Single photon source and preparation method thereof

Abstract

A single-photon source and a preparation method thereof, the single-photon source comprises: a single-photon generation module, comprising: a first substrate; a first distributed Bragg reflector located on the first substrate, formed by alternately stacking a first refractive index layer and a second refractive index layer; a quantum dot layer located on the first distributed Bragg reflector, generating electron-hole pairs under the action of incident laser, and generating single photons after the electron-hole pairs are recombined; a cavity mirror module located on a side of the single-photon generation module close to the quantum dot layer and forming a vacuum gap with the single-photon generation module; the cavity mirror module comprises: a second substrate; a second distributed Bragg reflector located on the second substrate, formed by alternately stacking a third refractive index layer and a fourth refractive index layer; the second distributed Bragg reflector and the first distributed Bragg reflector form a plano-concave resonant cavity, so that a single photon having a resonance frequency consistent with the plano-concave resonant cavity oscillates in the plano-concave resonant cavity and is output.

Description

Technical Field

[0001] The present invention relates to the field of quantum information science, and in particular to a single photon source and a preparation method thereof. Background Art

[0002] For single-photon sources, there are mainly three types: quasi-single-photon sources, probabilistic single-photon sources, and deterministic single-photon sources. Quasi-single-photon sources pulse the laser and attenuate the pulsed laser so that the average number of photons in a single pulse is close to 1. The advantage of this quasi-single-photon source is that it is simple and easy to obtain, but the disadvantage is that the single-photon count is small and multi-photon events cannot be avoided. Probabilistic light sources use nonlinear processes to generate single photons or entangled photon pairs, mainly including four-wave mixing and spontaneous parametric down-conversion (SPDC). However, the nature of its probabilistic light source determines that it is difficult to avoid multi-photon components. In order to suppress the multi-photon component, its single-photon generation efficiency is limited to about 1%. Deterministic light sources use the spontaneous radiation process of discrete energy level systems, which is a natural way to generate single photons. Based on the spontaneous radiation process of the two-level system, when the two-level system is pumped from the ground state to the excited state, the system cannot be pumped again during the relaxation process from the excited state to the ground state, so multi-photon events can be avoided in principle.

[0003] Semiconductor solid-state quantum dots, due to their natural three-dimensional potential well confinement, exhibit a discrete energy level structure similar to that of atoms. Thanks to their high quantum efficiency, they can achieve on-demand high-quality single-photon emission through pulse resonant excitation, external field regulation (such as external electric field, external stress, etc.) and coherent manipulation of their transition process between the ground state and the excited state. Therefore, they can be used in deterministic single-photon sources.

[0004] Currently commonly used semiconductor solid-state quantum dots include InAs / GaAs quantum dots, InAs / InP quantum dots and GaAs / AlGaAs quantum dots. Among them, compared with InAs / GaAs quantum dots and InAs / InP quantum dots, GaAs / AlGaAs quantum dots have the characteristics of long decoherence time and obvious biexciton energy levels. However, the overall efficiency of single-photon sources based on GaAs / AlGaAs quantum dots is currently low, which limits the application of GaAs / AlGaAs quantum dots in single-photon sources. Summary of the invention

[0005] In view of the above technical problems, the present invention provides a single photon source and a preparation method thereof.

[0006] As one aspect of the present invention, a single photon source is provided, comprising:

[0007] Single-photon generation module, comprising:

[0008] A first substrate;

[0009] A first distributed Bragg reflector, located on the first substrate, formed by alternately stacking a first refractive index layer and a second refractive index layer, the material of the first refractive index layer being SiO2, and the material of the second refractive index layer being Ta2O5;

[0010] A quantum dot layer, located on the first distributed Bragg reflector, the quantum dot layer comprising quantum dots, the material of the quantum dots being composed of GaAs and Al x Ga 1-x As, where 0 < x < 1, the quantum dots generate electron-hole pairs under the action of incident laser light, and single photons are generated after the electron-hole pairs recombine;

[0011] A cavity mirror module, located on the side of the single-photon generation module close to the quantum dot layer and forming a vacuum gap with the single-photon generation module, a recess is formed in the middle of the side of the cavity mirror module facing the single-photon generation module; the cavity mirror module comprises:

[0012] A second substrate;

[0013] A second distributed Bragg reflector, located on the second substrate, formed by alternately stacking a third refractive index layer and a fourth refractive index layer, the material of the third refractive index layer being SiO2, and the material of the fourth refractive index layer being Ta2O5; the second distributed Bragg reflector and the first distributed Bragg reflector form a plano-concave resonant cavity;

[0014] Wherein, the first distributed Bragg reflector and the second distributed Bragg reflector perform multi-stage reflection on the single photons generated by the quantum dot layer, so that the single photons consistent with the resonance frequency of the plano-concave resonant cavity oscillate and output in the plano-concave resonant cavity.

[0015] According to an embodiment of the present invention, the single-photon generation module further comprises:

[0016] An N-type metal contact layer, disposed on the first distributed Bragg reflector;

[0017] An electron tunneling barrier layer, disposed on the N-type metal contact layer; wherein, the quantum dot layer is disposed on the electron tunneling barrier layer; the electron tunneling barrier layer is adapted to prevent electrons in the N-type metal contact layer from entering the quantum dot layer;

[0018] A hole blocking barrier layer, disposed on the quantum dot layer;

[0019] A first P-type metal contact layer, disposed on the hole blocking barrier layer;

[0020] A second P-type metal contact layer, disposed on the first P-type metal contact layer;

[0021] Wherein, the hole blocking barrier layer is suitable for blocking the holes in the first P-type metal contact layer and the second P-type metal contact layer from entering the quantum dot layer;

[0022] The doping concentration of the material of the first P-type metal contact layer is lower than the doping concentration of the material of the second P-type metal contact layer.

