Preparation method of germanium photodetector and germanium photodetector
By forming a germanium nucleation layer at low temperature and a germanium absorption layer at high temperature and then doping it in situ during the fabrication of the germanium photodetector, the problems of germanium-silicon lattice mismatch and doping damage were solved, improving device performance and process compatibility, and reducing dark current.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- GUANGZHOU ZENGXIN TECH CO LTD
- Filing Date
- 2026-04-23
- Publication Date
- 2026-07-21
AI Technical Summary
In the fabrication of germanium photodetectors, lattice mismatch between germanium and silicon leads to high-density through-dislocations, increasing dark current. Furthermore, the doping method causes lattice damage, limiting bandwidth and responsivity.
A germanium nucleation layer is formed at low temperature on a silicon substrate, a germanium absorption layer is formed at high temperature, and a doped germanium layer is formed through in-situ doping technology. Electrodes are formed by combining deposition and etching processes to alleviate lattice mismatch and optimize the PN junction surface.
This technology improves the responsivity and bandwidth of germanium photodetectors, reduces dark current, optimizes carrier transit time, achieves efficient generation and collection of photogenerated carriers, and is compatible with CMOS processes, thus reducing manufacturing costs.
Smart Images
Figure CN122438409A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of semiconductor technology, and in particular to a method for fabricating a germanium photodetector and the germanium photodetector itself. Background Technology
[0002] Germanium photodetectors are key devices specifically designed to detect infrared light and convert it into electrical signals. They are characterized by high responsivity, high bandwidth, and low dark current. Therefore, germanium-based photodetectors have a wide range of applications.
[0003] However, in the fabrication of germanium photodetectors, epitaxially growing a high-quality germanium layer on a silicon substrate faces two problems: (1) Due to the lattice mismatch between germanium and silicon, a high density of through-dislocations will be generated during the epitaxial growth of the germanium layer on the silicon substrate. This will significantly increase the dark current of the germanium photodetector and severely degrade the device performance. (2) The doping method of injecting dopant ions into the germanium layer of the photodetector and then annealing it will cause lattice damage to the germanium layer and may cause diffusion of dopant ions, thereby limiting the bandwidth and responsivity of the photodetector. Summary of the Invention
[0004] This invention provides a method for fabricating a germanium photodetector and a germanium photodetector. By improving the quality of each germanium layer, the responsivity and bandwidth of the germanium photodetector are improved, and the dark current of the germanium photodetector is reduced.
[0005] According to a first aspect of the present invention, the present invention provides a method for fabricating a germanium photodetector, comprising: Provide silicon substrates; At a first temperature, a germanium nucleation layer is formed on a portion of the surface of the silicon substrate; At a second temperature, a germanium absorption layer is formed on the germanium nucleation layer, wherein the second temperature is higher than the first temperature; A germanium-doped layer is formed on the germanium absorption layer by in-situ doping technology, and the silicon substrate has a different conductivity type from the germanium-doped layer. A first electrode is formed on the surface of the silicon substrate; A second electrode is formed on the surface of the germanium-doped layer.
[0006] Optionally, a doped germanium layer is formed on the germanium absorber layer using in-situ doping technology, including: In the epitaxial growth reaction chamber, and during the epitaxial growth of germanium on the germanium absorber layer, dopant ions are introduced into the epitaxial growth reaction chamber.
[0007] Optionally, the ion doping concentration of the germanium-doped layer is: 1e 17 cm -3 up to 1e 19 cm-3 .
[0008] Optionally, the temperature range of the first temperature is 300°C to 500°C.
[0009] Optionally, the range of the second temperature is 600°C to 750°C.
[0010] Optionally, a dielectric layer is formed on the surface of the germanium-doped layer, wherein the second electrode penetrates the dielectric layer. Optionally, the thickness of the germanium nucleation layer ranges from 15 nm to 25 nm.
[0011] Optionally, the thickness of the germanium absorber layer is in the range of 450nm to 550nm.
[0012] Optionally, the thickness of the in-situ doped germanium layer ranges from 95 nm to 105 nm.
