A method of fabricating and structure of an electroabsorption modulated laser

Abstract

The application discloses a preparation method and structure of an electro-absorption modulated laser, and the method comprises the following steps: a substrate is symmetrically divided into a double-end modulation area, a gain area, a grating area and a phase area; a first mask pattern is made on the surface of the gain area; a selective epitaxy technology is used to grow an active layer containing a quantum well structure in the mask gap, so that the band gap of the gain area is red-shifted; then, a mask covering the gain area and the modulation area is made, and a non-functional area is etched to expose the substrate; a passive material with a wider band gap is grown on the exposed substrate area, so as to form a photon confinement structure; a sampling grating is made by electron beam direct writing, a cladding layer and a contact layer are grown, and an inverted mesa shallow ridge waveguide is etched; finally, an electrically isolated groove is etched, and double-sided electrodes are made to complete device integration. By using the selective epitaxy growth technology, the active materials with two kinds of band gap widths of the gain area and the modulation area are realized by one-time epitaxy growth, so that an extremely low-cost solution is provided for a wavelength tunable electro-absorption modulated laser.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor optoelectronic integrated devices, and in particular to a preparation method and structure of an electro-absorption modulated laser. BACKGROUND

[0002] With the rapid development of optical communication and artificial intelligence, semiconductor lasers and their integrated devices are expanding from communication core devices to photonic core devices for artificial intelligence, and performance breakthroughs will directly affect the competitiveness of the next generation of communication and intelligent systems. In order to improve transmission speed and make full use of optical network infrastructure to meet the needs of high precision and high reliability, the design and fabrication process of the laser need more precise control to ensure that the performance of the laser is maximally optimized.

[0003] In the prior art, a wide wavelength tuning range increases the flexibility and capacity of the system, which is very important for applications that require dynamic adjustment of wavelength resources. The integration of tunable lasers and electro-absorption modulation will solve the problems of modulation bandwidth and multi-wavelength utilization. However, most of the current wide wavelength lasers are integrated modulators through a material butt joint scheme, which requires two material growth processes and has too high manufacturing costs, which cannot meet the actual use requirements.

[0004] Therefore, the present application provides a preparation method and structure of an electro-absorption modulated laser, which uses a selective area epitaxial growth technique to realize active materials with two bandgap widths of gain and modulation regions through one epitaxial growth, greatly reducing the power consumption and manufacturing cost of the integrated chip, and providing a low-cost solution for wavelength tunable electro-absorption modulated lasers. SUMMARY

[0005] Therefore, the present application provides a preparation method and structure of an electro-absorption modulated laser, which uses a selective area epitaxial growth technique to realize active materials with two bandgap widths of gain and modulation regions through one epitaxial growth, greatly reducing the power consumption and manufacturing cost of the integrated chip, and providing a low-cost solution for wavelength tunable electro-absorption modulated lasers.

[0006] To achieve the above technical purpose, the present application adopts the following technical scheme:

[0007] In a first aspect, the present application provides a preparation method of an electro-absorption modulated laser, comprising:

[0008] The substrate is surface laid out, and the surface of the substrate is sequentially divided into a first modulation region, a first front grating region, a first gain region, a first phase region, a rear grating region, a second phase region, a second gain region, a second front grating region and a second modulation region along the length direction; wherein the first\second front grating region, the first\second gain region, the first\second modulation region and the first\second phase region are symmetrically arranged with the center longitudinal direction of the substrate as the axis.

[0009] A first mask pattern is formed on the first and second gain region surfaces of the substrate, and the first mask pattern is a two-bar pattern with a preset interval and width and the same length as the first and second gain regions;

[0010] The active layer is grown on the part of the substrate surface other than the first mask pattern, and the first mask pattern is removed by etching;

[0011] A second mask pattern is formed on the active layer surface and located in the first and second gain regions and the first and second modulation regions, and the active layer other than the second mask pattern is removed by etching;

[0012] The passive material is grown on the part of the substrate other than the first mask pattern by using the butt-joint growth technology to complete the growth of the back grating region, the first and second front grating regions, and the first and second phase regions;

[0013] The sampling grating is formed on the first front grating region, the back grating region, and the second front grating region by using the electron beam direct writing technology;

[0014] The cladding layer and the electrical contact layer are sequentially grown on the entire surface, and the inverted mesa ridge waveguide structure is formed on the cladding layer and the electrical contact layer;

[0015] The electrical isolation groove is etched on the electrical contact layer to achieve electrical isolation between the regions;

[0016] The P-face electrode is formed on the electrical contact layer of each region, and the N-face electrode is formed on the entire surface of the substrate bottom after the substrate is thinned, and the laser is completed.

