JPS603178A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To obtain a laser having excellent electrical characteristics by making the band-gap of an n type GaAlAs current stopping layer smaller than that of an un-doped GaAlAs active layer on the side close by the active layer and larger than that of the active layer on the side far from the active layer when a p type GaAlAs clad layer, an n type GaAs light absorption layer and the current stopping layer are formed on the active layer. CONSTITUTION:An n type Ga0.55Al0.45As clad layer 12, an un-doped Ga0.85Al0.15 As active layer 13 and a p type Ga0.55Al0.45As clad layer 14 are laminated on an n type GaAs substrate 11 and grown in a liquid phase in an epitaxial manner, and an n type GaAs light absorption layer 15 and an n type Ga0.55Al0.45As current stopping layer 16 from which striped sections are removed are formed on the layer 14 and the layer 16 is coated with a p type Ga0.55Al0.45As coating layer 17. In the constitution, the band-gap of the current stopping layer 16 is made smaller than that of the layer 13 on the side close by the active layer 13 and larger than that of the layer 13 on the side far from the layer 13. Accordingly, the layer 16 is given independently two functions of light absorption and current constriction, and current-optical output characteristics are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in a semiconductor laser device having a solid waveguide structure.

[Technical background of the invention and its problems]

Digital Audio Disc (DAD).

2. Description of the Related Art As semiconductor lasers are increasingly being used as light sources for optical disk devices such as video disks and document 7-isle devices and for optical communication, techniques for mass production of semiconductor lasers are becoming necessary. Conventionally, the liquid phase epitaxial growth method (LPE method) using a sliding boat method has been used as a manufacturing technology for multilayer heterojunction crystals for semiconductor radars, but the LPE method has a limit in increasing the wafer area. .

For this reason, metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MOCVD), which have excellent uniformity and controllability over large areas, have been developed.
Crystal growth techniques such as MBE (MBE) are attracting attention.

The work 9, which takes advantage of the characteristics of the MOCVD method, can be called a waveguide laser (Applied Physics Letter Magazine,
No. 37, No. 3, p. 262, 1980).
There is a semiconductor laser as shown in the figure. In addition, 1 in the figure is N
-GaAs substrate, 2 is N-GaAtAs cladding layer, 3
is a GaAtAs active layer, 4 is a P-GaAtAs cladding layer, 5 is an N-GaAs flow blocking layer is a P-Ga
AtAs covering layer, 7 is P-GaA++ contact layer, 8
．． Is 9 a metal? 1. It shows the pole. In this structure, the i=current injection into the active layer is limited to a stripe pattern by the current blocking layer, and at the same time, the light guided into the active layer passes through the current blocking layer 5 and 'tJ! , seeps out to the overlayer, and as a result, a different birefringence difference occurs between the portion directly below the stripe and the other portion, resulting in the formation of a guided mode in the HaS portion directly below the stripe. In other words, the current blocking layer 5 forms a gain waveguide structure due to current confinement and a 1-rate waveguide structure due to current confinement in a self-aligned manner. According to reports by famous authors, a low threshold value of about 50 [mA:I] can be obtained in room temperature pulse oscillation, and a truly single mode oscillation can be achieved and the transverse mode can be controlled sufficiently well. It is shown.

Note that the laser with the above structure is produced by the first crystal growth from the substrate 1 to the current blocking layer 11-J to 5''!, and by etching a part of the current blocking layer 5 in a stripe shape, followed by the coating layer 6 and the contact layer. Second crystal growth forming layer 7 52
Created by a step-by-step crystal growth process. Here, g
Cladding layer 7 at the start of PJ second crystal growth
The growth of GaAtAg occurs once the surface is exposed to air.
This is growth on the surface. For this reason, it is difficult to grow MOC using the conventional LPE method, and it is easy to grow on GaAtAs surfaces.
For the first time, the VD method made it possible to produce video in a convenient manner.

Incidentally, in this glazed laser, an N-type substrate is used as the GaAs substrate, but this is because it is advantageous for the current confinement layer 5 to be different from the N-type in terms of the current blocking effect. That is, in the laser with the structure shown in FIG. 1, when looking at Klr riri perpendicular to the electrode part, there is only a simple PN junction in the stripe part where the current confinement layer is missing, whereas in the stripe part there is only a PN junction. PNPN & joints are formed on both sides. Therefore, when a forward voltage is applied, a reverse bias is applied to one of the PNPN junctions.Therefore, almost no current flows through the PNPN junction, and current only flows through the stripe portion. will flow. However, the PNPN junction becomes a kind of thyristor structure, and the current blocking layer 5 is excited by the emission of active N3, or in a high bias state, majority carriers are injected into the current blocking layer 5, and the thyristor becomes O.
In the N state, a situation occurs in which the current blocking effect disappears. In order to suppress this, it is necessary to satisfy the condition that the thickness of the current blocking layer 5 is sufficiently larger than the diffusion length of minority carriers in the current blocking layer 5. In this case, the N-GaAg layer where the minority carriers are holes and the diffusion length is 1 [μm] or less is better than the p-GaAg layer where the minority carriers are t-tons and the diffusion length is several [μm] and long. Easy to meet the conditions. Based on the above, it can be concluded that it is more advantageous to use an N-type substrate than to use a PM substrate in which the current blocking layer 5 is P-type.

