High-responsivity photoelectric detector using air cavity

Abstract

The invention discloses a high-responsivity photoelectric detector using an air cavity, which is characterized in that a dilution waveguide, the air cavity and a photoelectric detector are integrated on a semi-insulating substrate, and the air cavity is obtained in a dilution waveguide layer in an etching and wafer bonding mode; and finally, the transition waveguide and the photoelectric detector table are etched according to a conventional technological process. When the photoelectric detector works, the vast majority of signal light incident from the side surface is gradually coupled to the active region under the guidance of the dilution waveguide in front of the air cavity, and the leakage of the light from the active region to the dilution waveguide and the semi-insulating substrate below is effectively inhibited due to the large refractive index difference between the air cavity and the surrounding material; most of the light is limited in the active area and is converted into an electric signal after being absorbed by the absorption layer. According to the air cavity structure, the penetration depth of evanescent waves at the interface of the dilution waveguide and the air cavity can be reduced, the concentration degree of light in an active area is effectively improved, and the responsivity of the photoelectric detector is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of optoelectronic technology, and particularly relates to a high-response photodetector using an air cavity. BACKGROUND

[0002] With the rapid development of optical communication technology, and the wide application of 5G networks, data center interconnection and next-generation optical fiber communication systems, the performance requirements of core devices at the receiving and transmitting ends are increasingly improved. As a core device at the optical receiving end, the bandwidth, responsivity, sensitivity and linearity of a photodetector directly determine the transmission rate, bandwidth and reliability of an optical communication system.

[0003] Traditional photodetectors mainly have PIN photodiodes or avalanche photodiodes. The former has the characteristics of simple structure, low noise and high bandwidth, but the responsivity and carrier transport time are mutually restricted, and it is difficult to simultaneously consider both performances. The latter uses avalanche effect under a high electric field to amplify the signal, and the responsivity is usually greater than 1A / W, but the multiplication noise introduced during operation, as well as the high operating voltage and power consumption, make it face challenges in the next-generation application scenarios that pursue low noise and low power consumption.

[0004] The signal light incident direction and the carrier transport direction of the waveguide-type photodetector based on evanescent wave coupling are perpendicular to each other during operation, breaking the restriction relationship between the responsivity and the carrier transport time in the PIN photodiode, effectively considering the responsivity and the bandwidth, and at the same time, due to the evanescent wave coupling characteristic, it will not cause oversaturation of a part of the absorption region. The absorption layer of the waveguide-type photodetector based on evanescent wave coupling is usually designed to be very thin, and a larger area is used to obtain high responsivity, but this structure will introduce a larger junction capacitance, so that the bandwidth of the photodetector is limited by the RC constant. In recent years, some types of photodetectors that consider both responsivity and bandwidth have been proposed. For example, in photodetectors based on III-V semiconductor materials, a single-row carrier photodetector places the absorption region at one end of the P contact layer, so that the low-mobility photo-generated holes can be quickly relaxed, and the transit time of the carriers is only determined by the high-mobility electrons, thereby considering the responsivity and bandwidth of the photodetector. After continuous exploration by researchers, the bandwidth of the photodetector has been well broken through, but the responsivity of the large-bandwidth photodetector still has a large room for improvement. Therefore, in the design of the photodetector, how to simultaneously obtain large bandwidth and high responsivity is a problem worthy of study for those skilled in the art. SUMMARY

[0005] The application aims to provide a high-response photodetector using an air cavity, to solve the problems in the prior art.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the application is as follows:

[0007] The photoelectric detector is formed by directly bonding the two wafers, and finally etching the transition waveguide and the photoelectric detector mesa according to a conventional process flow.

[0008] A high-response photoelectric detector using an air cavity is formed by bonding two wafers through a bonding process, one wafer including a semi-insulating substrate and a dilute waveguide I, wherein the dilute waveguide I is partially etched, and the other wafer including a photoelectric detector active region and a dilute waveguide II. When the two wafers are bonded, the dilute waveguide I and the dilute waveguide II are in direct contact, and the etched part of the dilute waveguide I forms an air cavity. After bonding, a transition waveguide and a photoelectric detector mesa are etched according to a conventional process flow. Signal light incident from the end face enters the transition waveguide formed by the dilute waveguide I and the dilute waveguide II, and gradually couples into the photoelectric detector active region, and finally is converted into photo-generated carriers in the photoelectric detector absorption layer to complete photoelectric detection. This structure can as much as possible prevent signal light from leaking to the semi-insulating substrate and the dilute waveguide, and restricts the signal light in the active region of the photoelectric detector, effectively improving the responsivity of the photoelectric detector.

