JP2000307192A - Ridge waveguide semiconductor laser and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To turn a clad layer which contains Al into a high-resistance layer by oxidation so as to control a current path by a method wherein the clad layer that contains Al is thermally treated in an atmosphere of oxygen or water vapor. SOLUTION: An InAlGaAs lower clad layer 2, an AlGaInAs MQW active layer 3, an InAlAs upper clad layer 4, an InP upper clad layer 5, and an InGaAs contact layer 6 are successively grown in crystal on an InP substrate 1. The Al compound upper clad layer 4 is exposed by selective etching and thermally treated, by which the upper clad layer 4 is oxidized to turn the oxidized part of the upper clad layer 4 of high resistance, and a high-resistance layer is formed. Therefore, a current path is controlled as mentioned above, by which a semiconductor laser can be lessened in threshold current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser,
In particular, the present invention relates to a structure and a manufacturing method of a ridge waveguide type semiconductor laser.

[0002]

2. Description of the Related Art Hitherto, it has been considered that a ridge waveguide type semiconductor laser is incompletely confined in the lateral direction of an active layer due to its structure, and cannot effectively supply carriers required for oscillation. For this reason, a structure is known in which a current constriction function is provided and a current path is controlled by ion-implanting a portion other than the ridge waveguide portion of the ridge waveguide type semiconductor laser. Such a method is disclosed in, for example,
-222800.

[0003]

However, in the apparatus for fabricating the above-described structure, an expensive ion implantation apparatus is required to perform ion implantation on portions other than the ridge waveguide portion, and the manufacturing cost increases. There was a problem.

[0004]

SUMMARY OF THE INVENTION Accordingly, the present invention is directed to a first aspect of the present invention for solving the problems described above.
In the embodiment, a cladding layer of an Al compound is used for the cladding layer in the ridge waveguide type semiconductor laser. next,
By heat-treating the Al-containing clad layer in oxygen or water vapor, the Al-containing clad layer is oxidized to obtain a high-resistance layer, thereby controlling the current path.

In the second embodiment of the present invention, the contact layer and the upper clad layer are etched into a ridge waveguide type until the active layer is exposed. Then, the exposed portion of the active layer and the exposed side wall portions of the contact layer and the upper clad layer are oxidized by plasma oxidation using oxygen gas, and a current path is controlled by obtaining a high-resistance layer.

In the third embodiment of the present invention, the contact layer and the upper clad layer are etched into a ridge waveguide type until the active layer is exposed. Next, in a solution using ethylene glycol liquid as a solvent and tartaric acid as a solute, a platinum electrode is formed on the positive electrode side, and a ridge waveguide type etching substrate is formed on the negative electrode side. Apply current. Then, an oxide film can be formed on the processing substrate. Therefore, a high resistance layer is formed on the processing substrate, and the current path can be controlled.

[0007] By controlling the current path as described above, an expensive ion implantation apparatus for performing ion implantation becomes unnecessary, and the effect of reducing the manufacturing cost can be obtained. Further, in a range other than the light emitting region of the MQW active layer,
Since the current injection is reduced, the threshold current of the ridge waveguide type semiconductor laser can be reduced.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. First, a first embodiment will be described. FIG. 1 is a cross-sectional view illustrating the structure of the laser device according to the first embodiment. Hereinafter, a manufacturing process of the laser device according to the first embodiment will be described with reference to FIGS.

First, a metal organic chemical vapor deposition (hereinafter referred to as MOCVD: Me) is performed on an InP substrate 1 having a (100) plane as a surface.
tal Organic Chemical Vap
rDeposition) method, InAlGaAs
Lower cladding layer 2, AlGaInAs MQW active layer 3,
InAlAs upper cladding layer 4, InP upper cladding layer 5, and InGaAs contact layer 6 are sequentially crystal-grown.
(FIG. 4-a).

Next, S is formed on the InGaAs contact layer 6.
An iO ₂ film 31 is formed. Next, the SiO ₂ film 31 is processed and formed into a stripe shape using photolithography (FIG. 4B). At this time, the direction of the stripe is (11
0) The plane direction. Using this SiO ₂ film 31 as an etching mask, In
The GaAs contact layer 6 is selectively removed by etching.
(FIG. 4-c). This sulfuric acid-based etchant is made of InGaAs.
s can be etched. However, a sulfuric acid-based etchant can hardly etch InP.
That is, the InP upper cladding layer 5 is hardly etched.

Next, the InP upper cladding layer 5 is etched using a mixed solution of aqueous hydrogen bromide and phosphoric acid as an etching solution. As a result, the InP upper cladding layer 5 is etched in the reverse mesa shape (111) A plane direction. Then, an inverted mesa ridge waveguide portion 7 having the (111) A plane on the side wall can be formed (FIG. 4D). This mixed solution of hydrogen bromide and phosphoric acid etches InP, but the InGaAs and I
Do not etch nAlAs. That is, the etching stops when the InAlAs upper cladding layer 4 is exposed by the etching. Therefore, an inverted mesa ridge waveguide structure can be formed with good control.

Next, heat treatment is performed for 10 minutes to several hours in an electric furnace in an oxygen atmosphere or a steam atmosphere. Here, a preferable heat treatment temperature is 300 ° C to 500 ° C.
Then, the InAl exposed by the previous etching
The As upper cladding layer 4 is oxidized. The oxidation is Al
It extends to a part of the GaInAs MQW active layer 3. Here, current hardly flows through the oxidized portion, that is, the oxidized portion has a high resistance. Accordingly, the high resistance layer 8 can be formed on a part of the InAlAs upper cladding layer 4 and the AlGaInAs MQW active layer 3 (FIG. 4E).

Next, the SiO 2 on the inverted mesa ridge waveguide 7 is
_{2 The} film 31 is removed. Next, a new SiO ₂ film 32 is applied to the entire surface. Next, polyimide 11 is applied so as to bury the side surfaces of the inverted mesa ridge waveguide portion 7. next,
The polyimide 11 on the portion corresponding to the upper surface of the reverse mesa ridge waveguide portion 7 is removed by photolithography. Next, only the SiO ₂ film 32 on the InGaAs contact layer 6 is removed by etching (FIG. 4F). Next, the ohmic electrode 12 is formed larger than the upper surface of the inverted mesa ridge waveguide portion 7 by a known method. The ohmic electrode 12 is formed on the SiO ₂ film 3 on the InGaAs contact layer 6.
It may be formed on the entire upper surface of the substrate after only 2 is removed by etching.

Next, the substrate after the formation of the ohmic electrode 12 is cleaved into a laser element having a desired size.
Next, when a current is injected into the ohmic electrode 12, a current is injected into the inverted mesa ridge waveguide portion 7. Next, a current is injected from the reverse mesa ridge waveguide portion 7 into the InAlAs upper cladding layer 4. At this time, InAl formed by thermal oxidation
No current is injected into the As oxide region. Therefore, I
The threshold current can be reduced by suppressing the current to the area other than the light emitting region of the nAlGaAs MQW active layer 3.

In the first embodiment, the upper cladding layer has
In the laser device using the upper cladding layer of the l-compound, the upper cladding layer of the Al compound is exposed by selective etching, and heat treatment is performed. Then, the upper cladding layer of the Al compound is oxidized, and the oxidized portion has a high resistance. Therefore, a high resistance layer can be formed. By controlling the current path in this way, the threshold current of the semiconductor laser can be reduced.

Next, a second embodiment will be described. In the second embodiment, an embodiment will be described in which an oxide layer is formed by plasma oxidation using an oxygen gas so that a high-resistance layer can be easily formed even if the clad layer does not contain Al.

FIG. 2 is a sectional view showing the structure of the laser device according to the second embodiment. Hereinafter, a manufacturing process of the laser device according to the second embodiment will be described with reference to FIGS.

First, an InP lower cladding layer 9, an InGaAs PMQW active layer 10, an InP upper cladding layer 5, and an InGaAs contact layer 6 are sequentially crystal-grown on an InP substrate 1 having a (100) plane on the surface by MOCVD. (FIG. 5-a).

Next, S is deposited on the InGaAs contact layer 6.
An iO ₂ film 41 is formed. Next, the SiO ₂ film 41 is processed and formed into a stripe shape using photolithography (FIG. 5B). At this time, the direction of the stripe is (110)
It is a plane direction. Using this SiO ₂ film 41 as an etching mask, a sulfuric acid-based etchant is used to form InGaAs.
The s-contact layer 6 is selectively removed by etching (FIG.
-C). This sulfuric acid-based etchant can etch InGaAs. However, a sulfuric acid-based etchant can hardly etch InP. That is, the InP upper cladding layer 5 is hardly etched.

