JPH07118559B2 - Semiconductor laser device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device which can be used for optical communication of information or optical erasing / recording / reproducing.

2. Description of the Related Art In recent years, semiconductor laser devices mainly use a so-called refractive index waveguide type structure in which a light absorption layer is provided in the vicinity of an active layer in order to obtain unity of transverse mode and good beam characteristics. It has developed. For example, Applied Physics Letter
Volume 40, p. 372 1982 Yamamoto, Hayashi, Yano, Sakurai, Hijikata (Appl.Phys.Lett.Vol.40, p372,1982 S.Ya
mamoto.H.Hayashi.S.Yano, T.Sakurai, T.Hijikata) Hereinafter, a conventional semiconductor laser as described above will be described with reference to the drawings.

FIG. 2 shows the structure of a conventional semiconductor laser device. In FIG. 2, 9 is an n-type GaAa substrate and 10 is an n-type GAa substrate.
_a1-x Al _x As clad layer, 11 is an undoped GaAs active layer, 12
Is a p-type Ga _1-x Al _x Aa cladding layer, 13 is an n-type GaAs cap layer, 14 is a Zn diffusion layer, and 15 is an n-type alloy electrode. Here, a ridge is formed in advance on the n-GaAs substrate.

The operation of the semiconductor laser device configured as described above will be described below. First, the Zn diffusion layer 14 side is an n-type electrode
When positively biased with respect to 15, holes or electrons are injected from both electrodes toward the active layer 11. At this time, due to the presence of the cap layer 13, the lateral spread of the hole current (along the junction direction) injected from 14 is limited only to the area immediately below the stripe of the Zn diffusion layer, and thus the current Passes through the active layer 11 with such a lateral spread, and finally flows into the lateral groove portion between the ridges of the n-GaAs substrate 9. The clad layers 10 and 12 sandwiching the active layer 11 also serve to confine current in the active layer 11 in the vertical direction (with respect to the junction direction). That is, the current is concentrated in the active layer 11 on the lateral groove, the laser gain is generated only in that portion, and the laser oscillation is generated. On the other hand, the clad layer
The other role of 10, 12 is to activate the active layer 11 along the vertical direction.
It is to confine the light inside. This confinement of light and current in the vertical direction serves to lower the threshold of laser operation.

The role of the ridge provided on the n-GaAs substrate 9 is as follows. That is, since the substrate 9 is a material having almost the same forbidden band width as the active layer 11, the wavelength range of the laser beam falls within the basic absorption band of the light.

On the other hand, the light generated in the active layer 11 leaks considerably outside the layer. The leaked light is particularly absorbed by the ridge portion where the distance between the active layer 11 and the substrate 9 is small. This means that the effective refractive index that light senses in the active layer 11 has an imaginary part derived from absorption,
It mainly means that the imaginary part has a lateral distribution symmetrical about the groove part. Due to this distribution, the laser light is confined in the lateral direction and gives good light beam characteristics. Furthermore, since the higher-order modes spread more laterally than the fundamental modes, the absorption of leaked light at the ridge portion is stronger than that of the higher-order modes, so that the oscillation of the higher-order modes is strongly suppressed. This is the reason why the light absorption layer represented by the ridge is provided close to the active layer. In order to further effectively confine light and suppress higher-order modes, a means of increasing absorption by making the forbidden band width of the material of the ridge portion smaller than that of the active layer material is used.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the above configuration, the effect of absorption can never be ignored even for the fundamental mode, and therefore, it is attempted to strongly suppress light confinement and higher modes. Inevitably results in an increase in optical loss with respect to the fundamental mode, and an increase in optical loss has a problem that an increase in threshold current of laser operation and a decrease in differential quantum efficiency are unavoidable.

The present invention has been made in view of the above-mentioned drawbacks, and an object of the present invention is to provide a semiconductor laser device capable of confining light laterally and achieving lateral multimode unification without using a light absorption layer.

Means for Solving the Problems In order to achieve the above object, a semiconductor laser device of the present invention includes a semiconductor layer of an opposite conductivity type having a through groove formed on a flat surface of a semiconductor substrate of one conductivity type. A first conductivity type clad layer formed to fill the through groove and have a flat surface on the semiconductor layer; an active layer formed on the first clad layer; A second cladding layer of opposite conductivity type formed on the layer, the semiconductor layer being made of a material having a smaller refractive index than the first cladding layer, and the width of the through groove. Is larger with increasing distance from the surface of the semiconductor substrate, and the width of the through groove in the portion in contact with the surface of the semiconductor substrate is 2 μm.

Action With this configuration, the light is laterally confined by the total reflection to the light at the boundary between the layer having a smaller refractive index and the first clad layer, and further, the first groove of the through groove of the part in contact with the semiconductor substrate is formed. By setting the width to 2 μm, the generation of higher-order modes can be suppressed.

