CN114552384A - Semiconductor laser device for realizing fundamental mode lasing by changing local lateral refractive index and preparation method thereof - Google Patents

Abstract

The invention relates to a semiconductor laser that realizes fundamental mode lasing by changing the local lateral refractive index. A protruding structure, through which the actual refractive index of the waveguide region under the structure is increased, and the high-order modes propagating here are guided to the waveguide layers on both sides and lost, thereby increasing the leakage loss of the high-order modes , which can realize a large fundamental mode optical mode volume, and can realize stable fundamental-side mode operation under large strip width and high current.

Description

A semiconductor laser that realizes fundamental mode lasing by changing local lateral refractive index and its preparation method

technical field

The invention relates to a semiconductor laser which realizes fundamental mode lasing by changing the local lateral refractive index and a preparation method thereof

Background technique

High-power semiconductor lasers are widely used in pumping, optical communication, medical and other fields. With the expansion and subdivision of application fields, the performance requirements of semiconductor lasers are also getting higher and higher. For semiconductor lasers, due to the need to couple the outgoing light into the optical fiber, the light spot is required to have high focusing ability and high energy density. Good fundamental mode working characteristics and spot shape.

In order to realize the fundamental mode operation, semiconductor lasers usually use a weak refractive index guiding structure. The weak refractive index guiding structure is a lateral change of the material structure at the light-emitting place in the active region, so that the refractive index on both sides of the stripe region is smaller than that of the stripe region. The index of refraction in the interior finally achieves the effect of confining the light field. The fundamental principle is to use the principle of total reflection of light to guide the wave. Using the principle of total reflection, the ridge strips need to be made very narrow, which is inconvenient to operate, generally less than 3 microns. At the same time, due to the diffusion of carriers, and the carrier concentration will affect the refractive index, that is, the carrier concentration The higher the refractive index, the higher the refractive index, which will cause the ridge current injection region and the refractive index difference on both sides to change under high current injection, resulting in high-order mode lasing. According to the single-mode lasing formula:

脊型区域折射率，

为脊型两侧折射率，λ为出射光的波长，因此，为提升功率，一般采用减小条形区域与两侧区域折射率差来增大激光器的条宽进而增大基模的光模式体积，而通过减小折射率差来增大条宽的会导致空间烧孔效应以及热透镜效应，进而导致高阶模激射。where W is the ridge current injection width,

ridge region refractive index,

is the refractive index on both sides of the ridge type, and λ is the wavelength of the outgoing light. Therefore, in order to increase the power, it is generally used to reduce the refractive index difference between the strip area and the two sides to increase the strip width of the laser and increase the optical mode of the fundamental mode. However, increasing the strip width by reducing the refractive index difference can lead to spatial hole burning and thermal lensing effects, which in turn lead to higher-order mode lasing.

Chinese patent document CN102324696A discloses a low lateral divergence angle Bragg reflection waveguide edge emitting semiconductor laser. The laser changes the traditional waveguide layer into a Bragg reflection waveguide with periodic distribution of high and low refractive indices, and uses the Bragg grating effect to separate the fundamental mode and the higher order mode. The gain loss difference between them increases, and the laser only controls the transverse mode and has no effect on the lateral mode. At the same time, there is no control of the current spread and divergence angle in the lateral direction.

Chinese patent document CN110021877A discloses a ridge-type waveguide semiconductor laser and its preparation method. In the method, ion implantation is performed on both sides of the ridge-shaped strip after etching the ridge-shaped strip, and the carriers can only be located outside the ion-implanted area. Passing through, can effectively suppress the current expansion. This method only uses the difference between the gain of the fundamental mode and the high-order mode to suppress the high-order mode lasing, so that the laser can maintain the fundamental mode operation under a larger strip width. According to the principle of semiconductor lasers, only the fundamental mode is used. The higher-order modes will still be lasing under high current injection, if the gain differs from that of the higher-order modes.

SUMMARY OF THE INVENTION

Aiming at the deficiencies of the prior art, especially the difficulty that the prior lasers cannot effectively suppress high-order mode lasing, the present invention provides a semiconductor laser capable of realizing fundamental mode lasing by changing the local lateral refractive index and a preparation method thereof.

