An electro-absorption modulator with a germanium modulation layer and a method for forming the same

Abstract

The present invention relates to the field of semiconductor technology, and particularly to an electro-absorption modulator with a germanium modulation layer and a forming method thereof; the modulator includes: a substrate layer, a doped layer formed on the top of the substrate layer, a buffer layer connected to the center of the top of the doped layer, a modulation layer formed on the top of the buffer layer, and a top dielectric layer formed on the top free region and the inner side surface of the doped layer, the side surface of the buffer layer, the top and side surfaces of the modulation layer; by adding a buffer layer, the strain of the modulation layer is reduced, so that the working wavelength of the modulator is in the range of 1540 nm to 1560 nm, and the defect that the working wavelength of a pure germanium electro-absorption modulator in the prior art cannot match the C band is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor packaging materials, and particularly to an electro-absorption modulator with a germanium modulation layer and a forming method thereof. Background Art

[0002] Silicon photonics provides low-cost, low-power, and high-bandwidth optoelectronic solutions, which is very important for realizing the integration of high-speed low-power optical modulators and silicon-based optical circuits. In order to achieve a low-power and high-density interconnection system, the optical modulator requires a very small capacitance. Since the capacitance of the electro-absorption modulator (EAM) is much smaller than that of the silicon-based MZI-type modulator, it is very promising. Currently, pure germanium electro-absorption modulators are all epitaxially grown Ge directly on a silicon substrate, which has a tensile strain as high as 0.2%. The bandgap energy of germanium will be reduced from 0.80 eV (1550 nm) without strain to 0.77 eV (1610 nm) with tensile strain. Therefore, most pure germanium electro-absorption modulators operate at the O band. In order to make them operate at the C band, a new structure and process flow need to be proposed to optimize the operating wavelength and move the operating wavelength of the pure germanium electro-absorption modulator to the C band. Summary of the Invention

[0003] In view of the above analysis, the present invention aims to provide an electro-absorption modulator with a germanium modulation layer and a forming method thereof, so as to solve at least one of the problems of small modulation speed and modulation bandwidth, large insertion loss, and inability to match the C band of the operating wavelength in the prior art problems of pure germanium electro-absorption modulators.

[0004] The present invention provides an electro-absorption modulator with a germanium modulation layer, including:

[0005] A substrate layer, including a back substrate and a bottom oxide dielectric layer disposed on the silicon substrate;

[0006] A doping layer, formed on the top of the bottom oxide dielectric layer, including: a heavily hole-doped layer, a lightly hole-doped layer, a lightly electron-doped layer, a heavily electron-doped layer; the lightly hole-doped layer and the lightly electron-doped layer protrude and are connected in the middle region on the top of the bottom oxide dielectric layer to form a PN junction, and serve as a bottom waveguide layer; the heavily hole-doped layer and the heavily electron-doped layer are respectively disposed at both ends on the top of the bottom oxide dielectric layer, the heavily hole-doped layer is connected to the lightly hole-doped layer, and the lightly electron-doped layer is connected to the heavily electron-doped layer;

[0007] A buffer layer, formed on the top of the PN junction;

[0008] A modulation layer, formed on the top of the buffer layer; including: a germanium hole-doped layer, a germanium waveguide layer, a germanium electron-doped layer; wherein, the germanium hole-doped layer and the germanium electron-doped layer are respectively disposed at both ends on the top of the buffer layer and are connected by the germanium waveguide layer;

[0009] The top oxidation dielectric layer is formed on the top free region and the inner side of the doped layer, the side of the buffer layer, the top and the side of the modulation layer.

[0010] Preferably, the buffer layer comprises a single layer or multiple layers.

[0011] Preferably, the single-layer buffer layer is composed of a two-component compound, and the multi-layer buffer layer is composed of two-component compounds with different component contents.

[0012] Preferably, in the multi-layer buffer layer, the two-component ratio of the two-component compounds in each layer changes according to a positive gradient or a negative gradient; among them, the general formula of the two-component compound satisfies: A 1-x B x , where A and B represent the constituent elements of the two-component compound; x ≤ 1 represents the number of atoms of element B in the two-component compound.

[0013] Preferably, the general formula of the two-component compound satisfies: The multi-layer buffer layer is sequentially labeled as: the first buffer layer,..., the Nth buffer layer according to the forming order from bottom to top; among them, the general formula of the two-component compound of the Nth buffer layer is A (1-x) N B x N , the general formula of the two-component compound of the N-1th buffer layer is A (1-x) N-1 B x N-1 , x N-1 < x N or x N-1 > x N ; where A and B represent the constituent elements of the two-component compound, x N represents the number of atoms of element B in the two-component compound of the Nth buffer layer, ( 1-x ) N represents the number of atoms of element A in the two-component compound of the Nth buffer layer.

[0014] Preferably, the doping concentrations of the germanium hole-doped layer and the germanium electron-doped layer are 1×10 18 cm 3 ~5×10 18 cm 3 .

[0015] Preferably, the width of the germanium waveguide layer is 100 nm to 400 nm, and the height is 200 nm to 500 nm.

[0016] Preferably, the operating wavelength is in the range of 1540 nm to 1560 nm.

[0017] Preferably, the buffer layer includes any one of a Group III-V semiconductor compound, a Group IV semiconductor compound, and a Group IV-V semiconductor compound.

[0018] A method for forming an electro-absorption modulator with a germanium modulation layer includes:

[0019] Step 1: Prepare a doped layer with different doping concentrations on a substrate layer;

[0020] Step 2: Etch the hole weakly doped layer and the electron weakly doped layer in the middle region of the doped layer, and prepare a bottom waveguide layer in the connection region between the two;

[0021] Step 3: Form a buffer layer on the top of the bottom waveguide layer;

[0022] Step 4: Form an original modulation layer on the top of the buffer layer;

[0023] Step 5: Form a germanium hole doped layer, a germanium waveguide layer, and a germanium electron doped layer with different doping concentrations on the original modulation layer.

[0024] Compared with the prior art, the present invention can at least achieve one of the following beneficial effects:

[0025] (1) By adding a buffer layer, the present invention reduces the strain of the modulation layer, making the working wavelength of the modulator vary from 1540 nm to 1560 nm, the modulation speed vary from 40 Gbps to 56 Gbps, the modulation bandwidth vary from 55 GHz to 67 GHz, and the insertion loss vary from 4.0 dB to 7.9 dB; it improves the defect that the working wavelength of the pure germanium electro-absorption modulator in the prior art cannot match the C band.

