Resonance enhancement type photoelectric detector based on chirp Bragg reflector

Abstract

The invention relates to the technical field of photoelectrons, in particular to a chirp Bragg reflector-based resonance enhanced mesa type photoelectric detector. Comprising a high reflection structure on a P-type ohmic contact layer, a P-type epitaxial layer, a gradient doping absorption layer, an annular metal electrode on an N-type ohmic contact layer, an N-type epitaxial layer, a chirp Bragg reflector and a semi-insulating indium phosphide substrate which are sequentially formed from top to bottom. Therefore, the restriction relationship between the response efficiency and the bandwidth of the conventional resonance enhanced mesa type photoelectric detector is broken.

Description

Technical Field

[0001] The invention relates to the field of optoelectronic technology, and in particular to a resonance-enhanced table-type photoelectric detector based on a chirped Bragg reflector. Background Art

[0002] Compared with waveguide detectors, table-type photodetectors have significant advantages in saturated output power and communication rate. However, traditional table-type photodetectors have constraints between quantum efficiency and bandwidth. When increasing bandwidth, a thinner absorption layer is required, resulting in a decrease in quantum efficiency and responsivity. Therefore, in order to ensure that the device still has high responsivity and bandwidth at a large output power, based on the original table-type photodetector, researchers proposed introducing a resonant enhanced photodetector with multi-layer uniform Bragg reflectors (Distributed Bragg mirrors, DBR) at the top and bottom of the detector to break the balance between quantum efficiency and bandwidth (Kishino, K., MS Unlu, J.-I. Chyi, J. Reed, L. Arsenault and H. Morkoc. "Resonant Cavity-Enhanced (RCE) Photodetectors". IEEE Journal of Quantum Electronics 27, Issue 8 (August 1991)). After the light incident on the absorption layer enters the detector, it will be repeatedly absorbed between the two reflectors of the resonant cavity, thereby improving the quantum efficiency without affecting the bandwidth. At the same time, the researchers also proposed a resonance-enhanced photodetector and its preparation method, using a subwavelength grating to replace the uniform Bragg reflectors at the top and bottom, and utilizing the high reflectivity of the subwavelength to enhance the absorption of the device at the resonance peak.

[0003] The uniform Bragg reflector structure (DBR) is a reflector structure composed of multiple layers of alternating high refractive index and substrate materials. When the thickness of each layer of the reflector is a quarter of the wavelength, the wavelength light will produce a resonance enhancement effect at a specific resonant wavelength, so it can have higher light absorption in the case of a thinner absorption layer thickness. It is the current mainstream choice of resonant cavity detector structure. However, a stronger resonant cavity will also bring certain adverse effects. For example, the optical bandwidth of the above-mentioned resonant cavity photodetector is often small, and its half-maximum full width is generally less than a few nanometers. Due to the extremely strong light sensitivity, the application of uniform DBR resonant enhanced photodetectors is limited to special fields. However, in general, it is often necessary to keep the quantum efficiency stable as the working wavelength changes, and a larger optical bandwidth is required. In general, the optical bandwidth of the device can be increased by reducing the uniform DBR logarithm. However, reducing the uniform DBR logarithm will make the device feedback weaker, reduce the overall light response, and weaken the resonance enhancement effect. Summary of the invention

[0004] The invention provides a resonance-enhanced table-type photoelectric detector based on a chirped Bragg reflector, which breaks the restricted relationship between the response efficiency and the bandwidth of a conventional resonance-enhanced table-type photoelectric detector.

[0005] The first aspect of the present invention provides a resonant enhanced table-type photodetector based on a chirped Bragg reflector, comprising: a high reflective structure on a P-type ohmic contact layer, a P-type epitaxial layer, a gradient doped absorption layer, an annular metal electrode on an N-type ohmic contact, an N-type epitaxial layer, a chirped Bragg reflector and a semi-insulating indium phosphide substrate, which are formed in sequence from top to bottom.

[0006] Optionally, the high reflective structure and the chirped Bragg reflector form a resonant cavity.

[0007] Optionally, the chirped Bragg reflector is composed of a reflective layer material and a base material that are lattice-matched to the semi-insulating indium phosphide substrate and are arranged alternately.

[0008] Optionally, the chirped Bragg reflector is a linear chirped Bragg reflector or a nonlinear chirped Bragg reflector.

