JPH07105569B2 - Semiconductor laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a semiconductor laser device capable of high-power operation especially in a basic mode. [Prior Art] FIG. 2B shows, for example, a top view of a conventional semiconductor laser device and a cross-sectional view as seen from the laser emission end face.

In FIG. 6, 1 is a p-type GaAs substrate and 2 is a p-type Al _0.3 Ga.
_0.7 As clad layer, 3 is an undoped GaAs active layer, 4 is n
Type Al _0.3 Ga _0.7 As clad layer, 5 n-type GaAs contact layer, 7 p-electrode, 8 n-electrode, 9 SiO ₂ insulating film, 10 striped openings formed in the SiO ₂ insulating film 9. Parts are shown respectively.

Next, the operation will be described.

In the semiconductor laser device of FIG. 6, when a current is applied to the pn junction in the forward direction, minority carriers are injected into the active layer 3. The electrons and holes trapped in the active layer 3 are recombined with each other to emit light. As the number of injected carriers increases, the rate of stimulated emission transition due to interaction with light increases.
When the stimulated emission amplification overcomes the loss of the resonator, laser light is emitted to the outside.

In the semiconductor laser device shown in FIG. 6, the current is constricted by the SiO ₂ insulating film 9, it flows only through the opening 10 in the SiO ₂ insulating film 9, as shown in FIG. 7 (a). Therefore, the injected carrier density distribution has a mountain shape as shown in FIG. 7 (b). Further, the gain coefficient distribution as shown in FIG. 7 (c) is almost proportional to the injected carrier density, so that it has a similar mountain-shaped distribution. In the semiconductor laser device having this structure, light is confined in the active layer 3 having a larger refractive index than the cladding layers 2 and 4 in the direction perpendicular to the active layer 3. This is because light has the property of gathering in a region having a large refractive index. However, no optical confinement mechanism due to a difference in refractive index is provided in the horizontal direction with respect to the active layer 3. However, even if there is no refractive index distribution, the light is amplified by stimulated emission along a portion where the optical gain is high, so that the gain guiding mechanism in which the high gain region serves as the waveguide region functions. As described above, the gain coefficient distribution has the highest mountain shape at the center of the opening 10. Therefore, as for the mode, it is easy to select a mode having a peak in the stripe central portion and a mode of a low order, that is, a basic mode.

With the mechanism as described above, the semiconductor laser device of FIG. 6 can obtain a single-peaked laser beam.

[Problems to be Solved by the Invention]

In the conventional semiconductor laser device configured as described above, the maximum light output of the semiconductor laser device is generally determined by the area of the light emitting region. This is because as the optical output is increased, the temperature in the vicinity of the end face rises, and finally it melts and does not function as a cavity end face. In order to increase the light emitting area in the semiconductor laser device of FIG. 6, it is only necessary to widen the width W of the stripe-shaped opening 10 in the SiO ₂ insulating film 9.
However, when the width W is widened, the injected carrier density distribution and the gain coefficient distribution become flat. Therefore, a higher-order mode having a peak at the edge of the stripe is likely to occur. Such a semiconductor laser device oscillates in the fundamental mode in the low current region, but when the current is increased, the higher order mode also occurs. As a result, a kink occurs in the optical output-current characteristics, and a far field pattern has multiple peaks, which is a practical obstacle.

The present invention has been made to solve the above problems, and an object thereof is to obtain a semiconductor laser device which oscillates in a fundamental mode even during high light output operation.

[Means for Solving the Problems]

A semiconductor laser device according to the present invention includes at least a first cladding layer, an active layer made of a superlattice, a second cladding layer, and a second cladding layer on a semiconductor substrate.
In a semiconductor laser device having a stacking structure in which each layer including a clad layer and a contact layer is sequentially formed, an active region having a constant width is formed in the active layer plane in a direction perpendicular to the traveling direction of laser light, In the vicinity of the end face of the resonator, the central part is shortest in the width direction of the active region and becomes longer toward the end, and the active layer made of a superlattice is disordered by impurity diffusion. Thereby forming a window structure region having a bandgap energy larger than that of the active layer.

[Action]

In the semiconductor laser device according to the present invention, since the window structure regions having different lengths in the stripe width direction are provided, the effective end face reflectance in the stripe width direction is large in the central portion and gradually increases toward the end portion. Therefore, it has a mountain-shaped distribution that decreases and the light intensity in the central portion also has a similar mountain-shaped distribution, so that only the fundamental mode having a peak in the central portion is easily selected.