[0017] Further, the substrate material is N-type indium phosphide.

[0018] Further, the second mask pattern is removed by using the ICP dry etching technology.

[0019] Further, the length of the first and second modulation regions is 150 microns, the length of the first and second gain regions is 300 microns, the length of the first and second phase regions is 100 microns, the length of the first and second front grating regions is 50 microns, and the length of the back grating region is 500 microns.

[0020] Further, the passive material is InGaAsP, and the photoluminescence wavelength is 1450 nm.

[0021] Further, the active layer is an InGaAlAs active layer, and the photoluminescence wavelength is 1545 nm; the active layer sequentially includes a lower confinement layer, a multiple quantum well layer, and an upper confinement layer from bottom to top.

[0022] Further, the multiple quantum well layer is formed by the growth of multiple quantum well layers and multiple barrier layers.

[0023] Further, the thickness of the substrate after thinning is 110 microns.

[0024] Further, the thickness of the cladding layer is 1.5 microns, the thickness of the electrical contact layer is 300 nm, and the width of the inverted mesa shallow ridge waveguide structure is 3 microns.

[0025] In another aspect, the present application also provides a structure of an electro-absorption modulated laser, which is prepared by the preparation method described above, and the laser comprises, from bottom to top, an N-face electrode, a substrate, an active layer, a cladding layer, an electrical contact layer, and a P-face electrode.

[0026] The laser is divided into, from one side and along the length direction, a first modulation region, a first front grating region, a first gain region, a first phase region, a rear grating region, a second phase region, a second gain region, a second front grating region, and a second modulation region.

[0027] The first / second front grating region, the first / second gain region, the first / second modulation region, and the first / second phase region are symmetrically arranged with the center of the substrate as the axis; the first front grating region, the rear grating region, and the second front grating region are provided with a sampling grating; the cladding layer and the electrical contact layer have an inverted mesa shallow ridge waveguide structure, and the electrical contact layer is etched with an electrical isolation groove to realize electrical isolation between the regions.

[0028] Compared with the prior art, the preparation method and structure of the electro-absorption modulated laser have the following advantages: the method of the present application first divides the surface of the substrate into a double-end symmetric modulation region, a grating region, a gain region, and a phase region along the length direction; a strip-shaped mask pattern is made on the surface of the gain region, a quantum well structure-containing active layer is grown in the gap between the mask by selective epitaxy technology, and the gain region is realized to have a red-shifted band gap; then, a secondary mask covering the gain region and the modulation region is made, and the non-functional region is etched to expose the substrate; a passive material with a wider band gap is grown on the exposed substrate region, and a photon confinement structure is formed; a sampling grating is made by electron beam direct writing, and a cladding layer and a contact layer are grown and etched to form an inverted mesa shallow ridge waveguide; finally, an electrical isolation groove is etched, and a double-sided electrode is made to complete the integration of the device.

[0029] The method realizes single epitaxial growth of the gain region and the modulation region by selective epitaxy technology, significantly reducing the manufacturing cost; the band gap of the passive layer and the gain region is designed to form a high-efficiency photon confinement, supporting a wide range of continuous wavelength tuning; through the symmetric functional region layout combined with the inverted ridge waveguide structure, the process is simplified while the photoelectric isolation performance and energy efficiency are improved. The present application realizes the growth of two kinds of active materials with different band gaps in the gain region and the modulation region by selective epitaxy growth technology, greatly reduces the manufacturing cost of the integrated chip, and provides a low-cost solution for the wavelength-tunable electro-absorption modulated laser. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The flow chart of the preparation method of the electro-absorption modulation laser provided by the present application;

[0031] Figure 2 The structure diagram of the substrate and the area division provided by the present application;

[0032] Figure 3 The structure top view of the first mask pattern of the selected area epitaxy for making the gain region on the substrate surface provided by the present application;