[0009] Optionally, the linear chirped Bragg reflector sets a thickness variation of adjacent film layers of the reflective layer material and the substrate material according to a preset chirp factor.

[0010] Optionally, the solution formula for the film thickness change is:

[0011] m=Δd i ·4n i / λ

[0012] Where m is the preset chirp factor, Δd i is the thickness variation between the adjacent reflective layer material and the substrate material, n i is the refractive index of the reflective layer material or the substrate material, and λ is the desired resonance wavelength.

[0013] Optionally, the nonlinear chirped Bragg reflector includes an exponential nonlinear chirped Bragg reflector and a transition chirped Bragg reflector, wherein:

[0014] The exponential nonlinear chirped Bragg reflector sets the thickness variation of the adjacent reflective layer material and the substrate material according to a preset exponential relationship;

[0015] There is a jump in the thickness of the adjacent film layers of the reflection layer material and the base material in the jump chirped Bragg reflector.

[0016] Optionally, the high-reflection structure is made of metal electrode material or a sub-wavelength reflection grating with high-reflection function.

[0017] Optionally, the sub-wavelength reflection grating with high reflection function is a strip sub-wavelength reflection grating or a ring sub-wavelength reflection grating, wherein:

[0018] The strip-shaped sub-wavelength reflection grating comprises a strip-shaped sub-wavelength grating and aluminum oxide, and the aluminum oxide is arranged at the bottom of the strip-shaped sub-wavelength grating;

[0019] The annular sub-wavelength reflection grating comprises an annular sub-wavelength grating and aluminum oxide, and the aluminum oxide is arranged at the bottom of the annular sub-wavelength grating.

[0020] The second aspect of the present invention provides a method for preparing a resonant enhanced mesa photodetector based on a chirped Bragg reflector, comprising: preparing an epitaxial layer wafer and cleaning the epitaxial layer wafer, wherein the epitaxial layer wafer comprises a semi-insulating substrate, a chirped Bragg reflector region, an N-type region, an absorption region and a P-type region; sputtering a high-reflection structure on the cleaned epitaxial layer wafer to obtain a first device; sequentially photolithography a P mesa and a P-type 2 mesa on the first device to obtain a second device; wet etching the second device to an N-type ohmic contact layer, A third device is obtained; an N electrode is sputtered on the third device, and an N table is photoetched on the N electrode, and then etched to the semi-insulating substrate to obtain a fourth device; the fourth device is passivated and leveled with silicon dioxide, and an electrode window is opened in the passivated and leveled fourth device by sputtering a coplanar waveguide line, and a P electrode and an N electrode are led out to obtain a fifth device; the fifth device is thinned, polished and anti-reflection film is deposited to obtain a sixth device, and the sixth device is cleaved to obtain a resonant enhanced photodetector chip based on a chirped Bragg reflector.

[0021] The resonance-enhanced table-type photodetector based on a chirped Bragg reflector proposed in the embodiment of the present invention integrates a weak-feedback chirped Bragg reflector at the bottom (i.e., a Bragg reflector whose thickness gradually changes along the epitaxial direction). The DBR period is no longer a constant, and together with the high-reflection structure at the top, it forms a broadband optical resonant cavity, thereby solving the contradiction between the responsivity and bandwidth of the table-type photodetector, so that the detector has a higher responsivity and a wider optical bandwidth without affecting the response speed. At the same time, the structure is aimed at ultra-high-speed photodetectors with a bandwidth exceeding 200GHz. For thinner absorption layers (below 200nm), light can be absorbed multiple times, which better solves the problem of low responsivity of ultra-high-speed photodetectors.

[0022] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0024] Figure 1 A schematic structural diagram of a resonance-enhanced table-type photodetector based on a chirped Bragg reflector provided in an embodiment of the present invention;

[0025] Figure 2 A schematic structural diagram of a linear chirped Bragg reflector provided in an embodiment of the present invention;

[0026] Figure 3 A refractive index distribution diagram of a uniform Bragg reflector and a linear chirped Bragg reflector provided in an embodiment of the present invention;

[0027] Figure 4 A schematic structural diagram of a nonlinear chirped Bragg reflector provided in an embodiment of the present invention;

[0028] Figure 5 A refractive index distribution diagram of a uniform Bragg reflector and a nonlinear chirped Bragg reflector provided in an embodiment of the present invention;

