JP2000269603A - Semiconductor laser - Google Patents

Abstract

(57) [Summary] A semiconductor laser having a buried structure has a high temperature and a high temperature.
It is an object of the present invention to reduce the degradation of laser characteristics even under high current injection conditions, to enable low threshold and high efficiency operation, and to expand design flexibility. A mesa stripe including a first conductive type first cladding layer formed on a first conductive type semiconductor substrate, an active layer, and a second conductive type second cladding layer. When,
A buried layer 8 of the second conductivity type formed on the semiconductor substrate 1 on both sides of the mesa stripe 6, a current blocking layer 9 of the first conductivity type formed on the buried layer 8, and a mesa stripe 6
And has a heterojunction between the semiconductor substrate 1 and the buried layer 8 on both sides of the mesa stripe 6, has an absorption edge wavelength shorter than the absorption edge wavelength of the buried layer 8, and At least one quantum well layer 7 made of a material lattice-matched to
w containing current leakage prevention layer 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser, and more particularly, to a semiconductor laser having a buried structure.

[0002]

2. Description of the Related Art At present, especially in optical communication applications, semiconductor lasers having a buried structure having a pnpn junction thyristor type current block layer on both sides of an active layer are widely used. This structure can realize a low threshold current and is excellent in controlling the transverse mode.

A conventional buried type semiconductor laser has a structure as shown in FIG. 1, for example. In FIG.
On the upper surface of an n-type semiconductor substrate 100, an n-type cladding layer 101, an active layer 102 and a p-type cladding layer 103 are formed in this order. The upper surface of the n-type cladding layer 101, the active layer 102, and the p-type cladding layer 103 are both processed into a stripe-shaped plane and a mesa-shaped cross section using a single mask.
On the semiconductor substrate 100 on both sides of the mesa stripe portion, a p-type buried layer 104 and an n-type current block layer 105 are sequentially formed.

The p-type cladding layer 103 and the current blocking layer 10
5, a p-type cladding layer 106 is formed, and a contact layer 107 is further formed thereon. A p-side electrode 108 is formed on the contact layer 107, and an n-side electrode 109 is formed on the lower surface of the semiconductor substrate 100.
In such a buried type semiconductor laser, pnpn junctions are formed on both sides of the mesa stripe, so that the junction between the buried layer 104 and the current block layer 105 is reverse-biased in the operation state of the semiconductor laser. The current is blocked, so that the current flowing between the n-side electrode 109 and the p-side electrode 108 is narrowed.

[0005]

SUMMARY OF THE INVENTION However, high temperature
It is known that in a buried semiconductor laser placed under a condition of a high injection current, a leak current flowing between the current blocking layer 105 and the active layer 102 increases, and the laser characteristics deteriorate. This is because the current flowing between the current blocking layer 105 and the active layer 102 is reduced by the current blocking layer 105, the buried layer 104,
It acts as a gate current of the npn transistor composed of the semiconductor substrate 100, and turns on when a certain voltage or more is applied to this portion. Such a phenomenon tends to occur during a high current injection operation in which a large voltage is applied between the n-side electrode 109 and the p-side electrode 108, or at a high temperature at which the built-in voltage decreases.

In order to prevent such turn-on,
JP-A-58-84485 and JP-A-64-82684 disclose semiconductor lasers in which a semiconductor layer (turn-on prevention layer) having an energy band gap smaller than that of a semiconductor substrate is interposed between the semiconductor substrate and the buried layer. ing. However, such a turn-on prevention layer has a very narrow range of materials selected to ensure lattice matching with the buffer layer, and tends to be unable to sufficiently prevent turn-on.

A semiconductor laser having a structure in which a strained superlattice layer is interposed between a buried layer and a semiconductor substrate is described in Japanese Patent Application Laid-Open No. 5-41559. However, since the thickness of the film constituting such a strained superlattice layer is extremely small, it is difficult to control the film thickness. SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor laser having a buried structure in which the laser characteristics are less deteriorated even under high-temperature and high-current injection conditions, a low-threshold operation can be performed with high efficiency, and the film thickness can be easily controlled. It is in.