〔Example〕

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

1 (a) and 1 (b) are a top view and a sectional view taken along line AA of a semiconductor laser device showing an embodiment of the present invention. First
In the figure, 1 is a p-type GaAs substrate, 2 is a p-type Al _0.5 Ga _0.5 As
Clad layer, 4 is n-type Al _0.5 Ga _0.5 As clad layer, 5 is n
Type GaAs contact layer, 6 is an impurity diffusion region, 7 is a p-electrode, 8 is an n-electrode, 10 is a striped opening, 11 is an active layer composed of a superlattice layer, and 12 is disordered by impurity diffusion. The active layers each consisting of a superlattice layer are shown.

2 (a) and 2 (b) are a top view and a BB sectional view of a semiconductor laser device showing another embodiment of the present invention. This embodiment differs from the semiconductor laser device of the embodiment of FIG. 1 only in the active layer 11 and the window structure region 13. That is, in FIG. 3, 3 is an undoped GaAs active layer, and 13 is a high resistance Al.
_This is a structural region consisting of _0.3 Ga _0.7 As layers.

Next, the operation of the semiconductor laser device of the present invention will be described.

Since the basic operation of the semiconductor laser device of each of the above embodiments is almost the same as that of the conventional semiconductor laser device, the role of the curved window structure region peculiar to the semiconductor laser device of the present invention will be described in detail.

Normally, in a semiconductor laser device without any end face coating, about 30% of the laser light generated in the active layer 11 is reflected by the end face of the cavity and returns to the active layer 11 again. The laser light returning to the inside of the active layer 11 interacts with the carriers and further undergoes a light amplification effect of emitting laser light.

In a laser having a window structure region, the effective reflectivity is not only determined by the end face reflectivity but also depends on the structure and length of the window structure region. This is because the confinement in the window structure region in the vertical direction is not as strong as that in the active layer, or there is no confinement in the window structure region. This state is shown in FIG. The effective reflectance is quantitatively It is represented by the following two equations. In the figure, S _{0 is} the spot diameter of the laser beam immediately before it goes out of the active layer to the window region S ₁ : The spot diameter when it returns to the position of the active layer after being reflected by the end face L ′: The length of the window region R ₀ : end face reflectance R _eff : effective reflectance λ _L : wavelength.

In the semiconductor laser device having the window structure region as shown in FIG. 1 and FIG. 2, the effective reflectance R _eff is also mountain-shaped as calculated by the equations (1) and (2) in the stripe width direction. Distribution.

In the above structure, the mode having a peak at the stripe center, for example, the fundamental mode, has an effective reflectance R at the center of the end face.
_{Since the} light is mainly reflected in the region where the _eff is large, the reflection component of the laser light inside the active layer has a value close to 30%. However, since a mode having a peak at the stripe edge, for example, a primary mode, has a low effective reflectance R _eff at the stripe edge, the reflection component to the inside of the active layer is smaller than that of the basic mode described above. By the way, the gain of each mode, that is, the value of the mode gain differs depending on each mode. This is because the electric field intensity distribution differs depending on the mode, and the gain coefficient distribution, that is, the carrier density distribution is not uniform. The mode gain G ₂ is the square of the electric field intensity distribution _Ex ² (x) and the local gain coefficient g, where x is the stripe width direction.
Integrated value throughout mode the product of (x), i.e. the value represented by the following formula, is represented by _{G = ∫g (x) E X} 2 (x) dx ...... (3). In the semiconductor laser device of the present invention, g (x)
Is almost constant, so only the term of _Ex ² (x) is affected by the waveguide. Since the light intensity portion is proportional to the square of the electric field intensity distribution, the equation (3) can be rewritten as G∝g∫P (x) dx (4). In the semiconductor laser device of the present invention,
Since P (x) is larger in the mode in which the component of the laser light returning to the inside of the active layer is larger due to the effective reflectance R _eff , the mode gain is larger. Therefore, the fundamental mode gain is larger than the other higher order mode gains.

Further, in the above embodiment, the gain region, that is, the active region excluding the window structure region has the longest length at the center and becomes shorter toward the end. Therefore, a mode having a peak at the central portion of the stripe is more susceptible to an amplification effect in the gain region than a mode having a peak at the end portion.

With the above effects, the basic mode is selected,
A single-peaked laser beam can be easily obtained.

Next, a method of manufacturing the semiconductor laser device of the embodiment shown in FIG. 1 will be described with reference to FIG.

First, as shown in FIG. 4 (a), a liquid phase epitaxy method (LPE method) or a vapor phase epitaxy method (MO-C) is performed on a p-type GaAs substrate 1.
VD method, MBE method, etc., p-type Al _0.5 Ga _0.5 As clad layer 2, GaAs
Each layer of an active layer 11, an n-type Al _0.5 Ga _0.5 As clad layer 4, and an n-type GaAs contact layer 5, which are composed of a superlattice layer including a well layer and an AlAs barrier layer, is sequentially grown.