[0029] Figure 6 A schematic diagram of the structure of a chirped Bragg reflector provided by an embodiment of the present invention;

[0030] Figure 7 A refractive index distribution diagram of a uniform Bragg reflector and a jump chirped Bragg reflector provided in an embodiment of the present invention;

[0031] Figure 8 Schematic diagram of the structure of the high-reflection structure provided by an embodiment of the present invention, wherein (a) is a top view of a metal electrode, (b) is a top view of an annular electrode structure combined with a strip high-contrast grating, (c) is a top view of an annular electrode structure combined with an annular high-contrast grating, and (d) is a cross-sectional view of an annular electrode structure combined with a high-contrast sub-wavelength grating;

[0032] Fig. 9 A schematic diagram of normalized longitudinal intensity distribution inside a detector after optimization provided by an embodiment of the present invention;

[0033] Fig.10 A one-dimensional longitudinal light field distribution diagram of a simulated uniform DBR deviating from the resonance peak by 30 nm provided by an embodiment of the present invention;

[0034] Fig.11 A one-dimensional longitudinal light field distribution diagram of a simulated uniform DBR at a resonance peak provided by an embodiment of the present invention;

[0035] Fig.12 A one-dimensional longitudinal light field distribution diagram of a simulated transition chirped DBR deviating from the resonance peak by 30nm provided by an embodiment of the present invention;

[0036] Fig.13 A one-dimensional longitudinal light field distribution diagram of a simulated transition chirped DBR located at a resonance peak provided by an embodiment of the present invention;

[0037] Fig.14 A graph showing the variation of reflectivity of a multi-period highly reflective sub-wavelength grating with wavelength under simulated different duty cycles provided by an embodiment of the present invention;

[0038] Fig.15 The present invention provides a flowchart of a method for preparing a resonance-enhanced mesa-type photodetector based on a chirped Bragg reflector according to an embodiment of the present invention.

[0039] Description of reference numerals:

[0040] 1-high reflective structure, 2-P-type epitaxial layer, 3-gradient doped absorption layer, 4-annular metal electrode, 5-N-type epitaxial layer, 6-chirped Bragg reflector and 7-semi-insulating indium phosphide substrate. DETAILED DESCRIPTION

[0041] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0042] The resonance enhanced mesa-type photodetector based on a chirped Bragg reflector according to an embodiment of the present invention will be described below with reference to the accompanying drawings.

[0043] Figure 1 A schematic structural diagram of a resonance-enhanced table-type photodetector based on a chirped Bragg reflector provided in an embodiment of the present invention.

[0044] like Figure 1 As shown, the resonant enhanced table-top photodetector based on the chirped Bragg reflector includes: a high reflective structure 1, a P-type epitaxial layer 2, a gradient doped absorption layer 3, an annular metal electrode 4, an N-type epitaxial layer 5, a chirped Bragg reflector 6 and a semi-insulating indium phosphide substrate 7.

[0045] The chirped Bragg reflector-based resonance-enhanced table-type photodetector 100 is formed from top to bottom in sequence of a high-reflection structure 1 on a P-type ohmic contact layer, a P-type epitaxial layer 2 (including a P-type ohmic contact layer and a P-type electron blocking layer), a gradient-doped absorption layer 3, a ring-shaped metal electrode 4 formed on an N-type ohmic contact, an N-type epitaxial layer 5, a chirped Bragg reflector 6, and a semi-insulating indium phosphide substrate 7. The chirped Bragg reflector-based resonance-enhanced table-type photodetector is composed of a high-reflection structure 1 at the top and a chirped Bragg reflector 6 at the bottom to form a resonant cavity, and a chirped Bragg reflector with weak feedback (i.e., a Bragg reflector whose thickness gradually changes along the epitaxial direction) is integrated at the bottom. The DBR period is no longer a constant, so that the detector has a higher responsivity and a wider optical bandwidth without affecting the response speed.

[0046] In some embodiments, the chirped Bragg reflector 6 is composed of a reflective layer material and a base material that are lattice-matched to the semi-insulating indium phosphide substrate 7 and are arranged alternately.

[0047] like Figure 2 , 4 As shown in FIG. 6 , in the actual implementation process, the chirped Bragg reflector 6 may be composed of a reflective layer material, indium phosphide (InP), which is lattice-matched with the semi-insulating indium phosphide substrate 7 , and a base material, indium gallium arsenic phosphide (InGaAsP(Q1.4)), which is lattice-matched with indium phosphide.