[0008]

Means for Solving the Problems The above-mentioned problems are shown in FIG.
As illustrated in FIG. 6 or FIG. 7B, a first conductive type first cladding layer 2 and an active layer 3 (13) formed on a first conductive type semiconductor substrate 1 and a second conductive type A mesa stripe 6 including a second clad layer 4 of a mold and formed to a position lower than the lower surface of the active layer 3 (13); and a semiconductor substrate 1 on both sides of the mesa stripe 6 A buried layer of the second conductivity type, a current blocking layer of the first conductivity type formed on the buried layer, and a lower portion of the mesa stripe; 6, a material which has a heterojunction between the semiconductor substrate 1 and the buried layer 8 on both sides of the semiconductor substrate 1 and has an absorption edge wavelength shorter than the absorption edge wavelength of the buried layer 8 and is lattice-matched to the semiconductor substrate 1 Current leakage prevention layer 7 (1) including at least one quantum well layer 7w (17w) made of And 7) solving the problem.

In the above-mentioned semiconductor laser, FIG.
As an example, a first conductivity type semiconductor layer 21 formed between the current leak prevention layer 7 (17) and the semiconductor substrate 1 may be further added. In the above-described semiconductor laser, the composition wavelength of the material forming the quantum well layer 7w (17w) in the current leak prevention layer 7 (17) is shorter than the emission wavelength of the active layer 3 (13). Is preferred.

In the above-described semiconductor laser, the active layer 3 is formed of a single-layer bulk semiconductor, and the quantum well layer 7w in the current leakage prevention layer 7 (17) is provided.
The quantum well layer 7w may be formed from a material having a wavelength corresponding to the quantum level of (17w) shorter than the emission wavelength of the active layer 3. In the above-described semiconductor laser, the quantum well layer 7w in the current leak prevention layer 7 (17) is provided.
(17w) may be made of a material having the same constituent elements and the same composition ratio as those of the active layer 3.

In the above-described semiconductor laser, the quantum well layer 7w (17) in the current leakage prevention layer 7 (17) is provided.
w) may be made of a material that is the same constituent element as the active layer 3 and that differs only in the composition ratio. In the above-described semiconductor laser, the quantum well layer 7w (17w) in the current leak prevention layer 7 (17) may be made of a constituent element different from that of the active layer 3.

In the above-described semiconductor laser, the active layer 13 is formed of a layer including a quantum well, and further, the quantum well layer 7w (1) in the current leakage prevention layer 7 (17) is formed.
It is preferable that the wavelength corresponding to the quantum level 7w) is shorter than the emission wavelength corresponding to the quantum level of the quantum well layer 13w of the active layer 13. In the above-described semiconductor laser, the quantum well layer 7w (17w) in the current leakage prevention layer 7 (17) is the same constituent element as the quantum well layer 3w (13w) of the active layer 3 (13). You may make it consist of materials of the same composition ratio.

In the above-described semiconductor laser, the quantum well layer 7w (17) in the current leakage prevention layer 7 (17) is provided.
w) may be made of a material having the same constituent element as that of the quantum well layer 13w of the active layer 13 except for the composition wavelength. In the above-described semiconductor laser, the quantum well layer 7w (17w) in the current leakage prevention layer 7 (17) is
The active layer 13 may be made of a constituent element different from that of the quantum well layer 13w.

[0014] The figures and symbols described above are cited for easy understanding of the invention, and the invention is not limited thereto. Next, the operation of the present invention will be described. According to the present invention, a current leak prevention layer having a quantum well structure heterojunction is formed between a semiconductor substrate and a buried layer at both sides of a mesa stripe having an active layer, and the current The absorption edge wavelength of the leak prevention layer is set to a shorter wavelength than the emission wavelength of the laser.
Thereby, the pnpn of the current block layer and the layer below it are
Alternatively, the breakdown voltage of the pnp junction at the time of high-temperature and high-current injection is increased, and the buried structure of the semiconductor laser is hardly turned on. Also,
Since the current leakage prevention layer has a quantum well structure, recombination current in the current leakage prevention layer is reduced, and the range of selection of materials such as constituent elements and composition ratios is widened. In addition, since the current leakage prevention layer has a steep absorption edge which is a characteristic characteristic of the quantum well structure, the occurrence of excessive optical loss due to the addition of such a current leakage prevention layer is suppressed.