[0023] According to an embodiment of the present invention, the cavity mode of the plano-concave resonant cavity can be adjusted by changing the size of the vacuum gap;

[0024] The Single Photon Generation Module also includes:

[0025] The optical field adaptation layer is arranged on the second P-type metal contact layer; the thickness of the optical field adaptation layer is configured to adjust the optical path of the vacuum electric field formed by the cavity mode of the plano-concave resonant cavity, so that the quantum dot layer is located at the peak of the vacuum electric field, and at the same time, the center position determined by the first P-type metal contact layer and the second P-type metal contact layer is located at the trough of the vacuum electric field.

[0026] According to an embodiment of the present invention, the above-mentioned single photon source further includes:

[0027] A P-terminal metal, located on the second P-type metal contact layer;

[0028] N-terminal metal, located on the N-type metal contact layer;

[0029] The external voltage signal is loaded between the second P-type metal contact layer and the N-type metal contact layer through the P-terminal metal and the N-terminal metal;

[0030] The material of the light field adaptation layer is Al 0.4 Ga 0.6 As, the thickness of the light field adaptation layer is 30-60 nm.

[0031] According to an embodiment of the present invention, in the first distributed Bragg reflector, the first refractive index layer is closest to the quantum dot layer, and in the second distributed Bragg reflector, the fourth refractive index layer is closest to the quantum dot layer.

[0032] According to an embodiment of the present invention, the reflection center wavelength of the first distributed Bragg reflector is the same as the reflection center wavelength of the second distributed Bragg reflector.

[0033] According to an embodiment of the present invention, in the first distributed Bragg reflector, the number of the first refractive index layer and the second refractive index layer are 10 to 25 respectively;

[0034] In the second distributed Bragg reflector, the number of the third refractive index layer and the number of the fourth refractive index layer are 1 to 20, respectively.

[0035] The sum of the number of the third refractive index layers and the number of the fourth refractive index layers is less than the sum of the number of the first refractive index layers and the number of the second refractive index layers.

[0036] According to an embodiment of the present invention, the material of the first P-type metal contact layer is P-type doped Al a Ga 1‐a As,0 <a<0.45;

[0037] The material of the second P-type metal contact layer is P-type doped Al b Ga 1‐b As,0 <b<0.45;

[0038] The material of the N-type metal contact layer is N-type doped Al c Ga 1‐c As,0 <c<0.45;

[0039] The material of the hole blocking barrier layer is Al d Ga 1‐d As,0 <d<0.45;

[0040] The material of the electron tunneling barrier layer is Al e Ga 1‐e As,0 <e<0.45。

[0041] As a second aspect of the present invention, a method for preparing a single photon source is also provided, which is used to prepare the above-mentioned single photon source, and the method comprises:

[0042] The material is Al prepared on a temporary substrate by molecular beam epitaxy. x Ga 1-x As first epitaxial layer, where 0 <x<1;

[0043] A nanopore is etched on the first epitaxial layer by using a localized droplet etching method, the nanopore is filled with GaAs, and a second epitaxial layer with the same material as the first epitaxial layer is grown on the filled first epitaxial layer by using a molecular beam epitaxy method to obtain a quantum dot layer, wherein the portions of the first epitaxial layer and the second epitaxial layer used for confining GaAs form quantum dots with the GaAs located in the nanopore;

[0044] The first distributed Bragg reflector is fabricated on the quantum dot layer by magnetron sputtering;

[0045] Bonding the first substrate to a side of the first distributed Bragg reflector away from the quantum dot layer, and removing the temporary substrate to obtain a single photon generation module;

[0046] A second distributed Bragg reflector is prepared on a second substrate by a magnetron sputtering method to obtain a cavity mirror module;

[0047] The cavity mirror module is arranged on a side of the single-photon generation module close to the quantum dot layer, and a vacuum gap is formed between the cavity mirror module and the single-photon generation module.

[0048] According to an embodiment of the present invention, a material Al is prepared on a temporary substrate by using a molecular beam epitaxy method. x Ga 1-x Before forming the first epitaxial layer of As, the method further comprises:

[0049] A light field adaptation layer, a second P-type metal contact layer, a first P-type metal contact layer and a hole blocking barrier layer are sequentially prepared on a temporary substrate by molecular beam epitaxy, wherein the first epitaxial layer is formed on the hole blocking barrier layer;

[0050] Before preparing the first distributed Bragg reflector on the quantum dot layer by magnetron sputtering, the method further includes:

[0051] An electron tunneling barrier layer and an N-type metal contact layer are sequentially prepared on the quantum dot layer using molecular beam epitaxy.

[0052] According to an embodiment of the present invention, by making the materials GaAs and Al x Ga 1-x Quantum dots composed of As (i.e., GaAs / AlGaAs quantum dots) are applied to a single-photon source based on a plano-concave resonant cavity, and SiO2 and Ta2O5 are used to form a first distributed Bragg reflector and a second distributed Bragg reflector, respectively. This enables the first distributed Bragg reflector and the second distributed Bragg reflector to have a high reflection effect on single photons generated by GaAs / AlGaAs quantum dots, and will not absorb single photons generated by GaAs / AlGaAs quantum dots. Therefore, the single-photon source prepared in this embodiment of the present invention has a high overall efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 shows a cross-sectional view of a single photon source provided according to an embodiment of the present invention;

[0054] Figure 2 A result diagram of simulating a single photon source using a finite element method provided in an embodiment of the present invention is shown;

[0055] Figure 3 A diagram showing simulation results of the collection efficiency and Purcell factor of a single photon source provided according to an embodiment of the present invention is shown.