[0013] According to a second aspect of the present invention, a germanium photodetector is provided, prepared using the above-described method for preparing a germanium photodetector, comprising: silicon substrate; A germanium nucleation layer is located on a portion of the surface of the silicon substrate, and the germanium nucleation layer is formed at a first temperature; A germanium absorption layer is located on the germanium nucleation layer, which is formed at a second temperature, which is higher than the first temperature. A germanium-doped layer is located on the germanium absorption layer. The germanium-doped layer is formed by in-situ doping technology. The silicon substrate has a different conductivity type from the germanium-doped layer. The first electrode is located on the surface of the silicon substrate; The second electrode is located on the surface of the germanium-doped layer.
[0014] Compared with the prior art, the technical solution of the embodiments of the present invention has the following beneficial effects: In the fabrication method and the germanium photodetector of this invention, a germanium nucleation layer is formed on a portion of the surface of a silicon substrate at a first temperature, and a germanium absorption layer is formed on the germanium nucleation layer at a second temperature, which is higher than the first temperature. This alleviates the lattice mismatch between silicon and germanium materials, improves the quality of the germanium nucleation layer, thereby reducing the dark current of the germanium photodetector and enhancing its performance. Furthermore, a doped germanium layer is formed on the germanium absorption layer using in-situ doping technology. Since the silicon substrate and the doped germanium layer have different conductivity types, a first electrode is formed on the surface of the silicon substrate, and a second electrode is formed on the surface of the doped germanium layer. Therefore, the doped germanium layer formed through in-situ doping technology creates a steep PN junction surface with few defects, reducing the junction capacitance, optimizing the carrier transit time, and improving the bandwidth and response speed of the germanium photodetector. Furthermore, since the germanium absorption layer is located on the germanium nucleation layer and below the germanium-doped layer, it is protected by both the germanium-doped layer and the germanium nucleation layer. Therefore, the germanium absorption layer has a high quality, ensuring the efficient generation and collection of photogenerated carriers, thereby improving the response speed of the germanium photodetector. Attached Figure Description
[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0016] Figures 1-6 This is a schematic diagram of the structure corresponding to each step in the fabrication method of the germanium photodetector according to an embodiment of the present invention. Attached image description: 100-Silicon substrate; 110 - Shallow trench; 200-germanium nucleation layer; 300-germanium absorber layer; 400-doped germanium layer; 500 - Dielectric layer; 600 - First electrode; 700 - Second electrode. Detailed Implementation
[0018] As described in the background section, the present invention aims to solve the technical problem of how to improve the quality of each germanium layer, improve the responsivity and bandwidth of the germanium photodetector, and reduce the dark current of the germanium photodetector.
[0019] In view of this, the present invention proposes a method for fabricating a germanium photodetector, comprising: providing a silicon substrate; forming a germanium nucleation layer on a portion of the surface of the silicon substrate at a first temperature; forming a germanium absorption layer on the germanium nucleation layer at a second temperature higher than the first temperature; forming a germanium-doped layer on the germanium absorption layer by in-situ doping, wherein the silicon substrate and the germanium-doped layer have different conductivity types; forming a first electrode on the surface of the silicon substrate; and forming a second electrode on the surface of the germanium-doped layer. This improves the quality of each germanium layer, thereby enhancing the responsivity and bandwidth of the germanium photodetector and reducing its dark current.
[0020] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.
[0021] The technical solution of the present invention will be described in detail below with reference to specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.
[0022] Figures 1-6 This is a schematic diagram of the structure corresponding to each step in the fabrication method of the germanium photodetector according to an embodiment of the present invention.
[0023] Please refer to Figure 1 , providing silicon substrate 100.
[0024] In this embodiment, the silicon substrate 100 can be silicon or SOI (Silicon On Insulator).
[0025] As an example, the silicon substrate 100 has shallow trenches 110, the bottom and walls of which are exposed on the surface of the silicon substrate 100. In this embodiment, the subsequent germanium nucleation layer is located on the surface of the silicon substrate 100 outside the shallow trenches 110.