[0048] In some embodiments, the chirped Bragg reflector 6 is a linear chirped Bragg reflector or a nonlinear chirped Bragg reflector.

[0049] In some embodiments, the linear chirped Bragg reflector sets the thickness variation of adjacent reflective layer materials and substrate materials according to a preset chirp factor.

[0050] In some embodiments, the nonlinear chirped Bragg reflector includes an exponential nonlinear chirped Bragg reflector and a transition chirped Bragg reflector, wherein:

[0051] The exponential nonlinear chirped Bragg reflector sets the thickness variation of the adjacent reflective layer material and the substrate material according to a preset exponential relationship;

[0052] There is a jump in the thickness of the adjacent reflection layer materials and substrate materials in the jump chirped Bragg reflector.

[0053] In actual implementation, the chirped Bragg reflector 6 may be a linear chirped Bragg reflector or a nonlinear chirped Bragg reflector.

[0054] like Figure 2As shown, the linear chirped Bragg reflector refers to the linear change of thickness of adjacent InGaAsP / InP high and low refractive index materials in the DBR, thereby defining a preset chirp factor m = Δd i ·4n i / λ is used to characterize the thickness variation of adjacent InGaAsP / InP high and low refractive index material layers in the linear chirped DBR, and the chirp factor m ranges from 0.5% to 10%. i The corresponding refractive index of InGaAsP or InP, λ is the desired resonant wavelength of the device, Δd i Indicates the thickness variation between adjacent InGaAsP and InP materials. Figure 3 As shown in the figure, according to the refractive index distribution diagram of uniform DBR and linear chirped DBR when the chirp factor m is 2%, it can be seen that when the linear factor is small, the structure of linear chirped DBR is slightly different from that of uniform DBR, and the thickness changes linearly with the increase of the number of layers. It can reduce the wavelength sensitivity within a certain range and maintain a high transmittance.

[0055] like Figure 4 As shown in , the nonlinear chirped Bragg reflector can be defined as the adjacent InGaAsP / InP high and low refractive index materials do not satisfy a linear relationship with respect to thickness changes, and the nonlinear chirp can satisfy exponential, logarithmic, polynomial and other relationships. Figure 5 As shown, the nonlinear chirped DBR that satisfies the exponential relationship has a more dramatic structural change as the number of layers increases, increases exponentially, and its sensitivity with wavelength decreases.

[0056] like Figure 6 As shown in the figure, the jump chirp DBR structure is also a nonlinear chirp structure. The thickness between each layer of DBR is non-uniform, and there is a jump in thickness between different layers. The Δd between adjacent layers is i There is no obvious regularity. Figure 7 As shown in the figure, according to the refractive index distribution diagram of the uniform DBR and the jump chirp Bragg reflector, it can be seen that the single-layer film thickness of the jump chirp DBR device does not increase or decrease linearly with the increase of the layer thickness in the structure, and there is a certain jump phenomenon. It has low sensitivity to wavelength and can achieve wide-spectrum reflection, which is suitable for wide-spectrum high-responsivity resonant cavity photodetectors that are less sensitive to wavelength.

[0057] In some embodiments, the high reflective structure 1 is made of metal electrode material or a sub-wavelength reflective grating with high reflective function.

[0058] In some embodiments, the sub-wavelength reflection grating with high reflection function is a strip sub-wavelength reflection grating or a ring sub-wavelength reflection grating, wherein:

[0059] The strip sub-wavelength reflection grating comprises a strip sub-wavelength grating and aluminum oxide, wherein the aluminum oxide is arranged at the bottom of the strip sub-wavelength grating;

[0060] The annular sub-wavelength reflection grating comprises an annular sub-wavelength grating and aluminum oxide, wherein the aluminum oxide is arranged at the bottom of the annular sub-wavelength grating.

[0061] like Figure 8 As shown, in the actual implementation process, the resonance enhancement effect becomes more significant as the reflectivity of the top high-reflection structure 1 increases. Therefore, in the design, it is usually hoped that the top reflectivity is as close to 1 as possible. The embodiment of the present invention provides three possible implementation plans, that is, the high-reflection structure 1 can be a metal electrode material or a strip-shaped and ring-shaped sub-wavelength reflective grating with a high-reflection function. It should be noted that the top high-reflection structure 1 provided in the embodiment of the present invention is not unique, and any structure with a high-reflection function can be used.

