JP2006032508A - Semiconductor laser device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser device which can improve laser characteristic, by preventing contact between an n-type layer forming a current block layer and an n-type clad layer or an n-type contact layer and by reducing leakage current, and to provide its manufacturing method. <P>SOLUTION: The semiconductor laser device is provided with a ridge structure, having a clad layer 4 which, is formed on a substrate 1 made of p-type InP and is formed of an active layer 3 and an n-type InP, and a current block layer which is formed on both sides of the ridge structure and is formed of stacked layers of a p-type InP layer 11, an n-type InP layer 12, and a p-type InP layer 13. Thus, swelling in ridge top width on the upper surface of the ridge structure is controlled to be 10 nm or smaller. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor laser element that can be used as a light source, an optical amplifier, an optical modulator, and the like in the field of optical communication and the like, and a manufacturing method thereof.

  In general, a semiconductor laser device has a carrier density in the active layer that is efficiently injected by arranging current blocking layers on both sides of the active layer, thereby improving the laser characteristics. Can be achieved.

  In a semiconductor laser device using an InP-based semiconductor material, a ridge structure including an active layer and a clad layer made of n-type InP is formed on an InP substrate, and then a p-type InP layer / n-type InP layer on both sides of the ridge structure. A current blocking layer composed of a stacked layer of / p-type InP layers is formed, and then a contact layer composed of n-type InP is formed on the ridge structure and the current blocking layer.

  In this configuration, when electrons are injected through the n-type contact layer, most of the electrons pass through the path from the n-type cladding layer to the active layer. On the other hand, since the current blocking layer has a high resistance due to the pn junction in the reverse bias state, it is difficult for current to flow.

JP 2002-232082 A (5th page, FIG. 10)

  In a conventional ridge-type semiconductor laser device, if an n-type InP layer constituting the current blocking layer comes into contact with the n-type cladding layer or the n-type contact layer due to an error in the film formation process, the current is bypassed to the current blocking layer. Leakage current occurs, and the current blocking function of the current blocking layer is degraded.

  An object of the present invention is to prevent a contact between an n-type layer constituting an electric current blocking layer and an n-type clad layer or an n-type contact layer, to reduce a leakage current, and to improve a laser characteristic, and its manufacture Is to provide a method.

A semiconductor laser device according to the present invention is formed on a substrate made of p-type InP, and includes a ridge structure including an active layer and a clad layer made of n-type InP;
A current blocking layer formed on both sides of the ridge structure and comprising a stack of p-type InP layer / n-type InP layer / p-type InP layer;
The ridge top width undulation on the upper surface of the ridge structure is 10 nm or less.

The method of manufacturing a semiconductor laser device according to the present invention includes a step of forming an active layer, a clad layer made of n-type InP, and a cap layer made of a semiconductor containing Al on a substrate made of p-type InP;
Forming a mask having a predetermined shape on the cap layer;
Etching the active layer, the clad layer, and the cap layer to form a ridge structure;
Forming a current blocking layer comprising at least a p-type InP layer / n-type InP layer / p-type InP layer on both sides of the ridge structure;
Removing the mask and cap layer;
Forming a contact layer made of n-type InP on the exposed cladding layer and current blocking layer.

The method of manufacturing a semiconductor laser device according to the present invention includes a step of forming an active layer, a clad layer made of n-type InP, and a cap layer on a substrate made of p-type InP,
Forming a mask having a predetermined shape on the cap layer;
Etching the active layer, the clad layer, and the cap layer to form a ridge structure;
Forming a current blocking layer comprising at least a p-type InP layer / n-type InP layer / p-type InP layer on both sides of the ridge structure;
Removing the mask and cap layer;
Forming a contact layer made of n-type InP on the exposed cladding layer and current blocking layer,
The step of forming the current blocking layer includes a step of forming an (111) B surface in the underlying p-type InP layer by introducing an etching gas before forming the n-type InP layer.

