JPH11289132A - Surface emission laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface emission laser producing high optical output by suppressing thermal saturation and deterioration of end face as much as possible. SOLUTION: An Al0.16 Ga0.84 As clad layer 64, a GaAs optical waveguide layer 63, an Al0.30 Ga0.70 As carrier block layer 62, a GaAs side barrier layer 61, an InGaAs active layer 60, a GaAs side barrier layer 59, an Al0.30 Ga0.70 As carrier block layer 58, a GaAs optical waveguide layer 57, an Al0.16 Ga0.84 As clad layer 56, an etching stop layer 55, and a contact layer 67 are formed sequentially on a GaAs substrate 65. An inclining end face 53 functioning as a reflector is formed in the optical axis of a resonator between horizontal and vertical resonator end faces 52a, 52b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface emitting laser device suitably used for communication and measurement, and particularly suitable for a multi-channel optical communication system.

[0002]

2. Description of the Related Art As a technique for transmitting and processing a large amount of information such as image information at high speed, a parallel information processing system using a two-dimensional integrated optical device has been actively studied. In such a system, a surface emitting laser device capable of two-dimensional arrangement is particularly important.

FIG. 3 is a configuration diagram showing an example of a conventional surface emitting laser device. This surface emitting laser device is described in the paper (IEE
E PHOTONICS TECHNOLOGY LETTERS, vol.7 No.12, DECEM
BER1995 p1391), and a cladding layer 10, an optical waveguide layer 9, and an
an active layer 8 composed of a quantum well layer made of nGaAs,
Optical waveguide layer 7, cladding layer 6, etching stop layer 5,
The contact layer 13 is formed. The active layer 8, the optical waveguide layers 7, 9 and the cladding layers 6, 10 are each composed of a graded index type separated confinement heterostructure (SCH: seperate).
confinementheterostrucure). Electrodes 4 and 12 for carrier injection are formed on the upper surface of contact layer 13 and the lower surface of substrate 11.

The etching stop layer 5 formed between the cladding layer 6 and the contact layer 13 is
In the step of forming the horizontal resonator end face 2a by etching the layer 3, the layer 3 functions to prevent etching of layers below the cladding layer 6. The remaining resonator end face 2b is formed by cleavage or the like so as to be perpendicular to each layer.

Further, an inclined end face 3 is formed so as to be interposed on the resonator optical axis between the horizontal resonator end face 2a and the vertical resonator end face 2b. The inclined end face 3 is inclined at, for example, 45 degrees with respect to the horizontal optical axis, and functions as a reflection mirror that bends the optical axis.

With such a configuration, the resonator end faces 2a, 2a
The laser light resonated during the period b is output to the outside from the resonator end face 2a, and functions as a surface emitting laser device that can obtain the emission beam 1 in the normal direction of the substrate 11 from the outside. Regarding the laser characteristics, at an operating current of 20 mA, the end face 2b
, An edge output of 8 mW, an end face 2 a of 5 mW, and a threshold current of 6 mA.

[0007]

In a communication light source, not only high-speed operation but also high-output operation is important. Factors that limit the output of the laser include thermal saturation and end face degradation. The thermal saturation is a phenomenon in which the element temperature rises due to Joule heat or other loss generated by laser oscillation, whereby the gain of the active layer decreases and oscillation cannot be maintained. On the other hand, end face deterioration is an irreversible phenomenon in which, when a surface level due to impurities or crystal defects is generated on an end face from which laser light is emitted, light absorption occurs and end face destruction occurs due to local heating.

In the surface emitting laser device having the inclined end face 3 having a triangular cross section as shown in FIG. 3, heat conduction from the inclined end face 3 to the substrate 11 having a large heat capacity becomes more difficult than the other end face 2b. There is a tendency that heat saturation and end face deterioration near the end face 3 are likely to occur. Further, the inclined end face 3 is the other end face 2
In this situation, damage during processing is more likely to occur, and end face deterioration is more likely to occur than in the cases of a and 2b.

Here, the damage during processing will be described in detail. In a surface emitting laser using an inclined end surface, the inclined end surface is required to be mirror-like and flat on the order of microns. Various layers constituting the laser, such as an active layer, a waveguide layer, and a cladding layer, exist on the actual inclined end face, and it is necessary to uniformly process these layers to form a mirror surface. Dry etching such as ion beam etching is generally used as a method for processing the inclined end face. However, if processing damage occurs on the inclined end face, reabsorption of laser light occurs on the inclined end face during laser oscillation, so-called COD (catastrophic opposition).
It causes end face deterioration such as tical damage).

