CN117293216A - Waveguide-type germanium-silicon avalanche photodiode and preparation method thereof - Google Patents
Waveguide-type germanium-silicon avalanche photodiode and preparation method thereof Download PDFInfo
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- LEVVHYCKPQWKOP-UHFFFAOYSA-N [Si].[Ge] Chemical compound [Si].[Ge] LEVVHYCKPQWKOP-UHFFFAOYSA-N 0.000 title claims abstract description 75
- 238000002360 preparation method Methods 0.000 title abstract description 6
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 68
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 68
- 239000010703 silicon Substances 0.000 claims abstract description 68
- 229910052732 germanium Inorganic materials 0.000 claims abstract description 44
- GNPVGFCGXDBREM-UHFFFAOYSA-N germanium atom Chemical compound [Ge] GNPVGFCGXDBREM-UHFFFAOYSA-N 0.000 claims abstract description 44
- 238000010521 absorption reaction Methods 0.000 claims abstract description 24
- 229910052751 metal Inorganic materials 0.000 claims abstract description 18
- 239000002184 metal Substances 0.000 claims abstract description 18
- 239000000758 substrate Substances 0.000 claims abstract description 18
- 239000004065 semiconductor Substances 0.000 claims abstract description 3
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 52
- 239000000377 silicon dioxide Substances 0.000 claims description 25
- 235000012239 silicon dioxide Nutrition 0.000 claims description 24
- 239000000463 material Substances 0.000 claims description 17
- 230000015556 catabolic process Effects 0.000 claims description 14
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- 238000005530 etching Methods 0.000 claims description 9
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- 238000005468 ion implantation Methods 0.000 claims description 7
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- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 3
- 238000011161 development Methods 0.000 description 3
- 238000009792 diffusion process Methods 0.000 description 3
- 238000001451 molecular beam epitaxy Methods 0.000 description 3
- 239000002210 silicon-based material Substances 0.000 description 3
- 239000010409 thin film Substances 0.000 description 3
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 2
- GYHNNYVSQQEPJS-UHFFFAOYSA-N Gallium Chemical compound [Ga] GYHNNYVSQQEPJS-UHFFFAOYSA-N 0.000 description 2
- 229910052796 boron Inorganic materials 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 229910052733 gallium Inorganic materials 0.000 description 2
- 229910052738 indium Inorganic materials 0.000 description 2
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 description 2
- 230000010354 integration Effects 0.000 description 2
- 238000005240 physical vapour deposition Methods 0.000 description 2
- 229910052814 silicon oxide Inorganic materials 0.000 description 2
- 238000001771 vacuum deposition Methods 0.000 description 2
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- H01L31/08—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
- H01L31/10—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors characterised by potential barriers, e.g. phototransistors
- H01L31/101—Devices sensitive to infrared, visible or ultraviolet radiation
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- H01L31/105—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier the potential barrier being of the PIN type
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- H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
- H01L31/1804—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof comprising only elements of Group IV of the Periodic Table
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Abstract
The invention discloses a waveguide-type germanium-silicon avalanche photodiode and a preparation method thereof, which relate to the field of photoelectric detectors and have the technical scheme that: the semiconductor device comprises a substrate layer, a silicon waveguide structure, a germanium absorption layer and a metal electrode from bottom to top in sequence; the ridge waveguide boss waveguide comprises a first boss part and a second boss part, and the first boss part and the second boss part are respectively arranged into a step shape with slopes on two sides; the metal electrode comprises a first electrode, a second electrode and a third electrode; the first electrode is arranged on the surface of the slab waveguide and is arranged on the slab waveguide at one side of the boss waveguide; the second electrode is arranged on the surface of the slab waveguide and is arranged on the slab waveguide at the other side of the slab waveguide; and the third electrode is arranged on the surface of the germanium absorption layer. The device is characterized by having lower avalanche noise, being capable of improving signal to noise ratio and realizing remote optical fiber communication.
Description
Technical Field
The invention relates to the field of photoelectric detectors, in particular to a waveguide-type germanium-silicon avalanche photodiode and a preparation method thereof.
Background
Avalanche photodiodes (Avalanche Photodiode, APD) are used as weak photodetectors, and have an internal gain to amplify a detected photocurrent, and thus are very important in various fields such as optical communication, laser imaging, and laser radar. The main ones used for optical communication integration are Ge/Si APDs and APDs based on III-V semiconductors. Ge/Si APDs are becoming more and more important in optical communication integration due to their compatibility with CMOS processes and the development of silicon-based germanium material epitaxy technology. The waveguide-type Ge/Si APD is a mainstream device structure of the Ge/Si APD because the waveguide-type Ge/Si APD can fully absorb light. The presence of avalanche noise in an APD device can affect the signal-to-noise ratio of the device in use, thus requiring the lower the avalanche noise of the device the better. However, in the conventional waveguide-type Ge/Si APD device, as the electric field intensity of the avalanche region of the device increases, the ratio of the electron ionization rate α and the hole ionization rate β of the avalanche region in the avalanche region decreases, and an electric field tip is generated at the edge of the device due to the concentration effect of the electric field, which increases the avalanche noise of the device.