Further, since the quantum well contained in the current leakage prevention layer is made of a material that lattice-matches with the semiconductor substrate, the thickness can be increased as compared with the case where a strained quantum well is employed. The selection range of the film thickness and the number of layers is wider than that of the strained quantum well, and the adjustment of the ground level of the quantum well becomes easy. The compound semiconductor constituting the semiconductor substrate, the buried layer, the current block layer, the clad layer, and the like becomes p-type or n-type due to the introduction of impurities during growth. One of the p-type and the n-type is expressed as a first conductivity type, and the other is expressed as a second conductivity type.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a sectional view showing a manufacturing process of a semiconductor laser according to a first embodiment of the present invention.

First, as shown in FIG. 1A, an n-InP substrate (semiconductor substrate) 1 is formed on a (100) plane with silicon (Si) doped at a concentration of 5 × 10 ¹⁷ / cm ^3. An n-type cladding layer 2 of about 0.5 μm thick made of -InP, a bulk active layer 3 of 0.15 μm thick made of undoped InGaAsP having a composition wavelength of 1.3 μm lattice-matched to InP, and zinc (Zn). Concentration 5 ×
A first p-type cladding layer 4 made of p-InP and having a thickness of about 0.25 μm doped with 10 ¹⁷ / cm ³ is formed in order by, for example, MOVPE (metal organic chemical vapor deposition).

Subsequently, an insulating film 5 made of, for example, SiO ₂ is formed on the first p-type clad layer 4 to a thickness of 0.3 μm, for example, by CVD (chemical vapor deposition). Then, the width of the insulating film 5 is about 1.5 μm by photolithography.
Is processed into the planar shape of the stripe. Next, as shown in FIG. 1B, the first p-type cladding layer 4 and the bulk active layer 3 are formed by dry etching using, for example, an ethane-based gas using the stripe-shaped insulating film 5 as a mask. Then, the n-type cladding layer 2 is sequentially etched to form a mesa stripe portion 6 including the first p-type cladding layer 4, the bulk active layer 3, and the n-type cladding layer 2. This etching is performed at least below the bottom surface of the bulk active layer 3. The etching stop surface appears in the upper part of the n-InP substrate 1 in FIG.

Next, as shown in FIG. 3A, using the insulating film 5 as a mask, a current leak prevention having a quantum well structure is formed on the n-InP substrate 1 on both sides of the mesa stripe portion 6. Layer 7
Is formed by the MOVPE method. This current leakage prevention layer 7 is formed such that its upper surface is located below the bottom surface of bulk active layer 3. The quantum well structure constituting the current leakage prevention layer 7 includes a well layer 7w of InGaAsP having the same material and the same composition as the bulk active layer 3 and having a thickness of 7 nm.
1.1 μm composition wavelength In
It has a structure in which barrier layers 7b made of GaAsP and having a thickness of 10 nm are alternately formed. The well layer 7w has two layers and the well layer 7b has three layers, for a total of five layers. The well layer 7w and the barrier layer 7b do not have a strained superlattice structure.

The well layer 7w may be composed of the same material (InGaAsP) as the bulk active layer 3 and a semiconductor layer having a different composition ratio, or a material different from the bulk active layer 3, such as InAlGaAs. It does not matter. In order to selectively grow the current leakage prevention layer 7 on the n-InP substrate 1, a chlorine compound gas such as methyl chloride gas (CH ₃ Cl) or Adopt the method of introducing chlorine. As a result, the current leakage prevention layer 7 grows sequentially from below the side wall of the mesa stripe portion 6.