[0026] (2) By setting the buffer layer in a reverse gradient, for example, marking the multi-layer buffer layer in the order of formation from bottom to top as: the first buffer layer,..., the Nth buffer layer; the general formula of the two-component compound of the Nth buffer layer satisfies: A( 1-x ) N B x N , the general formula of the two-component compound of the N-1th buffer layer satisfies: A( 1-x ) N-1 B x N-1 , and x N-1 < x N ; where A and B represent the constituent elements of the two-component compound, A is silicon or an element close to silicon in the periodic table, B is germanium or an element close to germanium in the periodic table; x N represents the number of atoms of element B in the two-component compound of the Nth buffer layer; ( 1-x )N , representing the number of atoms of component A of the two-component compound of the Nth buffer layer; with the above settings, the present invention can obtain a larger working wavelength, modulation speed, and modulation bandwidth, and a smaller insertion loss.

[0027] (3) By providing a hole weakly doped layer and an electron weakly doped layer in the bottom waveguide layer of the doped layer, the present invention improves the modulation speed, modulation bandwidth, and reduces the insertion loss, thereby improving the control sensitivity.

[0028] In the present invention, the above technical solutions can also be combined with each other to achieve more preferred combination schemes. Other features and advantages of the present invention will be described in the subsequent specification, and some advantages can be made obvious from the specification, or understood by implementing the present invention. The objectives and other advantages of the present invention can be realized and obtained from the content specifically pointed out in the embodiments of the specification and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings are only for the purpose of showing specific embodiments, and are not considered as limiting the present invention. Throughout the drawings, the same reference signs represent the same components.

[0030] Figure 1 Schematic diagram of preparing a doped layer with different doping concentrations on a substrate layer in an embodiment of the present invention;

[0031] Figure 2 Schematic diagram of etching to prepare a bottom waveguide layer in an embodiment of the present invention;

[0032] Figure 3 Schematic diagram of forming a buffer layer on the top of the bottom waveguide layer in an embodiment of the present invention;

[0033] Figure 4 Schematic diagram of forming an original modulation layer on the top of the buffer layer in an embodiment of the present invention;

[0034] Figure 5 Schematic diagram of forming a germanium hole doped layer, a germanium waveguide layer, and a germanium electron doped layer with different doping concentrations on the original modulation layer in an embodiment of the present invention;

[0035] Figure 6 Schematic diagram of growing electrodes on the electron strongly doped layer and the hole strongly doped layer in an embodiment of the present invention;

[0036] Figure 7 Schematic diagram of the finished electro-absorption modulator of Comparative Example 9 of the present invention.

[0037] REFERENCE SIGNS

[0038] Substrate layer 1; Doped layer 2; Buffer layer 3; Modulation layer 4; Top oxide dielectric layer 5; Original modulation layer 6; Electrode 7; Substrate 101; Bottom oxide dielectric layer 102; Hole strongly doped layer 201; Electron strongly doped layer 202; Hole weakly doped layer 203; Electron weakly doped layer 204; Germanium hole doped layer 401; Germanium waveguide layer 402; Germanium electron doped layer 403. Detailed implementation

[0039] The following will specifically describe the preferred embodiments of the present invention in conjunction with the accompanying drawings. The accompanying drawings form a part of the present invention and are used together with the embodiments of the present invention to explain the principles of the present invention, rather than to limit the scope of the present invention.

[0040] In order to better illustrate the technical solutions of the present invention, the following terms are explained:

[0041] SOI refers to placing a thin layer of silicon on an insulating substrate, and transistors will be fabricated on the thin layer of silicon called SOI. Devices with an SOI structure can reduce junction capacitance and leakage current compared to ordinary wafer structures, improve switching speed, reduce power consumption, and achieve high-speed and low-power operation, especially suitable for sub-micron and nanoscale chip structures.

[0042] Parasitic capacitance: It refers to the capacitance characteristics exhibited by inductors, resistors, chip pins, etc. at high frequencies. It is not very obvious at low frequencies, but at high frequencies, the equivalent value will increase; whether it is a resistor, an inductor, or an IC chip, we need to consider their equivalent capacitance values at high frequencies.

[0043] Chemical mechanical polishing (CMP): Under a certain pressure and in the presence of a polishing solution, the wafer to be polished makes relative movement with respect to the polishing pad. By means of the highly organic combination between the mechanical grinding action of nano-abrasives and the chemical action of various chemical reagents, the surface of the wafer to be polished can meet the requirements of high flatness, low surface roughness, and low defects.

[0044] The present invention discloses an electro-absorption modulator with a germanium modulation layer, including:

[0045] Substrate layer 1, including a back substrate 101 and a bottom oxide dielectric 102 disposed on the back substrate 101;

[0046] The doping layer 2 is formed on the top of the bottom oxide dielectric layer 102 and includes: a heavily hole-doped layer 201, a lightly hole-doped layer 203, a lightly electron-doped layer 204, and a heavily electron-doped layer 202; the lightly hole-doped layer 203 and the lightly electron-doped layer 204 protrude and are connected in the middle region on the top of the bottom oxide dielectric layer 102 to form a PN junction, which serves as the bottom waveguide layer; the heavily hole-doped layer 201 and the heavily electron-doped layer 202 are respectively disposed at both ends on the top of the bottom oxide dielectric layer 102, the heavily hole-doped layer 201 is connected to the lightly hole-doped layer 203, and the lightly electron-doped layer 204 is connected to the heavily electron-doped layer 202;

[0047] The buffer layer 3 is formed on the top of the PN junction;

[0048] The modulation layer 4 is formed on the top of the buffer layer 3 and includes: a germanium hole-doped layer 401, a germanium waveguide layer 402, and a germanium electron-doped layer 403; wherein, the germanium hole-doped layer 401 and the germanium electron-doped layer 403 are respectively disposed at both ends on the top of the buffer layer 3 and are connected by the germanium waveguide layer 402;

[0049] The top oxide dielectric layer 5 is formed on the top free region and the inner side of the doping layer 2, the side of the buffer layer 3, the top and the side of the modulation layer 4.

[0050] Regarding the modulation principle of the electro-absorption modulator, it should be noted that: a light beam with a specific wavelength is transmitted to the silicon waveguide through an external grating coupler, and the bottom waveguide layer and the germanium waveguide are in an up-and-down structure. Through evanescent coupling, the light in the silicon waveguide can be coupled to the germanium waveguide, and then modulated in the germanium waveguide; after modulation, it enters the modulation region composed of the modulation layer and the bottom waveguide layer and oscillates and propagates between the modulation layer and the bottom waveguide layer.

[0051] Specifically, the wavelength that the modulator can modulate is related to the material, size, and structure of the modulation layer. For example, for a pure germanium electro-absorption modulator, Ge is directly epitaxially grown on a silicon substrate as the back substrate, and it has a tensile strain as high as 0.2%. Due to the existence of this strain, the bandgap energy of germanium will decrease from 0.80 eV at 1550 nm without strain to 0.77 eV at 1010 nm with tensile strain.

[0052] Specifically, the modulation of the modulation layer includes: when a reverse modulation electrical signal is applied to the heavily hole-doped layer and the heavily electron-doped layer, the light absorption coefficient of the modulation layer for the light beam changes with the change of the modulation electrical signal, and the optical power of the light beam after passing through the modulation region also changes accordingly, thereby realizing the electro-optic modulation of the light beam.