After the above layers are grown, the SiO ₂ insulating film 9 is formed on the contact layer 5.
To form. After that, the SiO _{2 in the} area that should become the window structure area
The insulating film 9 is removed by using the photolithography technique and the etching technique to form the opening 14. This state is shown in FIGS. 4 (b) and 4 (c).

Next, impurities are diffused inside the crystal through the opening 14.
Due to this impurity diffusion, the active layer 11 composed of the superlattice layer is disordered to become the window structure region 13 shown in FIG.

After forming the window structure region 12, the SiO ₂ insulating film 9 above the region to be the active region is removed. The remaining SiO ₂ insulating film 9 plays a role of current confinement to the active region.

Finally, a p-side electrode 7 is formed on the substrate 1 side, an n-electrode 8 is formed on the contact layer 5 side, and a resonator is formed by cleavage to complete this semiconductor laser device.

The method of manufacturing the semiconductor laser device shown in FIG. 1 has been described above. Next, the method of manufacturing the semiconductor laser device shown in FIG. 2 will be described.

In the method of manufacturing the semiconductor laser device of FIG. 2, the layers are crystal-grown on the p-type GaAs substrate 1, and the SiO ₂ insulating film 9 having the opening 14 corresponding to the window structure region 13 is formed until the formation of the SiO ₂ insulating film 9 of FIG. The same steps as the method for manufacturing the semiconductor laser device can be applied. The active layer 3 of the semiconductor laser device shown in FIG. 2 need not be formed of a superlattice layer, unlike the active layer 11 of the semiconductor laser device shown in FIG.

Next, after forming an SiO ₂ insulating film 9 is etched through the opening 10 formed in the SiO ₂ insulating film 9 to the cladding layer 2. As the etching method, either wet etching or dry etching may be used, but a method with less side etching is preferable. This state is shown in FIG. After the etching, a high resistance Al _0.3 Ga _0.7 As layer to be a window structure region is formed by crystal growth in the groove region formed by the etching.

The subsequent steps are the same as the steps after the window structure region is formed in the manufacturing process of the semiconductor laser device of FIG.

Although the AlGaAs semiconductor laser device has been described in the above embodiments, the same applies to a semiconductor laser device composed of another III-V group compound semiconductor, for example, an InGaAsP semiconductor laser device or an AlGaAsP semiconductor laser device. It goes without saying that you can do it.

〔The invention's effect〕

As described above, according to the present invention, an active region having a constant width is formed in the plane of the active layer in the direction perpendicular to the traveling direction of the laser light, and the length is in the width direction of the active region near the end face of the resonator. On the other hand, since the window structure region with the shortest central part and the longer end part is formed, it oscillates only in the fundamental mode even if the stripe width is widened. There is an effect that a beam is obtained.

[Brief description of drawings]

1 (a) and 1 (b) are a top view and a sectional view of a semiconductor laser device showing one embodiment of the present invention, and FIGS.
FIG. 4B is a top view and a cross-sectional view of a semiconductor laser device showing another embodiment of the present invention, FIG. 3 is a view for explaining the vertical spread of laser light in a window structure region, and FIG.
FIG. 6 is a diagram for explaining a method of manufacturing a semiconductor laser device of the present invention, FIG. 5 is a sectional view showing an etching state for forming a window structure region of the present invention, and FIGS. 6 (a) and 6 (b).
Is a top view and a cross-sectional view showing a conventional semiconductor laser device,
FIGS. 7 (a), (b), and (c) are diagrams showing current distribution, injected carrier density distribution, and gain coefficient distribution of the conventional semiconductor laser device. In the figure, 1 is a p-type GaAs substrate, 2 is a p-type AlGaAs cladding layer, 3 is an undoped GaAs cladding layer, 4 is an n-type GaAs cladding layer, 5 is an n-type GaAs contact layer, 6 is an impurity diffusion region, and 7 is p. Electrode, 8 n-electrode, 9 SiO ₂ insulating film, 10 opening, 11 active layer composed of superlattice layer, 12 active layer composed of superlattice layer disordered by impurity diffusion, 13
Is a window structure region made of a high resistance AlGaAs layer, and 14 is an opening for forming the window structure region.

Claims (1)

[Claims] 1. A semiconductor laser device having a stack structure in which at least a first clad layer, an active layer made of a superlattice, a second clad layer, and a contact layer are sequentially formed on a semiconductor substrate. An active region having a constant width is formed in a direction perpendicular to the traveling direction of the laser light, and the length is the shortest in the central portion with respect to the width direction of the active region in the vicinity of the end face of the cavity and the end portion is formed. A semiconductor laser characterized by forming a window structure region having a band gap energy larger than that of the active layer by disordering the active layer composed of a superlattice by impurity diffusion to form a shape that becomes longer as apparatus.