JPH0195583A - Buried-type semiconductor laser device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an element structure of an index-guided semiconductor laser.

[Prior Art] Conventional semiconductor laser devices are classified by optical waveguide mechanism into gain waveguide type and refractive index waveguide type.

From the viewpoint of transverse mode stability, which is important in practical terms, the refractive index waveguide type is more advantageous in terms of heat insulation, and semiconductor lasers having refractive index waveguides with various structures have been developed. BH (Bu
rled l1eterostructure) laser and V S I S (v-channeled
5ubstrate inner 5tr1pc) laser is known.

The BH laser shown in FIG. 2 has a mesa-shaped double heterostructure in which a laser oscillation active layer 4 is sandwiched between cladding layers 3.5 on a substrate 1, and both sides of this mesa-shaped structure have a low refractive index. It has a structure filled with matter. Therefore, it exhibits a laser oscillation operation based on a perfect refractive index waveguide effect, and has the advantage that the threshold current is a very small value of 10 mA or less.

However, unless the refractive index of the buried layer 6 made of a low refractive index material and the waveguide width W corresponding to the width of the mesa structure are appropriately selected, there is a drawback that oscillation is likely to occur in a higher-order transverse mode. Therefore, there are many restrictions on manufacturing conditions, and in order to oscillate in the fundamental mode, the waveguide width W needs to be 2 μm or less, which makes the laser end face easy to break even at relatively low output, which reduces mass production and reliability. gender is not guaranteed. Note that 9 in FIG. 2 indicates a cap layer for obtaining ohmic contact with the electrode.

The VSIS laser shown in FIG. 3 has a current blocking layer 12 of opposite polarity provided on a substrate 11, a 7-shaped groove extending from the current blocking layer 12 to the substrate 11 to open a current path, and
It has a laminated double heterojunction structure in which a flat active layer 14 is sandwiched between cladding layers 13 and 15.

Even if the waveguide width W corresponding to the width of the 7-shaped groove is set widely to 4 to 7 μm, it has the advantage that higher-order transverse modes do not occur. This is because the light outside the waveguide is absorbed by the substrate 11, which suppresses the higher-order mode gain.

However, the threshold current is about 40 to 60 mA, and B
The drawback is that it is much more expensive than the H laser. The reason for this is that although the current is constricted by the internal stripe structure of the current blocking layer 12, carriers injected into the active layer 14 diffuse to both sides of the active layer 14, making them ineffective against laser oscillation. This is because your career will increase.

These invalid carriers are consumed by unnecessary spontaneous emission and heat generation, which increases the threshold current and adversely affects the reliability of the laser device. In addition, 19 in Figure 3
indicates a cap layer to obtain ohmic contact with the electrode.

In order to solve the above-mentioned problems of the BH laser and the VSIS laser, a structure has been considered in which both sides of the V groove of the VSIS laser are buried with a multilayer crystal including a pn reverse bias junction, as shown in FIG. The buried type VSIS laser shown in FIG.
A groove 32 is formed to open a current path, a double heterojunction structure in which a flat active layer 24 is sandwiched between cladding layers 23 and 25 is laminated thereon, and a protective layer 26 is further laminated. Both sides of the structure are removed until reaching the current blocking layer 22, buried layers 27 and 28 are provided in the removed portions with pn reverse bias junction, and on top of these are ohmic contact forming layers 29 for obtaining ohmic contact with the electrodes. is formed.

This structure limits carrier injection into the active layer 24 only to the striped mesa portion 33 to prevent it from spreading laterally, and utilizes light absorption by the GaAs layer of the substrate 21 and current blocking IL layer 22. Since it has a refractive index waveguide mechanism, it has the advantage of suppressing the generation of higher-order modes.

[Problems to be solved by the invention] Such an element structure is, for example, liquid phase epitaxial (
Although it is produced by the L P E) growth method, a current blocking layer,
The double heterojunction layer and the buried layer need to be grown three times, resulting in a complicated process and low yield. Furthermore, there is a problem in that the manufacturing cost also increases.

Therefore, an object of the present invention is to provide a buried semiconductor laser device that can suppress the complication of the process, the decrease in yield, and the increase in manufacturing cost caused by three-time growth, which are inherent in the conventional structure. It is in.

