JP2736382B2 - Embedded semiconductor laser and method of manufacturing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a laser light source used for optical communication, optical measurement, and the like. In particular, it relates to an AlGaAs-based embedded semiconductor laser.

〔Overview〕

The present invention provides a buried semiconductor laser having a structure in which a buried layer is formed on a side surface of a mesa structure including an active layer, and a method for manufacturing the same, wherein a mask is used by selectively growing a buried layer using a crystal plane. Instead, a highly accurate embedded semiconductor laser is manufactured.

[Conventional technology]

The buried semiconductor laser has a structure in which a striped mesa structure including an active layer is buried with a material having a low refractive index. In order to allow a current to flow in the active layer region and prevent the current from flowing in other regions, a high resistance buried layer is selectively grown on the side surface of the mesa structure, or zinc and other impurities are diffused to form an active layer. The formation of a current path to the area has been performed.

FIG. 6 is a view showing a method of manufacturing a buried type semiconductor laser by selective growth, and shows sectional views in two steps. Here, a case where n-type GaAs is used as a substrate and an AlGaAs-based buried semiconductor laser is formed on the substrate will be described.

First, an n-type buffer layer 62, an n-type cladding layer 63, an active layer 64, and a p-type guide layer 65 are grown on an n-type GaAs substrate 61 in this order. Thereafter, a stripe-shaped mask 66 is attached on the p-type guide layer 65, and a part of the p-type guide layer 65, the active layer 64, and a part of the n-type clad layer 63 are etched.
Thus, a mesa structure as shown in FIG. 6A is obtained.

Thereafter, as shown in FIG. 6B, a high-resistance buried layer 67 is selectively grown on the side surface of the mesa structure, that is, on the etched region. As the buried layer 67, not only a buried layer itself but also a pn junction which becomes reverse biased during operation can be used.

Further, as shown in FIG. 6 (c), the mask 66 is removed to form a p-type cladding layer 68 and a p-type cap layer 69.
An electrode (not shown) is provided on the mold cap layer 69 and on the back surface of the n-type GaAs substrate 61.

FIG. 7 is a view showing a method of manufacturing a buried semiconductor laser by impurity diffusion, and shows sectional views in three steps.

In this method, first, as shown in FIG. 7A, a mesa structure is formed in the same manner as in the case of selective growth. Thereafter, the mask used for the etching is removed.

Next, as shown in FIG. 7 (b), the mesa structure and n
A p-type cladding layer 71, an n-type current blocking layer 72, a p-type cladding layer 73 and a p-type cap layer 74 are formed on the surface of the type cladding layer 63.
Grow.

Thereafter, as shown in FIG. 7 (c), the p-type cap layer
A SiN _x film 75 is deposited on the surface of 74, a window is opened in the region of the active layer 64, and zinc is diffused to form a zinc diffusion region 76. Thus, the current block layer 72 in this region becomes a p-type semiconductor, and current can be concentrated in this region during operation.

After forming the zinc diffusion region 76, electrodes (not shown) are provided on the exposed portion of the p-type cap layer 74, the surface of the SiN _x film 75, and the back surface of the n-type GaAs substrate 61.

[Problems to be solved by the invention]

In the case of selective growth, it is necessary that no deposits are formed on the mask and that the mask can be removed after the selective growth. However, AlGa having a high Al composition ratio is used as the buried layer.
If As is used, it is difficult to select an etchant that can remove the mask without etching the buried layer, since an adhering substance is generated on the mask.

In the case of impurity diffusion, it is necessary to increase the accuracy of the diffusion location and depth in order to narrow the region through which current flows. However, the location requires mask alignment to open a window in the SiN _x film, and the depth is not precise enough, such as complicated control of diffusion conditions, and the active layer (and mesa structure) ) Had the drawback that the width could not be reduced too much.

The present invention solves the above problems and provides a structure of a buried semiconductor laser capable of selective growth without using a mask and a method of manufacturing the same.

[Means for solving the problem]

A first aspect of the present invention is a method of manufacturing a buried type semiconductor laser, in which a layer of a first material is crystal-grown on the side surface of a mesa structure, and the first material is used to form a ｛111 A step of forming a roof-shaped structure surrounded by the {B-plane, and a second material different from the first material on the side of the mesa structure in a state where crystal growth on the {111} B-plane of the roof-shaped structure is stopped. And crystal growing the layer.