[0056] Description of Reference Numerals

[0057] 101: a first substrate;

[0058] 102: The first distributed Bragg reflector;

[0059] 102-1: first refractive index layer;

[0060] 102-2: second refractive index layer;

[0061] 103: quantum dot layer;

[0062] 104: N-type metal contact layer;

[0063] 105: electron tunneling barrier layer;

[0064] 106: hole blocking barrier layer;

[0065] 107: first P-type metal contact layer;

[0066] 108: second P-type metal contact layer;

[0067] 109: light field adaptation layer;

[0068] 110: first passivation layer;

[0069] 111: second passivation layer;

[0070] 112: bonding dielectric layer;

[0071] 201: second substrate;

[0072] 202: second distributed Bragg reflector;

[0073] 202-1: third refractive index layer;

[0074] 202-2: fourth refractive index layer;

[0075] 300: vacuum interval;

[0076] 400: P-end metal;

[0077] 500: N-terminal metal. DETAILED DESCRIPTION

[0078] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0079] Figure 1 A cross-sectional view of a single photon source provided according to an embodiment of the present invention is shown.

[0080] like Figure 1As shown, the single-photon source includes: a single-photon generation module and a cavity mirror module. The single-photon generation module includes: a first substrate 101, a first distributed Bragg reflector 102, and a quantum dot layer 103. The first distributed Bragg reflector 102 is located on the first substrate 101 and is formed by alternately stacking a first refractive index layer 102-1 and a second refractive index layer 102-2. The material of the first refractive index layer 102-1 is SiO2, and the material of the second refractive index layer 102-2 is Ta2O5. The quantum dot layer 103 is located on the first distributed Bragg reflector 102. The quantum dot layer 103 includes quantum dots, and the material of the quantum dots is composed of GaAs and Al x Ga 1-x As, where 0 < x < 1. The quantum dots generate electron-hole pairs under the action of incident laser light, and single photons are generated after the electron-hole pairs recombine. According to an embodiment of the present invention, x can be, for example, 0.4.

[0081] The cavity mirror module includes: a second substrate 201 and a second distributed Bragg reflector 202. The cavity mirror module is located on the side of the single-photon generation module close to the quantum dot layer 103 and forms a vacuum gap 300 with the single-photon generation module. A recess is formed in the middle of the side of the cavity mirror module facing the single-photon generation module.

[0082] The second distributed Bragg reflector 202 is located on the second substrate 201 and is configured to have a periodic stacked structure formed by alternately arranging a third refractive index layer 202-1 and a fourth refractive index layer 202-2. The material of the third refractive index layer 202-1 is SiO2, and the material of the fourth refractive index layer 202-2 is Ta2O5. The second distributed Bragg reflector 202 and the first distributed Bragg reflector 102 form a plano-concave resonator.

[0083] Among them, the first distributed Bragg reflector 102 and the second distributed Bragg reflector 202 perform multiple reflections on the single photons generated by the quantum dot layer 103 located in the plano-concave resonator, so that the single photons consistent with the resonance frequency of the plano-concave resonator oscillate and output in the plano-concave resonator.

[0084] According to an embodiment of the present invention, by using materials GaAs and Al x Ga 1-xThe single-photon source provided by quantum dots composed of As (i.e., GaAs / AlGaAs quantum dots) is applied to a single-photon source based on a plano-concave resonant cavity, and SiO2 and Ta2O5 are used to form a first distributed Bragg reflector 102 and a second distributed Bragg reflector 202, respectively, so that the first distributed Bragg reflector 102 and the second distributed Bragg reflector 202 can have a high reflection effect on the single photons generated by the GaAs / AlGaAs quantum dots, and will not absorb the single photons generated by the GaAs / AlGaAs quantum dots. Therefore, the single-photon source prepared in this embodiment of the present invention has a high overall efficiency.

[0085] According to the embodiment of the present invention, since GaAs / AlGaAs quantum dots are used, which have obvious biexciton energy levels, two-photon resonant excitation can be used to replace the single-photon resonant excitation in the prior art. Compared with single-photon resonant excitation, when two-photon resonant excitation is used, since there is a gap (~1 nm) between the excitation light wavelength and the single-photon fluorescence wavelength, the background laser in the single photon can be better eliminated, which is conducive to the generation of single photons with higher purity.

[0086] According to an embodiment of the present invention, the wavelength of single photons generated by GaAs / AlGaAs quantum dots covers 780-795 nm, which matches the D1 and D2 lines of 87Rb atoms, one of the mainstream solutions for quantum storage, making it possible for the two to be combined to form the basic nodes of the quantum network.

[0087] According to an embodiment of the present invention, the electron decoherence time of GaAs / AlGaAs quantum dots is relatively long. Based on the spin cooling technology, the electron decoherence time has been increased to 608 ns. The longer electron decoherence time can better realize the spin-photon interface, the basic module of the quantum network, and is also more conducive to the deterministic preparation of large-scale cluster states to realize measurement-based quantum computing and other applications.

[0088] According to an embodiment of the present invention, the incident laser is a pulsed laser, which is incident on the surface of the single-photon generation module through the transparent cavity mirror module, excites the quantum dot layer 103 to generate single photons, and the single photons output by the single-photon source are collected by the confocal optical path to the spectrometer through the cavity mirror module. At the same time, the line width of the spectrum of the quantum dot can be reduced by adjusting the voltage of the external power supply of the single-atom source to obtain a better optical signal.