[0053] Specifically, a buried oxide layer (bottom oxide dielectric layer) is introduced between the back substrate and the doped layer. That is, the back substrate and the buried oxide layer form the SOI process substrate layer, which has the following advantages: it can achieve dielectric isolation of components in the integrated circuit and completely eliminate the parasitic latch-up effect in CMOS circuits; the integrated circuit made of this material also has the advantages of small parasitic capacitance, high integration density, high speed, simple process, and small short-channel effect.

[0054] Specifically, the back substrate is selected as silicon, and the bottom oxide dielectric layer is silicon dioxide.

[0055] Specifically, the doped layer is silicon.

[0056] Selecting silicon for the doped layer can be compatible with the SOI process, facilitating the selection of SOI wafers from the market and expanding the scope of application.

[0057] Specifically, the doping concentration of the hole strongly doped layer and the electron strongly doped layer is 1×10 19 cm 3 ~3×10 19 cm 3 。

[0058] Specifically, the doping of the hole strongly doped layer and the electron strongly doped layer can achieve ohmic contact between the strongly doped layer and the external electrode, reduce energy consumption, and improve the sensitivity of external voltage control; if the doping concentration of the hole strongly doped layer and the electron strongly doped layer is too large, it will diffuse, and then two overlapping regions will be generated with the lightly doped region, increasing the absorption loss.

[0059] Specifically, the doping concentration of the hole strongly doped layer and the electron strongly doped layer can be: 1×10 19 cm 3 、1.2×10 19 cm 3 、1.4×10 19 cm 3 、1.5×10 19 cm 3 、1.6×10 19 cm 3 、1.8×10 19 cm 3 、2.0×10 19 cm 3 、2.2×10 19 cm 3 、2.4×10 19 cm 3 、2.5×10 19 cm 3 、2.6×10 19 cm 3 、2.8×10 19 cm3 , 2.9×10 19 cm 3 , 3×10 19 cm 3 .

[0060] Specifically, the doping concentrations of the electron weakly doped layer and the hole weakly doped layer are 4×10 18 cm 3 ~6×10 18 cm 3 .

[0061] The advantages of doping the hole weakly doped layer and the electron weakly doped layer are as follows: increasing the number of carriers and improving the modulation rate; forming an electric field under the action of an applied bias voltage; if the doping concentrations of the electron weakly doped layer and the hole weakly doped layer exceed the specified range, excessive doping concentration will cause diffusion, and then two overlapping regions will be generated with the heavily doped region, increasing the absorption loss.

[0062] Specifically, the doping concentrations of the electron weakly doped layer and the hole weakly doped layer can be: 4×10 18 cm 3 , 4.2×10 18 cm 3 , 4.4×10 18 cm 3 , 4.5×10 18 cm 3 , 4.6×10 18 cm 3 , 4.8×10 18 cm 3 , 5.0×10 18 cm 3 , 5.2×10 18 cm 3 , 5.4×10 18 cm 3 , 5.5×10 18 cm 3 , 5.6×10 18 cm 3 , 5.8×10 18 cm 3 , 5.9×10 18 cm 3 , 6×10 18 cm 3 .

[0063] Specifically, the cross-sectional size of the modulation layer is 200 nm to 500 nm × 200 nm to 500 nm.

[0064] Preferably, the sizes of the germanium hole-doped layer and the germanium electron-doped layer are the same, symmetrically arranged with respect to the germanium waveguide layer, and have the same height as the germanium waveguide layer.

[0065] Preferably, the doping concentrations of the germanium hole doping layer and the germanium electron doping layer are 1×10 18 cm 3 ~5×10 18 cm 3 。

[0066] Specifically, the doping concentrations of the germanium hole doping layer and the germanium electron doping layer can be: 1×10 18 cm 3 、1.2×10 18 cm 3 、1.5×10 18 cm 3 、1.8×10 18 cm 3 、2.2×10 18 cm 3 、2.5×10 18 cm 3 、2.8×10 18 cm 3 、3.0×10 18 cm 3 、3.2×10 18 cm 3 、3.3×10 18 cm 3 、3.5×10 18 cm 3 、3.8×10 18 cm 3 、4.0×10 18 cm 3 、4.2×10 18 cm 3 、4.4×10 18 cm 3 、4.6×10 18 cm 3 、4.8×10 18 cm 3 、5.0×10 18 cm 3 。

[0067] Doping the germanium hole-doped layer and the germanium electron-doped layer enables the two doped layers to form a PIN junction with the germanium waveguide layer. The specific functions are as follows: There is a built-in electric field caused by the PIN junction within the modulation region. When a modulation electrical signal is reversely applied to the PIN junction, the built-in electric field within the modulation layer changes with the change of the modulation electrical signal. When the modulation electrical signal increases, the built-in electric field increases, and the absorption of the modulation layer for the light beam increases. When the modulation electrical signal decreases, the built-in electric field decreases, and the absorption of the modulation layer for the light beam decreases.

[0068] It should be noted that if the doping concentrations of the germanium hole-doped layer and the germanium electron-doped layer are too low, the number of carriers in the modulation layer will be too small, affecting the modulation rate; if the carrier concentration is too high, the absorption loss will increase.

[0069] Preferably, the width of the germanium waveguide layer is 100 nm to 400 nm, and the height is 200 nm to 500 nm.

[0070] Specifically, the width of the germanium waveguide layer is 100 nm, 150 nm, 160 nm, 180 nm, 200 nm, 220 nm, 230 nm, 250 nm, 260 nm, 280 nm, 300 nm, 320 nm, 340 nm, 350 nm, 360 nm, 380 nm, 390 nm, 400 nm.

[0071] Specifically, the height of the germanium waveguide layer is 200 nm, 250 nm, 260 nm, 280 nm, 300 nm, 320 nm, 330 nm, 350 nm, 360 nm, 380 nm, 400 nm, 420 nm, 440 nm, 450 nm, 460 nm, 480 nm, 490 nm, 500 nm.

[0072] It should be noted that doping layers of different sizes (mainly the width of the germanium waveguide layer) will affect the light absorption coefficient of the germanium waveguide layer and the capacitance resistance in the simulation. Among them, the light absorption coefficient affects the modulation effect of the device, and the capacitance resistance (RC) will affect the modulation bandwidth of the modulator. The modulation bandwidth is an important performance index of the modulator: Generally speaking, the wider the modulation bandwidth, the larger the modulation range of the modulator.

[0073] Preferably, the cross-section of the modulation layer is rectangular.

[0074] Preferably, the germanium waveguide layer is flush with the germanium hole-doped layer and the germanium electron-doped layer in height.

[0075] It should be noted that if the cross-section of the modulation layer is rectangular, the light overflow in all directions of the cross-section can be reduced, and the light can be better confined within the modulation layer, reducing the light loss during the modulation process.

