CN111384663A - Gallium nitride-based semiconductor laser and method of making the same - Google Patents

Abstract

The present invention provides a gallium nitride-based semiconductor laser, comprising a substrate, a bottom electrode arranged on the bottom of the substrate, an epitaxial structure, an insulating layer and a top electrode arranged in sequence on the top of the substrate, and the top of the epitaxial structure has a ridge shape The semiconductor layer, the ridge-shaped semiconductor layer has a first ridge portion and an ohmic contact layer, the ohmic contact layer is provided on the first ridge portion, the insulating layer is provided with an opening, the width of the opening is smaller than the width of the ohmic contact layer, and the top electrode passes through the opening in contact with the ohmic contact layer. Since the width of the opening is smaller than the width of the first ridge portion, the carrier density in the center of the first ridge portion is greater than that on both sides of the first ridge portion, and the gain of the fundamental mode is only slightly reduced, while The gain of the high-order mode is greatly reduced. At the same time, since the width of the first ridge is large enough, the optical power of the GaN-based semiconductor laser can be increased, thereby forming a single-mode GaN-based semiconductor laser with higher optical power.

Description

Gallium nitride-based semiconductor laser and method of making the same

technical field

The invention belongs to the field of semiconductor devices, and in particular relates to a gallium nitride-based semiconductor laser structure.

Background technique

Gallium Nitride (GaN)-based lasers have risen rapidly due to their small size, long life, high coupling efficiency, and simple structure, and have been widely used in laser display, laser lighting, laser printing, high-resolution lithography, etc. play an important role in the field. At the same time, many fields also put forward higher requirements for the single-mode property of GaN-based lasers.

The ridge waveguide structure has the advantages of simple structure, stability and easy processing, so this structure is widely used in the design of GaN-based lasers. However, for the ridge waveguide structure, the lateral mode control is more difficult due to the coexistence of the competition of the optical waveguide guiding mechanism and the mode competition, and the active region cannot well confine when the injected carriers change. Lateral current and optical field, so that multi-mode excitation is generated inside the laser. Although the lateral effective refractive index can be enhanced and the number of modes limited by reducing the width of the ridge and strictly controlling the etching depth, this will reduce the optical power of the laser due to the reduction of the injection current density, making it difficult to achieve large power requirements.

SUMMARY OF THE INVENTION

In order to solve the deficiencies of the prior art, the present invention provides a gallium nitride-based semiconductor laser and a manufacturing method thereof, which can realize fundamental mode excitation and increase optical power at the same time.

The present invention adopts the following technical scheme:

A gallium nitride-based semiconductor laser, comprising a substrate, a bottom electrode arranged at the bottom of the substrate, and an epitaxial structure, an insulating layer, and a top electrode sequentially stacked and arranged at the top of the substrate, wherein the top of the epitaxial structure has A ridge-shaped semiconductor layer, the ridge-shaped semiconductor layer has a first ridge portion and an ohmic contact layer, the ohmic contact layer is provided on the first ridge portion, the insulating layer is provided with an opening, and the opening is The width is smaller than the width of the first ridge portion, and the top electrode is in contact with the ohmic contact layer through the opening.

Preferably, the ridge-shaped semiconductor layer further has a second ridge-shaped part, the second ridge-shaped part is provided on the first ridge-shaped part, and the width of the second ridge-shaped part is smaller than that of the first ridge-shaped part the width of the shaped portion, the ohmic contact layer is provided on the second ridge portion, and the second ridge portion and the ohmic contact layer are located in the opening.

Preferably, the thickness of the second ridge portion is 0.1-0.2 μm.

Preferably, the width of the opening is 3˜5 μm.

Preferably, the width of the first ridge portion is 10-15 μm.

Preferably, the epitaxial structure includes a lower confinement layer, a lower waveguide layer, an active layer, an upper waveguide layer, an electron blocking layer, and an upper confinement layer stacked on top of the substrate in sequence, and the upper confinement layer is the Ridge-shaped semiconductor layer.

Preferably, the material of the substrate is gallium nitride, the material of the lower confinement layer is N-type doped aluminum gallium nitride, and the material of the lower waveguide layer is N-type doped gallium nitride. The material of the above-mentioned waveguide layer is gallium nitride, the material of the electron blocking layer is P-type doped aluminum gallium nitride, the material of the first ridge portion is P-type doped aluminum gallium nitride, so The material of the ohmic contact layer is P-type doped gallium nitride, the material of the insulating layer is silicon dioxide, and the active layer is a quantum well, which includes a plurality of gallium nitride barrier layers grown alternately in cycles and indium gallium nitride well layers.

The present invention also provides a manufacturing method of a gallium nitride-based semiconductor laser, the manufacturing method comprising the steps of:

providing a substrate;

An epitaxial structure is grown on the top of the substrate, the top of the epitaxial structure has a ridge-shaped semiconductor layer, the ridge-shaped semiconductor layer has a first ridge portion and an ohmic contact layer, and the ohmic contact layer is provided on the on the first ridge;

forming an insulating layer on the epitaxial structure, the insulating layer is provided with an opening, and the width of the opening is smaller than the width of the first ridge portion;

forming a top electrode on the insulating layer, the top electrode is in contact with the ohmic contact layer through the opening;

A bottom electrode is formed on the bottom of the substrate.

Preferably, growing and forming an epitaxial structure on the top of the substrate specifically includes:

A lower confinement layer, a lower waveguide layer, an active layer, an upper waveguide layer, an electron blocking layer, and an upper confinement material layer are sequentially grown on top of the substrate;

etching the upper confinement material layer to form a ridge layer;

etching the ridge portion layer to form a ridge semiconductor layer, the ridge semiconductor layer has a first ridge portion, a second ridge portion and an ohmic contact layer, the second ridge portion is provided on the On the first ridge portion, the width of the second ridge portion is smaller than the width of the first ridge portion, and the ohmic contact layer is provided on the second ridge portion.

The gallium nitride (GaN)-based laser in the present invention includes an epitaxial structure, an insulating layer, and a top electrode sequentially stacked on the top of the substrate, and the top of the epitaxial structure has a ridge-shaped semiconductor layer, and the ridge-shaped semiconductor layer has a first A ridge portion and an ohmic contact layer, the insulating layer is provided with an opening, the width of the opening is smaller than the width of the first ridge portion, and the top electrode is in contact with the ohmic contact layer through the opening. Since the width of the opening is smaller than the width of the first ridge portion, that is, the width of the contact surface between the top of the first ridge portion and the top electrode is smaller than the width of the first ridge portion, the current carrying in the center of the first ridge portion is The carrier density is greater than the carrier density on both sides of the first ridge, and the gain of the fundamental mode is only slightly reduced, while the gain of the higher-order mode is greatly reduced. At the same time, since the width of the first ridge is large enough, nitrogen The optical power of the gallium nitride-based semiconductor laser is reduced, thereby forming a single-mode gallium nitride-based semiconductor laser with higher optical power.

Description of drawings

The technical solutions and other beneficial effects of the present invention will be apparent through the detailed description of the specific embodiments of the present invention with reference to the accompanying drawings. of

1 is a schematic structural diagram of a GaN-based semiconductor laser in Embodiment 1;

2a-2e are schematic diagrams of a method for fabricating a GaN-based semiconductor laser in Embodiment 1;

3 is a schematic structural diagram of a GaN-based semiconductor laser in Embodiment 2;

FIGS. 4 a to 4 g are schematic diagrams of the fabrication method of the gallium nitride-based semiconductor laser in the second embodiment.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Examples of these preferred embodiments are illustrated in the accompanying drawings. The embodiments of the invention shown in the drawings and described with reference to the drawings are merely exemplary and the invention is not limited to these embodiments.

Here, it should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only the structures and/or processing steps closely related to the solution according to the present invention are shown in the drawings, and the related structures and/or processing steps are omitted. Other details not relevant to the invention.

Example 1

As shown in FIG. 1 , the gallium nitride-based semiconductor laser provided in this embodiment includes a substrate 1 , a bottom electrode 4 b arranged at the bottom of the substrate 1 , an epitaxial structure 2 , an insulating layer 3 , an epitaxial structure 2 , an insulating layer 3 , Top electrode 4a. The top of the epitaxial structure 2 has a ridge semiconductor layer, the ridge semiconductor layer has a first ridge portion 2a and an ohmic contact layer 27, the ohmic contact layer 27 is provided on the first ridge portion 2a, the insulating layer 3 is provided with an opening 3a, The width of the opening 3a is smaller than the width of the first ridge portion 2a, and the top electrode 4a is in contact with the ohmic contact layer 27 through the opening 3a.

The ohmic contact layer 27 at least completely covers the top of the first ridge portion 2a, and its area is equal to that of the first ridge portion 2a. The ohmic contact layer 27 is used to form an ohmic contact with the top electrode 4a. The insulating layer 3 covers the surface of the epitaxial structure 2 not covered by the ohmic contact layer 27 and extends to the edge of the ohmic contact layer 27 , and the opening 3 a is located on the top of the ohmic contact layer 27 .

In this embodiment, since the width of the opening 3a is smaller than the width of the first ridge portion 2a, that is, the width of the contact surface between the top of the first ridge portion 2a and the top electrode is smaller than the width of the first ridge portion 2a, so that The carrier density in the center of the first ridge portion 2a is greater than the carrier density on both sides of the first ridge portion 2a, so that the gain of the fundamental mode is only slightly reduced, while the gain of the high-order mode is greatly reduced. The width of a ridge portion 2a is large enough to increase the optical power of the GaN-based semiconductor laser, thereby forming a single-mode GaN-based semiconductor laser with higher optical power.

In this embodiment, the thickness of the first ridge portion 2 a is greater than the thickness of the ohmic contact layer 27 . In the actual manufacturing process, the thickness of the first ridge portion 2 a is determined according to the thickness of the ohmic contact layer 27 . The width of the opening 3a is 3 to 5 μm, and the width of the first ridge portion 2a is 10 to 15 μm. For example, the widths of the openings 3 a are 3 μm, 4 μm, and 5 μm, and the widths of the first ridge portions 2 a are 10 μm, 12 μm, and 15 μm. The width of the first ridge portion 2a can ensure that the entire GaN-based semiconductor laser has higher optical power, and the width of the opening 3a can ensure that the entire GaN-based semiconductor laser can work stably in the fundamental mode.

Specifically, the epitaxial structure 2 includes a lower confinement layer 21 , a lower waveguide layer 22 , an active layer 23 , an upper waveguide layer 24 , an electron blocking layer 25 , and an upper confinement layer 26 sequentially stacked on top of the substrate 1 . The upper confinement layer 26 is the It is a ridge semiconductor layer.

The material of the substrate 1 is preferably gallium nitride, the material of the lower confinement layer 21 is preferably N-type doped aluminum gallium nitride, the material of the lower waveguide layer 22 is preferably N-type doped gallium nitride, and the upper waveguide layer 24 is preferably made of N-type doped gallium nitride. The material is preferably gallium nitride, the material of the electron blocking layer 25 is preferably P-type doped aluminum gallium nitride, the material of the first ridge portion 2a is preferably P-type doped aluminum gallium nitride, and the ohmic contact layer 27 The material of the insulating layer 3 is preferably P-type doped gallium nitride, and the material of the insulating layer 3 is preferably silicon dioxide, which is used to prevent current leakage. The top electrode 4a and the bottom electrode 4b are metal electrodes for forming an ohmic contact and facilitating lead-out of the electrode leads. The active layer 23 is a quantum well, which includes a plurality of gallium nitride barrier layers and indium gallium nitride well layers that are alternately grown in multiple periods.

The lower confinement layer 21 is used to restrict the expansion of the light field in the direction toward the substrate 1 , and the upper confinement layer 26 is used to restrict the expansion of the light field in the direction away from the substrate 1 . The lower waveguide layer 22 and the upper waveguide layer 24 are used to increase the confinement effect on carriers, increase the distribution of carriers in the active region, improve the light confinement factor, reduce the threshold, and increase the luminous efficiency. The active layer 23 is used for providing light gain, and the electron blocking layer 25 is used for blocking electrons overflowing in the active layer 23 .

2a-2e, the present embodiment also provides a method for fabricating a gallium nitride-based semiconductor laser, the fabrication method comprising the steps of:

S1, providing a substrate 1, as shown in Figure 2a;

S2, growing on the top of the substrate 1 to form an epitaxial structure 2, the top of the epitaxial structure 2 has a ridge-shaped semiconductor layer, the ridge-shaped semiconductor layer has a first ridge portion 2a and an ohmic contact layer 27, and the ohmic contact layer 27 is provided on the first on the ridge portion 2a, as shown in Fig. 2b.

S3. An insulating layer 3 is formed on the epitaxial structure 2. The insulating layer 3 is provided with an opening 3a, and the width of the opening 3a is smaller than that of the ohmic contact layer 27, as shown in FIG. 2c.

S4, a top electrode 4a is formed on the insulating layer 3, and the top electrode 4a is in contact with the ohmic contact layer 27 through the opening 3a, as shown in FIG. 2d;

S5. A bottom electrode 4b is formed on the bottom of the substrate 1, as shown in FIG. 2e.

In step S2, forming the epitaxial structure 2 specifically includes:

S21. A lower confinement layer 21, a lower waveguide layer 22, an active layer 23, an upper waveguide layer 24, an electron blocking layer 25, and an upper confinement material layer 20 are sequentially grown on the top of the substrate 1, as shown in FIG. 2b. Specifically, MOCVD method is used to grow the lower confinement layer 21 sequentially. The material of the lower confinement layer 21 is N-type doped Al _0.1 Ga _0.9 N with a thickness of 1.2 m and a doping concentration of 3×10 ¹⁷ cm ^-3 ). The material of the lower waveguide layer 22 is N-type doped GaN, its thickness is 0.08 m, and the doping concentration is 5×10 ¹⁵ cm ⁻³ . The active layer 23 includes a barrier layer and a potential well layer that grow alternately in two periods, wherein the material of the barrier layer is undoped GaN, and its barrier width is 8 nm; the material of the potential well layer is undoped In _0.18 Ga _0.82 N with a well width of 3.5 nm. The material of the upper waveguide layer 24 is undoped GaN, and its thickness is 0.08m. The material of the electron blocking layer 25 is doped Al _0.2 Ga _0.8 N, its thickness is 20 nm, and the doping concentration is 5×10 ¹⁸ cm ⁻³ .

S22, etching the upper limit value material layer 20 to form a ridge-shaped semiconductor layer, the ridge-shaped semiconductor layer has a first ridge-shaped portion 2a and an ohmic contact layer 27, and the ohmic contact layer 27 is provided on the first ridge-shaped portion 2a, as shown in the figure 2c is shown. The material of the first ridge portion 2a is P-type doped Al _0.08 Ga _0.92 N, its thickness is 0.6 m, and the doping concentration is 8×10 ¹⁸ cm ⁻³ . The material of the ohmic contact layer 27 is doped GaN, its thickness is 0.05 m, and the doping concentration is 2.4×10 ²⁰ cm ⁻³ .

Example 2

As shown in FIG. 2 , the difference between this embodiment and Embodiment 1 is that the ridge-shaped semiconductor layer further has a second ridge-shaped portion 2b. The second ridge portion 2b is provided on the first ridge portion 2a, and the width of the second ridge portion 2b is smaller than that of the first ridge portion 2a. The ohmic contact layer 27 is provided on the second ridge portion 2b, and the second ridge portion 2b and the ohmic contact layer 27 are located in the opening 3a.

The area of the second ridge portion 2b and the ohmic contact layer 27 is equal to the area of the opening 3a. The ohmic contact layer 27 at least completely covers the top of the second ridge portion 2b. The insulating layer 3 covers the surface of the epitaxial structure 2 that is not covered by the ohmic contact layer 27 , and the side surfaces of the first ridge portion 2 a and the second ridge portion 2 b are both covered by the insulating layer 3 .

The top electrode 4a is in contact with the ohmic contact layer 27 through the opening 3a. Since the width of the second ridge portion 2b is smaller than that of the first ridge portion 2a, and the side surfaces of the second ridge portion 2b are covered by the insulating layer 3, further preventing The lateral diffusion of carriers is improved, thereby further increasing the carrier density in the center of the first ridge portion 2a, and improving the gain effect of the fundamental mode of the GaN-based semiconductor laser.

Preferably, the thickness of the second ridge portion 2b is 0.1˜0.2 μm. The thickness of the second ridge portion 2 b is greater than the thickness of the ohmic contact layer 27 . In the actual manufacturing process, the thickness of the second ridge portion 2 b is determined according to the thickness of the ohmic contact layer 27 .

Referring to FIGS. 4a-4g, the present embodiment provides a manufacturing method of a gallium nitride-based semiconductor laser, and the manufacturing method includes the steps:

S1. Provide a substrate 1, as shown in FIG. 4a.

S2. A lower confinement layer 21, a lower waveguide layer 22, an active layer 23, an upper waveguide layer 24, an electron blocking layer 25, and an upper confinement material layer 20 are sequentially grown on the top of the substrate 1, as shown in FIG. 4b. Specifically, MOCVD method is used to grow the lower confinement layer 21 sequentially. The material of the lower confinement layer 21 is N-type doped Al _0.1 Ga _0.9 N with a thickness of 1.2 m and a doping concentration of 3×10 ¹⁷ cm ^-3 ). The material of the lower waveguide layer 22 is N-type doped GaN, its thickness is 0.08 m, and the doping concentration is 5×10 ¹⁵ cm ⁻³ . The active layer 23 includes a barrier layer and a potential well layer that grow alternately in two periods, wherein the material of the barrier layer is undoped GaN, and its barrier width is 8 nm; the material of the potential well layer is undoped In _0.18 Ga _0.82 N with a well width of 3.5 nm. The material of the upper waveguide layer 24 is undoped GaN, and its thickness is 0.08m. The material of the electron blocking layer 25 is doped Al _0.2 Ga _0.8 N, its thickness is 20 nm, and the doping concentration is 5×10 ¹⁸ cm ⁻³ .

S3, etching the upper confinement material layer 20 to form a ridge portion layer A, as shown in FIG. 4c.

S4, the ridge portion layer A is etched to form a ridge semiconductor layer, the ridge semiconductor layer has a first ridge portion 2a, a second ridge portion 2b and an ohmic contact layer 27. The second ridge portion 2b is provided on the first ridge portion 2a, the width of the second ridge portion 2b is smaller than that of the first ridge portion 2a, and the ohmic contact layer 27 is provided on the second ridge portion 2b. The materials of the first ridge portion 2a and the second ridge portion 2b are both P-type doped Al _0.08 Ga _0.92 N, and the doping concentration is 8×10 ¹⁸ cm ⁻³ ; the width of the first ridge portion 2a is 8 μm , the height of the second ridge portion 2b is 0.2 μm and the width is 4 μm. The material of the ohmic contact layer 27 is doped GaN, its thickness is 0.05 m, and the doping concentration is 2.4×10 ²⁰ cm ⁻³ , as shown in FIG. 4d .

S5. An insulating layer 3 is formed on the epitaxial structure 2. The insulating layer 3 is provided with an opening 3a, and the second ridge portion 2b and the ohmic contact layer 27 are located in the opening 3a, as shown in FIG. 4e.

S6, the top electrode 4a is formed on the insulating layer 3, and the top electrode 4a is in contact with the ohmic contact layer 27 through the opening 3a, as shown in FIG. 4f;

S7. A bottom electrode 4b is formed on the bottom of the substrate 1, as shown in FIG. 4g.

Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, and substitutions can be made in these embodiments without departing from the principle and spirit of the invention and modifications, the scope of the present invention is defined by the appended claims and their equivalents.

Claims (9)

1. The utility model provides a gallium nitride based semiconductor laser, characterized in that, include substrate (1), locate bottom electrode (4b) of substrate (1) bottom and in proper order stack set up in epitaxial structure (2), insulating layer (3), top electrode (4a) at substrate (1) top, the top of epitaxial structure (2) has the ridge semiconductor layer, the ridge semiconductor layer has first ridge portion (2a) and ohmic contact layer (27), ohmic contact layer (27) are located on first ridge portion (2a), insulating layer (3) are equipped with opening (3a), the width of opening (3a) is less than the width of first ridge portion (2a), top electrode (4a) pass through opening (3a) with ohmic contact layer (27) contact.

2. A gallium nitride-based semiconductor laser according to claim 1, wherein the ridge semiconductor layer further has a second ridge portion (2b), the second ridge portion (2b) is provided on the first ridge portion (2a), the width of the second ridge portion (2b) is smaller than the width of the first ridge portion (2a), the ohmic contact layer (27) is provided on the second ridge portion (2b), and the second ridge portion (2b) and the ohmic contact layer (27) are located within the opening (3 a).

3. The gallium nitride-based semiconductor laser according to claim 2, wherein the thickness of the second ridge portion (2b) is 0.1 to 0.2 μm.

4. A gallium nitride based semiconductor laser according to any one of claims 1 to 3, wherein the width of the opening (3a) is 3 to 5 μm.

5. The gallium nitride-based semiconductor laser according to claim 4, wherein the width of the first ridge portion (2a) is 10 to 15 μm.

6. A gallium nitride-based semiconductor laser according to claim 1, wherein the epitaxial structure (2) comprises a lower confinement layer (21), a lower waveguide layer (22), an active layer (23), an upper waveguide layer (24), an electron blocking layer (25), and an upper confinement layer (26) which are sequentially stacked on top of the substrate (1), the upper confinement layer (26) being the ridge semiconductor layer.

7. The GaN-based semiconductor laser as claimed in claim 6, wherein the substrate (1) is GaN, the lower confinement layer (21) is N-type doped AlGaN, the lower waveguide layer (22) is N-type doped GaN, the upper waveguide layer (24) is GaN, the electron blocking layer (25) is P-type doped AlGaN, the first ridge (2a) is P-type doped AlGaN, the ohmic contact layer (27) is P-type doped GaN, the insulating layer (3) is silicon dioxide, and the active layer (23) is a quantum well comprising multiple periods of GaN barrier layers and InGaN well layers alternately grown.

8. A method for manufacturing a gallium nitride-based semiconductor laser is characterized by comprising the following steps:

providing a substrate (1);

growing an epitaxial structure (2) on top of the substrate (1), wherein the top of the epitaxial structure (2) is provided with a ridge-shaped semiconductor layer, the ridge-shaped semiconductor layer is provided with a first ridge-shaped part (2a) and an ohmic contact layer (27), and the ohmic contact layer (27) is arranged on the first ridge-shaped part (2 a);

forming an insulating layer (3) on the epitaxial structure, wherein the insulating layer (3) is provided with an opening (3a), and the width of the opening (3a) is smaller than that of the first ridge part (2 a);

forming a top electrode (4a) on the insulating layer (3), the top electrode (4a) being in contact with the ohmic contact layer (27) through the opening (3 a);

a bottom electrode (4b) is formed on the bottom of the substrate (1).

9. Method of manufacturing according to claim 8, wherein growing an epitaxial structure (2) on top of the substrate (1) comprises in particular:

sequentially growing and forming a lower limiting layer (21), a lower waveguide layer (22), an active layer (23), an upper waveguide layer (24), an electron blocking layer (25) and an upper limiting material layer (20) on the top of the substrate;

etching the upper limiting material layer (20) to form a ridge part layer (A);

and etching the ridge portion layer to form a ridge semiconductor layer, the ridge semiconductor layer having a first ridge portion (2a), a second ridge portion (2b) and an ohmic contact layer (27), the second ridge portion (2b) being provided on the first ridge portion (2a), the width of the second ridge portion (2b) being smaller than the width of the first ridge portion (2a), the ohmic contact layer (27) being provided on the second ridge portion (2 b).

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