[0062] like Figure 8 As shown in (a), the metal electrode needs to have high reflectivity in an ultra-wide spectral range (visible light to far infrared band), with a reflectivity usually between 50% and 70%, and has a small contact resistance and wavelength insensitivity. Common metal electrodes include Ti / Pt / Au or Pt / Ti / Pt / Au, etc.

[0063] The structure of the strip sub-wavelength reflection grating and the ring sub-wavelength reflection grating is two layers. The first layer is a strip sub-wavelength grating or a ring sub-wavelength grating. The grating pattern can be composed of InP and air arranged alternately, with a duty cycle between 0.5 and 0.7, a reflectivity greater than 90%, and a spectrum width of 1400nm to 1700nm. The second layer is the bottom of the grating, which includes a grating oxide layer of indium aluminum arsenide, in which the composition of In and Al is 0.52:0.48, and aluminum oxide is formed after high-temperature wet oxidation. The thickness of the grating layer is 460nm, and the thickness of the oxide layer is 150 to 300nm.

[0064] like Figure 8 As shown in (b), the strip subwavelength reflection grating has strong polarization selectivity. First, it is defined that the electric field direction of TE polarized light is parallel to the direction of the strip grating groove, and the electric field direction of TM polarized light is perpendicular to the direction of the strip grating groove. The strip grating has a reflectivity of more than 90% for TM polarized light in a wide spectrum band, while the average reflectivity of the TE mode is lower, generally less than 60%.

[0065] like Figure 8 As shown in (c) and (d), the annular subwavelength reflection grating is insensitive to linear polarization due to its centrally symmetrical structure. Therefore, it has a reflectivity greater than 90% in a wide spectrum range for linearly polarized light in any direction. The two types of gratings can be matched with an annular electrode to reduce the contact resistance of the device. The material of the annular electrode can be a metal electrode, a transparent electrode, etc.

[0066] Therefore, the embodiments of the present invention can respectively combine the top high-reflection structure and the different chirped DBR structures at the bottom to obtain different types of effects, for example: combining the jump chirped DBR structure with the metal electrode to form a new type of resonant cavity enhanced photodetector, combining the nonlinear chirped DBR with the one-dimensional annular subwavelength reflection grating to form a new type of photodetector, combining the linear chirped DBR with the one-dimensional strip subwavelength reflection grating to form a new type of polarization selective photodetector, etc.

[0067] The chirped DBR structure is combined with the metal electrode to form a new type of resonant cavity enhanced photodetector, which is composed of a metal electrode reflector 1 that simulates the real situation, a gradient doped absorption layer 3, and a chirped Bragg reflector 6 from top to bottom. 1 and 6 together constitute the resonant cavity of the detector. The incident light forms a standing wave in the resonant cavity and is repeatedly absorbed in the gradient doped absorption layer 3. Fig. 9 As shown, by regulating the position of the gradient-doped absorption layer 3, the peak position can be controlled in the gradient-doped absorption layer 3 when the absorption region is thin, so that the absorption of the device is strongest. The longitudinal normalized light field inside the optimized resonant cavity can show an obvious resonance enhancement effect.

[0068] In the embodiment of the present invention, the absorption region is fixed to 180nm during simulation. Figure 6 The one-dimensional longitudinal field distribution diagrams of the traditional uniform DBR photodetector and the optimized jump chirp DBR photodetector at different incident wavelengths with the same number of layers are shown. As can be seen from Figures 10 and 11, the uniform DBR is more sensitive to wavelength. When the incident wavelength deviates from the resonant wavelength by 30nm, most of the light does not enter the absorption region of the device, but is blocked outside the substrate by the DBR. Due to the special structure of the jump chirp DBR device, its sensitivity to wavelength is weak and it has a large optical bandwidth. At the same time, the metal electrode reflector in the top has a high reflection coefficient in a wide spectrum band (greater than 1.5um). The combination of the two can effectively reduce the device's sensitivity to wavelength. Fig.12 and Fig.13 As shown, when the wavelength deviates from 30nm, most of the light enters the absorption area of ​​the detector, which shows the superiority of the chirped DBR device design.

