Preparation method of quantum dot single photon source

Abstract

The invention discloses a preparation method of a quantum dot single photon source. The preparation method comprises the following steps: (1) depositing a SiO2 dielectric film on the back surface of a substrate material; (2) preparing a required pattern structure based on the SiO2 dielectric film through electron beam exposure and a dry etching process; (3) performing epitaxial growth of a quantum dot single-photon source structure on the front surface of the substrate by adopting a molecular beam epitaxial growth process; and (4) forming a light source unit through electron beam exposure and etching processes to complete the preparation of the quantum dot single photon source. The method completely adopts a standard semiconductor process, so that the yield of the quantum dot single photon source is improved, the preparation difficulty is reduced, the problem of difficulty in batch production is solved, and industrial production is facilitated.

Description

Technical Field

[0001] The present application relates to a method for growing regular and orderly quantum dots, and belongs to the field of semiconductor materials. Background Art

[0002] A single-photon source refers to a light source that can emit a single photon, and its application is very wide. In quantum communication, the use of a single-photon source can achieve highly confidential communication, because the photons emitted by a single-photon source cannot be eavesdropped, and it also facilitates the implementation of quantum key distribution. In quantum computing, the use of a single-photon source can achieve high precision and high reliability of quantum bits, and accelerate the speed and accuracy of quantum computing. In the field of optical measurement, a single-photon source can be used in high-resolution microscopes or other precision measurement equipment. Studies have shown that single-photon sources based on quantum dots have high oscillator strength, narrow spectral line width, and no photofading, and are a very promising technology.

[0003] The most commonly used method for preparing quantum dots is to use molecular beam epitaxy technology to self-organize in a "bottom-up" manner. In order to meet the single-photon emission requirements of the single-photon source, the surface density of quantum dots needs to be less than 10 7 -10 8 cm -2 However, it is difficult for self-organized quantum dots to achieve such a low surface density.

[0004] In the process of molecular beam epitaxy quantum dots growth, the growth temperature plays a very important role. Quantum dots cannot be formed if the temperature is too high or too low. The SiO2 dielectric film has a relatively low thermal conductivity, generally within the range of 1.0 to 1.4 W / (m*K), and the thermal conductivity is relatively poor. The thermal conductivity of a general semiconductor substrate is about 100 to 150 W / (m*K). The SiO2 dielectric film is deposited on the back of the substrate and the pattern is prepared in combination with electron beam exposure technology. The heat conduction is faster where there is no SiO2 dielectric film on the back, and slower where there is SiO2 dielectric film, so that the temperature on the front of the substrate is different during the MBE epitaxial growth process: thereby controlling the formation of quantum dots and realizing the growth of low-density quantum dots. This method improves the yield of quantum dot single-photon sources, solves the problem of difficulty in mass production of single-photon sources, and is conducive to industrial production. Summary of the invention

[0005] The present invention provides a method for preparing a quantum dot single-photon source, comprising the following steps: (1) depositing a SiO2 dielectric film on the back of a substrate material; (2) preparing a required graphic structure based on the SiO2 dielectric film by electron beam exposure and dry etching processes; (3) epitaxially growing a quantum dot single-photon source structure on the front of the substrate by a molecular beam epitaxial growth process; and (4) forming a light source unit by electron beam exposure and etching processes to complete the preparation of the quantum dot single-photon source.

[0006] Preferably, the deposition method of the SiO2 dielectric film in step (1) is a plasma enhanced chemical vapor deposition (PECVD) process; the thickness of the SiO2 dielectric film is 300-5000nm; and the substrate material is one of GaAs, InP, GaSb, and Si.

[0007] Step (2) is achieved by electron beam exposure and dry etching process; the pattern size is 10-100nm, and the distance between adjacent patterns is 1-10μm.

[0008] The graphic structure in step (2) can be obtained by retaining or removing the SiO2 dielectric film at the target shape position.

[0009] The epitaxial growth in step (3) includes the growth of a buffer layer, and / or a DBR reflective layer, an absorption layer, quantum dots and a cap layer in sequence; wherein the buffer layer, the reflective layer, the absorption layer and the cap layer are all thin layer structures with a thickness of 30-2000nm; wherein the buffer layer, the reflective layer, the absorption layer and the cap layer are all thin layer structures, are insensitive to the growth temperature, and can be grown in sequence on the entire front side of the substrate.