[0089] According to an embodiment of the present invention, the recessed portion is a spherical cap structure, the curvature radius of the recessed portion is 5-20 um, and the radius is 1-5 um.

[0090] According to the embodiment of the present invention, the central wavelengths of the first distributed Bragg reflector 102 and the second distributed Bragg reflector 202 are both in the range of 500-2000 nm, and the central wavelengths of the first distributed Bragg reflector 102 and the second distributed Bragg reflector 202 are the same.

[0091] According to an embodiment of the present invention, the emission wavelength of the single photon generated by the quantum dot is in the 780-795nm band. It can be seen that the central wavelengths of the first distributed Bragg reflector 102 and the second distributed Bragg reflector 202 can cover the emission wavelength of the quantum dot. Therefore, the first distributed Bragg reflector 102 and the second distributed Bragg reflector 202 have a high reflection on the single photon generated by the quantum dot.

[0092] According to an embodiment of the present invention, in the first distributed Bragg reflector 102, the number of layers of the first refractive index layer 102-1 and the second refractive index layer 102-2 is respectively 10 to 25. In the second distributed Bragg reflector 202, the number of layers of the third refractive index layer 202-1 and the fourth refractive index layer 202-2 is respectively 1 to 20. The sum of the number of layers of the third refractive index layer 202-1 and the number of layers of the fourth refractive index layer 202-2 is less than the sum of the number of layers of the first refractive index layer 102-1 and the number of layers of the second refractive index layer 102-2.

[0093] According to the embodiment of the present invention, in the first distributed Bragg reflector 102, the first refractive index layer 102-1 is closest to the quantum dot layer 103, and in the second distributed Bragg reflector 202, the fourth refractive index layer 202-2 is closest to the quantum dot layer 103. The thickness of each layer of the first distributed Bragg reflector 102 determines the reflection center wavelength of the first distributed Bragg reflector 102, and the thickness of each layer of the second distributed Bragg reflector 202 determines the reflection center wavelength of the second distributed Bragg reflector 202.

[0094] According to the embodiment of the present invention, the reflection center wavelength of the first distributed Bragg reflector 102 is the same as the reflection center wavelength of the second distributed Bragg reflector 202 .

[0095] According to an embodiment of the present invention, the first distributed Bragg reflector 102 includes a plurality of first reflection pairs, each of which includes a SiO2 material layer and a Ta2O5 material layer. The second distributed Bragg reflector 202 includes a plurality of second reflection pairs, each of which includes a SiO2 material layer and a Ta2O5 material layer. The number of first reflection pairs is 10 to 25. The number of second reflection pairs is 1 to 20. Preferably, the number of first reflection pairs in the first distributed Bragg reflector 102 is 20.5, that is, the first layer and the last layer of the first distributed Bragg reflector 102 are both SiO2 layers. Preferably, the number of second reflection pairs in the second distributed Bragg reflector 202 is 8 pairs. Al in quantum dots x Ga 1-x As is a high refractive index material. Among SiO2 and Ta2O5, SiO2 has a lower refractive index. SiO2 and Ta2O5 can achieve a higher refractive index contrast and better confine light in the active area. The first and last layers of the first distributed Bragg reflector 102 are set as SiO2 layers, so that the overall efficiency of single photons generated in the single photon source is higher.

[0096] According to an embodiment of the present invention, the calculation of the transmission matrix shows that when the center wavelength of the reflection spectrum of the first distributed Bragg reflector 102 and the second distributed Bragg reflector 202 is designed to be 790 nm, the reflectivity of 20 first reflection pairs and 20 second reflection pairs is 99.9995%. Similarly, the center wavelength of the reflection spectrum of the first distributed Bragg reflector 102 and the second distributed Bragg reflector 202 is designed to be 790 nm, and the material of the first distributed Bragg reflector 102 and the second distributed Bragg reflector 202 is replaced with Al 0.4 Ga 0.6 When using As and AlAs, the reflectivity of 30 pairs of first reflection pairs and 30 pairs of second reflection pairs is only 99.92%, and the bandwidth when using SiO2 and Ta2O5 materials is much smaller than that when using AlAs. 0.4 Ga 0.6 The bandwidth of As and AlAs is 2.7 times wider. The bandwidth is affected by the materials of the first distributed Bragg reflector 102 and the second distributed Bragg reflector 202, and the logarithm of the first reflection pair and the second reflection pair. The greater the difference in the refractive index of the material, the wider the bandwidth and the higher the reflectivity; the higher the logarithm, the wider the bandwidth and the higher the reflectivity. Therefore, in this case, SiO2 and Ta2O5 materials are selected to achieve reflection with higher reflectivity and wider bandwidth with fewer logarithms.

[0097] According to an embodiment of the present invention, the single photon generation module further includes: an N-type metal contact layer 104 , an electron tunneling barrier layer 105 , a hole blocking barrier layer 106 , a first P-type metal contact layer 107 and a second P-type metal contact layer 108 .

[0098] The N-type metal contact layer 104 is disposed on the first distributed Bragg reflector 102. The electron tunneling barrier layer 105 is disposed on the N-type metal contact layer 104. The quantum dot layer 103 is disposed on the electron tunneling barrier layer 105. The electron tunneling barrier layer 105 is adapted to prevent electrons in the N-type metal contact layer 104 from entering the quantum dot layer 103. The hole blocking barrier layer 106 is disposed on the quantum dot layer 103. The first P-type metal contact layer 107 is disposed on the hole blocking barrier layer 106. The second P-type metal contact layer 108 is disposed on the first P-type metal contact layer 107. Among them, the hole blocking barrier layer 106 is adapted to prevent holes in the first P-type metal contact layer 107 and the second P-type metal contact layer 108 from entering the quantum dot layer 103.