The technical scheme of the present invention is:

A semiconductor laser that realizes fundamental mode lasing by changing the local lateral refractive index, comprising a P-type confinement layer, a P-type waveguide layer, a light-emitting active layer, an N-type waveguide layer, an N-type waveguide layer and a A type confinement layer and an N-face metal, the P-type confinement layer includes a body layer, a ridge-type mesa protruding from the upper surface of the body layer is etched in the upper middle of the body layer, and the ridge-type mesa is elongated, and Both sides of the ridge-shaped stage are provided with a convex structure for filtering loss of high-order modes, and a P-surface electrode is provided on the upper surface of the ridge-shaped stage.

Preferably according to the present invention, the etching depth of the ridge-type mesa is less than the height of the P-type confinement layer.

Preferably according to the present invention, the width of the ridge-shaped mesa is less than or equal to 3 μm.

According to a preferred embodiment of the present invention, the protruding structure is in the shape of a cone or a strip. When the protruding structure is a cone, a side edge close to the ridge-shaped platform is the bottom edge of the protruding structure.

Preferably according to the present invention, the protruding structures are close to the ridge table but not in contact with each other.

Further preferably, the distance between the protruding structure and the ridge-shaped mesa is 5-10 μm.

Preferably according to the present invention, the height of the raised structure is smaller than the height of the ridge-shaped platform.

According to the preferred embodiment of the present invention, the positions of the protruding structures are located on both sides of the ridge strip and are close to the surface of the light emitting cavity.

The above-mentioned preparation method of a semiconductor laser for realizing fundamental mode lasing by changing the local lateral refractive index includes the following steps:

Step 1, growing an N-type confinement layer, an N-type waveguide layer, an active layer, a P-type waveguide layer, a P-type confinement layer, and an ohmic contact layer on the substrate in sequence;

Step 2, uniformly covering a layer of positive photoresist on the ohmic contact layer by a glue-sizing process, and leaving a photoresist pattern consistent with the pattern of the ridge mesa and the raised structure on the surface of the contact layer by the photolithography process;

Step 3, using a wet etching or dry etching process to etch and remove the area other than the area covered by the photoresist, and the etching depth is 600-800 nm;

Step 4, removing the photoresist after etching, then re-coating a layer of positive photoresist, removing the photoresist in the raised structure area through a photolithography development process, and leaking the ohmic contact layer on the surface of the raised structure area;

In step 5, a wet etching or dry etching process is used to etch the raised structure region to a certain depth, so that the height of the raised structure is smaller than the height of the ridge mesa.

The substrate, N-type confinement layer, N-type waveguide layer, active layer, P-type waveguide layer, P-type confinement layer, ohmic contact layer, insulating layer, N-surface electrode and P-surface electrode are consistent with the fundamental mode semiconductor laser. Inventions are not limited.

The laser ridge bar of the present invention has a high refractive index region on both sides close to the surface of the light exit cavity, and the high refractive index region is used to filter out high-order modes. According to the principle of total reflection of light, the incident angle of the high-order mode is large, and the incident angle of the fundamental mode is small. According to the principle of total reflection of light, the greater the refractive index difference, the greater the total reflection angle of light, and the larger So that the high-order mode can form total reflection, thereby forming light oscillation and lasing. The present invention designs a convex structure on both sides of the ridge stripe. According to the refractive index characteristics of the semiconductor material, the closer the semiconductor material is to the air, the actual refraction of the semiconductor material. The lower the ratio, the protruding structure is equivalent to making the waveguide layer under the region farther away from the air, so that the actual refractive index of the waveguide layer under the region is higher. The refractive index difference of the waveguide layer becomes smaller, and the smaller the refractive index difference will make the high-order mode with a large incident angle that arrives here unable to form total reflection and be extended to the two sides of the waveguide and lost, so the high-order mode cannot form oscillation. By controlling the height of the protruding structure, the size of the refractive index difference can be adjusted, and the incident angle of the fundamental mode itself is very small. Therefore, the size of the refractive index difference can be selected so that the high-order mode is lost and the fundamental mode forms total reflection and then optical oscillation occurs to form a laser. Therefore, Using the localized refractive index difference to decrease makes the high-order mode have a high loss relative to the fundamental mode, which in turn makes the laser have a large fundamental mode volume and a stable fundamental mode operating mode.

The beneficial effects of the present invention are:

Compared with the prior art, the semiconductor laser that realizes fundamental mode lasing by changing the local lateral refractive index of the present invention has the following outstanding advantages:

1. In the semiconductor laser of the present invention, which realizes fundamental mode lasing by changing the local lateral refractive index, a convex structure is designed on both sides of the semiconductor laser ridge, and the actual refractive index of the waveguide region under the structure is made through the convex structure. When it becomes larger, the high-order mode propagating here is guided to the waveguide layers on both sides and lost, which can achieve a large leakage loss between the fundamental mode and the high-order mode, and the high-order mode cannot form an effective oscillation, which can be realized in a large optical mode volume Fundamental mode lasing;

2. The laser of the present invention can effectively suppress high-order mode lasing.

3. The laser preparation method of the present invention can realize fundamental mode lasing under a large optical mode volume only by using a conventional photolithography etching process, which is suitable for mass production.

Description of drawings

1 is a schematic structural diagram of a semiconductor laser that realizes fundamental mode lasing by changing the local lateral refractive index of the present invention;

Fig. 2 is the top-view structure schematic diagram of the semiconductor laser that realizes fundamental mode lasing by changing the local lateral refractive index of the present invention;

Fig. 3 is the front view structure schematic diagram of the semiconductor laser that realizes fundamental mode lasing by changing the local lateral refractive index of the present invention;

1. P-surface electrode; 2. Ridge-type table; 3. Body layer; 4. Protruding structure; 5. P-type waveguide layer; 6. Light-emitting active layer; 7. N-type waveguide layer; 8. N-type confinement layer, 9. N-face metal.

Detailed ways

The technical solutions, implementation process and principles of the present invention will be further explained below in conjunction with the accompanying drawings.

Example 1

A semiconductor laser that realizes fundamental mode lasing by changing the local lateral refractive index, the structure is shown in Figures 1-3, including a P-type confinement layer, a P-type waveguide layer 5, The light-emitting active layer 6, the N-type waveguide layer 7, the N-type confinement layer 8 and the N-face metal 9, the P-type confinement layer includes the body layer 3, and the upper and middle part of the body layer 3 is etched and protruded from the body layer 3 Ridge-shaped table 2 on the upper surface, the ridge-shaped table 2 is elongated, and both sides of the ridge-shaped table 2 are provided with a raised structure 4 for filtering high-order modes of loss, and the upper surface of the ridge-shaped table 2 is provided with P-surface electrodes 1.

The etching depth of the ridge mesa is smaller than the height of the P-type confinement layer, and the width of the ridge mesa is 3 μm.

The protruding structure is tapered, and one side near the ridge-shaped platform is the bottom edge of the protruding structure. The protruding structure is close to the ridge table but not in contact with each other. The distance between the protruding structure and the ridge table is 5 μm. and close to the surface of the light-emitting cavity.

Example 2

It is different from the semiconductor laser described in Embodiment 1 that realizes fundamental mode lasing by changing the local lateral refractive index:

The etching depth of the ridge mesa is smaller than the height of the P-type confinement layer, and the width of the ridge mesa is 2 μm.

The protruding structures are close to the ridge mesa but not in contact with each other, and the distance between the protruding structures and the ridge mesa is 6 μm.

Example 3

It is different from the semiconductor laser described in Embodiment 1 that realizes fundamental mode lasing by changing the local lateral refractive index:

The etching depth of the ridge mesa is smaller than the height of the P-type confinement layer, and the width of the ridge mesa is 1 μm.

The protruding structures are close to the ridge-type mesa but not in contact with each other, and the distance between the protruding structure and the ridge-type mesa is 8 μm.

Example 4

It is different from the semiconductor laser described in Embodiment 1 that realizes fundamental mode lasing by changing the local lateral refractive index:

The etching depth of the ridge mesa is smaller than the height of the P-type confinement layer, and the width of the ridge mesa is 1 μm.

The protruding structures are close to the ridge-type mesa but not in contact with each other, and the distance between the protruding structure and the ridge-type mesa is 10 μm.

Example 5

A preparation method of a semiconductor laser for realizing fundamental mode lasing by changing the local lateral refractive index, comprising the following steps:

Step 1, growing an N-type confinement layer 8, an N-type waveguide layer 7, an active layer, a P-type waveguide layer 5, a P-type confinement layer, and an ohmic contact layer on the substrate in sequence;

Step 2, uniformly covering a layer of positive photoresist on the contact layer through a glue-smoothing process, and leaving a photoresist pattern consistent with the pattern of the ridge-type mesa 2 and the raised structure 4 on the surface of the contact layer through the photolithography process;

Step 3, using a wet etching or dry etching process to etch and remove the area other than the area covered by the photoresist, and the etching depth is 600-800 nm;

Step 4, remove the photoresist after etching, and then re-coat a layer of positive photoresist, remove the photoresist in the area of the raised structure 4 through a photolithography development process, and leak out the ohmic contact on the surface of the raised structure 4 area Floor;

Step 5 , using a wet etching or dry etching process, the region of the raised structure 4 is etched to a certain depth, so that the height of the raised structure 4 is smaller than the height of the ridge mesa 2 .

The above are only the preferred embodiments of the present patent. It should be pointed out that for those skilled in the art, without departing from the technical principles of the present patent, several improvements and replacements can be made. These improvements and replacements It should also be regarded as the protection scope of this patent.

Claims (9)

1. The utility model provides a semiconductor laser who realizes fundamental mode lasing through changing local side direction refracting index, its characterized in that includes from last P type restriction layer, P type waveguide layer, luminous active layer, N type waveguide layer, N type restriction layer and the N face metal that down stacks gradually the setting, P type restriction layer includes the body layer, the middle part corrodes out the ridge type platform that has protrusion in body layer upper surface on the body layer, the ridge type platform is rectangular shape, and the both sides of ridge type platform all are provided with a protruding structure that is used for filtering the loss high order mode, ridge type platform upper surface is provided with P face electrode.

2. The laser of claim 1, wherein the ridge mesa has an etch depth less than the height of the P-type confinement layer.

3. The laser of claim 1, wherein the ridge mesa has a width of 3 μm or less.

4. The laser of claim 1, wherein the raised structures are tapered or elongated, and when the raised structures are tapered, the side adjacent to the ridge platform is the bottom side of the raised structures.

5. The laser of claim 1, wherein the raised structures are adjacent to the ridge mesa but do not contact each other.

6. The laser of claim 5, wherein the distance between the protruding structures and the ridge mesa is 5-10 μm.

7. The laser of claim 1, wherein the height of the raised structures is less than the height of the ridge mesa.

8. The laser of claim 1, wherein the raised structures are positioned on both sides of the ridge stripe and adjacent to the emitting facet.

9. A method for preparing a semiconductor laser device for realizing fundamental mode lasing by changing local lateral refractive index comprises the following steps:

step 1, growing an N-type limiting layer, an N-type waveguide layer, an active layer, a P-type waveguide layer, a P-type limiting layer and an ohmic contact layer on a substrate in sequence;

step 2, uniformly covering a layer of positive photoresist on the ohmic contact layer through a photoresist homogenizing process, and leaving photoresist patterns consistent with the patterns of the ridge-shaped platform and the raised structure on the surface of the contact layer through a photoetching process;

step 3, removing the areas outside the area covered by the photoresist by means of wet etching or dry etching, wherein the etching depth is 600-800 nm;

step 4, removing the photoresist after corrosion, then recoating a layer of positive photoresist, removing the photoresist in the raised structure region through a photoetching development process, and leaking the ohmic contact layer on the surface of the raised structure region;

and 5, etching the raised structure region to a certain depth by using a wet etching or dry etching process, so that the height of the raised structure is smaller than that of the ridge-shaped platform.

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