JPH08306953A - Superluminescent diode - Google Patents

Abstract

PURPOSE: To constitute a superluminescent diode with a refractive index waveguide structure region, which obtains the main gain of a light emission, and a gain waveguide structure region, which is formed in the vicinity of a light emission end face. CONSTITUTION: An N<+> buffer layer 22, an N<-> Alx Ga1-x As clad layer 23, a GaAs/ Alx Ga1-x As active layer 24, a P<-> Alx Ga1-x As clad layer 25 and a P<+> GaAs cap layer 26 are continuously crystal grown on an N-type GaAs substrate 21 and moreover, an SiO2 film 27 is formed. The layer 26 of the part of a light absorption region 34 is removed for suppressing a laser oscillation and an amplitude region 32 for obtaining a light output gain is formed into a refractive index waveguide structure. At this time, an amplitude region 33, which is a gain waveguide region, is formed in the vicinity of a light emission end face in a region for performing current injection. Moreover, P side and N side electrodes 28 and 29 for performing current injection in an element are formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a super luminescent diode, and more particularly to a super luminescent diode which is a light source for an optical sensing system and which suppresses expansion of a beam of emitted light.

[0002]

2. Description of the Related Art Conventionally, a superluminescent diode is composed of an amplification region for generating light by current injection and an absorption region for suppressing laser oscillation by a Fabry-Perot resonator. Then, in order to obtain a large injection current density, a ridge structure, which is a refractive index waveguide structure, is formed over the entire amplification region on the light emitting side end face of the amplification region to emit light.

As described above, in the amplification region, in order to obtain a high optical output at a low current, a high current is usually obtained, and a higher amplification factor is obtained. In addition, light is efficiently emitted to the emission region. For confinement, not the current density distribution determined only by the width of the electrode, but the film thickness of the mold clad layer above the active layer is changed to positively make a difference in the effective refractive index. This structure is a conventionally used refractive index guided structure, that is, a ridge structure.

FIG. 3 is a diagram showing the basic structure of such a conventional super luminescent diode. In FIG. 3, the n-type buffer layers 2, n are formed on the GaAs substrate 1.
-Type AlGaAs clad layer 3, GaAs active layer 4, p-type AlGaAs clad layer 5, p-type GaAs cap layer 6
Are continuously formed. Furthermore, a SiO ₂ film 7 and a p-side electrode 8 are formed on the p-type GaAs cap layer 6. On the other hand, an n-side electrode 9 is formed on the back surface side of the GaAs substrate 1. Incidentally, 10 constitutes an antireflection film.

In addition, p constructed as shown in FIG.
A power supply 11 for current supply is connected to a part of the side electrode 8. The super luminescent diode has a refractive index waveguide structure region 12 and a gain waveguide structure region 13.
Is configured.

[0006]

The divergence angle of the emission beam in the above-mentioned ridge structure is the same as the divergence angle of the gain waveguide structure in the direction perpendicular to the active layer. However, the divergence angle in the direction parallel to the active layer is
There is a problem that the diffraction loss at the light emitting end face greatly expands and is larger than that of the gain waveguide structure, resulting in a large connection loss when connecting to an optical fiber or a waveguide.

The present invention focuses on the fact that the spread of the emission beam in the direction parallel to the active layer in the gain waveguide structure is smaller than that in the refractive index waveguide type structure, and the main gain of light emission is controlled by the refractive index waveguide structure. It is an object of the present invention to provide a super luminescent diode which is obtained from a structure and has a gain waveguide structure in the vicinity of a light emitting end face which determines the spread of a light beam.

[0008]

That is, according to the present invention, the upper and lower sides of an active layer are sandwiched by clad layers having different conductivity types, and a p-type or n-type high electrode for taking out an electrode to either one of the clad layers. In a super luminescent diode having a concentration region formed in contact with the cladding layer and having an amplification region for generating light and an absorption region for suppressing laser oscillation, the amplification region uses the emitted light thereof. It is characterized by comprising a gain guiding region formed near the end face on the side and a refractive index guiding region formed near the gain guiding region.