[0009] Further, the air cavity is obtained by first partially etching the dilute waveguide I and directly bonding the two groups of dilute waveguides. The position of the etched dilute waveguide I, i.e. the position of the air cavity, is determined by factors such as the required overall performance and the structural stability of the device. There is a large refractive index difference between the air medium in the air cavity and the surrounding semiconductor material. This structure can effectively block the signal light from continuing to propagate in the dilute waveguide along the length direction of the photoelectric detector, and the small evanescent wave penetration depth at the interface between the dilute waveguide II and the air cavity can inhibit the diffusion of signal light in the active region to the dilute waveguide layer and the semi-insulating substrate layer.

[0010] Further, the dilute waveguide I and the dilute waveguide II are both formed by periodically arranging two materials with different refractive indexes, and the number of periods can be the same or different. One material is a semi-insulating substrate material, and the thickness of each layer decreases from bottom to top; the other material is a material with a slightly larger refractive index than the semi-insulating substrate material, and the thickness of each layer remains unchanged. The number of periods of the two materials possessed by the dilute waveguide I and the dilute waveguide II is determined by the structure of the air cavity. This dilute waveguide structure with an air cavity can effectively couple the incident signal light to the absorption layer and restrict it in the active region of the photoelectric detector.

[0011] Further, the photoelectric detector is from bottom to top respectively a semi-insulating substrate, a dilute waveguide I, an air cavity, a dilute waveguide II, an optical matching layer, a double-mesa N electrode, an N contact layer, a sub-collection layer, a collection layer, a cliff layer, a transition layer, an absorption layer, an electron blocking layer, a P contact layer, and a P electrode. The material of only the absorption layer has an absorption effect on the signal light. The refractive index of the material gradually increases from the optical matching layer to the electron blocking layer, and then the refractive index of the electron blocking layer is smaller than that of the absorption layer.

[0012] Further, the N contact layer simultaneously serves as an optical matching layer, and the thickness and material selection of the optical matching layer and the N contact layer can improve the responsivity of the photoelectric detector.

[0013] Further, the sub-collection layer can expand the electric field distribution when the photoelectric detector works, so that the photoelectric detector has a smaller junction capacitance and reduces the limitation of the RC constant on the bandwidth.

[0014] Further, the size and arrangement of the air cavity, the structure and layer thickness of the dilute waveguide I and the dilute waveguide II can be adjusted and optimized according to the actual coupling light requirements, overall structural stability requirements, and overall performance requirements of the photoelectric detector, and the device size of the photoelectric detector needs to be adjusted to facilitate the performance of the device.

[0015] Compared with the prior art, the photoelectric detector has the beneficial effects of.

[0016] An innovation point of the scheme is that the high-responsivity photoelectric detector using an air cavity directly bonds a wafer with a partially etched dilute waveguide I and a wafer with an epitaxially grown photoelectric detector active region structure and a dilute waveguide II, obtains an air cavity inside the dilute waveguide without damaging or damaging the photoelectric detector active region, and side incident signal light enters a transition waveguide formed by the dilute waveguide I and the dilute waveguide II and is efficiently coupled upward to the photoelectric detector active region in the transition waveguide.

[0017] An innovation point of the scheme is that the high-responsivity photoelectric detector using an air cavity, side incident signal light is mostly coupled upward to the active region under the action of the dilute waveguide, and the smaller evanescent wave penetration depth caused by the higher refractive index difference at the interface between the air cavity and the semiconductor material can effectively suppress the leakage of the signal light in the active region downward to the dilute waveguide and the semi-insulating substrate, and concentrate the signal light in the absorption layer as much as possible. BRIEF DESCRIPTION OF DRAWINGS

[0018] 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 embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0019] Figure 1 This is a structural schematic diagram of a specific embodiment of the present invention.

[0020] Figure 2 This is a cross-sectional schematic diagram of the photodetector, dilution waveguide, and air cavity used in this invention.

[0021] Figure 3 This is a top view of a specific embodiment of the present invention.

[0022] Figure 4 This is a side view of the light field distribution coupled into the photodetector according to a specific embodiment of the present invention, with a corresponding responsivity of 1.04 A / W. Detailed Implementation

[0023] The following description, in conjunction with the appendix of the present invention, Figures 1-4 The technical solutions in the embodiments of the present invention are clearly and completely described herein. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] Example:

[0025] like Figure 1 As shown, a high-response photodetector using an air cavity integrates a diluted waveguide, an air cavity, and a photodetector on a semi-insulating substrate. The diluted waveguide is divided into two parts: diluted waveguide I and diluted waveguide II. Diluted waveguide I is grown on a wafer with the semi-insulating substrate, while diluted waveguide II is grown on another wafer containing the active region of the photodetector. After etching a portion of diluted waveguide I, the two wafers are directly bonded, with diluted waveguide I and diluted waveguide II in direct contact. The etched portion of diluted waveguide I forms the air cavity. The width of the photodetector mesa is slightly smaller than the width of the air cavity. The signal light coupled from the end face gradually couples upward into the active region of the photodetector within the transition waveguide composed of dilute waveguide I and dilute waveguide II. At the air cavity, due to the large refractive index difference with the surrounding semiconductor material, the intensity of the signal light is limited to the active region. That is, the light in the active region will be difficult to couple downward into the dilute waveguide layer and will be concentrated in the active region. The signal light is absorbed by the material in the absorption region and converted into photogenerated carriers. Under the action of the applied electric field, the carriers are transmitted to the electrodes and converted into electrical signal output.