The current leak prevention layer 7 having such a quantum well structure becomes a heterojunction with the n-InP substrate 1, and the light absorption edge wavelength of the quantum well structure is shorter than the emission wavelength of the laser. Become. Note that the quantum well structure may be a single quantum well structure having one well layer 7w.
Next, as shown in FIG. 3B, zinc (Zn) has a concentration of 5 × 10 5 on the current leakage prevention layer 7 on both sides of the mesa stripe 6.
A p-InP buried layer 8 doped at ¹⁷ / cm ³ and an InP current blocking layer 9 doped with silicon at a concentration of 2 × 10 ¹⁸ / cm ³ are formed in this order by MOVPE (metal organic chemical vapor deposition), for example. Thus, the buried crystal growth is completed. Its p-InGa
As buried layer 8 becomes a heterojunction with current leakage prevention layer 7.

It is to be noted that the current block layer 9 is grown under such a condition that it grows in contact with the edge of the upper surface of the first p-type cladding layer 4. Subsequently, after removing the insulating film 5 with an acid such as hydrofluoric acid, as shown in FIG. 4, a 1 μm-thick p-InP layer made of p-InP doped with zinc at a concentration of 2 × 10 ¹⁸ / cm ³ by MOVPE. A second p-type cladding layer 10 and a 0.5 μm-thick contact layer 11 made of p-InGaAs doped with zinc at a concentration of 1 × 10 ¹⁹ / cm ³ are connected to the first p-type cladding layer 4 and a current block. It is formed on the layer 9 in order.

Further, a p-side electrode 12 made of, for example, titanium (Ti) / platinum (Pt) / gold (Au) is formed on the contact layer 11, and gold germanium (AuG) is formed on the back surface of the n-InP substrate 10.
e) An n-side electrode 14 made of gold (Au) is formed. Thereby, the basic structure of the buried type semiconductor laser is completed.
In growing a compound semiconductor by MOVPE, trimethylindium was used as a source of indium.
Phosphine (PH ₃ ) is used as a source of phosphorus, trimethylgallium is used as a source of gallium, arsine (AsH ₃ ) is used as a source of arsenic, and trimethylaluminum is used as a source of aluminum. In addition, dimethyl zinc is used as a supply gas for zinc as a p-type impurity, and disilane (Si ₂ H ₆ ) is used as a supply gas for silicon as an n-type impurity. These gases are similarly applied to the embodiments described later.

In the buried type semiconductor laser shown in FIG. 4, the current leakage preventing layer 7 which becomes a heterojunction with the buried layer 8 and the n-InP substrate 1 is provided. Insert in between,
In addition, since the absorption edge wavelength of the current leakage prevention layer 7 is set to a wavelength shorter than the emission wavelength of the laser (that is, the emission wavelength of the bulk active layer 3), compared with the conventional semiconductor laser shown in FIG. The withstand voltage of the current block layer at the time of high temperature and high current injection increases, and it becomes difficult for the npnp junction of the buried region to turn on in the laser oscillation state.

Further, since the current leakage prevention layer 7 has a quantum well structure, the recombination current is reduced and the degree of freedom of the material and composition is increased as compared with the case where a bulk structure (single layer structure) is employed. Moreover, according to the quantum well structure, a steep light absorption edge is obtained as a unique feature thereof, so that an excessive increase in optical loss due to the current leakage prevention layer 7 can be suppressed.

Since the composition wavelength of the barrier layer 7b of the current leakage prevention layer 7 is shorter than the composition wavelength of the buried layer 8 thereabove, the flow of carriers in the hetero barrier can be effectively controlled by the height of the energy barrier. This improves the breakdown voltage of the block layer during high-temperature and high-current injection. In the above-described semiconductor laser, the well layer 7w in the current leakage prevention layer 7
Is shorter than the emission wavelength of the bulk active layer 3, so that part of the laser light guided through the mesa stripe portion 6 is less likely to be absorbed by the current leakage prevention layer 7.

Further, the quantum level of the well layer 7w is shifted to a shorter wavelength side than the band gap of the bulk active layer 3 of the same material and the same composition by making the well layer 7w constituting the current leak prevention layer 7 thinner. It is easy to do. Moreover, by making the well layer 7w the same material and the same structure as the bulk active layer 3, the well layer 7w can be easily crystal-grown without generating lattice defects.