Embodiment One embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the structure of a semiconductor laser device according to an embodiment of the present invention. In FIG. 1, 1 is density 1 ×
P-type GaAs substrate of 10 ¹⁹ cm ^-3, 2 concentration 5 × 10 ¹⁷ cm ^-3, n-type Ga _0.5 Al _0.5 As layer having a lateral groove in the center in a thickness of 1 [mu] m, 3 concentration 5 × 10 ¹⁷ cm ^{- 3} p-type Ga _0.6 Al _0.4 As clad layer, 4 is a 0.1 μm thick GaAs active layer with no impurities added, and 5 is 1 μm thick n-type Ga _0.6 Al _0.4 As with a concentration of 5 × 10 ¹⁷ cm _-3. Clad layer, 6 is n-type GaAs with a concentration of 5 × 10 ¹⁸ cm ^-3 and a thickness of 1 μm, 7
Is a Ti / Pt / Au alloy electrode, and 8 is an Au / Ge / Ni alloy electrode. Here, the length W of the trapezoidal upper base of the lateral groove of the Ga _0.5 Al _0.5 As layer 2 is 5 μm, the length W ₁ of the lower base is 2 μm, and the thickness of the clad layer 3 in the groove is 1 μm, and in the ridge portion. Has a thickness of 0.1
μm.

The operation of the semiconductor laser device configured as described above will be described below. First, the role of the clad layer for the active layer is the same as in the case of the conventional example shown in FIG. When the electrode 7 is positively biased with respect to the electrode 8, holes or electrons are injected from both electrodes toward the active layer 4. In particular, the hole current from the electrode 7 is blocked by the Ga _0.5 Al _0.5 As layer 2 and, as a result, flows into the active layer 4 from the lateral groove portion,
Therefore, the current concentrates on the active layer 4 above the lateral groove. The spread of this current is mainly determined by the length W _{1 of the} bottom of the groove. Generally, a material having a smaller forbidden band has a larger refractive index, and a larger X of Ga _1-x Al _x As has a larger forbidden band. Therefore, the refractive index of the Ga _0.5 Al _0.5 As layer 2 is about 0.06 smaller than the refractive index of the cladding layer 3. This difference in refractive index is comparable to the difference in effective refractive index in the case of the conventional example using the absorbing layer. Therefore, in the structure of FIG. 1, a refractive index distribution is generated in the lateral direction, and light is confined in the lateral direction. Furthermore, the above W ₁
By appropriately selecting, the ratio of the spread of light and the spread of current can be appropriately selected. The region where the current is small has a negative gain, that is, an absorption region. Therefore, the above width W ₁
Higher-order modes are selectively absorbed and lateral mode unification is achieved by making ω to be small to some extent. In this embodiment, the width W ₁ is set to 2 μm, but the threshold current at this time is 50% lower than that in the case of using the conventional absorption layer.
It was found that the transverse mode was sufficiently unified.

As described above, according to the present embodiment, by providing the low refractive index layer adjacent to the cladding layer, it is possible to obtain a single mode laser operation with a low threshold current.

In the example of FIG. 1, the cladding layer is Ga _0.6 Al _0.4 As, the active layer is GaAs, and the low refractive index layer is Ga _0.5 Al _0.5 As. However, the material is not limited to these, and Ga _1-x It may be any possible combination of double hetrojunction using Al _x As system and low refractive index layer, and may also be InGaAs, GaAlAsSb and various other possible mixed crystal systems.

EFFECTS OF THE INVENTION As described above, according to the present invention, a refractive index guided semiconductor laser device having no absorption loss is obtained by providing a layer having a lateral groove with a low refractive index in the vicinity of an active layer via a clad layer. Can be done, and its practical effect is great.

[Brief description of drawings]

FIG. 1 is a sectional view of a semiconductor laser device according to an embodiment of the present invention, and FIG. 2 is a sectional view of a conventional semiconductor laser device. 1 ... p-GaAs substrate, 2 ... n-Ga _0.5 Al _0.5 As low refractive index layer, 3 ... p-Ga _0.6 Al _0.4 As clad layer, 4 ... p-Ga
As active layer, 5 ... n-Ga _0.6 Al _0.4 As clad layer, 6 ...
n ⁺ -GaAs, 7 ... Pt / Ti / Au alloy electrode, 8 ... Au / Ge / Ni
Alloy electrode, 9 ... n-GaAs substrate, 10 ... n-Ga _1-x Al _x
As clad layer, 11 ... p-GaAs active layer, 12 ... p-Ga
_1-x Al _x As clad layer, 13 ... n-GaAs cap layer, 14 ...
… Zn diffusion layer, 15 …… n-type alloy electrode.

Claims (1)

[Claims] 1. A semiconductor layer of an opposite conductivity type having a through groove formed on a flat surface of a semiconductor substrate of one conductivity type, and a semiconductor layer filling the through groove and having a flat surface on the semiconductor layer. A first conductivity type first clad layer formed, an active layer formed on the first clad layer, and a reverse conductivity type second clad layer formed on the active layer. The semiconductor layer is made of a material having a refractive index smaller than that of the first cladding layer, and the width of the through groove increases as the distance from the semiconductor substrate surface increases, and contacts the semiconductor substrate surface. A semiconductor laser device, wherein the width of the through groove of the portion is 2 μm.