JPH06283816A - Semiconductor laser of embedded structure and fabrication thereof - Google Patents

Abstract

PURPOSE:To fabricate a semiconductor laser having an embedded structure, which can function at a low threshold level with high efficiency, without requiring any complicated fabrication step. CONSTITUTION:When a current confinement layer 5 is formed by vapor phase epitaxial growth of n-type InP, concentration of Se to be doped is set at 8X10<18>cm<-3> or above thus preventing deposition of the n-type InP on the (100) crystal face above a mesa stripe. Since the n-type InP is not grown on the upper plane including the (100) crystal face at the mesa stripe part of a clad layer 4, a current confinement layer 5 is formed such that the extensions of the upper plane including the (100) crystal plane at the mesa stripe part of the clad layer 4 are coplanar therewith on the opposite sides.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a buried structure semiconductor laser using a metal organic chemical vapor deposition method and a method for manufacturing the same.

[0002]

2. Description of the Related Art A buried structure semiconductor laser in which both sides of an active region for oscillating a laser are filled with a current block layer can operate at a low threshold and obtain high efficiency. In the manufacture of this embedded structure semiconductor laser, a metal organic chemical vapor deposition method, an LPE method, or the like is used to embed the active region of the mesa stripe structure that oscillates the laser. When embedding this active region by the metal organic chemical vapor deposition method, a selective growth mask is formed on the upper part of the active region, and using this, a current block layer is formed on both sides of the active region. However, the metal-organic vapor phase epitaxy method easily causes abnormal growth at both upper ends of the mesa stripe structure, which makes it difficult to bury it flatly.

As described above, conventionally, a buried structure semiconductor laser has been manufactured as shown in FIG. First, a buffer layer 42, an active layer 43, and a clad layer 44 are formed on a substrate 41 (FIG. 4A), a selective growth mask 45 having a width of about 2 μm is formed thereon, and etching is performed using this as a mask. The active region is processed into a mesa stripe having a height of about 1 μm (FIG. 4B). After that, as shown in FIG.
As shown in (d), the current blocking layer 46 and the current confinement layer 4 are processed by the same process as the normal growth of the buried layer.
7 was formed, the selective growth mask was removed, and then the over cladding layer 48 and the cap layer 49 were formed to manufacture a buried structure laser.

Further, conventionally, as shown in FIG. 5, a buffer layer 52, an active layer 53, a clad layer 54, and a cap layer 55 are formed on a substrate 51 in the same manner as described above (see FIG. 5).
(A)) Etching is performed using a mask having a width of about 4 μm, and side etching under this mask is used to form a mesa stripe having a width of about 2 μm and a height of about 2 μm having a selective growth mask 56 having an eaves on the upper side. To do. (Fig. 5
(B)). After that, by the metal organic chemical vapor deposition method, as shown in FIG.
As shown in (c), the current blocking layer 57 and the current confinement layer 58 were continuously deposited by using the selective growth mask 56 while suppressing abnormal growth.

However, in the method shown in FIG. 4, it is necessary to perform vapor phase growth three times or more and to form a mesa stripe-shaped active region on which a selective growth mask is formed, which complicates the process. there were. Also in the method shown in FIG. 5, vapor phase growth must be performed twice or more, and in addition, a selective growth mask having an eaves must be formed, and the process is also complicated. Since etching is used to form the active region into a mesa stripe shape, the side surface of the active layer is exposed, and InGaAs of MQW structure is exposed here.
When / InAlAs is used, the layer containing Al is exposed and oxidized, so that it is difficult to bury the side surface well.

