JPH05291685A - Semiconductor laser device and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a semiconductor laser device of a low threshold value, high output characteristics and high reliability which has a reduced leakage current. CONSTITUTION:On a semiconductor substrate 1 provided is a diffraction grating 4, on which a first semiconductor layer 2 is formed thick, on which a second semiconductor layer 3 is formed thereby to form a stripe groove, in which a third semiconductor layer 5 is formed, on which an active layer 6 is formed so that both sides thereof are brought in contact with the first semiconductor layer 2, and thereon a fourth semiconductor layer 7 is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device having a low threshold value, a high output characteristic, a low distortion characteristic and excellent reliability, and a manufacturing method thereof.

[0002]

2. Description of the Related Art FIG. 3 shows, for example, "semiconductor laser" pp.13.
9,1989.4.25, Semiconductor laser with conventional single longitudinal mode shown in Baifukan (hereinafter abbreviated as DFB-LD)
It is a sectional view showing an apparatus, in which 1 is n-I.
A semiconductor substrate made of nP, 2 is a first substrate made of p-InP
Semiconductor layer, 3 is a second semiconductor layer made of n-InP formed on the first semiconductor layer 2, 4 is a diffraction grating formed on the semiconductor substrate 1, and 5 is a forbidden band from the active layer. Third guide layer made of narrow n-InGaAsP
Semiconductor layer, 6 is an active layer made of n- or p-InGaAsP, and 7 is a clad layer made of p-InP.
Is a contact layer made of p-InGaAsP. This structure is called a BH type (embedded type) semiconductor laser.

In this structure, in order to enhance the efficiency of laser oscillation in the active region having a width of about 2 μm, the current is concentrated. That is, the second semiconductor layer 3
Is an energy barrier for holes, which are carriers of electric charges in the first semiconductor layer 2 of the second conductivity type, and a current does not flow beyond the second semiconductor layer 3 and the second
The semiconductor layer 3 serves as a slit for squeezing an electric current. Further, by setting the period of the diffraction grating 4 appropriately, a DFB laser device having a desired wavelength can be obtained.

[0004]

However, paying attention to the side surface of the active layer 6, the first semiconductor layer 2 of the second conductivity type (here, p-type) is thinly grown, which causes the activation. A relatively large amount of leakage current flows on the side of the layer 6, the threshold current also increases in the laser characteristics, the optical output decreases due to a decrease in efficiency, the distortion characteristics in harmonic modulation deteriorate, and active when the crystal layer is regrown. There are many problems such as a decrease in reliability due to the exposed layer 6, and a decrease in yield due to etching.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to obtain a highly reliable semiconductor laser device by reducing the leak current and eliminating the exposure of the active layer during growth. , And its manufacturing method.

[0006]

A semiconductor laser device according to the present invention has a first diffraction grating formed on a semiconductor substrate.
Of the semiconductor layer is grown flat (uniformly) and thickly, and the second
The semiconductor layer is grown to form a stripe groove, and an active layer whose both sides are in contact with the third semiconductor layer and the first semiconductor layer is formed by burying growth in the stripe groove.

Further, in the method for manufacturing a semiconductor laser device according to the present invention, a stripe-shaped insulating film is formed on a semiconductor substrate having a diffraction grating, and first and second insulating films are formed on both sides of the insulating film.
After forming the second semiconductor layer, the insulating film is removed to form a stripe groove by the first and second semiconductor layers without etching, and a third semiconductor is formed in the stripe groove by buried growth. A layer and an active layer are formed, and a fourth semiconductor layer is further formed thereon.

[0008]

In the semiconductor laser device according to the present invention,
Since the first semiconductor layer beside the active layer can be grown thick, the leak current can be reduced, and a low threshold and high output semiconductor laser device can be obtained.

Further, in the method for manufacturing a semiconductor laser device according to the present invention, since etching is not used for forming the stripe groove, the yield is improved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a semiconductor laser device showing an embodiment of the present invention. 1, the same reference numerals as those in FIG. 3 indicate the same components, but in the present embodiment, the first semiconductor layer 2 is formed thick.

That is, in FIG. 1, 1 is a semiconductor substrate of the first conductivity type, 2 is a flat second semiconductor layer of the second conductivity type, which is formed to a thickness of, for example, 1 to 3 μm, and 3 is the first semiconductor layer. In the second semiconductor layer of the first conductivity type formed on the first semiconductor layer 2, the stripe grooves are formed by these first and second semiconductor layers 2 and 3. 4 is a diffraction grating formed on the semiconductor substrate 1 in the stripe groove, 5 is a third semiconductor layer of the first conductivity type formed on the diffraction grating 4 in the stripe groove, and 6 is the third semiconductor layer. Is an active layer formed on the semiconductor layer 5, the second conductive type fourth semiconductor layer 7 is formed on the active layer 6 and the second semiconductor layer 3, and the contact layer 8 is a contact layer. As described above, the first semiconductor layer 2 is the active layer 6
The thickness of both sides is uniform with a sufficient thickness, which serves to reduce the leakage current. Further, since the active layer 6 is provided at the time of the second crystal growth, the active layer 6 as in the conventional case is formed.
Thus, a highly reliable semiconductor laser device can be obtained.