[0099] According to an embodiment of the present invention, the cavity mode of the plano-concave resonant cavity is adjusted by changing the size of the vacuum gap. The single-photon generation module and the cavity mirror module can be placed on different multi-axis translation stages, and the size of the vacuum gap can be adjusted to adjust the cavity mode by adjusting the spatial position and angle of the two translation stages, so that the single quantum dot and the plano-concave resonant cavity can be coupled to the maximum extent, so that the collection efficiency of single photons is high.

[0100] According to an embodiment of the present invention, the above-mentioned single photon generation module further includes a P-terminal metal 400 and an N-terminal metal 500. The P-terminal metal 400 is located on the second P-type metal contact layer 108, and the N-terminal metal 500 is located on the N-type metal contact layer 104. The external voltage signal is loaded between the second P-type metal contact layer 108 and the N-type metal contact layer 104 through the P-terminal metal 400 and the N-terminal metal 500.

[0101] According to an embodiment of the present invention, the single-photon generation module further includes an optical field adaptation layer 109. The optical field adaptation layer 109 is disposed on the second P-type metal contact layer 108. The thickness of the optical field adaptation layer 109 is configured to adjust the optical path of the vacuum electric field, so that the quantum dot layer 103 is located at the peak of the vacuum electric field and the center position determined by the first P-type metal contact layer 107 and the second P-type metal contact layer 108 is located at the valley of the vacuum electric field. The center position determined by the first P-type metal contact layer 107 and the second P-type metal contact layer 108 is the center position of the first P-type metal contact layer 107 and the second P-type metal contact layer 108 as a whole. The vacuum electric field is formed by the cavity mode of the plano-concave resonant cavity.

[0102] According to an embodiment of the present invention, the doping concentration of the material of the first P-type metal contact layer 107 is less than that of the second P-type metal contact layer 108. Based on the basic principle of cavity electrodynamics, the metal contact layer will introduce absorption loss, thereby reducing the quality factor of the plano-concave resonator. The absorption loss is mainly related to the concentration, thickness, and position of the metal contact layer. Reducing the doping concentration of the metal contact layer can reduce the loss, but it is not conducive to the preparation of the electrode process (not conducive to the metal contact with the P terminal). The embodiment of the present invention provides two metal contact layers, namely, the first P-type metal contact layer 107 with a lower doping concentration and the second P-type metal contact layer 108 with a higher doping concentration. Through the adjustment of the optical field adaptation layer 109, the first P-type metal contact layer 107 and the second P-type metal layer 108 are both in the region with the weakest vacuum electric field. Compared with the case without the optical field adaptation layer 109, it can not only reduce the introduced absorption loss but also be conducive to the electrode process preparation.

[0103] According to an embodiment of the present invention, the material of the optical field adaptation layer 109 is undoped Al 0.4 Ga 0.6 As, and the thickness of the optical field adaptation layer 109 is 30 - 60 nm. The material of the first P-type metal contact layer 107 is P-type heavily doped Al a Ga 1‐a As, 0 < a < 0.45. The material of the second P-type metal contact layer 108 is P-type heavily doped Al b Ga 1‐b As, 0 < b < 0.45. The material of the N-type metal contact layer 104 is N-type heavily doped Al c Ga 1‐c As, 0 < c < 0.45. The material of the hole blocking barrier layer 106 is undoped Al d Ga 1‐d As, 0 < d < 0.45. The material of the electron tunneling barrier layer 105 is undoped Al e Ga 1‐e As, 0 < e < 0.45.

[0104] According to an embodiment of the present invention, the N-type metal contact layer 104, the electron tunneling barrier layer 105, the quantum dot layer 103, the hole blocking barrier layer 106, the first P-type metal contact layer 107, the second P-type metal contact layer 108 and the light field adaptation layer 109 serve as the active region of the single photon generation module. In the active region provided by the embodiment of the present invention, the light field adaptation layer 109, the electron tunneling barrier layer 105, the quantum dot layer 103 and the hole blocking barrier layer 106 are intrinsic semiconductor layers (i.e., I-type semiconductor layers); the first P-type metal contact layer 107 and the second P-type metal contact layer 108 are P-type doped semiconductor layers (i.e., P-type semiconductor layers), and the N-type metal contact layer 104 is an N-type doped semiconductor layer (i.e., N-type semiconductor layers). Therefore, the active layer of the embodiment of the present invention forms an I-type semiconductor layer-P-type semiconductor layer-I-type semiconductor layer-N-type semiconductor layer (i.e., IPIN) structure from top to bottom.

[0105] According to an embodiment of the present invention, GaAs / AlGaAs quantum dots have an obvious scintillation phenomenon, and the scintillation efficiency is between 30% and 40% under resonant excitation. The reasons for the scintillation phenomenon of GaAs / AlGaAs quantum dots are as follows: under the action of external incident laser, the electrons in the valence band of GaAs / AlGaAs quantum dots absorb the photons of the incident laser and then transition to the conduction band, and at the same time, a hole is generated at the original position in the valence band. The electrons in the conduction band are unstable, so they transition to a low energy level. The electrons can transition to and recombine with the holes, which will generate a single photon. If the electrons transition to the impurity orbital energy level, no single photon will be generated, so the scintillation phenomenon will occur.

