Avalanche photodetector and method of manufacturing the same

Abstract

The application provides an avalanche photodetector and a preparation method thereof, and relates to the technical fields of photodetectors and photoelectronic materials. The avalanche photodetector comprises, from bottom to top, an InP substrate, a first ohmic contact layer, a buffer layer, a multiplication layer, a charge control layer, a gradient layer, an absorption layer, a second ohmic contact layer and a cladding layer. The multiplication layer is made of AlGaAsSb. The gradient layer is made of Al with gradually changed components and In with unchanged components. The absorption layer is made of InGaAs and GaAs which are alternately and periodically grown. x Al y Ga 1‑x‑y As x Ga 1‑x As and GaAs y Sb 1‑y The application can realize short-wave infrared detection with expanded wavelength and high signal-to-noise ratio, effectively reduce carrier capture caused by band gap difference, reduce lattice strain at the interface, thereby reduce defect density, optimize the injection efficiency of carriers from the absorption layer to the multiplication layer, and thus improve the performance of the device.

Description

Technical Field

[0001] This invention relates to the field of photodetectors and optoelectronic materials technology, and in particular to an avalanche photodetector and its fabrication method. Background Technology

[0002] Short-wave infrared (SWIR) photodetectors (detection wavelengths of 1–3 μm) have significant applications in various fields, such as Light Laser Detection and Ranging (LiDAR) systems, gas detection, medical imaging, and optical communication systems. Avalanche photodiodes (APDs), due to their photogenerated carrier multiplication effect, have become a key technology in high-sensitivity photodetection. The response wavelength and noise characteristics of APDs depend on the material selection of the absorption layer and the multiplication layer.

[0003] Regarding the response wavelength, the APD device based on an InP substrate and employing a lattice-matched InGaAs absorber layer has a response cutoff wavelength of [wavelength value missing]. It is difficult to meet the requirements of complex environment imaging and gas detection scenarios. The above-mentioned special requirements for the shortwave infrared band.

[0004] Regarding noise characteristics, commonly used multiplication layers in short-wave infrared APDs primarily consist of materials such as InP (hole injection multiplication layer) and InAlAs (electron injection multiplication layer). Since the effective mass of electrons is smaller than that of holes, they can achieve faster drift velocities, thereby improving the response speed of the APD device. In electron injection APD devices, InAlAs, as the multiplication layer, has a relatively large ratio k (k=β / α) of hole to electron ionization coefficients (β and α), which introduces significant excess noise, thus limiting the ability to detect weak signals.

[0005] Regarding differences in material band gaps or lattice constants, the operating principle of an APD (Active Photodiode) requires photogenerated carriers to rapidly cross the interface into the multiplication layer for avalanche multiplication after generation in the absorption layer. However, due to differences in material band gaps between different layers, carriers are often trapped at the interface, hindering efficient carrier transport. In traditional APD designs, the absorption layer and multiplication layer often use semiconductor materials with different band gaps. This creates significant obstacles to carrier transport between layers with different band gaps, especially in applications requiring high responsivity and low noise, where the carrier trapping problem caused by band gap differences is even more pronounced. Furthermore, lattice constant mismatches often occur when selecting materials for the absorption layer and multiplication layer, particularly at the junctions between different compound semiconductor materials, where lattice strain is particularly prominent. If this cannot be effectively mitigated, it can severely limit device performance. Existing solutions typically alleviate band gap differences and lattice mismatches by employing different epitaxial growth techniques or interface treatment methods, but these methods often fail to fundamentally solve the long-term performance problems caused by band gap differences and lattice constant mismatches. Meanwhile, traditional material design and structural layout have limited effectiveness in improving carrier injection efficiency and still face certain technical bottlenecks. Summary of the Invention

[0006] This invention provides an avalanche photodetector and its fabrication method, which enables extended wavelength short-wave infrared detection and a high signal-to-noise ratio, effectively reduces carrier trapping caused by bandgap differences, reduces lattice strain at the interface, thereby reducing defect density, and optimizes the carrier injection efficiency from the absorption layer to the multiplication layer, thus improving device performance.

[0007] The present invention provides an avalanche photodetector, which comprises, from bottom to top: an InP substrate, a first ohmic contact layer, a buffer layer, a multiplication layer, a charge control layer, a gradient layer, an absorption layer, a second ohmic contact layer, and a cladding layer;

[0008] The multiplication layer is made of AlGaAsSb; the gradient layer is made of In with a gradient Al composition and a constant In composition. x Al y Ga 1-x-y The absorber layer is made of As; the absorber layer is grown using multiple sets of periodically alternating In layers. x Ga 1-x As and GaAs y Sb 1-y Made.