In order to solve the above problems, 1
A method of manufacturing a buried structure semiconductor laser by a single round of metal organic chemical vapor deposition has been proposed. Hereinafter, a method of manufacturing this embedded structure semiconductor laser will be described with reference to FIG.
This buried structure semiconductor laser is an n-type In grown on a substrate 61 whose surface on which a stripe pattern 61a having a predetermined width is formed is a (100) crystal plane by metal organic chemical vapor deposition.
P layer 62, undoped InGaAsP layer 63, p-type In
The P layer 64 is sequentially deposited. At this time, the buffer layer 62a, the active layer 63a, and the cladding layer 64a are formed on the stripe pattern 61a with their side surfaces inclined, and these side surfaces form an angle of about 54 ° with the surface of the substrate 61 (111). ) It becomes a B crystal plane.

Next, a current confinement layer 65 made of n-type InP, an overclad layer 66 made of p-type InP,
The cap layer 67 made of p-type InGaAsP is sequentially formed by the organic vapor deposition method. In the metalorganic vapor phase epitaxy, no growth reaction occurs on the (111) B crystal plane, so that each layer is formed as shown in FIG. As a result, the current confinement layer 65 is grown and deposited so as to sandwich the active layer 63a, and a current confinement structure is formed.

[0008]

Since the prior art is constructed as described above, there are the following problems.
In FIG. 6, in the growth of the p-type InP for forming the cladding layer 64a, the formation of the cladding layer 64a automatically ends when the cross section becomes a triangular shape. Becomes thicker as the amount of growth increases. Therefore, in the growth of p-type InP for forming the clad layer 64a, as shown in FIG.
In the case where the p-type InP layer 64 is too thick and the current confinement layer 65 is formed at a position higher than the active layer 63a, FIG.
As shown in (c), the p-type InP layer 64 is too thin and is formed at a position lower than the active layer 63a.

As shown in FIG. 6B, when the current confinement layer 65 is formed above the active layer 63a, the interval between the current confinement layers 65 is narrowed and the region where the current flows is narrowed, so that the active layer 63a is formed. The amount of current supplied to On the other hand, when the current confinement layer 65 is formed below the active layer 63a as shown in FIG.
The contact area between the current confinement layer 65 made of P and the buffer layer 62a made of n-type InP is increased, so that the leak current passing therethrough is increased. Then, the same thing occurs when the height of the mesa stripe changes. That is, the conventional manufacturing method has a problem that the growth amount of the cladding layer and the height of the mesa stripe must be strictly controlled.

The present invention has been made in order to solve the above problems, and it is possible to manufacture a buried structure semiconductor laser which operates at a low threshold value and obtains high efficiency without requiring complicated steps. It is characterized by doing so.

[0011]

According to the method of manufacturing a buried structure semiconductor laser of the present invention, a stripe-shaped mesa stripe is formed on a semiconductor substrate having an n-type (100) crystal plane in the <011> direction of the semiconductor substrate. The first step of
A second step in which a semiconductor layer is grown on a semiconductor substrate by a metal organic chemical vapor deposition method so that the region on the mesa stripe becomes an active region for oscillating a laser, and the flat surface of the region on the active region is (100). Third step of forming the first p-type semiconductor layer on the semiconductor layer by a metal-organic chemical vapor deposition method so that the surface becomes a crystal plane and the angle between the side surface following this surface and the semiconductor substrate surface is less than 54 °. And a fourth step of selectively growing a first n-type semiconductor layer doped with a VI group element at a predetermined concentration in a region other than the (100) crystal plane in the region on the active region of the first p-type semiconductor layer, A fifth step of forming a second p-type semiconductor layer on the first p-type semiconductor layer and the second n-type semiconductor layer,
A sixth step of forming a third p-type semiconductor layer on the second p-type semiconductor layer.