[0076] Preferably, the buffer layer includes one or more layers.

[0077] Preferably, the single-layer buffer layer is composed of a two-component compound, and the multi-layer buffer layer can be optionally composed of two-component compounds with different component contents.

[0078] In the multi-layer buffer layer, the two-component ratios of the two-component compounds in each layer change according to a positive gradient or a negative gradient; among them, the general formula of the two-component compound satisfies:

[0079] Specifically, according to the forming order from bottom to top, the multi-layer buffer layer is sequentially labeled as: the first buffer layer,..., the Nth buffer layer; the general formula of the two-component compound of the Nth buffer layer is A( 1-x ) N B x N , the general formula of the two-component compound of the N-1th buffer layer is A( 1-x ) N-1 B x N-1 , x N-1 < x N or x N-1 > x N ; among them, A and B represent the constituent elements of the two-component compound, A is silicon or an element close to silicon in the periodic table, and B is germanium or an element close to germanium in the periodic table; x N represents the number of atoms of element B in the two-component compound of the Nth buffer layer;

[0080] ( 1-x ) N , represents the number of atoms of element A in the two-component compound of the Nth buffer layer.

[0081] Specifically, the two-component ratios of the two-component compounds in each layer of the multi-layer buffer layer changing according to a positive gradient or a negative gradient can both reduce strain.

[0082] Preferably, x N-1 > x N , that is, the B component decreases in the multi-layer buffer layer from bottom to top.

[0083] It should be noted that under the same conditions, the reverse gradient buffer layer has a better strain elimination effect; under the condition of the same stress reduction effect, the thickness of the reverse gradient buffer layer is smaller than that of the positive gradient buffer layer.

[0084] Specifically, the buffer layer includes any one of a group III-V semiconductor compound, a group IV semiconductor compound, and a group IV-V semiconductor compound.

[0085] Preferably, the buffer layer includes any one of germanium silicide semiconductor, silicon carbide semiconductor, and silicon nitride semiconductor.

[0086] Preferably, a germanium silicide semiconductor buffer layer is selected. The reasons are as follows: on the one hand, the energy band width of silicon is relatively large, and the energy band width of the germanium-silicon alloy can be adjusted according to the silicon content; on the other hand, the germanium-silicon semiconductor can well reduce the strain of the bottom waveguide layer and the germanium waveguide layer.

[0087] It should be noted that in the prior art, for a pure germanium electro-absorption modulator, Ge is directly epitaxially grown on a silicon substrate, which has a tensile strain as high as 0.2%. Due to the existence of this strain, the bandgap energy of germanium will decrease from 0.80 eV at 1550 nm without strain to 0.77 eV at 1010 nm with tensile strain. Therefore, most pure germanium electro-absorption modulators operate at the O band. In order to make it operate at the C band, the present invention provides a buffer layer to reduce and even eliminate the strain generated in the germanium modulation layer.

[0088] Preferably, the electro-absorption modulator can modulate the optical wave wavelength to be 1540 nm - 1560 nm.

[0089] Preferably, by selectively etching different regions of the hole weakly doped layer and the electron weakly doped layer, the heights of the joints between the two and the buffer layer are made flush with the hole strongly doped layer and the electron strongly doped layer, so that the PN junction connection region of the hole weakly doped layer and the electron weakly doped layer protrudes to form a bottom waveguide layer.

[0090] Specifically, except for the regions where the hole weakly doped layer and the electron weakly doped layer are connected to the buffer layer, the hole weakly doped layer and the electron weakly doped layer are etched to form a concave structure in the hole weakly doped layer and the electron weakly doped layer. Furthermore, the PN junction connection region corresponding to the projection of the hole weakly doped layer and the electron weakly doped layer on the buffer layer protrudes relative to the concave structure to form a bottom waveguide layer.

[0091] Preferably, an electrode 7 is provided on the tops of the hole strongly doped layer and the electron strongly doped layer; the height of the top oxidation dielectric layer 5 is lower than that of the electrode 7, which is convenient for the protruding part of the electrode 7 to be connected to an external power supply.

[0092] Preferably, the top oxidation dielectric layer selects silicon dioxide: on the one hand, the surface of the germanium layer can be passivated and insulated by using the dielectric constant of silicon dioxide; on the other hand, as an overlying layer of the modulation layer, the doping layer, and the buffer layer, silicon dioxide can balance the stresses of the layers it connects.

[0093] On the other hand, the present invention discloses a forming method of an electro-absorption modulator with a germanium modulation layer, as Figures 1-6 shown, including the following steps:

[0094] Step 1: Prepare a doped layer 2 with different doping concentrations on the substrate layer 1;

[0095] Step 2: Etch the hole weakly doped layer 203 and the electron weakly doped layer 204 in the middle region of the doped layer 2, and prepare a bottom waveguide layer in the connection region between the two;

[0096] Step 3: Form a buffer layer 3 on the top of the bottom waveguide layer;

[0097] Step 4: Form an original modulation layer 6 on the top of the buffer layer 3;

[0098] Step 5: Form a germanium hole doped layer 401, a germanium waveguide layer 402, and a germanium electron doped layer 403 with different doping concentrations on the original modulation layer 6.

[0099] Specifically, in Step 1, a doped base layer with different doping concentrations is prepared on the substrate layer by ion implantation.

[0100] Specifically, the preparation of the doped layer with different doping concentrations in Step 1 includes:

[0101] S101: Deposit a doped base layer on the substrate layer;

[0102] S102: Form a low-doped region by low-dose ion implantation;

[0103] S103: Form a high-doped region in a specific area of the low-doped region by high-dose ion implantation;

[0104] S104: Perform high-temperature annealing treatment to obtain a doped layer with different doping concentrations.

[0105] Specifically, the method for depositing the doped base layer is ion implantation.

[0106] Specifically, the low-dose ion implantation dose is: 4×10 18 cm 3 ~6×10 18 cm 3 .

[0107] Specifically, the high-dose ion implantation dose is: 1×10 19 cm 3 ~3×10 19 cm 3 .

[0108] Specifically, the etching of the hole weakly doped layer and the electron weakly doped layer in the middle region of the doped layer in Step 2 includes:

[0109] S201: Use a mask to mark the patterns to be etched on the hole weakly doped layer and the electron weakly doped layer;

[0110] S202: Based on the identified pattern, etch the doped layer to obtain a hole weakly doped layer and an electron weakly doped layer with the target shape. The connection region of the hole weakly doped layer and the electron weakly doped layer protrudes to form a bottom waveguide layer.

[0111] Specifically, dry etching is used in step S202.

[0112] Specifically, the dry etching includes any one of plasma etching and reactive ion etching.

