JPH1154835A - Semiconductor laser and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance further the efficiency of the laser oscillation of a semiconductor laser. SOLUTION: A semiconductor layer 102 introduced with silicon, which is an n-type dopant at a concentration of 1×10<17> cm<-3> is processed into a mesa shape, whereby an active layer 102a of an emission wavelength of 1.3 μm is formed. Then, a surface treatment is performed on the layer 102a by a wet treatment or the like, using an acid aqueous solution and after that, the layer 102a is embedded with a current-constricting layer 106 and a current-constricting layer 107 consisting of an n-type InP layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser having a current confinement structure and a method for manufacturing the same.

[0002]

2. Description of the Related Art In manufacturing a compound semiconductor device, a process of processing a semiconductor crystal is indispensable. For example, in a waveguide-type semiconductor laser or the like, a waveguide including an active layer is processed into a mesa or ridge structure to form a light emitting region. Then, the light emitting region is buried with a current confinement layer made of, for example, a high-resistance semiconductor to form a current confinement structure. However, when an element structure is formed by burying and growing (regrowing) a current constriction layer on the semiconductor surface processed in the light emitting region, if impurities are taken into the semiconductor crystal surface during the processing, buried growth occurs. The impurities remain at the interface with the current confinement layer and affect device characteristics, which is a problem. Therefore, it is important to remove impurities mixed (pile-up) into the processed semiconductor surface before regrowth.

FIG. 4 shows a conventional method for manufacturing a semiconductor laser having a current confinement structure. First, as shown in FIG. 4A, a substrate 401 made of an n-type InP semiconductor crystal
A semiconductor layer 40 made of undoped InGaAsP is formed thereon.
Form 2 The semiconductor layer 402 usually has a density of 10 ¹⁷ cm ⁻³ due to mixing of impurities (for example, Si) from a raw material.
It has a carrier concentration of less than. Next, FIG.
As shown in FIG. 7, by using an etching mask 403 made of silicon oxide, a portion of the substrate 401 is dry-etched and processed into a mesa shape to form an active layer 4 serving as a light emitting region.
02a is formed.

[0004] During the processing of the mesa shape, impurities 404 are mixed into the processed surface and defects 405 are generated. Here, as described later, since the impurities 404 particularly affect device characteristics, the impurities 404 are removed by performing a surface treatment by wet treatment with an acidic aqueous solution or the like. In this surface treatment, the processed surface is finely etched away. However, as shown in FIG. 4C, the impurity 404 cannot be completely removed. Also,
The defect 405 cannot be removed by wet processing. Next, a part of the substrate 401 processed into the mesa shape and the active layer 402a are replaced with a current confinement layer 406 made of p-type InP.
And a current confinement layer 407 made of n-type InP.
Then, after removing the etching mask 403, a cladding layer 408 made of p-type InP doped with Zn is formed thereon, as shown in FIG.
The configuration of the semiconductor laser is almost completed.

[0005]

However, FIG. 4 (b)
The impurities mixed during the processing of the mesa shape shown in (1) remain without being completely removed by the wet treatment using an acid. The remaining impurities are
As shown in FIG. 5A, it remains at the interface between the side surface of the active layer 402a processed into the mesa shape and the current confinement layer 406.
Oxygen is conceivable as an impurity mixed during this processing. As shown in FIG. 5B, the oxygen concentration along the line AA ′ from the active layer 402a to the current confinement layer 406 shown in FIG.

As described above, when oxygen is present at the interface, a part of the current injected for performing the laser oscillation operation becomes:
Instead of being injected into the active layer 402a, it flows at the interface between the active layer 402a and the current confinement layer 406. That is, conventionally,
Leakage current that does not contribute to the laser oscillation operation increases due to the remaining impurities 404, and there is a problem in that the element characteristics deteriorate.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to improve the efficiency of laser oscillation.

[0008]