[0106] Since the external voltage signal is loaded between the second P-type metal layer 108 and the N-type metal contact layer 104 through the P-terminal metal 400 and the N-terminal metal 500, the Coulomb shielding effect suppresses the transition of electrons generated in the quantum dots to the impurity orbital energy level, thereby eliminating the flickering phenomenon of GaAs / AlGaAs quantum dots, and further improving the overall efficiency of the single-photon source.

[0107] The "IPIN" structure provided according to the embodiment of the present invention can significantly reduce the inevitable absorption loss of each doping layer while eliminating the single-photon scintillation phenomenon, thereby achieving high-quality single-photon emission with high efficiency, high single-photon purity and high homogeneity.

[0108] According to an embodiment of the present invention, the single photon generation module further includes a first passivation layer 110 and a second passivation layer 111. The second passivation layer 111 is located between the first distributed Bragg reflector 102 and the N-type metal contact layer 104, and the first passivation layer 110 is located on the optical field adaptation layer 109.

[0109] According to an embodiment of the present invention, the active region further includes a first passivation layer 110 and a second passivation layer 111. A bonding dielectric layer 112 is provided between the first substrate 101 and the first distributed Bragg reflector 102 for bonding the first substrate 101 and the first distributed Bragg reflector 102.

[0110] According to an embodiment of the present invention, the first substrate 101 may be a GaAs substrate or a Si substrate. The second substrate 201 may be a SiO2 substrate.

[0111] As a second aspect of the present invention, a method for preparing a single photon source is also provided, which is used for the above-mentioned single photon source. The method includes operation S1 to operation S7.

[0112] In operation S1, a molecular beam epitaxy method is used to prepare Al on a temporary substrate. x Ga 1-x As first epitaxial layer, where 0 <x<1。

[0113] In operation S2, a nanopore is etched on the first epitaxial layer using a localized droplet etching method, the nanopore is filled with GaAs, and a second epitaxial layer of the same material as the first epitaxial layer is formed on the filled first epitaxial layer using a molecular beam epitaxy method to obtain a quantum dot layer 103, the quantum dot layer 103 including the etched first epitaxial layer, the GaAs located in the nanopore, and the second epitaxial layer. The first epitaxial layer and the second epitaxial layer, the portion used to confine the GaAs, form a quantum dot with the GaAs located in the pore.

[0114] In operation S3 , a first distributed Bragg reflector 102 is fabricated on the quantum dot layer 103 by using a magnetron sputtering method.

[0115] In operation S4, the first substrate 101 is bonded to a side of the first distributed Bragg reflector 102 away from the quantum dot layer, and then the temporary substrate is removed to obtain a single photon generation module.

[0116] In operation S5, a second distributed Bragg reflector 202 is fabricated on the second substrate 201 by using a magnetron sputtering method to obtain a cavity mirror module.

[0117] In operation S6 , a cavity mirror module is disposed on a side of the single-photon generation module close to the quantum dot layer 103 , and a vacuum gap is formed between the cavity mirror module and the single-photon generation module.

[0118] According to an embodiment of the present invention, when x is different or the GaAs filling thickness is different, the quantum dots are different, and the wavelengths of single photons generated by different quantum dots are different. According to an embodiment of the present invention, x may be 0.4, for example, and the GaAs filling thickness may be 2 nm.

[0119] According to an embodiment of the present invention, a material Al is prepared on a temporary substrate by using a molecular beam epitaxy method. x Ga 1-x Before forming the first epitaxial layer of As, the method further includes: sequentially preparing a light field adaptation layer 109, a second P-type metal contact layer 108, a first P-type metal contact layer 107 and a hole blocking barrier layer 106 on a temporary substrate by molecular beam epitaxy, and the first epitaxial layer is formed on the hole blocking barrier layer 106.

[0120] According to an embodiment of the present invention, the local droplet etching method includes: depositing a certain amount of group III atoms (such as Al atoms) on the GaAs surface to form droplets when As supply is stopped. At high temperature, these droplets will etch Al atoms below them. x Ga 1‐x The As crystal is locally etched to form nanopores, and then the As source is resupplied. At this time, As will crystallize with the group III element atoms to eliminate the excess group III atoms.

[0121] Before preparing the first distributed Bragg reflector 102 on the quantum dot layer 103 by magnetron sputtering, the method further includes: sequentially preparing an electron tunneling barrier layer 105 and an N-type metal contact layer 104 on the quantum dot layer 103 by molecular beam epitaxy.

[0122] According to an embodiment of the present invention, the materials of the N-type metal contact layer 104, the electron tunneling barrier layer 105, the first epitaxial layer, the hole blocking barrier layer 106, the second P-type metal contact layer 108 and the first P-type metal contact layer 107 are AlGaAs single crystals of different components, thicknesses and doping concentrations, and are therefore suitable for preparation by molecular beam epitaxy. Since the first distributed Bragg reflector 102 is composed of alternately stacked SiO2 and Ta2O5, it is suitable for preparation by magnetron sputtering. By controlling the coating time of magnetron sputtering, the thickness of each layer prepared by magnetron sputtering can be accurately controlled. Due to the limitation of the molecular beam epitaxy equipment, it is not suitable to put the first distributed Bragg reflector 102 prepared by magnetron sputtering into the molecular beam epitaxy equipment for preparation of other layer structures. Therefore, the present invention uses a temporary substrate. That is, the N-type metal contact layer 104, the electron tunneling barrier layer 105 and the first epitaxial layer are first prepared on a temporary substrate, and then the first distributed Bragg reflector 102 is prepared by magnetron sputtering.