[0069] The nonlinear chirped DBR is combined with a one-dimensional annular subwavelength reflection grating to form a new type of photodetector that is polarization-independent for linear polarization. The nonlinear chirped DBR can provide a strong resonance enhancement effect in a wide spectrum range. After optimization, the one-dimensional annular electrode has a higher reflectivity than the traditional metal electrode in a certain spectral range, and can have a reflectivity of more than 90% in the range of 1400nm to 1700nm. The increased reflectivity can improve the peak responsivity of the resonant cavity detector. Fig.14 The relationship between the reflectivity of a multi-period highly reflective sub-wavelength grating and wavelength at different duty cycles with an oxide layer thickness of 150nm is shown. The combination of a sub-wavelength grating and a ring electrode enables the resonant cavity PD to have a smaller ohmic resistance and an extremely high reflectivity of more than 90% over a wide spectrum. At high reflectivity, the resonance enhancement effect can be improved, thereby improving the peak responsivity of the device.

[0070] The linear chirped DBR is combined with a one-dimensional strip sub-wavelength reflection grating to form a new type of polarization-selective photodetector for linearly polarized light with TM polarization. Since its top electrode has a high reflectivity with a wide spectrum and the bottom linear chirped DBR has a certain wide spectrum reflectivity, the high top electrode responsivity can further improve the peak response of the device. This type of photodetector has the characteristics of high responsivity. For linearly polarized light with TE polarization, its reflection spectrum is different from that of TM polarized light, and the average reflectivity is low in a wide spectrum range. Therefore, this type of polarization-selective detector is suitable for situations where polarization sensitivity is required.

[0071] At the same time, the chirped photodetector is not limited to InP-based, but also applicable to silicon-based germanium silicon (GeSi) photodetectors, GaAs-based photodetectors, etc. The chirped DBR material can be two different materials with a refractive index difference that match the substrate lattice. Therefore, the working band is not limited to 1550nm, and any use of a chirped Bragg mirror as a weak feedback enhancement structure at the bottom of the detector falls within the protection scope of the present invention.

[0072] It should be noted that the thickness of the absorption zone in the embodiment of the present invention is not unique. The thickness of the gradient doped absorption layer 3 can be between 10nm and 1000nm. If the gradient doped absorption layer 3 is greater than 1000nm, the absorption zone is thick, and the incident light is fully absorbed when the light field propagates, and there is no need to additionally utilize the resonance effect to absorb the light. If the gradient doped absorption layer 3 is less than 10nm, the absorption zone is thin, and it is more difficult to control the resonance peak position in the absorption zone.

[0073] In summary, the resonance-enhanced table-type photodetector based on a chirped Bragg reflector proposed in an embodiment of the present invention has the following beneficial effects:

[0074] (1) The chirped DBR structure designed by optimizing the traditional uniform DBR structure can greatly improve the optical bandwidth of the device and meet the wide-spectrum resonance enhancement characteristics of the resonant cavity detector. Compared with the photodetector without DBR, the photodetector with uniform periodic DBR resonant cavity has great advantages;

[0075] (2) The top high-reflection structure is designed for different application scenarios. According to different actual application scenarios, the design can be flexibly combined to optimize and achieve the expected effect;

[0076] (3) The DBR period of the chirped Bragg reflector (i.e., a Bragg reflector whose thickness gradually changes along the epitaxial direction) with weak feedback integrated at the bottom is no longer a constant, and together with the high-reflection structure at the top, it forms a broadband optical resonant cavity, thereby resolving the contradiction between the responsivity and bandwidth of the table-top photodetector, so that the detector has a higher responsivity and a wider optical bandwidth without affecting the response speed;

[0077] (4) This structure is designed for ultra-high-speed photodetectors with a bandwidth exceeding 200 GHz. For thinner absorption layers (less than 200 nm), it can absorb light multiple times, which effectively solves the problem of low responsivity of ultra-high-speed photodetectors.

[0078] (5) Applicable to various types of table-top photodetectors such as traditional PIN photodetectors and single-pass carrier photodetectors (MUTC).

[0079] Next, a method for preparing a resonance-enhanced mesa-type photodetector based on a chirped Bragg reflector according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0080] Fig.15 A schematic flow chart of a method for preparing a resonance-enhanced mesa-type photodetector based on a chirped Bragg reflector provided in an embodiment of the present invention.