[Means and effects for solving the problems] The semiconductor laser device of the present invention has a striped mesa portion formed on a substrate and forming an active layer serving as a light emitting region, and a striped mesa portion formed on the substrate within the mesa portion. Light from the active layer is absorbed on both sides of the striped groove.

and an optical waveguide formed in the active layer, and buried layers buried in multiple layers on both sides of the mesa portion, and at least one of the buried layers is a crystal layer having a resistivity of 0.1 Ω·cm or more. It is characterized by

According to the laser element structure of the present invention, a buried layer including a crystal layer having a resistivity of 0.1 Ω·cm or more is formed on both sides of the striped mesa portion until reaching the substrate.

Therefore, leakage current on the side surface of the striped mesa portion and leakage current passing from the substrate through the buried layer region can be suppressed, and good device characteristics without leakage current can be obtained. Also, if you use this kind of structure, for example, 2
It can be formed by multiple liquid phase epitaxial (LPE) growth, which simplifies the manufacturing process, improves the yield of the device, and reduces manufacturing costs.

The crystal layer formed in the buried layer and having a resistivity of 0.1 Ω·cm or more is preferably a crystal layer that is in direct contact with the substrate and has a conductivity type opposite to that of the substrate and has a low carrier concentration. .

[Example] FIG. 1 is a diagram showing a light emitting surface of a buried semiconductor laser device according to an example of the present invention.

H is applied to the p-GaAs substrate 41 using photolithography.
With 2SO, /H2o2/H20 type etchant, ■
After forming the groove portion 52, a first liquid phase epitaxial process (
Similar to the double heterojunction structure in conventional VSIS lasers, pGa(,,5s
A11to, ii As cladding layer 43, non-doped Gao, aa AILo, +2AS active layer 44 (d-0.08 μm), n-Ga0. ss
A Q, o, a 5 As cladding layer 45, n-Ga
As protective layers 46 are sequentially laminated. Next, using the same etchant as above, a striped mesa portion 53 is formed so as to include the groove portion 52. At this time, the depth of the striped mesa portion 53 is set to reach the p-GaAs substrate 41 and have a sufficient height (for example, h-3 μm). By doing this, regrowth in this region is controlled by liquid phase epitaxial (L
This is also possible using the PE) method, and the thickness of the buried layer can be made sufficiently thick without forming a buried layer stacked with pn reverse bias polarity on the striped mesa portion 53.

By the second liquid phase epitaxial (LPE) growth, n Ga, ), 1 s AfLo, a s As
Low carrier concentration buried first layer 50 (carrier concentration 2.
Oxl O” cm-3) s p-G
a, ), 6 s AQ, o, +5 As buried second layer 48, n-GaAs ohmic contact forming layer 4
Layer 9.

As described above, since the low carrier concentration buried first layer 50 can be made sufficiently thick, the GaAs substrate 41, the low carrier concentration buried first layer 50, the buried second layer 48, and the ohmic contact forming layer 49 are formed in the buried layer region. The layer effectively acts as a current blocking layer for leakage current.

In this example, λ-780nm (L=250μm)
A device with an ILh of 24 mA was obtained with a good yield.

Further, in this embodiment, the carrier concentration of the low carrier concentration buried first layer 50 is 2.0XIO'6am-'', but no problem occurs if it is lXIO'cm-''.

Further, this buried layer may be a semi-insulating layer such as a C doped GaAs crystal.Furthermore, the method for forming the device structure of the present invention is not limited to liquid phase growth and wet etching; MOCVD
It is also possible to use growth methods such as the above, and dry etching such as RIE.

[Effects of the Invention] As explained above, according to the present invention, the manufacturing process can be greatly simplified compared to the conventional buried structure, and it can greatly contribute to improving the yield of devices and reducing manufacturing costs. can.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the present invention. FIG. 2 is a sectional view showing a conventional BH laser. FIG. 3 is a cross-sectional view showing a conventional VSIS laser. FIG. 4 is a sectional view showing a conventional buried semiconductor laser. In the figure, 41 is the substrate, 43.45 is the cladding layer, 4
4 is an active layer, 46 is a protective layer, 48 is a buried layer, 49 is an ohmic contact formation layer, 50 is a low carrier concentration buried layer, and 52 is a V? M section 53 indicates a striped mesa section.

Claims (1)

[Claims] (1) A striped mesa portion having an active layer serving as a light emitting region formed on a substrate, and absorbing light from the active layer on both sides of a stripe groove formed in the substrate within the mesa portion. In a buried semiconductor laser device comprising an optical waveguide formed in the active layer and buried layers buried in multiple layers on both sides of the mesa portion, at least one of the buried layers has a resistance of 0.1 Ω·cm or more. 1. A buried type semiconductor laser device, characterized in that it is a crystal layer having a crystalline layer having a high density.