JPH05183233A - Semiconductor laser and manufacturing method thereof - Google Patents

Abstract

PURPOSE:To develop the title high efficiently operable semiconductor laser in low threshold value current and the manufacturing method thereof. CONSTITUTION:Within the buried in hetero-structured semiconductor laser, a high concentration p type region 10 is provided close to an active layer 3 while a region 11 not invertible to p type when an n type impurities are diffused on an etching interface is provided to make a leakage current hardly run out. Through these procedures, the leakage current running out path can be restricted thereby enabling the title high efficiently operable semiconductor laser in low threshold value current running the least leakage current to be manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a semiconductor laser and a manufacturing method thereof.

[0002]

2. Description of the Related Art FIG. 6 shows, for example, Japanese Patent Laid-Open No. 62-06669.
4 is a cross-sectional view showing the conventional semiconductor laser shown in No. 4, in which 1 is an n-type semiconductor substrate, 2 is an n-type buffer layer provided on the semiconductor substrate 1, and 3 is the n-type buffer layer. 2 is an active layer provided above the active layer 3
It is a p-type clad layer provided on the top. 5 is the above 1-4
A region in which n-type impurities are diffused into an etching interface formed when a mesa is formed by etching the semiconductor layer formed by, 6 is a p-type current block layer formed in the etched region, and 7 is also etched. An n-type current blocking layer formed on the p-type current blocking layer 6 in a region,
Reference numeral 8 is a p-type clad layer formed on the entire substrate.

Incidentally, in an actual semiconductor laser, it is customary to provide an electrode for passing a current through the semiconductor laser on the lower side of the n-type semiconductor substrate 1 and the upper side of the p-type cladding layer 8. Since it is not directly related to the essence of the present invention, the description of the conventional example and the example is omitted.

Next, the operation will be described. The electrons and holes injected from the electrodes into the n-type semiconductor substrate 1 and the p-type clad layer 8 respectively pass through the n-type buffer layer 2 and the p-type clad layer 4, and then are injected into the active layer 3 to re-emit light. They combine with each other and emit light having an energy almost equal to the energy of the band gap of the active layer 3. This light travels along the waveguide composed of the active layer 3 and the semiconductor layer in the periphery thereof (in the direction perpendicular to the paper surface), promoting recombination of electrons and holes in the path (stimulated emission). While), increase its strength. Then, the light is partially reflected by the end face of the semiconductor laser, travels while increasing the intensity again, and this is repeated. When the number of electrons and holes injected into the active layer 3 is small, that is, when the injection current is small, the light loss at the laser end face is larger than the increase in the intensity inside the active layer. The strength of gradually weakens. However, when the injection current increases and the number of electrons and holes injected into the active layer increases, and the increase in strength inside the active layer increases, the loss at the end face is balanced. This state is called laser oscillation, and the injection current at this time is called a threshold current. When a current larger than the threshold current is injected, from the end face of the semiconductor laser,
Light having a large intensity with a uniform wavelength called laser light is emitted.

In a semiconductor laser, it is necessary to efficiently inject electrons and holes into the active layer 3 in order to cause laser oscillation, but generally there is a so-called leakage current that flows on both sides of the active layer 3. Therefore, there are problems that the threshold current described above becomes large and the current-light conversion efficiency decreases during laser oscillation.

The semiconductor laser shown in FIG. 6 does two things to solve this problem. one is,
By providing the p-type current blocking layer 6 and the n-type current blocking layer 7, the leakage current in the region relatively distant from the active layer 3 is reduced. However, in this case, since the leakage current flowing through the gap between the active layer 3 and the n-type current block layer 7 cannot be ignored, the second method is the n-type impurity diffusion region 5
By providing, the gap between the active layer 3 and the n-type current blocking layer 7 is substantially reduced to zero to reduce the leakage current.

[0007]

The conventional semiconductor laser is constructed as described above. However, in the case of such a configuration, the leakage current is p-type clad layer 8 → n-type current blocking layer 7 → n-type impurity diffusion region 5 → active layer 3 →
The leakage current flowing in the path from the n-type buffer layer 2 to the n-type semiconductor 1 becomes a problem. This current does not contribute to light emission because electrons flow through the active layer 3 in the form of passing electrons, and moreover, the path flowing through the n-type region having a smaller resistivity as compared to the p-type causes a large leakage current, which is rather a semiconductor laser. There was a problem of deteriorating the characteristics of.

