Superlattice multiplication layer avalanche diode and preparation method thereof

Abstract

This invention discloses a superlattice multiplication layer avalanche diode and its fabrication method. The single-photon avalanche diode includes a graphene transparent electrode and, from bottom to top, an InP substrate, an n-type buffer layer, a superlattice absorption region, a p-type charge layer, a superlattice gradient region, a superlattice multiplication region, a p-type contact layer with a p-type contact window, and a passivation layer. The graphene transparent electrode is grown on the passivation layer and the p-type contact window, forming an ohmic contact with the p-type contact region. Magnetic metal nanoparticles that generate a local magnetic field are embedded in the superlattice multiplication region. The magnetic metal nanoparticles are uniformly distributed in-plane within a depth range of 5-400 nm from the interface in the light-gathering direction of the superlattice multiplication region. This invention combines the internal bandgap optimization of the superlattice with the external limiting pump capability of graphene to produce a synergistic effect, providing a single-photon avalanche diode with low dark count rate, weak afterpulse effect, high detection efficiency, and the ability to operate at relatively high temperatures.

Description

Technical Field

[0001] This invention relates to the field of photoelectric detection technology, and in particular to a superlattice multiplication layer avalanche diode and its fabrication method. Background Technology

[0002] Traditional InGaAs / InP SPADs employ a bulk material heterojunction structure, which has inherent defects: (1) Hole blocking effect: There is a significant valence band step between the InGaAs absorption layer and the InP multiplication layer, which causes holes to accumulate at the interface, triggering the space charge effect, which is the main source of dark counting and afterpulse. (2) High excess noise: The electron-to-hole ionization coefficient ratio of InP material is not ideal, resulting in high randomness and noise in the avalanche process. (3) Limited counting rate: In order to suppress afterpulse, a long dead time needs to be set, which limits the maximum counting rate.

[0003] To address the aforementioned problems, existing technologies have introduced superlattices or graphene: Superlattice approach: Band engineering is used to smooth band steps and optimize the k value, but the carrier transport speed from the multiplication region to the metal electrode is still limited by the mobility of the semiconductor material itself.

[0004] Graphene approach: Utilizing its high mobility as a transparent electrode or carrier extraction layer, but usually combined with simple bulk material SPAD, it fails to fundamentally solve the problems of band structure and avalanche noise. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a superlattice multiplication layer avalanche diode and its fabrication method. This invention combines the internal bandgap optimization of the superlattice with the external extreme pumping capability of graphene to generate a synergistic effect. It provides a 1550nm band superlattice multiplication layer avalanche diode with low dark count rate, weak afterpulse effect, high detection efficiency, and the ability to operate at higher temperatures. The superlattice design fundamentally solves the problems of bandgap mismatch and high noise. Magnetic particles reduce low-energy thermally generated carriers and edge region carrier multiplication. Simultaneously, integrated graphene enables extremely fast carrier extraction, thereby comprehensively achieving single-photon detection capabilities with low dark count, low afterpulse, low excess noise, high count rate, and high operating temperature.

[0006] To achieve the above objectives, the technical solution provided by this invention is as follows: a superlattice multiplication layer avalanche diode for the 1550nm wavelength band, comprising a graphene transparent electrode and, from bottom to top, an n+ type InP substrate, an n-type buffer layer, a superlattice absorption region, a p-type charge layer, a superlattice gradient region, a superlattice multiplication region, a p-type contact layer with a p-type contact window, and a passivation layer; the graphene transparent electrode is grown on the passivation layer and the p-type contact window, forming an ohmic contact with the p-type contact region; the superlattice multiplication region comprises a hole-ionized InP / InGaAs multi-period superlattice or an InAlAs / InGaAs multi-period superlattice; the superlattice multiplication region is embedded with magnetic metal nanoparticles that generate a local magnetic field, and the magnetic metal nanoparticles are uniformly distributed in-plane within a depth range of 5-400nm from the interface in the light-gathering direction of the superlattice multiplication region, and the particle size range of the magnetic metal nanoparticles is 5-10nm.

[0007] Furthermore, the graphene transparent electrode is a single layer of graphene or a multilayer of graphene.

[0008] Furthermore, the superlattice absorption region is an InGaAs / InAlAs superlattice with a band gap corresponding to a wavelength of 1550 nm.

[0009] Furthermore, a metal electrode is grown on the graphene transparent electrode, and the metal electrode is connected to an active quenching circuit.