As a countermeasure, it is conceivable to employ a wet etching process for the purpose of mirror finishing while preventing processing damage. However, since the etching characteristics of each layer constituting the inclined end face are generally different, a step is generated between the layer having a high etching rate and the layer having a low etching rate, and it is difficult to obtain a good mirror surface. In particular, in the conventional surface emitting laser, there is a situation that the Al composition of the cladding layer cannot be set too low in order to maintain carrier confinement. Therefore, the high Al composition layer is liable to be oxidized and deteriorated by wet etching, which has been a major obstacle to increasing the output of the laser. Further, in the wet etching step, unevenness is easily generated on the surface due to the difference in etching characteristics between the high Al composition layer and the low Al composition layer, and the orientation of the mirror surface is not determined, so that it was difficult to form a good mirror surface.

In order to avoid thermal saturation and deterioration of the inclined end face during laser operation, it is important to reduce the electric resistance and the thermal resistance of the element and to suppress the light density.

FIG. 4A is a configuration diagram showing a typical example of the SCH structure, and FIG. 4B is a graph showing the light intensity distribution. The horizontal axis indicates the position in the layer thickness direction, the vertical axis in FIG. 4A indicates the Al composition and the In composition, and the vertical axis in FIG. 4B indicates the light intensity. The SCH laser has a layer configuration in which a pair of cladding layers C sandwich a waveguide layer G. The waveguide layer G corresponds to the active layer 8 and the optical waveguide layers 7 and 9 in FIG. 3 correspond to the cladding layers 6 and 10, respectively.

As shown in FIG. 4A, the cladding layer C is formed of, for example, Al _0.60 Ga _0.40 As. In the waveguide layer G, the Al composition continuously decreases toward the center of the active layer, and the center of the active layer is reduced. Has a quantum well layer made of InGaAs. Since the bandgap of AlGaAs-based materials tends to increase as the Al composition increases, the distribution of the bandgap almost coincides with the graph of FIG.

The cladding layer C is mainly responsible for optical confinement, but actually also has a function of confining carriers overflowing from the quantum well layer due to the height of the forbidden band width. In order to maintain good temperature characteristics, it is necessary for carriers present in the active layer to feel that the potential barrier of the cladding layer C is sufficiently high.

FIGS. 5A and 5B are graphs showing electrical resistance and thermal resistance of an AlGaAs-based material. The horizontal axis indicates the Al composition. Referring to FIG. 5A, as the Al composition increases, the electric resistance also increases. In particular, as a whole, the p-type has higher resistance than the n-type, but the n-type has an Al composition larger than about 0.3. It turns out that the rate of increase is steep. In addition, the calorific value increases as the electric resistance increases. 5B, the thermal resistance can be expressed by a quadratic function of the Al composition.
It can be seen that the composition has a parabolic shape that is maximum when the composition is around 0.5 and is convex upward.

Therefore, in order to enhance the carrier confinement function in the SCH structure, it is conceivable to employ a cladding layer C having a high Al composition. However, the increase in the Al composition increases the electric resistance and thermal resistance of the element, and The thermal properties of this have to be sacrificed considerably.

As for the light intensity, as shown in FIG. 4B, as the Al composition of the cladding layer C increases, the refractive index difference from the waveguide layer G increases. Will be concentrated. As a result, the light intensity distribution becomes an exponential function type having a high peak intensity, and end face deterioration near the peak is likely to occur.

An object of the present invention is to provide a surface emitting laser device capable of suppressing heat saturation and end face deterioration as much as possible and obtaining a high light output.

[0019]

SUMMARY OF THE INVENTION The present invention provides an active layer and a pair of optical waveguide layers provided on both sides of the active layer and having a forbidden band width equal to or larger than the forbidden band width of the active layer. A pair of cladding layers provided so as to sandwich the optical waveguide layer and having a forbidden band width equal to or larger than the forbidden band width of the optical waveguide layer, and provided between the active layer and at least one of the optical waveguide layers; And a carrier block layer having a forbidden band width equal to or greater than each of the forbidden band widths of the optical waveguide layer, and a layer formed so as to obliquely intersect an optical axis along the active layer, and to generate light generated in the active layer. And a slanted end surface for reflecting light in a direction.

According to the present invention, the carrier block layer located between the active layer and the optical waveguide layer functions to confine carriers in the active layer. Therefore, the composition and dimensions of the cladding layer can be designed without much consideration of the carrier confinement function of the cladding layer. Therefore, it is possible to employ a cladding layer in which the electrical resistance and the thermal resistance of the element are prioritized, and it is possible to realize a high-output and high-reliability surface-emitting laser having excellent thermal characteristics and low light peak intensity.