The present invention has been made to solve the above problems, and an object thereof is to obtain a semiconductor laser having a low threshold current and a high conversion efficiency by reducing the leakage current. An object of the present invention is to provide a method for manufacturing a semiconductor laser suitable for a device.

[0009]

According to a semiconductor laser and a method of manufacturing the same according to the present invention, an upper layer portion of a p-type cladding layer is doped with a high concentration of p-type impurities, and an n-type impurity diffusion region of the layer is an n-type impurity diffusion region. It is the one that is not inverted.

[0010]

According to the present invention, since the upper layer portion of the p-type cladding layer is doped with a high concentration of impurities, a region that does not invert from p-type to n-type when diffusing n-type impurities is formed, so that the region is inverted to n-type. Separation from the n-type current blocking layer greatly reduces the leakage current.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a semiconductor laser according to an embodiment of the present invention, in which 1 is an n-type semiconductor substrate, 2 is an n-type buffer layer provided on the semiconductor substrate 1, and 3 is the n-type buffer layer.
An active layer provided on the mold buffer layer 2, a low-concentration p-type clad layer 9 provided on the active layer 3, and a high-concentration p-type layer 10 provided on the low-concentration p-type clad layer 9. The type clad layer, 5 is a region in which n-type impurities are diffused into an etching interface formed when a mesa is formed by etching the semiconductor layer composed of 1 to 3 and 9 and 10, and 11 is the n-type impurity. In the diffusion region 5, a non-inversion region that overlaps the high-concentration p-type cladding layer 10, 6 is a p-type current block layer formed in the etched region, and 7 is the p-type current block 6 in the same etched region. An n-type current blocking layer formed on the substrate 8 is a p-type current blocking layer formed on the entire substrate.
The mold clad layer.

In order to describe the above embodiment in detail, a process flow of an InP semiconductor laser will be described with reference to FIG. First, as shown in FIG. 2 (a), an n-type InP buffer layer (S-doped, carrier concentration 0.5 × 10 ¹⁸ _cm ⁻³ ) 2 is formed on the n-type InP substrate 1 by a metal organic chemical vapor deposition method, for example. 0.
5 μm, undoped In _0.72 Ga _0.28 As _0.61 P _0.39 active layer 3 with a thickness of 0.1 μm, low-concentration p-type InP cladding layer (Zn-doped, carrier concentration 5 × 10 ¹⁷ _cm ⁻³ ) 9 with a thickness of 0.1 μm.
A 3 μm high-concentration p-type InP clad layer (Zn-doped, carrier concentration 3 × 10 ¹⁸ _cm ⁻³ ) 10 having a thickness of 0.3 μm is sequentially formed.

Next, a dielectric film 12 such as SiO ₂ is formed on the surface of the substrate and processed into a stripe shape by the photolithography technique, and then the substrate is etched to a depth of 3 μm using an etching solution such as Br-methanol. Then, the substrate is processed into a mesa shape as shown in FIG. Next, using sulfur (S), an impurity diffusion region (carrier concentration 2 × 10 ¹⁸ _{cm 2}
^-3 ) Form 5. Here, in the low-concentration p-type InP cladding layer 9 of the diffusion region 5, the n-type impurity concentration is higher than the p-type impurity concentration, so that the conductivity type is inverted to the p-type, but the high-concentration p-type. In the InP clad layer 10, the p-type impurity concentration is higher than the n-type impurity concentration, so that the non-inversion region 11 whose conductivity type remains p-type is formed. Next, the p-type current block layer 6 and the n-type current block layer 7 are sequentially crystal-grown on both sides of the stripe mesa to embed the mesa.

Thereafter, a p-type InP clad layer (carrier concentration 1 × 10 ¹⁸ _cm ⁻³ ) 8 is formed on the entire substrate. After this,
An electrode is formed on the clad layer 8 and on the back surface of the substrate 1 and has a length of 3
A semiconductor laser is completed by cleaving the substrate to about 00 μm.