The buried structure semiconductor laser of the present invention has a semiconductor substrate having an n-type (100) crystal plane in which stripe-shaped mesa stripes are formed in the <011> direction, and a mesa formed on the semiconductor substrate. A semiconductor layer in which a region on the stripe becomes an active region for oscillating a laser and a flat surface of the region formed on the semiconductor layer on the active region are (10
0) a first p-type semiconductor layer, which is a crystal plane, and an angle between a side surface following the plane and the semiconductor substrate surface is less than 54 °, and a region on the active region of the first p-type semiconductor layer. Flat (1
A VI having a predetermined concentration, which is formed in a plane other than the (00) crystal plane and which is continuous with the (100) crystal plane is the same plane as the flat plane.
A first n-type semiconductor layer doped with a group element and a second n-type semiconductor layer
A second p-type semiconductor layer formed on the n-type semiconductor layer,
And a third p-type semiconductor layer formed thereon.

[0013]

The first n-type semiconductor layer is formed in a region other than the (100) crystal plane of the region on the active layer of the first p-type semiconductor layer, and the (100) crystal face of the region on the active layer is a mesa stripe. Since the width of the first p-type semiconductor layer can be as wide as the width, the region of the first p-type semiconductor layer in which the current flows does not become narrow, and a sufficient current flows in the active layer. Then, the first p-type semiconductor layer and the first n-type semiconductor layer function as a current confinement layer.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. Example 1. FIG. 1 is a perspective view showing a method of manufacturing a semiconductor laser which is an embodiment of the present invention. Hereinafter, a method of manufacturing the buried structure semiconductor laser of the first embodiment will be described with reference to FIG. First, a SiO ₂ film is deposited on the substrate 1 made of n-type InP having a (100) crystal plane by a sputtering method. Next, this SiO ₂ film is formed into a stripe-shaped stripe mask having a width of 2 μm extending in the <011> direction of the substrate 1 by photolithography and etching. Next, using this stripe mask as a mask, chlorine
The substrate 1 is etched by reactive ion etching using an argon-based gas, and the stripe mask is removed by HF after etching to form a mesa stripe 1a as shown in FIG. 1 (a).

Next, Se-doped n-type InP, undoped InGaAsP, and p are formed on the substrate 1 on which the mesa stripes 1a are formed by using a metal organic chemical vapor deposition method.
-Type InP and Se-doped n-type InP and p-type InP
And p-type InGaAsP with a film thickness of 0.1 μm,
0.1 μm, 0.8 μm, 0.6 μm, 1.0 μm,
It is formed by sequentially switching the gas so that the thickness becomes 0.4 μm. As a result, as shown in FIG.
An n-type InP layer 2 and an InGaAsP layer 3 are formed on the substrate 1 on both sides of the mesa stripe 1a, a buffer layer 2a is formed on the mesa stripe 1a, and an active layer 3a having a wavelength gap of 1.5 μm is formed. The confinement layer 5, the over cladding layer 6, and the cap layer 7 are formed.

Here, n-type I when the current confinement layer 5 is formed
In vapor deposition of nP, the concentration of Se to be doped is 8 ×
By setting it to be 10 ¹⁸ cm ⁻³ or more, (10
0) The n-type InP is prevented from being deposited on the crystal plane. As a result, as shown in FIG. 1B, the upper plane having the (100) crystal plane of the mesa stripe-shaped portion of the cladding layer 4 has n Type InP does not grow, and clad layer 4 is formed on both sides of it.
The current confinement layer 5 is formed such that a part of the mesa-stripe-shaped portion following the upper plane having the (100) crystal plane is flush with this plane. As shown in FIG. 2, the width W
When p-type InP is deposited on the stripe pattern having a thickness of 1.1 μm, the cross section becomes a trapezoidal ridge structure. When Se-doped n-type InP is deposited on this,
The ratio of the thickness r deposited on the ridge structure to the thickness r0 deposited on the flat portion becomes smaller as the doping concentration is higher.

By the way, when the side surface of the mesa stripe-shaped portion of the clad layer 4 has an angle of about 54 ° with respect to the plane of the substrate 1 and is a (111) B crystal plane, it is formed on this. N-type In during the growth of the current confinement layer 5
Since P does not grow on the (111) B crystal plane, n-type InP is deposited on the upper plane of the cladding layer 4 having the (100) crystal plane in the mesa stripe shape. In such a state, the current supplied to the active layer 3a does not flow, and the laser does not oscillate.

