JPH08222809A - Semiconductor light-emitting device - Google Patents

Abstract

PURPOSE: To reduce pileup of impurities which causes a leak current, by a method wherein a part of the lateral side of a mesa stripe is constructed of a part of a semiconductor on which an active layer is disposed. CONSTITUTION: On the occasion when an active layer 3 is etched in the process of forming a mesa stripe, etching is made up to a semiconductor layer on which the active layer 3 is disposed, to obtain a structure that the lateral side of the active layer is not positioned at a mesa stripe corner constructed of the lateral side of a mesa stripe 11 and the surface of a substrate 1. As the result, a buried layer of good quality is formed on the lateral side of the active layer and a long-time stable operation of an element can be realized. Besides, the lateral side of a clad layer is held in a reversely tapering shape which makes it hard for impurities to pile up, as usual, and therefore an excellent element characteristic that a leak current is small can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device such as a semiconductor laser having a high resistance layer embedded structure which is important as a light source for optical transmission.

[0002]

2. Description of the Related Art A semiconductor laser having a high-resistance layer embedded structure having a semi-insulating InP crystal as an embedded layer has a small element capacitance and is capable of high-speed modulation, and is therefore regarded as an important light source for large-capacity optical transmission. .

FIG. 3 is a sectional view showing the structure of a conventional semiconductor laser with a high resistance layer embedded structure. (Reference: Applied Physics Letter, vol. 59 (1991).
p. 1269). The structure of such a semiconductor laser will be described with reference to the manufacturing process shown in FIG.

In this semiconductor laser, InP and GaIn
The mesa stripe is formed by using a selective etching solution of As and AlGaInAs. That is, first, n−
On the InP substrate 31, the n-InP buffer layer 32, Ga
InAs / AlGaInAs quantum well (MQW) active layer 33, p-InP cladding layer 34 and p-InGa
After stacking the As electrode layer 35, a SiO ₂ mask 41 is formed (FIG. 4A). Then, this SiO ₂ mask 4
1 is used as an etching mask, the p-InGaAs electrode layer 35 is selectively etched (FIG. 4B), the p-InP clad layer 34 is selectively etched (FIG. 4C), and finally. , MQW active layer 33 is selectively etched to form the mesa stripe 36 shown in FIG.
Is formed. After that, the mesa stripe 36 is embedded with an Fe—InP layer 37 made of a semi-insulating high-resistance InP crystal obtained by doping Fe, and the p-type electrode 39 and n are formed.
The mold electrode 40 is formed. The Fe-InP layer 37 and p
SiO ₂ is inserted between the mold electrode 39 and the mold electrode 39.

As described above, conventionally, the mesa stripe is formed only by the wet etching solution, so that the process is simple, and since the selective etching is used, the mesa stripe can be formed with good controllability and reproducibility. Can be made. Further, since the InP clad layer 34 is etched with a hydrochloric acid-based etching solution, the crystal plane on the side surface of the InP clad layer 34 is inclined from the (100) plane to an inverse taper, and the impurities causing the leak current are buried. During the growth, it has a crystal surface that does not easily pile up on the interface.

[0006]

However, the semiconductor laser manufactured by such a conventional method is
There are problems as described below.

That is, as shown in FIG. 4D, since the formation of the mesa stripe is completed by selectively etching the active layer 33, the side surface of the active layer 33 is exactly the side surface of the mesa stripe and the substrate. It will be located at the mesa stripe corner, which is composed of the surface and. At this position, it is difficult to grow a good quality crystal in the process of burying growth, and crystal defects are likely to concentrate. This causes leakage current and element deterioration, which impairs element characteristics and long-term stable operation of the element.

An object of the present invention is to reduce the pile-up of impurities causing a leak current at the buried regrowth interface and to effectively maintain a long-term stable operation of the device. The buried layer has good quality on the side surface of the active layer. It is an object of the present invention to provide a high resistance layer embedded structure semiconductor laser having a structure that can be formed.

[0009]

According to a first aspect of the present invention which achieves the above object, there is provided a (100) semiconductor substrate having a first conductivity type, an active layer disposed on the semiconductor substrate, and a second layer.
A clad layer having a second conductivity type, and a mesa stripe formed in a stripe shape at least including an electrode layer having a second conductivity type, the clad having the second conductivity type forming the mesa stripe. In a semiconductor light emitting device in which a part of the side surface of the layer is a crystal plane inclined from the (110) crystal plane to the reverse taper side, and semi-insulating high resistance current blocking layers are provided on both sides of the mesa stripe, A semiconductor light emitting device is characterized in that a part of a side surface of the mesa stripe is constituted by a part of a semiconductor layer on which the active layer is arranged or a part of the semiconductor substrate.