According to the present invention, there is provided a semiconductor laser comprising: a substrate made of a compound semiconductor; an active layer formed on the substrate and doped with an n-type impurity of 10 ¹⁷ cm ^-3 or more; And a cladding layer formed on the active layer for narrowing a current injected into the active layer, which is formed in contact with the side surface of the active layer so as to fill the active layer. Thus, the n-type impurity is 1 in the active layer.
Since it is in a state of being introduced at 0 ¹⁷ cm ⁻³ or more, impurities formed on the side surfaces of the active layer are easily removed before the current confinement layer is formed. In the method of manufacturing a semiconductor laser according to the present invention, first, a semiconductor layer in which an n-type impurity is introduced at 10 ¹⁷ cm ⁻³ or more is formed on a substrate made of a compound semiconductor. Next, the semiconductor layer is selectively removed by etching to form an active layer. Next, the side surface of the active layer exposed by the etching removal is finely etched by wet processing. Next, by selectively growing a semiconductor other than the active layer on the substrate, a current narrowing layer for narrowing a current injected into the active layer is formed so as to fill the active layer. Then, a clad layer was formed on the active layer. Therefore, an n-type impurity is added to the active layer by one.
Since 0 ¹⁷ cm ⁻³ or more is introduced, impurities mixed into the side surface of the active layer can be easily removed by minute etching by wet processing.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a method for manufacturing a semiconductor laser according to an embodiment of the present invention. FIG.
As shown in (a), first, on a substrate 101 made of an n-type InP semiconductor crystal, a semiconductor layer 102 in which silicon as an n-type dopant is introduced at 1 × 10 ¹⁷ cm ⁻³ is formed. The semiconductor layer 102 is composed of a 60-nm-thick InGaAsP6 layer serving as a well layer and a 10-nm-thick InGaAsP5 layer having a composition wavelength of 1.1 μm serving as a barrier layer.
A multiple quantum well structure in which layers are alternately stacked. The semiconductor layer 102 is made of InGaAs having a composition wavelength of 1.1 μm and a thickness of 100 nm above and below the multiple quantum well structure.
The structure is sandwiched between light guide layers made of sP.

Next, as shown in FIG. 1B, the substrate 1 is etched using an etching mask 103 made of silicon oxide.
The active layer 102a having a light emission wavelength of 1.3 μm is formed by dry-etching a part of the substrate 101 to form a mesa. Note that the mesa shape formed up to a part of the substrate 101 becomes a clad layer under the active layer 102a. By the way, during processing of this mesa shape, impurities 1
04 or a defect 105 occurs. Here, as described above, the impurity 104 particularly affects device characteristics. Therefore, as shown in FIG. 1C, surface treatment is performed by wet treatment with an acidic aqueous solution or the like.
The impurity 104 is removed. In this wet treatment, the processed surface is finely etched away. In addition,
The defect 105 cannot be removed by the wet processing.

Next, the substrate 101 processed into a mesa shape
Of the current confinement layer 106 made of p-type InP and the current confinement layer 1 made of n-type InP
Embed with 07. Then, after removing the etching mask 103, a p-type InP doped with Zn is formed thereon.
By forming the cladding layer 108 made of
As shown in (d), the configuration of the semiconductor laser is almost completed. In the above description, the current confinement layer 106 and the current confinement layer 1
Although the embedding is performed at 07, the present invention is not limited to this, and the processed mesa may be embedded with a semi-insulating semiconductor made of InP or the like doped with Fe to form a current confinement structure.

Here, in this embodiment, as shown in FIG. 2, it can be seen that impurities (oxygen) have been removed by the above-described wet treatment. Here, FIG.
(B) is a distribution diagram showing an oxygen concentration distribution around the line AA 'of the active layer 102a (FIG. 2 (a)) in this embodiment. This is estimated from SIMS measurement results. As is clear from FIG. 2 (b), at the interface between the active layer 102a and the current confinement layer 106a, mixing of oxygen at the interface where the oxygen concentration increases is not observed.

In this embodiment, since the active layer 102a is doped with an n-type impurity,
The electrons are in excess. On the other hand, the active layer 102a
The state where oxygen is taken into the side surface during processing is a state where the processed surface is oxidized. Therefore, when oxygen mixed in the processed surface is removed, a reduction reaction has occurred. The reduction reaction requires the supply of electrons. That is, according to this embodiment, the active layer 102a is in a state in which electrons necessary for removing oxygen mixed into the side surface can be sufficiently supplied. As a result, according to this embodiment, FIG.
Oxygen can be effectively removed by surface treatment such as wet treatment with an acidic aqueous solution described in (c). Further, impurities such as carbon and silicon which have entered during processing in a similar charged state are also removed by the same action.

FIG. 3A is a correlation diagram showing the relationship between the injected current and the optical output in the above-described semiconductor laser. Compared with the conventional semiconductor laser shown by the dotted line in FIG. 3A, the semiconductor laser according to this embodiment shown by the solid line can start laser oscillation with a lower current and obtain a larger optical output with a smaller current. Have been. That is, in the conventional semiconductor laser, a leak current flows at the interface due to impurities mixed into the side surface of the buried active layer, so that the threshold current increases and the light output efficiency decreases. On the other hand, according to the semiconductor laser according to the above embodiment, the mixing of oxygen (impurities) on the side of the active layer embedded in the current confinement layer is suppressed, so that the leak current at the interface is suppressed, and The characteristics are improved.