[0081] like Fig.15 As shown, the preparation method of the resonance enhanced table-type photodetector based on the chirped Bragg reflector comprises the following steps:

[0082] In step S1501, an epitaxial layer wafer is prepared and cleaned, wherein the epitaxial layer wafer includes a semi-insulating substrate, a chirped Bragg reflector region, an N-type region, an absorption region, and a P-type region.

[0083] In step S1502, a high-reflection structure is sputtered on the cleaned epitaxial layer wafer to obtain a first device.

[0084] Specifically, an epitaxial layer wafer is prepared, including an InP substrate, a bottom chirped DBR region, an N-type region, an absorption region, and a P-type region, and the wafer is cleaned. A top high-reflectivity P electrode is sputtered on the cleaned epitaxial layer wafer to obtain a first device.

[0085] In step S1503, P-mesa and P-type 2-mesa are sequentially photolithographically formed on the first device to obtain a second device.

[0086] In step S1504, wet etching is performed on the second device to the N-type ohmic contact layer to obtain a third device.

[0087] Specifically, a P mesa is photolithographically formed on the first device, and the mesa is etched in reactive plasma etching using the P mesa as a mask, a P-type 2 mesa is photolithographically formed, and the 2 mesa is etched in reactive plasma etching using the P mesa as a mask, and the N-type ohmic contact layer is wet-etched to obtain a third device. This method can effectively reduce the sidewall erosion of the device caused by the wet etching of the P mesa, and reduce the dark current of the device.

[0088] In step S1505, an N electrode is sputtered on the third device, an N mesa is photolithographically formed on the N electrode, and etching is performed to the semi-insulating substrate to obtain a fourth device.

[0089] Specifically, an N electrode is sputtered on the third device, an N table is photoetched, and deep etching is performed until the semi-insulating substrate is reached to obtain a fourth device.

[0090] In step S1506, the fourth device is passivated and filled with silicon dioxide, and an electrode window is opened in the passivated and filled fourth device by sputtering a coplanar waveguide line to lead out a P electrode and an N electrode to obtain a fifth device.

[0091] In step S1507, the fifth device is thinned and polished and an anti-reflection film is deposited to obtain a sixth device, and the sixth device is cleaved to obtain a resonance enhanced photodetector chip based on a chirped Bragg reflector.

[0092] Specifically, the fourth device is passivated and filled with silicon dioxide (SiO2), and after the electrode window is opened, the coplanar waveguide wire is sputtered to lead out the P and N electrodes, and the device is thickened by electroplating to obtain the fifth device. The fifth device is thinned, polished and deposited with an anti-reflection film in sequence to obtain the sixth device. The sixth device is cleaved to obtain a resonant enhanced photodetector chip based on a chirped Bragg reflector.

[0093] It should be noted that the aforementioned explanation of the embodiment of the resonant enhanced table-type photodetector based on a chirped Bragg reflector is also applicable to the preparation method of the resonant enhanced table-type photodetector based on a chirped Bragg reflector in this embodiment, which will not be repeated here.

[0094] The method for preparing a resonance-enhanced table-type photodetector based on a chirped Bragg reflector according to an embodiment of the present invention has the following beneficial effects:

[0095] (1) The chirped DBR structure designed by optimizing the traditional uniform DBR structure can greatly improve the optical bandwidth of the device and meet the wide-spectrum resonance enhancement characteristics of the resonant cavity detector. Compared with the photodetector without DBR, the photodetector with uniform periodic DBR resonant cavity has great advantages;

[0096] (2) The top high-reflection structure is designed for different application scenarios. According to different actual application scenarios, the design can be flexibly combined to optimize and achieve the expected effect;

[0097] (3) The DBR period of the chirped Bragg reflector (i.e., a Bragg reflector whose thickness gradually changes along the epitaxial direction) with weak feedback integrated at the bottom is no longer a constant, and together with the high-reflection structure at the top, it forms a broadband optical resonant cavity, thereby resolving the contradiction between the responsivity and bandwidth of the table-top photodetector, so that the detector has a higher responsivity and a wider optical bandwidth without affecting the response speed;

[0098] (4) This structure is designed for ultra-high-speed photodetectors with a bandwidth exceeding 200 GHz. For thinner absorption layers (less than 200 nm), it can absorb light multiple times, which effectively solves the problem of low responsivity of ultra-high-speed photodetectors.

[0099] (5) Applicable to various types of table-top photodetectors such as traditional PIN photodetectors and single-pass carrier photodetectors (MUTC).