[0033] Figure 4 The structure diagram of the laser after the growth of the active layer is completed provided by the present application;

[0034] Figure 5 The structure diagram of the laser after the active layer outside the second mask pattern is removed provided by the present application;

[0035] Figure 6 The structure diagram after the grating region layer and the phase region material are obtained by the butt joint growth technology provided by the present application;

[0036] Figure 7 The structure diagram after the grating is made, the cladding layer is grown and the electrical contact layer is made provided by the present application;

[0037] Figure 8 The side view of the completed laser provided by the present application;

[0038] Figure 9 The cross-sectional view of the completed laser provided by the present application;

[0039] In the figure, 1 is the first modulation region, 2 is the first front grating region, 3 is the first gain region, 4 is the first phase region, 5 is the rear grating region, 6 is the second phase region, 7 is the second gain region, 8 is the second front grating region, 9 is the second modulation region, 11 is the substrate, 12 is the first mask pattern, 13 is the lower confining layer, 14 is the multi-quantum well layer, 15 is the upper confining layer, 16 is the second mask pattern, 17 is the passive layer, 18 is the grating, 19 is the cladding layer, 20 is the electrical contact layer, 21 is the electrical isolation groove, 22 is the P-face electrode, and 23 is the N-face electrode. DETAILED DESCRIPTION

[0040] The preferred embodiments of the present application will be described in detail below with reference to the accompanying drawings, which form a part of this application. The accompanying drawings, together with the description, illustrate the principles of the present application, and are not intended to limit the scope of the present application.

[0041] Example 1

[0042] Please refer to Figure 1 ,Figure 1 A flowchart of a preparation method of the electro-absorption modulated laser provided by the embodiment is shown, which comprises the following steps:

[0043] Step S101: surface layout is performed on the substrate, and the surface of the substrate is sequentially divided into a first modulation region, a first front grating region, a first gain region, a first phase region, a rear grating region, a second phase region, a second gain region, a second front grating region and a second modulation region along the length direction; wherein the first\second front grating region, the first\second gain region, the first\second modulation region and the first\second phase region are symmetrically arranged with the center longitudinal direction of the substrate as the axis;

[0044] Step S102: a first mask pattern is made on the surface of the first and second gain regions of the substrate, and the first mask pattern is two strip patterns with a preset interval and width and the same length as the first\second gain region;

[0045] Step S103: the active layer is grown on the part of the surface of the substrate except the first mask pattern, and then the first mask pattern is removed by etching;

[0046] Step S104: a second mask pattern is made on the surface of the active layer and located in the first and second gain regions and the first and second modulation regions, and the active layer except the second mask pattern is removed by etching;

[0047] Step S105: the passive material growth of the part of the substrate after the first mask pattern is removed is completed by using butt joint growth technology for the rear grating region, the first and second front grating regions and the first and second phase regions;

[0048] Step S106: a sampling grating is made in the first front grating region, the rear grating region and the second front grating region by electron beam direct writing technology;

[0049] Step S107: a cladding layer and an electrical contact layer are sequentially grown and made on the whole surface, and an inverted mesa ridge waveguide structure is made on the cladding layer and the electrical contact layer;

[0050] Step S108: an electrical isolation groove is etched on the electrical contact layer to realize electrical isolation between regions;

[0051] Step S109: a P-face electrode is made on the electrical contact layer of each region, and an N-face electrode is made on the whole surface of the bottom of the substrate after the substrate is thinned, and the laser is completed.

[0052] The laser fabrication method provided in this embodiment achieves simultaneous formation of the gain region and modulation region in a single epitaxial growth process by fabricating a mask pattern on the surface of the gain region and performing selected-area epitaxial growth. This avoids the complex process of requiring two epitaxial growth steps for the gain and modulation regions in traditional methods, reducing the usage time of fabrication equipment and the number of wafer turnarounds. By defining the growth position of the gain region through the initial mask, and utilizing the gaseous precursor concentration gradient at the edge of the SAG (Self-Advanced Gland Amplifier), a gradual change in the quantum well composition of the gain region is achieved, inducing a redshift of the bandgap. The redshifted gain region enhances carrier confinement capability, reduces threshold current, and simplifies bandgap engineering design. The passive layer bandgap is designed to be smaller than the gain region bandgap, forming a photonic barrier and reducing carrier leakage. The functional region is designed with a centrally symmetrical layout, combined with a shared reflector cavity in the rear grating region, achieving dual-end light output. Furthermore, symmetrical current injection counteracts thermal drift, improving the stability of wavelength tuning. This method significantly reduces the power consumption and manufacturing cost of integrated chips, providing a low-cost solution for wavelength-tunable electro-absorption modulated lasers.

