JPH11135888A - Semiconductor laser device and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain a leakage current of a semiconductor laser device and to improve efficiency thereof by positioning an interface between a high- resistance layer and a current diffusion preventing layer above an optical active layer 32 and below the top surface of a mesa-stripe region on the sidewall surface of the mesa-stripe region. SOLUTION: A current block region 34 includes an InP layer 34A which forms a bottom layer and doped with Fe and having high resistance, a current diffusion preventing layer 34B formed on the layer 34A and comprising InP which is non-doped and hardly diffused of Zn, and a current block layer 34C formed on the layer 34B and comprising n-type InP. The InP layer 34A contains Fe at a concentration of 6.0×10<16> /cm<3> , for example, and has a thickness of 2.8 μm, for example, such that an interface between the layer 34A and the layer 34B is positioned above an optical active layer 32 and below the top surface of a mesa-stripe region on the sidewall surface of the mesa-stripe region. The non-doped layer 34B has a thickness of 0.4 μm, for example.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to an optical semiconductor device, and more particularly to a semiconductor laser and a method of manufacturing the same. 2. Description of the Related Art For information processing devices such as computers, research has been made on using an optical parallel connection configuration using an optical fiber instead of a conventional coaxial cable for high-speed signal transmission from the viewpoints of operation speed and mounting. In order to realize such optical parallel connection, an electro-optical conversion element that operates with low power is required as a light source. For this reason, a semiconductor laser with a low threshold and high efficiency has been studied.

[0002]

2. Description of the Related Art FIG. 11 shows an example of a conventional embedded semiconductor laser operating at a low threshold voltage.
-PBH (semi-insulating layer planar buried hete
1 shows a configuration of a semiconductor laser 10 having a rostructure) structure.
Referring to FIG. 11, a semiconductor laser 10 is formed on an n-type InP substrate 11, and an n-type InG
A photoactive region 12 is formed that includes an aAsP light guide layer and an undoped InGaAsP active layer. The photoactive region 1
A cladding layer 13 made of p-type InP is formed on 2, and the photoactive region 12 and the cladding layer 13 form a mesa region together with a part of the substrate 11. On both sides of the mesa region, buried layers 14 of high-resistance InP doped with a deep impurity element such as Fe are formed.

On the buried layer 14, another buried layer 15 made of n-type InP is formed. On the buried layer 15, a p-type InP is formed so as to cover the clad 13.
Another cladding layer 16 made of P is formed, and a p-side electrode 18 is formed on the cladding layer 16 via a p-type InGaAsP contact layer 17. An n-side electrode 19 is formed on the lower main surface of the substrate 11.

In the structure shown in FIG. 11, for example, semiconductor layers 12 and 13 are sequentially deposited on the substrate 11 by MOVPE,
After forming a dielectric mask in a stripe shape in the mesa formation region, a mesa stripe is formed by etching, and both sides of the mesa stripe are buried in the buried layer 1 by MOVPE.
Fill by selective fill growth of 4 and 15. After the formation of the buried layers 14 and 15, the p-type InP cladding layer 16 and the p-type InGaAs are formed by MOVPE.
A P contact layer 17 is sequentially formed, and the electrodes 18 and 1 are further formed.
9 is deposited to complete the semiconductor laser 10.

FIG. 12 shows an SI-BH (semi-insulating lasing) conventionally used as a buried semiconductor laser operating at a low threshold value, in addition to the SI-PBH structure.
Semiconductor laser 20 with yerburied heterostructure) structure
Is shown. Referring to FIG.
Is formed on an n-type InP substrate 21, and an n-type InGaAsP light guide layer and an undoped InGa
A photoactive region 22 including an AsP active layer is formed. A cladding layer 23 made of p-type InP and a contact layer 24 made of p-type InGaAsP are sequentially formed on the photoactive region 22, and the photoactive region 22 and the cladding layer 23 are formed.
The contact layer 24 forms a mesa region with a part of the substrate 21. Further, on both sides of the mesa region, Fe
A buried layer 25 made of doped high-resistance InP is formed.

On the buried layer 25, a p-side electrode 26 is provided so as to cover the contact layer 24.
An n-side electrode 27 is formed on the lower main surface of the first electrode 1.

[0007]

The SI-PBH shown in FIG.
In the type semiconductor laser 10, the holes injected from the p-side electrode 18 and the electrons injected from the n-side electrode 19 accumulate in the active region 12 and recombine to emit light.
The emitted light is amplified by stimulated emission, and laser oscillation occurs when the injection current exceeds a predetermined threshold.

In order to efficiently generate laser oscillation, it is important that the injected electrons and holes are accumulated in the active region 12. Therefore, the semiconductor laser 10 having the structure shown in FIG. A high-resistance buried region 14 and an n-type region 15 are formed in order to cut off a current path bypassing the active region 12 between the electrode and the electrode 19. However, even in the configuration of FIG. 11, the hole that has reached the p-type cladding layer 13 diffuses into the high-resistance buried layer 14 and escapes from the buried layer 14 to the substrate 11 through the first leak current path.
The holes injected into the mold cladding layer 16 may be considered as a second leak current path for escaping to the substrate 11 through the n-type buried layer 15 and the high-resistance buried layer 14, and the low threshold operation of the semiconductor laser 10 may be reduced. To achieve this, it is necessary to minimize the current flowing through these leak paths.

