High-efficiency bandwidth product photodiode structure

Abstract

The invention discloses a high-efficiency bandwidth product photodiode structure. According to the photodiode, the single-side N contact mesa is adopted, and the semiconductor material below the N contact layer is etched by adopting the selective etching liquid to form the undercut structure, so that the optical signal is further promoted to enter the absorption layer, and meanwhile, the parasitic capacitance of the device is greatly reduced. A unilateral N contact table board with an undercut structure is adopted, and micro-nano structures such as a DBR (Distributed Bragg Reflector), a composite optical waveguide and the like are integrated on a semi-insulating substrate in a monolithic manner, so that the efficiency bandwidth product of the photodiode is improved, and the basic scientific problem that the quantum efficiency and 3dB bandwidth of the photodiode are mutually restricted is solved.

Description

Technical Field

[0001] The present invention relates to the field of optical communication and optoelectronic technology, and more particularly to a high-efficiency bandwidth product photodiode structure. Background Art

[0002] With the continuous advancement of artificial intelligence technology, the information infrastructure plan has begun to change from the Internet of Everything to the Intelligent Internet of Everything. The infrastructure construction of the Intelligent Internet of Everything is inseparable from the development of high-speed wireless communication technology.

[0003] At present, optical fiber communication is the main road to building high-speed wireless communication networks. Photodiodes are key devices for converting optical signals into electrical signals in optical fiber communication systems, and their performance is a key factor in determining the communication system. In order to improve the response speed of the photodetector, it is inevitable to reduce the area of ​​the photosensitive table, but this will lead to a decrease in the quantum efficiency of the device.

[0004] Therefore, how to design the device micro-nano structure to compensate for the quantum efficiency and thus prepare a high-efficiency bandwidth product photodiode is an urgent problem to be solved by those skilled in the art. Summary of the invention

[0005] In view of this, the present invention provides a high-efficiency bandwidth product photodiode structure, which is used to at least solve part of the technical problems in the background technology.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A high-efficiency bandwidth product photodiode structure, comprising a semi-insulating substrate;

[0008] An optical waveguide is arranged on the semi-insulating substrate, and a DBR reflector is arranged at the end of the optical waveguide; the optical waveguide comprises, from bottom to top, an optical waveguide lower cladding, an optical waveguide core layer and an optical waveguide upper cladding, wherein the optical waveguide lower cladding is composed, from bottom to top, of a substrate etched to a certain thickness, a heterogeneous material lattice-matched with the substrate material, and a heavily doped epitaxial layer of the same material as the substrate;

[0009] The tail section of the optical waveguide lower cladding extends to one side to form a cathode contact table of the photodiode, and a cathode metal film electrode is arranged on the cathode contact table;

[0010] The tail section of the optical waveguide core layer is arranged as a photosensitive table, on which a light matching layer, an N-type semiconductor composite layer, a P-type semiconductor composite layer and an anode metal film electrode are arranged in sequence from bottom to top.

[0011] Preferably, the cathode contact mesa adopts a single-sided N-contact mesa with an undercut structure, and the undercut structure is formed by a wet etching process with selective etching.

[0012] Preferably, for the photosensitive mesa, the real part of the refractive index of the semiconductor material layer from the semi-insulating substrate to the anode metal film electrode shows an increasing trend.

[0013] Preferably, the geometric shape of the light incident end of the optical waveguide is rectangular or conical.

[0014] Preferably, the DBR reflector is composed of alternating semiconductor layers and solidified organic polymers or air, wherein the semiconductor layers are composed of an optical waveguide lower cladding layer, an optical waveguide core layer and a non-light absorbing semiconductor layer (4) and are formed by photolithography and dry etching;

[0015] The solidified organic polymer is prepared by spin coating, photolithography, development and other processes of liquid organic polymer;

[0016] The thickness of the semiconductor constituting the DBR reflector in the direction of incident light is equal to Nλ / (4n1), where N is a positive odd number, λ is the wavelength of the light to be detected, and n1 is the real part of the refractive index of the optical waveguide core layer; the thickness of the solidified organic polymer constituting the DBR reflector in the direction of incident light is equal to Mλ / (4n2), where M is a positive odd number, λ is the wavelength of the light to be detected, and n2 is the real part of the refractive index of the solidified organic polymer;

[0017] The number of semiconductor / organic polymer insulator pairs contained in the DBR reflector is determined by the desired light reflectivity.