[0053] The following is combined Figures 2-9 The above steps will be demonstrated and explained in detail.

[0054] As a specific embodiment, the steps of this manufacturing method include:

[0055] (1) Select an N-type indium phosphide substrate 11, such as Figure 2 As shown, the surface of substrate 11 is sequentially divided along its length into a first modulation region 1, a first front grating region 2, a first gain region 3, a first phase region 4, a rear grating region 5, a second phase region 6, a second gain region 7, a second front grating region 8, and a second modulation region 9. The first and second front grating regions, the first and second gain regions, the first and second modulation regions, and the first and second phase regions are arranged symmetrically about the longitudinal axis of the substrate center. The lengths of the first modulation region 1 and the second modulation region 9 are 150 micrometers, the length of the rear grating region 5 is 500 micrometers, the lengths of the first gain region 3 and the second gain region 7 are 300 micrometers, the lengths of the first phase region 4 and the second phase region 6 are 100 micrometers, and the lengths of the first front grating region 2 and the second front grating region 8 are 50 micrometers.

[0056] (2) Silicon dioxide of 150 nm is grown on the surface of substrate 11 using a PECVD device, and a first mask pattern 12 for selected area epitaxy of the first gain region 3 and the second gain region 7 is fabricated by photolithography and wet etching. The first mask pattern 12 for selected area epitaxy consists of two strip patterns with the same length as the first gain region 3 and the second gain region 7 (in practice, the length is set to 300 micrometers), a width of 12 micrometers, and a spacing of 20 micrometers, such as... Figure 3 As shown, Figure 3 This is a top view of the substrate surface.

[0057] (3) InGaAlAs active layer is grown on the surface of substrate 11 successively, the active layer includes lower confinement layer 13, multi-quantum well layer 14 and upper confinement layer 15; wherein the fluorescence wavelength of the active region is 1545nm, the thickness of lower confinement layer 13 is 100nm, multi-quantum well layer 14 is formed by 6 quantum well layers with a thickness of 5nm and 7 barrier layers with a thickness of 10nm grown alternately, the thickness of upper confinement layer 15 is 100nm, as shown in Figure 4 , Figure 4 is a side view of the laser.

[0058] (4) The first mask pattern 12 is etched away, 150nm of silicon dioxide is grown on the upper surface of upper confinement layer 15 again by PECVD equipment, and the second mask pattern 16 located in the first gain region 3, the second gain region 7 and the first modulation region 1, the second modulation region 9 is made by photoetch and wet etching, in practice, the width of the second mask pattern 16 is 20 microns, as shown in Figure 5 , Figure 5 shows a side view of the laser after the second mask pattern 16 is made.

[0059] (5) ICP dry etching technology is used to remove the active layer outside the second mask pattern 16, and the butt joint growth technology is used to obtain the passive layer 17 of the rear grating region 5, the first front grating region 2, the second front grating region 8 and the first phase region 4, the second phase region 6, the material of the passive layer 17 is InGaAsP, as shown in Figure 6 , the fluorescence wavelength of the passive layer is 1450nm.

[0060] (6) The silicon dioxide material of the second mask pattern 16 is etched away by hydrofluoric acid, and the sampling grating 18 is made by electron beam direct writing technology in the first front grating region 2, the rear grating region 5 and the second front grating region 8, as shown in Figure 7 .

