is difficult to realize by the selective growth method.

As a method of reducing the element resistance, activation of Zn dopant in the p-type semiconductor layer is effective. This phenomenon is particularly remarkable in the P-based semiconductor layer used in the AlGaInP-based red semiconductor laser or the like. To activate the Zn dopant, heat treatment is performed after the formation of the p-type semiconductor layer, or as in the method of the present invention, after the heavily-doped p-type contact layer is grown, an n-type or undoped semiconductor layer is formed to have a specific thickness. It is effective to form (about 0.3 μm or more).

FIG. 10 shows the relationship between the n-type or undoped semiconductor layer film thickness d and the activation rate of the Zn dopant in the AlGaInP-based red semiconductor laser. Figure 10
In the layer structure shown in (b), when the film thickness of the n-type (or undoped) semiconductor layer is d, as shown in FIG. 10 (a), d> 3000Å (0.3 μm) and the p-type clad layer It can be seen that the activation rate of the Zn dopant becomes sufficiently high.

In a semiconductor laser that performs buried growth, Zn can be activated during the buried growth, but since the low-cost laser of the present invention does not perform buried growth, Z
The above-mentioned method is effective for activating n. In a semiconductor laser, an n-type substrate is generally used, so that the contact layer is a p-type layer, and the above contents can be applied. That is, the contact resistance and the element resistance can be reduced by preliminarily forming an n-type or undoped semiconductor layer on the contact layer during crystal growth and selectively removing it.

On the other hand, even if the method of forming the ridge portion by selective growth is adopted, there are many problems in the following points. (1) Since the contact layer is crystal-grown following the lower layer,
As shown in (a), the contact layer has a shape without eaves, and the contact surface with the electrode is limited only to the upper surface and the side surface of the contact layer. (2) Since the electrode also contacts the clad layer having a high Al composition in the lower layer of the contact layer (Al composition> 0.5), the electrode may be peeled off. (3) When a semiconductor layer is further formed on the contact layer, it is very difficult to selectively remove it, and thus it is difficult to activate the Zn dopant as in the present invention.

The doping concentration of the contact layer (high concentration layer) is preferably 5 × 10 ¹⁸ cm ^-3 or more and 5 × 10 ¹⁹ cm ^-3 or less. The higher the doping concentration is, the more preferable it is. However, the high concentration doping requires lowering the crystal growth temperature, and the crystallinity is lowered by the lowering of the crystal growth temperature.

The thicker the contact layer, the larger the surface area of the contact layer and the larger the contact area, which is desirable. However, if the thickness is too large, the height of the ridge portion becomes high, and the ridge portion is likely to receive stress during assembly with the ridge portion side as a bonding surface, which may lead to deterioration of element characteristics. Further, when the contact layer is thin, the surface area of the high-concentration layer decreases, and when the eaves of the contact layer are large, the eaves may break during the process, and the contact layer area may decrease. This is greatly affected by the stripe width setting of the device. Considering the above reasons, the thickness of the contact layer is preferably 0.3 to 1.0 μm.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIG.

(First Embodiment) FIG. 1 shows a structure of a semiconductor laser device and a manufacturing method thereof according to the first embodiment. The first embodiment is an example in which the present invention is applied to a ridge type semiconductor laser device using an AlGaAs material.

First, as shown in FIG. 1A, n-GaA
The s substrate 101 is installed in a crystal growth apparatus (not shown),
On n-GaAs substrate 101 by the first round of crystal growth, n-AlGaAs cladding layer 102 (n-Al _0.5
Ga _0.5 As, carrier concentration 1E18 cm ^-3 , thickness 1.
0 μm), non-doped quantum well active layer 103, p-Al
GaAs first cladding layer 104 (p-Al _0.5 Ga _0.5 A
s, carrier concentration 1E18 cm ^-3 , thickness 0.2 μm),
p-AlGaAs etching stop layer 105 (p-A
l _0.20 Ga _0.80 As, carrier concentration 1E18 cm ⁻³ , thickness 100 Å), p-AlGaAs second cladding layer 106
(P-Al _0.5 Ga _0.5 As, carrier concentration 1E18 cm
^-3 , thickness 1 μm), p-GaAs contact layer 107
(P-GaAs, carrier concentration 2E19 cm ⁻³ , thickness 0.4 μm), n-AlGaAs current blocking layer 108
(N-Al _0.5 Ga _0.5 As, carrier concentration 1E18 cm
^-3 , thickness 0.1 μm) and n-GaAs protective layer 109
(Carrier concentration 1E18 cm ⁻³ , thickness 0.4 μm) are sequentially deposited and grown.