[0123] According to an embodiment of the present invention, the above method also includes forming a sacrificial layer on a temporary substrate, preparing a first passivation layer 110 on the sacrificial layer, forming a light field adaptation layer 109 on the first passivation layer 110, and after the N-type metal contact layer 104 is prepared, forming a second passivation layer 111 on the N-type metal contact layer 104, and then preparing a first distributed Bragg reflector 102 on the second passivation layer 111.

[0124] According to an embodiment of the present invention, after the first distributed Bragg reflector 102 is prepared by magnetron sputtering, the first substrate 101 coated with photoresist is bonded to the first distributed Bragg reflector 102 by a bonding machine, thereby transferring the prepared sample to the first substrate 101 to achieve flipping of the vertical structure of the sample.

[0125] According to an embodiment of the present invention, after the first distributed Bragg reflector 102 is prepared by magnetron sputtering, the prepared device is transferred to the first substrate 101 and the temporary substrate and the sacrificial layer are removed. According to an embodiment of the present invention, the first substrate 101 is thinned to only 50 um by chemical-mechanical planarization (CMP), and then the original temporary substrate and the sacrificial layer are completely removed by a wet solution to expose the first surface passivation layer 110. At this point, the sample structure has been flipped.

[0126] According to an embodiment of the present invention, a positioning mark of a specified shape can be made on the surface of the quantum dot layer 103 through electron beam exposure, gold plating and gold stripping processes to mark a single quantum dot.

[0127] Figure 2 A single-photon source cavity mode intensity diagram obtained by simulating a single-photon source provided according to an embodiment of the present invention is shown.

[0128] like Figure 2 As shown, Figure 2 Part (a) is located in Figure 2 The part on one side of the two-dimensional symmetry axis is the device structure diagram of the prepared single photon source. Figure 2 Part (b), located in Figure 2 The part on the other side of the two-dimensional symmetry axis is the single photon source cavity mode intensity diagram obtained by finite element method simulation. It should be noted that in the finite element method, the perfect matching layer (PML layer) is mainly used to define boundary conditions to ensure the convergence of the simulation. Figure 1-Figure 2 , it can be seen from the simulated cavity mode intensity that in the active region (reference Figure 1 There are two maximum values ​​of cavity mode intensity (such as Figure 2 ), setting the quantum dot layer 103 at the maximum value can effectively enhance the coupling degree between the quantum dots and the vacuum electric field, which is achieved through the optical field adaptation layer 109, that is, the optical field adaptation layer 109 compensates the optical path so that the quantum dot layer 103 is at the crest of the vacuum electric field, and at the same time, the center positions of the first P-type metal contact layer 107 and the second P-type metal contact layer 108 are located at the trough of the vacuum electric field.

[0129] Figure 3 A diagram showing simulation results of the collection efficiency and Purcell factor of a single photon source provided according to an embodiment of the present invention is shown.

[0130] like Figure 3 As shown, at 794 nm, the collection efficiency and Purcell factor of the single photon source reach their maximum values, wherein at 794 nm, the collection efficiency is 86% and the Purcell factor is 10.

[0131] In addition, since the vacuum gap determines the cavity length of the plano-concave cavity, the vacuum gap between the cavity mirror module and the single-photon generation module can be adjusted through a multi-axis translation stage to deterministically adjust the cavity mode position, thereby coupling the plano-concave cavity with different quantum dots and outputting single photons of different wavelengths.

[0132] The single-photon source provided according to the embodiment of the present invention can realize the emission of high-quality single photons without flickering, high collection efficiency, high single-photon purity, and high homogeneity.

[0133] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A single photon source, characterized in that: include: Single photon generation module, including: a first substrate; A first distributed Bragg reflector, located on the first substrate, is formed by alternately stacking first refractive index layers and second refractive index layers, wherein the material of the first refractive index layers is SiO2, and the material of the second refractive index layers is Ta2O5; A quantum dot layer is located on the first distributed Bragg reflector. The quantum dot layer includes quantum dots, and the material of the quantum dots is composed of GaAs and Al x Ga 1-x As, where 0 < x < 1. Under the action of incident laser light, the quantum dots generate electron-hole pairs, and single photons are generated after the recombination of the electron-hole pairs; A cavity mirror module is located on a side of the single-photon generation module close to the quantum dot layer and forms a vacuum gap with the single-photon generation module, and a concave portion is formed in the middle of a side of the cavity mirror module facing the single-photon generation module; the cavity mirror module comprises: a second substrate; A second distributed Bragg reflector is located on the second substrate and is formed by alternately stacking a third refractive index layer and a fourth refractive index layer, wherein the material of the third refractive index layer is SiO2, and the material of the fourth refractive index layer is Ta2O5; the second distributed Bragg reflector and the first distributed Bragg reflector form a plano-concave resonant cavity; The first distributed Bragg reflector and the second distributed Bragg reflector perform multi-stage reflection on the single photons generated by the quantum dot layer, so that the single photons consistent with the resonance frequency of the plano-concave resonant cavity oscillate in the plano-concave resonant cavity and are output; Wherein, the preparation method of the single photon generation module comprises: The material is Al prepared on a temporary substrate by molecular beam epitaxy. x Ga 1-x As first epitaxial layer, where 0 <x<1; Etching a nanopore on the first epitaxial layer by using a localized droplet etching method, filling the nanopore with GaAs, and growing a second epitaxial layer with the same material as the first epitaxial layer on the filled first epitaxial layer by using a molecular beam epitaxy method to obtain a quantum dot layer, wherein the portions of the first epitaxial layer and the second epitaxial layer used for limiting GaAs form quantum dots with the GaAs located in the nanopore; The first distributed Bragg reflector is fabricated on the quantum dot layer by magnetron sputtering; The first substrate is bonded to a side of the first distributed Bragg reflector away from the quantum dot layer, and the temporary substrate is removed to obtain a single photon generation module.