[0100] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or N embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0101] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "N" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

Claims

1. A resonance-enhanced table-type photodetector based on a chirped Bragg reflector, characterized in that: include: The highly reflective structure on the P-type ohmic contact layer, the P-type epitaxial layer, the gradient doped absorption layer, the annular metal electrode on the N-type ohmic contact, the N-type epitaxial layer, the chirped Bragg reflector and the semi-insulating indium phosphide substrate are sequentially formed from top to bottom.

2. The resonance-enhanced table-type photodetector based on a chirped Bragg reflector according to claim 1, characterized in that: The high reflection structure and the chirped Bragg reflector form a resonant cavity.

3. The resonance-enhanced table-type photodetector based on a chirped Bragg reflector according to claim 1, characterized in that: The chirped Bragg reflector is composed of a reflective layer material and a base material which are lattice-matched with the semi-insulating indium phosphide substrate and are arranged alternately.

4. The resonance-enhanced table-type photodetector based on a chirped Bragg reflector according to claim 3, characterized in that: The chirped Bragg reflector is a linear chirped Bragg reflector or a nonlinear chirped Bragg reflector.

5. The resonance-enhanced table-type photodetector based on a chirped Bragg reflector according to claim 4, characterized in that: The linear chirped Bragg reflector sets the thickness variation of the adjacent reflective layer material and the substrate material according to a preset chirp factor.

6. The resonance-enhanced table-type photodetector based on a chirped Bragg reflector according to claim 5, characterized in that: The solution formula for the film thickness change is: m=Δd i ·4n i / l Where m is the preset chirp factor, Δd i is the thickness variation between the adjacent reflective layer material and the substrate material, n i is the refractive index of the reflective layer material or the substrate material, and λ is the desired resonance wavelength.

7. The resonance-enhanced mesa-type photodetector based on a chirped Bragg reflector according to claim 4, characterized in that: The nonlinear chirped Bragg reflector includes an exponential nonlinear chirped Bragg reflector and a jump chirped Bragg reflector, wherein: The exponential nonlinear chirped Bragg reflector sets the thickness variation of the adjacent reflective layer material and the substrate material according to a preset exponential relationship; There is a jump in the thickness of the adjacent film layers of the reflection layer material and the base material in the jump chirped Bragg reflector.

8. The resonance-enhanced table-type photodetector based on a chirped Bragg reflector according to claim 1, characterized in that: The high reflection structure is made of metal electrode material or a sub-wavelength reflection grating with high reflection function.

9. The resonance-enhanced mesa-type photodetector based on a chirped Bragg reflector according to claim 8, characterized in that: The sub-wavelength reflection grating with high reflection function is a strip sub-wavelength reflection grating or a ring sub-wavelength reflection grating, wherein: The strip-shaped sub-wavelength reflection grating comprises a strip-shaped sub-wavelength grating and aluminum oxide, and the aluminum oxide is arranged at the bottom of the strip-shaped sub-wavelength grating; The annular sub-wavelength reflection grating comprises an annular sub-wavelength grating and aluminum oxide, and the aluminum oxide is arranged at the bottom of the annular sub-wavelength grating.

10. A method for preparing a resonance-enhanced table-type photodetector based on a chirped Bragg reflector, characterized in that: The following steps are involved: Preparing an epitaxial layer wafer and cleaning the epitaxial layer wafer, wherein the epitaxial layer wafer includes a semi-insulating substrate, a chirped Bragg reflector region, an N-type region, an absorption region, and a P-type region; sputtering a high-reflection structure on the cleaned epitaxial layer wafer to obtain a first device; Sequentially photolithography a P-type mesa and a P-type 2-type mesa on the first device to obtain a second device; Wet-etching the second device to the N-type ohmic contact layer to obtain a third device; sputtering an N electrode on the third device, photolithography an N mesa on the N electrode, and etching to the semi-insulating substrate to obtain a fourth device; Passivating and leveling the fourth device with silicon dioxide, and opening an electrode window for the passivated and leveled fourth device by sputtering a coplanar waveguide line, leading out a P electrode and an N electrode, to obtain a fifth device; The fifth device is thinned and polished and an anti-reflection film is deposited to obtain a sixth device, and the sixth device is cleaved to obtain a resonance-enhanced photodetector chip based on a chirped Bragg reflector.

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