[0018] Preferably, the DBR reflector, the composite optical waveguide, and the photodiode with a single-side N-contact mesa having an undercut structure are monolithically integrated on a semi-insulating substrate to achieve the goal of improving the efficiency-bandwidth product of the photodiode.

[0019] It can be seen from the above technical solutions that, compared with the prior art, the present invention discloses a high-efficiency bandwidth product photodiode structure, which has the following beneficial effects:

[0020] The present invention discloses a micro-nano structure monolithically integrated with a composite optical waveguide, a DBR reflector and a photodiode with a single-side N-contact table with a down-cut structure. In the designed structure, the single-side N-contact table with a down-cut structure is used, so that the optical signal can be limited to the photosensitive table as much as possible, and the parasitic capacitance of the device is also reduced (beneficial to the high-frequency response of the device). When the optical signal is coupled into the optical waveguide, due to the use of a photodiode with a single-side N-contact table with a down-cut structure, more optical signals can be limited to the photosensitive table area, promoting the absorption of optical signals, and the generated photogenerated carriers form a photocurrent under reverse bias. After the part of the optical signal that does not enter the light absorption layer reaches the end of the optical waveguide, it will be reflected by the DBR reflector and then enter the optical waveguide again in the reverse direction, realizing secondary absorption and increasing the effective absorption length of the device. Therefore, in order to achieve the same response speed, the quantum efficiency of the micro-nano structure proposed by the present invention will be higher than that of the ordinary structure under the same conditions, and it is a special photodiode structure with a high quantum efficiency bandwidth product. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0022] Figure 1 An overall device schematic diagram of a high-efficiency bandwidth product photodiode structure provided by the present invention;

[0023] Figure 2 A schematic cross-sectional view of a photosensitive mesa region perpendicular to the incident light direction provided for a high-efficiency bandwidth product photodiode structure provided by the present invention, wherein the photodiode is a PIN-type photodiode;

[0024] Figure 3 A schematic cross-sectional view of a photosensitive mesa region perpendicular to the incident light direction provided for a high-efficiency bandwidth product photodiode structure provided by the present invention, wherein the photodiode is a single-row carrier type photodiode;

[0025] Figure 4 A schematic cross-sectional view of a photosensitive mesa region perpendicular to the direction of incident light is provided for a high-efficiency bandwidth product photodiode structure provided by the present invention, and the photodiode is an avalanche photodiode. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] A high-efficiency bandwidth product photodiode structure comprises a semi-insulating substrate, an optical waveguide is arranged on the semi-insulating substrate, and a DBR reflector is arranged at the end of the optical waveguide; the optical waveguide comprises, from bottom to top, an optical waveguide lower cladding, an optical waveguide core layer and an optical waveguide upper cladding, wherein the optical waveguide lower cladding is formed by etching a substrate of a certain thickness, a heterogeneous material lattice-matched with the substrate material, and a heavily doped epitaxial layer (N contact layer) of the same material as the substrate through the optical waveguide lower cladding;

[0028] The optical waveguide lower cladding is also the cathode contact surface of the photodiode, and the optical waveguide lower cladding is asymmetrical on the left and right sides in the incident direction of the optical waveguide, that is, there is only one single-sided cathode contact surface (single-sided N contact surface), and the single-sided N contact surface adopts an undercut structure, and a cathode metal film electrode is arranged on the single-sided N contact surface;

[0029] An optical waveguide core layer is arranged on the optical waveguide lower cladding layer, an optical waveguide upper cladding layer having the same film structure is arranged on the L2 section of the optical waveguide core layer, and a photosensitive table is arranged on the L1 section of the optical waveguide core layer; the uppermost layer of the photosensitive table in the structure of the present invention is an anode metal film electrode;

[0030] In the present invention, the photosensitive table, the optical waveguide lower cladding, the optical waveguide core layer, the anode metal film electrode and the cathode metal film electrode constitute a photodiode, and the photodiode can be a PIN photodiode, a single carrier photodiode, an avalanche photodiode or other photodetector types.

[0031] The semiconductor material in the structure of the present invention may be InP material system, GaAs material system, Si material system, etc.