[0009] According to an avalanche photodetector provided by the present invention, the first ohmic contact layer adopts InP lattice matching. 0.53 Ga 0.47The first ohmic contact layer is made of As and has a thickness of 300-500 nm; the doping source of the first ohmic contact layer is Te, and the doping concentration is 7 × 10⁻⁶. 18 cm -3 ~2×10 19 cm -3 .

[0010] According to the present invention, an avalanche photodetector is provided, wherein the buffer layer is made of Al. 0.75 Ga 0.25 As 0.55 Sb 0.45 The buffer layer is fabricated with a thickness of 200-400 nm; the doping source of the buffer layer is Te, and the doping concentration is 9 × 10⁻⁶. 17 cm -3 ~2×10 18 cm -3 .

[0011] According to the avalanche photodetector provided by the present invention, the multiplication layer is an intrinsically doped Al layer with a lattice match to the InP substrate. 0.75 Ga 0.25 As 0.55 Sb 0.45 The process is carried out, and the thickness of the multiplication layer is 1000~1500nm.

[0012] According to the avalanche photodetector provided by the present invention, the charge control layer adopts Al 0.75 Ga 0.25 As 0.55 Sb 0.45 The charge control layer is fabricated with a thickness of 135-150 nm; the doping source of the charge control layer is Be, and the doping concentration is 1×10⁻⁶. 16 cm -3 ~2×10 16 cm -3 The doping type is p-type doping.

[0013] According to the present invention, an avalanche photodetector is provided, wherein In in the gradient layer x Al y Ga 1-x-y The Al content of As decreases along the direction from the charge control layer to the absorption layer.

[0014] According to an avalanche photodetector provided by the present invention, the Al composition of the gradient layer decreases from 0.4 to 0.1, where 0.1≤y≤0.4.

[0015] According to the avalanche photodetector provided by the present invention, the gradient layer consists of three layers, each with a thickness of 15 nm.

[0016] According to the avalanche photodetector provided by the present invention, the absorption layer is an unintentionally doped In material grown in 150 sets of periodically alternating layers. x Ga 1-x As and GaAs y Sb 1-y Made, 0.5≤x≤0.7, 0.4≤y≤0.5, each group In x Ga 1-x As and GaAs y Sb 1-y The thickness of each layer is 3~5nm, and the total thickness of the absorption layer is 1300~1500nm.

[0017] According to an avalanche photodetector provided by the present invention, the second ohmic contact layer adopts InP lattice matching. 0.53 Ga 0.47 The second ohmic contact layer is made of As, and its thickness is 160~200 nm; the doping source of the second ohmic contact layer is Be, and the doping concentration is 9×10⁻⁶. 17 cm -3 ~2×10 18 cm -3 .

[0018] According to the present invention, an avalanche photodetector is provided, wherein the cladding is made of In. 0.53 Ga 0.47 The cladding is made of As, with a thickness of 30-50 nm; the doping source of the cladding is Be, and the doping concentration is 7 × 10⁻⁶. 18 cm -3 ~2×10 19 cm -3 .

[0019] This invention also provides a method for fabricating an avalanche photodetector, comprising:

[0020] Molecular beam epitaxy (MBE) was used to grow an epitaxial wafer on an InP substrate from bottom to top, consisting of a first ohmic contact layer, a buffer layer, a multiplication layer, a charge control layer, a gradient layer, an absorption layer, a second ohmic contact layer, and a cladding layer. The multiplication layer was made of AlGaAsSb, and the gradient layer was made of In with a gradient Al composition and a constant In composition. x Al y Ga 1-x-y The absorber layer is made of As; the absorber layer is grown using multiple sets of periodically alternating In layers. x Ga 1-x As and GaAs y Sb 1-y Made;

[0021] The epitaxial wafer is cleaned, and a silicon dioxide sacrificial layer is grown on the cleaned epitaxial wafer;

[0022] A first photoresist layer is coated on the silicon dioxide sacrificial layer, and the first photoresist is photolithographically etched to form a patterned first photoresist.

[0023] Using the patterned first photoresist as a mask, the silicon dioxide sacrificial layer is etched to form a patterned silicon dioxide sacrificial layer;

[0024] Remove any remaining first photoresist and clean the area.