Next, a method of manufacturing a semiconductor laser device having this structure will be described with reference to FIGS. First, after the diffraction grating 4 is formed on the semiconductor substrate 1 (FIG. 2A), the SiO ₂ film 9 as an insulating film having a width of about 2 μm is formed in a stripe shape on the diffraction grating 4. Then M
By the OCVD method, the first and second semiconductor layers 2 and 3 are formed into Si.
The O ₂ film 9 is grown to have a desired thickness on both sides (FIG. 2B). Here, no single crystal grows on the SiO ₂ film 9. Next, the SiO ₂ film 9 is removed with hydrofluoric acid to form stripe grooves.

Then, n-InP is placed in the stripe groove.
A third semiconductor layer 5 serving as a GaAsP guide layer 5, an active layer 6, and a fourth semiconductor layer 7 serving as a cladding layer are sequentially grown so as to fill the stripe groove, and then the contact layer 8 is formed.
Grow (FIG. 2 (c)). The forbidden band width of the third semiconductor layer 5, the active layer 6 and the like is In _1-x Ga _x As _y P
_{As 1-y} , for example, 0 <x ≦ 0.35, 0 <y ≦ 0.
80.

By using this manufacturing method, the etching of the stripe groove, which was necessary in the case of the conventional BC (buried channel) laser, becomes unnecessary in this embodiment,
It is possible to form the diffraction grating 4 directly below the active layer 6, which is difficult by the conventional method. In addition, the yield is not reduced due to etching.

[0015]

As described above, in the semiconductor laser device according to the present invention, the first semiconductor layer is flatly (uniformly) grown thick on the diffraction grating formed on the semiconductor substrate, and the first semiconductor layer is grown thereon. The stripe groove is formed by growing the second semiconductor layer, and the active layer contacting both sides of the third semiconductor layer and the first semiconductor layer is formed by the buried growth in the stripe groove. A highly reliable semiconductor laser which is reduced in number can be obtained.

Further, in the method for manufacturing a semiconductor laser device according to the present invention, etching is not used for forming the stripe groove, the first semiconductor layer is formed thickly on both sides of the stripe-shaped insulating film, and the second semiconductor layer is formed thereon. A semiconductor layer is formed, and a stripe groove is formed by removing the stripe-shaped insulating film, and an active layer is formed by burying growth in the stripe groove, so that the yield is improved and a highly reliable semiconductor laser device is formed. There is an effect that can be obtained.

[Brief description of drawings]

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

FIG. 2 is a sectional view showing a manufacturing flow of a semiconductor laser device of the present invention.

FIG. 3 is a cross-sectional view showing a conventional semiconductor laser device.

[Explanation of symbols]

1 semiconductor substrate 2 1st semiconductor layer 3 2nd semiconductor layer 4 diffraction grating 5 3rd semiconductor layer 6 active layer 7 4th semiconductor layer 8 contact layer 9 SiO ₂ film

Claims (2)

[Claims] 1. A semiconductor substrate of a first conductivity type, a diffraction grating formed on this semiconductor substrate, a first semiconductor layer of a second conductivity type formed on this diffraction grating, on this first semiconductor layer. A second semiconductor layer of the first conductivity type formed on the
An active layer formed of a semiconductor layer of a first or second conductivity type formed in contact with a part of a side surface of the first semiconductor layer in a stripe groove formed by a second semiconductor layer, the active layer and the active layer A third semiconductor layer of the first conductivity type, a second semiconductor layer, and an active layer having an intermediate forbidden band width wider than the active layer and narrower than the semiconductor substrate formed between the semiconductor substrate including a diffraction grating. A semiconductor laser device comprising a fourth semiconductor layer of the second conductivity type formed on the semiconductor laser device. 2. A step of forming a diffraction grating on a semiconductor substrate of a first conductivity type, a stripe-shaped insulating film is formed on the diffraction grating, and then a first semiconductor layer of a second conductivity type and a first semiconductor layer.
A step of sequentially selectively growing a conductive second semiconductor layer, removing the stripe-shaped insulating film to form a stripe groove, and then forming a stripe groove in the stripe groove, the first conductive type having a forbidden band width narrower than that of the semiconductor substrate; Of the third semiconductor layer and an active layer having a band gap narrower than that of the third semiconductor layer are buried and grown, and a fourth semiconductor layer of the second conductivity type is further formed thereon. And a method for manufacturing a semiconductor laser device.