[0032] The present invention integrates a DBR reflector, a composite optical waveguide (optical waveguide lower cladding, optical waveguide core layer 3, optical waveguide upper cladding 9), and a photodiode with a single-sided N-contact table with an undercut structure on a semi-insulating substrate to achieve the goal of improving the efficiency-bandwidth product of the photodiode.

[0033] In the embodiment of the present invention, the photosensitive mesa, the optical waveguide lower cladding, the optical waveguide core layer 3, the anode metal film electrode 7 and the cathode metal film electrode 8 constitute a photodiode.

[0034] In the embodiment of the present invention, the optical waveguide lower cladding layer, the optical waveguide core layer 3 and the optical waveguide upper cladding layer 9 together constitute a composite optical waveguide.

[0035] In an embodiment of the present invention, the geometric shape of the light incident end of the optical waveguide is a cone.

[0036] In an embodiment of the present invention, the DBR reflector is composed of alternating semiconductor layers and solidified organic polymers or air, wherein the semiconductor layers are composed of an optical waveguide lower cladding, an optical waveguide core layer and a non-light-absorbing semiconductor layer and are formed by photolithography and dry etching; the thickness of the semiconductor constituting the DBR reflector in the direction of incident light is equal to 7λ / (4n1), λ is the wavelength of the detected light, and n1 is the real part of the refractive index of the optical waveguide core layer; the thickness of the solidified organic polymer constituting the DBR reflector in the direction of incident light is equal to 3λ / (4n2), λ is the wavelength of the detected light, and n2 is the real part of the refractive index of the solidified organic polymer; the number of semiconductor / organic polymer insulator pairs contained in the DBR reflector is 5.

[0037] In the embodiment of the present invention, the solidified organic polymer is prepared by spin coating, photolithography, development and other processes of liquid organic polymer. In the embodiment of the present invention, the DBR reflector, composite optical waveguide, and photodiode with single-side N-contact mesa are monolithically integrated on a semi-insulating substrate to achieve the goal of improving the efficiency-bandwidth product of the photodiode.

[0038] Example 1

[0039] Example 1 discloses Figure 2 The PIN photodiode shown in the cross-sectional schematic diagram mainly adopts the InP material system as the semiconductor material, and the material layers from the bottom to the top are: InP semi-insulating substrate 1, InP optical waveguide lower cladding 2, N-type InGaAsP (bandgap width is 1.18eV) optical waveguide core layer 3, N-type InGaAsP (bandgap width is 1.0eV) optical matching layer 4, n-type InGaAsP (bandgap width is 1.0eV) depletion layer 5a, intrinsic InGaAsP (bandgap width linearly changes from 0.8eV to 0.75eV) light absorption layer 5b, P-type InGaAs (bandgap width is 0.75eV) light absorption layer 6a, P-type InGaAsP (bandgap width is 0.9eV) electron blocking layer 6b, P-type InGaAsP (bandgap width linearly changes from 0.9eV to 0.6eV) contact layer 6c, and anode metal electrode 7.

[0040] In the embodiment of the present invention, the optical waveguide lower cladding 2 is also a component of the N-contact table. The optical waveguide lower cladding is sequentially formed from top to bottom by etching a heavily doped epitaxial layer 2c (N-contact layer) with a thickness of 0.9 μm, which is the same as the substrate material, a heterogeneous material (Al2O3) with a thickness of 1 μm that matches the InP substrate lattice, and a highly doped epitaxial layer 2c (N-contact layer) with a thickness of 0.9 μm. 0.9 Ga 0.1 As 0.64 Sb 0.36 ) 2b (to facilitate selective wet etching to form an undercut structure), and a 3μm thick substrate 2a, the doping concentration of the N contact layer is 1×10 19 atoms / cm 3 , and the optical waveguide lower cladding 2 is asymmetric on the left and right sides in the incident direction of the optical waveguide, that is, there is only one single-sided cathode contact table (single-sided N contact table).

[0041] In the embodiment of the present invention, the thickness of the N-type optical waveguide core layer 3 is 1 μm, and the doping concentration is 1×10 19 atoms / cm 3 .

[0042] In the embodiment of the present invention, the thickness of the N-type optical matching layer 4 is 0.1 μm and the doping concentration is 5×10 18 atoms / cm 3 .

