Resonance-enhanced photodetector based on chirped bragg reflector

Abstract

The present disclosure relates to the technical field of optoelectronics, and in particular to a resonance-enhanced mesa-type photodetector based on a chirped Bragg reflector. The photodetector comprises: a high-reflectance structure on a P-type ohmic contact layer, a P-type epitaxial layer, a graded doping 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 sequentially formed from top to bottom.

Description

Resonant cavity enhanced photodetector based on chirped Bragg mirrors

[0001] Cross-reference to Related Applications

[0002] The present disclosure claims priority to the Chinese patent application No. 202411332632.8, filed on September 24, 2024, entitled “Resonant cavity enhanced photodetector based on chirped Bragg mirrors” and invented by Tsinghua University. TECHNICAL FIELD

[0003] The present disclosure relates to the field of optoelectronic technology, and in particular to a resonant cavity enhanced mesa photodetector based on chirped Bragg mirrors. BACKGROUND

[0004] Compared with waveguide photodetectors, mesa photodetectors have more significant advantages in terms of saturated output power and communication rate. However, the traditional mesa photodetectors have a trade-off between quantum efficiency and bandwidth. When the bandwidth is improved, a thinner absorption layer is needed, which leads to a decrease in quantum efficiency and responsivity. Therefore, in order to ensure that the device still has high responsivity and bandwidth under a large output power, researchers have proposed a resonant cavity enhanced photodetector with a multi-layer uniform Bragg mirror (Distributed Bragg mirrors, DBR) on the top and bottom of the photodetector based on the original mesa photodetector, so as to break the trade-off between quantum efficiency and bandwidth (Kishino, K., M. S. Unlu, J.-I. Chyi, J. Reed, L. Arsenault, and H. Morkoc. Resonant Cavity-Enhanced (RCE) Photodetectors. IEEE Journal of Quantum Electronics 27, no. 8 (Aug 1991)). The light incident on the absorption layer will be repeatedly absorbed between the two mirrors of the resonant cavity after entering the photodetector, thereby improving the quantum efficiency without affecting the bandwidth. At the same time, researchers have also proposed a resonant cavity enhanced photodetector and a preparation method thereof, which uses a sub-wavelength grating to replace the uniform Bragg mirror on the top and bottom, and uses the high reflectivity of the sub-wavelength to enhance the absorption of the device at the resonant peak.

[0005] The uniform Bragg reflector mirror structure (DBR) is a mirror structure composed of multiple layers of high refractive index and base material arranged alternately. When the thickness of each layer of the mirror is a quarter of the wavelength, the wavelength of the light will be resonantly enhanced at a specific resonant wavelength, so that a higher light absorption can be achieved with a thinner absorption layer thickness. It is currently the mainstream choice of resonant cavity type detector structure. However, the strong resonant cavity also has some adverse effects, such as the above-mentioned resonant cavity type photodetector light bandwidth is usually small, and the full width at half maximum is generally below several nanometers. Due to the extremely strong light sensitivity, the application of the uniform DBR resonant enhanced photodetector is limited to special fields. However, in general, the quantum efficiency needs to remain stable with the change of the working wavelength, and a larger light bandwidth is needed. Generally, the light bandwidth of the uniform DBR logarithmic amplifier device can be increased by reducing the number of uniform DBR, but reducing the number of uniform DBR will make the device feedback weaker, the overall light responsivity will be reduced, and the resonant enhancement effect will be weakened.

[0006] DISCLOSURE

[0007] The present disclosure provides a resonant enhanced mesa photodetector based on a chirped Bragg reflector, which breaks the response efficiency and bandwidth constraint relationship of the conventional resonant enhanced mesa photodetector.

[0008] The first aspect of the present disclosure provides a resonant enhanced mesa photodetector based on a chirped Bragg reflector, comprising: a high reflection structure on a P-type ohmic contact layer, a P-type epitaxial layer, a gradient-doped absorption layer, a ring-shaped metal electrode on an N-type ohmic contact, an N-type epitaxial layer, a chirped Bragg reflector and a semi-insulating indium phosphide substrate formed in order from top to bottom.

[0009] In some embodiments, the high reflection structure and the chirped Bragg reflector constitute a resonant cavity.