The method of manufacturing a semiconductor laser device according to the present invention includes a step of forming an active layer, a clad layer made of n-type InP, and a cap layer on a substrate made of p-type InP,
Forming a mask having a predetermined shape on the cap layer;
Etching the active layer, the clad layer, and the cap layer to form a ridge structure;
Forming a current blocking layer comprising at least a p-type InP layer / n-type InP layer / p-type InP layer on both sides of the ridge structure;
Removing the mask and cap layer;
Forming a contact layer made of n-type InP on the exposed cladding layer and current blocking layer,
The step of forming the current blocking layer includes the step of removing the n-type InP grown on the (111) B surface of the p-type InP layer by introducing an etching gas after forming the n-type InP layer. It is characterized by.

  According to the present invention, the n-type cladding layer or the n-type contact layer is formed when the n-type InP layer constituting the current blocking layer grows by controlling the ridge top width undulation on the upper surface of the ridge structure to 10 nm or less. Can be prevented. As a result, the leakage current to the current blocking layer can be reduced, so that the laser characteristics can be improved.

  Further, when forming the current blocking layer, InP growth on the side surface of the ridge can be suppressed by forming a cap layer made of a semiconductor containing Al as the uppermost layer of the ridge structure. Therefore, contact with the n-type cladding layer or the n-type contact layer can be prevented when the n-type InP layer constituting the current blocking layer is grown. As a result, the leakage current to the current blocking layer can be reduced, so that the laser characteristics can be improved.

Embodiment 1 FIG.
1 to 3 are cross-sectional views showing an example of a method of manufacturing a semiconductor laser device according to the present invention. For easy understanding, cross-sectional hatching is given to some layers.

  First, as shown in FIG. 1A, a buffer layer 2 made of p-type InP, an active layer 3, a clad layer 4 made of n-type InP, and a cap layer 5 are sequentially formed on a substrate 1 made of p-type InP. It is formed using MOCVD (metal organic chemical vapor deposition) or the like.

  The active layer 3 has a multiple quantum well structure including, for example, an InGaAsP well layer and an InGaAsP barrier layer, and is a region where an optical gain is generated due to carrier inversion distribution.

  The cap layer 5 can be formed of InGaAs or the like, serves to protect the cladding layer 4 when forming the current block layer in a later step, and is removed by etching after the current block layer is formed.

Next, as shown in FIG. 1B, an SiO ₂ film is formed on the entire surface of the cap layer 5 by sputtering or the like, and then a photoresist is applied, and a predetermined shape (using a photoengraving technique) For example, a mask 6 having a stripe shape with a width of 3 μm is formed.

  Next, as shown in FIG. 1C, the cap layer 5 to the middle of the buffer layer 2 are removed by wet etching such as HBr so that a ridge structure is formed below the mask 6. This ridge structure has a substantially trapezoidal cross section and is elongated along the stripe direction (the direction perpendicular to the paper surface) of the mask 6. The width and contour shape of the ridge structure can be controlled by the dimensions of the mask 6, the etching time, the etching temperature, and the like.

  Here, with respect to the direction of the ridge structure, when the upper surface of the p-type InP substrate 1 has a (100) plane, the longitudinal direction of the ridge structure is set to the [011] direction corresponding to the reverse mesa direction.

Subsequently, current blocking layers are formed on both sides of the ridge structure using selective buried growth by MOCVD. First, as shown in FIG. 2D, a p-type InP layer 11 serving as a first layer of a current blocking layer is formed so as to cover from the upper surface of the buffer layer 2 to the cap layer 5 having a ridge structure. In this case selective growth is performed by the mask 6, on the mask 6 made of SiO ₂ is InP does not grow. The upper part of the p-type InP layer 11 grows while forming a (111) B surface from the interface between the mask 6 and the ridge structure.

  Next, as shown in FIG. 2 (e), an n-type InP layer 12 serving as a second layer of the current blocking layer is formed on the p-type InP layer 11.