[0113] Specifically, in step 3, forming a buffer layer includes:

[0114] S301: Deposit a top oxide dielectric layer on the etched area for the first time;

[0115] S302: Use a mask to identify the pattern to be etched on the top oxide dielectric layer;

[0116] S303: Based on the identified pattern, etch the top oxide dielectric layer in the top region of the waveguide layer to obtain a recessed area matching the target shape of the buffer layer;

[0117] S304: Chemically vapor deposit and grow a buffer layer in the recessed area.

[0118] Specifically, in step S301, a top oxide dielectric layer is grown by thin film deposition.

[0119] Preferably, in step S301, CMP treatment is also included for the silicon oxide layer grown by thin film deposition.

[0120] It can be understood that it is difficult to precisely control the thickness of the top oxide dielectric layer deposited by thin film, and the thickness uniformity of each region is poor. CMP treatment is required to obtain precise dimensions.

[0121] Specifically, in step S301, the height of the top oxide dielectric layer grown by the first thin film deposition is higher than that of the bottom waveguide layer, reserving the depth for further deposition on the top of the bottom waveguide layer to obtain a modulation layer.

[0122] Specifically, dry etching is used in step S303.

[0123] Specifically, the dry etching includes any one of plasma etching and reactive ion etching.

[0124] Specifically, after step S304, high-temperature annealing of the buffer layer is also included.

[0125] Specifically, in step S304, CMP treatment of the buffer layer is also included.

[0126] Specifically, in step 4, forming an original modulation layer on the top of the buffer layer includes:

[0127] S401: Deposit the top oxidation dielectric layer on the buffer layer and the top oxidation dielectric layer for the second time;

[0128] S402: Use a mask to mark the pattern that needs to be etched on the top oxidation dielectric layer;

[0129] S403: Etch the top oxidation dielectric layer in the top region of the buffer layer based on the marked pattern to obtain a concave region that matches the target shape of the original modulation layer;

[0130] S404: Chemically vapor deposit and grow the original modulation layer in the concave region.

[0131] Specifically, growing the original modulation layer in step S404 includes: preparing the original modulation layer by two-step epitaxial growth at different temperatures through chemical vapor deposition.

[0132] Specifically, in step S401, the top oxidation dielectric layer is deposited for the second time by thin film deposition to grow the top oxidation dielectric layer.

[0133] Preferably, step S301 also includes CMP processing of the silicon oxide layer grown by thin film deposition.

[0134] It can be understood that it is difficult to precisely control the thickness of the top oxidation dielectric layer deposited by thin film, and the thickness uniformity of each region is poor. CMP processing is required to obtain precise dimensions.

[0135] Specifically, in step S401, the height of the top oxidation dielectric layer grown by thin film deposition for the second time is higher than the buffer layer, and a depth for further depositing the modulation layer on the top of the buffer layer is reserved.

[0136] Specifically, growing the original modulation layer in step S404 includes:

[0137] S4041: Epitaxially grow the original modulation layer to a thickness of A1 at a temperature T1, and continue to epitaxially grow the original modulation layer to a thickness of A2 at a temperature T2, where A2 > A1 and T2 > T1;

[0138] S4042: Annealing treatment;

[0139] S4043: After annealing, reduce its thickness to A3 through CMP processing, and A2 > A3 > A1.

[0140] Specifically, the thickness range of A1 is 150 nm to 300 nm; the thickness range of A2 is 600 nm to 1000 nm; the thickness range of A3 is 200 nm to 500 nm; the temperature range of T1 is 300 °C to 500 °C; the temperature range of T2 is 700 °C to 1000 °C.

[0141] It should be noted that performing two-step growth of the original modulation layer helps to obtain a high-quality germanium modulation layer.

[0142] Specifically, the annealing treatment conditions in step S4042 are 600°C to 1000°C for 30 minutes to 60 minutes.

[0143] Specifically, in step 5, a germanium hole doping layer, a germanium waveguide layer, and a germanium electron doping layer with different doping concentrations are formed in the original modulation layer, including:

[0144] S501: For the original modulation layer, ion implantation and annealing are performed to form a lateral PIN junction;

[0145] S502: A top oxidation dielectric layer is grown by third thin film deposition on the PIN junction and the original top oxidation dielectric layer.

[0146] Preferably, the ion implantation concentration of the germanium hole doping layer and the germanium electron doping layer is 1×10 18 cm 3 ~5×10 18 cm 3 .

[0147] Preferably, the ion implantation concentrations of the germanium hole doping layer and the germanium electron doping layer are 1×10 18 cm 3 、1.2×10 18 cm 3 、1.5×10 18 cm 3 、1.8×10 18 cm 3 、2.2×10 18 cm 3 、2.5×10 18 cm 3 、2.8×10 18 cm 3 、3.0×10 18 cm 3 、3.2×10 18 cm 3 、3.3×10 18 cm 3 、3.5×10 18 cm 3 、3.8×10 18 cm 3 、4.0×10 18 cm 3 、4.2×10 18 cm 3 、4.4×10 18 cm 3 、4.6×10 18 cm 3 、4.8×10 18cm 3 and 5.0×10 18 cm 3 。

[0148] Specifically, after step 5, it further includes forming a top dielectric layer on the top free region and inner side surface of the doped layer, the side surface of the buffer layer, and the top and side surfaces of the modulation layer.

[0149] Specifically, the forming method of the top dielectric layer is: after chemical vapor deposition, CMP to the target size.

[0150] Specifically, after the top dielectric layer is formed, electrodes are grown on the electron strongly doped layer and the hole strongly doped layer. Specifically, it includes:

[0151] S601: Use a mask to mark the required pattern;

[0152] S602: Form contact holes with the electrodes in the electron strongly doped layer and the hole strongly doped layer through UV lithography and dry etching processes;

[0153] S603: Deposit a metal electrode and perform patterning to obtain a metal electrode with the target shape.

[0154] In step S603, the metal electrode includes a Ti / TiN / Al metal electrode, where the Ti electrode is connected to an external power supply; the Al electrode is connected to the electron / hole strongly doped layer.

[0155] It should be noted that the Ti / TiN / Al metal electrode is connected to the electron strongly doped layer and the hole strongly doped layer, which has a lower contact barrier and improves the electro-control sensitivity.

[0156] To further illustrate the advantages of the present invention, the following examples and comparative examples are set:

[0157] Example 1

[0158] This example discloses a forming method of an electro-absorption modulator with a germanium modulation layer, including the following steps:

[0159] Step 1: Prepare a hole weakly doped layer, an electron weakly doped layer, a hole strongly doped layer, and an electron strongly doped layer on a substrate layer; the ion implantation doses of the hole weakly doped layer and the electron weakly doped layer are 5×10 18 cm 3 ; the ion implantation doses of the hole strongly doped layer and the electron strongly doped layer are 2×10 19 cm 3 , and annealing is performed after ion implantation; the substrate layer is a silicon substrate + a silicon oxide dielectric layer;

[0160] Step 2: Use plasma etching on the hole weakly doped layer and the electron weakly doped layer in the middle region of the doped layer to prepare a bottom waveguide layer in the connection region between the two;

[0161] Step 3: Deposit the top oxide dielectric layer for the first time in the etched area; use a mask to mark the pattern to be etched on the top oxide dielectric layer; etch the top oxide dielectric layer in the top area of the waveguide layer based on the marked pattern to obtain a concave area matching the target shape of the buffer layer; chemically vapor deposit and grow the buffer layer in the concave area; the top oxide dielectric layer is silicon dioxide; the buffer layer includes four layers of germanium silicide with the same thickness and different combined ratios, and the germanium-to-silicon ratios are 0.1:0.9, 0.3:0.7, 0.6:0.4, and 0.8:0.2 in the order from top to bottom of the buffer layer.