[0010] In some embodiments, the chirped Bragg reflector is composed of reflection layer materials and base materials alternately arranged in lattice matching with the semi-insulating indium phosphide substrate.

[0011] In some embodiments, the chirped Bragg reflector adopts a linear chirped Bragg reflector or a nonlinear chirped Bragg reflector.

[0012] In some embodiments, the linear chirped Bragg reflector sets the film layer thickness variation of adjacent reflection layer materials and base materials according to a preset chirp factor.

[0013] In some embodiments, the solving formula of the film layer thickness variation is: m = Δd i · 4n i / λ

[0014] wherein m is a preset chirp factor, Δd i is a film thickness variation between adjacent reflective layer materials and base materials, n i is a refractive index of the reflective layer material or the base material, and λ is a desired resonance wavelength.

[0015] In some embodiments, the nonlinear chirped Bragg mirror includes an exponential nonlinear chirped Bragg mirror and a jump chirped Bragg mirror, wherein

[0016] The exponential nonlinear chirped Bragg mirror sets a film thickness variation of adjacent reflective layer materials and base materials according to a preset exponential relationship.

[0017] In the jump chirped Bragg mirror, a film thickness of adjacent reflective layer materials and base materials has a jump.

[0018] In some embodiments, the high-reflection structure uses a metal electrode material or a subwavelength reflective grating with high-reflection function.

[0019] In some embodiments, the subwavelength reflective grating with high-reflection function is a strip-shaped subwavelength reflective grating or a ring-shaped subwavelength reflective grating, wherein

[0020] The strip-shaped subwavelength reflective grating includes a strip-shaped subwavelength grating and aluminum oxide, and the aluminum oxide is arranged at the bottom of the strip-shaped subwavelength grating.

[0021] The ring-shaped subwavelength reflective grating includes a ring-shaped subwavelength grating and aluminum oxide, and the aluminum oxide is arranged at the bottom of the ring-shaped subwavelength grating.

[0022] A second aspect of the present disclosure provides a preparation method of a resonant enhancement mesa photodetector based on a chirped Bragg mirror, including: preparing an epitaxial wafer, and cleaning the epitaxial wafer, wherein the epitaxial wafer includes a semi-insulating substrate, a chirped Bragg mirror region, an N-type region, an absorption region, and a P-type region; sputtering a high-reflection structure on the cleaned epitaxial wafer to obtain a first device; sequentially photolithographing 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 to obtain a third device; sputtering an N electrode on the third device, and photolithographing an N mesa on the N electrode and etching to the semi-insulating substrate to obtain a fourth device; passivating and filling the fourth device with silicon dioxide, and opening an electrode window of 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; thinning and polishing the fifth device and depositing an anti-reflection film on the fifth device to obtain a sixth device, and cleaving the sixth device to obtain a resonant enhancement photodetector chip based on a chirped Bragg mirror.

[0023] The resonant enhancement mesa photodetector based on the chirped Bragg reflector provided by the embodiments of the present disclosure has a weak feedback chirped Bragg reflector (i.e. a Bragg reflector whose thickness gradually changes along the epitaxial direction) integrated at the bottom, and the period of the DBR is no longer constant, and the top high-reflection structure together forms a broadband optical resonant cavity, thereby solving the contradiction between the responsivity and the bandwidth of the mesa photodetector, so that the detector has higher responsivity and wider optical bandwidth without affecting the response speed. Meanwhile, the structure is directed to an ultrahigh-speed photodetector with a bandwidth exceeding 200GHz, and for a relatively thin absorption layer (less than 200nm), the light can be absorbed multiple times, thereby better solving the problem of low responsivity of the ultrahigh-speed photodetector.