  FIG. 4A is a partial perspective view showing the growth state of the p-type InP layer 11 of the current blocking layer, and FIG. 4B shows the A1-A1 line and A2-A2 in FIG. It is sectional drawing which shows the mode of the cross section along a line. For easy understanding, the mask 6 is omitted in FIG. 4A.

  InP has a property of growing while forming a (111) B plane. Since only the P atoms are exposed on the (111) B surface, the growth rate of InP decreases once the (111) B surface is formed, so that it functions as a growth stop surface. In FIG. 4A, the (111) B surface appears flat on the p-type InP layer 11.

  When the n-type InP layer 12 serving as the second layer of the current blocking layer is formed on the p-type InP layer 11, ideally the n-type InP layer 12 does not grow on the (111) B plane. However, when the (111) B surface of the p-type InP layer 11 is not formed in a uniform plane due to the ridge top width undulation or the contamination of the mask 6, the n-type InP is formed on the (111) B surface. Growth of layer 12 may proceed.

  For example, when there is a undulation in the ridge top width, as shown in FIG. 4A, a plurality of inclined surfaces having a (111) B surface are formed in a step shape along the edge line of the undulation. When the n-type InP layer 12 is formed in this state, the n-type InP grows on the step surfaces of the inclined surfaces. That is, n-type InP grows in the direction perpendicular to the paper surface of FIG. 4B, and the (111) B surface is aligned in the A1-A1 cross section having the widest ridge width, and the (111) B in the A2-A2 cross section is aligned. A step is formed along the surface. Such step-like growth occurs in the same manner when the back surface of the mask is contaminated.

  If n-type InP is present on the (111) B surface of the p-type InP layer 11, the n-type InP layer 12 and the n-type cladding layer 4 or the n-type contact layer 7 above the ridge are in electrical contact, and the current The current blocking function of the block layer is degraded.

  In this embodiment, as shown in FIG. 1C, when the ridge structure is formed by etching, the ridge top width undulation is suppressed to 10 nm or less by optimizing the etching conditions. The waviness of the ridge top width is a fluctuation width related to one edge when viewed from the top surface of the ridge. When the p-type InP layer 11 of the current blocking layer is formed by reducing the undulation, the step area of the inclined surface having the (111) B plane is reduced, so that the next n-type InP layer 12 is formed. In the process, the growth of n-type InP on the (111) B plane can be suppressed. As a result, the leakage current to the current blocking layer can be reduced, so that the laser characteristics can be improved.

Returning to FIG. 2 (e), when the n-type InP layer 12 to be the second layer is formed on the p-type InP layer 11, the p-type InP layer 11 can be formed even if undulation of the ridge top width is suppressed. There is a possibility that n-type InP grows on the (111) B plane. As a countermeasure, the concentration of S (sulfur) acting as a dopant in the n-type InP layer 12 is preferably set to 1.5 × 10 ¹⁹ cm ⁻³ or more. This makes it possible to increase the In diffusion length (migration length) on the (111) B plane, and to suppress n-type InP growth on the (111) B plane.

  Further, it is desirable that a uniform (111) B surface is formed on the p-type InP layer 11 at the stage where the film formation process of the p-type InP layer 11 is completed, but the (111) B surface is formed. The part which is not done may occur. As a countermeasure, it is preferable to lightly etch the exposed surface of the p-type InP layer 11 by introducing an etching gas such as HCl gas into the MOCVD reactor after the film formation process of the p-type InP layer 11 is completed. As a result, the portion where the (111) B surface is not formed is selectively etched, and the (111) B surface of the p-type InP layer 11 can be formed in this portion.

  Next, as shown in FIG. 2F, after the n-type InP layer 12 is formed, an etching gas such as HCl gas is introduced into the MOCVD reactor so that the exposed surface of the n-type InP layer 12 is lightly etched. preferable. Thereby, the n-type InP remaining on the (111) B surface of the p-type InP layer 11 can be removed cleanly. Note that n-type InP grown on the (111) B plane has a high etching rate in the [111] direction and can be removed by HCl gas.