Well layer 7w constituting current leakage prevention layer 7
Even if the constituent material is the same as that of the bulk active layer 3, it is possible to change only the absorption edge wavelength while maintaining the lattice matching condition by changing the composition ratio, thereby increasing the degree of freedom in design. By the way, a material that is substantially lattice-matched with the barrier layer 7b and has a narrower band gap than the barrier layer 7b is selected for the well layer 7w constituting the current leakage prevention layer 7,
Not a strained quantum well. Therefore, the range of selection of the thickness of the well layer 7w of the current leakage prevention layer 7 is widened as compared with the case where a strained quantum well is employed, and thereby the adjustment of the ground level in the well layer 7w becomes easy.

The well layer 7w in the current leak prevention layer 7
May be different from the material system of the bulk active layer 3. (Second Embodiment) A second embodiment of the present invention will be described with reference to FIG. First, an n-type cladding layer 2, an active layer 13, and a p-type cladding layer 4 are formed on an n-InP substrate 1 by M
After the formation by the OVPE method, a striped insulating film 5 is formed on the p-type cladding layer 4.

The thicknesses and materials of the n-type cladding layer 2 and the p-type cladding layer 4 are the same as in the first embodiment. The thickness and material of the insulating film 5 are the same as those of the first embodiment. Unlike the first embodiment, the active layer 13 has a composition wavelength of 1.1.
10 nm thick barrier layer 13b made of InGaAsP of μm
And a thickness of 7 nm made of InGaAsP having a composition wavelength of 1.4 μm.
And a multiple quantum well structure in which a total of 17 well layers 13w are alternately formed. The active layer 13 is
A single quantum well structure having one well layer 13w may be used.

Next, as in the first embodiment, the first p-type layer is formed by dry etching using, for example, an ethane-based gas using the insulating film 5 processed in a stripe shape as a mask.
The type clad layer 4, the active layer 13, and the n-type clad layer 2 are etched in a mesa shape in cross section to form a mesa stripe portion 6 including the first p-type clad layer 4, the bulk active layer 13, and the n-type clad layer 2. . At this time, the etching is stopped at least below the bottom surface of the bulk active layer 3. In this embodiment, the etching stop position is located above the n-InP substrate 1.

Subsequently, as shown in FIG.
Is used as a mask, and n-In on both sides of the mesa stripe portion 6 is used.
On the P substrate 1, a current leak prevention layer 1 having a quantum well structure is formed.
7. A p-InP buried layer 8 and an n-InP current blocking layer 9 are formed in this order by MOVPE. The current leakage preventing layer 17 is formed under the condition that its upper surface is located lower than the bottom surface of the bulk active layer 3, and the current blocking layer 9 is formed on the edge of the upper surface of the first p-type cladding layer 4. Conditions are such that they grow so as to be in contact with each other.

The quantum well structure constituting the current leakage prevention layer 17 has a thickness of 1 μm of InGaAsP having a composition wavelength of 1.1 μm.
A barrier 17b of 0 nm and a thickness of 3 nm made of InGaAsP having the same constituent elements and the same composition as the well layer 13w of the active layer 13
And well layers 17w are alternately formed. Here, the well layer 17w has a composition wavelength of InGaAsP.
Other materials such as InAlGaAs having a shorter wavelength may be used. The quantum well structure may be a single quantum well structure having one well layer 17w.

When growing the current leak preventing layer 17, a chlorine compound gas or chlorine is introduced into the growth atmosphere. As a result, the current leakage prevention layer 17 having such a quantum well structure becomes a heterojunction with the n-InP substrate 1 and the p-InP buried layer 8, and the absorption edge wavelength of the quantum well structure is a laser. Wavelength is shorter than the emission wavelength of.