Disclosure of Invention
The first object of the present invention is to provide a waveguide-type germanium-silicon avalanche photodiode, which has low avalanche noise, and can improve signal-to-noise ratio and realize remote optical fiber communication.
In order to achieve the above purpose, the invention adopts the following technical scheme: the waveguide-type germanium-silicon avalanche photodiode sequentially comprises a substrate layer, a silicon waveguide structure, a germanium absorption layer and a metal electrode from bottom to top; the substrate layer comprises a silicon substrate and a silicon dioxide buried layer; the silicon waveguide structure comprises an incident waveguide, a tapering structure and a ridge waveguide which are sequentially connected, wherein the ridge waveguide comprises a flat waveguide and a boss waveguide which is positioned in the middle of the flat waveguide and is arranged on the surface of the flat waveguide. The slab waveguide is connected with the tapering structure and comprises a first silicon doping area, wherein the first silicon doping area is used for carrying out first type doping; the boss waveguide comprises a first boss part and a second boss part from bottom to top; the first boss part is an avalanche breakdown region and is arranged on the surface of the slab waveguide, which is far away from the silicon dioxide buried layer, the first boss part is in a step shape with slopes on two sides, and the width of the first protruding structure, which is far away from the surface of one side of the slab waveguide, is larger than the width of the first protruding structure, which is close to the surface of one side of the slab waveguide; the second boss part comprises a second silicon doping area for doping of a second type, is arranged on the surface of the first boss part, which is far away from the slab waveguide, is in a step shape with slopes on two sides, and the width of the second protruding structure, which is far away from the surface of one side of the slab waveguide, is larger than the width of the second protruding structure, which is close to the surface of one side of the slab waveguide; the metal electrode comprises a first electrode, a second electrode and a third electrode; the first electrode is arranged on the surface of the slab waveguide and is arranged on the slab waveguide at one side of the boss waveguide; the second electrode is arranged on the surface of the slab waveguide and is arranged on the slab waveguide at the other side of the slab waveguide; and the third electrode is arranged on the surface of the germanium absorption layer.
Further, the slope of the second boss portion is continuous with the slope of the first boss portion.
Further, the slope of the second boss portion coincides with the slope of the first boss portion.
Further, a center-hanging surface of the first boss portion in the width direction coincides with a center-hanging surface of the tapering structure in the width direction.
Further, the slope of one side of the first boss portion coincides with the slope of the other side of the first boss portion, and is symmetrical with respect to the midplane of the first boss portion in the width direction.
Further, the gradient of the first boss portion and the gradient of the second boss portion are both in the range of 0.5. Ltoreq.arctan θ. Ltoreq.1.5.
The invention further aims to provide the waveguide type germanium-silicon avalanche photodiode, which is characterized in that the manufactured waveguide type germanium-silicon avalanche photodiode has lower avalanche noise, can improve the signal-to-noise ratio and realizes long-distance optical fiber communication.
In order to achieve the above purpose, the invention adopts the following technical scheme: a preparation method of a waveguide-type germanium-silicon avalanche photodiode is used for manufacturing the waveguide-type germanium-silicon avalanche photodiode and comprises the following steps:
preparing an SOI wafer with a substrate layer and a silicon waveguide layer, etching the silicon waveguide layer of the SOI wafer by photoetching and etching to form an incident waveguide, a tapered structure and a slab waveguide, and doping a preset area of the slab waveguide to form a first silicon doped area;
preparing a boss waveguide on the surface of the slab waveguide; the boss waveguide comprises a first boss part and a second boss part from bottom to top; the first boss part is an avalanche breakdown region and is arranged on the surface of the slab waveguide, which is far away from the silicon dioxide buried layer, the first boss part is in a step shape with slopes on two sides, and the width of the first protruding structure, which is far away from the surface of one side of the slab waveguide, is larger than the width of the first protruding structure, which is close to the surface of one side of the slab waveguide; the second boss part comprises a second silicon doping area for doping of a second type, is arranged on the surface of the first boss part, which is far away from the slab waveguide, is in a step shape with slopes on two sides, and the width of the second protruding structure, which is far away from the surface of one side of the slab waveguide, is larger than the width of the second protruding structure, which is close to the surface of one side of the slab waveguide;
preparing a germanium absorption layer of the waveguide-type germanium-silicon avalanche photodiode by epitaxy and dry etching;
and preparing a first electrode and a second electrode above the slab waveguide by depositing a film and dry etching, and preparing a third electrode above the germanium absorption layer.
Further, the preparing the boss waveguide on the surface of the slab waveguide specifically includes:
epitaxially growing a boss waveguide material on the surface of the slab waveguide;
preparing a second silicon doped region by ion implantation in a preset region on the upper surface of the formed boss waveguide material;
and forming the boss waveguide at a preset position on the doped boss waveguide material by photoetching and dry etching.
Further, a silicon dioxide film is deposited to prepare a silicon dioxide cladding layer which wraps the silicon waveguide structure, the germanium absorption layer and the metal electrode.
The invention also aims to provide a chip which is characterized in that a receiving end of the chip has lower avalanche noise, can improve the signal to noise ratio and realizes remote optical fiber communication.