[0010] Preferably, in step (3), InAs / GaAs quantum dots are epitaxially grown, firstly, a GaAs buffer layer with a thickness of 200-600nm and a growth temperature of 550-630°C, a GaAs / AlGaAs DBR reflective layer with a quantity of 10-30 pairs and a growth temperature of 550-630°C, and a GaAs absorption layer with a thickness of 500-2000nm and a growth temperature of 550-630°C are sequentially grown; then, the temperature is lowered so that the temperature of the graphic area (the front side corresponding to the exposed part of the substrate material on the back side of the substrate in the figure) meets the requirement of 500-530°C for growing InAs / GaAs quantum dots, while the temperature of other areas (the front side corresponding to the part covered by the SiO2 dielectric film on the back side of the substrate in the figure) is higher than the quantum dot growth temperature, which makes it difficult to grow quantum dots; then, a GaAs cap layer with a thickness of 50-800nm ​​is continued to be grown; the DBR reflective layer refers to the distributed Bragg grating reflective layer of the central wavelength.

[0011] Preferably, in step (3), the quantum dots are one of InAs / GaAs, InAs / InP, InSb / GaAs, GaSb / GaAs, InAs / GaSb, and InSb / GaSb; the buffer layer is one of GaAs buffer layer, GaSb buffer layer, InGaAs buffer layer, and InP buffer layer; the absorption layer is one of GaAs absorption layer, GaSb absorption layer, InGaAs absorption layer, and InP absorption layer; the cap layer is one of GaAs cap layer, GaSb cap layer, InGaAs cap layer, and InP cap layer; the DBR reflection layer refers to a distributed Bragg grating reflection layer of the central wavelength, which is one of GaAs / AlGaAs and InP / GaInAsP, the number is generally 10-30 pairs, and it is selected to grow or not grow according to actual conditions.

[0012] The position where the quantum dot single photon source is formed in step (4) can be adjusted by controlling the temperature of the target position where the quantum dot is formed.

[0013] In a preferred embodiment, when a target pattern is formed by etching part of a SiO2 dielectric film, the temperature of the pattern area (the front side corresponding to the exposed portion of the substrate material on the back side of the substrate in the figure) is controlled within the quantum dot growth temperature range, and the temperature of other areas (the front side corresponding to the portion covered by the SiO2 dielectric film on the back side of the substrate in the figure) is higher than the quantum dot growth temperature, so that quantum dots are grown only in the pattern area.

[0014] In another preferred embodiment, when the target pattern is formed by using the retained portion of the SiO2 dielectric film, the temperature of the graphic area (the front side corresponding to the portion covered by the SiO2 dielectric film on the back side of the substrate in the figure) is controlled within the quantum dot growth temperature range, and the temperature of other areas (the front side corresponding to the portion exposed by the substrate material on the back side of the substrate in the figure) is lower than the quantum dot growth temperature, so that quantum dots are grown only in the graphic area.

[0015] The beneficial technical effects of the present application are as follows: by taking advantage of the poor thermal conductivity of the SiO2 dielectric film, the growth of quantum dots is controlled by changing the temperature, thereby solving the problem that self-organized quantum dots are difficult to achieve low surface density, and realizing the preparation of quantum dot single-photon sources; this method uses all standard semiconductor processes, improves the yield of quantum dot single-photon sources, reduces the difficulty of preparation, solves the problem of difficulty in mass production, and facilitates industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 : Cross-sectional view of SiO2 dielectric film deposited on the back of substrate in Example 1;

[0017] Figure 2 : A top view of the back side of the substrate after etching in Example 1;

[0018] Figure 3 : Cross-sectional view of the back side of the substrate after etching in Example 1;

[0019] Figure 4 : A cross-sectional view of an epitaxial wafer grown by molecular beam epitaxy in Example 1;

[0020] Figure 5 : The quantum dot single photon source prepared in Example 1 is finally completed;

[0021] Figure 6 : SEM image of the graphic structure produced by electron beam exposure (EBL) during the production process of Example 1

[0022] Figure 7 : Temperature distribution during the growth of quantum dots simulated in Example 1

[0023] Figure 8 : Top view of the back side of the substrate after etching in Example 2

[0024] Fig. 9 : Example 2: The quantum dot single photon source finally prepared

[0025] Wherein: 1 substrate; 2 SiO2 dielectric film; 3 buffer layer; 4 DBR reflective layer; 5 absorption layer; 6 cap layer; 7 quantum dots; 8 front side of substrate; 9 back side of substrate; 10 unetched SiO2 dielectric film; 11 back side of substrate after etching. DETAILED DESCRIPTION

[0026] Embodiment 1:

[0027] (1) Plasma enhanced chemical vapor deposition (PECVD) is used to deposit SiO2 dielectric film on the back of the substrate. The process gas and its flow rate are SiH4 10sccm, N2O 460sccm, N2 220sccm, process temperature 350℃, RF power 45W, SiO2 dielectric film thickness 300-5000nm. The substrate can be GaAs, InP, GaSb, Si, etc.