2. The single photon source according to claim 1, characterized in that The single photon generation module also includes: An N-type metal contact layer is disposed on the first distributed Bragg reflector; An electron tunneling barrier layer is disposed on the N-type metal contact layer; wherein the quantum dot layer is disposed on the electron tunneling barrier layer; and the electron tunneling barrier layer is adapted to prevent electrons in the N-type metal contact layer from entering the quantum dot layer; A hole blocking barrier layer is disposed on the quantum dot layer; A first P-type metal contact layer is disposed on the hole blocking barrier layer; A second P-type metal contact layer, disposed on the first P-type metal contact layer; Wherein, the hole blocking barrier layer is adapted to block the holes in the first P-type metal contact layer and the second P-type metal contact layer from entering the quantum dot layer; The doping concentration of the material of the first P-type metal contact layer is lower than the doping concentration of the material of the second P-type metal contact layer.

3. The single photon source according to claim 2, characterized in that The cavity mode of the plano-concave resonant cavity can be adjusted by changing the size of the vacuum gap; The single photon generation module also includes: A light field adaptation layer is arranged on the second P-type metal contact layer; the thickness of the light field adaptation layer is configured to adjust the optical path of the vacuum electric field formed by the cavity mode of the plano-concave resonant cavity, so that the quantum dot layer is located at the crest of the vacuum electric field, and at the same time, the center position determined by the first P-type metal contact layer and the second P-type metal contact layer is located at the trough of the vacuum electric field.

4. The single photon source according to claim 3, characterized in that Also includes: A P-terminal metal, located on the second P-type metal contact layer; N-terminal metal, located on the N-type metal contact layer; An external voltage signal is loaded between the second P-type metal contact layer and the N-type metal contact layer through the P-terminal metal and the N-terminal metal; The material of the optical field adaptation layer is Al 0.4 Ga 0.6 As, the thickness of the optical field adaptation layer is 30-60 nm.

5. The single photon source according to claim 1, characterized in that: In the first distributed Bragg reflector, the first refractive index layer is closest to the quantum dot layer, and in the second distributed Bragg reflector, the fourth refractive index layer is closest to the quantum dot layer.

6. The single photon source according to claim 1, characterized in that: A reflection center wavelength of the first distributed Bragg reflector is the same as a reflection center wavelength of the second distributed Bragg reflector.

7. The single photon source according to claim 1, characterized in that In the first distributed Bragg reflector, the number of layers of the first refractive index layer and the second refractive index layer is 10 to 25 respectively; In the second distributed Bragg reflector, the number of layers of the third refractive index layer and the fourth refractive index layer is 1 to 20 respectively; The sum of the number of the third refractive index layers and the number of the fourth refractive index layers is less than the sum of the number of the first refractive index layers and the number of the second refractive index layers.

8. The single photon source according to claim 2, characterized in that: The material of the first P-type metal contact layer is P-type doped Al a Ga 1‐a As,0 <a<0.45; The material of the second P-type metal contact layer is P-type doped Al b Ga 1‐b As,0 <b<0.45; The material of the N-type metal contact layer is N-type doped Al c Ga 1‐c As,0 <c<0.45; The material of the hole blocking barrier layer is Al d Ga 1‐d As,0 <d<0.45; The material of the electron tunneling barrier layer is Al e Ga 1‐e As,0 <e<0.45。 9. A method for preparing a single photon source, used for preparing the single photon source according to any one of claims 1 to 8, characterized in that: Methods include: The material is Al prepared on a temporary substrate by molecular beam epitaxy. x Ga 1-x As first epitaxial layer, where 0 <x<1; Etching a nanopore on the first epitaxial layer by using a localized droplet etching method, filling the nanopore with GaAs, and growing a second epitaxial layer with the same material as the first epitaxial layer on the filled first epitaxial layer by using a molecular beam epitaxy method to obtain a quantum dot layer, wherein the portions of the first epitaxial layer and the second epitaxial layer used for limiting GaAs form quantum dots with the GaAs located in the nanopore; The first distributed Bragg reflector is fabricated on the quantum dot layer by magnetron sputtering; Bonding the first substrate to a side of the first distributed Bragg reflector away from the quantum dot layer, and removing the temporary substrate to obtain a single photon generation module; A second distributed Bragg reflector is prepared on a second substrate by a magnetron sputtering method to obtain a cavity mirror module; The cavity mirror module is arranged on a side of the single-photon generation module close to the quantum dot layer, and a vacuum gap is formed between the cavity mirror module and the single-photon generation module.

10. The method according to claim 9, characterized in that The material is Al prepared on a temporary substrate by molecular beam epitaxy. x Ga 1-x Before forming the first epitaxial layer of As, the method further comprises: Using molecular beam epitaxy to sequentially prepare a light field adaptation layer, a second P-type metal contact layer, a first P-type metal contact layer and a hole blocking barrier layer on a temporary substrate, wherein the first epitaxial layer is formed on the hole blocking barrier layer; Before preparing the first distributed Bragg reflector on the quantum dot layer by magnetron sputtering, the method further comprises: An electron tunneling barrier layer and an N-type metal contact layer are sequentially prepared on the quantum dot layer by using a molecular beam epitaxy method.

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