Next, the InP upper cladding layer 5 is etched using a mixed solution of hydrogen bromide and phosphoric acid as an etching solution. As a result, the InP upper cladding layer 5 is etched in the reverse mesa shape (111) A plane direction. Then (1
11) The inverted mesa ridge waveguide portion 7 having the side A on the side wall can be formed (FIG. 5D). This mixed solution of hydrogen bromide and phosphoric acid etches InP, but the InGaAs and InP
GaAsP is not etched. That is, the etching stops when the InGaAsPMQW layer 10 is exposed by the etching. Therefore, an inverted mesa ridge waveguide structure can be formed with good control.

Next, oxidation is performed by plasma using oxygen gas using an apparatus used for ordinary plasma CVD or the like (FIG. 5E). The SiO ₂ film 41 used for etching is
Since it remains on the upper portion of the inverted mesa ridge waveguide portion 7, only the side surface of the inverted mesa ridge waveguide portion 7 and the exposed portion of the InGaAs PMQW active layer 10 can be selectively oxidized. Here, current hardly flows through the oxidized portion, that is, the oxidized portion has a high resistance. Therefore, the high resistance layer 8 can be formed on the InAlAs upper cladding layer 4 and a part of the AlGaInAs MQW active layer 3.

Next, a polyimide 11 is applied so as to be embedded in the side surface of the reverse mesa ridge waveguide portion 7. Next, the portion of the polyimide 11 corresponding to the upper surface of the inverted mesa ridge waveguide portion 7 is removed by photolithography. Next, InGa
The SiO ₂ film 41 on the As contact layer 6 is removed by etching (FIG. 5F). Next, the ohmic electrode 12 is formed larger than the upper surface of the inverted mesa ridge waveguide portion 7 by a known method. The ohmic electrode 12 is formed of InGa
The SiO ₂ film 41 on the As contact layer 6 may be formed on the entire upper surface of the substrate from which the SiO ₂ film 41 has been removed by etching.

Next, the substrate after the formation of the ohmic electrode 12 is cleaved into a laser element having a desired size. When a current is applied to the ohmic electrode 12, the ohmic electrode 12
A current is further injected into the inverted mesa ridge waveguide portion 7. Next, the InGaAs PMQW active layer 10 is
Current is injected from a portion where the AsPMQW active layer 10 and the reverse mesa portion are in contact. That is, InGaAsPMQW
Since a part of the active layer 10 is oxidized, current hardly flows from a part other than a part in contact with the reverse mesa part. Thus, the current path can be controlled. Therefore, a ridge waveguide type semiconductor laser having a low threshold current can be manufactured.

In the second embodiment, even in the case of a clad layer having a composition not containing Al, an InP upper clad layer is formed in a waveguide having an inverted mesa structure by using an etchant capable of selectively etching the clad layer. it can. Next, a high-resistance layer can be formed by selectively oxidizing the InP upper cladding layer and the InGaAs PMQW active layer by plasma using oxygen gas. By controlling the current path in this way, light emission due to leakage current can be suppressed, and the spread of the emission beam diameter can be suppressed. Further, the threshold current can be reduced.

Next, a third embodiment will be described.
In the third embodiment, an embodiment in which an oxide film can be easily formed at room temperature regardless of the presence or absence of Al in the cladding layer will be described. FIG. 3 is a sectional view showing the structure of the laser device according to the third embodiment. Hereinafter, a manufacturing process of the laser device according to the third embodiment will be described with reference to FIG.

First, an InP lower cladding layer 9, an InGaAs PMQW active layer 10, an InP upper cladding layer 5, and an InGaAs contact layer 6 are sequentially crystal-grown on an InP substrate 1 having a (100) plane on the surface by MOCVD. (FIG. 5-a).

Next, S is formed on the InGaAs contact layer 6.
An iO ₂ film 41 is formed. Next, the SiO ₂ film 41 is processed and formed into a stripe shape using photolithography (FIG. 5B). At this time, the direction of the stripe is (110)
It is a plane direction. This SiO ₂ film 41 is used as an etching mask.

Next, the InG
The aAs contact layer 6 is selectively removed by etching.
(FIG. 5-c). This sulfuric acid-based etchant is made of InGaAs.
s can be etched. However, a sulfuric acid-based etchant can hardly etch InP.
That is, the InP upper cladding layer 5 is hardly etched.

Next, the InP upper cladding layer 5 is etched using a mixed solution of hydrogen bromide and phosphoric acid as an etching solution. The InP upper cladding layer 5 has an inverted mesa shape (11
1) Etching is performed in the A-plane direction. Then (111) A
A reverse mesa ridge waveguide portion 7 having a surface as a side wall can be formed.
(FIG. 5-d). The mixed solution of the hydrogen bromide water and the phosphoric acid is In
Etch P, but with InGaAs and InGaAs
Do not etch P. That is, I
Etching stops when the nGaAs PMQW layer 10 is exposed. Therefore, an inverted mesa ridge waveguide structure can be formed with good control. Here, the substrate formed with the inverted mesa ridge waveguide structure is referred to as a processing substrate 13.