[0028] (2) The pattern is prepared by electron beam exposure and dry etching process, the pattern size is 10-100nm, and the distance between adjacent patterns is 1-10μm. Electron beam gel ZEP520 is used as a mask, C7H 14 O2 is used as the developer. RIE equipment is used to etch the SiO2 dielectric film. The process gases and their flow rates are SF6 5.5sccm, CHF3 32sccm, He 150sccm, RF power 200W, and the etching depth is the thickness of the deposited SiO2.

[0029] (3) A molecular beam epitaxial growth process is used to epitaxially grow a quantum dot single photon source structure on the front side of the substrate, and the buffer layer, and / or DBR reflective layer, absorption layer, quantum dot and cap layer are grown in sequence. The buffer layer, reflection layer, absorption layer and cap layer are all thin layer structures, which are not sensitive to the growth temperature and can be grown in sequence on the entire front side of the substrate. However, the growth of quantum dots is sensitive to temperature. When growing quantum dots, the temperature is precisely controlled so that the temperature of the graphic area (the front side corresponding to the exposed part of the substrate material on the back side of the substrate in the figure) is within the quantum dot growth temperature range, and the temperature of other areas (the front side corresponding to the part covered by the SiO2 dielectric film on the back side of the substrate in the figure) is higher than the quantum dot growth temperature, so that quantum dots are grown only in the graphic area. Taking the growth of InAs / GaAs quantum dots as an example, first grow a GaAs buffer layer with a thickness of 200-600nm and a growth temperature of 550-630℃, a GaAs / AlGaAs DBR reflective layer with a quantity of 10-30 pairs and a growth temperature of 550-630℃, and a GaAs absorption layer with a thickness of 500-2000nm and a growth temperature of 550-630℃. Then lower the temperature so that the temperature of the graphic area (the front side corresponding to the exposed part of the substrate material on the back side of the substrate in the figure) meets the temperature of 500-530℃ to grow InAs / GaAs quantum dots, while the temperature of other areas (the front side corresponding to the part covered by the SiO2 dielectric film on the back side of the substrate in the figure) is still high and it is not easy to grow quantum dots. Then continue to grow a GaAs cap layer with a thickness of 50-800nm. The DBR reflective layer refers to the distributed Bragg grating reflective layer of the central wavelength.

[0030] In particular, the quantum dot can also be one of InAs / InP, InSb / GaAs, GaSb / GaAs, InAs / GaSb, InSb / GaSb, etc. The buffer layer can also be one of GaSb buffer layer, InGaAs buffer layer, InP buffer layer, etc. The absorption layer can also be one of GaSb absorption layer, InGaAs absorption layer, InP absorption layer, etc. The cap layer can also be one of GaSb cap layer, InGaAs cap layer, InP cap layer, etc. The DBR reflective layer can also be InP / GaInAsP, etc., and the DBR reflective layer is grown or not grown according to the actual situation. Other epitaxial layers are not limited to the above types, but suitable materials are selected according to the different substrates and quantum dot structures.

[0031] (4) Prepare the quantum dot single photon source by preparing the pattern on the front of the epitaxial wafer through electron beam exposure or photolithography and etching process. Taking the above InAs / GaAs as an example, the electron beam exposure uses electron beam glue ZEP520 as a mask, C7H 14O2 is used as the developer; ICP equipment is used to etch the epitaxial wafer, the process gas and its flow rate are Cl2 8sccm and BCl3 12sccm respectively, the RF power is 50W, the ICP power is 300W, the temperature is 20℃, and the etching depth is to the absorption layer.