The mesa structure is obtained by etching a layer structure including an active layer. According to the present invention, the <1
10> A stripe formed along the direction is used. Here, () indicates a crystal plane, and <> indicates a crystal direction. Further, {} represents an equivalent crystal plane.

In this specification, "up" means a direction away from the substrate. Similarly, “bottom”, “lateral”, and “side” also refer to directions with respect to the substrate.

A second aspect of the present invention is a buried semiconductor laser manufactured by the above-described method, which has a roof-shaped structure in contact with the upper surface of the mesa structure and surrounded by a {111} B plane.

[Action]

If a mesa structure is formed along the <110> direction on a (100) GaAs substrate, and the angle θ of the upper end of the mesa structure is set to 125 ° or less, the growth condition is selected, so that a ｛111 ｝ The B surface is formed. This plane is maintained until the height of the layer grown on the side of the mesa structure matches the height of the mesa structure.
There is no further growth. Therefore, after the roof structure is formed, a layer of a material different from the material forming the roof structure can be selectively grown on the side surface of the mesa structure.

That is, selective growth can be performed without using a mask. Therefore, it is not necessary to remove only the mask after the selective growth, and the composition of the buried layer is not limited. Further, the step of mask alignment becomes unnecessary.

〔Example〕

FIG. 1 shows a method of manufacturing a buried semiconductor laser according to a first embodiment of the present invention. In this example, a substrate using n-type GaAs as a substrate will be described.

First, as a first step, a layer structure including an active layer 4 on a (100) n-type GaAs substrate 1, that is, an n-type buffer layer 2, p-type
The type clad layer 3, the active layer 4, and the p-type guide layer 5 are grown in this order. MOCVD is used for crystal growth.
(Organic metal chemical vapor deposition), MBE (Molecular beam epitaxy), LPE (Liquid phase epitaxy), and other conventionally used methods can be used.

Next, as a second step, a part of the n-type cladding layer 3, the active layer 4 and the p-type guide layer 5 are etched to form a stripe-shaped mesa structure along the layer structure <110> direction. At this time, the angle θ of the upper end of the mesa structure is set to 125 ° or less.

The relationship between the width W and the depth d of the mesa structure needs to satisfy d> [W / 2] tan54 ° + b. Here, b is the thickness of the current block layer formed in a later step.

Through the above steps, the structure shown in FIG. 1A is obtained.

Next, as a third step, a buried layer is selectively grown on the side surface of the mesa structure.

In the first step, a p-type cladding layer 6 is grown as a first material layer on the side surfaces of the mesa structure by MOCVD, and a roof-shaped structure surrounded by {111} B planes is formed on the mesa structure by this material. Form structure 7. The resulting structure is shown in FIG.

Since the angle between the {100} plane and the {111} B plane is 54 °, the height h of the roof-shaped structure 7 having the width W is h = [W / 2] tan 54 °. When the roof-shaped structure 7 is formed, crystal growth on the surface of the mesa structure is stopped until the heights of the upper surface and the side surface layer of the mesa structure match. The thickness a of the p-type cladding layer 6 is a>
h.

As a second step, while crystal growth on the {111} B plane of the roof-shaped structure 7 is stopped, an n-type current having a thickness b is formed on a side surface of the mesa structure as a layer of a second material different from the first material. The block layer 8 is crystal-grown.

Further, as a step following the third step, a p-type cladding layer 9 and a p-type cap layer 10 are crystal-grown on the roof structure 7 and the n-type current blocking layer 8. Thereafter, electrodes 11 and 12 are provided on the upper surface of the p-type cap layer 10 and the rear surface of the (100) n-type GaAs substrate 1, respectively. The resulting structure is shown in FIG. 1 (c).

The material forming the n-type current blocking layer 8 cannot grow on the roof structure 7 until its height matches the height of the mesa structure. Therefore, when the area of the roof-shaped structure 7 is viewed up and down, a pin double heterostructure including the active layer 4 is formed. When the other region is viewed up and down, a pnpn structure is formed. Further, since the n-type current blocking layer 8 is close to the active layer 4, a current component that does not pass through the region of the active layer 4 can be extremely reduced. This allows
The current can be concentrated on the region of the active layer 4.

Further, by using a material having a low refractive index as the material of the p-type cladding layers 6 on both sides of the mesa structure, light can be confined satisfactorily.