In the buried structure semiconductor laser formed as in Example 1, the side surfaces of the buffer layer 2a and the active layer 3a are (111) B crystal planes having an angle of about 54 ° with respect to the plane of the substrate 1. Has become. However, the plane of the region on the active layer 3a deposited and formed on this is (100)
The side surfaces on both sides of the clad layer 4, which are the crystal planes, form an angle of less than 54 ° with respect to the plane of the substrate 1, and (111) B
It does not become a crystal plane. Therefore, as described above, on both sides of the mesa stripe portion of the clad layer 4, a part of the mesa stripe portion of the clad layer 4 following the upper plane having the (100) crystal plane is flush with the plane. The current confinement layer 5 is formed.

As described above, according to the first embodiment, since the buried structure semiconductor laser can be manufactured by one-time metal organic chemical vapor deposition, the active region including the active layer and the buried layer are formed. , Can be performed without contact with an atmosphere containing oxygen. Therefore, InGaAs / I of MQW structure
Even if nAlAs is used for the active layer, the buried structure semiconductor laser can be easily formed without oxidizing the layer containing Al.

Example 2. FIG. 3 is a perspective view showing a method of manufacturing a semiconductor laser according to the second embodiment of the present invention.
A method of manufacturing the embedded semiconductor laser according to the second embodiment will be described with reference to FIG. First, as shown in FIG.
Substrate 31 made of n-type InP having a (100) crystal plane
On top, using interferometric exposure and wet etching, <01
A diffraction grating in the 1> direction is formed. Next, in the same manner as in Example 1, a SiO ₂ film is deposited on the substrate 31 by the sputtering method, and the photolithography technique and etching are performed.
This SiO ₂ film is formed on a stripe-shaped stripe mask having a width of 2 μm and extending in the <011> direction of the substrate 31.
Then, using this stripe mask as a mask, the substrate 31 is etched by reactive ion etching using a chlorine / argon-based gas. After etching, the stripe mask is removed by HF, and the mesa stripe 31a is removed as shown in FIG. To form

Next, on the substrate 31 having the mesa stripe 31a formed thereon, undoped InGaAsP, undoped InGaAsP, Zn are formed by metalorganic vapor phase epitaxy.
Doped p-type InP, Se having a concentration of 8 × 10 ¹⁸ cm
^-3 or more doped n-type InP, p-type InP, p-type In
GaAsP with a film thickness of 0.1 μm, 0.1 μm,
It is formed by sequentially switching the gas so that the thickness becomes 0.8 μm, 0.6 μm, 1.0 μm, 0.4 μm.
As a result, as shown in FIG. 3C, the InGaAsP layers 32, I are formed on the substrate 31 on both sides of the mesa stripe 31a.
The nGaAsP layer 33 is formed. An optical waveguide layer 32a having a wavelength gap of 1.3 μm and an active layer 33a having a wavelength gap of 1.5 μm are formed on the mesa stripe 31a, and the cladding layer 34 and the current confinement layer 3 are formed thereon.
5, the over cladding layer 36 and the cap layer 37 are formed.

From the above, as in the first embodiment, 1
A distributed feedback buried structure semiconductor laser can be manufactured by performing metalorganic vapor phase growth once. In the above embodiment, the mesa stripe is formed on the substrate by dry etching using a chlorine-argon gas, but the present invention is not limited to this, and the mesa stripe may be formed by another method. Further, the dopant (impurity) for n-type InP used for the current confinement layer is not limited to Se, but may be VI.
Obviously, elements of the group may be used. Further, although the InP / InGaAsP system is shown in the above embodiment, other III-type of GaAs / aluminum GaAs system is shown.
A group V semiconductor material may be used.