[0010] A method for fabricating a superlattice multiplication layer avalanche diode according to the above-mentioned method includes the following steps: S1. On an n+ type InP substrate, an n-type buffer layer, a superlattice absorption region, a p-type charge layer, a superlattice gradient region, a superlattice multiplication region, and a p-type contact layer are epitaxially grown sequentially using MOCVD technology. Before growing the p-type contact layer, the epitaxy is interrupted, and magnetic metal nanoparticles are uniformly distributed into the adjacent interface region of the superlattice multiplication region using ion implantation. S2. Deposit a passivation layer on the P-type contact layer using PECVD technology; S3. Photolithography is used to etch the passivation layer to form a p-type contact window; S4. Using wet transfer technology, the CVD-grown graphene transparent electrode is transferred to the entire device surface, covering the p-type contact window and passivation layer. S5. Electron beam evaporation is used to prepare a metal electrode, which is then brought into contact with a graphene transparent electrode, and the metal electrode is connected to an external active quenching circuit.

[0011] Furthermore, step S1 includes: The doping concentration of the n-type InP buffer layer is 3e17 cm⁻³, and the n-type InP buffer layer is an InP layer with a thickness of 300 nm. The superlattice absorption region is provided with 200 pairs of InGaAs / InAlAs superlattices, and its band gap corresponds to the absorption at a wavelength of 1550nm. The thickness of InGaAs is 7nm and the thickness of InAlAs is 3nm. The doping concentration of the p-type charge layer is 1e17 cm⁻³, and the p-type charge layer is an InP layer with a thickness of 50 nm; The superlattice gradient region is a superlattice gradient region that transitions from InAlAs / InGaAs to InGaAs / InAlAs, with a gradient in layer thickness and a total thickness of 100nm. The superlattice multiplication region has 150 pairs of InAlAs / InGaAs superlattices, wherein the InAlAs thickness is 5nm and the InGaAs thickness is 5nm. The p-type contact layer is an InGaAs contact layer that is further grown using MOCV technology, and the p-type region is formed by Zn diffusion.

[0012] Furthermore, the magnetic metal nanoparticles have a particle size range of 5-10 nm.

[0013] Furthermore, the magnetic metal nanoparticles are cobalt, iron, nickel, or their alloy nanoparticles.

[0014] Furthermore, the graphene transparent electrode is a single layer of graphene or a multilayer of graphene.

[0015] Furthermore, the metal electrode is a Ti / Au electrode.

[0016] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. Synergistic noise reduction: The superlattice multiplication region optimizes the avalanche process from the energy band perspective, eliminating the intrinsic energy band barrier and optimizing the k value; magnetic metal nanoparticles filter noise from the carrier transport path; graphene solves the carrier retention problem; the combination of the above three factors reduces the dark count and afterpulse of the single-photon avalanche diode to extremely low levels.

[0017] 2. Extreme speed: The extremely high mobility of graphene allows avalanche charges to be cleared in nanoseconds, greatly reducing dead time and achieving a counting rate in the GHz range.

[0018] 3. High-temperature operating potential: Excellent noise control and graphene-assisted heat dissipation enable the device to achieve commercial-grade performance at temperatures ranging from -30°C to -10°C or even higher, reducing reliance on deep cooling equipment.

[0019] 4. High detection efficiency: The low operating voltage and efficient absorption and avalanche of the superlattice, the suppression of afterpulse by magnetic metal nanoparticles, and the transparent conductivity of graphene ensure high light input efficiency and charge extraction speed, which together guarantee high photon detection efficiency. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of a superlattice multiplication layer avalanche diode.

[0021] Figure 2 This is a schematic diagram illustrating the working principle of non-magnetic metal nanoparticles deflecting charge carriers within a superlattice multiplication region.

[0022] Figure 3 This is a schematic diagram illustrating the working principle of magnetic metal nanoparticles deflecting charge carriers within a superlattice multiplication region.

[0023] Figure 4 This is the energy band diagram of a current InGaAs / InP single-photon avalanche diode.

[0024] Figure 5 This is the energy band diagram of the superlattice multiplication layer avalanche diode of the present invention.