[0026] Please refer to Figure 2 At a first temperature, a germanium nucleation layer 200 is formed on a portion of the surface of the silicon substrate 100.
[0027] In one alternative embodiment, forming a germanium nucleation layer 200 on a portion of the surface of the silicon substrate 100 at a first temperature may include: forming an epitaxial window on the surface of the silicon substrate 100, the epitaxial window being located on the surface of the silicon substrate 100 outside the shallow trench 110; lowering the temperature of the reaction chamber to the first temperature; pretreating the silicon substrate 100 in the reaction chamber using silane (SiH4) and germanane (GeH4); and epitaxially forming a germanium nucleation layer 200 on the surface of the silicon substrate 100 in the reaction chamber.
[0028] In this embodiment, a germanium nucleation layer 200 is formed by low-temperature nucleation technology, thereby effectively suppressing through dislocations caused by lattice mismatch between the silicon substrate 100 and the germanium nucleation layer 200, reducing the dark current of the germanium photodetector, and improving the performance of the germanium photodetector.
[0029] In a preferred embodiment, the first temperature range is 300°C to 500°C. However, it should be understood that the invention is not limited to this, and the first temperature may be less than 500°C.
[0030] Specifically, there is a lattice mismatch of 3.8% to 4.2% between germanium (Ge) and silicon (Si). If a germanium nucleation layer 200 is grown directly on the surface of a silicon substrate 100 at a high temperature greater than 600°C, the growth mode will tend to be a Volmer-Weber mode due to the large difference in surface energy between the two. That is, Ge atoms tend to aggregate into small islands to release the stress caused by the lattice mismatch. However, at a low temperature of 300°C-500°C, the surface diffusion ability of Ge atoms is significantly suppressed. Atoms cannot migrate long distances to find the "lowest energy" nucleation point to form large islands, but instead spread out in smaller islands or a more two-dimensional layered pattern. This growth method can form a more continuous and smoother germanium nucleation layer 200, laying the foundation for subsequent high-temperature growth and avoiding local stress concentration and high defects caused by three-dimensional island growth. At high temperatures, when a germanium nucleation layer is formed, the stress caused by the lattice mismatch between germanium and silicon is immediately released through the generation of penetrating dislocations. These penetrating dislocations extend throughout the subsequently formed germanium absorption layer, creating leakage current channels. However, at lower temperatures (300°C-500°C), the growth of the germanium nucleation layer reduces the mobility of germanium atoms and alters the stress release mechanism. Although lattice mismatch also exists in the germanium nucleation layer grown at low temperatures, the defects and penetrating dislocations are confined to a certain range and do not extend upwards into the subsequently grown germanium absorption layer in large quantities. This results in a higher quality germanium absorption layer.
[0031] In this embodiment, the pretreatment of silicon substrate 100 with silane (SiH4) and germanane (GeH4) serves to remove native oxides or impurities from the surface of silicon substrate 100, ensuring that the germanium nucleation layer grows on silicon rather than on native oxides or impurities. In addition, hydrogen atoms can be used to protect the cleaned surface of the silicon substrate, avoiding secondary contamination. This provides a chemically clean and atomically flat surface of silicon substrate 100 for the formation of the germanium nucleation layer, thereby reducing the generation of defects in the grown germanium nucleation layer.
[0032] In a preferred embodiment, the thickness of the germanium nucleation layer 200 can be in the range of 15nm to 25nm.
[0033] In this embodiment, the germanium nucleation layer 200 of this thickness range releases the lattice mismatch stress at the silicon-germanium interface and transforms it into a localized dislocation network, thereby protecting the subsequently formed germanium absorption layer and enabling the formed detector to have a lower dark current.
[0034] Please refer to Figure 3 At a second temperature, a germanium absorption layer 300 is formed on the germanium nucleation layer 200, and the second temperature is higher than the first temperature.
[0035] In a preferred embodiment, the second temperature can be in the range of 600°C to 750°C.
