JPH07321402A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To provide a semiconductor laser device in which the absorption loss of an electric field due to an electrode is reduced. CONSTITUTION:A semiconductor laser device is provided with a tensile-strain MQW active layer 4 whose optical oscillation mode is a TM mode. When a dielectric film 9 is inserted between a ridge part and a p-electrode 10 in the semiconductor laser device, an electric field in a direction perpendicular to a heterojunction face is reflected by the dielectric film 9, and the absorption loss of the electric field due to the p-electrode 10 is reduced.

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.

[0002]

2. Description of the Related Art A semiconductor laser device having an active layer having a multiple quantum well structure has been developed for the purpose of reducing an oscillation threshold current, improving temperature characteristics, and shortening an oscillation wavelength.

FIG. 15 is a sectional view showing the structure of a conventional AlGaInP based semiconductor laser device having an active layer having a multiple quantum well structure.

In FIG. 15, an n-buffer layer 2 made of n-Ga _0.5 In _0.5 P, an n-clad layer 3 made of n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P, on an n-GaAs substrate 1, And multiple quantum wells (hereinafter MQW
The active layer 4 is formed. On the MQW active layer 4, a p-cladding layer 5 made of p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P and a p-contact layer 6 made of p-Ga _0.5 In _0.5 P are formed. 5
And the p-contact layer 6 are stripe-shaped ridge portions.

An n-current blocking layer 7 made of n-GaAs is formed on both sides of the ridge and on the p-clad layer 5, and p-type is formed on the ridge and on the n-current blocking layer 7. A p-cap layer 8 made of GaAs is formed. A p-electrode 10 made of Au-Cr is formed on the upper surface of the p-cap layer 8, and an n-electrode 11 made of Au-Sn-Cr is formed on the lower surface of the n-GaAs substrate 1.

In the semiconductor laser device of FIG. 15, the current from the p-electrode 10 is blocked by the n-current blocking layer 7 and injected only into the striped ridge portion. Further, since the thickness of the flat portion of the p-cladding layer 5 is formed to be thin to some extent in order to confine light in the MQW active layer 4 below the ridge portion, n- in the region excluding the ridge portion.
Light is absorbed by the current blocking layer 7, and the optical waveguide is formed only in the ridge portion. In this way, light is confined in the horizontal direction.

Further, the band gaps of the n-clad layer 3 and the p-clad layer 5 are larger than the band gap of the MQW active layer 4, and the refractive index of the MQW active layer 4 of the cladding layers sandwiching it. Since it is higher than the refractive index, light is confined in the MQW active layer 4. Such double hetero structure confine light in the vertical direction.

[0008]

The horizontal width W of the semiconductor laser device of FIG. 15 is usually about 300 μm, while the distance H from the MQW active layer 4 to the p-electrode 10 is H.
1 is about several μm. Since the metal absorbs the electric field, a part of the electric field of the oscillation light generated and amplified in the MQW active layer 4 is absorbed by the p-electrode 10 located at a distance of only a few μm from the MQW active layer 4. As a result, an electric field loss occurs, which causes a decrease in laser oscillation efficiency. The distance H from the MQW active layer 4 to the n-electrode 11
Since 2 is usually about 100 μm, in the n-electrode 11,
Such a problem does not occur.

Among the semiconductor laser devices having the MQW active layer, the semiconductor laser device having the compressive strain MQW active layer and the semiconductor laser device having the MQW active layer having no strain have TE (transverse ele) as the oscillation mode.
ctric) mode is dominant, and the amplitude (oscillation direction) of the oscillated light field is parallel to the heterojunction plane. On the other hand, in the semiconductor laser device having the tensile strain MQW active layer, TM (transverse m) is set as the oscillation mode.
(Magnetic) mode is dominant, and the electric field amplitude (oscillation direction) of the oscillated light is perpendicular to the heterojunction plane. Therefore, in the semiconductor laser device having the tensile strain MQW active layer, the electric field absorption loss due to the p-electrode becomes significant.

Therefore, an object of the present invention is to provide a semiconductor laser device in which the absorption loss of the electric field by the electrodes is reduced.

[0011]

A semiconductor laser device according to the present invention is a semiconductor laser device in which an electrode is arranged above an optical waveguide, and a reflective film for reflecting an electric field of oscillation light between the optical waveguide and the electrode. Is inserted.

In particular, in a semiconductor laser device that oscillates in the TM mode, it is preferable to insert a reflection film that reflects the electric field of the oscillation light between the optical waveguide and the electrode.