[0162] Step 4: Deposit the top oxide dielectric layer for the second time on the buffer layer and the top oxide dielectric layer; use a mask to mark the pattern to be etched on the top oxide dielectric layer; etch the top oxide dielectric layer in the top area of the buffer layer based on the marked pattern to obtain a concave area matching the target shape of the original modulation layer; chemically vapor deposit and grow the original modulation layer in the concave area, deposit to 200 nm at a low temperature of 400 °C, deposit to 1000 nm at a high temperature of 850 °C, anneal at 800 °C for 30 min, and then perform CMP processing to 300 nm; the top oxide dielectric layer is silicon dioxide;

[0163] Step 5: Form germanium hole-doped layers and germanium electron-doped layers with different doping concentrations in the original modulation layer by ion implantation; no ion implantation is performed on the germanium waveguide layer, and the height and width dimensions of the germanium waveguide layer are 300 nm × 200 nm.

[0164] Step 6: Form contact holes with the electrodes in the electron / hole highly doped layers through UV lithography and dry etching processes; deposit Al, TiN, and Ti in sequence to prepare Ti / TiN / Al metal electrodes.

[0165] This embodiment discloses an electro-absorption modulator with a germanium modulation layer prepared by the above method, including: a substrate layer, a doped layer, a buffer layer, a modulation layer, and a top oxide dielectric layer formed in sequence from bottom to top; the modulation layer includes: a germanium hole-doped layer, a germanium waveguide layer, and a germanium electron-doped layer; wherein, the germanium hole-doped layer and the germanium electron-doped layer are respectively arranged at both ends of the top of the buffer layer and are connected by the germanium waveguide layer; the top oxide dielectric layer is formed in the free area and inner side of the top of the doped layer, the side of the buffer layer, the top and side of the modulation layer.

[0166] The doping concentrations of the hole highly doped layer and the electron highly doped layer are 2×10 19 cm 3 ; the doping concentrations of the electron weakly doped layer and the hole weakly doped layer are 5×10 18 cm 3 .

[0167] The cross-sectional size of the modulation layer is 300 nm × 300 nm.

[0168] The germanium hole-doped layer and the germanium electron-doped layer have the same size, are symmetrically arranged relative to the germanium waveguide layer, and are of the same height as the germanium waveguide layer. The doping concentrations of the germanium hole-doped layer and the germanium electron-doped layer are 2×10 18 cm 3 .

[0169] Example 2

[0170] This example discloses a forming method of an electro-absorption modulator with a germanium modulation layer, including the following steps:

[0171] Step 1: Prepare a hole weakly doped layer, an electron weakly doped layer, a hole strongly doped layer, and an electron strongly doped layer on the substrate layer; the ion implantation doses of the hole weakly doped layer and the electron weakly doped layer are 4×10 18 cm 3 ; the ion implantation doses of the hole strongly doped layer and the electron strongly doped layer are 1×10 19 cm 3 ; annealing after ion implantation; the substrate layer is a silicon substrate + silicon oxide dielectric layer;

[0172] Step 2: Use reactive ion etching on the hole weakly doped layer and the electron weakly doped layer in the middle region of the doped layer to prepare a bottom waveguide layer in the connection region between the two;

[0173] Step 3: Deposit a top oxide dielectric layer for the first time in the etched region; use a mask to mark the pattern to be etched on the top oxide dielectric layer; etch the top oxide dielectric layer in the top region of the waveguide layer based on the marked pattern to obtain a concave region matching the target shape of the buffer layer; chemically vapor deposit and grow a buffer layer in the concave region; the top oxide dielectric layer is silicon dioxide; the buffer layer includes six layers of germanium silicide with the same thickness and different combined ratios. The germanium-silicon ratios are respectively: 0.1:0.9, 0.2:0.8, 0.3:0.7, 0.5:0.5, 0.6:0.4, 0.8:0.2 in the order from top to bottom of the buffer layer.

[0174] Step 4: Deposit a top oxide dielectric layer for the second time on the buffer layer and the top oxide dielectric layer; use a mask to mark the pattern to be etched on the top oxide dielectric layer; etch the top oxide dielectric layer in the top region of the buffer layer based on the marked pattern to obtain a concave region matching the target shape of the original modulation layer; chemically vapor deposit and grow the original modulation layer in the concave region, deposit to 150 nm at a low temperature of 300 °C, deposit to 600 nm at a high temperature of 700 °C, and after annealing, perform CMP treatment to 200 nm; the top oxide dielectric layer is silicon dioxide;

[0175] Step 5: Form germanium hole-doped layers and germanium electron-doped layers with different doping concentrations in the original modulation layer through ion implantation; the germanium waveguide layer is not subjected to ion implantation, and the height and width dimensions of the germanium waveguide layer are 200 nm × 100 nm.

[0176] Step 6: Form contact holes with electrodes in the electron / hole highly doped layers through UV lithography and dry etching processes; deposit Al / TiN / Ti in sequence to prepare Ti / TiN / Al metal electrodes.

[0177] This embodiment discloses an electro-absorption modulator with a germanium modulation layer prepared by the above method, including: a substrate layer, a doped layer, a buffer layer, a modulation layer, and a top oxidation dielectric layer formed in sequence from bottom to top; the modulation layer includes: a germanium hole-doped layer, a germanium waveguide layer, and a germanium electron-doped layer; wherein, the germanium hole-doped layer and the germanium electron-doped layer are respectively arranged at both ends of the top of the buffer layer and are connected through the germanium waveguide layer; the top oxidation dielectric layer is formed in the free area and the inner side of the top of the doped layer, the side of the buffer layer, the top and the side of the modulation layer.

[0178] The doping concentrations of the hole highly doped layer and the electron highly doped layer are 1×10 19 cm 3 ; the doping concentrations of the electron weakly doped layer and the hole weakly doped layer are 4×10 18 cm 3 .

[0179] The cross-sectional dimension of the modulation layer is 200 nm × 200 nm.

[0180] The germanium hole-doped layer and the germanium electron-doped layer have the same size, are symmetrically arranged relative to the germanium waveguide layer, and are of the same height as the germanium waveguide layer. The doping concentrations of the germanium hole-doped layer and the germanium electron-doped layer are 1×10 18 cm 3 .