[0025] Using the patterned silicon dioxide sacrificial layer as a mask, the epitaxial wafer is etched to form an epitaxial wafer with mesa.

[0026] Remove the remaining silica sacrificial layer;

[0027] A passivation layer is deposited on the epitaxial wafer with the mesa;

[0028] A second photoresist layer is coated on the passivation layer, and the second photoresist is photolithographically patterned to form a patterned second photoresist.

[0029] Using the patterned second photoresist as a mask, the passivation layer is etched to expose the electrode window;

[0030] Remove any remaining second photoresist and clean the area.

[0031] A metal layer is grown using magnetron sputtering.

[0032] A third photoresist layer is coated on the metal layer, and the third photoresist is photolithographically etched to form a patterned third photoresist.

[0033] Using the patterned third photoresist as a mask, the metal layer is etched to form electrodes;

[0034] Remove the remaining third photoresist and clean the area.

[0035] The back side of the epitaxial wafer with the mesa is thinned, polished, and then cleaved to obtain the final avalanche photodetector.

[0036] The avalanche photodetector and its fabrication method provided by this invention comprise, from bottom to top: an InP substrate, a first ohmic contact layer, a buffer layer, a multiplication layer, a charge control layer, a gradient layer, an absorption layer, a second ohmic contact layer, and a cladding layer. The multiplication layer is made of AlGaAsSb. Using AlGaAsSb, a low-k material, as the multiplication layer can effectively reduce the excess noise factor of the avalanche photodetector and achieve a high signal-to-noise ratio. The gradient layer is made of In with a gradient Al composition and a constant In composition. x Al y Ga 1-x-y Made of As, using In x Al y Ga 1-x-y As a gradient layer, As can alleviate problems caused by differences in material band gap or lattice constant by changing the Al composition. This effectively reduces carrier trapping due to band gap differences, reduces lattice strain at the interface, thereby lowering defect density and optimizing carrier injection efficiency from the absorption layer to the multiplication layer, thus improving device performance. The absorption layer is grown using multiple sets of periodically alternating In layers. x Ga 1-x As and GaAs y Sb 1-y This invention utilizes an InGaAs / GaAsSb superlattice structure instead of the traditional InGaAs as the absorption layer, extending the response wavelength from 1.55 μm to 2 μm, thus enabling extended-wavelength short-wave infrared detection. Therefore, this invention achieves extended-wavelength short-wave infrared detection with a high signal-to-noise ratio, effectively reduces carrier trapping caused by bandgap differences, reduces lattice strain at the interface, thereby lowering defect density and optimizing carrier injection efficiency from the absorption layer to the multiplication layer, thus improving device performance. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0038] Figure 1 This is a schematic diagram of the avalanche photodetector provided in an embodiment of the present invention.

[0039] Figure 2 This is a schematic diagram of the antimony-suppressed k-value provided in an embodiment of the present invention.

[0040] Figure 3 This is a schematic diagram of the energy band structure of two types of superlattices provided in an embodiment of the present invention.

[0041] Figure 4 This is a schematic flowchart of the fabrication method of the avalanche photodetector provided in an embodiment of the present invention.

[0042] Figure 5 This is a schematic diagram of the process flow for the fabrication method of the avalanche photodetector provided in an embodiment of the present invention. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0044] The following is combined with Figures 1-5 The avalanche photodetector and its fabrication method of the present invention are described.

[0045] Please refer to Figure 1 , Figure 1 This is a schematic diagram of the avalanche photodetector provided in an embodiment of the present invention. Figure 1 As shown, the avalanche photodetector comprises, from bottom to top: an InP substrate 1, a first ohmic contact layer 2, a buffer layer 3, a multiplication layer 4, a charge control layer 5, a gradient layer 6, an absorption layer 7, a second ohmic contact layer 8, and a cladding layer 9.

[0046] The InP substrate 1 is made of InP and has a thickness of 320 μm.

[0047] Optionally, the first ohmic contact layer 2 is made of InP lattice-matched InP. 0.53 Ga 0.47 The first ohmic contact layer 2 is made of As and has a thickness of 300-500 nm. The doping source for the first ohmic contact layer 2 is Te, with a doping concentration of 7 × 10⁻⁶. 18 cm -3 ~2×10 19 cm -3 .