[0061] (7) Cladding layer 19 with a thickness of 1.5 microns and electrical contact layer 20 with a thickness of 300nm are grown on the surface of the entire laser, and a 3-micron-wide inverted mesa ridge waveguide structure is made on the cladding layer 19 and the electrical contact layer 20, as shown in Figure 8 . An electrical isolation trench 21 is etched on the electrical contact layer 20, the depth of the electrical isolation trench 21 is 300nm, and the width is 50 microns, and the electrical isolation between the various regions of the laser is realized through the electrical isolation trench 21;

[0062] (8) P-face electrode 22 (including a 50nm-thick titanium thin layer and a 300nm-thick gold film) is made on the electrical contact layer 20 of the first modulation region 1, the second modulation region 9, the rear grating region 5, the first gain region 3, the second gain region 7, the first phase region 4, the second phase region 6, the first front grating region 2, and the second front grating region 8, the thickness of the substrate 11 is reduced to 110 microns, and then N-face electrode 23 (including a 50nm-thick titanium thin layer and a 300nm-thick gold film) is made on the bottom of the entire die, and the fabrication of the laser is completed. As shown in Figure 9 Figure 9 A cross-sectional view of the completed laser chip is shown.

[0063] The method of the embodiment has three core advantages: first, the selective epitaxy technology realizes single epitaxial homo growth of the gain region and the modulation region, significantly reduces the manufacturing cost, deposits the material between the masks, realizes PLmaping spectrum red shift, reduces the band gap of the laser, and moves the wavelength of the absorbed light to a longer direction; second, the band gap of the passive layer and the gain region is designed to form high-efficiency photon confinement, supporting wide-range continuous wavelength tuning; third, the symmetrical functional region layout combined with the inverted mesa waveguide structure simplifies the process while improving the photoelectric isolation performance and energy efficiency. The method provides a high-bandwidth, low-cost photonic integration solution for optical communication and artificial intelligence fields.

[0064] Embodiment 2

[0065] The embodiment of the application also provides a structure of an electroabsorption modulated laser, which is made by the preparation method of the electroabsorption modulated laser according to the embodiment 1, as shown in Figure 8 The laser includes, from bottom to top, N-face electrode 23, substrate 11, active layer (including lower confinement layer 13, multi-quantum well layer 14, and upper confinement layer 15), cladding layer 19, electrical contact layer 20, and P-face electrode 22.

[0066] The laser is divided into, from one side and along the length direction, first modulation region 1, first front grating region 2, first gain region 3, first phase region 4, rear grating region 5, second phase region 6, second gain region 7, second front grating region 8, and second modulation region 9.

[0067] The first / second front grating region, the first / second gain region, the first / second modulation region, and the first / second phase region are symmetrically arranged with the center of the substrate 11 as the axis; the first front grating region 2, the rear grating region 5, and the second front grating region 8 are provided with a sampling grating; the cladding layer 19 and the electrical contact layer 20 have an inverted mesa shallow ridge waveguide structure, and the electrical contact layer 20 is etched with an electrical isolation groove 21 to realize electrical isolation between the regions.

[0068] Figure 9 ​The cross-sectional view of the laser structure is shown. The wavelength tuning range of the laser is greater than 30 nm, and can be continuously tuned.

[0069] The laser structure provided by the embodiment can ensure that the performance of each functional area is independently optimized by dividing the laser area into multiple different functional areas along the length direction and longitudinally symmetrically arranging the two ends with the substrate as the center. Through the accurate design and optimization of the gain area, the modulation area and other areas, the optical performance and modulation efficiency of the laser can be greatly improved, and the requirements of high power, low noise and strong stability can be met. The sampling grating is made on the first front grating area, the rear grating area and the second front grating area, so that the optical feedback and mode control of the laser are more accurate. The design of the sampling grating can improve the wavelength selectivity and mode selectivity of the laser, ensure the stability of the optical performance, and thus improve the output quality of the laser. By etching the electrically isolated groove on the electrically contacted layer, the electrical isolation between the functional areas can be realized, and the current interference between the different functional areas is avoided. The design of the electrical isolation ensures the independent work of the different areas, improves the overall electrical efficiency and the reliability of the laser, and reduces the influence of the thermal effect on the performance. The inverted shallow ridge waveguide structure is arranged on the cladding layer and the electrically contacted layer, which helps to improve the light guiding efficiency of the laser. The structure optimizes the light propagation path, reduces the loss, improves the quality and propagation efficiency of the light beam, and further enhances the overall performance of the laser.

[0070] The above merely describes the preferred embodiments of the present application, but the protection scope of the present application is not limited to this. Any changes or replacements within the technical scope disclosed by the present application can be easily thought by those skilled in the art, and should be covered within the protection scope of the present application.