  Next, as shown in FIG. 3G, a p-type InP layer 13 serving as a third layer of the current blocking layer is formed on the n-type InP layer 12. Thus, the p-type InP layer 13 is formed on the (111) B surface of the p-type InP layer 11, and the n-type InP layer 12 can be completely separated from the ridge, so that the leakage current to the current blocking layer can be reduced.

After the current blocking layer is formed in this way, as shown in FIG. 3H, the mask 6 is removed by wet etching such as HF, and then the cap layer 5 is removed by wet etching such as HNO ₃ .

  Next, as shown in FIG. 3I, a contact layer 7 made of n-type InP is formed on the exposed cladding layer 4 and current blocking layer using MOCVD or the like. Subsequently, after forming electrodes on the upper surface of the contact layer 7 and the lower surface of the substrate 1, a semiconductor laser device is obtained by performing chip division and optical resonance surface formation by cleavage or the like.

Embodiment 2. FIG.
In this embodiment, as a material for forming the cap layer 5, a group III-V semiconductor containing Al and not containing P (phosphorus) such as AlGaInAs or AlInAs is used instead of InGaAs. The cap layer 5 may be composed of a single layer made of AlGaInAs or AlInAs, or may be made of a composite structure of a first layer made of AlGaInAs or AlInAs and a second layer made of InGaAs.

  With this configuration, when forming the p-type InP layer 11 serving as the first layer of the current blocking layer, the upper end of the (111) B surface at the top of the p-type InP layer 11 is not the interface between the mask 6 and the ridge. It comes to be located at the interface between the cap layer 5 and the n-type InP cladding layer 4. Therefore, when the n-type InP layer 12 to be the second layer is formed, the n-type InP growth on the (111) B plane can be suppressed without being affected by the ridge top width waviness or the contamination of the mask 6.

  When the cap layer 5 is formed of a composite structure of a first layer made of AlGaInAs or AlInAs and a second layer made of InGaAs, the cap layer 5 preferably has a thickness of 50 nm or more. As a result, a sufficient distance between the upper end of the (111) B surface and the mask 6 can be secured, and when the n-type InP layer 12 is formed, the influence of the ridge top width undulation and the contamination of the mask 6 can be eliminated. .

At this time, the layer made of AlGaInAs or AlInAs constituting the cap layer 5 preferably has an O (oxygen) concentration of 1 × 10 ¹⁷ cm ⁻³ or more. Thereby, the surface concentration of aluminum oxide becomes high, and InP growth on the side surface of the cap layer 5 can be suppressed. Further, it is preferable to add a step of oxidizing the surface of the layer made of AlGaInAs or AlInAs after forming the ridge structure and before forming the current blocking layer, so that the InP growth on the side surface of the cap layer 5 can be further suppressed. .

  In each of the above-described embodiments, the ridge structure includes the buffer layer 2, the active layer 3, and the cladding layer 4. However, the present invention is the same even if other semiconductor layers are included. It is applicable to.

  In each of the embodiments, the current blocking layer has an example of a laminated structure including three layers of the p-type InP layer 11, the n-type InP layer 12, and the p-type InP layer 13, but other semiconductors are also available. The present invention can be similarly applied even if a layer is included.

It is sectional drawing which shows an example of the manufacturing method of the semiconductor laser element concerning this invention. It is sectional drawing which shows an example of the manufacturing method of the semiconductor laser element concerning this invention. It is sectional drawing which shows an example of the manufacturing method of the semiconductor laser element concerning this invention. FIG. 4A is a partial perspective view showing the growth state of the p-type InP layer 11 of the current blocking layer, and FIG. 4B shows the A1-A1 line and A2-A2 in FIG. It is sectional drawing which shows the mode of the cross section along a line.

Explanation of symbols

1 substrate, 2 buffer layer, 3 active layer, 4 cladding layer, 5 cap layer,
6 mask, 7 contact layer, 11 p-type InP layer, 12 n-type InP layer,
13 p-type InP layer.