In a semiconductor laser device in which an electrode is arranged above an active layer having a tensile strained multiple quantum well structure, it is preferable to insert a dielectric film between the light emitting portion of the active layer and the electrode.

An electrode is laminated on a heterojunction composed of an active layer and a clad layer with a predetermined semiconductor layer interposed therebetween.
In a semiconductor laser device that oscillates in a mode, a dielectric film may be inserted above the light emitting portion of the active layer and inside a predetermined semiconductor layer, or alternatively, above the light emitting portion of the active layer and within the predetermined region. A dielectric film may be inserted in a region between the semiconductor layer and the electrode.

[0015]

In the semiconductor laser device according to the present invention, the electric field of the oscillation light is reflected by the reflection film interposed between the optical waveguide and the electrode, and the electric field does not reach the electrode. Thereby, the absorption loss of the electric field by the electrodes is reduced.

Particularly, in the semiconductor laser device oscillating in the TM mode, the electric field of the oscillated light is deflected in the direction perpendicular to the heterojunction surface, so that the effect of reducing the electric field absorption loss becomes remarkable.

Further, in the semiconductor laser device having the active layer of the tensile strain multiple quantum well structure, the electric field of the oscillation light is reflected by the dielectric film interposed between the light emitting portion of the active layer and the electrode, Does not reach the electrode. Thereby,
The absorption loss of the electric field by the electrodes is reduced.

Also in the semiconductor laser device having the active layer of the tensile strained multiple quantum well structure, the electric field of the oscillated light is deflected in the direction perpendicular to the heterojunction surface, so that the effect of reducing the absorption loss of the electric field becomes remarkable. .

[0019]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 shows Al in the first embodiment of the present invention.
FIG. 3 is a cross-sectional view showing the structure of a GaInP-based semiconductor laser device.

In FIG. 1, on an n-GaAs substrate 1,
n-buffer layer 2 made of n-Ga _0.5 In _0.5 P, n
-(Al _0.7 Ga _0.3 ) _0.5 In _0.5 P n-clad layer 3 and tensile strain MQW active layer (hereinafter referred to as MQ
A W active layer) 4 is formed. As shown in the energy band diagram of FIG. 2, the MQW active layer 4 is formed by stacking a plurality of well layers 41 and a plurality of barrier layers 42. The well layer 41 is made of Ga _0.58 In _0.42 P having a thickness of 70 Å, and the barrier layer 42 is (Al _0.5 Ga _0.5 ) having a thickness of 40 Å.
_{It is} composed of _0.5 In _0.5 P.

Referring again to FIG. 1, on the MQW active layer 4, a p-clad layer 5 made of p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P and a p-contact layer 6 made of p-Ga _0.5 In _0.5 P. Are formed, and the upper region of the p-cladding layer 5 and the p-contact layer 6 are stripe-shaped ridge portions.

An n-current blocking layer 7 made of n-GaAs is formed on both sides of the ridge and on the p-cladding layer 5, and p-GaAs is formed on the ridge and on the n-current blocking layer 7. The p-cap layer 8 is formed.

Above the ridge and on the p-cap layer 8
The dielectric film 9 having a low refractive index is inserted in the internal region.
This dielectric film 9 is SiO₂, TiO₂, ZnO, Li
NbO₃, LiTaO₃, Ta₂O_Five, Al₂O₃, N
H_FourH₂PO_Four, KH₂PO _FourFrom oxide dielectrics such as
It

A p-electrode 10 made of Au-Cr is formed on the upper surface of the p-cap layer 8, and an n-electrode 11 made of Au-Sn-Cr is formed on the lower surface of the n-GaAs substrate 1.

In the semiconductor laser device of FIG. 1, current paths 12 are formed in the ridge portion from both sides of the dielectric film 9,
A light emitting region 13 is formed in the center of the MQW active layer 4 below the ridge.

This semiconductor laser device has an MQW active layer 4
Has a tensile strain, the oscillation mode is the TM mode, and the amplitude of the electric field of light (vibration direction) is perpendicular to the heterojunction surface. The electric field in the direction perpendicular to the heterojunction surface is reflected by the dielectric film 9 and does not reach the p-electrode 10. Therefore, the absorption loss of the electric field by the p electrode 10 is reduced.

Next, a method of manufacturing the semiconductor laser device of FIG. 1 will be described with reference to process sectional views of FIGS.