[0043] In the embodiment of the present invention, the n-type depletion layer 5a is a non-light absorbing depletion layer and the intrinsic light absorbing layer 5b are collectively referred to as Figure 1 The thickness of the N-type semiconductor composite layer 5, the n-type depletion layer 5a is 0.2 μm, and the doping concentration is from 3×10 17 atoms / cm 3 (Close to the end of the N-type optical matching layer 4) linearly gradient to 1×10 16 atoms / cm 3 (close to one end of the intrinsic light absorption layer 5b), the thickness of the intrinsic light absorption layer 5b is 0.1 μm, and the doping concentration is 5×10 15 atoms / cm 3 .

[0044] In the embodiment of the present invention, the P-type light absorbing layer 6a, the P-type electron blocking layer 6b and the P-type contact layer 6b are collectively referred to as Figure 1 The thickness of the P-type semiconductor composite layer 6 and the P-type light absorption layer 6a are 0.2 μm and the doping concentration is from 1×10 18 atoms / cm 3 (close to the end of the intrinsic light absorption layer 5b) linearly gradient to 1×10 19 atoms / cm 3(close to one end of the P-type electron blocking layer 6b), the thickness of the P-type electron blocking layer 6b and the P-type contact layer 6c are 0.015 μm and 0.20 μm respectively, and the doping concentrations are 2×10 19 atoms / cm 3 and 3×10 19 atoms / cm 3 .

[0045] In the embodiment of the present invention, a cathode metal electrode 8 is disposed on the N-contact mesa, and its thickness is about 0.555 μm, and it is composed of Pt / Ti / Pt / Au=2nm / 20nm / 30nm / 500nm.

[0046] In the embodiment of the present invention, an optical waveguide upper cladding layer 9 made of a solidified organic polymer is disposed on the N-type optical waveguide core layer 3 and on the L2 segment, and its thickness is equal to the total thickness of the material layers 4, 5, 6, and 7, and L2 is equal to 15 μm.

[0047] In the embodiment of the present invention, a photosensitive table is provided on the L1 segment of the optical waveguide core layer, and L1 is equal to 5 μm.

[0048] In the embodiment of the present invention, the uppermost layer of the photosensitive mesa is the anode metal film electrode 7, which has a thickness of about 0.555 μm and is composed of Pt / Ti / Pt / Au=2nm / 20nm / 30nm / 200nm.

[0049] Example 2

[0050] Example 2 discloses Figure 3 The single-row carrier type photodiode shown in the cross-sectional schematic diagram, at this time: the optical waveguide core layer 4 is an N-type optical waveguide core layer; the optical matching layer 4 is an N-type optical matching layer; the N-type semiconductor composite layer 5 includes, from bottom to top, an n-type electron collection layer 5c and an n-type gradient band gap layer 5d; the corresponding P-type semiconductor composite layer 6 includes, from bottom to top, a P-type light absorption layer 6a, a P-type electron blocking layer 6b and a P-type contact layer 6c.

[0051] Example 3

[0052] Example 3 discloses Figure 4 In the avalanche photodiode shown in the cross-sectional schematic diagram, at this time: the optical waveguide core layer 3 is still an N-type optical waveguide core layer; the optical matching layer 4 is still an N-type optical matching layer; the N-type semiconductor composite layer 5 includes an N-type light absorption layer 5e and an N-type multiplication layer 5f from bottom to top; and the corresponding P-type semiconductor composite layer 6 is a P-type contact layer 6c.

[0053] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0054] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A high efficiency bandwidth product photodiode structure, characterized in that: comprising, a semi-insulating substrate (1); An optical waveguide (10) is arranged on the semi-insulating substrate (1), and a DBR reflector (11) is arranged at the end of the optical waveguide (10); the optical waveguide (10) comprises, from bottom to top, an optical waveguide lower cladding, an optical waveguide core layer (3), and an optical waveguide upper cladding (9), wherein the optical waveguide lower cladding is, from bottom to top, composed of a substrate (2a) etched to a certain thickness, a heterogeneous material (2b) lattice-matched with the substrate material, and a heavily doped epitaxial layer (2c) having the same material as the substrate; The tail section of the optical waveguide lower cladding extends to one side to form a cathode contact table of the photodiode, and a cathode metal film electrode (8) is arranged on the cathode contact table; The tail section of the optical waveguide core layer (3) is arranged as a photosensitive table, on which a light matching layer (4), an N-type semiconductor composite layer (5), a P-type semiconductor composite layer (6) and an anode metal film electrode (7) are arranged in sequence from bottom to top.