Claims (13)

a ridge structure formed on a substrate made of p-type InP and including an active layer and a clad layer made of n-type InP;
A current blocking layer formed on both sides of the ridge structure and comprising a stack of p-type InP layer / n-type InP layer / p-type InP layer;
A semiconductor laser device, wherein a ridge top width undulation on an upper surface of a ridge structure is 10 nm or less. 2. The semiconductor laser device according to claim 1, wherein the n-type InP layer in the current blocking layer has an S concentration of 1.5 × 10 ¹⁹ cm ⁻³ or more. forming an active layer, a clad layer made of n-type InP, and a cap layer made of a semiconductor containing Al on a substrate made of p-type InP;
Forming a mask having a predetermined shape on the cap layer;
Etching the active layer, the clad layer, and the cap layer to form a ridge structure;
Forming a current blocking layer comprising at least a p-type InP layer / n-type InP layer / p-type InP layer on both sides of the ridge structure;
Removing the mask and cap layer;
And a step of forming a contact layer made of n-type InP on the exposed cladding layer and current blocking layer.   4. The method of manufacturing a semiconductor laser device according to claim 3, wherein the cap layer includes a layer made of AlGaInAs or AlInAs.   5. The method of manufacturing a semiconductor laser device according to claim 4, wherein the cap layer has a composite structure of a first layer made of AlGaInAs or AlInAs and a second layer made of InGaAs.   6. The method of manufacturing a semiconductor laser device according to claim 5, wherein the cap layer has a thickness of 50 nm or more. 5. The method of manufacturing a semiconductor laser device according to claim 4, wherein the layer made of AlGaInAs or AlInAs constituting the cap layer has an O concentration of 1 × 10 ¹⁷ cm ⁻³ or more.   4. The method of manufacturing a semiconductor laser device according to claim 3, further comprising a step of oxidizing the surface of the cap layer before forming the current blocking layer. 4. The method of manufacturing a semiconductor laser device according to claim 3, wherein the n-type InP layer in the current blocking layer has an S concentration of 1.5 × 10 ¹⁹ cm ⁻³ or more.   The step of forming the current blocking layer includes a step of forming an (111) B surface in the underlying p-type InP layer by introducing an etching gas before forming the n-type InP layer. Item 4. A method for manufacturing a semiconductor laser device according to Item 3.   The step of forming the current blocking layer includes the step of removing the n-type InP grown on the (111) B surface of the p-type InP layer by introducing an etching gas after forming the n-type InP layer. The method of manufacturing a semiconductor laser device according to claim 3. forming an active layer, a clad layer made of n-type InP, and a cap layer on a substrate made of p-type InP;
Forming a mask having a predetermined shape on the cap layer;
Etching the active layer, the clad layer, and the cap layer to form a ridge structure;
Forming a current blocking layer comprising at least a p-type InP layer / n-type InP layer / p-type InP layer on both sides of the ridge structure;
Removing the mask and cap layer;
Forming a contact layer made of n-type InP on the exposed cladding layer and current blocking layer,
The step of forming the current blocking layer includes a step of introducing an etching gas and forming a (111) B surface in the underlying p-type InP layer before forming the n-type InP layer. A method for manufacturing a laser element. forming an active layer, a clad layer made of n-type InP, and a cap layer on a substrate made of p-type InP;
Forming a mask having a predetermined shape on the cap layer;
Etching the active layer, the clad layer, and the cap layer to form a ridge structure;
Forming a current blocking layer comprising at least a p-type InP layer / n-type InP layer / p-type InP layer on both sides of the ridge structure;
Removing the mask and cap layer;
Forming a contact layer made of n-type InP on the exposed cladding layer and current blocking layer,
The step of forming the current blocking layer includes the step of removing the n-type InP grown on the (111) B surface of the p-type InP layer by introducing an etching gas after forming the n-type InP layer. A method for manufacturing a semiconductor laser device, comprising:

Images