Next, using ethylene glycol solution as a solvent,
In a solution containing tartaric acid as a solute, a platinum electrode is provided on the positive electrode side, and the processing substrate 13 is provided as an electrode on the negative electrode side. In this embodiment, the preferred solution concentration is 1-10%. An oxide film is formed on the processing substrate 13 by applying a current to the positive electrode and the negative electrode. At this time, since the SiO ₂ film 41 used in the previous etching remains on the inverted mesa ridge waveguide, it is not oxidized.
Therefore, the side wall of the inverted mesa ridge waveguide portion 7 and the exposed I
The nGaAs PMQW active layer 10 can be oxidized. here,
Current does not easily flow through the oxidized portion, that is, the oxidized portion has a high resistance. Therefore, the high resistance layer 8 can be formed (FIG. 5-E).

Next, a polyimide 11 is applied so as to be embedded in the side surface of the inverted mesa ridge waveguide portion 7. Next, the polyimide 11 on the reverse mesa ridge waveguide portion 7 is removed by photolithography. Next, the SiO ₂ film 41 on the InGaAs contact layer 6 is removed by etching (FIG. 5F). Next, the ohmic electrode 12 is formed larger than the upper surface of the inverted mesa ridge waveguide portion 7 by a known method. The ohmic electrode 12 may be formed on the entire upper surface of the substrate from which the SiO ₂ film 41 on the InGaAs contact layer 6 has been removed by etching.

Next, the substrate is cleaved into laser elements of a desired size. When a current is applied to the ohmic electrode 12, a current is injected into the InGaAs PMQW active layer 10 only from a portion where the reverse mesa portion and the InGaAs PMQW active layer 10 are in contact. Thus, the current path can be controlled. Therefore, a ridge waveguide type semiconductor laser having a low threshold current can be manufactured.

In the above embodiment, the side surface of the ridge waveguide portion 7 and the exposed portion of the InGaAs PMQW active layer 10 are oxidized to increase the resistance. By controlling the current path in this way, light emission due to leakage current can be suppressed, and the spread of the emission beam diameter can be suppressed. Further, the threshold current can be reduced.

In the second embodiment, an oxide film can be formed even with a device structure having a clad layer of an Al compound. Further, even in the device structure having the cladding layer of the Al compound in the third embodiment, an oxide film can be formed.

In this embodiment, the ridge waveguide portion has been described as having an inverted mesa structure. However, the same effect can be obtained in a forward mesa and a vertical mesa. In this embodiment,
Although the semiconductor substrate has been described as an InP-based semiconductor substrate, GaAs
The same effect can be obtained by using a material such as a system, an InGaP system, or a GaN system. Further, although the MOCVD method is used as the crystal growth method, a crystal growth method for a multilayer structure layer other than the MOCVD method may be used.

[0036]

As described above, according to the first embodiment, in the cladding layer of the Al compound, the cladding layer is formed by selective etching so that the cladding layer of the Al compound is exposed, and heat treatment is performed. Then, the cladding layer of the Al compound is oxidized, and the oxidized portion has a high resistance. Therefore, a high resistance layer can be formed. By controlling the current path in this way, the threshold current of the semiconductor laser can be reduced.

As described above, according to the second embodiment,
Even in the case of a clad layer having a composition not containing Al, by using an etching solution capable of selectively etching, the InP
The upper cladding layer can be formed in a waveguide having an inverted mesa structure. Next, a high-resistance layer can be formed by selectively oxidizing the InP upper cladding layer and the InGaAs PMQW active layer by plasma using oxygen gas. By controlling the current path in this way, light emission due to leakage current can be suppressed, and the spread of the emission beam diameter can be suppressed. Further, the threshold current can be reduced.

As described above, according to the third embodiment,
The side surface of the ridge waveguide and the exposed portion of the InGaAs PMQW active layer are oxidized to increase the resistance. By controlling the current path in this way, light emission due to leakage current can be suppressed, and the spread of the emission beam diameter can be suppressed. Further, the threshold current can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a laser structure according to a first embodiment.

FIG. 2 is a cross-sectional view illustrating a laser structure according to a second embodiment.