Next, the operation of the semiconductor laser according to the present invention will be described. The basic laser oscillation is almost the same as the conventional example, but the way the leakage current flows is different. As described above, in the conventional example, since the n-type current block layer and the region inverted to the n-type by the impurity diffusion are connected,
There is a problem that the leakage current flowing through both is very large, but in the case of the present invention, there is no such leakage current because the two are separated. Instead, a leakage current flows through the route of p-type clad layer 8 → high-concentration p-type clad layer 10 → p-type current blocking layer 6 → n-type semiconductor substrate 1. However, compared with the case of the conventional example, (1) n The path through the p-type semiconductor, which has a higher resistivity than the p-type semiconductor, is longer. (2) Since the thickness of the non-inversion region 11 can be made sufficiently narrow at the narrowest part of the path through which the leakage current flows, the leakage current can be suppressed sufficiently small.

As clearly shown in FIG. 3, the path of the leakage current is clearly shown. In the present invention, only the difference in conductivity type and the leakage current are clearly shown. In the figure, 21 is an n-type region, 22 is a P-type region,
Arrows indicate leakage current.

Although the n-type semiconductor substrate is used in the above embodiment, a p-type semiconductor substrate may be used. Another embodiment of the present invention using a p-type semiconductor substrate will be described below with reference to the drawings. In FIG. 4, 31 is a p-type semiconductor substrate, 32 is a high-concentration p-type buffer layer provided on the semiconductor substrate 31, and 33 is a high-concentration p-type buffer layer 3.
2 is an active layer, 34 is an n-type cladding layer provided on the active layer 33, and 35 is an etching interface formed when a semiconductor layer composed of 31 to 34 is etched to form a mesa. Regions where n-type impurities are diffused into the region, 3
6 is the high concentration p of the n-type impurity diffusion region 35.
A non-inversion region overlapping the type buffer layer 32, 37 is a p-type current blocking layer A formed in the etched region, 38
Is an n-type current block layer formed on the p-type current block layer A37, 39 is a p-type current block layer B formed on the n-type current block layer 38, and 40 is an n-type current block layer formed on the entire substrate. It is a clad layer. In order to clearly understand the path of the leakage current in this case, only the difference in conductivity type and the leakage current are shown in FIG. In the figure, 21 is an n-type region, 22
Indicates the p-type region, and the arrow indicates the leakage current. Leakage current is confined between the active layer 33 and the n-type current block layer 38 and between the active layer 33 and the n-type impurity diffusion region 35 which is inverted from p-type to n-type, and therefore is significantly reduced. You can

In the first embodiment, the InP semiconductor laser is shown, but other semiconductor lasers including the second embodiment, for example, a GaAs semiconductor laser may be used. Although sulfur (S) is used as the diffusion impurity, other impurities such as silicon (Si) may be used.

[0019]

As described above, according to the semiconductor device and the method of manufacturing the same according to the present invention, the high-concentration doping region is provided in the vicinity of the active layer, and the region where the conductivity type is not inverted even by the impurity diffusion after the mesa etching is formed. Since the semiconductor laser is provided, it becomes difficult for leak current to flow, and a semiconductor laser capable of low threshold current operation and high efficiency operation can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing a semiconductor laser according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a manufacturing process flow of a manufacturing method according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a conductivity type and a leakage current in the semiconductor laser of the above embodiment.

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

FIG. 5 is a cross-sectional view showing a conductivity type and a leakage current in a semiconductor laser according to another embodiment.

FIG. 6 is a cross-sectional view showing a conventional semiconductor laser.