[0026] Further, by adjusting the material, period number, thickness variation of the dilution waveguide I and dilution waveguide II, the signal light can be uniformly coupled to the absorption region of the photodetector. The dilution waveguide I and dilution waveguide II are both formed by periodic arrangement of two materials with different refractive indexes, one of which is semi-insulating substrate material, and the thickness of each layer decreases from bottom to top; the other material has a slightly larger refractive index than the semi-insulating substrate material, and the thickness of each layer remains unchanged. The dilution waveguide with air cavity is formed by Figure 1 The upper and lower parts of the dashed line in the middle are dilution waveguide I and dilution waveguide II, which are formed when the two wafers are bonded. Dilution waveguide I has three periods described above, and dilution waveguide II has two periods described above.

[0027] Further, the air cavity is formed when the wafer including dilution waveguide I is bonded with the wafer including dilution waveguide II. The air cavity corresponds to the etched part of dilution waveguide I and is located directly below the active region of the photodetector. One end of the air cavity extends to the end of the photodetector in the length direction, and the other end extends to the transition waveguide. In one embodiment, the end face of the air cavity is connected to the end face of the transition waveguide. In another embodiment, there is a gap between the end face of the air cavity and the end face of the transition waveguide.

[0028] Further, there is a large refractive index difference between the air in the air cavity and the surrounding semiconductor material. This structure can effectively block the signal light from continuing to propagate along the length direction of the photodetector in the dilution waveguide. At the same time, the small penetration depth of evanescent wave at the interface between dilution waveguide II and the air cavity can inhibit the diffusion of signal light from the active region to the dilution waveguide layer and the semi-insulating substrate layer, effectively confining the signal light within the active region.

[0029] Figure 2 Figure 1 is a schematic cross-sectional view of the photodetector, dilution waveguide and air cavity used in the example, perpendicular to the direction of incident light. The epitaxial structure includes semi-insulating substrate 4, dilution waveguide 1, air cavity 2, optical matching layer 5, N contact layer 6, N electrode 7, sub-collection layer 8, collection layer 9, cliff layer 10, transition layer 11, absorption layer 12, electron blocking layer 13, P contact layer 14 and P electrode 15. The materials used in the epitaxial layers are all lattice matched to the material used in the semi-insulating substrate 4.

[0030] The semi-insulating substrate 4 uses InP material, which has the lowest refractive index in all epitaxial layers of the photodetector. The difference in refractive index between the substrate material and the active region material of the photodetector can effectively reduce the leakage of signal light to the substrate.

[0031] The dilution waveguide 1 is formed by alternately stacking two materials with low refractive index, the first material is the same as the semi-insulating substrate 4, and the thickness gradually decreases from 0.16 μm to 0.16 μm, and the second material is a material with slightly higher refractive index, and the thickness is fixed at 0.23 μm. The transition waveguide formed by the dilution waveguide I and the dilution waveguide II has a length of 20 μm.

[0032] The thickness of the air cavity 2 is the same as that of the dilution waveguide I, and the width is 6 μm, which can effectively block the signal light from continuing to propagate along the transition waveguide direction or to the semi-insulating substrate layer below.

[0033] The optical matching layer 5 is located above the dilution waveguide 1, and has a thickness of 0.2 μm, and is made of a material with slightly higher refractive index than the dilution waveguide 1, which can alleviate the large refractive index difference between the dilution waveguide 1 and the N contact layer 6, and improve the coupling efficiency of the signal light to the upper active region.

[0034] The N contact layer 6 is located above the optical matching layer 5 and has the same width as the optical matching layer 5, and has a thickness of 0.3 μm, and is made of a material with a higher refractive index than the optical matching layer 5 to improve the coupling efficiency. A heavily doped layer is used to form an ohmic contact with the N electrode to reduce the contact resistance. The N electrode 7 is located above the N contact layer 6, and has a width of 2 μm and a thickness of 0.05 μm.

[0035] The sub-collection layer 8 is located above the N contact layer 6 and has a thickness of 0.2 μm, and is made of a material with a higher refractive index than the N contact layer 6, which can improve the light coupling efficiency, and the use of a heavily doped layer can reduce the diffusion of the heavily doped dopant in the N contact layer to the collection layer.

[0036] The collection layer 9 is located above the sub-collection layer 8 and has a thickness of 0.35 μm, and is made of a material with a slightly higher refractive index than the sub-collection layer 8, and is doped with a donor type.