[0181] Example 3

[0182] This embodiment discloses a forming method of an electro-absorption modulator with a germanium modulation layer, including the following steps:

[0183] Step 1: Prepare a hole weakly doped layer, an electron weakly doped layer, a hole highly doped layer, and an electron highly doped layer on the substrate layer; the ion implantation doses of the hole weakly doped layer and the electron weakly doped layer are 6×10 18 cm 3 ; the ion implantation doses of the hole highly doped layer and the electron highly doped layer are 3×10 19 cm 3 ; annealing is performed after ion implantation; the substrate layer is a silicon substrate + silicon oxide dielectric layer;

[0184] Step 2: Use plasma etching on the hole weakly doped layer and the electron weakly doped layer in the middle region of the doped layer to prepare a bottom waveguide layer in the connection region between the two.

[0185] Step 3: Deposit a top oxide dielectric layer for the first time on the etched region; Use a mask to mark the pattern to be etched on the top oxide dielectric layer; Etch the top oxide dielectric layer in the top region of the waveguide layer based on the marked pattern to obtain a concave region matching the target shape of the buffer layer; Chemically vapor deposit and grow a buffer layer in the concave region; The top oxide dielectric layer is silicon dioxide; The buffer layer includes seven layers of silicon carbide with the same thickness and different combined ratios. The carbon-silicon ratios are respectively: 0.1:0.9, 0.2:0.8, 0.3:0.7, 0.5:0.5, 0.6:0.4, 0.8:0.2, 0.9:0.1 in the order from bottom to top of the buffer layer.

[0186] Step 4: Deposit a top oxide dielectric layer for the second time on the buffer layer and the top oxide dielectric layer; Use a mask to mark the pattern to be etched on the top oxide dielectric layer; Etch the top oxide dielectric layer in the top region of the buffer layer based on the marked pattern to obtain a concave region matching the target shape of the original modulation layer; Chemically vapor deposit and grow the original modulation layer in the concave region, deposit to 300 nm at a low temperature of 500 °C, deposit to 1000 nm at a high temperature of 1000 °C, and after annealing, process to 500 nm by CMP; The top oxide dielectric layer is silicon dioxide;

[0187] Step 5: Form germanium hole-doped layers and germanium electron-doped layers with different doping concentrations in the original modulation layer by ion implantation; Do not perform ion implantation on the germanium waveguide layer. The height and width dimensions of the germanium waveguide layer are 500 nm × 400 nm.

[0188] Step 6: Form contact holes with the electrodes in the electron / hole strongly doped layer through UV lithography and dry etching processes; Deposit Ti / TiN / Al in sequence to prepare a Ti / TiN / Al metal electrode.

[0189] This embodiment discloses an electro-absorption modulator with a germanium modulation layer prepared by the above method, including: a substrate layer, a doped layer, a buffer layer, a modulation layer, and a top oxide dielectric layer formed in sequence from bottom to top; The modulation layer includes: a germanium hole-doped layer, a germanium waveguide layer, and a germanium electron-doped layer; Among them, the germanium hole-doped layer and the germanium electron-doped layer are respectively arranged at both ends of the top of the buffer layer and are connected by the germanium waveguide layer; The top oxide dielectric layer is formed in the free region and the inner side of the top of the doped layer, the side of the buffer layer, the top and the side of the modulation layer.

[0190] The doping concentrations of the hole strongly doped layer and the electron strongly doped layer are 3×10 19 cm 3 ; The doping concentrations of the electron weakly doped layer and the hole weakly doped layer are 6×10 18 cm3 。

[0191] The cross-sectional size of the modulation layer is 500 nm × 500 nm.

[0192] The germanium hole-doped layer and the germanium electron-doped layer have the same size, are symmetrically arranged relative to the germanium waveguide layer, and are of the same height as the germanium waveguide layer. The doping concentrations of the germanium hole-doped layer and the germanium electron-doped layer are 5 × 10 18 cm 3 。

[0193] Example 4

[0194] This example discloses a forming method of an electro-absorption modulator with a germanium modulation layer. The only difference from Example 1 is that the buffer layer includes five layers of gallium nitride with different combination ratios. The nitrogen-gallium ratios are 0.1:0.9, 0.3:0.7, 0.5:0.5, 0.8:0.2, and 0.9:0.1 in the order from bottom to top of the buffer layer.

[0195] Example 5

[0196] This example discloses a forming method of an electro-absorption modulator with a germanium modulation layer. The only difference from Example 1 is that the buffer layer includes four layers of germanium silicide with the same thickness and different combination ratios. The germanium-silicon ratios are 0.1:0.9, 0.3:0.7, 0.6:0.4, and 0.8:0.2 in the order from bottom to top of the buffer layer.

[0197] Example 6

[0198] This example discloses an electro-absorption modulator with a germanium modulation layer and its forming method. Compared with Example 1, the only difference is that the buffer layer is only provided with one layer of germanium silicide, and the germanium-silicon molar ratio is 0.5:0.5.

[0199] Comparative Example 1

[0200] This example discloses an electro-absorption modulator with a germanium modulation layer and its forming method. Compared with Example 1, the only difference is that there is no buffer layer, and the buffer layer thickness of Comparative Example 1 is replaced by increasing the same height of the electron weakly doped layer and the hole weakly doped layer.

[0201] Comparative Example 2

[0202] This example discloses an electro-absorption modulator with a germanium modulation layer and its forming method. Compared with Example 1, the only difference is that the original modulation layer is deposited by one-step forming at 400 °C to 1000 nm, annealed at 800 °C for 30 min, and then processed by CMP to 300 nm, and the other conditions are the same as those in Example 1.

[0203] Comparative Example 3

[0204] This embodiment discloses an electro-absorption modulator with a germanium modulation layer and a forming method thereof. Compared with Embodiment 1, the only difference is that the original modulation layer is deposited in one step at 850 °C to 1000 nm, annealed at 800 °C for 30 min, and then processed by CMP to 300 nm. The other conditions are the same as those in Embodiment 1.

[0205] Comparative Example 4

[0206] This embodiment discloses an electro-absorption modulator with a germanium modulation layer and a forming method thereof. Compared with Embodiment 1, the only difference is that it is deposited to 200 nm at the same low temperature of 400 °C as in Embodiment 1, deposited to 300 nm at the high temperature of 850 °C as in Embodiment 1, annealed, and not processed by the CMP process; the other conditions are the same as those in Embodiment 1.

[0207] Comparative Example 5

[0208] This embodiment discloses an electro-absorption modulator with a germanium modulation layer and a forming method thereof. Compared with Embodiment 1, the only difference is that the width of the modulation layer is 100 nm, and the other conditions are the same as those in Embodiment 1.

[0209] Comparative Example 6

[0210] This embodiment discloses an electro-absorption modulator with a germanium modulation layer and a forming method thereof. Compared with Embodiment 1, the only difference is that the width of the modulation layer is 500 nm, and the other conditions are the same as those in Embodiment 1.