[0025] Figure 6 This is a schematic diagram of the rapid pumping of holes in the graphene lateral pumping layer. Detailed Implementation

[0026] The present invention will be further described below with reference to specific embodiments. Example

[0027] See Figure 1 As shown, the superlattice multiplication layer avalanche diode for the 1550nm band provided in this embodiment includes a graphene transparent electrode and, from bottom to top, an n+ type InP substrate 1, an n-type buffer layer 2, a superlattice absorption region 3, a p-type charge layer 4, a superlattice gradient region 5, a superlattice multiplication region 6, a p-type contact layer 7 with a p-type contact window, and a passivation layer 8.

[0028] The graphene transparent electrode 9 is a single layer of graphene, on which a metal electrode 10 is grown. The metal electrode 10 is connected to an active quenching circuit (not shown in the figure). The graphene transparent electrode 9 is grown on the passivation layer 8 and the p-type contact window, forming an ohmic contact with the p-type contact region 7. The superlattice absorption region 3 is an InGaAs / InAlAs superlattice with a band gap corresponding to a wavelength of 1550 nm. The passivation layer 8 is a SiNx passivation film. The superlattice multiplication region 6 includes a hole-ionized InP / InGaAs multi-period superlattice or an InAlAs / InGaAs multi-period superlattice. The lattice is designed with hole ionization dominance (k << 1) to achieve low-noise avalanche. Magnetic metal nanoparticles a are embedded in the superlattice multiplication region 6 to generate a local magnetic field. Considering the effective action of magnetic particles on the low-energy thermally generated carrier region at the interface in the light-incident direction, and to reduce the influence of doped particles on the quality of the multiplication layer material, magnetic metal nanoparticles a are injected only near the interface of the superlattice multiplication region 6. The magnetic metal nanoparticles a are uniformly distributed in-plane within a depth range of 5-400 nm from the interface in the light-incident direction of the superlattice multiplication region 6, and the particle size range of the magnetic metal nanoparticles a is 5-10 nm.

[0029] See Figures 2 to 3 As shown, the superlattice multiplication region is a strong electric field region where avalanches occur, traversed by a high electric field line. The edge of the mesa, b, is a concentrated electric field region and a weak point prone to edge breakdown. Within the superlattice multiplication region, several spherical magnetic metal nanoparticles a are dispersed. Each magnetic metal nanoparticle a acts as a tiny magnet, generating a local magnetic field, as shown by concentric magnetic field lines c. Photogenerated electrons injected from the superlattice absorption region are injected vertically upward at high speed into the superlattice multiplication region. Thermally generated electrons, generated by thermal excitation within the device, move randomly in various directions. The trajectory of these thermally generated electrons happens to pass through the high-field region at the edge, triggering an unwanted avalanche, i.e., generating dark count m and edge breakdown n. Similarly, when photogenerated and thermally generated electrons are injected, their trajectories are significantly bent when they approach or pass through the magnetic field of the magnetic particles.

[0030] For photogenerated electrons, due to their high kinetic energy and strong directionality, their trajectory d only undergoes slight bending in the magnetic field, but still successfully traverses the entire superlattice multiplication region, completing normal avalanche multiplication. For thermally generated electrons, due to their low initial kinetic energy and random motion direction, their trajectory e undergoes severe bending under the Lorentz force, becoming a spiral or a large arc. These deflected charge carriers are eventually "thrown out" of the high-field region or collide with the sidewalls and are recombine and annihilated. In particular, at the left edge, a charge carrier trajectory e that would normally cause edge breakdown is deflected by the magnetic field, bypassing the high-field region at the edge, thus avoiding edge breakdown.

[0031] Magnetic metal nanoparticles a embedded in the superlattice multiplication region generate tiny local magnetic fields on their own without the need for an external magnetic field. Charge carriers, namely electrons and holes, moving at high speed under the operating voltage, are subjected to a Lorentz force F=q(v×B) perpendicular to their direction of motion when passing through these magnetic fields.

[0032] First, this design enables selective filtering, filtering out thermally generated carriers and reducing dark counts. Low-energy, randomly oriented thermally generated carriers are extremely sensitive to the Lorentz force, causing their trajectories to deflect sharply, preventing them from crossing the multiplication region and triggering avalanches, thus effectively "filtering" them out. Second, this design can suppress edge breakdown and improve uniformity. In regions with concentrated electric fields at the device edges, the magnetic field can "push away" carrier paths, preventing them from accumulating and multiplying at the edges, thereby forcing avalanches to occur in a more uniform bulk, improving the stability and reliability of the device. Furthermore, high-energy, vertically oriented photogenerated carriers experience only slight trajectory shifts, sufficient to ensure normal avalanche multiplication, with minimal impact on photon detection efficiency. In summary, this "magnetic filtering" effect actively removes noise-causing carriers at the physical level, which is key to the significant reduction in dark count rate and afterpulse probability in this embodiment.