In the semiconductor laser 20 having the SI-BH structure shown in FIG. 12, there is a leakage current path flowing from the p-type InP clad layer 23 to the substrate 21 through the high-resistance buried region 25. In order to effectively block these leak currents, the current blocking action of the high resistance buried region 14 or 25 doped with Fe, particularly its high resistance becomes very important. In the configuration,
High resistance buried region, for example, buried region 14 in FIG.
Is the p-type cladding layer 13 and particularly the p-type cladding layer 16
Buried region 1
After the selective growth of No. 4, when the cladding layer 16 is grown by the MOVPE method, the Zn dopant in the cladding layer 16 diffuses into the buried region 14 doped with Fe. It may change to p-type along the side wall surface of the mesa stripe. When such a p-type region is formed in the buried region 14, a leak current path bypassing the photoactive region 12 is formed along the formed p-type region.

A similar problem also occurs in the SI-BH type semiconductor laser 20 shown in FIG. 12, but in the semiconductor laser 10 shown in FIG. 11, in particular, the n-type buried layer 15 is formed to cut off the second leak current path. It is necessary to make the distance from the n-type mesa region below the photoactive region 12 as large as possible,
For this reason, the Fe-doped buried region 14 and the cladding layer 16 are in direct contact with each other, and a leak current path is easily formed.

Further, conventionally, in order to cut off a leakage current path in the Fe-doped buried region 14, when forming the buried region 14, an undoped semiconductor layer in which Zn diffusion hardly occurs at the initial stage of selective growth is grown. Let F
Although it has been proposed to grow an e-doped high resistance layer, such an undoped semiconductor layer tends to grow along the side wall surface of the mesa stripe, and the undoped semiconductor layer itself becomes a leak current path. It does not solve the problem.

Accordingly, it is a general object of the present invention to provide a semiconductor laser and a method of manufacturing the same that have solved the above-mentioned problems. A more specific object of the present invention is to provide a highly efficient semiconductor laser in which a leakage current is particularly suppressed and a method for manufacturing the same.

[0013]

According to the present invention, there is provided a compound semiconductor substrate having a first conductivity type defined by a (100) plane, as defined in claim 1; Formed on a part of the semiconductor substrate, at least (10
A mesa stripe region including a substrate surface defined by a 0) plane, an active layer formed on the substrate surface, and a first cladding layer having a second conductivity type formed on the active layer. And a pair of current block regions formed on both sides of the mesa stripe region, and on the mesa stripe region,
Formed to cover the pair of current block regions,
In a semiconductor laser including a second cladding layer having a second conductivity type, a first electrode formed on the second cladding layer, and a second electrode formed on the compound semiconductor substrate Each of the current blocking regions includes a high-resistance region including a deep impurity element and a diffusion formed on the high-resistance region and configured to suppress diffusion of a second conductivity type impurity element in the second cladding layer. Including a suppression region, a boundary surface between the high resistance region and the diffusion suppression region, on a side wall surface of the mesa stripe region, above the active layer,
3. A compound semiconductor having a first conductivity type defined by a (100) plane by a semiconductor laser, which is located below an upper surface of the mesa stripe region, or as described in claim 2, A substrate, a substrate surface formed on a part of the compound semiconductor substrate and defined by at least a (100) plane, and an active layer formed on the substrate surface;
A mesa stripe region including a cladding layer having a second conductivity type formed on the active layer, a contact layer formed on the cladding layer, and a pair of currents formed on both sides of the mesa stripe region In a semiconductor laser including a block region, a first electrode formed on the mesa stripe region so as to cover the pair of current block regions, and a second electrode formed on the compound semiconductor substrate, Each of the current block regions is formed on a high resistance region including a deep impurity element and the high resistance region,
A diffusion suppressing region for suppressing diffusion of a second conductivity type impurity in the cladding layer, wherein a boundary surface between the high resistance region and the diffusion suppressing region is formed on a side wall surface of the mesa stripe region; 4. The semiconductor device according to claim 3, wherein the current blocking region is made of InP, and the deep impurity is formed by a semiconductor laser located above the active layer and below the lower surface of the cladding layer. The semiconductor laser according to claim 2 or 3, wherein the element is made of Fe. In the semiconductor laser according to claim 1 or 2, the diffusion suppressing region is non-conductive. A compound semiconductor having a first conductivity type defined by a semiconductor laser comprising a doped region, or as defined in claim 5, having a (100) plane. A plate, a substrate surface formed on a part of the compound semiconductor substrate and defined by at least a (100) plane, an active layer formed on the substrate surface, and a second layer formed on the active layer. A mesa stripe region including a first cladding layer having a conductivity type of: and a pair of current block regions formed on both sides of the mesa stripe region;
A second cladding layer having a second conductivity type formed on the mesa stripe region so as to cover the pair of current blocking regions; and a first electrode formed on the second cladding layer. And a second electrode formed on the compound semiconductor substrate, wherein each of the current blocking regions includes:
A high-resistance region including a deep impurity element; and a diffusion suppression region formed on the high-resistance region and configured to suppress diffusion of a second conductivity-type impurity element in the second cladding layer. A method of manufacturing a semiconductor laser in which a boundary surface between a region and the diffusion suppression region is located on a sidewall surface of the mesa stripe region above the active layer and below an upper surface of the mesa stripe region. The method according to claim 1, wherein the current block region is formed by selective growth using metal organic chemical vapor deposition in which chlorocarbon having one Cl atom in one molecule is added to a growth atmosphere. Or a compound semiconductor substrate defined by the (100) plane and having the first conductivity type, and at least a part of the compound semiconductor substrate, wherein A substrate surface defined by the (100) plane, an active layer formed on the substrate surface, a cladding layer having a second conductivity type formed on the active layer, and a cladding layer formed on the cladding layer. And a pair of current block regions formed on both sides of the mesa stripe region, and a first formed on the mesa stripe region to cover the pair of current block regions. And a second electrode formed on the compound semiconductor substrate, wherein each of the current blocking regions is formed on a high-resistance region containing a deep impurity element, and the cladding is formed on the high-resistance region. A diffusion suppression region for suppressing diffusion of a second conductivity type impurity in the layer, wherein a boundary surface between the high resistance region and the diffusion suppression region is formed on a side wall surface of the mesa stripe region; In the method for manufacturing a semiconductor laser located above the active layer and below the lower surface of the cladding layer, the current blocking region is formed by adding chlorocarbon having one Cl atom per molecule to a growth atmosphere. A monolithic methane or monochloroethane is used as the chlorocarbon by a method of manufacturing a semiconductor laser characterized in that the chlorocarbon is formed by selective growth using an added metalorganic vapor phase epitaxy method. A method of manufacturing a semiconductor laser according to claim 5 or claim 6, or as described in claim 8, a compound semiconductor substrate defined by a (100) plane and having a first conductivity type; A substrate surface formed on a part of the compound semiconductor substrate and defined by at least a (100) plane; and an active layer formed on the substrate surface;
A mesa stripe region including a first cladding layer having a second conductivity type formed on the active layer; a pair of current block regions formed on both sides of the mesa stripe region; A second cladding layer having a second conductivity type formed so as to cover the pair of current blocking regions, a first electrode formed on the second cladding layer, and the compound semiconductor A second electrode formed on a substrate, wherein each of the current block regions has an upper surface above an upper surface of the mesa stripe region and extends obliquely upward from the upper surface of the mesa stripe region. Wherein the semiconductor laser is defined by a slope that is continuous with an upper surface of the current block region, and the semiconductor laser includes an upper surface of the mesa stripe region, an upper surface of the current block region, and the slope. The semiconductor layer further includes a covering semiconductor layer, the semiconductor layer simultaneously contains the first conductivity type impurity and the second conductivity type impurity, and the semiconductor layer includes an upper surface of the mesa stripe region and the current block region. A portion covering the upper surface of the semiconductor laser having the second conductivity type, and a portion covering the slope having the first conductivity type, or a semiconductor laser having the first conductivity type, or as described in claim 9,
Each of the current block regions is formed on the high resistance region including a deep impurity element and the second resistance region.
A diffusion suppression region for suppressing the diffusion of the second conductivity type impurity element in the cladding layer, wherein a boundary surface between the high resistance region and the diffusion suppression region is formed on a side wall surface of the mesa stripe region. 9. The semiconductor laser according to claim 8, wherein the semiconductor laser is located above the active layer and below an upper surface of the mesa stripe region. [Action] The applicant of the present invention has an aspect of approximately (011)
On both sides of the mesa stripe which is defined in terms, in the experiments of growing the buried layer by the MOVPE method, generally buried layer is where to grow along the sidewall surface of the mesa stripe, monochloromethane during growth atmosphere (CH ₃ C
1) or the addition of monochloroethane (C ₂ H ₅ Cl) suppresses the deposition of the buried layer on the (011) side wall surface, so that the buried layer has a growth plane approximately parallel to the (100) plane. Have been found to be able to form. See FIG.