[0036] In this embodiment, setting the second temperature within this range can ensure the migration rate of germanium atoms, thereby achieving the generation of a high-quality germanium absorber layer 300 at a high speed, and preventing the germanium material from being decomposed, doped out of control, or damaged due to high temperature.
[0037] In one embodiment, the thickness of the germanium absorber layer 300 ranges from 450 nm to 550 nm.
[0038] In this embodiment, the thickness of the germanium absorption layer 300 is set within this range, which ensures the light absorption rate of the germanium absorption layer (i.e., ensures the responsivity of the device) and also ensures that the germanium absorption layer is not too thick, thus excessively increasing the thickness of the formed detector.
[0039] Please refer to Figure 4 On the germanium absorber layer 300, a germanium-doped layer 400 is formed by in-situ doping technology. The silicon substrate 100 and the germanium-doped layer 400 have different conductivity types.
[0040] In one embodiment, forming a doped germanium layer 400 on the germanium absorber layer 300 using in-situ doping technology may include: During the epitaxial growth reaction chamber, and during the epitaxial growth of germanium on the germanium absorber layer 300, dopant ions are introduced into the epitaxial growth reaction chamber.
[0041] In one embodiment, the silicon substrate 100 is doped with P-type ions, and the germanium doped layer is doped with N-type ions.
[0042] In another embodiment, the silicon substrate 100 is doped with N-type ions, and the germanium doped layer is doped with P-type ions.
[0043] In this embodiment, the germanium-doped layer is formed using in-situ doping technology. This reduces the lattice damage caused by ion implantation to the germanium layer, which is typically achieved in existing technologies where a germanium layer is first formed and then ion implanted. Furthermore, the germanium-doped layer obtained through in-situ doping has a more uniform ion distribution and higher ion implantation precision. This is beneficial for improving the consistency and yield of the germanium photodetector's performance.
[0044] In one embodiment, the ion doping concentration of the germanium-doped layer 400 is 1e17cm. -3 up to 1e 19 cm -3 .
[0045] In this embodiment, the ion doping concentration of the germanium-doped layer 400 is set within this range, which ensures that the germanium-doped layer can form a low ohmic contact with the metal, while avoiding free carrier absorption loss due to excessive concentration.
[0046] In one embodiment, the thickness of the in-situ doped germanium layer ranges from 95 nm to 105 nm.
[0047] In this embodiment, the germanium doped layer of this thickness range can achieve the best balance between ensuring PN junction quality, realizing low-resistance ohmic contact and avoiding light absorption loss, thereby optimizing key performance indicators such as dark current, responsivity and bandwidth of germanium photodetector.
[0048] Please refer to Figure 5 A dielectric layer 500 is formed on the surface of the germanium-doped layer 400.
[0049] In this embodiment, a dielectric layer 500 located on the surface of the germanium-doped layer 400 can be formed by a deposition process.
[0050] In this embodiment, the dielectric layer 500 can be silicon dioxide. Of course, the present invention is not limited thereto, and the dielectric layer 500 can also be aluminum oxide (Al2O3).
[0051] In this embodiment, a dielectric layer 500 is formed on the germanium doped layer 400 to protect the germanium doped layer 400 and improve the quality of the germanium doped layer.
[0052] Please refer to Figure 6 A first electrode 600 is formed on the surface of a silicon substrate 100.
[0053] Please continue to refer to this. Figure 6A second electrode 700 is formed on the surface of the germanium-doped layer 400.
[0054] In this embodiment, the second electrode 700 penetrates the dielectric layer 500.
[0055] Specifically, the dielectric layer 500 can be etched to form electrode vias that penetrate the dielectric layer 500.
[0056] Furthermore, electrode material is filled into the electrode via to form a second electrode 700, such that the second electrode 700 is in contact with the germanium-doped layer 400.