[0048] Optionally, buffer layer 3 uses Al 0.75 Ga 0.25 As 0.55 Sb 0.45 The buffer layer 3 is fabricated with a thickness of 200-400 nm. The doping source for buffer layer 3 is Te, with a doping concentration of 9 × 10⁻⁶. 17 cm -3 ~2×10 18 cm -3 .

[0049] The 4th multiplication layer is made of AlGaAsSb. By using AlGaAsSb, a low-k material, as the 4th multiplication layer, the introduction of antimony (Sb) significantly improves the splitting energy level of the valence band of the 4th multiplication layer and moves it away from the heavy hole and light hole bands. This can effectively suppress hole ionization, reduce the k value, and thus effectively reduce the excess noise factor of the avalanche photodetector, achieve a higher signal-to-noise ratio, and improve the performance of the 4th multiplication layer.

[0050] Optionally, the multiplication layer 4 is an intrinsically doped Al layer with a lattice match to the InP substrate. 0.75 Ga 0.25 As 0.55 Sb 0.45 The process is completed, and the thickness of the multiplication layer 4 is 1000~1500nm.

[0051] Experiments have shown that the introduction of antimony (Sb) can lower the k-value. Specifically, Figure 2 Figure (a) illustrates the transition process of a hole, with the arrows indicating the hole's trajectory. This can be achieved by increasing the energy of the spin-splitting coupling band, such as... Figure 2 As shown in Figure (b), the spin-splitting coupling level and the light-heavy hole band are separated. The collisional ionization of holes located on the heavy hole band is suppressed, and the collisional ionization coefficient ratio of electron to hole increases, i.e., the k value decreases.

[0052] Optionally, the charge control layer 5 uses Al 0.75 Ga 0.25 As 0.55 Sb 0.45 The charge control layer 5 is fabricated with a thickness of 135-150 nm. The doping source for the charge control layer 5 is Be, with a doping concentration of 1 × 10⁻⁶. 16 cm -3 ~2×10 16 cm -3 The doping type is p-type doping.

[0053] Gradient layer 6 uses an In layer with a gradient Al composition and a constant In composition. x Al y Ga 1-x-y Made of As. Using In x Al y Ga 1-x-y As a gradient layer 6, As can alleviate the problems caused by differences in material band gap or lattice constant by changing the Al composition, effectively reduce carrier trapping caused by band gap differences, reduce lattice strain at the interface, thereby reducing defect density, optimizing the carrier injection efficiency from absorption layer 7 to multiplication layer 4, and thus improving device performance.

[0054] Optionally, in gradient layer 6 Inx Al y Ga 1-x-y The Al content of As decreases along the direction from the charge control layer 5 to the absorption layer 7.

[0055] Optionally, the Al composition of the gradient layer 6 decreases from 0.4 to 0.1, where 0.1 ≤ y ≤ 0.4.

[0056] Optionally, the gradient layer 6 consists of 3 layers, each with a thickness of 15nm.

[0057] The absorber layer 7 is grown using multiple sets of periodically alternating In layers. x Ga 1-x As and GaAs y Sb 1-y Made. (e.g.) Figure 3 As shown, the InGaAs / GaAsSb type-two superlattice structure material system possesses high conduction band shift and low valence band shift. Therefore, by using the InGaAs / GaAsSb superlattice structure instead of the traditional InGaAs as the absorption layer 7, the response wavelength can be effectively extended from 1.55 μm to above 2 μm, enabling extended-wavelength short-wave infrared detection.

[0058] Optionally, the absorber layer 7 is an unintentionally doped In layer grown in 150 sets of periodically alternating stacked layers. x Ga 1-x As and GaAs y Sb 1-y Made, 0.5≤x≤0.7, 0.4≤y≤0.5, each group In x Ga 1-x As and GaAs y Sb 1-y The thickness of each layer is 3~5nm, and the total thickness of the absorption layer 7 is 1300~1500nm.

[0059] Optionally, the second ohmic contact layer 8 employs InP lattice-matched In... 0.53 Ga 0.47 The second ohmic contact layer 8 is made of As and has a thickness of 160-200 nm. The doping source for the second ohmic contact layer 8 is Be, with a doping concentration of 9 × 10⁻⁶. 17 cm -3 ~2×10 18 cm -3 .

[0060] Optionally, cladding 9 uses In 0.53 Ga 0.47 The cladding layer 9 is made of As and has a thickness of 30-50 nm. The doping source for cladding layer 9 is Be, with a doping concentration of 7 × 10⁻⁶. 18 cm -3~2×10 19 cm -3 .