2. The high efficiency bandwidth product photodiode structure according to claim 1, characterized in that: The type of the photodiode is a PIN photodiode. When the type of the photodiode is a PIN photodiode: The optical waveguide core layer (3) is an N-type optical waveguide core layer; the optical matching layer (4) is an N-type optical matching layer; The N-type semiconductor composite layer (5) comprises, from bottom to top, an n-type depletion layer (5a) and an intrinsic light absorption layer (5b); The corresponding P-type semiconductor composite layer (6) comprises, from bottom to top, a P-type light absorption layer (6a), a P-type electron blocking layer (6b) and a P-type contact layer (6c).

3. The high efficiency bandwidth product photodiode structure according to claim 1, characterized in that: The type of the photodiode is a single-carrier type photodiode. When the type of the photodiode is a single-carrier type photodiode: The optical waveguide core layer (3) is an N-type optical waveguide core layer; the optical matching layer (4) is an N-type optical matching layer; The N-type semiconductor composite layer (5) comprises, from bottom to top, an n-type electron collection layer (5c) and an n-type gradient bandgap layer (5d); The corresponding P-type semiconductor composite layer (6) comprises, from bottom to top, a P-type light absorption layer (6a), a P-type electron blocking layer (6b) and a P-type contact layer (6c).

4. The high efficiency bandwidth product photodiode structure according to claim 1, characterized in that: The type of the photodiode is an avalanche photodiode. When the type of the photodiode is an avalanche photodiode: The optical waveguide core layer (3) is an N-type optical waveguide core layer; the optical matching layer (4) is an N-type optical matching layer; The N-type semiconductor composite layer (5) comprises, from bottom to top, an n-type light absorption layer (5e) and an N-type multiplication layer (5f); The corresponding P-type semiconductor composite layer (6) is the P-type contact layer (6c).

5. The high efficiency bandwidth product photodiode structure according to claim 1, characterized in that: The cathode contact mesa adopts a single-side N-contact mesa with an undercut structure.

6. The high efficiency bandwidth product photodiode structure according to claim 1, characterized in that: For the photosensitive mesa, the real part of the refractive index of the semiconductor material layer between the semi-insulating substrate (1) and the anode metal thin film electrode (7) shows an increasing trend.

7. The high efficiency bandwidth product photodiode structure according to claim 1, characterized in that: The geometric shape of the light incident end of the optical waveguide is rectangular or conical.

8. The high efficiency bandwidth product photodiode structure according to claim 1, characterized in that: The DBR reflector (11) is composed of semiconductor layers and solidified organic polymers or air alternately, wherein the semiconductor layer is formed by photolithography and dry etching of an optical waveguide lower cladding layer, an optical waveguide core layer (3) and a semiconductor layer on the optical waveguide core layer (3) that cannot absorb light; The solidified organic polymer is prepared by spin coating, photolithography, development and other processes on liquid organic polymer.

9. The high efficiency bandwidth product photodiode structure according to claim 8, characterized in that: The thickness of the semiconductor layer constituting the DBR reflector (11) in the direction of incident light is equal to Nλ / (4n1), wherein N is a positive odd number, λ is the wavelength of the detected light, and n1 is the real part of the refractive index of the optical waveguide core layer; The thickness of the solidified organic polymer constituting the DBR reflector (11) in the incident light direction is equal to Mλ / (4n2), where M is a positive odd number, λ is the wavelength of the detected light, and n2 is the real part of the refractive index of the solidified organic polymer.

10. The high efficiency bandwidth product photodiode structure according to claim 1, characterized in that: A DBR reflector, a composite optical waveguide, and a photodiode with a single-side N-contact table with an undercut structure are monolithically integrated on a semi-insulating substrate. The composite optical waveguide comprises an optical waveguide lower cladding layer, an optical waveguide core layer (3), and an optical waveguide upper cladding layer (9).

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