However, even when an N-type substrate is used, it is not necessarily easy to obtain a reliable current confinement effect. this is,
As mentioned above, GaA is photoexcited by light emission from the active layer.
This is because s is treated as a flying current constriction layer. From this point of view, a structure can be considered in which the current blocking layer is replaced with eight layers of N-Gao, 5sAto, and 45A, which are crystals that are transparent to light emission from the active layer. However, in this structure, although the current confinement effect becomes clear when compared with the structure shown in FIG. 1, the waveguide effect becomes completely different when the structure is constructed. In other words, in the structure shown in Figure 1, the light guided in the active layer leaks through the cladding layer to the current-stopping layer and is absorbed, so that the imaginary part of the isometric birefringence is distributed horizontally to the junction surface. However, if the current blocking layer is made of a crystal that is transparent to the light emitted by the active layer, the light guided by the active layer will pass through the cladding layer to the current blocking layer. What is felt is the real part of the complex refractive index, and light is guided by the difference in the real parts, but the waveguide effect is very different from the case where a current limiting layer absorbs light. For example, when the current blocking layer is transparent, the scattered laser light is emitted through the current blocking layer due to the unevenness of the hetero interface on the side surface of the striped groove, causing disturbance in the beam pattern emitted from the laser. It was causing a lot of trouble. Such disturbances do not occur when the current blocking layer absorbs light.

[Purpose of the invention]

The purpose of the present invention is that cropping using the complex refractive index difference can reliably obtain both the waveguide effect and the current confinement effect due to the current Ij1 stop layer, and reduce the threshold current and the current-light output characteristics. It is an object of the present invention to provide a semiconductor laser device m'lr& which can achieve improvements in performance, etc.

[Summary of the invention]

The gist of the present invention is to divide the current blocking layer inserted between the cladding layer and the covering layer into two layers, and to make each layer independently have the functions of light absorption and current confinement.

In other words, in Kinei BIJ, a heterogeneous layer for current confinement and light absorption is formed on the cladding layer on the side opposite to the substrate from the active layer, excluding the striped portion, and a covering layer is formed on this. In a semiconductor laser device having a waveguide effect, the current confinement effect and the current confinement effect are achieved by forming at least two layers of the above-mentioned disparate layers, with the side closer to the active layer being connected to the active layer in a semiconductor laser device having a waveguide effect. The semiconductor layer is a small semiconductor layer, and the side far from the active layer is a semiconductor layer that has a larger shunt gap than the active layer and has a different conductivity type from the cladding layer.

〔Effect of the invention〕

According to the present invention, a light absorption layer, which is a layer having a complex refractive index different from that of the cladding layer, is formed on the side near the active layer of the different types of layers, and a light absorption layer having a conductivity type opposite to that of the cladding layer is formed on the side far from the active layer. layer, the blocking layer is completely formed. Therefore, the light guided by the active layer leaks into the light absorption layer. Therefore, the current blocking layer shown in FIG. Unlike when the layer is a crystalline layer that is transparent to the light emitted by the active layer, unnecessary reflected light is not emitted and the beam pattern is not disturbed, and compared to the laser shown in Figure 1, the generation method is waveguided. The effect is small and it does not require much force.

Furthermore, in the present invention, the band f of the current blocking layer on the side far from the active layer is made larger than that of the active layer, so the current blocking layer, which is transparent to the emission wavelength of the active layer, is not photoexcited. . Therefore, the current confinement effect is more reliable, and a decrease in threshold current and abnormal phenomena in current-light output characteristics at high injection levels can be suppressed.

[Embodiments of the invention]

FIG. 2 is a sectional view showing a schematic structure of a semiconductor laser according to an embodiment of the present invention. In the figure, 11 is N-GaAs,
2+! :, plate, 12 is N'-Ga o , s 5At
o, 45A8 cladding layer, 13 is undoped Gao,
asAtg, 15A8 active layer, 14 is P-GaO, 5
5AtO, 45As cladding layer, 15 is N-GaAs light absorption layer, 16 is N-Ga0055Ato, 4sA8 i
1st flow blocking layer, 17 is P-GaO, 55AZO, 45
A 8 am, 18 is P-GaAs contact layer, 1
9.20 indicates the total gold h%, respectively.