FIG. 3B is a correlation diagram showing the relationship between the n-type impurity concentration of the active layer and the threshold current of laser oscillation in the semiconductor laser described above. Figure 3 is clear from (b), the n-type impurity concentration is close to 10 ¹⁷ cm ^-3 begun threshold current is decreased, n-type impurity concentration of 10 ¹⁷
At cm ^−3, the threshold current is reduced to 5 mA or less, which is practically no problem. And 10 ¹⁸
The threshold current increases from around cm ^-3 . This is because the high-concentration impurities are doped, and the crystal quality of the active layer is starting to deteriorate.
However, also in this region, the threshold current is 5 mA or less. And it is very difficult to dope impurities to 10 ¹⁹ cm ⁻³ or more. As described above, according to this embodiment, the n-type impurity is introduced into the active layer at 10 ¹⁷ cm ⁻³ or more, so that the impurity mixed during the processing of the active layer into the mesa or the ridge structure is reduced. ,
It will be efficiently removed. As a result, according to this embodiment, as described above, a semiconductor laser having better characteristics can be obtained.

In the above embodiment, 1.3 μm is used.
Although an active layer having an oscillation wavelength in the m wavelength band has been described as an example, the present invention is not limited to this. The same applies to the configuration of another active layer having an oscillation wavelength in the 1.5 μm wavelength band. Further, in the above embodiment, the active layer has a multiple quantum well structure of six quantum wells and five barrier layers. However, the present invention is not limited to this, and another number of layers may be used. Further, for example, a double hetero structure having no multiple quantum well structure in which the active layer is made of InGaAsP having a single composition may be used.

In the above embodiment, InP or InP
Although GaAsP is used, the present invention is not limited to these, and GaAsP, which is another group III-V compound semiconductor, is used.
s, InGaAs, AlAs, AlGaAs, AlIn
GaAs or AlGaInP may be used.
Further, ZnS, CdS, which is a II-VI group compound semiconductor,
The same applies to the case where e, ZnSSe or the like is used.
In the above embodiment, Zn is used as the p-type impurity. However, the present invention is not limited to this.
g, Be, C, etc. may be used as p-type impurities. Further, Si, Sn, S, Se may be used as the n-type impurity.

[0018]

As described above, according to the present invention, a semiconductor laser is constituted as follows. First, an n-type impurity is added to a substrate made of a compound semiconductor by 10 ^17.
A semiconductor layer having a ^{size of} cm ^-3 or more is formed. Next, the semiconductor layer is selectively removed by etching to form an active layer. Next, the side surface of the active layer exposed by the etching removal is finely etched by wet processing. Next, by selectively growing a semiconductor other than the active layer on the substrate, a current narrowing layer for narrowing a current injected into the active layer is formed so as to fill the active layer. And
A cladding layer is formed on the active layer. Therefore, since the n-type impurity is introduced into the active layer in an amount of 10 ¹⁷ × cm ⁻³ or more, the impurity mixed into the side surface of the active layer can be easily removed by the fine etching by the wet processing. As a result, according to the present invention, in the formed semiconductor laser having the current confinement structure, the contamination of impurities at the interface between the active layer and the current confinement layer is suppressed, and the current leakage at the interface can be suppressed. This has the effect of increasing efficiency.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a method for manufacturing a semiconductor laser according to an embodiment of the present invention.

FIG. 2 is a distribution diagram showing a configuration of a semiconductor laser in this embodiment and an oxygen concentration distribution around an active layer.

FIG. 3 is a correlation diagram (a) showing the relationship between the injected current and the optical output in the semiconductor laser, and the correlation showing the relationship between the n-type impurity concentration of the active layer and the threshold current of laser oscillation in the semiconductor laser. FIG.

FIG. 4 is an explanatory view showing a conventional method for manufacturing a semiconductor laser having a current confinement structure.

FIG. 5 is a distribution diagram showing a configuration of a conventional semiconductor laser and an oxygen concentration distribution around an active layer.

[Explanation of symbols]

101: substrate, 102: semiconductor layer, 102a: active layer,
103: etching mask, 104: impurity, 105:
Defects, 106, 107: current confinement layer, 108: cladding layer.

Claims (3)

[Claims] A substrate made of a compound semiconductor, an active layer formed on the substrate and having an n-type impurity of 10 ¹⁷ cm ⁻³ or more introduced therein, and a side surface of the active layer in contact with the active layer so as to bury the active layer. A semiconductor laser, comprising: a formed current confinement layer for constricting a current injected into the active layer; and a cladding layer formed on the active layer. 2. The semiconductor laser according to claim 1, wherein said active layer is sandwiched between light guide layers. 3. A first step of forming a semiconductor layer in which an n-type impurity is introduced at 10 ¹⁷ cm ⁻³ or more on a substrate made of a compound semiconductor, and selectively removing the semiconductor layer by etching to form an active layer. A second step of forming; a third step of finely etching the side surface of the active layer exposed by the etching removal in the second step by wet processing; and selectively forming a semiconductor other than the active layer on the substrate. A fourth step of forming a current confinement layer for constricting a current injected into the active layer by burying the active layer, and a step of forming a cladding layer on the active layer. 5. A method of manufacturing a semiconductor laser, comprising: