JP3317271B2 - Semiconductor optical device and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor optical device and a method for manufacturing the same, and more particularly to a semiconductor laser, a semiconductor optical amplifier, a semiconductor optical modulator, an optical integrated device and the like which are main components of an optical communication system. And a method of manufacturing the same.

[0002]

2. Description of the Related Art Metal organic vapor phase epitaxy (hereinafter referred to as MOVPE).
Vapor phase epitaxial growth methods, such as controllability of film thickness during thin film growth, film thickness within wafer surface, uniformity of electrical and optical characteristics, and reproducibility between wafers under the same crystal growth condition. Is excellent. Therefore, it is often used particularly as a growth method for compound semiconductor electronic devices and optical devices.

In crystal growth by MOVPE, crystal growth is suppressed by forming a mask on a part of the substrate with a dielectric film or the like. That is, the composition and growth rate of the mixed crystal semiconductor in the selective growth region (mask opening) are changed depending on the width of the mask. In particular, multiple quantum wells (hereinafter referred to as MQ
In a W (Multiple Quantum Well) structure, the band gap changes depending not only on the composition of each layer but also on the thickness of the well layer. Accordingly, an optical integrated device or the like in which a laser and an optical modulator are simultaneously grown by changing the mask width in the light waveguide direction using this is manufactured.

On the other hand, as a structure of a semiconductor optical device, a buried structure in which an active layer region for generating, amplifying or modulating a laser beam is formed as a mesa stripe and both sides thereof are buried with a current block layer is widely used. Further, in order to unify the transverse mode of the emitted laser light, it is necessary to suppress the width of the active layer to approximately 2 μm or less. Therefore, in order to manufacture an optical element having a buried structure, a step of forming a mesa stripe having a width of 2 μm or less and a burying step of forming a current block layer on both sides thereof are required.

In the case of manufacturing an optical device having a buried structure having a current block layer by using such selective growth,
The following two methods are mainly used. One is 10 μm width
After performing selective growth using a mask having a relatively large opening width of at least about 1, a stripe of a width of about 1 to 2 μm made of a dielectric is formed on the growth area by photolithography, and this is used as a mask for etching. After the formation of the mesa structure, a current blocking layer is grown.
The other is selective growth using a mask having an opening width of about 1 to 2 μm. In this case, a mesa-shaped active layer region having (111) B facets as side surfaces is formed by growth. You.

In the latter method, the shape of the active layer mesa structure to be formed is very excellent in reproducibility. Further, since the active layer region mesa stripe having a width of about 1 to 2 μm is formed by the growth, it is not necessary to adjust the width of the active layer by etching, and the burying growth of the current block layer and the like can be performed as it is. Therefore, there is an advantage that there is no introduction of crystal defects due to the etching of the semiconductor and there is no variation in the structure due to the distribution of the etching shape in the substrate.

Due to the above characteristics, the use of such a conventional method makes it possible to manufacture an optical device having excellent uniformity, reproducibility and reliability. However, in order to perform the buried growth on the mesa structure formed by this method, a step of forming a dielectric film only on the mesa having a width of about 1 μm is required.
However, in normal photolithographic alignment,
It is very difficult to form such a dielectric film. Therefore, a self-alignment process utilizing the fact that the thickness of the SiO ₂ film formed by thermal CVD is different between the upper portion and the side surface of the mesa has been devised (Sakata et al., Photon. Tech.
Lett., Vol.8 No.2, 1996), thereby making it possible to form a dielectric film only on the upper portion of the mesa having a width of 1 μm or less. In this method, the following steps are required.

FIG. 5 is a sectional view showing a manufacturing process by a self-alignment process disclosed in the above-mentioned document.
Each step is as follows. (A) Step of forming SiO ₂ film 102 using thermal CVD (that is, after forming mesa structure 103 on substrate 101, the whole is covered with SiO ₂ film 102) (b) Mesa structure by etching SiO on the side of 103
₍₂ ) Step of removing the film 102 (c) Step of forming a resist stripe 104 so as to cover the mesa structure 103 by photolithography (d) Removing the SiO ₂ films 102 on both outer sides of the mesa structure 103 by side etching Step (e) Step of removing resist stripe 104

[0009]

However, in such a conventional manufacturing process, the etching rate and the etching time must be strictly controlled in the step (b), and the resist stripe 104 is formed in the step (c). Strict alignment is required so that the mesa structure 103 is located substantially at the center. Therefore, forming a dielectric film only on the upper portion of the mesa structure having a width of about 1 μm formed by selective growth requires many steps, including those requiring high precision. It is difficult to improve. The present invention has been made under such a background, and the above process can be greatly simplified, and although strict control of the etching rate and alignment at the time of photolithography are not required. Another object of the present invention is to provide a semiconductor optical device excellent in reproducibility, uniformity, and throughput, and a method for manufacturing the same.

[0010]

In order to achieve such an object, a semiconductor optical device according to the present invention is provided with a semi-insulating semiconductor substrate and a semiconductor optical device provided on the semiconductor substrate and formed by selective growth. A mesa structure including an active layer; a first conductive type semiconductor layer provided on the upper surface of the mesa structure and the semiconductor substrate on one side of the mesa structure; and a first conductive type semiconductor layer provided on the first conductive type semiconductor layer. A current block structure comprising a second conductive type semiconductor layer, a first conductive type semiconductor layer provided on the second conductive type semiconductor layer, and an opposite side to one side of the mesa structure A semiconductor layer of the second conductivity type provided in contact with the mesa structure.

The current block structure includes a semiconductor layer of a first conductivity type provided on the upper surface of the mesa structure and the semiconductor substrate on one side of the mesa structure, and a semiconductor layer of the first conductivity type. And a semi-insulating semiconductor layer provided thereon. In addition, the current block structure includes a first conductive type semiconductor layer provided on the upper surface of the mesa structure and provided on the semiconductor substrate on one side of the mesa structure, and a first conductive type semiconductor layer. And a layer containing oxidized Al provided thereon.

Further, the semiconductor optical element may be any one of a semiconductor laser, a semiconductor optical amplifier, and a semiconductor optical modulator. Further, the semiconductor substrate is made of Fe-doped InP, and the first conductivity type semiconductor layer is made of nP.
The semiconductor layer of the second conductivity type is made of p-type InP.
It may be made of type InP. Further, the active layer,
It may have a multiple quantum well structure.

On the other hand, according to a method of manufacturing a semiconductor optical device according to the present invention, a pair of masks are formed on a semi-insulating semiconductor substrate, and a mesa structure including an active layer is selectively grown between the pair of masks. A first step of forming a current block structure including a semiconductor of the first conductivity type and a semiconductor of the second conductivity type after removing one of the pair of masks; Removing the other of the pair of masks and then forming a semiconductor layer of the second conductivity type so as to be in contact with the mesa structure.

The second step is a step of removing one of the pair of masks and then forming a current block structure including a semiconductor layer of the first conductivity type and a semi-insulating semiconductor layer. Is also good. The second step is a step of removing one of the pair of masks and then forming a current block structure composed of a semiconductor layer of the first conductivity type and a layer containing Al. May be a step of removing the other of the pair of masks, forming a second conductivity type semiconductor layer in contact with the mesa structure, and oxidizing the Al-containing layer.

The semiconductor optical element may be any one of a semiconductor laser, a semiconductor optical amplifier, and a semiconductor optical modulator. Further, the semiconductor substrate is made of Fe-doped InP, and the first conductivity type semiconductor layer is made of nP.
The semiconductor layer of the second conductivity type is made of p-type InP.
It may be made of type InP. Further, the active layer,
It may have a multiple quantum well structure.

[0016]

Next, one embodiment of the present invention will be described. In the present embodiment, a current block layer having a thyristor structure made of first and second conductivity type semiconductors is formed on the upper side and one side of the mesa structure using a mask used for growing a mesa structure including an active layer. . Alternatively, a current block layer formed of a semi-insulating semiconductor is formed, or a layer containing Al is formed using the mask and then the layer is oxidized to form a current block layer.

In this embodiment, unlike the current block layer structure used in the conventional laser, there is no need to form a mask on the upper surface of the active layer mesa, and the buried structure can be easily formed. Can be. In addition, the current block structure can be formed without being affected by the height of the mesa structure at all, and even when manufacturing a device having a portion having a different mesa height such as a spot size conversion laser or a modulator integrated laser, Excellent uniformity and reproducibility can be realized more than before. Further, since the laser manufactured by this manufacturing method is a so-called lateral injection type laser in which electrons and holes are injected from both sides of the active layer, a hole to each well, which is a problem particularly when the number of well layers is large, is used. There is also an advantage that non-uniform implantation does not occur.

In the following, a semiconductor laser is taken as an optical element, and its configuration and manufacturing method will be described.

[First Embodiment] FIG. 1 shows a first embodiment of the present invention.
FIG. 2 is a perspective view and a sectional view showing the first embodiment, and FIG.
FIG. 2 is a cross-sectional view showing a step subsequent to that of FIG. 1. First, FIG.
As shown in (a), the surface is a (100) crystal plane of F
A thermal CV is applied on a substrate 1 made of e-doped semi-insulating InP.
100 nm thick SiO by D _TwoForm a film.

Next, as shown in FIG. 1 (b), by photolithography and etching with BHF, the substrate 1 is 5 μm wide and 1.5 μm apart in the <011> direction.
This set of SiO ₂ stripe masks (hereinafter referred to as mask 2)
Is formed at a pitch of 300 μm. Then, the cladding layer 3a (thickness 0.1) made of n-type InP is formed on the substrate 1 patterned as described above by MOVPE.
5 μm, a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ )
On top of this, InGa having a wavelength composition of 1.1 μm and a thickness of 60 nm was used.
SCH (Separate Confinement Heteros) composed of AsP
(tructure) Layer 3b is grown.

Further thereon, a wavelength composition of 1.4 μm, a thickness of 5 nm, a compressive strain of 1%, an InGaAsP well layer, and a wavelength composition of 1.1 μm, a thickness of 10 nm, InGaAs
An MQW layer 3c (emission wavelength: 1.3 μm), in which seven P barrier layers are stacked, is grown. An SCH layer 3d made of InGaAsP having a wavelength composition of 1.1 μm and a thickness of 60 nm is grown thereon, and a p-type InP cladding layer 3e (0.1 μm in thickness and a carrier concentration of 7 × 10 ¹⁷⁾ is formed thereon.
cm ⁻³ ). As a result, a mesa structure 3 is completed on the substrate 1. Then, photolithography and BH
By etching using F, one of the pair of masks 2 is removed.

Next, as shown in FIG.
A current blocking layer 4 made of nP (thickness 0.3 μm, carrier concentration 3 × 10 ¹⁸ cm ⁻³ ), and a current blocking layer 5 made of p-type InP (thickness 0.6 μm, carrier concentration 6 × 10 6)
¹⁷ cm ⁻³ ), and a current blocking layer 6 (thickness 0.5 μm, carrier concentration 3 × 10 ¹⁸ cm ⁻³ ) made of n-type InP are sequentially grown. At this time, the InP layer does not grow on the side where the mask 2 remains.

Next, as shown in FIG.
After the growth in (c), the remaining SiO ₂ mask 2 is removed, and then the buried layer 7 made of p-type InP is formed.
(Thickness: 3 μm, carrier concentration: 1 × 10 ¹⁸ cm ⁻³ ), and a contact layer 8 made of p-type InGaAs (thickness: 0.3 μm, carrier concentration: 5 × 10 ¹⁸ cm ⁻³ )
Grow.

Next, as shown in FIG. 2E, the current blocking layer 4 is formed by photolithography and etching.
Is formed. Then, SiO ₂ is deposited thereon by thermal CVD, and the surface of the contact layer 8 and the side surfaces of the groove 12 are covered with the SiO ₂ film 9. Thereafter, the SiO ₂ film 9 at the bottom of the groove 12 is removed by photolithography and etching using BHF, and a part of the SiO ₂ film 9 on the contact layer 8 is removed. The laser structure is completed by forming the p-side electrode 10 and the n-side electrode 11 at the portion where the SiO ₂ film 9 has been removed.

As described above, in the manufacturing method according to the present embodiment, it is not necessary to form a dielectric film on the mesa structure 3 and a buried structure can be easily formed. Further, the current block structure can be formed without being affected by the height of the mesa structure 3 at all. Further, the laser of the present embodiment constitutes a so-called lateral injection type laser in which electrons and holes are injected from the lateral direction of the active layer (hole injection direction 13, electron injection direction 14). Therefore, there is an advantage that uneven injection of holes into each well does not occur.

Next, a semiconductor laser according to a second embodiment of the present invention will be described.

[Second Embodiment] FIG. 3 is a sectional view showing a second embodiment of the present invention. First, by the same process as in the first embodiment (FIGS. 1A and 1B), Fe
A mesa structure 3 including an active layer is formed by selective growth on a substrate 1 made of semi-insulating InP doped with Si.

Next, as shown in FIG. 3 (c '), by photolithography and etching using BHF,
One of the pair of masks 2 is removed. Then n-type I
nP current blocking layer 4 (thickness 0.3 μm, carrier concentration 3 × 10 ¹⁸ cm ⁻³ ), Fe-doped semi-insulating In
A current blocking layer 5a (1.0 μm thick) made of P and an undoped InP layer 6a (0.2 μm thick) are sequentially grown. At this time, the InP layer does not grow on the side where the mask remains. The undoped InP layer 6a is provided to prevent contact between the current blocking layer 5a and a buried layer 7 made of p-type InP, which will be described later. Interdiffusion with certain Zn can be prevented.
In the case where a dopant (for example, Ru or the like) that has little interdiffusion with Zn and realizes semi-insulating properties is used as the dopant of the current blocking layer 5a, undoped InP
The layer 6a becomes unnecessary.

Next, as shown in FIG.
After removing the mask 2 on the side, the p-type InP
Embedded layer 7 (thickness 3 μm, carrier concentration 1 × 10¹⁸
cm ^-3) And contact layer made of p-type InGaAs
8 (thickness 0.3 μm, carrier concentration 5 × 10¹⁸cm^-3)
Grow.

Next, as shown in FIG.
By etching as with the embodiment after forming the grooves 12 having a depth reaching the current blocking layer 4, SiO ₂ film 9
The laser structure is completed through the opening of the SiO ₂ film 9 and the formation of the p-side electrode 10 and the n-side electrode 11 by etching.

In this case, as in the first embodiment, there are advantages that the buried structure can be easily formed, the mesa height is not affected, and the non-uniform hole injection between the wells by the lateral injection type is eliminated. Further, in the present embodiment, since the current blocking layer 5a is made of semi-insulating InP, the capacitance of the current blocking layer can be significantly reduced. For this reason, it is very advantageous for high-speed modulation and low distortion required for an analog laser.

Next, a semiconductor laser according to a third embodiment of the present invention will be described.

[Third Embodiment] FIG. 4 is a sectional view showing a third embodiment of the present invention. First, by the same steps (FIGS. 1A and 1B) as in the first and second embodiments,
A mesa structure 3 including an active layer is formed by selective growth on a substrate 1 made of semi-insulating InP doped with Fe.

Next, as shown in FIG. 4C, by photolithography and etching using BHF,
One of the pair of masks 2 is removed. Subsequently, a current blocking layer 4 made of n-type InP (thickness 0.3 μm, carrier concentration 3 × 10 ¹⁸ cm ⁻³ ) and an InAlAs layer 5 b
(Thickness 0.1 μm) and an undoped InP layer 6 a (thickness 0.2 μm) are sequentially grown. At this time, the InP layer does not grow on the side where the mask 2 remains. Undoped In
The P layer 6a is provided to prevent surface oxidation of the InAlAs layer 5b during a process of removing SiO ₂ (mask 2) performed between the growth of the current block layer and the growth of a buried layer described later. Therefore, this layer may be made of n-type InP or p-type InP other than undoped InP, and a layer other than InP may be used as long as it does not contain Al.

Next, as shown in FIG.
After removing the mask 2 on the side, the p-type InP
Embedded layer 7 (thickness 3 μm, carrier concentration 1 × 10¹⁸
cm ^-3) And contact layer made of p-type InGaAs
8 (thickness 0.3 μm, carrier concentration 5 × 10¹⁸cm^-3)
Grow.

[0036] Then, as shown in FIG. 4 (e "), to form a groove 12 having a depth reaching the current blocking layer 4 by etching. In this later in a N ₂ atmosphere containing water vapor 670
Perform an oxidation step at 20 ° C. for 20 minutes. Since the InAlAs layer 5b contains Al, the current blocking layer 5c containing the oxidized Al is formed by being oxidized from the side surface of the groove 12 toward the inside. On the other hand, the other layers do not contain Al and are not oxidized.

Next, as shown in FIG.
As in the first and second embodiments, SiO 2 _TwoDeposit a film 9,
SiO by etching_TwoThe opening of the film 9 and the p-side electrode 10 and
Through the formation of the n-side electrode 11, the laser structure is completed.
You.

As described above, also in the present embodiment, as in the first and second embodiments, the hole between the wells of the lateral injection type is easy to form the buried structure and is not affected by the height of the mesa structure. It has the advantage of eliminating uneven injection. Further, in this embodiment, the current blocking layer has
An AlAs layer is used. Because this film is an insulator,
It has a very high withstand voltage and exhibits an excellent current blocking effect even at high temperature operation and high output.

The present embodiment is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention. For example, in the above example, after removing one of the masks used for growing the active layer, the n-type InP and the current block layer are grown, and then the remaining mask is removed to form a p-type InP buried layer. After inverting the conduction type and growing a p-type InP current blocking layer,
A structure in which a type InP buried layer is formed may be used.

Further, by combining the second and third embodiments, an InAlAs layer and an Fe-doped semi-insulating InP layer are laminated on one side of the mesa of the active layer, and thereafter, the InAlAs is oxidized and the semi-insulating InP layer is oxidized. Both AlInAs layers can be used as current blocking layers. This allows
It is possible to realize a semiconductor laser that is low in capacity, has excellent withstand voltage and high temperature characteristics.

In the above example, InG on the InP substrate is used.
aAsP-based and InAlGaAs-based lasers, GaAs
The InGaAsP laser on the substrate has been described.
The active layer may be made of InGaAlP, InGaNAs, or another material, and the substrate is not limited to InP or GaAs, and is applicable to an AlInGaN laser on a GaN substrate. Further, the present invention is applicable not only to semiconductor lasers but also to various optical devices such as semiconductor optical amplifiers, semiconductor optical modulators, and optical integrated devices obtained by combining them.

[0042]

As described above, according to the present invention, since it is not necessary to form a dielectric film on the upper surface of the mesa structure, strict control of the etching rate and alignment at the time of photolithography can be achieved. A buried structure having a current block structure can be easily formed for a mesa structure including an active layer formed by selective growth. Further, a semiconductor optical device can be manufactured with high throughput and high reproducibility and uniformity. Further, even in the manufacture of a device having a portion with a different mesa height, such as a laser diode integrated with a spot size converter, excellent uniformity and reproducibility can be realized more than before.

[Brief description of the drawings]

FIG. 1 shows a first embodiment (semiconductor laser) of the present invention.
FIG. 6 is a cross-sectional view showing a manufacturing process of the second embodiment.

FIG. 2 is a sectional view showing a step continued from FIG.

FIG. 3 shows a second embodiment (semiconductor laser) of the present invention.
FIG. 6 is a cross-sectional view showing a manufacturing process of the second embodiment.

FIG. 4 shows a third embodiment (semiconductor laser) of the present invention.
FIG. 6 is a cross-sectional view showing a manufacturing process of the second embodiment.

FIG. 5 is a cross-sectional view showing a step of forming a dielectric film only on an upper surface of a mesa structure including an active layer formed by selective growth, which is a manufacturing process according to a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Mask, 3 ... Mesa structure, 4 ... Current block layer (n-type InP), 5 ... Current block layer (P-type In)
P), 5a ... current blocking layer (Fe-doped semi-insulating In)
P), 5b ... InAlAs layer, 5c ... current blocking layer (been InAlAs) 6 ... current blocking layer oxide (n-type InP), 6a ... undoped InP layer, 7 ... buried layer 8 ... contact layer, 9 ... SiO ₂ Film: 10 ... p-side electrode, 11 ... n-side electrode, 12 ... groove, 13 ... hole injection direction, 14 ... electron injection direction.

Claims (12)

(57) [Claims] A semi-insulating semiconductor substrate; a mesa structure provided on the semiconductor substrate and including an active layer formed by selective growth; an upper surface of the mesa structure and the semiconductor substrate on one side of the mesa structure A first conductive type semiconductor layer provided thereon, a second conductive type semiconductor layer provided on the first conductive type semiconductor layer, and a second conductive type semiconductor layer provided on the second conductive type semiconductor layer. A current block structure comprising a first conductive type semiconductor layer provided; and a second conductive type semiconductor layer provided in contact with the mesa structure on the opposite side to one side of the mesa structure. A semiconductor optical device characterized by the above-mentioned. 2. The semiconductor device according to claim 1, wherein the current block structure is provided on an upper surface of the mesa structure and on the semiconductor substrate on one side of the mesa structure.
And a semi-insulating semiconductor layer provided on the semiconductor layer of the first conductivity type. 3. The semiconductor device according to claim 1, wherein the current block structure is provided on a top surface of the mesa structure and a first conductivity type semiconductor layer provided on the semiconductor substrate on one side of the mesa structure. A layer containing oxidized Al provided on the semiconductor layer of the first conductivity type. 4. The semiconductor optical device according to claim 1, wherein the semiconductor optical device is a semiconductor laser, a semiconductor optical amplifier,
Alternatively, the semiconductor optical device is any one of a semiconductor optical modulator. 5. The semiconductor device according to claim 1, wherein the semiconductor substrate is made of Fe-doped InP, the first conductivity type semiconductor layer is made of n-type InP, A semiconductor optical device, wherein the conductive semiconductor layer is made of p-type InP. 6. The semiconductor optical device according to claim 1, wherein the active layer has a multiple quantum well structure. 7. A first step of forming a pair of masks on a semi-insulating semiconductor substrate, and then forming a mesa structure including an active layer between the pair of masks by selective growth; A second step of forming a current block structure comprising a semiconductor of the first conductivity type and a semiconductor of the second conductivity type after removing one of the masks; and removing the mesa after removing the other of the pair of masks. Forming a semiconductor layer of the second conductivity type so as to be in contact with the structure. 8. The current block structure according to claim 7, wherein in the second step, after removing one of the pair of masks, a current block structure including a semiconductor layer of a first conductivity type and a semi-insulating semiconductor layer is formed. A method of manufacturing a semiconductor optical device. 9. The method according to claim 7, wherein in the second step, after removing one of the pair of masks, a current block structure including a semiconductor layer of the first conductivity type and a layer containing Al is formed. The third step is a step of removing the other of the pair of masks, forming a second conductivity type semiconductor layer so as to be in contact with the mesa structure, and oxidizing the Al-containing layer. A method for manufacturing a semiconductor optical device. 10. The semiconductor optical device according to claim 7, wherein the semiconductor optical device is a semiconductor laser, a semiconductor optical amplifier,
Alternatively, a method for manufacturing a semiconductor optical device, wherein the method is any one of semiconductor optical modulators. 11. The semiconductor device according to claim 7, wherein the semiconductor substrate is made of Fe-doped InP, the first conductivity type semiconductor layer is made of n-type InP, A method for manufacturing a semiconductor optical device, wherein the conductive semiconductor layer is made of p-type InP. 12. The method of manufacturing a semiconductor optical device according to claim 7, wherein the active layer has a multiple quantum well structure.