Therefore, the first feature of the present invention is to use the feature that such a growth plane is substantially parallel to the (100) plane to prevent the diffusion of Zn into the current blocking layer. A non-doped layer effective for suppressing a boundary between the high-resistance layer and the undoped layer is formed on a side wall surface of the mesa stripe region above the active layer and below a top surface of the mesa stripe region. It is formed so as to be located on the side.
The undoped layer thus formed acts as a Zn diffusion suppressing region, and when the second cladding layer is deposited by MOVPE in an atmosphere containing Zn, the high-resistance layer contains Zn. The contact with the atmosphere is eliminated, and the problem of forming a leak current path due to the diffusion of Zn in the high resistance layer is solved. Since the undoped layer does not extend along the side wall surface of the mesa stripe region, the undoped layer does not form a leak current path.

A second feature of the present invention is that the Zn-doped cladding layer has an M
The problem of Zn diffusion during deposition by the OVPE method
As described in claim 9, the high-resistance buried layer is made of Zn.
This can be avoided by covering the semiconductor layer with a semiconductor layer that is unlikely to cause diffusion. In order to block a leakage current path from the second cladding layer to the substrate, the semiconductor layer particularly covers a portion of the current block region covering a slope portion of the (111) B plane above the upper surface of the mesa stripe. Doping is performed to a conductivity type opposite to the conductivity type of the cladding layer. A portion of the semiconductor layer covering the (100) plane other than the slope portion is doped with the same conductivity type as the conductivity type of the cladding layer. Such doping depending on the crystal plane can be easily performed in the case of vapor phase growth of a compound semiconductor layer such as InP by doping a p-type dopant and an n-type dopant simultaneously.
For example, when an InP layer is epitaxially grown on a (111) B plane using Zn and Se as dopants, Se
Is taken in preferentially, the InP layer is doped n-type. On the other hand, when the InP layer is grown on the (100) plane under the same conditions, Zn is preferentially taken in and the InP layer is grown.
The P layer is doped p-type. With this configuration, a leak current path between the substrate and the cladding layer, particularly, passing through the slope portion is effectively blocked, and the efficiency of the semiconductor laser is improved.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION

[Embodiment 1] FIG.
1 shows a configuration of a semiconductor laser 30 having a PBH structure. Referring to FIG. 2, a semiconductor laser 30 is formed on an n-type substrate 31 and is formed on the substrate 31 to form an n-type InGaAsP.
A light active layer 32 composed of a light guide layer and an undoped InGaAsP light emitting layer; and Zn formed on the light active layer 32.
And a cladding layer 33 which is doped p-type with the same. The light emitting layer has a composition having a band gap corresponding to, for example, a 1.3 μm wavelength, and the photoactive layer 32 and the cladding layer 33 extend in the axial direction of the semiconductor laser 30 together with a part of the substrate 31. A mesa stripe is formed, and a current block region 34 is formed on both sides of the mesa stripe.
As will be described in detail later, it is formed by selective growth. The side wall surface of the mesa stripe is a (011) plane,
Alternatively, it is composed of a crystal plane close to this.

The current block region 34 has a lower portion of Fe.
A doped high-resistance InP layer 34A and a diffusion suppression layer 34B made of undoped InP, in which diffusion of Zn is unlikely to occur, are further formed on the diffusion suppression layer 34B. A current blocking layer 34C is formed. The InP layer 34A is made of, for example, Fe.
^{Containing at} a concentration of 0 × 10 ¹⁶ cm ⁻³ , wherein the boundary surface between the layer 34A and the layer 34B is located above the photoactive layer 32 and below the top surface of the mesa stripe region on the mesa stripe side wall surface. 2.8 μm, for example
It is formed in the thickness of. The undoped layer 34B has a thickness of, for example, 0.4 μm, while the n-type current blocking layer 34
C has a thickness of, for example, 0.4 μm and contains Si as an n-type dopant at a concentration of 2.0 × 10 ¹⁸ cm ⁻³ .

In this configuration, the current block region 3
4, the interface between the undoped InP layer 34B and the n-type InP current blocking layer 34C, that is, the current blocking layer 34C is formed above the upper surface of the mesa stripe, and the current blocking region 34 is It is defined by a (111) B plane extending obliquely upward from the upper surface of the stripe, or a slope formed of a crystal plane close to the (111) B plane.
The slope is connected to the upper surface of the n-type InP current blocking layer 34C having the (100) plane.

In the semiconductor laser 30 of FIG. 2, another p-type cladding layer 35 is formed on the p-type InP cladding layer 33 constituting the uppermost layer of the mesa stripe so as to cover the upper surface and the slope of the current block region 34. But about 1μ
m. The p-type cladding layer 35 is made of Zn.
Is doped to a concentration of 5.0 × 10 ¹⁷ cm ⁻³ , and 1.0 × 10 ¹⁹ c
A contact layer 36 of p-type InGaAsP doped to a concentration of m ^-3 is formed to a thickness of typically 0.5 μm.

On the contact layer 36, Ti / Pt
A p-side electrode 37 made of an Au film is formed.
An n-side electrode 3 made of AuGe / Au on the lower main surface
8 are formed. In the semiconductor laser 30 having such a configuration,
The Zn-doped cladding layer 35 does not directly contact the Fe-doped high-resistance layer 34A, and the cladding layer 35 contacts the diffusion suppressing layer 34B made of undoped InP on the slope. Therefore, the cladding layer 35
Is formed by the MOVPE method, Zn contained in the growth atmosphere gas is not taken into the high-resistance layer 34A, and a high resistance value is guaranteed in the high-resistance layer 34A. The high resistance layer 34A and the undoped layer 34B
Similar to the structure shown in FIG. 1, the boundary surface is substantially parallel to the (100) plane. Does not occur. For this reason, the semiconductor laser 30 has a feature that the leak current is reduced. When the resonator length is 300 μm, the threshold current is about 4.5 m.
The result of A was obtained. This threshold current is 0.5 mA lower than the conventional value.

FIGS. 3A to 3C and FIGS.
(F) shows a manufacturing process for manufacturing the semiconductor laser 30 of FIG. 2. Referring to FIG. 3A, on the n-type InP substrate 31, an optical guide layer made of n-type InGaAsP and undoped InGaAs having a band gap wavelength of 1.3 μm are provided.
a light active layer 32 including a light emitting layer made of sP;
Further, the p-type cladding layer 33 is formed on the photoactive layer 32.
Is formed.

Next, in the step of FIG.
A mask pattern 33 made of SiO ₂ on the structure of FIG.
A is formed along the axial direction of the semiconductor laser 30 by CVD and photolithography.
In the step (C), RIE using an ethane-based gas is performed using the mask pattern 33A as a mask, thereby forming a mesa stripe 31A having a height of about 3 μm.

Next, in the step of FIG.
iO_TwoWhile leaving the mask pattern 33A, TMIn
And PH_ThreeBy the MOVPE method using
On the P substrate 31, a region on both sides of the mesa region 31 </ b> A is
The Fe-doped high-resistance InP layer 34A and the undoped I
The nP layer 34B and the n-type InP layer 34C are
Selective growth is performed sequentially at a substrate temperature of 0 ° C.
An area 34 is formed. At this time, the Fe dopant is
Using Elocene and Si as the n-type dopant _TwoH₆To
use.