[0024] Additional aspects and advantages of the present disclosure will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0025] The above-mentioned and / or additional aspects and advantages of the present disclosure will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings:

[0026] Fig. 1 is a structural schematic diagram of a resonant enhancement mesa photodetector based on a chirped Bragg reflector provided by an embodiment of the present disclosure;

[0027] Fig. 2 is a structural schematic diagram of a linear chirped Bragg reflector provided by an embodiment of the present disclosure;

[0028] Fig. 3 is a refractive index distribution diagram of a uniform Bragg reflector and a linear chirped Bragg reflector provided by an embodiment of the present disclosure;

[0029] Fig. 4 is a structural schematic diagram of a nonlinear chirped Bragg reflector provided by an embodiment of the present disclosure;

[0030] Fig. 5 is a refractive index distribution diagram of a uniform Bragg reflector and a nonlinear chirped Bragg reflector provided by an embodiment of the present disclosure;

[0031] Fig. 6 is a structural schematic diagram of a jump chirped Bragg reflector provided by an embodiment of the present disclosure;

[0032] Fig. 7 is a refractive index distribution diagram of a uniform Bragg reflector and a jump chirped Bragg reflector provided by an embodiment of the present disclosure;

[0033] Fig. 8 is a structural schematic diagram of a high-reflection structure provided by an embodiment of the present disclosure, wherein (a) is a top view of a metal electrode, (b) is a top view of a ring electrode structure combined with a strip-shaped high-contrast grating, (c) is a top view of a ring electrode structure combined with a ring-shaped high-contrast grating, and (d) is a sectional view of a ring electrode structure combined with a high-contrast sub-wavelength grating;

[0034] Fig. 9 is a schematic diagram of an optimized internal normalized longitudinal intensity distribution of a detector provided by an embodiment of the present disclosure;

[0035] Fig. 10 is a one-dimensional longitudinal light field distribution diagram of a simulated uniform DBR deviating from a resonance peak by 30 nm provided by an embodiment of the present disclosure;

[0036] Fig. 11 is a one-dimensional longitudinal light field distribution diagram of a simulated uniform DBR located at a resonance peak provided by an embodiment of the present disclosure;

[0037] Fig. 12 is a one-dimensional longitudinal light field distribution diagram of a simulated jump-chirped DBR deviating from a resonance peak by 30 nm provided by an embodiment of the present disclosure;

[0038] Fig. 13 is a one-dimensional longitudinal light field distribution diagram of a simulated jump-chirped DBR located at a resonance peak provided by an embodiment of the present disclosure;

[0039] Fig. 14 is a reflectivity versus wavelength diagram of a multi-period high-reflection sub-wavelength grating under different duty cycles simulated provided by an embodiment of the present disclosure;

[0040] Fig. 15 is a flowchart of a preparation method of a resonant-enhanced mesa photodetector based on a chirped Bragg reflector provided by an embodiment of the present disclosure.

[0041] Legend of reference signs: 1-high-reflection structure, 2-P-type epitaxial layer, 3-gradiently-doped absorption layer, 4-ring-shaped metal electrode, 5-N-type epitaxial layer, 6-chirped Bragg reflector, and 7-semi-insulating indium phosphide substrate. DETAILED DESCRIPTION

[0042] A resonant-enhanced mesa photodetector based on a chirped Bragg reflector of an embodiment of the present disclosure is described below with reference to the accompanying drawings.

[0043] Fig. 1 is a structural schematic diagram of a resonant-enhanced mesa photodetector based on a chirped Bragg reflector provided by an embodiment of the present disclosure.

[0044] As shown in Fig. 1, the resonant-enhanced mesa photodetector based on a chirped Bragg reflector includes a high-reflection structure 1, a P-type epitaxial layer 2, a gradiently-doped absorption layer 3, a ring-shaped metal electrode 4, an N-type epitaxial layer 5, a chirped Bragg reflector 6, and a semi-insulating indium phosphide substrate 7.

[0045] The resonant enhancement mesa photodetector based on the chirped Bragg reflector is composed of the high reflection structure 1 at the top and the chirped Bragg reflector 6 at the bottom, and the weak feedback chirped Bragg reflector (i.e. a Bragg reflector whose thickness gradually changes along the epitaxial direction) DBR period at the bottom is no longer constant, so that the detector has higher responsivity and wider optical bandwidth without affecting the response speed.

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

[0047] As shown in FIGS. 2, 4 and 6, in actual implementation, the chirped Bragg reflector 6 can be composed of the reflective layer material indium phosphide (InP) and the substrate material indium gallium arsenide phosphide (InGaAsP (Q1.4)) which are lattice matched with the semi-insulating indium phosphide substrate 7.