[0023]

As described above, according to the present invention, since the buried structure semiconductor laser can be manufactured by one-time metal organic chemical vapor deposition, there is an effect that the manufacturing process can be greatly simplified. Further, there is an effect that it is possible to use InGaAs / InAlAs having an MQW structure for the active layer, which has been difficult in the past. Then, the current injection region can be widened, and similar current constriction characteristics can be obtained even if the structure of the mesa stripe or the film thickness of the formation layer is slightly changed.

[Brief description of drawings]

FIG. 1 is a perspective view showing a method of manufacturing a buried structure semiconductor laser which is an embodiment of the present invention.

FIG. 2 is a correlation diagram showing the correlation between the Se doping concentration of n-type InP and the deposition amount when n-type InP is deposited on p-type InP having a mesa stripe shape.

FIG. 3 is a perspective view showing a method of manufacturing a buried structure semiconductor laser according to another embodiment of the present invention.

FIG. 4 is a perspective view showing a method for manufacturing a conventional buried structure semiconductor laser.

FIG. 5 is a perspective view showing a method of manufacturing a conventional buried structure semiconductor laser.

FIG. 6 is a perspective view showing a configuration of a conventional embedded structure semiconductor laser.

[Explanation of symbols]

 1 substrate 1a mesa stripe 2 n-type InP layer 2a buffer layer 3 InGaAsP layer 3a active layer 4 clad layer 5 current confinement layer 6 overclad layer 7 cap layer

Claims (4)

[Claims] 1. A first step of forming a stripe-shaped mesa stripe in a <011> direction of the semiconductor substrate on a semiconductor substrate having an n-type (100) crystal plane, and an organometallic vapor film on the semiconductor substrate. A second step of growing a semiconductor layer by a phase growth method so that the region on the mesa stripe becomes an active region for oscillating a laser, and the flat surface of the region on the active region becomes a (100) crystal plane. A third step of forming a first p-type semiconductor layer on the semiconductor layer by a metal organic chemical vapor deposition method so that an angle between a side surface following the surface and the surface of the semiconductor substrate is less than 54 °; (1 of the region on the active region of the first p-type semiconductor layer
00) a fourth step of selectively growing a first n-type semiconductor layer doped with a predetermined concentration of group VI element in addition to the crystal plane, and the first p-type semiconductor layer and the first n-type semiconductor layer A fifth step of forming a second p-type semiconductor layer thereon, and a sixth step of forming a third p-type semiconductor layer on the second p-type semiconductor layer. Embedded structure semiconductor laser manufacturing method. 2. The method for manufacturing a buried structure semiconductor laser according to claim 1, wherein a step of forming a diffraction grating on the surface of the semiconductor substrate, and a second n-type semiconductor layer between the semiconductor substrate and the semiconductor layer. And a step of forming the embedded structure semiconductor laser. 3. A semiconductor substrate having an n-type (100) crystal plane in which stripe-shaped mesa stripes are formed in the <011> direction, and a region formed on the semiconductor substrate and on the mesa stripes serves as a laser. A semiconductor layer serving as an active region that oscillates, a flat surface of the region formed on the semiconductor layer on the active region is a (100) crystal face, and a side surface following the (100) crystal face and the semiconductor substrate. A first p-type semiconductor layer having an angle of less than 54 ° with a flat (100) crystal plane in a region on the active region of the first p-type semiconductor layer. ) A first n-type semiconductor layer doped with a predetermined concentration of a group VI element, the surface of which is continuous with the crystal plane is the same plane as the flat surface, and formed on the first n-type semiconductor layer. A second p-type semiconductor layer, and the second The third feature that buried structure semiconductor laser that has a p-type semiconductor layer formed on the type semiconductor layer. 4. The buried structure semiconductor laser according to claim 3, wherein the diffraction grating formed on the surface of the mesa stripe and the second diffraction grating formed between the semiconductor substrate and the semiconductor layer.
And an n-type semiconductor layer.