In the selective growth step shown in FIG. 4D, monochloromethane is supplied to the gaseous source at a flow rate such that Cl / In = 6 when depositing the layers 34A to 34C. As a result, each of the selective growth layers 34A to 34C grows so as to have a main surface substantially parallel to the (100) plane as described above with reference to FIG. 3, and crawls along the side wall surface of the mesa stripe. The growth mode is suppressed. The suppression of the creeping growth mode can also be obtained by adding chlorocarbon having one Cl atom in one molecule, such as monochloroethane, to the growth atmosphere gas instead of the monochloromethane.

Next, in the step of FIG. 4E, the mask pattern 33A is removed, and a p-type I
MOV using Zn as a dopant for nP cladding layer 35
By the PE method, the clad layer 35 is deposited so as to cover not only the clad layer 33 in the mesa stripe 31A but also the slope and the upper surface of the current block region 34, and further the p-type InGaAsP contact layer 3 is formed thereon.
6 is similarly deposited by MOVPE.

Further, in the step of FIG. 4F, an ohmic electrode 37 is formed on the contact layer 36 and an ohmic electrode 38 is formed on the lower main surface of the substrate 31 by vapor deposition. Semiconductor laser 30
Is obtained. FIG. 5 shows a configuration 30 'of a modification of the semiconductor laser 30 of FIG. However, in FIG. 5, the parts described above are denoted by the same reference numerals, and description thereof will be omitted.

Referring to FIG. 5, in the semiconductor laser 30 ', a p-type InP current blocking layer 34D is inserted between the n-type InP current blocking layer 34C and the undoped InP diffusion suppressing layer 34B thereunder. In such a configuration, layer 34
The depletion layer formed at the junction interface between C and the layer 34D further contributes to the prevention of the leak current, and the current narrowing efficiency is improved.

FIG. 6 shows the configuration of FIG. 2 by replacing the SI-B of FIG.
Semiconductor laser 4 when applied to H-structure semiconductor laser
0 is shown. However, in FIG. 6, the parts described above are denoted by the corresponding reference numerals, and description thereof will be omitted. Referring to FIG. 6, the buried layer 25 includes a lower layer 25A made of Fe-doped InP and an undoped layer 25B thereon, and the boundary between the layers 25A and 25B is located above the active layer 22. To position. Even in such a configuration, the undoped layer 25B effectively suppresses diffusion of the impurity element into the Fe-doped layer,
The problem of increased leakage current is avoided. [Embodiment 2] FIG. 7 shows a configuration of a semiconductor laser 50 according to a second embodiment of the present invention.

Referring to FIG. 7, the semiconductor laser 50 has n
The n-type InGaAsP light guide layer and the undoped InGa
A photoactive layer 52 composed of an AsP light emitting layer;
2 and a clad layer 53 doped p-type with Zn. The light emitting layer has a composition having a band gap corresponding to, for example, a 1.3 μm wavelength, and the photoactive layer 52 and the cladding layer 53 extend in the axial direction of the semiconductor laser 50 together with a part of the substrate 51. Form a mesa stripe, on both sides of the mesa stripe,
As described in detail later, the current block region 54
It is formed by selective growth. The side wall surface of the mesa stripe is a (011) plane or a crystal plane close to the (011) plane.

The current block region 54 has a lower side with Fe
A doped high-resistance InP layer 54A is further provided thereon, and a diffusion suppressing layer 54B made of undoped InP, which does not easily diffuse Zn, is further provided on the diffusion suppressing layer 54B. A current blocking layer 54C is formed. The InP layer 54A is made of, for example, Fe.
At a concentration of 0 × 10 ¹⁶ cm ⁻³ , and a boundary surface between the layer 54A and the layer 54B is on the side wall surface of the mesa stripe above the photoactive layer 52 and below the top surface of the mesa stripe region. 2.8 μm, for example
It is formed in the thickness of. The undoped layer 54B has a thickness of, for example, 0.4 μm, while the n-type current blocking layer 54B has a thickness of 0.4 μm.
C has a thickness of, for example, 0.4 μm and contains Si as an n-type dopant at a concentration of 2.0 × 10 ¹⁸ cm ⁻³ .

In this configuration, the current block region 5
4, the interface between the undoped InP layer 54B and the n-type InP current blocking layer 54C, that is, the current blocking layer 54C is formed above the mesa stripe upper surface, and the current blocking region 54 It is defined by a (111) B plane extending obliquely upward from the upper surface of the stripe, or a slope formed of a crystal plane close to the (111) B plane.
The slope is connected to the upper surface of the n-type InP current blocking layer 54C having the (100) plane.

In the semiconductor laser 50 of FIG. 7, the n-type is further formed on the p-type InP cladding layer 53 constituting the uppermost layer of the mesa stripe so as to cover the upper surface of the current block region 54 and the (111) B slope. An InP layer 55 containing both Se as a dopant and Zn as a p-type dopant as a dopant is epitaxially deposited by MOVPE. At this time, the incorporation efficiency of Se and Zn into the InP layer 55 greatly differs depending on the crystal plane where the layer 55 is deposited.
In the portion growing on the (0) plane, Zn is preferentially taken in and the layer 55 is doped p-type, while
1) In the portion growing on the B-plane, Se is preferentially taken in, so that the layer 55 is doped n-type. As a result, the InP layer 55 becomes a region 55 covering the cladding layer 53.
The region 55B covering the upper surfaces of the A and n-type InP layers 54C is doped p-type, while the portion covering the (111) B slope is doped n-type.