[0033] See Figures 4 to 5 As shown, traditional InGaAs / InP heterojunctions exhibit a significant valence band step ΔEv, leading to the accumulation of photogenerated holes at the interface and triggering a space charge effect, thereby increasing noise and slowing down the response speed. This embodiment 'tailors' the band structure by introducing a compositionally graded superlattice transition region between the superlattice absorption region and the superlattice multiplication region, successfully eliminating the sharp valence band step and achieving a smooth valence band transition. This design enables efficient and rapid hole extraction, fundamentally suppressing noise caused by hole accumulation, such as afterpulses and partial dark counting, while significantly improving the device's response speed and count rate.

[0034] Traditional single-photon avalanche diodes employ localized metal electrodes. Photogenerated holes in regions far from the electrode must traverse a long and highly resistive lateral path to be collected, resulting in significant propagation delay, hole accumulation, and series resistance. This limits the device's response speed and count rate, and causes localized heating. See also Figure 6 As shown, this embodiment uses a fully covered monolayer of graphene as a transparent electrode. Photogenerated holes g can be vertically injected into the graphene, and then transported laterally at the edge of the metal contact thanks to the graphene's extremely high carrier mobility and in-plane conductivity. This 'vertical injection-lateral ultrafast pumping' mechanism greatly shortens the hole collection time, effectively suppresses hole accumulation, and reduces series resistance and thermal effects, providing a key guarantee for achieving low-noise, high-speed single-photon detection. Example

[0035] See Figure 1 As shown, this embodiment provides a method for fabricating a superlattice multiplication layer avalanche diode according to Embodiment 1, including the following steps: S1. On an n+ type InP substrate 1, an n-type buffer layer 2, a superlattice absorption region 3, a p-type charge layer 4, a superlattice gradient region 5, a superlattice multiplication region 6, and a p-type contact layer 7 are epitaxially grown sequentially using MOCVD technology. Among them, the magnetic metal nanoparticles a are cobalt nanoparticles. Before growing the p-type contact layer 7, the epitaxy is interrupted, and the magnetic metal nanoparticles a are uniformly distributed in the adjacent interface region of the superlattice multiplication region 6 by ion implantation. The particle size range of the magnetic metal nanoparticles a is 5-10 nm.

[0036] The doping concentration of the n-type InP buffer layer 2 is 3e17 cm⁻³, and the n-type InP buffer layer 2 is an InP layer with a thickness of 300 nm.

[0037] The superlattice absorption region 3 has 200 pairs of InGaAs / InAlAs superlattices, and its band gap corresponds to the absorption at a wavelength of 1550nm. The thickness of InGaAs is 7nm and the thickness of InAlAs is 3nm.

[0038] The doping concentration of the p-type charge layer 4 is 1e17 cm⁻³, and the p-type charge layer 4 is an InP layer with a thickness of 50 nm.

[0039] Superlattice gradient region 5 is a superlattice gradient region that transitions from InAlAs / InGaAs to InGaAs / InAlAs, with a gradient in layer thickness and a total thickness of 100nm.

[0040] The superlattice multiplication region 6 has 150 pairs of InAlAs / InGaAs superlattices, with InAlAs having a thickness of 5 nm and InGaAs having a thickness of 5 nm.

[0041] The p-type contact layer 7 is an InGaAs contact layer grown using MOCV technology, with a thickness of 100 nm, and forms a p-type region through Zn diffusion.

[0042] S2. Deposit a SiNx passivation layer 8 on the P-type contact layer 7 using PECVD technology.

[0043] S3. The SiNx passivation layer 8 is etched using photolithography to form a p-type contact window.

[0044] S4. Using wet transfer technology, the CVD-grown graphene transparent electrode 9 is transferred to the entire device surface, covering the p-type contact window and the SiNx passivation layer 8; the graphene transparent electrode 9 is a single layer of graphene or a multilayer of graphene.

[0045] S5. Electron beam evaporation is used to prepare Ti / Au electrode 10, which is then in contact with graphene transparent electrode 9, and Ti / Au electrode 10 is connected to an external active quenching circuit.

[0046] The above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Therefore, any changes made in accordance with the shape and principle of the present invention should be covered within the protection scope of the present invention.