[0061] The avalanche photodetector provided in this embodiment of the invention comprises, from bottom to top: an InP substrate, a first ohmic contact layer, a buffer layer, a multiplication layer, a charge control layer, a gradient layer, an absorption layer, a second ohmic contact layer, and a cladding layer. The multiplication layer is made of AlGaAsSb. Using AlGaAsSb, a low-k material, as the multiplication layer can effectively reduce the excess noise factor of the avalanche photodetector and achieve a high signal-to-noise ratio. The gradient layer is made of In with a gradient Al composition and a constant In composition. x Al y Ga 1-x-y Made of As, using In x Al y Ga 1-x-y As a gradient layer, As can alleviate problems caused by differences in material band gap or lattice constant by changing the Al composition. This effectively reduces carrier trapping due to band gap differences, reduces lattice strain at the interface, thereby lowering defect density and optimizing carrier injection efficiency from the absorption layer to the multiplication layer, thus improving device performance. The absorption layer is grown using multiple sets of periodically alternating In layers. x Ga 1-x As and GaAs y Sb 1-y The device is fabricated using an InGaAs / GaAsSb superlattice structure instead of the traditional InGaAs as the absorption layer, extending the response wavelength from 1.55 μm to 2 μm, thus enabling extended-wavelength short-wave infrared detection. Therefore, this embodiment of the invention achieves extended-wavelength short-wave infrared detection and a high signal-to-noise ratio, effectively reducing carrier trapping caused by bandgap differences, reducing lattice strain at the interface, thereby reducing defect density, and optimizing carrier injection efficiency from the absorption layer to the multiplication layer, thus improving device performance.

[0062] The fabrication method of the avalanche photodetector provided by the present invention is described below. The fabrication method of the avalanche photodetector described below can be referred to in correspondence with the avalanche photodetector described above.

[0063] Please refer to Figure 4 , Figure 4 This is a schematic flowchart of the fabrication method of the avalanche photodetector provided in an embodiment of the present invention. Figure 4 As shown, the method may include steps 401-416.

[0064] Step 401: Using molecular beam epitaxy, an epitaxial wafer is grown sequentially from bottom to top on an InP substrate, consisting of a first ohmic contact layer, a buffer layer, a multiplication layer, a charge control layer, a gradient layer, an absorption layer, a second ohmic contact layer, and a cladding layer; wherein, the multiplication layer is made of AlGaAsSb; the gradient layer is made of InxAl with a gradient Al composition and a constant In composition. y Ga 1-x-y Made of As; the absorber layer is grown using multiple sets of periodically alternating In layers. x Ga 1-x As and GaAs y Sb 1-y Made.

[0065] Specifically, the multiplication layer is made of AlGaAsSb. Using AlGaAsSb, a low-k material, as the multiplication layer can effectively reduce the excess noise factor of the avalanche photodetector and achieve a higher signal-to-noise ratio.

[0066] The gradient layer uses an Al composition that is gradually changed while the In composition remains constant. x Al y Ga 1-x-y Made of As, using In x Al y Ga 1-x-y As a gradient layer, As can alleviate problems caused by differences in material band gap or lattice constant by changing the Al composition, effectively reduce carrier trapping caused by band gap differences, reduce lattice strain at the interface, thereby reducing defect density and optimizing the carrier injection efficiency from the absorption layer to the multiplication layer, thus improving device performance.

[0067] The absorber layer is grown using multiple sets of periodically alternating In layers. x Ga 1-x As and GaAs y Sb 1-y It is fabricated by using an InGaAs / GaAsSb superlattice structure instead of the traditional InGaAs as the absorption layer, which extends the response wavelength from 1.55μm to 2μm, enabling extended wavelength short-wave infrared detection.

[0068] Step 402: Clean the epitaxial wafer and grow a silicon dioxide sacrificial layer on the cleaned epitaxial wafer.

[0069] Specifically, such as Figure 5 As shown in Figure (a), the epitaxial wafer is cleaned. Figure 5 As shown in Figure (b), a silicon dioxide sacrificial layer is grown on the cleaned epitaxial wafer.

[0070] Step 403: Coat a layer of first photoresist on the silicon dioxide sacrificial layer, and perform photolithography on the first photoresist to form a patterned first photoresist.