[0057] In this embodiment, when the photon energy of the infrared light illuminating the germanium photodetector is greater than or equal to the germanium bandgap, the photon energy is absorbed by electrons in the valence band, thereby exciting electrons to transition from the valence band to the conduction band and generating photogenerated carriers. The germanium bandgap is 0.62 eV to 0.72 eV, corresponding to a wavelength range of approximately 1720 nm to 2000 nm. Specifically, under room temperature operating conditions, the germanium bandgap is approximately 0.66 eV to 0.67 eV, corresponding to an intrinsic absorption wavelength threshold of approximately 1850 nm to 1880 nm. Considering temperature variations and material doping effects, the germanium bandgap can fluctuate within the range of 0.62 eV to 0.72 eV, with the corresponding absorption cutoff wavelength covering the 1720 nm to 2000 nm range. This absorption cutoff wavelength is beneficial for exciting photogenerated carriers in the germanium absorption layer, which are then collected by the first and second electrodes to form a photocurrent.
[0058] In the fabrication method of the germanium photodetector provided in the above embodiments of the present invention, a germanium nucleation layer 200 is formed on a portion of the surface of the silicon substrate 100 at a first temperature, and a germanium absorption layer 300 is formed on the germanium nucleation layer 200 at a second temperature, where the second temperature is higher than the first temperature. This alleviates the lattice mismatch between the silicon and germanium materials, improves the quality of the germanium nucleation layer 200, thereby reducing the dark current of the germanium photodetector and improving its performance. Furthermore, a doped germanium layer 400 is formed on the germanium absorption layer 300 using in-situ doping technology. Since the silicon substrate 100 and the doped germanium layer 400 have different conductivity types, a first electrode 600 is formed on the surface of the silicon substrate 100, and a second electrode 700 is formed on the surface of the doped germanium layer 400. Therefore, the doped germanium layer 400 formed through in-situ doping technology creates a steep PN junction surface with few defects, reducing the junction capacitance, optimizing the carrier transit time, and improving the bandwidth and response speed of the germanium photodetector. Furthermore, since the germanium absorption layer 300 is located on the germanium nucleation layer 200 and below the doped germanium layer 400, the germanium absorption layer 300 is protected by the doped germanium layer 400 and the germanium nucleation layer 200. Therefore, the germanium absorption layer 300 has a high quality, which ensures the efficient generation and collection of photogenerated carriers, thereby improving the response speed of the germanium photodetector.
[0059] Furthermore, in the above-mentioned method for fabricating germanium photodetectors, a germanium nucleation layer 200, a germanium absorption layer 300, and a germanium-doped layer 400 are formed on a silicon substrate through epitaxial growth and doping techniques. A dielectric layer 500 and electrodes located within the dielectric layer 500 are formed based on deposition and etching processes. This allows the fabrication process of the germanium photodetector to be matched with the CMOS process flow. The fabrication of the germanium photodetector can be integrated into the CMOS front-end or intermediate process stage, achieving matching of different device processes. Compared with the traditional method of customizing independent process fabrication modules, this reduces process development time and saves manufacturing costs.
[0060] Accordingly, this invention also provides a germanium photodetector formed by the above-described method for preparing a germanium photodetector. Please refer to [link / reference]. Figure 6 It may include: a silicon substrate 100, a germanium nucleation layer 200, a germanium absorption layer 300, a doped germanium layer 400, a first electrode 600, and a second electrode 700.
[0061] The germanium nucleation layer 200 is located on a portion of the surface of the silicon substrate 100, and the germanium nucleation layer 200 is formed at a first temperature.
[0062] The germanium absorber layer 300 is located on the germanium nucleation layer 200, which is formed at a second temperature, which is higher than the first temperature.
[0063] The germanium-doped layer 400 is located on the germanium absorber layer 300. The germanium-doped layer 400 is formed by in-situ doping technology. The silicon substrate 100 and the germanium-doped layer 400 have different conductivity types.
[0064] The first electrode 600 is located on the surface of the silicon substrate 100.
[0065] The second electrode 700 is located on the surface of the germanium-doped layer 400.