Further, on the InP layer 55, another p-type
Cladding layer 56 is formed to a thickness of about 1 μm. Said
The p-type cladding layer 56 is made of¹⁸cm
^-3, And on the cladding layer 56, Z
1.0 × 10 by n¹⁹cm ^-3P doped to a concentration of
A contact layer 57 of type InGaAsP is typically
Is formed to a thickness of 0.5 μm.

On the contact layer 57, Ti / Pt
A p-side electrode 58 of an Au film is formed.
An n-side electrode 5 made of AuGe / Au on the lower main surface
9 is formed. In this embodiment, the selective growth region 54
Is covered with the n-type region 55c, even if the cladding layer 56 is formed by the MOVPE method, the diffusion of the Zn dopant into the high-resistance layer 54A is more effectively suppressed. Even if the dopant concentration is set high, for example, about 1 × 10 ¹⁸ cm ⁻³ , no problem occurs. Further, since the slope portion of the selective growth region 54 is covered with the n-type region 55C, a leak current path passing through the slope portion is effectively cut off.

For this reason, the semiconductor laser 50 has a feature that the leak current is reduced. In the case of a device having a resonator length of 300 μm, a result was obtained in which the threshold current was about 4.5 mA. This threshold current is 0.5 mA lower than the conventional value. Further, the semiconductor laser 50 has an advantage that the impurity concentration of the cladding layer 56 can be further increased and the series resistance is reduced.

FIGS. 8 (A) to 8 (C) and FIGS. 9 (D) to 9 (D)
(F) shows a manufacturing process for manufacturing the semiconductor laser 50 of FIG. 7. Referring to FIG. 8A, on the n-type InP substrate 51, a light guide layer made of n-type InGaAsP and undoped InGaAs having a band gap wavelength of 1.3 μm are provided.
a light active layer 52 including a light emitting layer made of sP;
Further, on the photoactive layer 52, the p-type cladding layer 53 is formed.
Is formed.

Next, in the step of FIG.
A mask pattern 53 made of SiO ₂ on the structure of FIG.
8A is formed along the axial direction of the semiconductor laser 50 by CVD and photolithography.
In the step (C), RIE using an ethane-based gas is performed using the mask pattern 53A as a mask, thereby forming a mesa stripe 51A having a height of about 3 μm.

Next, in the step of FIG.
iO_TwoWhile leaving the mask pattern 53A, TMIn
And PH_ThreeBy the MOVPE method using
On the P substrate 51, the region on both sides of the mesa region 51A is
The Fe-doped high-resistance InP layer 54A and the undoped I
The nP layer 54B and the n-type InP layer 54C are
Selective growth is performed sequentially at a substrate temperature of 0 ° C.
An area 54 is formed. At this time, the Fe dopant is
Using Elocene and Si as the n-type dopant _TwoH₆To
use.

In the selective growth step of FIG. 9D, when depositing the layers 54A to 54C, monochloromethane is added to the gaseous phase material and Cl / In =
6 is supplied at a flow rate. As a result, each of the selective growth layers 54A to 54C grows so as to have a main surface approximately parallel to the (100) plane as described above with reference to FIG. 3, and crawls along the side wall surface of the mesa stripe. The growth mode is suppressed. The suppression of the creeping growth mode can also be obtained by adding chlorocarbon having one Cl atom in one molecule, such as monochloroethane, to the growth atmosphere gas instead of the monochloromethane.

Next, in the step of FIG. 9E, the mask pattern 33A is removed, and the InP layer 55 is formed on the cladding layer 33 by H ₂ Se and dimethyl zinc (DMZn) by MOVPE. It is formed to a thickness of 0.15 μm while supplying as a dopant gas, and a p-type InP cladding layer 56 is formed thereon by MO
It is deposited by the VPE method. Further, the cladding layer 56
A p-type InGaAsP contact layer 57 is formed on the
It is deposited by the OVPE method. However, in FIG.
The illustration of the p-type regions 55A and 55B in the nP layer 55 is omitted. As described above, in such a configuration, when the InP layer 55 is grown, the (111)
The region 55C growing on the B-plane selectively takes in Se and is doped n-type.

Further, in the step of FIG. 9F, an ohmic electrode 58 is formed on the contact layer 57 and an ohmic electrode 59 is formed on the lower main surface of the substrate 51 by vapor deposition. Semiconductor laser 50
Is obtained. FIG. 10 shows a modification 50 'of the semiconductor laser 50 of FIG. However, in FIG. 10, the same reference numerals are given to the parts described above, and the description will be omitted.

In the present embodiment, the current block region 54
In the above, the undoped layer 54B is formed as a p-type InP layer 54.
Replace with B '. Accordingly, the upper surface of the Fe-doped high-resistance layer 54A reaches a slope portion above the upper surface of the mesa stripe region.
The cladding layer 56 is covered by the P region 55C.
Zn is effectively prevented from diffusing into the high resistance layer 54A. By interposing the p-type InP layer 54B ', the leakage current path from the cladding layer 56 to the substrate 51 in a direction substantially perpendicular to the main surface of the substrate is further effectively prevented.