[Explanation of symbols]

 1 n-type semiconductor substrate 2 n-type semiconductor layer 3 active layer 4 p-type clad layer 5 n-type impurity diffusion region 6 p-type current block layer 7 n-type current block layer 8 p-type clad layer 9 low concentration p-type clad layer 10 high Concentration p-type cladding layer 11 Non-inversion region 31 p-type semiconductor substrate 32 High-concentration p-type buffer layer 33 Active layer 34 n-type cladding layer 35 n-type impurity diffusion region 36 Non-inversion region 37 p-type current block layer A 38 n-type current Block layer 39 p-type current block layer B 40 n-type clad layer

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[Procedure amendment]

[Submission date] June 17, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction content]

[0007]

The conventional semiconductor laser is constructed as described above. However, in the case of such a configuration, the leakage current is p-type clad layer 8 → n-type current blocking layer 7 → n-type impurity diffusion region 5 → active layer 3 →
The leakage current flowing in the path from the n-type buffer layer 2 to the n-type semiconductor 1 becomes a problem. This current does not contribute to light emission to flow the active layer 3 in a manner to pass through electrons, moreover, it is a large leakage current in the compared to p-type Ru flow Do n-type region low resistivity, rather semiconductor laser There was a problem of deteriorating the characteristics.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction content]

In order to describe the above embodiment in detail, a process flow of an InP semiconductor laser will be described with reference to FIG. First, as shown in FIG. 2 (a), an n-type InP buffer layer (S-doped, carrier concentration 5 × 10 ¹⁷ _cm ⁻³ ) 2 is formed on the n-type InP substrate 1 by metalorganic vapor phase epitaxy, for example. 0.5
μm, undoped In _0.72 Ga _0.28 As _0.61 P _0.39 Active layer 3 having a thickness of 0.1 μm, low-concentration p-type InP cladding layer (Z
n-doped, carrier concentration 5 × 10 ¹⁷ _cm ^-3 ) 9, thickness 0.3 μ
m, a high concentration p-type InP clad layer (Zn-doped, carrier concentration 3 × 10 ¹⁸ _cm ⁻³ ) 10 having a thickness of 0.3 μm is sequentially formed.

Claims (4)

[Claims] 1. An n-type buffer layer on an n-type semiconductor substrate,
A structure in which an active layer and a first p-type clad layer are sequentially stacked is etched in a mesa shape, and n-type impurities are diffused at an etching interface, and then a p-type current block layer and an n-type current block layer are sequentially stacked in an etching portion. In addition, the second p
In a semiconductor laser having a laser structure in which a p-type clad layer is formed, the p-type clad layer has a high concentration of p
A semiconductor laser having a layer containing a type impurity, wherein the n-type impurity diffusion region of the layer is not inverted to n-type. 2. A p-type buffer layer on a p-type semiconductor substrate,
A structure in which an active layer and a first n-type clad layer are sequentially stacked is etched into a mesa shape, and n-type impurities are diffused at the etching interface, and then a p-type buried layer, an n-type current blocking layer, and a p-type current are formed in the etched portion. In a semiconductor laser having a laser structure in which block layers are sequentially laminated and a second n-type clad layer is formed over the entire substrate, the p-type buffer layer has a high-concentration p-type layer in a part thereof in the layer thickness direction.
A semiconductor laser having a layer containing a type impurity, wherein the n-type impurity diffusion region of the layer is not inverted to n-type. 3. An n-type buffer layer on an n-type semiconductor substrate,
A step of etching a structure in which an active layer and a first p-type clad layer are sequentially stacked in a mesa shape, a step of diffusing n-type impurities at an etching interface, and a p-type current block layer and an n-type current block layer at an etching portion. And a step of forming a second p-type clad layer on the entire substrate, wherein the p-type clad layer has a high concentration of p
A method of manufacturing a semiconductor laser, comprising a layer containing a type impurity, wherein the n-type impurity diffusion region of the layer is not inverted to n-type. 4. A p-type buffer layer on a p-type semiconductor substrate,
A step of etching a structure in which an active layer and a first n-type cladding layer are sequentially stacked in a mesa shape, a step of diffusing n-type impurities at an etching interface, a p-type buried layer, an n-type current blocking layer, p
Including a step of sequentially stacking a type current block layer and a step of forming a second n-type cladding layer on the entire substrate, wherein the p-type buffer layer has a high concentration of p
A method of manufacturing a semiconductor laser, comprising a layer containing a type impurity, wherein the n-type impurity diffusion region of the layer is not inverted to n-type.