In order to achieve the above purpose, the invention adopts the following technical scheme: a chip incorporating the waveguide-type germanium-silicon avalanche photodiode described above.
The waveguide-type germanium-silicon avalanche photodiode and the manufacturing method thereof have the beneficial effects that the electric field concentration at the edges of the first boss part and the second boss part is avoided, and local electric field spikes are avoided, so that avalanche noise of the waveguide-type germanium-silicon avalanche photodiode is reduced. Meanwhile, the electric field intensity of the middle area of the active area of the device is reduced, so that the avalanche noise of the waveguide-type germanium-silicon avalanche photodiode is further reduced to a certain extent. Therefore, the waveguide-type germanium-silicon avalanche photodiode can effectively reduce avalanche noise, increase the signal-to-noise ratio of the waveguide-type germanium-silicon avalanche photodiode in circuit use, and realize application in remote optical communication.
Drawings
FIG. 1 is a schematic three-dimensional structure of a waveguide-type germanium-silicon avalanche photodiode of embodiment 1;
fig. 2 is a line graph showing the ratio α/β of electron ionization rate α and hole ionization rate β of silicon and germanium as a function of electric field strength;
fig. 3 is an end view of a waveguide-type germanium-silicon avalanche photodiode of embodiment 1;
FIG. 4 is a diagram of a simulation of the electric field distribution at the cross section of a prior art waveguide-type germanium-silicon avalanche photodiode;
FIG. 5 is a simulation diagram of the electric field distribution at the cross section of a waveguide-type germanium-silicon avalanche photodiode of example 1;
FIG. 6 is a graph of the electric field intensity in the middle region of a cross section of a waveguide-type germanium-silicon photodetector of example 1 and the prior art;
FIG. 7 is a flow chart of the preparation method of example 2;
fig. 8 is a flow chart of the method of step S2 in example 2.
Reference numerals: 1. a substrate layer; 11. a silicon substrate; 12. a buried layer of silicon dioxide; 2. a silicon waveguide structure; 21. an incident waveguide; 22. a tapering structure; 23. 231, slab waveguide; 232. a boss waveguide; 2321. a first boss portion; 2322. a second boss portion; 3. a germanium absorption layer; 31. an intrinsic i-Ge region; 32. a germanium doped region; 4. a metal electrode; 41. a first electrode; 42. a second electrode; 43. and a third electrode.
Description of the embodiments
Example 1
A waveguide-type germanium-silicon avalanche photodiode, as shown in fig. 1 and 3, comprises a substrate layer 1 and a silicon waveguide structure 2 from bottom to top. The Y-axis in fig. 1 and 3 represents the width direction referred to in this embodiment, the X-axis represents the length direction referred to in this embodiment, and the Z-axis represents the height direction referred to in this embodiment. Wherein,
a substrate layer 1 for supporting and stabilizing the main elements of the detector. The design and fabrication are performed on an SOI process platform. The substrate layer 1 comprises a silicon substrate 11 and a buried silicon dioxide layer 12 from bottom to top, wherein the thickness of the buried silicon dioxide layer 12 is usually 2um. It should be noted that the thickness of the buried silicon oxide layer 12 may be determined according to the design requirements of the actual waveguide-type germanium-silicon avalanche photodiode.
The silicon waveguide structure 2 includes an incident waveguide 21, a tapered structure 22, and a ridge waveguide 23 connected in this order. Wherein,
an incident waveguide 21 for transmitting incident light to couple the incident light into the tapering structure 22.
The tapering structure 22 is used for performing mode-spot conversion on the incident light so as to enable the incident light to enter the ridge waveguide 23.
The ridge waveguide 23 includes a slab waveguide 231 and a boss waveguide 232 located in the middle of the slab waveguide 231 and disposed on the surface of the slab waveguide 231.
The slab waveguide 231 is connected to the tapered structure 22 and includes a first silicon doped region for performing a first type of doping. Specifically, the first silicon doped region is formed by doping and diffusing the upper surface of the slab waveguide 231 to the lower surface of the slab waveguide 231. The first silicon doped region may cover the entire slab waveguide 231, or the first silicon doped region may cover a partial region of the slab waveguide 231. The thickness of the first silicon doped region is equal to the thickness of the slab waveguide 231. The slab waveguide 231 is typically 220nm thick. It should be noted that the thickness of the slab waveguide 231 may be determined according to the design requirement of the actual waveguide type silicon germanium avalanche photodiode.
The boss waveguide 232 includes a first boss portion 2321 and a second boss portion 2322 from bottom to top. Wherein,
the first boss portion 2321 is an avalanche breakdown region, and is disposed on a surface of the slab waveguide 231, which is far away from the buried silicon dioxide layer 12, the first boss portion 2321 is in a step shape with slopes on two sides, and a width of a side surface of the first protruding structure, which is far away from the slab waveguide 231, is greater than a width of a side surface of the first protruding structure, which is close to the slab waveguide 231.
The second boss portion 2322 includes a second silicon doped region for doping of a second type, and is disposed on a surface of the first boss portion 2321, which is far away from the slab waveguide 231, the second boss portion 2322 is in a step shape with slopes on two sides, and a width of the second protruding structure, which is far away from the surface of one side of the slab waveguide 231, is greater than a width of the second protruding structure, which is near to the surface of one side of the slab waveguide 231. Specifically, the second silicon doped region covers the entire second boss portion 2322.