First, as shown in FIG. 3, an n-buffer layer 2 having a thickness of 0.3 μm and a thickness of 0.
An n-clad layer 3 having a thickness of 9 μm and an MQW active layer 4 having the structure shown in FIG. 2 are formed. Then, on the MQW active layer 4, a p-clad layer 5 having a thickness of 0.9 μm and a thickness of 0.
A 1 μm p-contact layer 6 is formed. Crystals are continuously grown from the n-buffer layer 2 to the p-contact layer 6 by MOCVD (metal organic chemical vapor deposition).

Next, a stripe-shaped SiO ₂ mask (not shown) is formed on the p-contact layer 6 by photolithography and etching with a hydrofluoric acid-based etching solution, and a phosphoric acid-based etchant and hydrogen bromide (HBr) are used. And by wet etching with hydrochloric acid (HCl).
As shown in, a striped ridge portion is formed.

Next, as shown in FIG. 5, by the MOCVD method, n− on both sides of the ridge and on the p− cladding layer 5.
The current blocking layer 7 is crystal-grown and the SiO ₂ mask (not shown) on the ridge is removed by hydrofluoric acid-based wet etching.

Further, as shown in FIG. 6, a p-cap layer 8 having a thickness d (d> 0 μm) is grown on the upper portion of the ridge portion and the upper portion of the n-current blocking layer 7 by MOCVD. The thickness d of the p-cap layer 8 is preferably about 1 μm.

Next, as shown in FIG. 7, a dielectric film having a low refractive index is formed on the p-cap layer 8 by an EB method (electron beam evaporation method), a sputtering method or the like, and then photolithography and etching are performed. The dielectric film is patterned by, and the dielectric film 9 is formed in the region above the ridge portion.

The width W1 of the dielectric film 9 is set to 3 μm or more, but the width of the lower portion of the ridge is usually about 4 to 6 μm, so that the width W1 of the dielectric film 9 is preferably set to about 6 to 10 μm. . The thickness of the dielectric film 9 is 1000 Å or more,
It is preferably 2000 to 3000Å. Further, the shape of the dielectric film 9 may be a stripe shape continuous from one end surface to the other end surface as shown in FIG. 9, or a fragmentary shape as shown in FIG. Good.

Next, as shown in FIG. 8, a thickness of 1 is formed on the p-cap layer 8 and the dielectric film 9 by MOCVD.
A μm p-cap layer 8 is formed and a dielectric film 9 is embedded. Finally, the p electrode 10 and the n electrode 11 are formed (see FIG. 1).

FIG. 11 is a sectional view showing the structure of an AlGaInP semiconductor laser device according to the second embodiment of the present invention.

In the semiconductor laser device of FIG. 11, a dielectric film 9 having a low refractive index is inserted between the p-cap layer 8 and the p electrode 10 on the ridge portion. The configuration of the other parts is similar to that of the semiconductor laser device of FIG.

Next, a method of manufacturing the semiconductor laser device of FIG. 11 will be described with reference to the process sectional views of FIGS.

Similar to the manufacturing process of FIGS. 3 to 5 in the first embodiment, the n-buffer layer 2, the n-clad layer 3, the MQW active layer 4, and the p-clad layer are formed on the n-GaAs substrate 1. 5 and p-contact layer 6 were crystal-grown,
Upper region of p-cladding layer 5 and p-contact layer 6
Are formed in a striped ridge portion, and an n-current blocking layer 7 is formed on both sides of the ridge portion and on the p-clad layer 5. The thickness of each layer is the same as in the first embodiment.

Thereafter, as shown in FIG. 12, MOCVD is performed.
Upper part of the ridge and the n-current blocking layer 7 by
A p-cap layer 8 having a thickness of 2 μm is crystal-grown on the upper part of the.

Further, as shown in FIG. 13, a dielectric film 9 is formed on the p-cap layer 8 in the same manner as in the first embodiment. The material, forming method, thickness, width and shape of the dielectric film 9 are the same as in the first embodiment. Finally, the p electrode 10 is formed on the p-cap layer 8 and the dielectric film 9, and the n electrode is formed on the lower surface of the n-GaAs substrate 1 (see FIG. 11).

In the semiconductor laser devices according to the first and second embodiments, the electric field in the direction perpendicular to the heterojunction plane is reflected by the dielectric film 9, so that the electric field does not reach the p-electrode 10. As a result, the absorption loss of the electric field by the p-electrode 10 is reduced. As a result, as is clear from the current-light output characteristics shown in FIG. 14, the oscillation threshold current is reduced and the light emission efficiency is increased as compared with the conventional semiconductor laser device. Further, the deflection ratio between the TM mode and the TE mode also becomes large.