In the first step, a diffraction grating can be formed on the p-type guide layer 5. Thereby, a distributed feedback type embedded semiconductor laser is obtained.

FIG. 2 shows a scanning electron micrograph of a cross section of the embedded semiconductor laser actually obtained by the above steps. In this example, the p-type cladding layer 9 has a three-layer structure by changing the impurity concentration in order to check the state of growth.

FIG. 3 is a sectional view of a buried semiconductor laser according to a second embodiment of the present invention.

This embodiment differs from the first embodiment in that the cladding layer and the cap layer above the active layer are provided in the mesa structure rather than on the block layer and the roof type structure. Further, p-type GaAs is used as the substrate, and accordingly, the conductivity type of each layer is different from that of the first embodiment.

To manufacture this semiconductor laser, as a first step,
On a (100) p-type GaAs substrate 31, a p-type buffer layer 32, a p-type cladding layer 33, an active layer 34, an n-type
Mold guide layer 35, n-type cladding layer 36 and n-type cap layer
37 is grown. As a second step, a p-type cladding layer
33, active layer 34, n-type guide layer 35, n-type cladding layer
36 and the n-type cap layer 37 are formed in a stripe-shaped mesa structure along the <110> direction. As a third step, an n-type cladding layer 38 and a p-type current blocking layer 40 are selectively grown as buried layers on the side surfaces of the mesa structure.

In the third step, an n-type cladding layer 38 is grown as a first material layer on the side surface of the mesa structure, and {111} B
Form a roof-shaped structure 39 surrounded by surfaces.
In the state where crystal growth on the {111} B plane has stopped, n
On the side surface of the mold cap layer 37, a p-type current blocking layer 40 is grown as a layer of a second material different from the first material.

Electrodes (not shown) are provided on the surface of the roof-shaped structure 39, the surface of the p-type current blocking layer 40, and the back surface of the (100) p-type GaAs substrate 31, as in the first embodiment.

As a result, the mesa structure region becomes a nip double hetero structure, and the other region becomes a pnp structure, and the active layer 34
Current can be concentrated in a certain area.

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

This embodiment is different from the second embodiment in that n-type GaAs is used as a substrate, a roof-shaped structure is removed, and a high-resistance cladding layer is used as a buried layer.

To manufacture this semiconductor laser, as a first step,
(100) On an n-type GaAs substrate 1, an n-type buffer layer 2, an n-type cladding layer 3, an active layer 4, a p-type
Mold guide layer 5, p-type cladding layer 41 and p-type cap layer
42 is grown. As a second step, a part of the n-type cladding layer 3, the active layer 4, the p-type guide layer 5, the p-type cladding layer
41 and the p-type cap layer 42 are formed in a stripe-shaped mesa structure along the <110> direction. As a third step, a high resistance cladding layer 43 and a GaAs cap layer 44 are selectively grown as buried layers on the side surfaces of the mesa structure.

In the third step, a high-resistance clad layer 43 is grown as a first material layer on the side surface of the mesa structure,
With this first material, {111} B
In the state where the crystal growth on the {111} B plane of the roof-shaped structure is stopped, the side surface of the p-type cap layer 42 is formed of a second material different from the first material. A GaAs cap layer 44 is grown as a layer.

Further, following the third step, the roof-shaped structure is selectively removed by etching. For this purpose, Al _x Ga _{1 -x} As (where x> 0.4) is used as the material of the roof-shaped structure and the high-resistance cladding layer 43. With this material, an etching agent having a high etching rate for GaAs can be easily obtained. Therefore, only the roof-shaped structure can be selectively etched without etching the GaAs cap layer 44. As an etching agent, for example, HF, heated HCl or the like is used.

Electrodes (not shown) are provided on the surface of the p-type cap layer 42 and the surface of the GaAs cap layer 44, and on the back surface of the (100) n-type GaAs substrate 1, as in the first and second embodiments. Provide.

In the first step, the p-type guide layer 5 and the p-type clad layer
By providing a diffraction grating between the semiconductor laser and the semiconductor laser 41, a distributed feedback embedded semiconductor laser can be manufactured.

FIG. 5 is a sectional view of a buried semiconductor laser according to a fourth embodiment of the present invention.