The active layer 103, Al _0.07 Ga _0.93 As well layer (thickness _{65Å), Al 0.3 Ga 0 .7} As barrier layers (thickness 50 Å) and triple quantum consisting guide layer of the same composition (thickness 550 Å) It is a well structure.

Next, n-G having the above-mentioned semiconductor layer is formed.
The aAs substrate 101 is taken out from the growth apparatus, and a known selective etching technique is used, as shown in FIG.
N-A so as to reach the -GaAs contact layer 107
The 1GaAs current blocking layer 108 and the n-GaAs protective layer 109 are etched. In addition, in FIG.
An example is shown in which the AlGaAs current blocking layer 108 and the n-GaAs protective layer 109 are all removed.

Next, as shown in FIG. 1B, a p-GaAs contact layer 1 is formed by using a known photolithography technique.
A stripe-shaped SiO ₂ mask 110 is formed on 07. Using this SiO ₂ mask 110 as an etching mask, a known selective etching technique is used, and the structure shown in FIG.
As shown in FIG. 2, the p-GaAs contact layer 10 is reached until the p-AlGaAs etching stop layer 105 is reached.
7 and the p-AlGaAs second cladding layer 106 are processed into a ridge shape.

In this embodiment, hydrofluoric acid is used as the selective etching solution for the AlGaAs layer, and a solution obtained by adding hydrogen peroxide solution to ammonia water is used as the selective etching solution for the GaAs layer. The width of the bottom of the ridge (stripe width)
Was 1 to 4 μm.

Thereafter, as shown in FIG. 1D, a SiO ₂ insulating film 111 is formed on the surface of the wafer, and the opening portion of the resist mask 114 is formed by using a stepper exposure method which is a known high precision photolithography technique. It is formed on the p-type contact layer 107. Next, as shown in FIG.
SiO ₂ insulating film 1 on the p-GaAs contact layer 107
11 (thickness 0.1 to 0.3 μm) is removed by wet etching with hydrofluoric acid. Finally, Fig. 1 (f)
, The p-side ohmic electrode 113 is formed on the upper surface of the p-GaAs contact layer 107 side, and the n-GaAs substrate 1 is formed.
The n-side ohmic electrode 112 is formed on the lower surface of 01, the cavity length is adjusted to 200 μm by the cleavage method, and a coating film having a reflectance of 30% is provided on the emission side end face and a reflectance of 50% is provided on the opposite side end face. Formed (not shown).

An enlarged cross section of the ridge portion in the ridge type semiconductor laser device manufactured as described above is shown in FIG.
Shown in (b) and (c). 2 (b) and 2 (c) are shown in FIG.
It is the figure which expanded and showed the area | region of the ridge part A shown with a circle in (a).

In the case of the element of the present embodiment, when forming the ridge portion, a hydrofluoric acid-based anisotropic etching solution was used to form the ridge portion on the GaAs substrate having the (100) plane as the main surface. By etching the AlGaAs layer in a stripe shape in the <011> direction, the forward mesa structure shown in FIG. 2C is obtained. By rotating the stripe direction by 90 °, the inverted mesa structure shown in FIG. 2B is obtained. Since the etching rate of the hydrofluoric acid-based etching solution is sufficiently smaller than that of the (100) plane, the side surface of the ridge portion is formed of the (111) crystal plane.

In the case of the conventional example shown in FIG. 9B, that is, in the case of a ridge type semiconductor laser in which only the surface of the high concentration layer is opened and the doping concentration of the p type contact layer 7 is 5E18 cm ⁻³ , the p side ohmic electrode is formed. Device resistance when assembled on a SiC submount with 13 as the bonding surface is
It was about 30Ω. On the other hand, in the case of the ridge type semiconductor laser according to the present embodiment shown in FIG. 2, in addition to the surface of the high concentration layer, the SiO ₂ insulating film 111 on the side surface is also removed to increase the contact area with the electrode. The doping concentration of the mold contact layer 107 is set to 2E19 cm ^-3 . as a result,
When the ridge-type semiconductor laser device having the forward mesa structure shown in FIG. 2C is assembled in the same manner as above, the device resistance is about 8
It was Ω. The width of the upper surface of the high concentration layer of the device in this case was about 1 μm.

As a method of lowering the element resistance value, as shown in FIG. 2B, the ridge portion A may be formed into an inverted mesa shape. From the geometrical calculation, the area of the upper portion of the ridge A is about 2 to 3 times that of the forward mesa structure in the reverse mesa structure (ridge height = 1.0 μm, stripe width = 3 to 5 μm).
In this case), the contact area with the electrode is increased by the inverted mesa structure, so that the contact resistance is reduced, and as a result, the series resistance value of the element can be reduced.