[0043]

According to the features of the present invention, a compound semiconductor substrate defined by the (100) plane and having the first conductivity type and a part of the compound semiconductor substrate are formed. A substrate surface defined by at least a (100) plane, an active layer formed on the substrate surface, and a first cladding layer having a second conductivity type formed on the active layer. A mesa stripe region, a pair of current block regions formed on both sides of the mesa stripe region, and a second conductivity type formed on the mesa stripe region to cover the pair of current block regions. A second clad layer, a first electrode formed on the second clad layer, and a second electrode formed on the compound semiconductor substrate.
And a high-resistance region containing a deep impurity element,
A boundary between the high resistance region and the diffusion suppression region is formed by a diffusion suppression region formed on the high resistance region and suppressing diffusion of a second conductivity type impurity element in the second cladding layer. On the side wall surface of the mesa stripe region, above the active layer, and below the upper surface of the mesa stripe region,
Diffusion of the p-type dopant into the high-resistance region, which occurs when the second cladding layer is formed, is prevented by the diffusion suppressing region, and the threshold characteristics of the semiconductor laser are improved.

In particular, when selectively growing the high resistance region and the diffusion suppression region constituting the current block region by MOVPE, one Cl atom is contained in one molecule. By adding chlorocarbon to the growth atmosphere, a high resistance region and a diffusion suppression region to be formed can be formed as a semiconductor layer having a main surface substantially parallel to the (100) plane. The formation of a structure that crawls on the side wall surface can be suppressed. As a result, it is possible to avoid the problem of forming a leak current path due to the structure that crawls on the side wall surface.

According to the features of the present invention as set forth in claims 8 and 9, a compound semiconductor substrate defined by the (100) plane and having the first conductivity type is formed on a part of the compound semiconductor substrate, A mesa including a substrate surface defined by at least a (100) plane, an active layer formed on the substrate surface, and a first cladding layer having a second conductivity type formed on the active layer. A stripe region, a pair of current block regions formed on both sides of the mesa stripe region, and a second conductive type formed on the mesa stripe region to cover the pair of current block regions. A second electrode formed on the compound semiconductor substrate, a first electrode formed on the second clad layer, and a second electrode formed on the compound semiconductor substrate.
Each of the current block regions has an upper surface above the upper surface of the mesa stripe region, extends obliquely upward from the upper surface of the mesa stripe region, and is continuous with the upper surface of the current block region. A semiconductor layer covering the upper surface of the mesa stripe region, the upper surface of the current block region, and the slope, wherein the semiconductor layer is formed of an impurity of the first conductivity type. The second conductivity type is simultaneously contained with the impurity of the second conductivity type, and the portion covering the upper surface of the mesa stripe region and the upper surface of the current block region has the second conductivity type, and the portion covering the slope has the first conductivity type. The current blocking regions selectively grown on both sides of the mesa stripe are separated from the second cladding layer by providing Dopant diffusion problems from the cladding layer to the current blocking layer is avoided. In the semiconductor layer, a conductivity type of a portion covering the slope portion is:
Since the conductivity type of the first or second cladding layer is reversed, a leakage current path passing through the slope portion is cut off.

[Brief description of the drawings]

FIG. 1 is a diagram showing the principle of the present invention.

FIG. 2 is a diagram showing a configuration of a semiconductor laser according to a first embodiment of the present invention.

FIGS. 3A to 3C are diagrams (part 1) for explaining a manufacturing process of the semiconductor laser of FIG. 2;

FIGS. 4D to 4F are diagrams (part 2) for explaining a manufacturing process of the semiconductor laser of FIG. 2;

FIG. 5 is a diagram showing a modification of the first embodiment.

FIG. 6 is a diagram showing a configuration when the first embodiment is applied to an SI-BH type semiconductor laser.

FIG. 7 is a diagram showing a configuration of a semiconductor laser according to a second embodiment of the present invention.

FIGS. 8A to 8C are diagrams (part 1) for explaining a manufacturing process of the semiconductor laser of FIG. 7;

FIGS. 9 (D) to 9 (F) are diagrams (part 2) for explaining a manufacturing process of the semiconductor laser of FIG. 7;

FIG. 10 is a diagram showing a modification of the first embodiment.

FIG. 11 is a diagram showing a configuration of a conventional SI-PBH type semiconductor laser.

FIG. 12 is a diagram showing a configuration of a conventional SI-BH type semiconductor laser.

[Explanation of symbols]

10, 20, 30, 30 ', 40, 50, 50' Semiconductor laser 11, 21, 31, 51 Substrate 12.22, 32.52 Photoactive layer 13, 16, 23, 33, 53, 56 Cladding layer 14, 34, 54 Current block region 15, 35 N-type layer 17, 24.36, 57 Contact layer 18, 19, 26, 27.37, 38, 58, 59 Electrode 31A, 51A Mesa stripe 33A. 53A Mask 34A, 54A High resistance layer 34B, 54B Non-doped diffusion suppressing layer 34C, 54C n-type current blocking layer 34D, 54B 'p-type current blocking layer 55 InP layer 55A, 55B n-type region 55C p-type region

Claims (9)