Claims

1. A superlattice multiplication layer avalanche diode for the 1550nm wavelength band, characterized in that: The system comprises a graphene transparent electrode and, from bottom to top, an n+ type InP substrate, an n-type buffer layer, a superlattice absorption region, a p-type charge layer, a superlattice gradient region, a superlattice multiplication region, a p-type contact layer with a p-type contact window, and a passivation layer. The graphene transparent electrode is grown on the passivation layer and the p-type contact window, forming an ohmic contact with the p-type contact region. The superlattice multiplication region includes a hole-ionized InP / InGaAs multi-period superlattice or an InAlAs / InGaAs multi-period superlattice. The superlattice multiplication region contains embedded magnetic metal nanoparticles that generate a local magnetic field. The magnetic metal nanoparticles are uniformly distributed in-plane within a depth range of 5-400 nm from the interface in the light-gathering direction of the superlattice multiplication region, and the particle size range of the magnetic metal nanoparticles is 5-10 nm.

2. The superlattice multiplication layer avalanche diode according to claim 1, characterized in that: The graphene transparent electrode is a single layer of graphene or a multilayer of graphene.

3. The superlattice multiplication layer avalanche diode according to claim 1, characterized in that: The superlattice absorption region is an InGaAs / InAlAs superlattice with a band gap corresponding to a wavelength of 1550 nm.

4. The superlattice multiplication layer avalanche diode according to claim 2, characterized in that: A metal electrode is grown on the graphene transparent electrode, and the metal electrode is connected to an active quenching circuit.

5. A method for fabricating a superlattice multiplication layer avalanche diode according to any one of claims 1-4, characterized in that, Includes the following steps: S1. On an n+ type InP substrate, an n-type buffer layer, a superlattice absorption region, a p-type charge layer, a superlattice gradient region, a superlattice multiplication region, and a p-type contact layer are epitaxially grown sequentially using MOCVD technology. Before growing the p-type contact layer, the epitaxy is interrupted, and magnetic metal nanoparticles are uniformly distributed into the adjacent interface region of the superlattice multiplication region using ion implantation. S2. Deposit a passivation layer on the P-type contact layer using PECVD technology; S3. Photolithography is used to etch the passivation layer to form a p-type contact window; S4. Using wet transfer technology, the CVD-grown graphene transparent electrode is transferred to the entire device surface, covering the p-type contact window and passivation layer. S5. Electron beam evaporation is used to prepare a metal electrode, which is then brought into contact with a graphene transparent electrode, and the metal electrode is connected to an external active quenching circuit.

6. The method for fabricating a superlattice multiplication layer avalanche diode according to claim 5, characterized in that, Step S1 includes: The doping concentration of the n-type InP buffer layer is 3e17 cm⁻³, and the n-type InP buffer layer is an InP layer with a thickness of 300 nm. The superlattice absorption region is provided with 200 pairs of InGaAs / InAlAs superlattices, and its band gap corresponds to the absorption at a wavelength of 1550nm. The thickness of InGaAs is 7nm and the thickness of InAlAs is 3nm. The doping concentration of the p-type charge layer is 1e17 cm⁻³, and the p-type charge layer is an InP layer with a thickness of 50 nm; The superlattice gradient region is a superlattice gradient region that transitions from InAlAs / InGaAs to InGaAs / InAlAs, with a gradient in layer thickness and a total thickness of 100nm. The superlattice multiplication region has 150 pairs of InAlAs / InGaAs superlattices, wherein the InAlAs thickness is 5nm and the InGaAs thickness is 5nm. The p-type contact layer is an InGaAs contact layer that is further grown using MOCV technology, and the p-type region is formed by Zn diffusion.

7. The method for fabricating a superlattice multiplication layer avalanche diode according to claim 5, characterized in that, The magnetic metal nanoparticles have a particle size range of 5-10 nm.

8. The method for fabricating a superlattice multiplication layer avalanche diode according to claim 5, characterized in that, The magnetic metal nanoparticles are cobalt, iron, nickel, or their alloy nanoparticles.

9. The method for fabricating a superlattice multiplication layer avalanche diode according to claim 5, characterized in that, The graphene transparent electrode is a single layer of graphene or a multilayer of graphene.

10. The method for fabricating a superlattice multiplication layer avalanche diode according to claim 5, characterized in that, The metal electrode is a Ti / Au electrode.

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