[0032] Embodiment 2:

[0033] The steps are the same as those in Scheme 1, except that the regions of SiO2 and substrate are exchanged when preparing the pattern in step (2), and when growing quantum dots in step (3), the temperature of the pattern region (the front side corresponding to the part covered by the SiO2 dielectric film on the back side of the substrate in the figure) is within the quantum dot growth temperature range by precise temperature control, and the temperature of other regions (the front side corresponding to the part exposed by the substrate material on the back side of the substrate in the figure) is lower than the quantum dot growth temperature, so that quantum dots are grown only in the pattern region. Taking the growth of InAs / GaAs quantum dots as an example, first, a GaAs buffer layer with a thickness of 200-600nm and a growth temperature of 550-630℃ is grown in sequence, a GaAs / AlGaAsDBR reflective layer with a number of 10-30 pairs and a growth temperature of 550-630℃, and a GaAs absorption layer with a thickness of 500-2000nm and a growth temperature of 550-630℃ are grown in sequence. Then lower the temperature to make the graphic area (the front side corresponding to the part covered by SiO2 dielectric film on the back side of the substrate in the figure) meet the temperature of 500-530℃ to grow InAs / GaAs quantum dots, while the other areas (the front side corresponding to the part exposed by substrate material on the back side of the substrate in the figure) have a lower temperature and it is not easy to grow quantum dots. Then continue to grow GaAs cap layer with a thickness of 50-800nm.

[0034] The above contents are merely examples and explanations of the concept of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing a quantum dot single photon source, comprising the following steps: (1) Depositing a SiO2 dielectric film on the back of the substrate material; (2) Preparing the required graphic structure based on the SiO2 dielectric film through electron beam exposure and dry etching process; (3) Using molecular beam epitaxial growth process to perform epitaxial growth of quantum dot single photon source structure on the front of the substrate; (4) Forming the light source unit through electron beam exposure and etching process to complete the preparation of quantum dot single photon source.

2. The method according to claim 1, characterized in that The deposition method of the SiO2 dielectric film in step (1) is a plasma enhanced chemical vapor deposition (PECVD) process; the thickness of the SiO2 dielectric film is 300-5000nm; and the substrate material is one of GaAs, InP, GaSb, and Si.

3. The method according to claim 1, characterized in that Step (2) is achieved by electron beam exposure and dry etching process; the pattern size is 10-100nm, and the distance between adjacent patterns is 1-10μm.

4. The method according to claim 1, characterized in that The graphic structure in step (2) can be obtained by retaining or removing the SiO2 dielectric film at the target shape position.

5. The method according to claim 1, characterized in that The epitaxial growth in step (3) includes the growth of a buffer layer, and / or a DBR reflective layer, an absorption layer, quantum dots and a cap layer in sequence; wherein the buffer layer, the reflective layer, the absorption layer and the cap layer are all thin layer structures with a thickness of 30-2000nm; the buffer layer, the reflective layer, the absorption layer and the cap layer are not sensitive to the growth temperature and can be grown in sequence on the entire front side of the substrate.

6. The method according to claim 1, characterized in that In step (3), the quantum dots are one of InAs / GaAs, InAs / InP, InSb / GaAs, GaSb / GaAs, InAs / GaSb, and InSb / GaSb; the buffer layer is one of GaAs buffer layer, GaSb buffer layer, InGaAs buffer layer, and InP buffer layer; the absorption layer is one of GaAs absorption layer, GaSb absorption layer, InGaAs absorption layer, and InP absorption layer; the cap layer is one of GaAs cap layer, GaSb cap layer, InGaAs cap layer, and InP cap layer; the DBR reflection layer refers to a distributed Bragg grating reflection layer of the central wavelength, which is one of GaAs / AlGaAs and InP / GaInAsP, the number is generally 10-30 pairs, and it is selected to grow or not grow according to actual conditions.

7. The method according to claim 1, characterized in that The position where the quantum dot single photon source is formed in step (4) can be adjusted by controlling the temperature of the target position where the quantum dot is formed.

8. The method according to claim 1, characterized in that When the target pattern is formed by etching part of the SiO2 dielectric film, the temperature of the pattern area is controlled within the quantum dot growth temperature range, and the temperature of other areas is higher than the quantum dot growth temperature, so that quantum dots are grown only in the pattern area.

9. The method according to claim 1, characterized in that When the target pattern is formed by using the retained SiO2 dielectric film, the temperature of the pattern area is controlled within the quantum dot growth temperature range, and the temperature of other areas is lower than the quantum dot growth temperature, so that quantum dots are grown only in the pattern area.

10. A quantum dot single photon source prepared according to the method according to any one of claims 1 to 9.

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