The slope is two end surfaces perpendicular to the propagation direction of the incident light on the first boss portion 2321 or the second boss portion 2322, and are oppositely arranged and form an included angle with the upper surface of the slab waveguide 231. In this embodiment, an included angle formed by the slope and the upper surface of the slab waveguide 231 is defined as a slope of the slope.
The germanium absorption layer 3 is disposed on a surface of the boss waveguide 232 away from the slab waveguide 231. The germanium absorber layer 3 includes an intrinsic i-Ge region 31 and a germanium doped region 32. Wherein,
an intrinsic i-Ge region 31 is provided on the surface of the second boss portion 2322.
A germanium-doped region 32, disposed on the surface of the intrinsic i-Ge region 31, is used for performing a third type of doping. The germanium-doped region 32 is formed by doping and diffusing the upper surface of the germanium absorber layer 3 in the direction of the lower surface of the germanium absorber layer 3. The germanium-doped region 32 may cover the entire upper surface of the germanium-absorbing layer 3, or the germanium-doped region 32 may cover a localized region of the upper surface of the germanium-absorbing layer 3.
A metal electrode 4 including a first electrode 41, a second electrode 42, and a third electrode 43; wherein,
the first electrode 41 is disposed on the surface of the slab waveguide 231 and disposed on the slab waveguide 231 at one side of the boss waveguide 232;
the second electrode 42 is arranged on the surface of the slab waveguide 231 and is arranged on the slab waveguide 231 at the other side of the boss waveguide 232;
the third electrode 43 is provided on the surface of the germanium absorption layer 3.
Specifically, the first type of doping refers to n++ silicon doping, with doping concentrations typically required to be greater than 1e19/cm 3 To form ohmic contacts with the first electrode 41 and the second electrode 42. The second type of doping refers to P+ silicon doping, typically at a doping concentration of 1e17/cm 3 Left and right. The third type of doping is p++ germanium doping, typically at a doping concentration of greater than 1e19/cm 3 To form an ohmic contact with the third electrode 43. The doping concentration given here is just a doping concentration commonly used in the industry and can be adjusted according to the design requirements of different waveguide-type germanium-silicon avalanche photodiodes.
The working principle of this embodiment is as follows: light is transmitted along the incident waveguide 21, is incident on the ridge waveguide 23 through the tapering structure 22 and coupled into the germanium absorbing layer 3, and the ridge waveguide 23 and the germanium absorbing layer 3 together form an active region of the waveguide-type germanium-silicon avalanche photodiode, where the light is gradually coupled into and absorbed by the germanium absorbing layer 3, generating corresponding photo-generated electron-hole pairs. The photo-generated electrons generated in the germanium absorbing layer 3 under the action of the electric field are injected into an avalanche breakdown region of the waveguide-type germanium-silicon avalanche photodiode through the p+ doped silicon charge region, and the photo-generated electrons can trigger the avalanche multiplication effect in the avalanche region due to the action of the strong electric field, so that the photocurrent of the waveguide-type germanium-silicon avalanche photodiode is amplified.
In this way, after the ridge waveguide 23 is configured to have a slope, the electric field can diffuse along the slope direction of the first boss portion 2321, that is, the slope of the first boss portion 2321 is an obtuse angle, and the electric field lines can diffuse along the slope direction of the first boss portion 2321, so that the electric field concentration effect is effectively solved. As fig. 7 shows the electric field distribution diagram of the cross section of the graded waveguide type silicon germanium avalanche photodiode obtained by simulation, the gradient angle in fig. 7 satisfies arctan θ=1, and it can be seen from fig. 7 that at the edge of the interface between the first boss portion 2321 (i.e., the avalanche breakdown region) and the second boss portion 2322 (i.e., the p+ doped silicon charge region), the electric field spike has disappeared. Therefore, by introducing the gradient structure into the second boss portion 2322 and the first boss portion 2321 of the waveguide-type germanium-silicon avalanche photodiode, the electric field concentration effect at the edge of the waveguide-type germanium-silicon avalanche photodiode is released, so that avalanche noise of the waveguide-type germanium-silicon avalanche photodiode is reduced, signal-to-noise ratio of the waveguide-type germanium-silicon avalanche photodiode is improved, and long-distance optical fiber communication is realized.
Fig. 4 and 5 are electric field subsection simulation diagrams of a conventional waveguide type germanium-silicon avalanche photodiode and an optimized waveguide type germanium-silicon avalanche photodiode at a Z-Y section, respectively. A in fig. 4 and 5 represents an electric field at the edge of the interface of the avalanche breakdown region and the p+ doped silicon charge region. Fig. 4 and 5 are simulation results obtained under the same bias voltage conditions. The difference between the simulation conditions of fig. 5 and fig. 4 is that the other set conditions are exactly the same except that a ramp is provided on the bump waveguide. As can be seen from a comparison of fig. 5 and 4, after the avalanche breakdown region and the p+ doped silicon charge region are ramped, the electric field spike at the edge of the interface of the avalanche breakdown region and the p+ doped silicon charge region is significantly improved. Therefore, after the p+ doped silicon charge region and the avalanche breakdown region are made into structures with certain gradients, the fringe electric field peak of the waveguide-type germanium-silicon avalanche photodiode can be effectively solved, and the avalanche noise of the waveguide-type germanium-silicon avalanche photodiode is reduced.