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

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

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

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

[0052] In the jump chirped Bragg reflector, the film layer thickness of the adjacent reflective layer material and substrate material has a jump.

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

[0054] As shown in FIG. 2, the linear chirped Bragg reflector refers to the linear variation of the thickness variation of the adjacent InGaAsP / InP high and low refractive index material pairs in the DBR, and thus a preset chirp factor m = Δdi • 4n i / λ to represent the degree of thickness variation of adjacent InGaAsP / InP high and low refractive material layers in the linearly chirped DBR, the chirp factor m ranges from 0.5% to 10%. Wherein, n i corresponds to the refractive index of InGaAsP or InP, λ is the desired resonant wavelength of the device, and Δd i represents the thickness variation between adjacent InGaAsP and InP materials. As shown in FIG. 3, according to the refractive index distribution diagrams of the uniform DBR and the linearly chirped DBR with a chirp factor m of 2%, it can be seen that when the linear factor is small, the structure of the linearly chirped DBR is less different from the uniform DBR, and the thickness varies linearly with the increase of the number of layers. It can reduce the sensitivity of the wavelength within a certain range and maintain a high transmittance.

[0055] As shown in FIG. 4, the nonlinearly chirped Bragg reflector can be defined as the thickness variation of adjacent InGaAsP / InP high and low refractive material pairs does not satisfy the linear relationship, and the nonlinear chirp can satisfy the exponential, logarithmic, polynomial, etc. As shown in FIG. 5, the nonlinearly chirped DBR satisfying the exponential relationship changes more drastically with the increase of the number of layers, increases in the form of an exponential, and the sensitivity to the wavelength is weakened.

[0056] As shown in FIG. 6, the jump chirped DBR structure is also a structure of nonlinear chirp, and the thickness between each layer of the DBR is non-uniform. The thickness between different layers exists a jump, and the thickness variation Δd i does not have obvious regularity. As shown in FIG. 7, according to the refractive index distribution diagrams of the uniform DBR and the jump chirped Bragg reflector, it can be seen that the single layer film thickness of the jump chirped 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 the wavelength and can realize wide spectrum reflection, which is suitable for wide spectrum high responsivity resonant cavity photodetectors which are less sensitive to the wavelength.

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

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

[0059] The strip-shaped sub-wavelength reflective 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.

[0060] The ring-shaped sub-wavelength reflective grating comprises a ring-shaped sub-wavelength grating and aluminum oxide, and the aluminum oxide is arranged at the bottom of the ring-shaped sub-wavelength grating.

[0061] As shown in FIG. 8, in actual implementation, the resonance enhancement effect becomes more significant with the increase of the reflectivity of the top high-reflection structure 1, and thus it is generally desired in design that the top reflectivity is as close to 1 as possible. The present embodiment provides three implementable schemes, i.e., the high-reflection structure 1 can be a metal electrode material or a strip-shaped and ring-shaped sub-wavelength reflective grating with high-reflection function. It should be noted that the top high-reflection structure 1 provided in the present embodiment is not unique, and any structure with high-reflection function can be used.

[0062] As shown in FIG. 8(a), the metal electrode needs to have high reflectivity in a super-wide spectrum range (from visible light to far infrared waveband), generally between 50% and 70%, with small contact resistance and wavelength insensitivity. Common metal electrodes include Ti / Pt / Au or Pt / Ti / Pt / Au, etc.

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

[0064] As shown in FIG. 8(b), the strip-shaped sub-wavelength reflective grating has strong polarization selectivity. First, define the TE polarized light whose electric field direction is parallel to the direction of the strip-shaped grating groove, and the TM polarized light whose electric field direction is perpendicular to the direction of the strip-shaped grating groove. The strip-shaped grating has a reflectivity of greater than 90% for TM polarized light in a wide spectrum waveband, while the average reflectivity of the TE mode is relatively low, generally less than 60%.