Next, after the insulating film 5 is removed with an acid such as hydrofluoric acid, a thickness of p-InP is formed on the first p-type cladding layer 4 and the current blocking layer 9 as shown in FIG. 1 μm
A second p-type cladding layer 10 and a contact layer 11 of p-InGaAs having a thickness of 0.5 μm are formed in this order. Then, a p-side electrode 12 having the same structure as in the first embodiment is formed on the contact layer 11, and an n-side electrode 14 having the same structure as in the first embodiment is formed on the back surface of the n-InP substrate 10.

Thus, the basic structure of the buried type semiconductor laser is completed. Also in the semiconductor laser of the present embodiment, similarly to the semiconductor laser of the first embodiment, the flow of carriers in the hetero barrier is effectively prevented, and the withstand voltage of the current block layer at the time of high-temperature and high-current injection can be improved. Further, according to the semiconductor laser of the present embodiment, the emission wavelength corresponding to the quantum level of the well layer 17w in the current leakage prevention layer 17 is made larger than the emission wavelength corresponding to the quantum level of the well layer 13w of the active layer 13. By setting the wavelength to be short, a part of the laser light guided through the mesa stripe portion 6 is hardly absorbed by the current leak prevention layer 17.

Further, as a material for forming the well layer 17w in the current leak preventing layer 17, the well layer 1 in the active layer 13 is used.
A material having the same compositional element as that of 3w and having a composition ratio shorter than the wavelength of the well layer 13w may be selected. Further, the constituent elements of the well layer 17w of the current leakage prevention layer 17 may be different from those of the well layer 13w of the active layer 13, such as InAlGaAs. Further, the barrier layer 7 in the current leakage prevention layer 7
As b, InAlGaAs having a shorter composition wavelength than InP may be used to increase the barrier at the heterojunction. (Third Embodiment) In the first and second embodiments, n-
The current leakage prevention layer 7 is formed directly on the InP substrate 1. However, the semiconductor laser of the present invention is not limited to such a structure, and an n-InP layer may be interposed between the n-InP substrate 1 and the current leakage prevention layer 7.

That is, from the state shown in FIG. 2B, as shown in FIG. 7A, the n-Ins on both sides of the mesa stripe portion 6 are formed.
An n-InP layer 21 is formed on the P substrate 1 by MOVPE.
After being formed to a thickness of 0 nm, similarly to the first embodiment, the current leakage prevention layer 7, the buried layer 8, and the current block layer 9 are formed.
Are sequentially formed by the MOVPE method. When growing the n-InP buffer layer 21, the growth gas is made to contain a chlorine compound gas or chlorine.

Thereafter, n-sides on both sides of the mesa stripe portion 6 are formed.
On the InP buffer layer 21, the p-type buried layer 8 and the n-type current block layer 9 are MOV-mounted under the same conditions as in the first embodiment.
It is formed by the PE method. Then, after removing the insulating film 5, under the same conditions as in the first embodiment, as shown in FIG. 7B, a second layer is formed on the current blocking layer 9 and the first p-type cladding layer 4. A p-type cladding layer 10 and a contact layer 11 are formed. Further, a p-side electrode 12 is formed on the contact layer 11, and an n-side electrode 14 is formed below the p-InP substrate 1.

According to the semiconductor laser of this embodiment, the first
As in the embodiment, it is possible to effectively prevent the flow of carriers in the hetero barrier and improve the withstand voltage of the current block layer at high temperature and high current injection. In addition, since a semiconductor layer (n-InP layer) 21 of the same conductivity type (n-type) as the n-InP substrate 1 is inserted between the current leak prevention layer 7 and the n-InP substrate 1, the mesa stripe is formed. In addition to eliminating the substrate damage that may occur when the portion 6 is formed, it is possible to prevent the substrate from being exposed to the atmosphere after the mesa stripe portion 6 is formed.

Here, for convenience, the description has been made based on the structure shown in the first embodiment, but this structure may be formed based on the structure shown in the second embodiment. In the first to third embodiments, the quantum well structure is entirely undoped.