In addition, after the p+ doped silicon charge region and the avalanche breakdown region are made in a graded structure, the electric field intensity at the middle region of the waveguide-type germanium-silicon avalanche photodiode is also reduced, that is, the electric field intensity at the region of the middle portion in the width direction of the ridge waveguide 23 and the germanium absorption layer 3 is also reduced. The gain of the waveguide-type germanium-silicon avalanche photodiode is the integral of the electric field intensity and the avalanche distance, and the equivalent avalanche distance of the waveguide-type germanium-silicon avalanche photodiode is increased due to the fact that the slopes on two sides can increase the transmission path of electrons to a certain extent, but due to the fact that the slope structure is arranged, the electric field concentration effect at the edge of the waveguide-type germanium-silicon avalanche photodiode is released, the electric field intensity of the optimized waveguide-type germanium-silicon avalanche photodiode is reduced, and therefore the gain of the waveguide-type germanium-silicon avalanche photodiode is basically kept unchanged. Meanwhile, as the electric field strength is reduced, as can be seen from fig. 2, the ratio alpha/beta of the electron ionization rate alpha and the hole ionization rate beta of silicon and germanium is increased, so that the avalanche noise of the waveguide-type germanium-silicon avalanche photodiode can be effectively reduced. In fig. 2, the broken line where the square point is located is used to indicate that the ratio α/β of the electron ionization rate α and the hole ionization rate β of the silicon material varies with the electric field intensity, and the broken line where the circular point is located is used to indicate that the ratio α/β of the electron ionization rate α and the hole ionization rate β of the germanium material varies with the electric field intensity.
Fig. 6 shows the bottom-up electric field intensity diagram of the waveguide-type silicon germanium photodetector of example 1 and the prior art at the middle position in the width direction of the Z-Y section. In fig. 6, the starting position of the horizontal axis is the lower surface of the slab waveguide 231, the horizontal axis represents the height from the lower surface of the slab waveguide 231, and the vertical axis represents the electric field strength. The red line in fig. 6 shows the electric field intensity curve of the waveguide type sige photodetector of the prior art, and the black line in fig. 6 shows the electric field intensity curve of the waveguide type sige photodetector of embodiment 1, and the simulation conditions of the two are identical except that a slope is provided on the bump waveguide. As can be seen from the simulation structure of fig. 6, the electric field strength at the region of the middle portion in the width direction of the ridge waveguide 23 and the germanium absorption layer 3 of embodiment 1 is reduced.
Preferably, the slope of the second boss portion 2322 is continuous with the slope of the first boss portion 2321; that is, the width of the side surface of the second protruding structure near the slab waveguide 231 is equal to the width of the side surface of the first protruding structure far from the slab waveguide 231, and the bottom edge of the slope of the second boss portion 2322 on the same side coincides with the top edge of the slope of the first boss portion 2321. By means of the arrangement, the boss waveguide 232 can be formed through one-time photoetching, the processing steps of the device are reduced, the processing difficulty is reduced, and the yield of the device is improved.
Further, the slope of the second boss portion 2322 coincides with the slope of the first boss portion 2321; i.e., the slope of the second bump structure is in the same plane as the same-side slope of the first boss portion 2321. By the arrangement, the difficulty of photoetching processing can be further reduced, and the yield of devices is improved.
Preferably, the first boss portion 2321 is disposed corresponding to the tapering structure 22; specifically, the middle vertical surface of the first boss portion 2321 in the width direction coincides with the middle vertical surface of the tapering structure 22 in the width direction. The arrangement can enable light of multiple modes to be coupled into the absorption layer 33 from two sides or near the tail end of the mode selection structure 32, so that the light field distribution in the absorption layer 33 is more uniform, and the responsivity of the waveguide-type germanium-silicon avalanche photodiode is improved.
Preferably, the slope of one side of the first boss portion 2321 coincides with the slope of the other side of the first boss portion 2321, and is symmetrical with respect to the midplane of the first boss portion 2321 in the width direction. Preferably, the second boss portion 2322 is disposed corresponding to the tapering structure 22; specifically, the middle vertical surface of the second boss portion 2322 in the width direction coincides with the middle vertical surface of the tapering structure 22 in the width direction. The slope of one side of the second boss portion 2322 coincides with the slope of the other side of the second boss portion 2322 and is symmetrical with respect to the middle vertical plane of the second boss portion 2322 in the width direction. By the arrangement, when light is coupled into the first boss portion 2321 from the tapering structure 22 or is coupled into the second boss portion 2322 from the first boss portion 2321, the light field distribution is symmetrical relative to the middle vertical plane of the first boss portion 2321 or the second boss portion 2322, the electric field generated by photo-generated carriers is symmetrically distributed relative to the middle vertical plane of the first boss portion 2321 or the second boss portion 2322, the electric fields of the slopes at two sides are symmetrical, serious electric field peaks of the slopes at one side are avoided, noise is reduced, and the responsiveness of the waveguide-type germanium-silicon avalanche photodiode is improved.