The laser having the above structure is realized by the steps shown in FIGS. 3(a) to 3(c). First, as shown in FIG. 3(a), an N-GaAs substrate 1z (st dodo I
N-Ga with a thickness of 3 [μm] on
0A'i'''n, 45A8 layer 12 (Se doped fl x I 917 cm-3), thickness 0.1 [μm
] Gao, B5Ato, 15A8 active layer 13, thickness 0
．． 4 [μm] of P”-Ga o, 5sAZo, 4
5Aa cladding layer 14 (Zn doped f7×1018 crr
L-3), N-GaAs light absorption layer J with thickness o5 [μm]
5 (Se dodo 5
Current blocking layer 16 (Se-doped 705×1018Crn-3
) were formed by sequential growth. In this first vapor phase growth, M
Using the OCVD method, the growth conditions are a substrate temperature of 750 [℃],
V/m-20, carrier gas (H2) flow 'IJ~10
(13/m1n), the raw material is trimethyl gallium (T
MG: (cH)sGa), trimethylaluminum (TMA: (CH3)3ht), arsine (
AsF3), p dopant: diethylzinc (DEZ2(C2H5)2Zn), n dopant: hydrogen selenide (H2S e ), and the growth rate was 0.25 Ckm/
min]. Although it is not always necessary to use the MO-CVD method for the first crystal growth, the use of the MO-CVD method, which allows crystal growth with good uniformity over a large area, is better than the LPE method when considering mass production. It is advantageous compared to

Next, as shown in FIG. 3(b), a photoresist 21 is coated on the current blocking layer 16, and the resist 21 has a width of 3 μm.
] was formed, and using this as a mask, the different layers consisting of the current blocking layer 16 and the light absorption layer 15 were selectively etched to form striped grooves 22. Then,
After removing the resist 21 and performing surface cleaning treatment, the second
The second crystal growth was performed by MOCVD method. That is, as shown in FIG. 3(c), the entire surface is covered with P-Ga with a thickness of 2 [μm].
o, 5 sALg, 45 A8 coating layer 17 (zn
Doped 5×1018 m−3) and 2 μm thick P
-GaAs contact layer 18 (Zn dodo lXl0.)
were formed by sequential growth.

From this point on, the contact layer 1 of the normal electrode material is
A Cu-Ar'% electrode layer is formed on the substrate 11, and an Au-
Get4 Cedar wave light. The thus obtained sample was cleaved into a 7 Abry-Perot laser with a cavity length of 250 [μm].The characteristics of the device were as follows: threshold current 50 [μm]
mA], and the differential/i-element effect was also good at 70 [%]. Also, the difference in beam waist in the horizontal and vertical directions of the laser beam emitted from the laser end facet is 5.
It was confirmed that the mode was as small as [μm] and was well guided in the striped portion.

Note that the present invention is not limited to the embodiments described above. For example, the light absorption layer is preferably of N type from the viewpoint of current blocking, but may be of P type since an N type current blocking layer is present thereabove. Also, as a member of the feather family, G.
Not limited to aAtAg, but also InGaAsP +A
A compound semiconductor material such as tGaInP may also be used. Furthermore, as a crystal growth method, MBE is used instead of the MOCvD method.
It is also possible to use the method. Alternatively, it is also possible to use a P-type substrate as the substrate and reverse the conductivity type of each layer.

In addition, various modifications can be made without departing from the gist of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing a schematic structure of a conventional semiconductor laser, FIG. 2 is a cross-sectional view showing a schematic structure of a semiconductor laser according to an embodiment of the present invention, and FIGS. FIG. 3 is a cross-sectional view showing the manufacturing process of the laser according to the embodiment. 11” N-GaAs top plate, 12-’ N-Gao
,55Aj,,4. As cladding layer, l 3-...Andog GILo, B5Ato, 15kB active layer, 14
”' P-Gao, 55Ato, 45As cladding layer,
15-N-GaAs light absorption layer, 16・”N-Gao
, 55AL0.45A8 current blocking layer, 17'''P
-Gao, 55AtO, 45A8 coated 11- layer, 18
...P-GaAs contact layer. Applicant I (Embedded Patent Attorney Takehiko Suzue Figure 1)

Claims (1)

[Claims] On the cladding layer on the side opposite to the substrate with respect to the active layer, a layer of a different type having a conductivity type and a complex refractive index different from that of the cladding layer is formed except for the striped portion, and on this, a layer of a different type having the same conductivity type as the cladding layer is formed. In a Dapro heterojunction type semiconductor laser device in which a coating layer is not formed and a current confinement effect and a waveguide effect are provided, the dissimilar layer has at least two layers.
The side closer to the active layer is a semiconductor layer with a Sibando gap of /b smaller than the active layer, and the side far from the active layer is a semiconductor layer with a larger Sibando gap than the active layer and a conductivity opposite to that of the cladding layer. A semiconductor laser device characterized in that the semiconductor layer is a type semiconductor layer.