[0042]

As described above, according to the present invention, a current leakage prevention layer having a quantum well structure, which has a heterojunction, is inserted between a semiconductor substrate and a buried layer on both sides of a mesa stripe having an active layer, and Since the absorption edge wavelength of the current leakage prevention layer is set to a wavelength shorter than the emission wavelength of the laser, the current blocking layer and the pnpn or npnp junction under the current blocking layer are exposed to high temperatures.
The breakdown voltage at the time of high current injection can be increased, and the embedded structure of the semiconductor laser can be hardly turned on.

Further, since the current leakage prevention layer has a quantum well structure, recombination current in the current leakage prevention layer is reduced, and the range of selection of materials such as constituent elements and composition ratios can be widened. In addition, since the current leakage prevention layer has a steep absorption edge which is a characteristic characteristic of the quantum well structure, it is possible to suppress the occurrence of excessive optical loss due to the addition of such a current leakage prevention layer.

Since the quantum well included in the current leakage prevention layer is made of a material that lattice-matches with the semiconductor substrate, the thickness can be increased as compared with the case where a strained quantum well is employed. The selection range of the film thickness and the number of layers is wider than that of the well, so that the ground level of the quantum well can be easily adjusted.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a conventional buried semiconductor laser.

FIGS. 2A and 2B are cross-sectional views (part 1) illustrating a manufacturing process of the semiconductor laser according to the first embodiment of the present invention.

FIGS. 3A and 3B are cross-sectional views (No. 2) showing the steps of manufacturing the semiconductor laser according to the first embodiment of the present invention.

FIG. 4 is a sectional view showing a semiconductor laser according to the first embodiment of the present invention.

FIGS. 5A and 5B are cross-sectional views showing a manufacturing process of a semiconductor laser according to a second embodiment of the present invention.

FIG. 6 is a sectional view showing a semiconductor laser according to a second embodiment of the present invention.

FIGS. 7A and 7B are cross-sectional views showing a part of a manufacturing process of a semiconductor laser according to a third embodiment of the present invention and the semiconductor laser.

[Explanation of symbols]

1 ... n-InP substrate (semiconductor substrate), 2 ... n-type cladding layer,
3 ... bulk active layer, 4 ... p-type cladding layer, 5 ... insulating film,
6: mesa stripe portion, 7, 17: current leakage prevention layer,
7w, 17w: well layer, 7b, 17b: barrier layer, 8: buried layer, 9: current blocking layer, 10: second p-type cladding layer, 11: contact layer, 12: p-side electrode, 13: active Layers, 14 ... n-side electrode, 21 ... buffer layer.

Claims (5)

[Claims] A first conductive type first cladding layer formed on a first conductive type semiconductor substrate; an active layer; and a second conductive type second cladding layer. A mesa stripe formed to a position lower than the lower surface of the semiconductor substrate, a second conductivity type buried layer formed on the semiconductor substrate on both sides of the mesa stripe, and formed on the buried layer A current blocking layer of a first conductivity type, in contact with a lower portion of the mesa stripe, and heterojunction between the semiconductor substrate 1 and the buried layer on both sides of the mesa stripe; A semiconductor laser having an absorption edge wavelength shorter than the wavelength and a current leakage prevention layer including at least one quantum well layer made of a material lattice-matched to the semiconductor substrate 1. 2. The semiconductor laser according to claim 1, further comprising a first conductivity type semiconductor layer formed between said current leakage prevention layer and said semiconductor substrate. 3. The method according to claim 1, wherein a composition wavelength of a material constituting the quantum well layer in the current leakage prevention layer is shorter than an emission wavelength of the active layer. A semiconductor laser as described in the above. 4. The active layer is made of a single-layer bulk semiconductor, and a wavelength corresponding to a quantum level of the quantum well layer in the current leakage prevention layer is shorter than an emission wavelength of the active layer 3. The semiconductor laser according to any one of claims 1, 2, and 3, wherein 5. The active layer comprises a layer including a quantum well, and a wavelength corresponding to a quantum level of the quantum well layer in the current leakage prevention layer is equal to a quantum level of the quantum well layer of the active layer. 4. The semiconductor laser according to claim 1, wherein the wavelength is shorter than the emission wavelength corresponding to the position.