In the first embodiment, the case where the present invention is applied to a low-power semiconductor laser device used for reading a CD or the like has been described. However, the present invention is directed to AlGaInP.
The same can be applied to a red semiconductor laser of a system, a high-power semiconductor laser element used for recording and reproduction, and a self-excited oscillation type semiconductor laser.

In the conventional structure shown in FIG. 6, the p-type contact layer 7 is the final layer of crystal growth, and the Zn dopant is inactivated by atomic hydrogen (edited by Isamu Akasaki,
III-V group compound semiconductor, Baifukan, pp.312-313) occurred, and there was also a problem that the element resistance became high. On the other hand, in the structure of the present embodiment shown in FIG. 1, since the n-type semiconductor layer is grown on the p-type contact layer 107, there is also an advantage that inactivation due to hydrogen can be suppressed. Zn activation is A
Although it is not remarkable in the 1GaAs-based semiconductor laser, it is particularly remarkable in the case of the AlGaInP-based red semiconductor laser.

(Second Embodiment) FIG. 3 shows the structure of a semiconductor laser device according to the second embodiment. FIG. 3B is an enlarged view of a region of the ridge portion B indicated by a circle in FIG. In the second embodiment, the etching of the ridge portion is performed by using a solution obtained by adding hydrogen peroxide solution to tartaric acid instead of a solution obtained by adding hydrogen peroxide solution to hydrofluoric acid and ammonia water (mixing ratio is tartaric acid: peroxide). Hydrogen water = 5: 1 (volume ratio)). Other than that, the configuration is the same as that of the first embodiment. The etching stop layer 105 has a high A
It is preferable to use an AlGaAs layer having an l composition (Al composition> 0.7) or a P-based semiconductor layer.

By the above etching, as shown in FIG. 3B, the eaves of the high-concentration contact layer are eliminated in the ridge portion, and the ridge shape is similar to that in the case of selective growth. The solution obtained by adding hydrogen peroxide solution to the tartaric acid is
This is because there is no selectivity between the GaAs layer and the AlGaAs layer (Al composition <0.6), and both are etched.

Also in the second embodiment, high precision mask alignment (pattern alignment precision of 0.1 μm) by the stepper is performed.
m or less) and selective etching, the same shape of the SiO ₂ insulating film 111 as that of the first embodiment as shown in FIG. 3 is obtained. Thereby, the p-type second clad layer 10 having a high Al composition
6 The electrode is not brought into contact with the surface, and the electrode is brought into contact with the surface and the side surface of the highly-doped p-type contact layer 107, whereby there is no electrode peeling and the effect of reducing the contact resistance can be obtained.

[0046]

The ridge type semiconductor laser of the present invention can be manufactured at a low cost by performing the crystal growth once, and the contact resistance is reduced, and as a result, the element resistance is reduced.

Further, according to the manufacturing method of the present invention, the p-type impurity Zn can be sufficiently activated by one crystal growth, and the element resistance can be easily reduced even though the buried growth is not performed. . The activation of Zn by the manufacturing method of the present invention is more remarkable in the P-based semiconductor material represented by the red semiconductor laser.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a ridge type semiconductor laser and a manufacturing method thereof according to a first embodiment of the present invention.

2 is an enlarged sectional view showing a ridge portion in the semiconductor laser of FIG.

FIG. 3 is a sectional view of a ridge type semiconductor laser according to a second embodiment of the present invention.

FIG. 4 is a sectional view showing a structure of a conventional ridge type semiconductor laser and a manufacturing method thereof.

FIG. 5 is a cross-sectional view showing a structure of a conventional groove type semiconductor laser and a manufacturing method thereof.

FIG. 6 is a cross-sectional view showing the structure of another conventional ridge type semiconductor laser and a manufacturing method thereof.

FIG. 7 is a sectional view showing the structure of still another conventional ridge type semiconductor laser and a method for manufacturing the same.

FIG. 8 is a sectional view showing the structure of still another conventional ridge type semiconductor laser and a method for manufacturing the same.

FIG. 9 is an enlarged sectional view showing a ridge portion in a conventional ridge type semiconductor laser.