This embodiment differs from the third embodiment in that zinc is diffused as a p-type impurity in the roof structure and a part of the GaAs cap layer 44 without etching the roof structure. AlGaAs
Inside, the diffusion rate of zinc is three to four times faster than in GaAs. Therefore, when zinc is diffused to the entire surface of the roof-type structure and the GaAs cap layer 44, zinc diffusion regions 51 are formed in the entire roof-type structure and a part of the GaAs cap layer 44. Electrodes (not shown) are provided on the surface of the zinc diffusion region 51 and on the back surface of the (100) n-type GaAs substrate 1 as in the above-described embodiments.

〔The invention's effect〕

As described above, according to the method of the present invention, MOCVD
A buried semiconductor laser using a buried layer having a high Al composition, which has been difficult by the method, can be manufactured without a mask alignment step. Further, since the structure including the active layer is formed in a stripe-shaped mesa structure, a distributed feedback laser can be formed by forming a guide layer provided with a diffraction grating on the active layer.

[Brief description of the drawings]

FIG. 1 is a diagram showing a method of manufacturing a buried semiconductor laser according to a first embodiment of the present invention. FIG. 2 is a scanning electron micrograph showing the crystal structure of the cross section of the actually obtained embedded semiconductor laser. FIG. 3 is a sectional view of a buried semiconductor laser according to a second embodiment of the present invention. FIG. 4 is a sectional view of a buried semiconductor laser according to a third embodiment of the present invention. FIG. 5 is a sectional view of a buried semiconductor laser according to a fourth embodiment of the present invention. FIG. 6 is a view showing a method of manufacturing a buried semiconductor laser by selective growth. FIG. 7 is a view showing a method of manufacturing a buried semiconductor laser by impurity diffusion. 1 ... (100) n-type GaAs substrate, 2, 62 ... n-type buffer layer,
3, 36, 38, 63 ... n-type cladding layer, 4, 64, 34 ... active layer, 5, 65 ... p-type guide layer, 6, 9, 33, 41, 68, 71,
73 ... p-type cladding layer, 7, 39 ... roof structure, 8, 72 ... n
Type current block layer, 10, 42, 69, 74 ... p-type cap layer,
11, 12 ... electrodes, 31 ... (100) p-type GaAs substrate, 32 ... p-type buffer layer, 35 ... n-type guide layer, 37 ... n-type cap layer, 40
... p-type current block layer, 43 ... high resistance cladding layer, 44 ... Ga
As cap layers, 51, 76: zinc diffusion region, 61: n-type GaAs substrate, 66: mask, 67: buried layer, 75: SiN _x film.

Claims (7)

(57) [Claims] 1. A first step of crystal-growing a layer structure including an active layer on a (100) GaAs substrate, and a second step of forming the layer structure into a stripe-shaped mesa structure along a <110> direction. A third step of selectively growing a buried layer on the side surface of the mesa structure, wherein the third step comprises crystal-growing a layer of a first material on the side surface of the mesa structure. And forming a roof-shaped structure surrounded by the {111} B surface on the mesa structure with the first material, and in a state where crystal growth on the {111} B surface of the roof-shaped structure is stopped. Growing a layer of a second material different from the first material on the side surface of the mesa structure. 2. The method of claim 1, wherein the first step comprises crystal growing a guide layer on the active layer, and the third step comprises crystallizing a cladding layer and a cap layer on the roof-type structure and the second material layer. The method for manufacturing a buried semiconductor laser according to claim 1, comprising a step of growing. 3. The method according to claim 1, wherein the first step includes a step of crystal-growing a guide layer, a clad layer, and a cap layer on the active layer. 4. The method for manufacturing a buried semiconductor laser according to claim 3, further comprising a step of removing the roof-shaped structure by selective etching, following the third step. 5. The first material is Al _x Ga _{1 -x} As (where x> 0.
5. The method according to claim 4, wherein said material is etched with HF or heated HCl. 6. The method of claim 3, further comprising the step of: diffusing p-type impurities into the roof-shaped structure and the layer of the second material.
A method for manufacturing the embedded semiconductor laser according to the above. 7. A (100) GaAs substrate comprising: a stripe-shaped mesa structure formed along the <110>direction; and a buried layer formed on a side surface of the mesa structure. A buried semiconductor laser comprising: a buried structure surrounded by a {111} B surface in contact with an upper surface of the mesa structure.