Claims

1. A method of fabricating an electroabsorption modulated laser, comprising: The application relates to a laser device and a preparation method thereof. The surface of a substrate is arranged, and the surface of the substrate is sequentially divided into a first modulation area, a first front grating area, a first gain area, a first phase area, a rear grating area, a second phase area, a second gain area, a second front grating area and a second modulation area along the length direction; wherein the first / second front grating area, the first / second gain area, the first / second modulation area and the first / second phase area are symmetrically arranged with the longitudinal center of the substrate as an axis. A first mask pattern is formed on the surfaces of the first and second gain areas of the substrate, the first mask pattern is two strip patterns with the same length as the length of the first / second gain area, and the first mask pattern has a preset interval and width; the length of the first / second modulation area is 150 microns, the length of the first / second gain area is 300 microns, the length of the first / second phase area is 100 microns, the length of the first / second front grating area is 50 microns, and the length of the rear grating area is 500 microns; the length of the first mask pattern selected by epitaxy is set as 300 microns, the width is 12 microns, and the interval is 20 microns; the active layer is grown on the part of the substrate surface except the first mask pattern, and then the first mask pattern is etched and removed. The active layer is an InGaAlAs active layer, and the optical fluorescence wavelength is 1545 nm; the active layer sequentially comprises a lower limiting layer, a multi-quantum well layer and an upper limiting layer from bottom to top. A second mask pattern is formed on the surfaces of the first and second gain areas and the first and second modulation areas of the active layer, and the active layer outside the second mask pattern is removed by etching technology; the etching technology adopts ICP dry etching technology. The passive material growth of the rear grating area, the first and second front grating areas, the first and second phase areas and the part of the substrate after the first mask pattern is removed is completed by butt joint growth technology; the passive material is InGaAsP, and the optical fluorescence wavelength is 1450 nm. A sampling grating is formed on the first front grating area, the rear grating area and the second front grating area by electron beam direct writing technology. A cladding layer and an electrical contact layer are sequentially grown and formed on the whole surface area, and an inverted mesa shallow ridge waveguide structure is formed on the cladding layer and the electrical contact layer. An electrical isolation groove is etched on the electrical contact layer to realize electrical isolation between the areas. A P-face electrode is formed on the electrical contact layer of each area, an N-face electrode is formed on the whole surface of the bottom of the substrate after the substrate is thinned, and the laser device is completed.

2. The method of claim 1, wherein the method further comprises: The substrate material is N-type indium phosphide.

3. The method of claim 1, wherein the step of forming the active region comprises the steps of: forming a first quantum well layer; forming a first barrier layer; forming a second quantum well layer; and forming a second barrier layer. The second mask pattern is removed by ICP dry etching technology.

4. The method of claim 1, wherein the step of forming the electroabsorption modulator is performed by the steps of: The multi-quantum well layer is formed by the growth of a plurality of quantum well layers and a plurality of barrier layers. ​ 5. The method of claim 1, wherein the step of forming the electroabsorption modulator is performed by the steps of: forming a first layer of InGaAs on a substrate; forming a second layer of AlAs on the first layer; and forming a third layer of InGaAs on the second layer. The thickness of the substrate after being thinned is 110 microns.

6. The method of claim 1, wherein the step of forming the electroabsorption modulator is performed by the steps of: The thickness of the cladding layer is 1.5 microns, the thickness of the electrical contact layer is 300 nm, and the width of the inverted mesa shallow ridge waveguide structure is 3 microns. ​ 7. A structure of an electroabsorption modulated laser, characterized by, The laser device is prepared by the preparation method in any one of claims 1-6, and the laser device sequentially comprises an N-face electrode, a substrate, an active layer, a cladding layer, an electrical contact layer and a P-face electrode from bottom to top. The laser is divided into a first modulation area, a first front grating area, a first gain area, a first phase area, a rear grating area, a second phase area, a second gain area, a second front grating area and a second modulation area in sequence along the length direction from one side; The first / second front grating area, the first / second gain area, the first / second modulation area and the first / second phase area are symmetrically arranged with the longitudinal center of the substrate as the axis; the first front grating area, the rear grating area and the second front grating area are provided with a sampling grating; the cladding layer and the electrical contact layer have an inverted mesa ridge waveguide structure, and the electrical contact layer is etched with an electrical isolation groove to realize electrical isolation between the areas.

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