[Claims] 1. A compound semiconductor substrate defined by a (100) plane and having a first conductivity type; and a substrate surface formed on a part of the compound semiconductor substrate and defined by at least a (100) plane. An active layer formed on the substrate surface, and a second active layer formed on the active layer.
A first cladding layer having a conductivity type of: a pair of current blocking regions formed on both sides of the mesa stripe region; and covering the pair of current blocking regions on the mesa stripe region. A second cladding layer having a second conductivity type, a first electrode formed on the second cladding layer, and a second electrode formed on the compound semiconductor substrate Wherein each of the current block regions is formed on a high-resistance region containing a deep impurity element, and
A diffusion suppression region for suppressing the diffusion of the second conductivity type impurity element in the cladding layer, wherein a boundary surface between the high resistance region and the diffusion suppression region is formed on a side wall surface of the mesa stripe region. A semiconductor laser, which is located above the active layer and below an upper surface of the mesa stripe region. 2. A compound semiconductor substrate defined by a (100) plane and having a first conductivity type, and a substrate surface formed on a part of the compound semiconductor substrate and defined by at least a (100) plane. An active layer formed on the substrate surface, and a second active layer formed on the active layer.
A mesa stripe region including a cladding layer having a conductivity type of, and a contact layer formed on the cladding layer; a pair of current blocking regions formed on both sides of the mesa stripe region; A semiconductor electrode comprising: a first electrode formed so as to cover the pair of current blocking regions; and a second electrode formed on the compound semiconductor substrate, wherein each of the current blocking regions has a deep impurity. A high-resistance region containing an element; and a diffusion-suppressing region formed on the high-resistance region and suppressing diffusion of a second conductivity type impurity in the cladding layer. A boundary surface between the active layer and the lower surface of the mesa stripe region on the side wall surface of the mesa stripe region. Semiconductor laser. 3. The semiconductor laser according to claim 2, wherein said current block region is made of InP, and said deep impurity element is made of Fe. 4. The semiconductor laser according to claim 1, wherein said diffusion suppressing region comprises an undoped region. 5. A compound semiconductor substrate defined by a (100) plane and having a first conductivity type, and a substrate surface formed on a part of the compound semiconductor substrate and defined by at least a (100) plane. A mesa stripe region including an active layer formed on the substrate surface and a first cladding layer having a second conductivity type formed on the active layer; and a mesa stripe region formed on both sides of the mesa stripe region. A pair of current blocking regions, a second cladding layer having a second conductivity type formed on the mesa stripe region so as to cover the pair of current blocking regions, and on the second cladding layer. A first electrode formed on the compound semiconductor substrate and a second electrode formed on the compound semiconductor substrate, wherein each of the current blocking regions includes a high-resistance region containing a deep impurity element and a high-resistance region on the high-resistance region. Formed in front A diffusion inhibiting region for inhibiting diffusion of a second conductivity type impurity element in the second cladding layer, wherein a boundary surface between the high resistance region and the diffusion inhibiting region is
In a method for manufacturing a semiconductor laser located on a sidewall surface of the mesa stripe region above the active layer and below an upper surface of the mesa stripe region, the current block region may be formed by Cl atoms in one molecule. A method of forming a semiconductor laser by selective growth using a metalorganic vapor phase epitaxy method in which chlorocarbon having one is added to a growth atmosphere. 6. A compound semiconductor substrate defined by a (100) plane and having a first conductivity type, and a substrate surface formed on a part of the compound semiconductor substrate and defined by at least a (100) plane. An active layer formed on the substrate surface, a cladding layer having a second conductivity type formed on the active layer, and a mesa stripe region including a contact layer formed on the cladding layer; A pair of current block regions formed on both sides of the mesa stripe region, a first electrode formed on the mesa stripe region to cover the pair of current block regions, and formed on the compound semiconductor substrate. Each of the current blocking regions includes a high-resistance region containing a deep impurity element,
A second layer formed on the high resistance region and in the cladding layer;
A diffusion inhibition region that inhibits diffusion of impurities of the conductivity type, and a boundary surface between the high resistance region and the diffusion inhibition region,
In a method for manufacturing a semiconductor laser located on a side wall surface of the mesa stripe region above the active layer and below a lower surface of the cladding layer, the current blocking region may include Cl atoms in one molecule. A method for manufacturing a semiconductor laser, wherein the semiconductor laser is formed by selective growth using a metal organic chemical vapor deposition method in which one chlorocarbon is added into a growth atmosphere. 7. The method according to claim 5, wherein monochloromethane or monochloroethane is used as the chlorocarbon. 8. A compound semiconductor substrate defined by a (100) plane and having a first conductivity type, and a substrate surface formed on a part of the compound semiconductor substrate and defined by at least a (100) plane. An active layer formed on the substrate surface, and a second active layer formed on the active layer.
A first cladding layer having a conductivity type of: a pair of current blocking regions formed on both sides of the mesa stripe region; and covering the pair of current blocking regions on the mesa stripe region. A second cladding layer having a second conductivity type, a first electrode formed on the second cladding layer, and a second electrode formed on the compound semiconductor substrate Wherein each of the current block regions has an upper surface above the upper surface of the mesa stripe region, extends obliquely upward from the upper surface of the mesa stripe region, and The semiconductor laser further includes a semiconductor layer covering the top surface of the mesa stripe region, the top surface of the current block region, and the slope. The semiconductor layer includes an impurity of the first conductivity type impurity and the second conductivity type at the same time,
The semiconductor layer has the second conductivity type in a portion covering the top surface of the mesa stripe region and the top surface of the current block region, and has the first conductivity type in a portion covering the slope. Semiconductor laser. 9. Each of the current blocking regions is formed on a high resistance region containing a deep impurity element, and a second conductivity type impurity element in the second cladding layer is formed on the high resistance region. And a boundary between the high resistance region and the diffusion suppressing region, on a side wall surface of the mesa stripe region, above the active layer, and above a top surface of the mesa stripe region. 9. The semiconductor laser according to claim 8, wherein said first laser is also located on the lower side.