[0065] As shown in FIGS. 8(c) and (d), the ring-shaped sub-wavelength reflective grating has a central symmetric structure and is not sensitive to linear polarization, and thus has a reflectivity of greater than 90% for linearly polarized light in any direction in a wide spectrum range. The combination of the two types of gratings with a ring-shaped electrode can reduce the contact resistance of the device. The material of the ring-shaped electrode can be a metal electrode, a transparent electrode, etc.

[0066] Therefore, the embodiments of the present disclosure can combine the top high-reflection structure and the bottom different-chirp DBR structure respectively, so as to obtain different effect types, for example, combining the jump-chirp DBR structure and the metal electrode to form a new type of resonant cavity enhanced photodetector, combining the nonlinear-chirp DBR and the one-dimensional ring-shaped subwavelength reflection grating to form a new type of photodetector, combining the linear-chirp DBR and the one-dimensional strip-shaped subwavelength reflection grating to form a new type of polarization-selective photodetector, and the like.

[0067] The jump-chirp DBR structure and the metal electrode form a new type of resonant cavity enhanced photodetector, and from top to bottom, the metal electrode mirror 1 simulating a real situation, the gradient-doped absorption layer 3, and the chirp Bragg mirror 6 are sequentially arranged, and the 1 and the 6 jointly form a resonant cavity of the photodetector. The incident light forms a standing wave in the resonant cavity and is repeatedly absorbed in the gradient-doped absorption layer 3. As shown in FIG. 9, by adjusting the position of the gradient-doped absorption layer 3, the wave peak position can be controlled in the gradient-doped absorption layer 3 in the case of a thin absorption region, so that the absorption of the device is the strongest, and the optimized longitudinal normalized light field in the resonant cavity can obviously show a resonant enhancement effect.

[0068] In the simulation, the absorption region is fixed to 180 nm, and FIG. 6 shows the one-dimensional longitudinal field distribution diagrams of the conventional uniform DBR photodetector and the optimized jump-chirp DBR photodetector under different incident wavelengths under the same number of layers. As can be seen from 10 and 11, the uniform DBR is sensitive to the wavelength, and when the incident wavelength deviates from the resonant wavelength by 30 nm, most of the light does not enter the absorption region of the device, but is blocked by the DBR outside the substrate. The jump-chirp DBR device has weak sensitivity to the wavelength due to its special structure, has a large optical bandwidth, and the top metal electrode mirror has a high reflection coefficient in a wide spectral band (greater than 1.5 um), which can effectively reduce the sensitivity of the device to the wavelength. As shown in FIG. 12 and FIG. 13, when the wavelength deviates by 30 nm, most of the light enters the absorption region of the photodetector, and thus the superiority of the design of the chirp DBR device can be seen.

[0069] The nonlinear chirped DBR combined with a one-dimensional annular subwavelength reflection grating forms a new type of photodetector, which is polarization-independent for linear polarization. The nonlinear chirped DBR can provide strong resonance enhancement effect in a wide spectral range, and the one-dimensional annular electrode has higher reflectivity than the traditional metal electrode in a certain spectral range, and can have a reflectivity of greater than 90% in the range of 1400 nm to 1700 nm. The increased reflectivity can improve the peak responsivity of the resonant cavity photodetector. The subwavelength grating 14 shows the relationship between the reflectivity of the multi-period high-reflection subwavelength grating and the wavelength under different duty cycles when the oxide layer thickness is 150 nm. The combination of the subwavelength grating and the annular electrode makes the resonant cavity PD have a smaller ohmic resistance and a very high reflectivity of greater than 90% in a wide spectral range. Under high reflectivity, the resonance enhancement effect can be improved, thereby improving the peak responsivity of the device.

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

[0071] Meanwhile, the chirped photodetector is not limited to InP-based, and is also applicable to silicon-based germanium-silicon (GeSi) photodetectors, GaAs-based photodetectors, etc. The material of the chirped DBR can be two different materials with refractive index difference matched with the substrate lattice. Thus, the working wavelength band is not limited to 1550 nm, and any detector using a chirped Bragg mirror as a weak feedback enhancement structure at the bottom belongs to the protection scope of the present disclosure.