[0071] Specifically, such as Figure 5 As shown in Figure (c), a first photoresist layer is coated on the silicon dioxide sacrificial layer. Figure 5 As shown in Figure (d), the first photoresist is photolithographically etched to form a patterned first photoresist.

[0072] Step 404: Using the patterned first photoresist as a mask, etch the silicon dioxide sacrificial layer to form a patterned silicon dioxide sacrificial layer.

[0073] Specifically, such as Figure 5 As shown in Figure (e), a patterned silicon dioxide sacrificial layer is formed by etching a patterned silicon dioxide sacrificial layer using a patterned first photoresist as a mask.

[0074] Step 405: Remove the remaining first photoresist and clean it.

[0075] Specifically, such as Figure 5 As shown in Figure (f), the remaining first photoresist is removed and the area is cleaned.

[0076] Step 406: Using a patterned silicon dioxide sacrificial layer as a mask, the epitaxial wafer is etched to form an epitaxial wafer with mesa.

[0077] Specifically, such as Figure 5 As shown in Figure (g), an epitaxial wafer with mesa is formed by etching an epitaxial wafer with a patterned silicon dioxide sacrificial layer as a mask.

[0078] Step 407: Remove the remaining silicon dioxide sacrificial layer.

[0079] Specifically, such as Figure 5 As shown in Figure (h), the remaining silica sacrificial layer is removed.

[0080] Step 408: Deposit a passivation layer on the epitaxial wafer with mesa.

[0081] Specifically, such as Figure 5 As shown in Figure (i), a passivation layer is deposited on an epitaxial wafer with mesa. The material of the passivation layer can be silicon dioxide.

[0082] Step 409: Coat a second photoresist layer on the passivation layer and perform photolithography on the second photoresist to form a patterned second photoresist.

[0083] Specifically, such as Figure 5 As shown in Figure (j), a second photoresist layer is coated on the passivation layer. Figure 5As shown in Figure (k), the second photoresist is photolithographically etched to form a patterned second photoresist.

[0084] Step 410: Using the patterned second photoresist as a mask, etch the passivation layer to expose the electrode window.

[0085] Specifically, such as Figure 5 As shown in Figure (l), a patterned second photoresist is used as a mask to etch the passivation layer, exposing the electrode window.

[0086] Step 411: Remove the remaining second photoresist and clean the area.

[0087] Specifically, such as Figure 5 As shown in the (m) diagram, the remaining second photoresist was removed and the area was cleaned.

[0088] Step 412: Grow a metal layer using magnetron sputtering.

[0089] Specifically, such as Figure 5 As shown in Figure (n), a metal layer is grown using magnetron sputtering. The material of the metal layer is Ti or Au.

[0090] Step 413: Coat a layer of third photoresist on the metal layer and perform photolithography on the third photoresist to form a patterned third photoresist.

[0091] Specifically, such as Figure 5 As shown in Figure (o), a third photoresist layer is coated on the metal layer.

[0092] Step 414: Using patterned third photoresist as a mask, etch the metal layer to form an electrode.

[0093] Step 415: Remove the remaining third photoresist and clean the area.

[0094] Step 416: Thin and polish the back side of the epitaxial wafer with a mesa, and then cleave it to obtain the final avalanche photodetector.

[0095] Specifically, for Figure 5 After photolithography, etching, resist removal, cleaning, thinning, polishing, and dicing of the (o) image, a wafer is prepared as shown. Figure 5 The avalanche photodetector shown in Figure (p) is an example.

[0096] It should be noted that epitaxial wafers can also be grown using other methods, and this embodiment is not limited to molecular beam epitaxy.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An avalanche photodetector, characterized by, From bottom to top, sequentially include: InP substrate, first ohmic contact layer, buffer layer, multiplication layer, charge control layer, graded layer, absorption layer, second ohmic contact layer and cladding layer; The multiplication layer is made of AlGaAsSb; the gradient layer is made of Al component gradient, In component unchanged In x Al y Ga 1-x-y As; the absorption layer is made of multiple groups of periodical alternating layer growth In x Ga 1-x As and GaAs y Sb 1-y .

2. The avalanche photodetector of claim 1, wherein, The first ohmic contact layer is made of In matched with InP lattice 0.53 Ga 0.47 As, the thickness of the first ohmic contact layer is 300-500 nm; the doping source of the first ohmic contact layer is Te, and the doping concentration is 7×10 18 cm -3 ~2×10 19 cm -3 .

3. The avalanche photodetector of claim 1, wherein, The buffer layer is made of Al 0.75 Ga 0.25 As 0.55 Sb 0.45 The thickness of the buffer layer is 200-400 nm; the doping source of the buffer layer is Te, and the doping concentration is 9×10 17 cm -3 ~2×10 18 cm -3 .

4. The avalanche photodetector of claim 1, wherein, The multiplication layer is made of intrinsic doped Al 0.75 Ga 0.25 As 0.55 Sb 0.45 The thickness of the multiplication layer is 1000-1500 nm.

5. The avalanche photodetector of claim 1, wherein, The charge control layer is made of Al 0.75 Ga 0.25 As 0.55 Sb 0.45 The thickness of the charge control layer is 135-150 nm; the doping source of the charge control layer is Be, the doping concentration is 1×10 16 cm -3 -2×10 16 cm -3 , and the doping type is p-type doping.

6. The avalanche photodetector of claim 1, wherein, In of the graded layer x Al y Ga 1-x-y The Al component of As decreases in a direction of the charge control layer pointing toward the absorption layer.

7. The avalanche photodetector of claim 6, wherein, The Al component of the graded layer decreases from 0.4 to 0.1, and 0.1<=y<=0.

4.

8. The avalanche photodetector according to claim 6 or 7, wherein, The graded layer is divided into three layers in total, and the thickness of each layer is 15nm.

9. The avalanche photodetector of claim 1, wherein, The absorption layer is made of 150 groups of periodically and alternately stacked unintentionally doped In x Ga 1-x As and GaAs y Sb 1-y , 0.5≤x≤0.7, 0.4≤y≤0.5, the thickness of each group of In x Ga 1-x As and GaAs y Sb 1-y is 3-5 nm, and the total thickness of the absorption layer is 1300-1500 nm.

10. The avalanche photodetector of claim 1, wherein, The second ohmic contact layer is made of In which matches the InP crystal lattice 0.53 Ga 0.47 As, the thickness of the second ohmic contact layer is 160-200 nm; the doping source of the second ohmic contact layer is Be, and the doping concentration is 9x1018-2x1019cm-3. 17 cm -3 ~2x1019 18 cm -3 .

11. The avalanche photodetector of claim 1, wherein, The cladding layer is made of In 0.53 Ga 0.47 As, the thickness of the cladding layer is 30-50 nm; the doping source of the cladding layer is Be, and the doping concentration is 7×10 18 cm -3 ~2×10 19 cm -3 .

12. A method for fabricating an avalanche photodetector, characterized in that, Comprise: The first ohmic contact layer, the buffer layer, the multiplication layer, the charge control layer, the gradual change layer, the absorption layer, the second ohmic contact layer and the cladding layer of the epitaxial wafer are sequentially grown from bottom to top on an InP substrate by using a molecular beam epitaxy technology; the multiplication layer is made of AlGaAsSb; the gradual change layer is made of Al component gradually changing and In component keeping unchanged x Al y Ga 1-x-y As; the absorption layer is made of In x Ga 1-x As and GaAs y Sb 1-y which are alternately and periodically grown. The epitaxial wafer is cleaned, and a silicon dioxide sacrificial layer is grown on the cleaned epitaxial wafer; A first photoresist is coated on the silicon dioxide sacrificial layer, and the first photoresist is subjected to photolithography to form a patterned first photoresist; The silicon dioxide sacrificial layer is etched with the patterned first photoresist as a mask to form a patterned silicon dioxide sacrificial layer; The remaining first photoresist is removed and cleaned; The epitaxial wafer is etched with the patterned silicon dioxide sacrificial layer as a mask to form an epitaxial wafer with a mesa; The remaining silicon dioxide sacrificial layer is removed; A passivation layer is deposited on the epitaxial wafer with a mesa; A second photoresist is coated on the passivation layer, and the second photoresist is subjected to photolithography to form a patterned second photoresist; The passivation layer is etched with the patterned second photoresist as a mask to expose the electrode window; The remaining second photoresist is removed and cleaned; A metal layer is grown by a magnetron sputtering process; A third photoresist is coated on the metal layer, and the third photoresist is subjected to photolithography to form a patterned third photoresist; The metal layer is etched with the patterned third photoresist as a mask to form an electrode; The remaining third photoresist is removed and cleaned; The back of the epitaxial wafer with a mesa is thinned and polished, and the final avalanche photodetector is obtained after wafer slicing and cleaving.

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