According to a second aspect of the present invention, a part of a semiconductor layer which constitutes the side surface of the mesa stripe and on which the active layer is arranged, or a crystal plane which is a part of the semiconductor substrate is formed. According to another aspect of the present invention, there is provided a semiconductor light emitting device having a crystal plane perpendicular to the surface of the semiconductor substrate.

[0011]

In the conventional semi-insulating high-resistance layer buried structure semiconductor laser, the side surface of the cladding layer has an inverse taper shape in which impurities are hard to pile up, but the mesa stripe is formed by selective etching of the active layer. Since it is completed, the side surface of the active layer is located at the mesa stripe corner, and the buried layer where crystal defects are likely to concentrate is formed at that position, so that long-term stable operation of the device is difficult to achieve. It was.

On the other hand, according to the present invention, when the active layer is etched in the mesa stripe forming step, the active layer is etched up to the semiconductor layer or the semiconductor substrate on which the active layer is formed. The side surface of the active layer is not located at the mesa stripe corner formed by the substrate surface. As a result, a good quality buried layer is formed on the side surface of the active layer, and long-term stable operation of the device can be realized.

Further, since the side surface of the clad layer is maintained in the reverse taper shape in which impurities are hardly piled up as in the conventional case, good device characteristics with a small leak current can be realized.

Further, in the mesa stripe, the side surface shape of the active layer, the semiconductor layer on which the active layer is disposed, or the side surface of the semiconductor substrate is perpendicular to the semiconductor surface, thereby forming such a position in a forward taper shape. As compared with the case, impurities are less likely to pile up on the interface, and therefore, a buried layer that causes a leak current is also less likely to be formed on the side surface of the active layer.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention.

The active layer 3 is an InGaAsP semiconductor crystal having an emission wavelength of 1.3 μm. The active layer 3 is a p-type I layer in the mesa stripe 11 on the n-type InP substrate 1.
It is sandwiched from above and below by the nP clad layer 4 and the n-type InP buffer layer 2. Both sides of the mesa stripe 11 are filled with a current blocking layer 7 made of a semi-insulating high-resistance InP crystal obtained by doping Fe. At the upper end of the mesa stripe 11, p-type In is formed so that a good contact with the p-type electrode 9 can be obtained.
A GaAs electrode layer 6 is provided. Further, a 1.3 μm band −p type InGaAsP buffer layer 5 is inserted between the electrode layer 6 and the p type InP clad layer 2 in order to improve hole injection efficiency. The first mesa side surface 12, which is a part of the side surface of the p-type InP clad layer 4 forming the mesa stripe, is inclined from the plane perpendicular to the substrate surface 13 to the reverse taper side by a few degrees. A second mesa side surface 14, which is a side surface of the n-type buffer layer 2 forming the mesa stripe 11,
And a third mesa side surface 1 which is a side surface of the n-type InP substrate 1.
5 is orthogonal to the substrate surface 13. n-type electrode 10
Are formed on the entire back surface of the n-type substrate 1. The p-type electrode 9 is formed on the upper surface of the element, and the p-type electrode 9 and the current blocking layer 7 are partially separated by the SiO ₂ film 8.

The method of manufacturing the semiconductor laser shown in FIG.
This will be described with reference to FIG.

First, as shown in FIG.
0) plane n-type InP substrate 1 (carrier concentration 2 × 10 ¹⁸ cm
^-3 ) on top of which an n-type InP buffer layer 2 having Se as a dopant (carrier concentration 1 × 10 ¹⁸ cm ⁻³ , thickness 0.2 μm)
m), non-doped InG having an emission wavelength of 1.3 μm
aAsP active layer 3 (thickness 0.15 μm), p-type InP clad layer 4 using Zn as a dopant (carrier concentration 1 ×
10 ¹⁸ cm ⁻³ , thickness 1.5 μm), 1.3 μm band with Zn as a dopant, p-type InGaAsP buffer layer 5
(Carrier concentration 3 × 10 ¹⁸ cm ⁻³ , thickness 0.2 μm),
After forming the p-type InGaAs electrode layer 6 (carrier concentration 8 × 10 ¹⁸ cm ⁻³ , thickness 0.3 μm) using Zn as a dopant by the low pressure metal organic vapor phase epitaxy, the SiO ₂ mask 16 (width 2. 0 μm, thickness 0.2 μm) is formed.

Next, as shown in FIG. 2 (b), reactive ion etching is used, and etching is advanced to a part of the p-type InP clad layer 4 using the SiO ₂ mask 16 as an etching mask to increase the height. Second about 0.7 μm
To form the mesa stripe 17.

Then, as shown in FIG. 2C, only the p-type InP clad layer 4 is selectively etched using a hydrochloric acid-based etching solution and the SiO ₂ mask 16 as an etching mask to obtain a height of 2. A third mesa stripe 18 of about 0 μm is formed. At this time, the first mesa side surface 12 formed by selective etching is inclined from the surface perpendicular to the substrate surface 13 to the reverse taper side by several degrees.