[0072] It should be noted that the thickness of the absorption region of the embodiment of the present disclosure is not unique. The thickness of the gradient-doped absorption layer 3 can be 10 nm to 1000 nm. If the thickness of the gradient-doped absorption layer 3 is greater than 1000 nm, the absorption region is thick, and the light is fully absorbed during light field propagation, so there is no need to additionally use resonance effect to absorb light. If the thickness of the gradient-doped absorption layer 3 is less than 10 nm, the absorption region is thin, and it is difficult to control the resonance peak position in the absorption region.

[0073] In summary, the resonant enhancement type mesa photodetector based on the chirped Bragg mirror according to the embodiment of the present disclosure has the following beneficial effects:

[0074] (1) The traditional uniform DBR structure is optimized and the designed chirped DBR structure can greatly improve the optical bandwidth of the device and meet the broadband resonance enhancement characteristics of the resonant cavity detector. Compared with the photodetector without DBR, the photodetector with uniform periodic DBR resonant cavity has a greater advantage.

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

[0076] (3) The chirped Bragg reflector with weak feedback integrated at the bottom (i.e., a Bragg reflector whose thickness gradually changes along the epitaxial direction) no longer has a constant DBR period. 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 higher responsivity and wider optical bandwidth without affecting the response speed.

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

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

[0079] Next, with reference to the accompanying drawings, a method for fabricating a resonant-enhanced mesa photodetector based on a chirped Bragg mirror, according to an embodiment of this disclosure, is described.

[0080] Figure 15 is a schematic flowchart of the fabrication method of the resonant enhancement mesa photodetector based on a chirped Bragg mirror provided in the embodiments of this disclosure.

[0081] As shown in Figure 15, the fabrication method of the resonant enhancement mesa photodetector based on a chirped Bragg mirror includes the following steps:

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

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

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

[0085] In step S1503, P mesa and P-type 2 mesa are sequentially photoetched 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, P mesa is photoetched on the first device, and the mesa is etched in reactive plasma etching using the photoetched P mesa as a mask; P-type 2 mesa is photoetched, and 2 mesa is etched in reactive plasma etching using the photoetched P-type 2 mesa as a mask; and wet etching is performed to the N-type ohmic contact layer to obtain the third device. This method can effectively reduce the sidewall etching phenomenon of the P mesa in wet etching and reduce the dark current of the device.

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

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

[0091] In step S1507, thinning polishing and anti-reflection film deposition are performed on the fifth device to obtain a sixth device, and cleaving is performed on the sixth device to obtain a resonant enhancement type photodetector chip based on a chirped Bragg reflector.

[0092] Specifically, the fourth device is passivated and planarized by using silicon dioxide (SiO2), an electrode window is opened, and a coplanar waveguide line is sputtered to lead out the P and N electrodes, and electroplating is performed to thicken the electrodes to obtain the fifth device; thinning polishing and deposition of anti-reflection film are sequentially performed on the fifth device to obtain the sixth device; and cleaving is performed on the sixth device to obtain the resonant enhancement type photodetector chip based on the chirped Bragg reflector.

[0093] It should be noted that the foregoing explanation and description of the resonant enhancement type mesa photodetector based on the chirped Bragg reflector also applies to the preparation method of the resonant enhancement type mesa photodetector based on the chirped Bragg reflector of this embodiment, which will not be described here.

[0094] The preparation method of the resonant enhancement mesa photodetector based on the chirped Bragg reflector has the following beneficial effects:

[0095] (1) The chirped DBR structure is designed by optimizing the traditional uniform DBR structure, which can greatly improve the optical bandwidth of the device, and can meet the wide-spectrum resonant 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 for different application scenarios is designed, and according to different actual application scenarios, it can be flexibly combined and designed to optimize and achieve the expected effect;

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

[0098] (4) The structure is aimed at the ultra-high-speed photodetector with a bandwidth exceeding 200GHz, and for a relatively thin absorption layer (below 200nm), the light can be absorbed multiple times, which better solves the problem of low responsivity of the ultra-high-speed photodetector;

[0099] (5) It is suitable for various types of mesa photodetectors such as traditional PIN photodetectors and single-row carrier photodetectors (MUTC).