It should be noted that, in the solution of the present application, an error of 100nm is included in the vertical distance between the middle vertical surface of the second boss portion 2322 in the width direction and the middle vertical surface of the tapering structure 22 in the width direction due to the requirement of mass production or unavoidable errors in the industrialization process.
Specifically, the gradient of the first boss portion 2321 and the gradient of the second boss portion 2322 are both in the range of 0.5+.arctan θ+.1.5. It should be noted that, in other embodiments, the slope of the first boss portion 2321 and the slope of the second boss portion 2322 may be determined according to the design requirement of the actual waveguide type germanium-silicon avalanche photodiode, and may be designed with other slopes.
In a specific embodiment, the waveguide-type germanium-silicon avalanche photodiode further comprises a silicon dioxide cladding layer for protecting the silicon waveguide structure 2, the germanium absorption layer 3 and the metal electrode 4, and improving the stability of the waveguide-type germanium-silicon avalanche photodiode. The silicon dioxide cladding layer is arranged on the silicon dioxide buried layer 12, and the silicon waveguide structure 2, the germanium absorption layer 3 and the metal electrode 4 are all wrapped in the silicon dioxide cladding layer and the silicon dioxide buried layer 12.
The waveguide-type germanium-silicon avalanche photodiode provided by the invention is characterized in that a p+ doped silicon charge region and an avalanche breakdown region are arranged to have slopes. The slope is introduced to effectively avoid the concentration of an electric field at the edges of the p+ doped silicon charge region and the avalanche breakdown region, avoid local electric field peaks and effectively reduce the noise of the waveguide-type germanium-silicon avalanche photodiode; the electric field in the middle area of the waveguide-type germanium-silicon avalanche photodiode is slightly reduced, but the equivalent avalanche distance of the waveguide-type germanium-silicon avalanche photodiode is improved, and the gain is determined by the integral of the electric field intensity and the avalanche distance, and the gain of the waveguide-type germanium-silicon avalanche photodiode is basically kept unchanged by adding one to the other and subtracting one from the other. The avalanche noise of the waveguide-type germanium-silicon avalanche photodiode is also reduced to some extent due to the reduced electric field strength in the middle region of the active region of the waveguide-type germanium-silicon avalanche photodiode. Therefore, the avalanche noise of the waveguide-type germanium-silicon avalanche photodiode can be effectively reduced, the signal-to-noise ratio of the waveguide-type germanium-silicon avalanche photodiode in circuit use is increased, and the application in long-distance optical communication is realized.
Example 2
A method of making a waveguide-type germanium-silicon avalanche photodiode for making a waveguide-type germanium-silicon avalanche photodiode of example 1, comprising the steps of:
s1: an SOI wafer with a substrate layer 1 and a silicon waveguide layer is prepared, the incident waveguide 21, the tapered structure 22 and the slab waveguide 231 are formed on the silicon waveguide layer by etching through photolithography and etching, and a preset area of the slab waveguide 231 is doped to form a first silicon doped region. Specifically, an appropriate SOI wafer is selected as a starting substrate, and the SOI wafer generally includes a silicon substrate 11, a buried silicon oxide layer 12, and a silicon waveguide layer. Then, the incident waveguide 21, the tapered structure 22 and the slab waveguide 231 are etched on the silicon waveguide layer by using photolithography and etching technology, which specifically includes: a photoresist is spin coated on the silicon waveguide layer to form a predetermined waveguide pattern through an exposure and development process. Next, the silicon waveguide layer is etched according to a pattern using dry etching (e.g., reactive ion etching) while forming the incident waveguide 21, the tapered structure 22, and the slab waveguide 231. Finally, the remaining photoresist is removed. Next, a first silicon doped region is prepared in the slab waveguide 231. This step typically requires the use of an ion implantation or diffusion process, including in particular: an appropriate dopant (e.g., phosphorus, arsenic, etc.) is selected and then brought into a predetermined region of slab waveguide 231 by ion implantation or diffusion. Thereby forming a first silicon doped region in the slab waveguide 231.
S2: a boss waveguide 232 is prepared on the surface of the slab waveguide 231. As shown in the drawings, the method comprises the following steps of, in particular,
s2.1: and epitaxially growing a boss waveguide 232 material on the surface of the slab waveguide 231. Specifically, the sample treated in step S1 is cleaned and pretreated to prepare for epitaxial growth. The pre-treated sample is placed in an epitaxial growth apparatus, such as a Chemical Vapor Deposition (CVD) or Molecular Beam Epitaxy (MBE) apparatus. A new layer of silicon material, i.e., the material of the boss waveguide 232, is formed on the surface of the slab waveguide 231 by Chemical Vapor Deposition (CVD) or Molecular Beam Epitaxy (MBE) or the like.