Further, according to the present invention, the upper and lower sides of the active layer are sandwiched by clad layers having different conductivity types, and a p-type or n-type high-concentration region for taking out an electrode is provided in one of the clad layers. In a super luminescent diode having an amplification region for generating light and an absorption region for suppressing laser oscillation, a region other than the vicinity of the end face on the outgoing light utilization side of the amplification region is formed on the ridge. It is characterized by having a structure.

[0010]

In the superluminescent diode of the present invention, the upper and lower sides of the active layer are sandwiched by clad layers having different conductivity types, and a p-type or n-type for taking out an electrode to either one of the clad layers is provided. High-concentration region is formed in contact with the cladding layer. The super luminescent diode has an amplification region that generates light and an absorption region that suppresses laser oscillation. The amplification region is composed of a gain waveguide region formed in the vicinity of the end face on the emitted light utilization side and a refractive index waveguide region formed in the vicinity of the gain waveguide region, and the main gain of light emission is Obtained from the index guiding region, the divergence of the light beam is determined in the gain guiding region.

Further, in the superluminescent diode of the present invention, the upper and lower sides of the active layer are sandwiched by clad layers having different conductivity types, and a p-type or An n-type high concentration region is formed in contact with the cladding layer. The super luminescent diode has an amplification region that generates light and an absorption region that suppresses laser oscillation.
The region of the amplification region other than the vicinity of the end face on the side where the emitted light is used has a ridge structure.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention.
It is a structure drawing of a super luminescent diode.

In FIG. 1, an n-type GaAs substrate (100
μm) 21 on the n ⁺ -buffer layer (2 μm) 22, n ⁻
-Al _x Ga _1-x As clad layer (1 μm) 23, Ga
As / Al _x Ga _1-x As active layer (0.1 μm) 24,
_{^{p - -Al x Ga 1-x}} As cladding layer (1 [mu] m) 25,
The p ⁺ -GaAs cap layer (1 μm) 26 is continuously formed by MOCVD or molecular beam epitaxy, or O.
Crystals are grown by the MVPE method.

In the above, the numerical values shown in parentheses represent the thickness of each layer and the length of each region. From this crystal substrate, a portion of the p ⁺ -GaAs that will become the absorption region 34
The cap layer 26 is removed. Further, in order to form the pumping region 32 of the refractive index guiding structure, a p ⁺ -GaAs cap layer 26 which becomes a removal region in the vicinity of the central portion 28a of the p-type electrode 28 described later in the refractive index guiding structure region 32, p ^-
-Al _x Ga _1-x As cladding layer 25 is removed. In _{^{this, p - -Al x Ga 1-}} x As cladding layer 25 may be completely removed in the thickness direction of the layer may leave 0.5μm from 0.1 [mu] m.

When the refractive index guiding structure region 32 is formed, a region having a predetermined length in advance is formed as the gain guiding structure region 33 instead of the refractive index guiding structure. . The length of the gain waveguide structure region 33 is, for example, about 1
It is set to 0 μm to 50 μm.

After this, a SiO ₂ film (0.15 μm) 27 is formed on the surface of the element except the refractive index waveguide structure region (pumping region) 32 and the gain waveguide structure region 33. Further, a p-side electrode 28 for injecting a current from a power supply 31 for supplying a current to the element is provided on the SiO ₂ film 27 and an n-side electrode 29
Are formed on the back surface side of the n-type GaAs substrate 21. The electrodes are formed at 400 [deg.] C. or below in order to obtain ohmic contact between each electrode and the device front surface and back surface after forming both electrodes 28 and 29.
Heat treatment is performed at 450 ° C. After the heat treatment, cleavage is performed in the resonator direction.

After that, the antireflection film 30 is formed on the end face of the cleaved end face on the gain waveguide structure region side, or on the end face on the absorption region side and the end face on the gain waveguide structure region side. The above GaAs
A quantum barrier is provided in the / Al _x Ga _1-x As active layer 24. Further, this quantum barrier layer is configured by alternately arranging a barrier layer having a band gap larger than that of the active layer and a well layer having a band gap smaller than that of the barrier layer.

Furthermore, having the quantum barrier layer _{GaAs / Al x Ga 1-x} As active layer ^24, p - -Al _x Ga
GaAs / Al _x Ga in the _1-x As clad layer 25
_A multi-barrier structure is formed in a region close to the _1-x As active layer 24.

Next, the operation of suppressing the spread of the emission beam in the superluminescent diode thus constructed will be described. The purpose of this embodiment is to suppress the divergence angle of the emission beam in the horizontal plane. The active layer portion in the gain waveguide structure region 33 and the refractive index waveguide structure region 3
The effective refractive index of the active layer portion of the 2, when the refractive index waveguide structure region formed in, p ^- varies depending remaining thickness of the -Al _x Ga _1-x As cladding layer 25. This effective refractive index difference Δ
The smaller n is, the larger the divergence angle of the emission beam in the horizontal plane due to the diffraction effect is.

That is, the divergence angle of the emission beam is large only in the refractive index waveguide structure region 32. On the other hand, in the gain waveguide structure region 33, the effective refractive index of the active layer portion in the region where the p-type electrode 28 is in contact with the p ⁺ -GaAs cap layer 26,
Comparing the difference Δn ′ with the effective refractive index of the portion where the p-type electrode 28 is not in contact with the p ⁺ -GaAs cap layer 26,
n'is smaller than the difference Δn.

Therefore, the gain waveguide structure region 3 described above is used.
By forming 3 on the light emitting end face, it is possible to suppress the horizontal divergence angle of the light emitting beam. With such a configuration, most of the optical output is obtained by the refractive index waveguide structure region 32, and the gains from the gain waveguide structure region 33 near the light emitting end face overlap. Therefore, the light emission spot size at the light emitting end surface is obtained from the refractive index waveguide structure region 32.

In the superluminescent diode having such a structure, when current is injected, gain is obtained in both the gain waveguide structure region 33 and the refractive index waveguide structure region 32 to emit light. At this time, the main optical gain is obtained from the refractive index waveguide structure region 32.

The beam divergence of the emitted light beam is diverged in both vertical and horizontal directions to the active layer due to the diffraction effect due to the structure of the light emitting end face. However, in this structure, the light-emitting end face has a gain waveguide structure, so that the refractive index distribution in the horizontal direction in the active layer is relaxed. Therefore, the diffraction effect is alleviated, and it becomes possible to suppress the spread of the light beam in the direction parallel to the active layer.
In the experiment by the present inventors, the beam divergence angle in the direction perpendicular to the active layer was 50 ° and the beam divergence angle in the direction parallel to the active layer was 21 ° in the conventional structure. In the structure, 35 ° and 11 ° are obtained, respectively.

By the way, the refractive index guiding structure has the above-mentioned p
There is another method than the method of positively forming the film thickness distribution of the mold cladding layer. In the above-described embodiments, the material of the p-type cladding layer is Al _x Ga _1-x As, and x = 0.3 to 0.5.
Although the Al composition was constant in the range of A, the width of the light emitting region itself was limited to 2 μm to 5 μm, and both sides thereof had a high resistance of A.
It may be embedded with an l _y Ga _1-y As layer.

This refractive index guiding structure can effectively inject a current into the light emitting region and can effectively confine light in the light emitting region, but has a drawback that the emission beam diverges from the light emitting end face. It was a structure. This positively makes a difference in the effective refractive index in the active layer, so that the emission beam in the horizontal plane becomes large due to the diffraction effect at the emission end face.

On the other hand, the gain waveguide structure is intended to limit the current injection width by the electrode width. However, in reality, the current spreads two-dimensionally through the p ⁺ -GaAs cap layer 26, and even if the contact width with the p-type electrode 28 in the central portion 28 is 2 μm, the injection current is 20 μm- 5
It spreads to 0 μm and the injection current density cannot be increased.

Therefore, when comparing the drive currents required to obtain the same light output, the refractive index waveguide structure has a lower drive current than the gain waveguide structure. The gain waveguide structure has a gentler refractive index distribution in the active layer than the refractive index waveguide structure, and the diffraction effect on the light emitting end face is small. Therefore,
The feature is that the spread of the emission beam is small.

As described above, the present invention has the advantages that the gain waveguide structure has a low beam divergence and the refractive index waveguide structure has a low drive current and a high gain. And
The region length ratio of the gain waveguide structure region to the refractive index waveguide structure region is set to 1 in order to take advantage of the characteristics of the low refractive index waveguide structure with high gain at low drive current and the small beam divergence of the gain waveguide structure.
/ 6 to 1/10.

FIG. 2 shows the relationship between the drive current and the optical output in the super luminescent diode having a general gain waveguide structure and the super luminescent diode having the structure of the above-described embodiment. .

In the gain waveguide structure represented by A in FIG.
The amount of change in light output is small in the high drive current region. On the other hand, in the structure represented by B in the figure, the optical output in the low drive current region is slightly lower than that in the gain waveguide structure, but the optical output changes even in the high drive current region. The quantity does not decrease and a high light output is obtained.

Further, in the structure according to this embodiment, the light output density at the light emitting end face is lower than that of the refractive index guiding structure. Therefore, optical damage is suppressed, and it is possible to operate up to a high light output without damaging the device.

[0032]

As described above, according to the present invention, the main gain of light emission is obtained from the refractive index guiding structure, and the vicinity of the light emitting end face that determines the divergence of the light beam has a gain guiding structure. A cent diode can be provided.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention and is a structural diagram of a super luminescent diode.

FIG. 2 is a characteristic diagram showing the relationship between drive current and light output in a super luminescent diode having a general gain waveguide structure and the super luminescent diode having the structure of the above-described embodiment.

FIG. 3 is a diagram showing a basic structure of a conventional super luminescent diode.

[Explanation of symbols]

21 ... n-type GaAs substrate, 22 ... n ⁺ -buffer layer, 2
_{^{3 ... n - -Al x Ga 1}} -x As cladding layer, 24 ... Ga
_{As / Al x Ga 1-x} As active layer, 25 ... ^p - -Al _x
Ga _1-x As cladding layer, 26 ... p ⁺ -GaAs cap layer, 27 ... SiO ₂ film, 28 ... p type electrode, 28a ... p
Central part of mold electrode, 29 ... N-side electrode, 30 ... antireflection film,
31 ... Power source, 32 ... Refractive index waveguide structure region (pumping region), 33 ... Gain waveguide structure region, 34 ... Absorption region.

Claims (8)

[Claims] 1. An active layer is sandwiched between clad layers having different conductivity types, and a p-type or n-type high-concentration region for extracting an electrode is in contact with the clad layer in either one of the clad layers. In a super luminescent diode having an amplification region that generates light and an absorption region that suppresses laser oscillation, the amplification region is formed by a gain formed near the end face on the side where the emitted light is used. A super luminescent diode comprising a waveguide region and a refractive index waveguide region formed in the vicinity of the gain waveguide region. 2. The super luminescent diode according to claim 1, wherein a quantum barrier layer is provided in the active layer. 3. The quantum barrier layer is configured by alternately arranging a barrier layer having a larger band gap than the active layer and a well layer having a smaller band gap than the barrier layer. Item 2. A superluminescent diode according to item 2. 4. The multi-barrier structure is formed in a region adjacent to the active layer in a p-type cladding layer of the cladding layers formed on both sides of the active layer. Super luminescent diode. 5. An active layer is sandwiched between clad layers having different conductivity types, and a p-type or n-type high-concentration region for taking out an electrode is in contact with the clad layer in either one of the clad layers. In a super luminescent diode having an amplification region for generating light and an absorption region for suppressing laser oscillation, a region other than the vicinity of the end face on the side of utilizing emitted light of the amplification region has a ridge structure. A super luminescent diode characterized in that. 6. The super luminescent diode according to claim 5, wherein a quantum barrier is provided in the active layer. 7. The quantum barrier layer is configured by alternately arranging a barrier layer having a larger band gap than the active layer and a well layer having a smaller band gap than the barrier layer. Item 7. A superluminescent diode according to item 6. 8. The multi-barrier structure is formed in a region adjacent to the active layer in a p-type cladding layer of the cladding layers formed on both sides of the active layer. Super luminescent diode.