[0066] In the germanium photodetector provided in the above embodiments of the present invention, a germanium nucleation layer 200 is formed on a portion of the surface of the silicon substrate 100 at a first temperature, and a germanium absorption layer 300 is formed on the germanium nucleation layer 200 at a second temperature, which is higher than the first temperature. Therefore, the lattice mismatch between the silicon and germanium materials is alleviated, the quality of the germanium nucleation layer 200 is improved, thereby reducing the dark current of the germanium photodetector and improving its performance. Furthermore, a doped germanium layer 400 is formed on the germanium absorption layer 300 using in-situ doping technology. Since the silicon substrate 100 and the doped germanium layer 400 have different conductivity types, a first electrode 600 is formed on the surface of the silicon substrate 100, and a second electrode 700 is formed on the surface of the doped germanium layer 400. Therefore, the doped germanium layer 400 formed by in-situ doping technology forms a steep PN junction surface with few defects, reducing the junction capacitance, optimizing the carrier transit time, and improving the bandwidth and response speed of the germanium photodetector. Furthermore, since the germanium absorption layer 300 is located on the germanium nucleation layer 200 and below the doped germanium layer 400, the germanium absorption layer 300 is protected by the germanium nucleation layer 200 and the doped germanium layer 400, resulting in high quality and ensuring efficient generation and collection of photogenerated carriers, thereby improving the response speed of the germanium photodetector.
[0067] Since the germanium photodetector in this embodiment corresponds to the fabrication method of the germanium photodetector described above, please refer to the detailed explanation of the corresponding part of the fabrication method of the germanium photodetector for the explanation of each feature structure in the germanium photodetector in this embodiment, and it will not be repeated here.
[0068] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.
Claims
1. A method for fabricating a germanium photodetector, characterized in that, The method includes: Provide silicon substrates; At a first temperature, a germanium nucleation layer is formed on a portion of the surface of the silicon substrate; At a second temperature, a germanium absorption layer is formed on the germanium nucleation layer, wherein the second temperature is higher than the first temperature; A germanium-doped layer is formed on the germanium absorption layer by in-situ doping technology, and the silicon substrate has a different conductivity type from the germanium-doped layer. A first electrode is formed on the surface of the silicon substrate; A second electrode is formed on the surface of the germanium-doped layer.
2. The method for fabricating a germanium photodetector as described in claim 1, characterized in that, A doped germanium layer is formed on the germanium absorber layer using in-situ doping technology, including: In the epitaxial growth reaction chamber, and during the epitaxial growth of germanium on the germanium absorber layer, dopant ions are introduced into the epitaxial growth reaction chamber.
3. The method for fabricating a germanium photodetector as described in claim 2, characterized in that, The ion doping concentration of the germanium-doped layer is: 1e 17 cm -3 up to 1e 19 cm -3 .
4. The method for fabricating a germanium photodetector as described in claim 1, characterized in that, The temperature range of the first temperature is 300°C to 500°C.
5. The method for fabricating a germanium photodetector as described in claim 1, characterized in that, The second temperature range is 600°C to 750°C.
6. The method for fabricating a germanium photodetector as described in claim 1, characterized in that, Also includes: A dielectric layer is formed on the surface of the germanium-doped layer, wherein the second electrode penetrates the dielectric layer.
7. The method for fabricating a germanium photodetector as described in claim 1, characterized in that, The thickness of the germanium nucleation layer ranges from 15 nm to 25 nm.
8. The method for fabricating a germanium photodetector as described in claim 1, characterized in that, The thickness of the germanium absorber layer ranges from 450 nm to 550 nm.
9. The method for fabricating a germanium photodetector as described in claim 1, characterized in that, The thickness of the in-situ doped germanium layer ranges from 95 nm to 105 nm.
10. A germanium photodetector, characterized in that, include: silicon substrate; A germanium nucleation layer is located on a portion of the surface of the silicon substrate, and the germanium nucleation layer is formed at a first temperature; A germanium absorption layer is located on the germanium nucleation layer, which is formed at a second temperature, which is higher than the first temperature. A germanium-doped layer is located on the germanium absorption layer. The germanium-doped layer is formed by in-situ doping technology. The silicon substrate has a different conductivity type from the germanium-doped layer. The first electrode is located on the surface of the silicon substrate; The second electrode is located on the surface of the germanium-doped layer.