S2.2: and preparing a second silicon doped region on a preset region of the upper surface of the formed boss waveguide 232 material by ion implantation. Specifically, a second silicon doped region is formed by selecting an appropriate dopant (e.g., boron, aluminum, gallium, indium, etc.), and using an ion implantation apparatus to accelerate and drive the dopant ions into a predetermined region of the mesa waveguide 232 material. The process can control the type, energy and dosage of the implanted ions, so that the depth and doping concentration of the doped region are adjusted, and the thickness of the formed second silicon doped region is consistent with the thickness of the second boss structure set in the design of the device. The position of the preset area is also consistent with the position of the second boss structure set during device design.
S2.3: and forming the boss waveguide 232 at a preset position on the doped boss waveguide 232 material by photoetching and dry etching. Specifically, a photoresist layer is uniformly spin-coated on the doped boss waveguide 232 material. This step is required to ensure that the photoresist thickness is uniform in order to obtain an accurate pattern during subsequent exposure and development. And exposing the photoresist according to a preset pattern by using a photoetching machine. During exposure, the photoresist reacts chemically under the irradiation of light so that the photoresist in the exposed area becomes soluble by the developer. The exposed photoresist is partially dissolved in a developer to form an initial stepped pattern at a predetermined position. Baking the developed sample. During baking, the photoresist undergoes physical and chemical changes, including curing, polycondensation, reflow, and the like. In particular, under some high temperature or long baking conditions, the photoresist may reflow, i.e., the flow of photoresist over the surface, such that the originally sharp steps become smooth and sloped. This results in a smoother and more continuous stepped structure with a slope. The wafer with the stepped photoresist is etched using a dry etch, such as a reactive ion etch. During this process, the photoresist acts as a guard against etching of the underlying silicon material. Since the photoresist is stepped, the etched silicon may also have a stepped structure, thereby forming the boss waveguide 232 including the first boss portion 2321 and the second boss portion 2322. The predetermined position also corresponds to the position of the boss waveguide 232 set at the time of device design.
S3: the germanium absorption layer 3 of the waveguide-type germanium-silicon avalanche photodiode is prepared by epitaxy and dry etching. Specifically, the sample treated in step S2 is cleaned and pretreated to prepare for epitaxial growth. Placing the pretreated sample into an epitaxial growth apparatus, forming a germanium layer on the surface of the slab waveguide 231 by Chemical Vapor Deposition (CVD) or Molecular Beam Epitaxy (MBE) and other techniques, and then preparing a germanium doped region 32 on the material of the prepared germanium absorbing layer 3, which specifically includes: appropriate dopants (e.g., boron, aluminum, gallium, indium, etc.) are selected and then ion-implanted into predetermined regions of the germanium layer by ion implantation or diffusion. Thereby forming a germanium-doped region 32 in the germanium layer. The process can control the type, energy and dosage of the implanted ions, thereby adjusting the depth and doping concentration of the germanium-doped region 32 to make the thickness of the formed germanium-doped region 32 consistent with the thickness of the germanium-doped region 32 set during device design. The location of the predetermined region also corresponds to the location of the germanium-doped region 32 that is set during device design. Next, excess germanium material is removed by photolithography and etching to form the germanium absorber layer 3.
S4: a first electrode 41 and a second electrode 42 are prepared on the surface of the slab waveguide 231 by depositing a thin film and dry etching, and a third electrode 43 is prepared on the surface of the germanium absorption layer 3. Specifically, the sample formed in the step S4 is placed in a vacuum deposition machine, and a layer of metal film is deposited on the surface of the device by physical vapor deposition or chemical vapor deposition. Commonly used metals include aluminum, copper, titanium, tungsten, etc., the choice of which needs to be determined by the requirements and performance of the device. A mask is prepared on a metal thin film by a photolithography technique, and the mask needs to include information of the shape and position of an electrode. The mask may be made using photoresist or other materials, the thickness and shape of which need to be determined according to the requirements of the electrode. The sample is put into a dry etcher, and dry etching is performed using an oxide or oxygen gas or the like, and the metal thin film not protected by the mask is etched away to form the first electrode 41 and the second electrode 42 over the slab waveguide 231 and the third electrode 43 on the germanium absorbing layer 3.
S5: and depositing a silicon dioxide film to prepare a silicon dioxide cladding layer, and wrapping the silicon waveguide structure 2, the germanium absorption layer 3 and the metal electrode 4. And (3) placing the sample obtained in the step (S4) into a vacuum deposition machine, and depositing a layer of silicon dioxide film on the surface of the device by using methods such as chemical vapor deposition or physical vapor deposition. The silicon dioxide film can be used as a silicon dioxide cladding layer of a device, protects the device from the external environment, and can be used as a base layer for subsequent processing.
Further, the metal electrode 4 is exposed by photolithography and dry etching of the silica cladding layer to facilitate connection of external leads to the electrode.
Example 3
A chip incorporating a waveguide-type silicon germanium avalanche photodiode of embodiment 1 above. Specifically, the receiving end of the chip is provided with a plurality of waveguide-type germanium-silicon avalanche photodiodes provided by any of the embodiments. The waveguide-type germanium-silicon avalanche photodiode provided by any embodiment of the invention has lower avalanche noise, so that the receiving end of the chip provided by the invention also has lower avalanche noise, the signal-to-noise ratio can be improved, and the remote optical fiber communication can be realized.