Subsequently, as shown in FIG. 2D, the reactive ion etching is used, and the etching is advanced to a part of the n-type InP substrate 1 by using the SiO ₂ mask 16 as an etching mask. A first mesa stripe 11 of about 2.4 μm is formed. The second mesa side surface 14 and the third mesa side surface 15 formed at this time are vertical surfaces with respect to the substrate surface 13. Also, mesa stripe 11
Mesa stripe corner 1 composed of
9 is located at a position deviated from the active layer 3.

Then, as shown in FIG. 2 (e), both sides of the mesa stripe 11 are filled with a Fe-doped InP layer by using a low pressure metal organic chemical vapor deposition method to form a current blocking layer 7.

Finally, the n-type electrode 10 and SiO ₂
A mask 8 and a p-type electrode 9 were formed and cut into individual laser chips to obtain a semiconductor laser having a structure as shown in FIG.

The characteristics of the manufactured semiconductor laser at room temperature are an oscillation threshold current of 15 mA and an external differential quantum efficiency of 0.25 mW / mA at the threshold value. I couldn't do it. Also, 50
No remarkable deterioration of the device characteristics was observed under the use environment of ° C and 10 mW.

In this embodiment, InG is used as the active layer.
The one consisting of only the aAsP semiconductor layer has been described. On the other hand, in a semiconductor laser having an active layer composed of a plurality of semiconductor layers such as a multi-quantum well structure and a strained layer superlattice, a semi-insulating high resistance layer embedded structure semiconductor laser having the same structure as that of the present invention is also provided. Can be obtained.

InGaAsP is used as a material system for the active layer.
However, the material is not limited to this, and InGaAs / InAlAs, GaAs may be used.
/ AlGaAs system may be used.

The semiconductor laser is not limited to the Fabry-Perot type laser described in this embodiment, but may be a distributed feedback type semiconductor laser having a diffraction grating or a distributed Bragg reflection type semiconductor laser. .

Further, the present invention is not limited to the semiconductor laser, but may be applied to an integrated light emitting device in which a plurality of elements such as a semiconductor laser provided with an external modulator are integrated.
An element structure similar to that of this embodiment can be obtained.

[0030]

As described above, according to the present invention, the side surface of the active layer is not located at the corner of the mesa stripe where crystal defects are likely to concentrate in the buried growth, and the side surface of the active layer is formed by a good quality crystal layer. Since it is embedded and the side surface of the clad layer is inversely tapered, the impurity that causes the leakage current does not pile up at the embedded interface. Therefore, according to the present invention, it is possible to obtain a semiconductor light emitting device capable of reducing the leak current, improving the element characteristics, and performing stable operation for a long period of time.

[Brief description of drawings]

FIG. 1 is a structural diagram of a semiconductor laser which is an embodiment of the present invention.

FIG. 2 is a diagram showing a structure at each stage of a manufacturing process according to an embodiment of the present invention.

FIG. 3 is a structural diagram of a semiconductor laser according to a conventional technique.

FIG. 4 is a diagram showing a structure at each stage of a manufacturing process of a semiconductor laser according to a conventional technique.

[Explanation of symbols]

1 n-type InP substrate 2 n-type InP buffer layer 3 1.3 band-non-doped InGaAsP active layer 4 p-type InP clad layer 5 1.3 μm band-p-type InGaAsp buffer layer 6 p-type InGaAs electrode layer 7 semi-insulating Fe- InP current blocking layer 8 SiO ₂ film 9 p-type electrode 10 n-type electrode 11 first mesa stripe 12 first mesa side surface 13 substrate surface 14 second mesa side surface 15 third mesa side surface 16 SiO ₂ mask 17 second Mesa Stripe 18 Third Mesa Stripe 19 Mesa Stripe Corner

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuo Fukuda 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (2)

[Claims] 1. A (100) semiconductor substrate having a first conductivity type, an active layer, a clad layer having a second conductivity type, and an electrode layer having a second conductivity type, the active layer being disposed on the semiconductor substrate. And a mesa stripe formed in a stripe shape, wherein at least a part of a side surface of the cladding layer having the second conductivity type, which constitutes the mesa stripe, has a reverse taper side from a (110) crystal plane. In a semiconductor light-emitting device having a crystal plane tilted to and a semi-insulating high resistance current blocking layer on both sides of the mesa stripe, a part of a side surface of the mesa stripe has the active layer disposed thereon. A semiconductor light emitting device characterized by being constituted by a part of the semiconductor layer or a part of the semiconductor substrate. 2. A side surface of the mesa stripe is formed,
A semiconductor light emitting device characterized in that a crystal plane formed by a part of the semiconductor layer on which the active layer is arranged or a part of the semiconductor substrate is a crystal plane perpendicular to the surface of the semiconductor substrate.