Further, by reducing the thermal resistance of the cladding layer on the substrate side, the heat generated in the vicinity of the inclined end face is smoothly transmitted to the substrate side, so that the heat saturation and the end face deterioration on the inclined end face can be suppressed. .

Further, since the design flexibility of the clad layer is increased by providing the carrier block layer, the difference in the composition ratio between the clad layer and the optical waveguide layer can be reduced as compared with the case where the carrier block layer is not provided. Although the cladding layer and the optical waveguide layer occupy most of the inclined end faces, the inclination of the inclined end faces formed by etching is uniform because the difference in composition ratio between the two is small, so that good reflection characteristics can be obtained, and the output further increases. And increase the oscillation efficiency. In particular, these layers are made of AlGaAs
In the case where the cladding layer and the optical waveguide layer are composed of
The effect is great because the amount of 1 itself can be reduced.

Further, the present invention is characterized in that a carrier block layer is provided between the active layer and both optical waveguide layers.

According to the present invention, by providing a carrier block layer between the active layer and both optical waveguide layers, the function of confining carriers in the active layer can be more efficiently exhibited.

Further, the present invention is characterized in that the optical waveguide layer is formed of GaAs. According to the invention, AlG
In an aAs-based material, since the electrical resistance and the thermal resistance increase as the Al composition increases, the Al composition of the optical waveguide layer is preferably as low as possible, and is more preferably formed of GaAs.

Further, the present invention is characterized in that the active layer is formed of InGaAs. According to the present invention, since the forbidden band width of the active layer can be reduced, the potential barrier for carriers existing in the active layer can be set sufficiently high, and the effect of confining carriers in the active layer can be enhanced.

The present invention is also characterized in that the thickness of the carrier block layer is in the range of 5 nm to 50 nm.

According to the present invention, the carrier block layer needs to have a certain thickness so that the carriers existing in the active layer do not leak due to the tunnel effect. A layer thickness of 50 nm or less is preferred because of the decrease. Conversely, if the thickness is too small, a band bending phenomenon in which the band peak of the carrier block layer is alleviated or carrier leakage due to a tunnel effect occurs, and the carrier blocking function is deteriorated. Therefore, a layer thickness of 5 nm or more is preferable.

Further, according to the present invention, the cladding layer has an Al composition x ≦
It formed in 0.3 of Al _x Ga _1-x As, wherein the are.

According to the present invention, as the Al composition increases, the electrical resistance and the thermal resistance increase as the Al composition increases. Therefore, the lower the Al composition of the cladding layer, the more preferable. More preferably, the cladding layer is formed of AlGaAs having an Al composition of 0.3 or less.

Next, the principle of the present invention will be described. FIG.
FIG. 1A is a configuration diagram showing a typical example of a laser device according to the present invention, and FIG. 1B is a graph showing the light intensity distribution. The horizontal axis indicates the position in the layer thickness direction, the vertical axis in FIG. 1A indicates the Al composition and the In composition, and the vertical axis in FIG. 1B indicates the light intensity. This laser device has a layer configuration in which a pair of cladding layers C sandwich a waveguide layer G. The waveguide layer G is composed of a central active layer Q, a carrier block layer B adjacent to both outer sides thereof, and a further outer side. Including an optical waveguide layer.

Carriers composed of electrons and holes are injected from the outside of the cladding layer C, recombine in the active layer Q to emit light, and laser oscillation is caused by the optical resonator. Once the carriers enter the active layer Q, they are confined in the active layer Q by the potential barrier of the carrier block layer B. Therefore, the cladding layer C does not need to confine carriers, and can concentrate on carrier introduction, light distribution control, heat conduction control, and the like. As a result, for example, by setting the Al composition in the AlGaAs system low, it is possible to reduce the electric resistance and the thermal resistance of the device and to suppress the light peak intensity.

On the other hand, since the overall Al composition is reduced, oxidation deterioration is suppressed, and a mirror surface having good flatness can be easily obtained. In particular, it is preferable that the optical waveguide layer be formed of GaAs, whereby an atomic-level mirror surface reflecting the crystal orientation can be easily obtained.

When a certain kind of etchant is used, GaAs can form a favorable inclined mirror surface having a certain angle reflecting the crystal orientation. On the other hand, the respective layers
When the layer is formed of aAs, the layer having a high Al content has a different etching rate, and thus the anisotropy corresponding to the crystal orientation changes for each layer, and the orientation of the etched surface becomes non-uniform. As a result, when a surface emitting laser is manufactured by performing wet etching on a laser device composed of an AlGaAs multilayer film, the inclined end face tends to have irregularities in each layer, and the plane orientation tends to vary in each layer. Such a tendency is not limited to AlGaAs-based materials, and may always occur in ternary or higher material systems.

Further, since the carrier block layer B has a thickness necessary for confining carriers, the influence on light distribution can be minimized. As shown in FIG. 1B, the overall shape of the light intensity distribution is uniquely defined only in the waveguide layer G and the cladding layer C. By setting the thickness of the waveguide layer G to be large, the light distribution shape can be reduced. From a conventional exponential function type having a sharp peak, it becomes possible to approach a gentle Gaussian type, and the peak intensity with respect to the total light amount can be significantly reduced. as a result,
The degree of end face deterioration can be greatly improved.

Also, since the amount of A1 in the carrier block layer is large, the inclined end face changes its inclination or has irregularities at that portion due to etching, but its influence on light reflection is small since its thickness is small.

[0037]

FIG. 2 is a block diagram showing an embodiment of the present invention. The surface emitting laser device includes a cladding layer 64 (thickness 2000 nm) made of Al _0.16 Ga _0.84 As, an optical waveguide layer 63 (thickness 700 nm) made of GaAs, and an Al _0.30 Ga
_The carrier block layer 62 (thickness: 30 n) made of _0.70 As
m), a side barrier layer 61 of GaAs (thickness 50
active layer 60 (8 nm thick) composed of a quantum well layer composed of InGaAs, a side barrier layer 59 composed of GaAs (50 nm thick), and a carrier block layer 58 composed of Al _0.30 Ga _0.70 As (thickness 30 nm). ), Ga
Optical waveguide layer 57 (700 nm thick) made of As, Al
Cladding layer 56 made of _0.16 Ga _0.84 As (having a thickness of 200
0 nm), an etching stop layer 5 made of AlAs
5. Contact layer 67 made of GaAs (thickness: 1000)
nm) is formed using MOCVD (metal organic chemical vapor deposition) or the like. When the layers from the active layer 60 to the substrate 65 are n-type, the layers from the active layer 60 to the contact layer 67 are p-type. Conversely, when the former is p-type, the latter is n-type. Electrodes 54 and 66 for carrier injection are formed on the upper surface of the contact layer 67 and the lower surface of the substrate 65.

The band gap of AlGaAs-based materials tends to increase as the Al composition increases. In the present embodiment, the forbidden band widths of the optical waveguide layers 57 and 63 and the side barrier layers 59 and 61 are larger than the forbidden band width of the active layer 60, and the optical waveguide layers 57 and 63 and the side barrier layers 59 and 61 are further larger. The forbidden band width of each of the cladding layers 56 and 64 is larger than
Further, the forbidden band width of the carrier block layers 58 and 62 is larger than those of the optical waveguide layers 57 and 63 and the side barrier layers 59 and 61.

The active layer 60, the side barrier layers 59 and 61,
The optical waveguide layers 57 and 63 and the cladding layers 56 and 64 constitute a waveguide.

The etching stop layer 55 formed between the cladding layer 56 and the contact layer 67 is formed by forming the contact layer 67 in a step below the cladding layer 56 in the step of forming the horizontal resonator end face 52a by wet etching. Performs the function of preventing the etching of. The remaining resonator end face 52b is formed by cleavage or the like so as to be perpendicular to each layer.

Further, in order to interpose the resonator optical axis between the horizontal resonator end face 52a and the vertical resonator end face 52b,
The inclined end face 53 is formed using anisotropic etching.
The inclined end face 53 is inclined at, for example, 45 degrees with respect to the horizontal optical axis, and functions as a reflection mirror that bends the optical axis.

Since the side barrier layers 59 and 61 and the optical waveguide layers 57 and 63 are formed of GaAs, the inclined end face 53 having excellent flatness can be easily formed by using wet etching. A reflection film having a reflectivity of 10% is formed on the cavity end face 52a serving as a laser light emission end face.
A reflection film having a reflectance of 95% is formed on the other resonator end face 52b, and a reflection film having a reflectance of 95% is formed on the inclined end face.

Next, the operation will be described. Electrode 54 and electrode 66
When a bias voltage is applied during this period, electrons and holes are injected into the active layer 60 as carriers, and light is radiated by carrier recombination. Further, as the amount of injected current is increased, stimulated emission starts, and then laser oscillation starts between the end faces 52a and 52b constituting the optical resonator. Although the laser light oozes into the optical waveguide layers 57 and 63 and the cladding layers 56 and 64 on both sides of the active layer 60 and is guided, the waveguide mode plays a role of confining light because the optical waveguide layer can be made thicker. It can be spread toward the cladding layer. Therefore, the peak intensity with respect to the total light amount can be significantly reduced, and the degree of end face deterioration can be greatly improved. On the other hand, the carriers in the active layer 60 are confined in the active layer 60 by the presence of the carrier block layers 58 and 62, so that the recombination efficiency is improved.

The laser light resonating between the resonator end faces 52a and 52b is output to the outside from the resonator end face 52a, and functions as a surface emitting laser device from which the emission beam 51 can be obtained in the normal direction of the substrate 65 from the outside. I do.

In this embodiment, the carrier block layer 5
By providing the cladding layers 8 and 62, the Al composition of the cladding layers 56 and 64 can be significantly reduced to 0.16, so that the overall electric resistance and thermal resistance are significantly reduced. Further, since the carrier block layers 58 and 62 are sufficiently thin so as to hardly affect the light distribution, the light intensity distribution is widened, and FIG.
As shown in (b), generation of a peak can be eliminated, and end face deterioration can be greatly suppressed.

In the above description, an example in which an AlGaAs-based semiconductor material is used has been described. However, P (phosphorus) -based and GaN-based semiconductor materials having the same relationship between the forbidden band width and the electrical resistance and the thermal resistance are also used. Can be used.

The active region is also formed of InGaAs.
Not only the quantum well layer but also other materials such as InGaAs
The present invention can also be applied to a quantum well layer using P or GaN or a normal double heterostructure that is not a quantum well.

[0048]

As described above in detail, according to the present invention, the carrier blocking layer located between the active layer and the optical waveguide layer performs the function of confining carriers in the active layer. , A high-output, high-reliability surface-emitting laser with excellent thermal characteristics and low light peak intensity can be realized. Further, by reducing the thermal resistance of the cladding layer on the substrate side, the heat generated in the vicinity of the inclined end face is smoothly transmitted to the substrate side, so that the heat saturation on the inclined end face and deterioration of the end face can be suppressed.

Furthermore, since the design flexibility of the clad layer is increased by providing the carrier block layer, the difference in the composition ratio between the clad layer and the optical waveguide layer can be reduced as compared with the case where the carrier block layer is not provided. Although the cladding layer and the optical waveguide layer occupy most of the inclined end faces, the inclination of the inclined end faces formed by etching is uniform because the difference in composition ratio between the two is small, so that good reflection characteristics can be obtained, and the output further increases. And the oscillation efficiency can be increased.

[Brief description of the drawings]

FIG. 1A is a configuration diagram illustrating a typical example of a laser device according to the present invention, and FIG. 1B is a graph illustrating a light intensity distribution thereof.

FIG. 2 is a configuration diagram showing one embodiment of the present invention.

FIG. 3 is a configuration diagram illustrating an example of a conventional surface emitting laser device.

FIG. 4A is a configuration diagram showing a typical example of an SCH structure, and FIG. 4B is a graph showing a light intensity distribution thereof.

FIG. 5 is a graph showing the electrical resistance and the thermal resistance of an AlGaAs-based material.

[Explanation of symbols]

 Reference Signs List 51 Emission beam 52a, 52b Resonator end face 53 Slant end face 55 Etching stop layer 56, 64 Cladding layer 57, 63 Optical waveguide layer 59, 61 Side barrier layer 58, 62 Carrier block layer 60 Active layer 65 Substrate 67 Contact layer

Claims (6)

[Claims] An active layer, a pair of optical waveguide layers provided on both sides of the active layer and having a forbidden band width equal to or larger than the forbidden band width of the active layer, provided so as to sandwich the active layer and the optical waveguide layer. A pair of cladding layers having a forbidden band width equal to or larger than the forbidden band width of the optical waveguide layer, provided between the active layer and at least one of the optical waveguide layers,
A carrier block layer having a forbidden bandwidth equal to or greater than each of the forbidden bandwidths of the active layer and the optical waveguide layer; and a light generated in the active layer formed obliquely to an optical axis along the active layer. And a slanted end surface for reflecting light in a layer thickness direction. 2. The surface emitting laser device according to claim 1, wherein a carrier block layer is provided between the active layer and both of the optical waveguide layers. 3. The surface emitting laser device according to claim 1, wherein the optical waveguide layer is formed of GaAs. 4. The surface emitting laser device according to claim 1, wherein the active layer is formed of InGaAs. 5. The carrier block layer has a thickness of 5 nm to 5 nm.
3. The method according to claim 1, wherein the range is 0 nm.
The surface emitting laser device according to claim 1. 6. A method according to claim 1, wherein the cladding layer has an Al composition x ≦ 0.3.
The surface emitting laser device according to claim 1, wherein the surface emitting laser device is formed of l _x Ga _1-x As.