In the semiconductor laser device of the first embodiment, since the dielectric film 9 is arranged near the MQW active layer 4, the effect of reducing the absorption loss of the electric field is the semiconductor laser of the second embodiment. Although larger than the device, the manufacturing process of the semiconductor laser device of the second embodiment is easier.

The width and shape of the dielectric film 9 are not limited to the width and shape in the above-mentioned embodiment, but may be other widths and shapes as long as the current path is formed above the ridge portion.

In the above embodiment, the present invention is applied to AlGa
The case where the invention is applied to an InP-based semiconductor laser device has been described.
The same can be applied to an aAs semiconductor laser device.

Further, in the above-mentioned embodiment, the case where the present invention is applied to the semiconductor laser device having the ridge portion has been described. However, the present invention is not limited to the semiconductor laser device having the ridge portion, and various types of semiconductor laser devices are also provided. It is also possible to apply to.

Further, in the above embodiment, the case where the present invention is applied to the semiconductor laser device having the tensile strained MQW active layer is explained, but the present invention is also applied to other semiconductor laser devices which oscillate in the TM mode. You can

[0048]

As described above, according to the present invention, the electric field of the oscillated light is reflected by the reflection film or the dielectric film and does not reach the electrode, so that the absorption loss of the electric field by the electrode is reduced. As a result, the threshold current is reduced, the luminous efficiency is increased, and the deflection ratio between the TM mode and the TE mode is increased.

[Brief description of drawings]

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

FIG. 2 is an energy band diagram showing a structure of an MQW active layer.

FIG. 3 is a first diagram showing a method of manufacturing the semiconductor laser device of FIG.
FIG.

FIG. 4 is a second view showing a method for manufacturing the semiconductor laser device of FIG.
FIG.

5 shows a third method for manufacturing the semiconductor laser device of FIG.
FIG.

6 is a fourth view showing a method of manufacturing the semiconductor laser device of FIG.
FIG.

FIG. 7 is a fifth view showing the method for manufacturing the semiconductor laser device of FIG.
FIG.

FIG. 8 is a sixth view showing a method for manufacturing the semiconductor laser device of FIG.
FIG.

FIG. 9 is a perspective view showing an example of the shape of a dielectric film.

FIG. 10 is a perspective view showing another example of the shape of the dielectric film.

FIG. 11 is a sectional view showing a structure of a semiconductor laser device according to a second embodiment of the present invention.

12 is a first step sectional view showing the method of manufacturing the semiconductor laser device of FIG. 11. FIG.

FIG. 13 is a second process sectional view showing the method of manufacturing the semiconductor laser device of FIG. 11.

FIG. 14 is a diagram showing current-light output characteristics of the semiconductor laser devices of the first and second examples.

FIG. 15 is a sectional view showing a structure of a conventional semiconductor laser device.

[Explanation of symbols]

 1 n-GaAs substrate 4 MQW active layer 5 p-clad layer 8 p-cap layer 9 dielectric film 10 p-electrode In addition, the same code | symbol shows the same or corresponding part in each figure.

Claims (5)

[Claims] 1. A semiconductor laser device in which an electrode is arranged above an optical waveguide, wherein a reflective film for reflecting an electric field of oscillation light is interposed between the optical waveguide and the electrode. Laser device. 2. An electrode is arranged on the upper part of the optical waveguide,
A semiconductor laser device that oscillates in a mode, wherein a reflection film that reflects an electric field of oscillation light is interposed between the optical waveguide and the electrode. 3. A semiconductor laser device in which an electrode is arranged on an active layer of a tensile strained multiple quantum well structure, wherein a dielectric film is interposed between a light emitting portion of the active layer and the electrode. Characteristic semiconductor laser device. 4. An electrode is laminated on a heterojunction composed of an active layer and a clad layer via a predetermined semiconductor layer,
A semiconductor laser device that oscillates in a TM mode, wherein a dielectric film is interposed above the light emitting portion of the active layer and in a region inside the predetermined semiconductor layer. 5. An electrode is laminated on a heterojunction composed of an active layer and a clad layer via a predetermined semiconductor layer,
A semiconductor laser device that oscillates in a TM mode, characterized in that a dielectric film is interposed above the light emitting portion of the active layer and in a region between the predetermined semiconductor layer and the electrode. .