[0100] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" 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 disclosure. In the specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or N embodiments or examples in a suitable manner. In addition, the skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0101] Moreover, the terms "first", "second", "third", etc. are used herein for descriptive purposes only and cannot be construed as indicating or implying relative importance or an indicated number of features so defined. Thus, features defined with "first", "second" or "third" can include, explicitly or implicitly, at least one of such features. In the description of the disclosure, the meaning of "N" is at least two, for example two, three, etc., unless otherwise explicitly and specifically limited.

Claims

1. A resonant enhanced mesa photodetector based on a chirped Bragg mirror, wherein, The high reflection structure and the chirped Bragg reflector constitute a resonant cavity. The chirped Bragg reflector is composed of reflective layer materials and base materials alternately arranged in lattice matching with the semi-insulating indium phosphide substrate.

2. The resonant enhanced mesa photodetector based on a chirped Bragg mirror according to claim 1, wherein, The chirped Bragg reflector adopts a linear chirped Bragg reflector or a nonlinear chirped Bragg reflector.

3. The chirped Bragg-mirror-based resonant-enhanced mesa photodetector of claim 1, wherein, The linear chirped Bragg reflector sets the film thickness of the adjacent reflective layer materials and base materials to vary according to a preset chirp factor.

4. The resonant enhanced mesa photodetector based on a chirped Bragg mirror of claim 3, wherein, The nonlinear chirped Bragg reflector includes an exponential nonlinear chirped Bragg reflector and a jump chirped Bragg reflector, wherein, 5. The resonant enhanced mesa photodetector based on a chirped Bragg mirror of claim 4, wherein, The exponential nonlinear chirped Bragg reflector sets the film thickness of the adjacent reflective layer materials and base materials to vary according to a preset exponential relationship; 6. The resonant enhanced mesa photodetector based on a chirped Bragg mirror of claim 5, wherein, The solution formula of the film layer thickness variation is: m=Ad i ·4n i / λ where m is a preset chirp factor, Δd i is the film thickness variation between adjacent reflective layer material and substrate material, n i is the refractive index of the reflective layer material or substrate material, and λ is the desired resonance wavelength.

7. The resonant enhanced mesa photodetector based on chirped Bragg mirror of claim 4, wherein, The film thickness of the adjacent reflective layer materials and base materials in the jump chirped Bragg reflector jumps. The high reflection structure adopts a metal electrode material or a subwavelength reflective grating with high reflection function. The subwavelength reflective grating with high reflection function is a strip-shaped subwavelength reflective grating or a ring-shaped subwavelength reflective grating, wherein, 8. The resonant enhanced mesa photodetector based on a chirped Bragg mirror of claim 1, wherein, The strip-shaped subwavelength reflective grating includes a strip-shaped subwavelength grating and aluminum oxide, and the aluminum oxide is arranged at the bottom of the strip-shaped subwavelength grating; 9. The resonant enhanced mesa photodetector based on a chirped Bragg mirror of claim 8, wherein, The ring-shaped subwavelength reflective grating includes a ring-shaped subwavelength grating and aluminum oxide, and the aluminum oxide is arranged at the bottom of the ring-shaped subwavelength grating. The method comprises the following steps: Preparation of an epitaxial wafer, and cleaning of the epitaxial wafer, wherein the epitaxial wafer comprises a semi-insulating substrate, a chirped Bragg reflector region, an N-type region, an absorption region, and a P-type region; 10. A method for fabricating a resonant-enhanced mesa photodetector based on a chirped Bragg mirror, wherein, Sputtering of a high reflection structure on the cleaned epitaxial wafer to obtain a first device; Sequential photolithography of a P mesa and a P-type 2 mesa on the first device to obtain a second device; Wet etching of the second device to the N-type ohmic contact layer to obtain a third device; Sputtering of an N electrode on the third device, and photolithography of an N mesa on the N electrode and etching to the semi-insulating substrate to obtain a fourth device; Passivation and filling of the fourth device by silicon dioxide, and opening of an electrode window of the passivated and filled fourth device by sputtering of a coplanar waveguide line to lead out P and N electrodes to obtain a fifth device; Thinning and polishing of the fifth device, deposition of an anti-reflection film on the sixth device, and cleaving of the sixth device to obtain a chirped Bragg reflector-based resonant enhanced photodetector chip. ​ ​

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