FIG. 3 is a cross-sectional view illustrating a laser structure according to a third embodiment.

FIG. 4 is an explanatory diagram showing a manufacturing process of the first embodiment.

FIG. 5 is an explanatory diagram showing a manufacturing process of the second and third embodiments.

[Explanation of symbols]

1: InP substrate 2: InAlGaAs lower cladding layer 3: InAlGaAs MQW active layer 4: InAlAs upper cladding layer 5: InP upper cladding layer 6: InGaAs contact layer 7: reverse mesa ridge waveguide section 8: high resistance layer 9: InP lower cladding layer 10: InGaAs PMQW layer 11: polyimide 12: ohmic electrode 13: processing substrate 31.32.41: SiO ₂ film

Claims (6)

[Claims] 1. A ridge waveguide type semiconductor laser in which at least an active layer, an upper cladding layer and a contact layer are sequentially laminated on a semiconductor substrate, and the upper cladding layer and the contact layer are etched to form a ridge waveguide portion. In the above, an upper clad layer of an Al compound is used for the upper clad layer, and the upper clad layer of the Al compound is heat-treated in oxygen or water vapor to form a high-resistance layer portion in which the upper clad layer of the Al compound is oxidized. A ridge waveguide type semiconductor laser characterized by the above-mentioned. 2. A ridge waveguide type semiconductor laser in which at least an active layer, an upper cladding layer and a contact layer are sequentially laminated on a semiconductor substrate, and the upper cladding layer and the contact layer are etched to form a ridge waveguide portion. In the method, the contact layer and the upper clad layer are etched and formed in a ridge waveguide type until the active layer is exposed, and the exposed portion of the active layer exposed by the etching and the exposure of the upper clad layer exposed by the etching are formed. A ridge waveguide type semiconductor laser characterized in that a portion is oxidized by plasma oxidation using oxygen gas to form a high resistance layer portion. 3. A ridge waveguide type semiconductor laser in which at least an active layer, an upper cladding layer, and a contact layer are sequentially laminated on a semiconductor substrate, and the upper cladding layer and the contact layer are etched to form a ridge waveguide portion. In the above, the contact layer and the upper cladding layer are etched and formed into a ridge waveguide type until the active layer is exposed, and then, in a solution using ethylene glycol solution as a solvent and tartaric acid as a solute, A processing substrate after etching and forming a ridge waveguide type on a platinum electrode and a negative electrode side is installed as an electrode, and a current is applied to the platinum electrode on the positive electrode side and the electrode of the processing substrate on the negative electrode side to perform the processing. A ridge waveguide type semiconductor laser characterized by forming a high resistance layer on a substrate. 4. A ridge waveguide type semiconductor laser in which at least an active layer, an upper cladding layer and a contact layer are sequentially laminated on a semiconductor substrate, and the upper cladding layer and the contact layer are etched to form a ridge waveguide portion. A step of etching the contact layer and the upper clad layer into a ridge waveguide type until the active layer is exposed; and using the upper clad layer of an Al compound as the upper clad layer, Heat treating the upper cladding layer of the compound in oxygen or water vapor, and oxidizing the exposed portion of the upper cladding layer of the Al compound exposed by the etching to form a high-resistance layer portion. A method for manufacturing a waveguide type semiconductor laser. 5. A ridge waveguide type semiconductor laser in which at least an active layer, an upper cladding layer and a contact layer are sequentially laminated on a semiconductor substrate, and the upper cladding layer and the contact layer are etched to form a ridge waveguide portion. A step of etching the contact layer and the upper cladding layer into a ridge waveguide type until the active layer is exposed; and an exposed portion of the active layer exposed by the etching and the ridge waveguide portion. Oxidizing an exposed portion of the semiconductor laser with plasma using oxygen gas to form a high-resistance layer portion. 6. A ridge waveguide type semiconductor laser in which at least an active layer, an upper cladding layer and a contact layer are sequentially laminated on a semiconductor substrate, and the upper cladding layer and the contact layer are etched to form a ridge waveguide portion. A step of etching the upper cladding layer into a ridge waveguide type until the active layer is exposed; and forming a platinum electrode on the positive electrode side in a solution using ethylene glycol solution as a solvent and tartaric acid as a solute. The processing substrate after the ridge waveguide type etching is formed on the negative electrode side is provided as an electrode, and a current is applied to the platinum electrode on the positive electrode side and the electrode of the processing substrate on the negative electrode side to apply a current to the processing substrate. Forming an oxide film. A method of manufacturing a ridge waveguide type semiconductor laser, comprising: