A monolithic integrated laser chip and its preparation method and application

Abstract

The present invention relates to the field of laser chip technology, and more specifically to a monolithic integrated laser chip, its preparation method, and application. The method comprises the following steps: growing a buffer layer material on a substrate, growing corresponding active materials on the laser region, amplifier region, and modulator region, respectively, covering with a second dielectric mask, covering the surface of the second rectangular dielectric mask and the buffer material with silicon dioxide material, photolithographically forming a photoresist mask pattern, etching with hydrofluoric acid to form a silicon dioxide mask pattern, growing a passive waveguide material, covering the active material in the laser region with a grating structure, growing a cladding material and a contact layer material, the photoresist mask pattern being symmetrically arranged on both sides of the central axis of the laser region, amplifier region, and modulator region, the silicon dioxide mask pattern having a width of Wa in the laser region and amplifier region and a width of Wm in the modulator region, where Wm>Wa. The present invention reduces light transmission loss between different regions and reduces the far-field divergence angle of the device.

Description

Technical Field

[0001] The present invention relates to the technical field of laser chips, and in particular to a monolithic integrated laser chip and a preparation method and application thereof. Background Art

[0002] Electroabsorption modulated distributed feedback semiconductor lasers (EMLs) are the most promising optical signal sources for wavelength division multiplexing networks. This is primarily due to their numerous unique advantages, including: small size, ease of mass production, and therefore relatively low cost; low operating voltage and power consumption; high optical coupling efficiency and low insertion loss; no need to consider polarization issues; stable and reliable structure; and, most importantly, ease of monolithic integration with other semiconductor optoelectronic devices, resulting in strong functional scalability. Consequently, EMLs have been a research hotspot for major optoelectronic device companies and research institutions both domestically and internationally for many years.

[0003] The thickness of the quantum well material in the modulator region of the EMLs chip is generally greater than that in the laser region. This, on the one hand, increases the optical transmission loss from the laser to the modulator, and on the other hand, also leads to a large far-field divergence angle at the modulator end, reducing its coupling efficiency with the optical fiber. Summary of the Invention

[0004] The purpose of the present invention is to propose a monolithic integrated laser chip, its preparation method and application. This method realizes that the thickness of the passive waveguide core material in the isolation area of ​​the EML chip gradually changes between the modulator and the laser and amplifier, which is beneficial to reducing the transmission loss of light between different areas.

[0005] To this end, the present invention provides the following technical solutions:

[0006] In a first aspect, the present invention provides, in an optional embodiment, a method for preparing a monolithically integrated laser chip, comprising the following steps:

[0007] S1: growing a buffer layer material on a substrate, growing active materials for forming a laser and an amplifier on top of the buffer layer material, setting a laser region and an amplifier region on the active material, covering the active materials in the laser region and the amplifier region with a first rectangular dielectric mask, then selectively removing the active materials outside the laser region and the amplifier region, then butt-growing a modulator active material in the region outside the laser region and the amplifier region, and finally removing the first rectangular dielectric mask;

[0008] S2: providing a modulator region on the modulator active material, then covering the laser region, the amplifier region, and the modulator region with a second rectangular dielectric mask, selectively removing the modulator active material outside the laser region, the amplifier region, and the modulator region, and then covering the surface of the second rectangular dielectric mask and the buffer material with a silicon dioxide material, photolithographically forming a photoresist mask pattern, and etching the silicon dioxide material outside the photoresist mask pattern with hydrofluoric acid to form a silicon dioxide mask pattern;

[0009] S3: After the passive waveguide material is butt-grown in the areas outside the laser, amplifier, and modulator regions, the second dielectric mask is removed, and the grating structure is covered on the active material in the laser region. Finally, the cladding material and the contact layer material are grown in sequence.

[0010] In step S2, the photoresist mask pattern is symmetrically arranged on both sides of the central axis of the laser area, the amplifier area and the modulator area, and the width of the silicon dioxide mask pattern in the laser area and the amplifier area is Wa, and the width in the modulator area is Wm, Wm>Wa.

[0011] In this invention, selective area epitaxy (SAGE) is used to achieve a gradual thickness change in the passive waveguide core material within the isolation region of the EML chip, between the modulator and the laser and amplifier. This helps reduce light transmission losses between these regions. Furthermore, SAGE also creates an output waveguide region with a gradually decreasing thickness of the passive waveguide material, which helps reduce the far-field divergence angle of the device.

[0012] Preferably, there is an isolation region between the modulator region and the laser region. In step S2, the width of the silicon dioxide mask pattern in the isolation region from the modulator region to the laser region gradually changes from Wm to Wa, and the gradual change is linear or nonlinear.

[0013] Preferably, there is a second isolation region between the modulator region and the amplifier region. In step S2, the width of the silicon dioxide mask pattern in the second isolation region from the modulator region to the amplifier region gradually changes from Wm to Wa, and the gradual change is linear or nonlinear.

[0014] Preferably, there is an output waveguide region on the side of the amplifier region away from the modulator region. In step S2, the width of the silicon dioxide mask pattern in the output waveguide region gradually changes from Wa to 0, and the gradual change is linear or nonlinear.

[0015] Preferably, the height of the active material in the laser region and the amplifier region is Ta, the height of the active material in the modulator region is Tm, and Tm>Ta.

[0016] Preferably, in the first isolation region, the thickness of the passive waveguide material increases from the edge of the laser region to the edge of the modulator region. In the second isolation region, the thickness of the passive waveguide material decreases from the edge of the modulator region to the edge of the amplifier region. In the output waveguide region, the thickness of the passive waveguide material decreases from the edge of the amplifier region to the light-emitting end face.

[0017] In a second aspect, the present invention provides a monolithic integrated laser chip in an optional embodiment, characterized in that it is prepared using the above-mentioned preparation method.

[0018] In a third aspect, the present invention provides an electro-absorption modulated distributed feedback semiconductor laser in an optional embodiment, characterized in that it includes the above-mentioned monolithic integrated laser chip.

[0019] Compared with the prior art, the present invention has one of the following beneficial effects:

[0020] This invention utilizes selective area epitaxy (SAGE) technology to achieve a gradual thickness change in the passive waveguide core material within the isolation region of the EML chip, between the modulator and the laser and amplifier. This helps reduce light transmission losses between these regions. Furthermore, SAGE also creates an output waveguide region where the passive waveguide material thickness gradually decreases, helping to reduce the far-field divergence angle of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The advantages of the above and / or additional aspects of the present application will become apparent and readily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0022] Figure 1 1 is a top view of a mask pattern during the manufacturing process of a monolithically integrated laser chip according to embodiment 1 of the present invention;

[0023] Figure 2 1 is a cross-sectional view of the structure of the chip at each stage in the manufacturing process of the monolithic integrated laser chip according to Example 1 of the present invention;

[0024] Among them, 10-substrate, 20-buffer layer material, 30-laser and amplifier active material, 31-first rectangular dielectric mask, 32-second rectangular dielectric mask, 33-silicon dioxide material layer, 34-silicon dioxide mask pattern, 35-grating structure, 40-modulator active material, 50-passive waveguide material, 60-cladding material, 70-contact layer material. DETAILED DESCRIPTION

[0025] In order to more clearly understand the above-mentioned objectives, features and advantages of the present application, the present application is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present application and the features therein can be combined with each other in the absence of conflict.

[0026] In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present application is not limited to the specific embodiments disclosed below.

[0027] The technical solution of the present invention will be described in detail below with reference to the embodiments and drawings.

[0028] Example 1

[0029] Please refer to the attached Figure 1-2 Taking an InP-based material system as an example, this embodiment provides a method for preparing a monolithic integrated laser chip, comprising the following steps:

[0030] Step 1: Grow an n-type InP buffer layer material 20 on an n-type InP substrate 10, and grow an active material 30 for forming a laser (LD) and an amplifier (SOA) on top of the n-type InP buffer layer material 20, which is an InGaAsP or InGaAlAs multi-quantum well material with a thickness of Ta.

[0031] Step 2: Set the laser region and amplifier region on the active material 30 of the laser and amplifier, and cover the active material of the laser region and amplifier region with a first rectangular dielectric mask 31 of silicon nitride (SiN) (see Figure 1 a), after selectively removing the laser and amplifier active materials 30 outside the LD region and SOA region (see Figure 2 a), then grow the modulator active material 40 in the area outside the laser area and the amplifier area, which is InGaAsP or InGaAlAs multi-quantum well material with a thickness of Tm, Tm>Ta( Figure 2 b) Finally, remove the first rectangular dielectric mask 31.

[0032] Step 3: A modulator region (EAM) is provided on the modulator active material 40, and then a SiN second rectangular dielectric mask 32 is covered on the laser region, amplifier region and modulator region (see FIG. Figure 1 b), then selectively remove the modulator active material 40 outside the laser region, amplifier region and modulator region (see Figure 2 c).

[0033] Step 4: Then deposit silicon dioxide (SiO2) material 33 to cover the surface of the second rectangular dielectric mask and the buffer material (see Figure 1 c) Photolithography forms a photoresist mask pattern, and HF is used to etch the silicon dioxide material in the area outside the photoresist mask pattern to form a silicon dioxide mask pattern 34 (see Figure 1d). When fabricating the silica mask pattern 34, first form a photoresist pattern by lithography, and then etch the silica material outside the photoresist using HF. During this process, the silica material above the second rectangular dielectric mask 32 is also etched away. The second rectangular dielectric mask 32 is made of silicon nitride material with a relatively slow etching rate. After obtaining the silica mask pattern 34 by etching, the second rectangular dielectric mask 32 remains. As Figure 1 shown in d, the silica mask pattern 34 includes two parts, symmetrically distributed on both sides of the central axis of the quantum wells in the laser region, amplifier region, and modulator region. Its width in the LD region and SOA region is Wa, and its width in the EAM region is Wm, where Wa < Wm. Moreover, the mask width of the silica mask pattern 34 increases from Wa to Wm in the isolation area 1 (S1), decreases from Wm to Wa in the isolation area 2 (S2), and decreases from Wm to 0 in the output waveguide region (WG). The gradual change in the mask width can be a linear gradient or a non-linear gradient.

[0034] Step 5: Use the new metalorganic chemical vapor deposition (MOCVD) technology to grow the InGaAsP passive waveguide material 50 by butt-joint growth in the regions outside the laser region, amplifier region, and modulator region (see Figure 2 d), and then remove the second dielectric mask 32. During the butt-joint growth process, the material only grows in the regions outside the second rectangular dielectric mask 32 and the silica mask pattern 34, which is the so-called selective area epitaxial growth. The presence of the silica mask pattern 34 makes the growth rate of the material in its middle region greater than that in the region without the pattern, and the greater the mask width and the smaller the spacing, the greater the growth rate. Therefore, after the butt-joint growth is completed, the thickness of the passive waveguide material in the S1 region increases from the laser end to the modulator end, the passive waveguide material in the S2 region decreases from the modulator end to the amplifier end, and the thickness of the passive waveguide material in the WG region decreases from the amplifier end to the light-emitting end face. In the S1 and S2 regions, the gradual change in the waveguide material thickness reduces the optical transmission loss from the laser to the modulator and from the modulator to the amplifier. In the WG region, the reduction in the waveguide thickness is beneficial to increasing the far-field divergence angle of the light-emitting end face of the device, thereby improving the coupling efficiency between the device and the optical fiber.

[0035] Step 6: After fabricating the grating structure 35 on the active material in the LD region, sequentially grow the InP cladding material 60 and the InGaAs contact layer material 70 (see Figure 2 e).

[0036] In addition, the inventors noticed that the edge slope of the transition part between the S1 region and the S2 region will affect the performance of the laser. The optimal slope is between 4 - 25 degrees. Too large or too small will affect the coupling efficiency.

[0037] Although the present application is disclosed in detail with reference to the accompanying drawings, it should be understood that these descriptions are merely exemplary and are not intended to limit the application of the present application. The scope of protection of the present application is defined by the appended claims and may include various modifications, alterations and equivalents made to the invention without departing from the scope and spirit of the present application.

Claims

1. A method for preparing a monolithic integrated laser chip, characterized in that: The following steps are involved: S1: growing a buffer layer material on a substrate, growing active materials for forming a laser and an amplifier on top of the buffer layer material, setting a laser region and an amplifier region on the active material, covering the active materials in the laser region and the amplifier region with a first rectangular dielectric mask, then selectively removing the active materials outside the laser region and the amplifier region, then butt-growing a modulator active material in the region outside the laser region and the amplifier region, and finally removing the first rectangular dielectric mask; S2: providing a modulator region on the modulator active material, then covering the laser region, the amplifier region, and the modulator region with a second rectangular dielectric mask, selectively removing the modulator active material outside the laser region, the amplifier region, and the modulator region, and then covering the surface of the second rectangular dielectric mask and the buffer material with a silicon dioxide material, photolithographically forming a photoresist mask pattern, and etching the silicon dioxide material outside the photoresist mask pattern with hydrofluoric acid to form a silicon dioxide mask pattern; S3: After the passive waveguide material is butt-grown in the areas outside the laser, amplifier, and modulator regions, the second dielectric mask is removed, and the grating structure is covered on the active material in the laser region. Finally, the cladding material and the contact layer material are grown in sequence. In step S2, the photoresist mask pattern is symmetrically arranged on both sides of the central axis of the laser area, the amplifier area and the modulator area, and the width of the silicon dioxide mask pattern in the laser area and the amplifier area is Wa, and the width in the modulator area is Wm, Wm>Wa.

2. The method for preparing a monolithically integrated laser chip according to claim 1, wherein: There is an isolation region between the modulator region and the laser region. In step S2, the width of the silicon dioxide mask pattern in the isolation region from the modulator region to the laser region is gradually changed from Wm to Wa, and the gradual change is linear or nonlinear.

3. The method for preparing a monolithically integrated laser chip according to claim 1, wherein: There is a second isolation region between the modulator region and the amplifier region. In step S2, the width of the second isolation region of the silicon dioxide mask pattern in the direction from the modulator region to the amplifier region is gradually changed from Wm to Wa, and the gradual change is linear or nonlinear.

4. The method for preparing a monolithically integrated laser chip according to claim 1, wherein: There is also an output waveguide region on the side of the amplifier region away from the modulator region. In step S2, the width of the silicon dioxide mask pattern in the output waveguide region gradually changes from Wa to 0, and the gradual change is linear or nonlinear.

5. The method for preparing a monolithically integrated laser chip according to claim 1, wherein: The height of the active material in the laser region and the amplifier region is Ta, and the height of the active material in the modulator region is Tm, where Tm>Ta.

6. The method for preparing a monolithically integrated laser chip according to claim 2, wherein: In the isolation region, the thickness of the passive waveguide material increases from the edge of the laser region to the edge of the modulator region.

7. The method for preparing a monolithically integrated laser chip according to claim 3, wherein: In the second isolation region, the thickness of the passive waveguide material decreases from the edge of the modulator region to the edge of the amplifier region.

8. The method for preparing a monolithically integrated laser chip according to claim 4, wherein: In the output waveguide region, the thickness of the passive waveguide material decreases from the edge of the amplifier region to the light-emitting end face.

9. A monolithic integrated laser chip, characterized in that: The preparation method is described in any one of claims 1 to 8.

10. An electro-absorption modulated distributed feedback semiconductor laser, characterized in that: Comprising the monolithic integrated laser chip according to claim 9.

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