FIG. 10A is a graph showing the relationship between the n-type or undoped semiconductor layer film thickness d and the activation rate of Zn dopant in an AlGaInP-based red semiconductor laser;
(B) is a sectional view showing the layer structure of the semiconductor laser used for obtaining the graph of (a)

[Explanation of symbols]

1 n-type semiconductor substrate 2 n-type clad layer 3 active layer 4 p-type first clad layer 5 p-type etching stop layer 6 p-type second clad layer 7 p-type contact layer 8 n-type current block layer 9 n-type protective layer 10 SiO ₂ mask 11 insulating film (dielectric film) 12 n-side ohmic contact electrode 13 p-side ohmic contact electrode 101 n-GaAs substrate 102 n-AlGaAs clad layer 103 active layer 104 p-AlGaAs first clad layer 105 p-AlGaAs etching Stop layer 106 p-AlGaAs second cladding layer 107 p-GaAs contact layer 110 SiO ₂ mask 111 SiO ₂ insulating film 112 n-side ohmic electrode 113 p-side ohmic electrode 114 resist mask

Continued front page    (72) Inventor Toshiya Kawada             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Hiroshi Asaka             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Akira Takamori             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F-term (reference) 5F073 AA13 AA53 AA74 AA83 BA02                       BA06 CA05 CB02 DA22 DA33                       FA15

Claims (9)

[Claims] 1. In a semiconductor laser having a refractive index guided ridge structure including a stack of a plurality of compound semiconductor layers, an upper electrode and a lower electrode, a compound in which an uppermost layer of a ridge portion is heavily doped. The second semiconductor layer, which is a contact layer made of a semiconductor layer and is in contact with the contact layer below the contact layer, has an upper surface whose width is narrower than that of the bottom surface of the contact layer, and the contact in the ridge portion. The semiconductor laser, wherein the upper electrode is in direct contact with the surface of the layer and at least one of both side surfaces and the bottom surface of the layer, and the other surface of the ridge portion is covered with an insulating film. 2. A semiconductor laser having a refractive index guided ridge structure, comprising a stacked body of a plurality of compound semiconductor layers, an upper electrode and a lower electrode, wherein the uppermost layer of the ridge portion is highly doped. A contact layer formed of a semiconductor layer, wherein the upper electrode is in direct contact with the surface of the contact layer of the ridge portion and both side surfaces thereof, and the other surface of the ridge portion is covered with an insulating film. And a semiconductor laser. 3. The thickness of the contact layer is d, the bottom width of the contact layer in the direction perpendicular to the stripe direction is A,
When the upper surface width of the second semiconductor layer in the direction perpendicular to the stripe direction is B, 0.1 <d <1.0 μm, (A−
2. The semiconductor laser according to claim 1, wherein B) / B <2 and 0.5 μm <A <10 μm. 4. The doping concentration of the contact layer is
4. The semiconductor laser according to claim 1, wherein the semiconductor laser has a size of 5 × 10 ¹⁸ cm ⁻³ or more and 5 × 10 ¹⁹ cm ⁻³ or less. 5. The insulating layer comprises SiO ₂ , SiNx, S
5. The semiconductor according to claim 1, wherein the semiconductor is formed of a single layer of any one of iON, Al ₂ O ₃ , ZnO, SiC, and amorphous Si, or a plurality of layers thereof. laser. 6. The method of manufacturing a semiconductor laser according to claim 2, wherein a double hetero structure in which an active layer is sandwiched by a clad layer having a band gap larger than that of the active layer on an n-type semiconductor substrate. A step of stacking a heavily doped p-type contact layer and an n-type or undoped semiconductor layer in this order, a step of removing a part or all of the n-type or undoped semiconductor layer, A step of selectively removing a part of the clad layer so that the p-type contact layer becomes an eaves step, a step of coating a wafer surface with an insulating film, and a resist having an opening on the p-type contact layer surface. Forming step, a step of selectively removing the insulating film using the resist as a mask, and a step of forming an electrode by coating the wafer surface with a metal electrode. A method for manufacturing a semiconductor laser, comprising: 7. The film thickness of the contact layer is d, and the bottom width of the contact layer in the direction perpendicular to the stripe direction is A.
When the upper surface width of the lower layer of the contact layer in the direction perpendicular to the stripe direction is B, 0.1 <d <1.0 μm,
7. The method of manufacturing a semiconductor laser according to claim 6, wherein (AB) / B <2 and 0.5 [mu] m <A <10 [mu] m. 8. The doping concentration of the contact layer is
^{8. The} method for manufacturing a semiconductor laser according to claim 6, wherein it is 5 × 10 ¹⁸ cm ⁻³ or more and 5 × 10 ¹⁹ cm ⁻³ or less. 9. The insulating layer comprises SiO ₂ , SiNx, S
9. The semiconductor according to claim 6, wherein the semiconductor is formed of a single layer of iON, Al ₂ O ₃ , ZnO, SiC, or amorphous Si, or a plurality of layers thereof. Laser manufacturing method.