[0211] Comparative Example 7

[0212] This embodiment discloses an electro-absorption modulator with a germanium modulation layer and a forming method thereof. Compared with Embodiment 1, the only difference is that the height of the modulation layer is 100 nm, and the other conditions are the same as those in Embodiment 1.

[0213] Comparative Example 8

[0214] This embodiment discloses an electro-absorption modulator with a germanium modulation layer and a forming method thereof. Compared with Embodiment 1, the only difference is that the height of the modulation layer is 600 nm, and the other conditions are the same as those in Embodiment 1.

[0215] Comparative Example 9

[0216] This embodiment discloses an electro-absorption modulator with a germanium modulation layer and a forming method thereof. Compared with Embodiment 1, as Figure 7 shown, the only difference is that the doped layer does not have a weakly doped hole layer and a weakly doped electron layer, and the region between the strongly doped hole layer and the strongly doped electron layer is not doped. The other conditions are the same as those in Embodiment 1.

[0217] Experimental Example

[0218] The optoelectronic modulation performance of Examples 1-6 and Comparative Examples 1-9 was tested, and the test results are as follows:

[0219]

[0220]

[0221]

[0222] Experimental conclusion:

[0223] As can be seen from the above table: In Examples 1-3 and Example 5, the working wavelength can vary from 1550 nm to 1560 nm, the modulation speed can vary from 40 Gbps to 56 Gbps, the modulation bandwidth can vary from 55 GHz to 67 GHz, and the insertion loss can vary from 4.0 dB to 7.9 dB.

[0224] Comparing Example 1 and Example 5, it can be seen that setting the buffer layer with a reverse gradient has a larger working wavelength, modulation speed, and modulation bandwidth, and a smaller insertion loss than setting it with a forward gradient.

[0225] Comparing Example 1 and Comparative Example 1, it can be seen that Comparative Example 1 without a buffer layer has a smaller working wavelength and a larger loss.

[0226] Comparing Example 1 and Comparative Examples 2 and 3, it can be seen that the modulator obtained by using the method of preparing the modulation layer in Example 1 has a larger working wavelength, modulation speed, and modulation bandwidth, and a smaller insertion loss. Comparing Example 1 and Comparative Example 4, it can be seen that the modulator obtained by using the method of preparing the modulation layer in Example 1 has a larger working wavelength, modulation speed, and modulation bandwidth, and a smaller insertion loss.

[0227] Comparing Example 1 and Comparative Examples 5 and 6, it can be seen that when the width of the modulation layer is too large or too small, the modulation speed, modulation bandwidth, and insertion loss all deteriorate to a certain extent.

[0228] Comparing Example 1 and Comparative Examples 7 and 8, it can be seen that when the height of the modulation layer is too large or too small, the modulation speed, modulation bandwidth, and insertion loss all deteriorate to a certain extent.

[0229] Comparing Example 1 and Comparative Example 9, it can be seen that the setting of the hole weakly doped layer and the electron weakly doped layer helps to optimize the modulation speed, modulation bandwidth, and insertion loss, and improve the control sensitivity.

[0230] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention.

Claims

1. An electro-absorption modulator with a germanium modulation layer, characterized in that, comprising: a substrate layer including a back substrate and a bottom oxide dielectric layer disposed on the back substrate; a doping layer formed on the top of the bottom oxide dielectric layer, including: a heavily hole-doped layer, a lightly hole-doped layer, a lightly electron-doped layer, a heavily electron-doped layer; the lightly hole-doped layer and the lightly electron-doped layer protrude and are connected in the middle region on the top of the bottom oxide dielectric layer to form a PN junction, which serves as a bottom waveguide layer; the heavily hole-doped layer and the heavily electron-doped layer are respectively disposed at both ends on the top of the bottom oxide dielectric layer, the heavily hole-doped layer is connected to the lightly hole-doped layer, and the lightly electron-doped layer is connected to the heavily electron-doped layer; a buffer layer formed on the top of the PN junction; a modulation layer formed on the top of the buffer layer; including: a germanium hole-doped layer, a germanium waveguide layer, a germanium electron-doped layer; wherein, the germanium hole-doped layer and the germanium electron-doped layer are respectively disposed at both ends on the top of the buffer layer and are connected by the germanium waveguide layer; a top oxide dielectric layer formed on the top free region and the inner side of the doping layer, the side of the buffer layer, the top and the side of the modulation layer; the buffer layer comprises multiple layers; the multiple buffer layers are composed of a two-component compound with different component contents; In each layer of the multi-layer buffer layer, the two-component ratio of the two-component compound changes according to a positive gradient or a negative gradient; among them, the general formula of the two-component compound satisfies: A 1-x B x , where A and B represent the constituent elements of the two-component compound; x ≤ 1 represents the number of atoms of element B in the two-component compound; The general formula of the two-component compound satisfies: the multi-layer buffer layers are sequentially labeled as the first buffer layer, …, the Nth buffer layer in the forming order from bottom to top; the general formula of the two-component compound of the Nth buffer layer is A (1-x) N B x N , and the general formula of the two-component compound of the (N−1)th buffer layer is A (1-x) N-1 B x N-1 , x N-1 < x N or x N-1 > x N ; where A and B represent the constituent elements of the two-component compound, x N represents the number of atoms of element B of the two-component compound of the Nth buffer layer, ( 1-x ) N , represents the number of atoms of element A of the two-component compound of the Nth buffer layer.

2. The electro-absorption modulator according to claim 1, characterized in that, The doping concentrations of the germanium hole-doped layer and the germanium electron-doped layer are 1×10 18 cm 3 ~5×10 18 cm 3 .

3. The electro-absorption modulator according to claim 2, characterized in that, the width of the germanium waveguide layer is 100 nm to 400 nm, and the height is 200 nm to 500 nm.

4. The electro-absorption modulator according to claim 3, characterized in that, the operating wavelength is 1540 nm to 1560 nm.

5. The electro-absorption modulator according to claim 1, characterized in that, the buffer layer includes: any one of a Group III-V semiconductor compound, a Group IV semiconductor compound, and a Group IV-V semiconductor compound.

6. A forming method of an electro-absorption modulator with a germanium modulation layer, characterized in that, for preparing the electro-absorption modulator according to any one of claims 1-5, including: Step 1: Prepare a doping layer with different doping concentrations on the substrate layer; Step 2: Etch the lightly hole-doped layer and the lightly electron-doped layer in the middle region of the doping layer, and prepare a bottom waveguide layer in the connection region between the two; Step 3: Form a buffer layer on the top of the bottom waveguide layer; Step 4: Form an original modulation layer on the top of the buffer layer; Step 5: Form a germanium hole-doped layer, a germanium waveguide layer, and a germanium electron-doped layer with different doping concentrations on the original modulation layer.

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