[0037] The cliff layer 10 is located above the collection layer 9 and has a thickness of 0.02 μm, and is made of the same material as the collection layer 9, and is doped with a heavily doped layer to increase the width of the depletion region and improve the frequency response performance.

[0038] The transition layer 11 is located above the cliff layer 10 and has a thickness of 0.02 μm, and is made of the same material as the collection layer 9, and the layer is not doped to achieve a gradual change in the energy band, so that the carriers can smoothly cross the heterojunction.

[0039] The absorption layer 12 is located above the transition layer 11 and has a thickness of 0.28 μm, and is made of a material with the highest refractive index in the entire photodetector. The selection of the materials of the above layers can make the light coupled to the absorption layer as much as possible. The material that can absorb the signal light is used to absorb the photons to generate photo-generated carriers. A acceptor type graded doping is used to form an electric field inside the absorption layer to promote the transport of carriers.

[0040] The electron blocking layer 13 is located above the absorption layer 12, with a thickness of 0.02 μm, and is made of the same low refractive index material as the substrate, and forms a higher refractive index difference with the absorption layer 12, so as to effectively limit the light propagation to the upper P contact layer 14. The doping type of the layer is heavy acceptor type doping, and the wider energy band gap can block the reverse propagation of the photo-generated electrons.

[0041] The P contact layer 14 is located above the electron blocking layer 13, with a thickness of 0.05 μm, and is made of the same material as the absorption layer 9, and is doped with heavy acceptor type doping to form an ohmic contact with the P electrode 15.

[0042] The P electrode 15 is located above the P contact layer 14, with a width of 2 μm and a thickness of 0.05 μm.

[0043] Figure 3 is a top view of a specific embodiment of a high responsivity photodetector using an air cavity provided by the present application. The side cross-sectional view in the example is consistent with the structure shown in Figure 2 , where the dashed line part is the air cavity shown in Figure 1 , and the width of the air cavity is slightly larger than the width of the active region of the photodetector.

[0044] Figure 4 is the light field distribution diagram of the photodetector in the specific embodiment, and the responsivity of the photodetector is calculated to be 1.04 A / W; the responsivity of the same photodetector without the air cavity structure is only 0.87 A / W.

[0045] The principle of the present application is as follows: by means of etching first and bonding later, an air cavity structure is formed inside the dilute waveguide, and the laterally incident light propagates along the transition waveguide formed by the dilute waveguide. Under the joint action of the large refractive index difference between the air cavity and the surrounding material and the dilute waveguide, most of the signal light is coupled to the upper active region in the transition waveguide in front of the air cavity. Due to the small penetration depth of the evanescent wave, the light coupled from the upper active region to the lower dilute waveguide is also limited, so that most of the light field is limited in the absorption region, the signal leakage to the lower dilute waveguide and the substrate is reduced, and the responsivity of the photodetector is improved.

[0046] The above description of disclosed embodiments enables one of ordinary skill in the art to make or use the application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Accordingly, the application is not to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A high-response photodetector using an air cavity, characterized in that, The photodetector is constructed by bonding two wafers. One wafer includes a semi-insulating substrate and a diluted waveguide I, while the other wafer includes the active region of the photodetector and a diluted waveguide II. After partially etching the diluted waveguide I, the two wafers are directly bonded together, and finally, a transition waveguide and a photodetector mesa are etched using conventional processes.

2. A high-response photodetector using an air cavity as described in claim 1, characterized in that, The etched portion of the diluted waveguide I and the bonded contact of the diluted waveguide II form an air cavity, the structure of which is determined by factors such as the overall performance of the photodetector and the requirements for structural stability.

3. A high-response photodetector using an air cavity as described in claim 1, characterized in that, Both the diluted waveguide I and the diluted waveguide II are formed by periodically arranging two materials with different refractive indices. The number of periods of the diluted waveguide I and the diluted waveguide II are determined by the required air cavity structure.

4. A high-response photodetector using an air cavity as described in claim 1, characterized in that, When the photodetector is working, there is a large refractive index difference between the air medium in the air cavity and the surrounding semiconductor material. This structure can effectively block the signal light from continuing to propagate along the length of the photodetector in the diluted waveguide. At the same time, the small evanescent wave penetration depth at the interface between the diluted waveguide II and the air cavity can effectively suppress the diffusion of the signal light in the active region to the diluted waveguide layer and the semi-insulating substrate layer, thereby improving the concentration of the signal light in the active region.

5. A high-response photodetector using an air cavity as described in claim 1, characterized in that, The periodic distribution of the air cavity structure and the dilution waveguide I and dilution waveguide II can be adjusted according to actual detection requirements. At the same time, the size of the active region of the photodetector needs to be adjusted accordingly to improve device performance.

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