It should be noted that the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same. While the invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents substituted for elements thereof without departing from the scope of the invention, which is to be encompassed by the appended claims.
Claims (10)
1. A waveguide-type germanium-silicon avalanche photodiode characterized by: the semiconductor device comprises a substrate layer, a silicon waveguide structure, a germanium absorption layer and a metal electrode from bottom to top in sequence; wherein,
the substrate layer comprises a silicon substrate and a silicon dioxide buried layer;
the silicon waveguide structure comprises an incident waveguide, a tapered structure and a ridge waveguide which are connected in sequence; wherein,
the ridge waveguide comprises a slab waveguide and a boss waveguide which is positioned in the middle of the slab waveguide and is arranged on the surface of the slab waveguide;
the slab waveguide is connected with the tapering structure and comprises a first silicon doping area, wherein the first silicon doping area is used for carrying out first type doping;
the boss waveguide comprises a first boss part and a second boss part from bottom to top; wherein,
the first boss part is an avalanche breakdown region and is arranged on the surface of the slab waveguide, which is far away from the silicon dioxide buried layer, the first boss part is in a step shape with slopes on two sides, and the width of the first protruding structure, which is far away from the surface of one side of the slab waveguide, is larger than the width of the first protruding structure, which is close to the surface of one side of the slab waveguide;
the second boss part comprises a second silicon doping area for doping of a second type, is arranged on the surface of the first boss part, which is far away from the slab waveguide, is in a step shape with slopes on two sides, and the width of the second protruding structure, which is far away from the surface of one side of the slab waveguide, is larger than the width of the second protruding structure, which is close to the surface of one side of the slab waveguide;
the metal electrode comprises a first electrode, a second electrode and a third electrode; wherein,
the first electrode is arranged on the surface of the slab waveguide and is arranged on the slab waveguide at one side of the boss waveguide;
the second electrode is arranged on the surface of the slab waveguide and is arranged on the slab waveguide at the other side of the slab waveguide;
and the third electrode is arranged on the surface of the germanium absorption layer.
2. The waveguide-type silicon-germanium avalanche photodiode of claim 1, wherein: the slope of the second boss portion is continuous with the slope of the first boss portion.
3. The waveguide-type silicon-germanium avalanche photodiode of claim 2, wherein: the slope of the second boss portion coincides with the slope of the first boss portion.
4. The waveguide-type silicon-germanium avalanche photodiode of claim 1, wherein: a middle vertical surface of the first boss part along the width direction coincides with a middle vertical surface of the tapering structure along the width direction.
5. The waveguide-type silicon-germanium avalanche photodiode of claim 4, wherein: the slope of one side of the first boss portion is identical to the slope of the other side of the first boss portion, and is symmetrical with respect to the midplane of the first boss portion in the width direction.
6. The waveguide-type silicon-germanium avalanche photodiode of claim 1, wherein: the gradient of the first boss portion and the gradient of the second boss portion are both in the range of 0.5-1.5 arctan θ.
7. A method of making a waveguide-type silicon-germanium avalanche photodiode according to any one of claims 1-6, comprising the steps of:
preparing an SOI wafer with a substrate layer and a silicon waveguide layer, etching the silicon waveguide layer of the SOI wafer by photoetching and etching to form an incident waveguide, a tapered structure and a slab waveguide, and doping a preset area of the slab waveguide to form a first silicon doped area;
preparing a boss waveguide on the surface of the slab waveguide; the boss waveguide comprises a first boss part and a second boss part from bottom to top; wherein,
the first boss part is an avalanche breakdown region and is arranged on the surface of the slab waveguide, which is far away from the silicon dioxide buried layer, the first boss part is in a step shape with slopes on two sides, and the width of the first protruding structure, which is far away from the surface of one side of the slab waveguide, is larger than the width of the first protruding structure, which is close to the surface of one side of the slab waveguide;
the second boss part comprises a second silicon doping area for doping of a second type, is arranged on the surface of the first boss part, which is far away from the slab waveguide, is in a step shape with slopes on two sides, and the width of the second protruding structure, which is far away from the surface of one side of the slab waveguide, is larger than the width of the second protruding structure, which is close to the surface of one side of the slab waveguide;
preparing a germanium absorption layer of the waveguide-type germanium-silicon avalanche photodiode by epitaxy and dry etching;
and preparing a first electrode and a second electrode above the slab waveguide by depositing a film and dry etching, and preparing a third electrode above the germanium absorption layer.
8. The method for preparing the slab waveguide according to claim 7, wherein the preparing the slab waveguide on the surface of the slab waveguide specifically comprises:
epitaxially growing a boss waveguide material on the surface of the slab waveguide;
preparing a second silicon doped region by ion implantation in a preset region on the upper surface of the formed boss waveguide material;
and forming the boss waveguide at a preset position on the doped boss waveguide material by photoetching and dry etching.
9. The method of manufacturing according to claim 7, wherein: the method further comprises the steps of depositing a silicon dioxide film to prepare a silicon dioxide cladding layer, and wrapping the silicon waveguide structure, the germanium absorption layer and the metal electrode.
10. A chip having the waveguide-type germanium-silicon avalanche photodiode according to any one of claims 1 to 6 built therein.
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